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[This report, prepared by ATSDR at the request of Imperial County, is an analysis of threats to public health posed by pathogens and contaminants in the New River. The report is based on brief site visits by ATSDR personnel in 1994-1995 and on data from government agency monitoring programs. S. Hurlbert, SDSU, December 1998]

The New River

Petitioned Public Health Consultation

Imperial County, California

February 28, 1996

 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
PUBLIC HEALTH SERVICE

Agency for Toxic Substances and Disease Registry

Division of Health Assessment and Consultation

Atlanta, Georgia

 

Table of Contents

Page

BACKGROUND AND STATEMENT OF ISSUES

2

SITE VISIT

3

ENVIRONMENTAL CONTAMINANTS BY MEDIA

4

SURFACE WATER

4

FOAM

5

SEDIMENT

5

BIOTA

5

PATHWAYS ANALYSIS

8

SURFACE WATER

8

FOAM

9

SEDIMENT

9

BIOTA

9

PUBLIC HEALTH IMPLICATIONS

10

A. Toxicological Evaluation

10

Biological Hazards

12

Radioactive Hazards

12

Metals

12

Pesticides and PCBs

13

Vocs

16

CONCLUSIONS

18

RECOMMENDATIONS

20

Cease\Reduce Exposure Recommendations

20

Site Characterization Recommendations

20

Health Activities Recommendation Panel

21

PUBLIC HEALTH ACTION PLAN

21

B. Public Health Actions

21

Actions Undertaken

22

Actions Planned

22

REFERENCES

24

PREPARERS OF REPORT

28

APPENDIX A - FIGURES [Not provided here - see comment in document]

29

APPENDIX B - TABLES

32

Table 1. Contaminants in On-Site Surface Water at New River

33

Table 2. Pesticides and PCBs in Fish at New River - Summary of 1978-1987 & 1990 Data (PPB, lipid weight)

37

Table 3. Metals in Fish at New River - Summary of 1978-1987 & 1990 Data (PPB, dry weight)

39

Table 4. Pesticides and PCBs in Fish at New River - Summary of 1978-1987 & 1990 Data (PPB, dry weight)

40

Table 5 Volatile Organic Chemical Detected in New River Fish (PPM, wet weight)

42

Table 6. Organic and Inorganic Chemical detected in New River Sediments. (Dry wight in PPM)

44

Table 7. Contaminants in Soft Shelled Turtle Tissue at New River (wet weight)

45

Table 8. Organic and Inorganic Chemicals in Fish at the Salton Sea. (PPB, wet weight)

46

Table 9. Organic Chemicals in Fish at Salton Sea. Summary of 1978-1987 & 1990 Data (PPB, lipid weight)

47

APPENDIX C - COMPARISON VALUES

48

BACKGROUND AND STATEMENT OF ISSUES

The Agency for Toxic Substances and Disease Registry (ATSDR) was petitioned by Imperial County, California, to evaluate the public health impact of the New River. Area residents have a long history of concern that contaminants in the New River could affect public health. To address this concern, ATSDR evaluated available environmental data for the New River from 1969 to 1994 in this Public Health Consultation.

The New River channel was created in the early 1900's when the Colora do River changed its course and, instead of emptying into the Gulf of California, formed a new channel flowing into the Salton Sea. The river stems from the Colorado River in Mexico about 20 miles southeast of the city of Mexicali. It flows through Mexicali, courses across the International Boundary to the U.S.A. and then flows 60 miles northward through Imperial County to the Salton Sea (1). As the New River flows through Imperial County, it runs near the communities of Calexico, Seely, El Centro, Imperial, Brawley, and Westmorland. Figures 1 and 2 in Appendix A show important features near the New River. According to 1990 census data, 66% of people in Imperial Valley are of hispanic origin, 2% are black, 29% are white, and 3% are of other races (2).

The New River is primarily composed of agricultural drainage and waste water from the Mexicali Valley in Mexico and Imperial Valley in California. Both the drainage and wastewater are of Colorado River origin. Approximately one-third of the cumulative river flow is contributed by Mexico, with the remaining two-thirds contributed from sources within California's Imperial Valley. The flow of the New River at the International Boundary averages about 250 cubic feet per second (cfs) and increases to about 700 cfs at the outlet to the Salton Sea (1).

Land use in Imperial Valley, California, is largely agricultural. As a result, the flow from the United States consists primarily of agricultural surface runoff (35%). Groundwater seepage (32%), tile drainage (30%), and canal spillage (1%) also contribute to the total flow of the river. Treated sewage accounts for approximately 1% of the total flow while geothermal wastewater, industrial wastewater, and wastewater from livestock each account for less than 1% of the total flow (1).

In Imperial Valley, the New River is not used as a source of drinking water. Drinking water for the County comes from the Colorado River and is transported to Imperial County via the All American Canal. Waterfowl hunting, fishing, and frog catching have been reported in the New River along with consumption of the waterfowl, fish and frogs. In addition, the Salton Sea is a major recreational area with campgrounds and wildlife preserves. Fishing, camping, hunting and bird watching are among the activities reported at the Salton Sea (3,4).

In Mexico, outside the city limits of Mexicali, agriculture is the predominant land use and the New River receives surface runoff from adjacent fields. Groundwater seepage (45%), agricultural drainage water (20%), canal spillage (9%) and wastewater from livestock (1%) account for 75% of the total water input into New River from Mexico (1). In addition, industrial wastewater (2%) and geothermal wastewater (10%) contribute to the total flow into the New River from Mexico. Several tributaries of the New River flow through an industrial zone where most of the direct industrial discharges to the river system occurs (1).

Untreated (5%) and partially treated sewage (8%) account for 13% of the total flow into New River from Mexico. Most of the sewage from the sewered area of Mexicali is conveyed upgradient to sewage treatment lagoons at a location west of the city. The effluent from the treatment lagoons (approximately 20 cfs) is conveyed in a drain, which discharges to the New River at the International Boundary. Mexicali's sewage system has had numerous failures, generally related to breaks in the main collector pipelines and pumping plant breakdowns. These failures have resulted in the release of untreated and partially treated sewage into the New River (1).

In Mexico, the New River is reportedly used for bathing, drinking, household chores, and irrigation of crops, particularly among lower socioeconomic status residents. Homes are present along at least one tributary immediately downstream from industrial facilities. Children have been reported playing and swimming in the river immediately downstream of the industries and amid floating sewage (3).

SITE VISIT

ATSDR representatives conducted a tour of the New River in California from the Mexican border to the Salton Sea in July 1994 and June 1995. Untreated sewage was seen floating on top of New River, with higher amounts of sewage visible close to the Mexican border. Access to the New River was possible in the towns of Calexico and Brawley. Bike paths were noted along the river and a housing development is located within one-half mile of the river in Calexico. Signs (some both in English and Spanish) warning against contact with the river were noted at obvious access points, such as bridges, with some in need of repair. Besides Calexico and Brawley, New River primarily flows through agricultural areas until it meets the Salton Sea. The Salton Sea had a black tar-like substance extending about 20 feet from shoreline. A foul odor was also present and was clearly evident even inside an automobile with closed windows (3).

ENVIRONMENTAL CONTAMINANTS BY MEDIA

Environmental sampling of the New River has been conducted at the International Boundary since 1969, with additional samples collected between the International Boundary and the Salton Sea. The U.S. Geological Survey (U.S.G.S.), the California Regional Water Quality Control Board (CRWQCB), the California State Water Resource Control Board (CSWRCB) and the California Department of Fish and Game (DFG) collected these samples to assess the concentration of contaminants in surface water, sediment, and fish and turtle tissue. Each media was analyzed for trace elements, metals, pesticides, VOC's and PCB's. Surface water was also analyzed for biological contamination.

The tables in Appendix B list the contaminants identified in each environmental medium at the site. Contaminants are compared with available ATSDR standard comparison values. ATSDR standard comparison values are used only to select contaminants of concern for further consideration. Identification of a contaminant of concern in this section does not necessarily mean that exposure will be associated with illnesses. We evaluate the contaminants of concern in subsequent sections and determine whether exposure has public health significance.

SURFACE WATER

Surface Water samples have been collected on a regular basis since 1975 at the International Boundary and between the International Boundary and the Salton Sea by the CRWQCB. In general, most of the surface water samples were composites of grab samples collected at different times intervals at the International Boundary (DWR station 57)(5). Less data are available for the New River between the International Boundary and the Salton Sea. ATSDR evaluated surface water data collected at the New River outlet to the Salton Sea in 1969, 1970, and 1985 and biological contaminants detected at various locations between the International Boundary and the Salton Sea in 1977 (5,6,7,8,9). Table 1 in Appendix B shows the locations and maximum concentrations of contaminants found in surface water from the New River.

a. Biological Contamination

Fecal coliforms and fecal streptococci have been consistently detected in the New River at the International Boundary. The presence of fecal coliforms and fecal streptococci in the New River indicates that fecal contamination of the river has occurred. The highest concentration for fecal coliform was 93,000,000 MPN/100ml (most probable number/100 mililiter), detected in July 28, 1976. Also, in June 1982, the CRWQCB reported a fecal coliform concentration of 35,000,000 MPN/100ml. As recently as February 1995, fecal coliforms were detected at 2,200,000 MPN/100 ml. The concentration for fecal streptococci detected between 1969 and 1995 ranged from a minimum of 400 colonies/100 ml and a maximum of 1,170,000 colonies/100 ml detected in April 16, 1979 (5,6,7,8,9).

The Imperial County Health Department informed ATSDR that, in 1979, pathogenic microorganisms were found in the New River. These organisms were reported to be capable of producing polio, typhoid, cholera and tuberculosis. Imperial County also reports that the arbovirus that causes encephalitis has been detected in the New River. In addition, the County informed ATSDR that at least one hospitalization has resulted after a contact with the New River (10). However, no data are available to more fully evaluate these reports.

b. Metals

Over twenty-five metals were detected in surface water between 1969 and 1995 at the International Boundary. Metals that exceeded ATSDR comparison values include lead (100 ppb), arsenic (19 ppb), cadmium (18 ppb), thallium (6.8 ppb), antimony (129.2 ppb), boron (1,100 ppb), and manganese (740 ppb) (5,6,7,8,9).

c. Pesticides

The highest concentration of pesticides were detected at Calexico gage near the International Boundary between 1969 and 1982. Pesticides exceeding ATSDR comparison values are: aldrin (.002 ppb); chlordane (0.2 ppb); DDD (0.45 ppb); 4,4'-DDD (0.99 ppb); DDE (0.18 ppb), DDT (1.20 ppb) and heptachlor epoxide (1.1 ppb). In addition, PCB 1260 (0.53 ppb) exceeded its respective comparison value (5,6,7,8,9).

d. Volatile Organic Compounds (VOC's)

The CRWQCB has sampled the surface water in the New River at the International Boundary for VOC's since 1980. Over sixty-five volatile and semi-volatile organic compounds have been detected near the International Boundary. Three of these [Tetrachloroethylene (6.6 ppb), Methylene Chloride (7 ppb) and n-Nitrosodiphenylamine (9 ppb)] were detected in concentrations above their respective comparison values for drinking water. Forty had no standard ATSDR comparison value. The other VOC's were in concentrations below their respective comparison values (5).

e. Radioactivity

Levels of radioactivity were assessed in the New River in 1977. See Table 1 in Appendix B for a further description of levels detected.

FOAM

A layer of foam frequently forms on the surface of the New River near the International Boundary. This foam is often blown by the wind to areas near the river, including parking lots and a shopping center. In particular, foam often blows into the parking lot of a grocery store located near the International Boundary (11).

In 1980, the CRWQCB investigated the source and composition of the foam. The CRWQCB attributed the presence of foam at the International Boundary to the rerouting of effluent from Mexicali's wastewater treatment facilities to a point of discharge at the International Boundary. The data indicated that the foam in the New River is largely composed of detergents. It was unknown whether the primary source of detergent discharge in Mexico is of industrial or domestic origin (12). The CRWQCB also found that the foam contains fecal coliform. Fecal coliform was detected at 240,000 MPN/100ml in February 1980 and at 700,000 MPN/100ml in March 1980 (11).

SEDIMENT

In 1986, the Environmental Protection Agency (EPA Region 9) analyzed a sediment sample collected from the New River at the International Boundary. The sediments sample was a grab sample collected from bottom muds of the river. Volatile organic chemicals and pesticides detected were all below ATSDR comparison values. Some metals exceeded ATSDR comparison values (13). Table 6 in Appendix B shows the maximum concentrations of contaminants found in sediment from the New River.

BIOTA

a. Fish\Turtle Tissue

The California Department of Fish and Game (DFG) has sampled and analyzed fish tissue for pesticides and metals since 1978 through the Toxic Substances Monitoring Program (TSMP). The collection stations for the New River were located at the International Boundary and near the town of Westmoreland (14,15). In addition, the U.S. Environmental Protection Agency (Region IX) sampled and analyzed New River fish for pesticides, metals and VOC's between 1984 and 1986 (13). The collection stations used by EPA were at the International Boundary and at the outlet of the New River into the Salton Sea. Some samples collected by DFG and EPA were grab samples while others were composite samples (13,14,15). In some cases, the data available to ATSDR did not indicate whether the samples were grab or composite samples (13,14,15).

Various contaminants were detected in fish sampled from the New River. These included metals, pesticides, and volatile organic compounds (VOCs). Tables 2,3,4 & 5 in Appendix B list maximum concentrations of the contaminants found in fish from the New River.

Because the New River empties into the Salton Sea, ATSDR also reviewed data for fish from the Salton Sea. This data was collected since 1978 through the TSMP. Metals and pesticides were detected in fish tissue from the Salton Sea (14,15). Table 8 in Appendix B lists the maximum concentrations of contaminants found in fish from the Salton Sea.

One turtle tissue sample was taken in 1984 from the New River at the International Boundary. Several contaminants, including p,p'-DDE, p,p'-DDT and VOC's, were detected (13). Table 7 in Appendix B lists the maximum concentrations of the contaminants detected in the turtle tissue.

b. Mosquitoes

Imperial County representatives expressed concern that mosquitoes living in the New River could cause encephalitis in area residents. As a result of this concern, ATSDR examined available data regarding mosquitoes and encephalitis in Imperial County.

The University of California and the State of California Department of Public Health have isolated the encephalitis virus in mosquitoes in Imperial Valley. The mosquito specie Culex tarsalis is the primary vector of Western Equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses in southeastern California. This mosquito is present and active all months of the year. It prefers blood from birds, the primary reservoir hosts of some arboviruses, but it bites man readily enough to be an efficient vector of encephalitis. This mosquito prefers to live in permanent pools, fresh or foul, and it can live in sunlit or shaded habitats. While this mosquito probably lives in the New River, it is also likely that it exists in other water bodies in Imperial Valley as well (16,17,18,19).

No human cases were detected by the Encephalitis Virus Surveillance (EVS) program in Imperial Valley between 1990-1992. However, in 1977, a study of 577 blood samples from patients attending a clinic in Brawley, Imperial Valley, revealed that 12.1 % of the patients were found to have neutralizing antibodies to the SLE virus and 1.5 % of the patients were found to have neutralizing antibodies to the WEE virus, indicating previous infections.

Possible explanations for the low number of human cases of encephalitis as compared to the percentage of the population with antibodies to encephalitis viruses were discussed in the Journal of Medical Entomology. These explanations include: 1) humans are not being infected because they infrequently contact infected mosquitoes, 2) viral strains circulating in SE California are attenuated and infections rarely produce central nervous system disease, or 3) cases remain undetected or are listed as undiagnosed viral or aseptic meningitis or encephalitis. The article states that area residents are probably bitten frequently by mosquitoes and infected with both WEE or SLE viruses because many residents are engaged in agricultural activities, frequently work or fish outdoors at night or early morning, and reside in substandard housing (16).

PATHWAYS ANALYSIS

To determine whether nearby residents may be exposed to contaminants from a particular site, ATSDR evaluates the environmental and human components that lead to human exposure. That pathways analysis considers five elements: (1) sources of contamination, (2) environmental media in which the contaminants may be present or from which contaminants may migrate, (3) points of human exposure, (4) routes of human exposures such as ingestion, inhalation, or dermal absorption, and (5) exposed populations.

SURFACE WATER

Surface water in the New River is contaminated with metals, pesticides, VOC's, and bacteria. Pathogenic viruses have also been reported in the New River. Human exposure to contaminants in the surface water occurred in the past and could occur in the present and in the future. The New River flows near several communities in Imperial County as it traverses the 60 miles between the International Boundary and the Salton Sea. Residential areas are located near the river. Bike and hiking trails are located along the River near the towns of Calexico and Brawley. Homeless persons have also been reported living along the River. In some areas, signs warn against contact with the river. However, access is otherwise unrestricted in most areas. The length of the river hinders efforts to completely restrict access to the New River.

FOAM

Surface water contaminants could also migrate to areas where human exposure is likely through wind blown foam. As previously stated, foam frequently forms in the New River at the International Boundary. This foam has been attributed to the discharge of wastewater just prior to the International Boundary in Mexico. While the foam has been found to contain detergents and fecal coliforms, it has not been sampled for other contaminants found in the New River.

SEDIMENT

Sediment represents a potential exposure pathway through dermal contact and inadvertent ingestion of contaminants for children and adults who play, work or fish close to the river. In 1986, EPA analyzed a sediment sample from the New River at the International Boundary for VOC's, pesticides and metals. Volatile organic chemicals and pesticides detected were all below ATSDR comparison values. Some metals exceeded ATSDR comparison values. Human contact with contaminants in the sediments may have occurred in the past, may be currently occurring, and have the potential to occur in the future. Information is not available on contaminant levels in the sediment of other areas of the New River. Therefore, ATSDR can not fully assess this potential exposure pathway.

BIOTA

a. Fish\Turtle Tissue

Fish from the New River are contaminated with metals, pesticides, PCBs, and volatile organic compounds (VOC's). According to Imperial County health officials, area residents have been noted fishing in the New River. The New River also empties into the Salton Sea where fishing is a common recreational activity. Metals and pesticides have been detected in fish from the New River and the Salton Sea. Therefore, exposure to contaminants detected in fish from the New River and Salton Sea has probably occurred in the past and may occur in the future through fish ingestion.

Pesticides and VOC's were detected in one turtle sampled from the New River in 1984. It is not known whether area residents eat turtles from New River. ATSDR has been informed that area residents sometimes eat frogs from the New River. The number of frogs consumed and frequency of consumption is not known and no sampling data of frog tissue are available. As a result of these data gaps, ATSDR can not fully evaluate these potential exposure pathways.

b. Mosquitoes

Mosquitoes in Imperial Valley are known to carry the encephalitis virus. Mosquitoes which carry the encephalitis virus are frequently found in surface water, such as the New River, which is contaminated with sewage. These mosquitoes, however, also live in other aquatic habitats and their presence in Imperial Valley cannot be attributed solely to the New River.

PUBLIC HEALTH IMPLICATIONS 

A. Toxicological Evaluation

In this section, ATSDR discusses health effects that could plausibly result from exposures to site contaminants. While the relative toxicity of a chemical is important, the response of the human body to a chemical exposure is actually determined by several additional factors, including the concentration (how much), the duration of exposure (how long), and the route of exposure (breathing, eating, drinking or skin contact). Lifestyle factors (e.g., occupation and personal habits) have a major impact on the likelihood, magnitude, and duration of exposure. Individual characteristics such as age, sex, nutritional status, overall health, and genetic constitution affect how a contaminant is absorbed, distributed, metabolized, and eliminated from the body. Together, all these factors help determine the individual's physiological response to chemical contaminants and what, if any, adverse health effects he or she may suffer as a result of the chemical exposure.

ATSDR has determined levels of chemicals that can reasonably (and conservatively) be regarded as harmless, based on the scientific data the agency has collected in its Toxicological Profiles. The resulting comparison values and health guidelines (which include ample safety factors to ensure protection of sensitive populations) are used to screen contaminant concentrations at a site, and to select substances that warrant closer scrutiny by agency health assessors and toxicologists. (see Appendix C for a more complete description of ATSDR's comparison values, health guidelines and other values ATSDR uses to screen site contaminants.)

It must be emphasized, however, that ATSDR's comparison values and health guidelines do not represent thresholds of toxicity. They are merely screening values used to facilitate the initial selection of site-specific chemical substances (the contaminants of concern) for further evaluation of potential health effects. After the contaminants of concern at a site have been identified, they must then be individually scrutinized in more detail (considering all the different factors mentioned in the first paragraph of this section) to determine whether or not, under site-specific conditions, they represent a realistic threat to human health. Although concentrations at or below the ATSDR's comparison values may reasonably be considered "safe", it does not automatically follow that any concentration above a comparison value will necessarily produce toxic effects. In fact, comparison values are intentionally designed so as to be orders of magnitude lower than the corresponding no-effect levels determined in laboratory experiments.

Only those contaminants that have been detected in concentrations exceeding comparison values will be discussed in any detail. In addition, since a contaminant must first enter the body before it can possibly produce any effect, adverse or otherwise, on the body, the discussion below will focus on contaminants for which there is at least some evidence of actual exposure. All of the estimated safe levels of fish consumption mentioned below are base solely on the "wet weight" data in Tables 3, 4, 5, 7, and 8. The "lipid weight" data in Tables 2 and 9 could not be used in dose calculations because determinations of the percent fat in sampled fish tissues were not reported, making it impossible to estimate what the corresponding amount of a given contaminant would have been in the edible portion of the fish. It should also be noted that, since the estimated safe levels of consumption are calculated from comparison values, the same caveats that apply to the later also apply to the former. Specifically, the designation of any consumption level as "safe" does not imply that any higher consumption level will necessarily be unsafe.

A large number of metals, pesticides, and volatile organic compounds (VOCs) have been detected over the years at elevated levels in water, sediments, and wildlife from the New River. Some of those contaminants (discussed below), at the maximum levels detected, could present a potential health threat to individuals using the river as a primary source of drinking water and/or dietary supplements (e.g., fish and turtles). However, ATSDR believes that actual exposures to chemical contaminants in New River media are relatively low, infrequent, and unlikely to be of toxicological significance. Nevertheless, due to the presence in the river of untreated or partially treated sewage, these lower levels of exposure could still pose a potential hazard to public health. Therefore, the safest course is not to consume any water or wildlife from the New River.

Biological Hazards:

Very high levels of fecal coliforms have been repeatedly measured in the New River, principally near the International border (Table 1). Although these bacteria do not themselves represent a direct hazard to health, they are markers for contamination by human sewage, and indicators of possible contamination by enteric viruses and pathogenic bacteria (22). The latter possibility has been confirmed in the past by the detection in the New River of high numbers of fecal streptococci. The implications of these findings are that, persons living downstream who drink water or consume other media from the New River, risk contracting any waterborne diseases that may infect people living upstream. Although ATSDR has no clear evidence that anyone in Imperial County is drinking water from New River, the possibility of human exposure does exist, particularly South of the border. Therefore, ATSDR considers the high fecal coliform counts in the New River to be indicative of a potential public health hazard.

Radioactive Hazards:

The dissolved gross alpha particle activity in water from the New River exceeds the 20 ppb MCL for uranium in drinking water (Table 1). Also, the maximum detected dissolved gross beta particle activity of water from the New River exceeded the 50 picocurie/liter screening level. When the gross beta particle activity of a sample exceeds 50 pCi/l, an analysis must be performed to identify the major radioactive constituents present, so that the appropriate doses can be calculated and summed to determine compliance with Sec. 141.64 of the Drinking Water Regulations (22). However, since the New River is not identified as a drinking water source, such an analysis has not been performed, and without such an analysis, it is virtually impossible to estimate radiation doses and possible adverse health effects.

Metals:

The New River is contaminated with numerous metals (Table 1), including antimony, arsenic, boron, cadmium, iron, lead, manganese, thallium, and zinc. By themselves, the metals in water from the New River should not pose a health threat to people with only occasional, low-level exposure (e.g., the equivalent of drinking 2 ounces of water per day). However, at the maximum levels detected, these metals would represent a potential health hazard to persons using the New River as a primary source of drinking water.

The highest concentrations of nickel and silver ever detected in New River sediment (Table 6) marginally exceeded ATSDR's lowest comparison values (i.e., those for pica children) for these metals in soil, but not those for other children or adults. However, given the relatively limited access to the New River, it is highly unlikely that a pica child, or any child for that matter, would actually consume a toxicologically significant amount of contaminated sediments.

The maximum detected levels of arsenic (1.8 ppm) and copper (91 ppm) in fish from the New River (Table 3) exceeded EPA's Risk-Based Concentrations of 0.41 and 50 ppm, respectively, for non-carcinogenic effects. (Note that these maxima, which are used for purposes of conservatism, were detected 16 years ago and do not necessarily reflect current levels.) EPA's Risk-Based Concentrations in fish assume consumption of 54 grams (about 2 ounces) of fish per day, or about one large meal per week (23). The maximum intake dose of these metals for a person consuming only 3 ounces of fish per week (approximately one large meal per month) would not exceed ATSDR's chronic MRLs for either metal (24,25). However, fishing in the New River is still inadvisable, since it would expose one to the potentially more serious biological hazards mentioned in the previous section. Fish from the Salton Sea also contain excess arsenic (max.= 0.8 ppm), but maximum levels are less than half those found in New River fish. Based on metals content alone, consumption of 7 ounces of Salton Sea fish per week should be safe, i.e., free of any risk of non-cancer health effects.

It is important to note that the preceding discussion of arsenic in fish only applies if the reported values actually represent inorganic arsenic. Fish typically contain higher levels of arsenic than do other foods, but most of it is in organic forms (e.g., arsenobetaine) that are rapidly excreted and are much less toxic to humans than are inorganic forms of arsenic (25).

Pesticides and PCBs:

The maximum concentrations of several pesticides (and PCBs), including aldrin, chlordane, heptachlor epoxide, DDT and its metabolites DDD and DDE (and Aroclors 1254 and 1260) measured in water from the New River (Table 1) exceed ATSDR's comparison values based on cancer effects (CREGs). However, it remains debatable whether or not these pesticides (and PCBs) can, in fact, cause cancer in humans (27,28,29,30,31). Most are not genotoxic, i.e., mutagenicity tests are generally negative or inconsistent. High doses of these pesticides have increased the frequency of liver cancer in some rodents (usually mice), but not in others (usually rats). In animals that do develop cancer, a promotion mechanism appears to be involved, which suggests that the carcinogenicity of these substances may exhibit a relatively high threshold. These considerations, combined with the questionable relevance of mouse liver tumors to human cancer risk (32) and the absence of convincing epidemiological evidence, provide little support for the supposition that very low oral doses of these pesticides may be carcinogenic in humans.

Under site-specific conditions of exposure, none of these substances was found at concentrations that would be of concern for non-cancerous effects. Heptachlor epoxide could represent a potential non-cancer health hazard, if New River water were used as a primary source of drinking water, but not if - as seems to be the case - consumption rates are 12 ounces/day or less (26). The consumption of 12 oz/day of New River water containing the maximum detected concentration (1.1 ppb) of heptachlor epoxide would be equivalent to drinking 2 L/day of water containing residues of this pesticide at the MCL of 0.2 ppb. For a 70-kg adult, the resulting dose would be less than half of EPA's chronic RfD of 0.013 ug/kg/day. The maximum levels of PCBs detected (0.53 ppb) did not significantly exceed the MCL (0.5 ppb) for these compounds (27).

EPA's Risk Based Concentrations (RBCs) for pesticides in fish were exceeded by the maximum detected levels of chlordane, DDT and degradation products, hexachlorocyclohexane (lindane), heptachlor epoxide, toxaphene, and Aroclor 1254/1260 (Table 4). However, EPA's RBCs for all of these pesticides assume (a) carcinogenicity in humans at very low levels, and (b) consumption of 54 grams of fish per day for 70 years. Whatever the validity of the first assumption, which is not supported by epidemiological studies, the actual rate of consumption of fish from the New River is expected to be much smaller than the default of 54 g/day for 70 years (23).

None of the individual pesticides listed in Table 4 was found in fish at concentrations that would be expected to produce non-cancer effects, even under default conditions of exposure. That is to say that, assuming consumption of 54 grams (1.9 ounces) or less of New River fish per day, the resulting maximum doses of the congener-specific pesticides listed in Table 4 would be within ATSDR's Minimum Risk Levels (MRLs) and EPA's chronic Reference Doses (RfDs) for those pesticides (27,29,30,31). The latter statement also applies to "Total Chlordane" and "Total HHC", but not to the maximum value for "Total DDT" (Table 4), which includes isomers for which ATSDR has no MRLs. If one were to apply ATSDR's intermediate oral MRL for p,p-DDT to "Total DDT" (a conservative approach), the calculated "safe" consumption rate would be 5 times lower than EPA's default value. Since the extent of pollution in the New River has been common knowledge among residents of Imperial Valley for several decades now, it is probable that, for the vast majority of residents, this lower value (i.e., 2.7 oz/wk,) is a more accurate reflection of actual local consumption rates than is the default value of 1.9 oz/day (13 oz/wk). It should also be noted that the maximum concentration of total DDT in New River fish, which is used for purposes of conservatism, was detected almost 18 years ago and does not necessarily reflect current levels. Furthermore, ATSDR's intermediate oral MRL for DDT includes an uncertainty factor of 100, which represents a substantial margin of safety (29).

DDT and its degradation products were also elevated in New River soft shell turtles and Salton Sea fish. Compared to New River fish, the maximum levels of DDT/DDE were slightly higher in New River turtles (Table 7) and considerably lower in Salton Sea fish (Table 8). The elevated levels of DDT in Salton Sea fish do not currently represent a health threat to recreational consumers. Assuming an equivalent daily consumption rate of 54 grams or 1.9 ounces of fish containing DDT at the maximum levels measured in Salton Sea fish (Table 8), the corresponding maximum doses would be lower than ATSDR's MRL and EPA's RfD. At a 9-fold lower consumption rate (i.e., 42 grams per week, or 6 ounces per month), the resulting maximum doses of DDT would also be lower than those corresponding to comparison values based on cancer effects in animals. Again, however, it should be noted that several epidemiological studies have not established an association between much higher DDT exposures and cancer in workers (29).

The levels of PCBs in New River fish (Table 4) exceed EPA's RBCs for cancer effects, assuming a consumption rate of 54 grams/day (23). EPA, IARC, and NTP all classify PCBs as probable human carcinogens based on sufficient evidence in animals. However, prolonged administration of high doses of highly chlorinated PCBs are required to cause cancer in animals and, even under these conditions, the only treatment-related cancers produced are late-appearing nonmetastasizing liver tumors that are not life-shortening (27). In fact, both the incidence of certain extrahepatic cancers and the animals' overall mortality may actually be decreased in treated animals relative to controls (27). Furthermore, PCBs in the environment do not represent a genotoxic hazard to humans, and even the highest exposures experienced by humans are orders of magnitude lower than those required to promote cancer in animals (27,35).

Consumption rates would have to be 10-30 times lower than the default of 54 grams/day (i.e., approximately 2 ounces per month) - and they probably are for most residents of Imperial Valley - in order for the resulting doses of PCB's (based on the maximum concentrations in Table 4) to be within ATSDR's chronic oral MRL of 0.02 ug/kg/day (27). This MRL, which includes an uncertainty factor of 300, is based on subclinical reductions of antibody response (and no other immunological parameters) in monkeys treated with as little as 5 ug Arolclor 1254/kg/day for 23-55 months (33). However, the health effects of PCB vary greatly with dose and species. Similar effects were not observed in monkeys treated with 100 ug Aroclor 1248/kg/day for 11 months (34). In mice, high doses of PCBs (e.g., 22 mg/kg/day) appear to be immunosupressors, but lower doses (e.g., 0.7 mg/kg/day) may actually be immunostimulators (27). Immunosuppression in humans has been reported only in patients acutely poisoned by high-level exposure to mixtures of PCBs, PCDFs (i.e., polychlorinated dibenzofurans), quarterphenyls, and dioxins. However, in these cases of yusho-yucheng syndrome, PCDFs rather than PCBs are believed to have been responsible for the toxic effects observed (35). Most relevant, perhaps, is the fact that (a) immunotoxicity has not been observed in humans exposed only to PCBs (35), and (b) significant immunosuppression has not been observed in men who consume large amounts of Baltic Sea fish contaminated with PCBs, DDT, PCDDs and PCDFs (36). No data were available on PCBs in fish from the Salton Sea. However, DDT levels were less than half those in New River fish, and PCBs might be expected to follow a similar pattern. Finally, the maximum concentration of total PCBs, which is used for purposes of conservatism, was detected at least 5 years ago, and does not necessarily reflect current levels. Although alternate interpretations are possible, comparison of the maxima for total PCBs in 1990 with PCB 1260 in 1984 (Table 4) could be interpreted as indicating that PCB levels decreased over that period of time. No current data are available.

In conclusion, based on a toxicological evaluation of the available monitoring data, ATSDR considers that the levels of pesticides and PCBs in fish from the New River or Salton Sea would not be expected to produce adverse health effects under the conditions of exposure believed to prevail at these sites. Although no adverse health effects would be expected to result from infrequent, low-level consumption of New River fish (e.g., 2 ounces per month), based solely on the content of pesticides and PCBs, it must be emphasized that the more substantial risk of concomitant exposure to pathogens is sufficient reason to avoid altogether any consumption of water or wildlife from the New River.

As mentioned earlier, all calculations of "safe" fish consumption levels are based on "wet weight" data only (Tables 3,4,5,7, and 8). The "lipid weight" data in Tables 2 and 9 and are not directly comparable to EPA's RBC values, because the latter are based on concentrations in the edible portion of fish rather than on concentrations in fat. The sources of the data in Tables 2 and 9 did not provide the additional information required (specifically, the percent fat of the sample) to convert concentrations on a fat basis to concentrations in edible fish.

VOCs:

The volatile organic compounds detected in water from the New River were generally present at levels that were within drinking water standards (Table 1). Maximum concentrations of methylene chloride (7 ppb) and tetrachloroethylene or PCE (6.6 ppb) did marginally exceed the MCL of 5 ppb for these compounds in drinking water (37,38). However, these levels would not be expected to produce any adverse effects in humans. The classification of PCE and methylene chloride as possible/probable human carcinogens is based on the induction of rodent liver tumors of questionable relevance to human cancer risk (37,38). In a 2-yr drinking water study, modest but statistically significant tumor yields were observed in high-dose female rats, but not in male rats or in mice of either sex (37). Extremely high, nephrotoxic doses of PCE increased the incidence of liver tumors in mice, but not in rats (38). The lowest dose of PCE used (386 mg/kg/day for 78 weeks) was comparable (mathematically, but not necessarily toxicologically) to the intake dose for a 70-kg adult drinking water containing 13 million ppb PCE at a rate of 2 liters/day for 50 years or more. Finally, the probable mechanisms by which these cancers were induced (i.e., peroxysome proliferation and glutathione conjugate formation) involve elements of rodent biology that are not operative in humans at low levels of exposure (39).

The maximum concentrations of 1,1,2,2-tetrachloroethane (500 ug/kg) and PCE (800 ug/kg) detected in New River fish exceed EPA's Risk-Based Concentrations (23), and comparable levels were also found in turtle tissue samples. However, the EPA's Risk-Based Concentrations for these two substances are based on the assumption of low-dose carcinogenicity in humans and lifetime exposure at a rate of 54 grams or about 2 ounces of fish per day. Neither assumption is likely to apply under the prevailing conditions of exposure at this site. Considering only the non-cancer effects of PCE and 1,1,2,2-tetrachloroethane, unlimited consumption of such fish would be safe for children as well as adults (38,40). It must be emphasized, however, that the New River and its wildlife contain several other contaminants (metals, pesticides and PCBs) at much higher concentrations, and that the potential for concomitant exposure to pathogens renders any level of consumption a potential health hazard. 

CONCLUSIONS

1. The New River poses a potential public health hazard because area residents could be exposed to fecal streptococci, and other pathogens through contact with contaminated surface water and foam. In addition, metals in the New River would represent a potential health hazard should people use the river as a primary source of drinking water. The maximum levels of several pesticides and PCBs detected in the New River exceeded comparison values for both cancer (CREGs and RBCs) and non-cancer effects (MRLs). However, these levels were generally insufficient to cause non-carcinogenic affects under site-specific conditions of exposure. Moreover, the assumptions on which CREGs for pesticides and PCBs are based may not be applicable to the probable exposure scenarios at New River. VOC's detected in the New River were generally within drinking water standards, and are unlikely to produce any adverse effects in exposed humans.

2. Water quality in the New River is affected by numerous point and non-point discharges on both sides of the border.

3. Based on available data, sediment from the New River does not present a public health threat, except in the unlikely circumstance where a pica child would consume a toxicologically significant amount of contaminated sediments. However, no sediment data are available for evaluation except for one sample taken in 1986. ATSDR therefore can not fully assess this potential exposure pathway.

4. New River fish are contaminated with metals, pesticides, PCBs, and VOCs. Salton Sea fish are contaminated with metals and pesticides. Fishing reportedly does occur in the New River and the Salton Sea, but the frequency and extent of fish consumption is not known. Several of the contaminants in New River water pose an increased (theoretical) risk of cancer, assuming a consumption rate of 54 grams per day for life. Smaller amounts of fish (2 ounces per month or about 1 small meal per month) could be consumed without exceeding ATSDR's non-cancer health guidelines for any of the contaminants. However, considering the potential biological hazards (i.e., pathogens from human sewage), the safest course of action is not to consume anything at all from the New River. Contaminant levels (i.e., of arsenic and DDT) in fish from the Salton Sea (a recreational area) are lower than those from the New River, and should not pose a health hazard to sport fishermen. Due to the saltiness of the water and its distance from the source of sewage contamination, no pathogenic hazard is expected to pertain to the Salton Sea.

5. Some area residents may be consuming turtles and frogs from the New River. Only limited data are available regarding contamination of turtle tissue, while area frogs have not been sampled at all. ATSDR also does not know the frequency and extent of consumption of turtles or frogs from the New River. However, considering the risk of concomitant exposure to pathogens, ATSDR considers it inadvisable for residents to hunt and/or consume any New River biota.

6. Some mosquitoes of Imperial Valley carry viruses which cause encephalitis. While some of these mosquitoes probably live in the New River, others may be found in different water bodies in the area. Therefore, cases of encephalitis can not be attributed solely to mosquitoes from the New River. It is possible, however, that a decrease in sewage in the New River could result in a decrease in mosquitoes because the mosquitoes have a preference for sewage contaminated water.

RECOMMENDATIONS

Cease\Reduce Exposure Recommendations

1. Restrict access to the New River at major road crossings and in the populated areas of Brawley and Calexico, where human contact is likely to occur.

2. Increase and improve the existing signs warning against contact with the New River. These sign should be clearly visible, specifically in those areas where human contact is more likely to occur.

3. Promote coordination and cooperation between the U.S. and Mexican governments to reduce contamination in New River surface water. In addition, work with the Mexican government to reduce production of foam in the river.

4. Raise awareness about contamination of the river among residents of Imperial County.

5. Raise awareness about contamination in New River among government officials and area residents in Mexico.

6. Advise area residents against collecting and eating fish\turtles\frogs from New River.

7. Advise area residents that contact with the foam generated by the New River should be avoided.

Site Characterization Recommendations

1. Surface water in the New River should continue to be monitored for fecal coliform, fecal streptocci, metals, pesticides and PCBs.

2. Additional sediment samples from the New River should be collected and analyzed for contaminants. It is particularly important to sample sediment in areas where human contact is more likely to occur.

3. If area residents regularly consume frogs or turtles from the New River, additional samples of these animals should be collected and analyzed.

4. Additional samples of the foam generated by the New River should be collected and analyzed for contaminants found in the surface water.

5. ATSDR will review additional sampling data currently being collected from the New River when that data becomes available.

Health Activities Recommendation Panel

The public health assessment for the New River Health Consultation was reviewed by the Health Activities Recommendation Panel on December 13, 1995. Based on the recommendations of the panel, it is proposed that the following statement be included in the health consultation.

The data and information developed in the New River Health Consultation have been evaluated by the Health Activities Recommendation Panel for appropriate public health actions. Viral, microbial and chemical contaminants are present in the New River at levels which pose a potential public health threat. The Health Activities Recommendation Panel (HARP) has determined that site-specific environmental health education is warranted. The California Department of Health Services, through it's cooperative agreement with the ATSDR Division of Health Education, will lead this educational effort. HARP also recognizes the potential for exposure to Mexican citizens and supports the state's efforts to inform Mexican citizens of their potential for exposure. ATSDR will evaluate any new data or information it receives about this site to determine if additional public health actions are appropriate.

PUBLIC HEALTH ACTION PLAN

 B. Public Health Actions

The actions described in this section are actions for the New River will be or have been taken by ATSDR, the U.S. Environmental Protection Agency, the U.S. Geological Survey (U.S.G.S.), the California Department of Health Services (CDHS), the California Environmental Protection Agency (CAEPA), the California State Water Resource Control Board (CSWRCB), the California Regional Water Quality Control Board (CRWQCB) the California Department of Fish and Game (DFG), and the Imperial County Department of Health. The purpose of this plan is to ensure that the petitioned public health assessment not only identifies public health hazards, but provides a plan of action designed to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. The public health actions to be implemented are as follows:

Actions Undertaken

1. Environmental sampling of the New River has been conducted at the International Boundary since 1969, with additional samples collected between the International Boundary and the Salton Sea. The U.S. Geological Survey (U.S.G.S.), the California Regional Water Quality Control Board (CRWQCB), the California State Water Resource Control Board (CSWRCB) and the California Department of Fish and Game (DFG) collected these samples to assess the concentration of contaminants in surface water, sediment, and fish and turtle tissue. Each media was analyzed for trace elements, metals, pesticides, VOC's and PCB's. Surface water was also analyzed for biological contamination.

2. Environmental Protection Agency Region IX New River Binational Toxics Monitoring Program: In 1995 the Environmental Protection Agency initiated a two year program to monitor the occurrence of toxic materials in the New River. Water and sediment samples from three locations along the New River at Mexicali, the International Border in Calexico, and the Westmoreland outlet to the Salton Sea were analyzed for metals, organic compounds, and pesticides. Fish were also collected along the New River and are being analyzed for bioaccumulation of toxic materials. Additionally the water from the New River is being tested on a monthly basis for the presence of materials that may affect the mortality or growth or reproduction of three sensitive surrogate organisms: green algae, water fleas, and juvenile fish. Sampling will continue through 1996. The results of the Binational Toxics Monitoring Program will report current contaminant levels.

Actions Planned

1. An environmental health education program is recommended for the purposes of educating the public health professionals serving the community of New River. This program will target the local medical communities on the U.S. and Mexican border to educate them on the nature and possible consequences of exposure to the varied contaminants of the New River. A complete and accurate needs-assessment will determine the most effective course of education, which will include--but not limited to--obtaining comprehensive exposure histories, and professional health training on contaminants. The program will also include community health education on contaminants and the possible consequences resulting from river use and a public awareness campaign. These activities will be conducted by the ATSDR Department of Health Education cooperative agreement with California, in conjunction with the California State Department of Health Services.

2. Pathogen monitoring along the New River will be a priority for EPA Region IX, provided funding for such a project can be secured.

3. ATSDR will contact appropriate federal and state officials to request that additional data or new data be sent to ATSDR as it is available. ATSDR will ensure that recommendations made in this petitioned public health consultation are forwarded to the appropriate agencies for action.

4. ATSDR will coordinate with EPA, Region IX, and state agencies in their ongoing site investigation of the New River site, and in implementing the site characterization recommendations in this public health assessment.

5. If any new data or information are found to be of significant public health concern, the Division of Health Assessment and Consultation will revise the New River Health Consultation as appropriate.

REFERENCES

1. California Regional Water Quality Control Board. Water Quality Investigation of New River Watershed in Mexico. California:CRWQCB, July 1983.

2. Imperial County Community Economic Development. Imperial County Demographics Packet. California; 1990.

3. Agency for Toxic Substances and Disease Control. Trip Report for New River. July 26-29, 1994.

4. Agency for Toxic Substances and Disease Control. ATSDR Record of Activity for telephone communication with Imperial Valley Fish and Game staff. August 1995.

5. California Regional Water Quality Control Board. Quality of New River Water at Calexico, Gage Near International Boundary (DWR station 57) California:CRWQCB, Sept. 2, 1976 - Feb. 8, 1995.

6. U.S. Department of the Interior-Geological Survey. Water Quality Data for Selected Sites Tributary to the Salton Sea. California, August 1969 - June 1970.

7. U.S. Department of the Interior - Geological Survey. Water Quality in the New River from Calexico to the Salton Sea. California, May 1977 - June 1978.

8. U.S. Department of the Interior - Geological Survey. Water Quality Conditions in the New River. California, 1979-1986.

9. California Regional Water Quality Control Board. Report on Preliminary Study of Fate of Selected Pollutants Discharged from Mexicalli, Mexico to the New River. California:CRWQCB, December 1984.

10. Appendices To Petition Under Compensation and Liability Act. Declaration of Lee Cottrell,M.D. Volume 1. December 7, 1993.

11. Letter dated March 25, 1980, from Arthur Swaijan, CRWQCB, to Sam Kalichman, State Department of Health Services, and Dr. L. Lee Cottrell, Imperial County Health Department.

12. California Regional Water Quality Control Board. Investigation of Foaming in the New River. California: CRWQCB 1980.

13. U.S. Environmental Protection Agency Region IX. Priority Pollutants Data Reports. New River, Imperial County, Ca. 1984-1986.

14. California State Water Resources Control Board. Toxic Substances Monitoring Program: Ten Years Summary Report 1978-1987. California: CSWRCB, August 1990.

15. California State Water Resources Control Board - California Environmental Protection Agency. Toxic Substances Monitoring Program: 1990 Data Report. California: SWRCB-CEPA, May 1992.

16. W.K. Reisen, H.D. Lothrop, S.B. Presser, M.M. Milby, J.L. Hardy, M.J. Wargo, E.W. Gordon and R.W. Emmons. Landscape Ecology of Arboviruses in the Coachela and Imperial Valleys of California. Journal of Medical Entomology. 1993.

17. C.J. Mitchell, D. Bruce Fancy and T.P. Monath.1980. Arthropods Vectors. In: Monath, T.P. [ed.];St. Louis Encephalitis. American Public Health Assoc., Inc. Washington. pp.313-314.

18. State of California Department of Public Health. Bureau of Vector Control. A Mosquito Survey of Imperial Valley. Imperial County, California. Dec. 1953-Jan.1955.

19. E.B. Workman, M.B. Madon, R.W. Emmons, H.I. Magy, D.L. Rohe, L.J. Krone. ArbovirusAnd Mosquito Vector Surveillance in Coastal and Irrigated Desert Areas of Southern California 1972-1973. Bull. Soc. Vector Ecol. 1976.

20. California Regional Water Quality Control Board. Letter to CA Department of Health Services. May 20, 1983.

21. Imperial County, California. Letter to ATSDR. December 15, 1993.

22. Koren, H. (1991). Handbook of Environmental Health and Safety: Principles and Practices. Vol. II. Second Edition. Lewis Publishers, 1991.

23. EPA (1995). Risk-Based Concentration Tables. Environmental Protection Agency, Region III, Philadelphia, Pa., June 1995.

24. ATSDR (1990a). Toxicological Profile for Copper. TP-90/08. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. April, 1990.

25. ATSDR (1993a). Toxicological Profile for Arsenic (Update). TP-92/02. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. April, 1993.

26. ATSDR (1993c). Toxicological Profile for Heptachlor/Heptachlor Epoxide. TP-92/11. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. April, 1993.

27. ATSDR (1993b). Toxicological Profile for Polychlorinated Biphenyls. TP-92/16. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. April, 1993.

28. EPA (1992). Compendium of body burden biomarkers for Pesticides. EPA/600/X-93/082. Environmental Protection Agency. Environmental Monitoring Systems Laboratory. Las Vegas, Nevada. May 1992.

29. ATSDR (1994a). Toxicological Profile for 4,4'-DDT, 4,4'-DDE, 4,4'-DDD (update). TP-93/05. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. May, 1994.

30. ATSDR (1994b). Toxicological Profile for Chlordane (update). TP-93/03. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. May, 1994.

31. ATSDR (1994c). Toxicological Profile for Alpha-, Beta, Gamma, and Delta-hexachlorocyclohexane (update). TP-93/09. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. May, 1994.

32. Goodman, J.I., Ward, J.M., Popp, J.A., Klaunig, J.E., and Fox, T.R. (1991). Mouse liver carcinogenesis: Mechanisms and relevance. Fundamental and Applied Toxicology 17: 651-665

33. Tryphonas, H., Luster, M.I., Schiffman, G., et al. (1991). Effect of chronic exposure of PCB (Aroclor 1254) or specific and low specific immune parameters in the rhesus (Macaca mulatta) monkey. Fundamental and Applied Toxicology 16: 773-789.

34. Thomas, P.T. and Hinsdill, R.D. (1978). Effect of polychlorinated biphenyls on the immune responses of rhesus monkeys and mice. Toxicology and Applied Pharmacology 44: 41-51.

35. Kimbrough, R.D. (1994). The human health effects of polychlorinated biphenyls. In: Phantom Risk: Scientific Inference and the Law (Kenneth R. Foster, David E. Bernstein, and Peter W. Huber, Eds.), The MIT Press, Cambridge, Massachusetts, pp. 211-228.

36. Svensson, B.G., Hallberg, T., Nilsson, A., et al. (1994). Parameters of immunological competence in subjects with high consumption of fish contaminated with persistent organochlorine compounds. International Archives of Occupational and Environmental Health 65: 351-358.

37. ATSDR (1993d). Toxicological Profile for Methylene Chloride. TP-92/13. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. April, 1993.

38. ATSDR (1993e). Toxicological Profile for Tetrachloroethylene. TP-92/18. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. April, 1993.

39. Green, Trevor (1990). Species differences in carcinogenicity: the role of metabolism in human risk evaluation. Teratogenesis, Carcinogenesis, and Mutagenesis 10: 103-11

40. ATSDR (1994d). Toxicological Profile for 1,1,2,2-Tetrachloroethane. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. August, 1994.

Also reviewed:

EPA (1993). Compendium of body burden biomarkers for volatile organic compounds and halogenated hydrocarbons. EPA/600/X-93/082. Environmental Protection Agency. Environmental Monitoring Systems Laboratory. Las Vegas, Nevada.

ATSDR (1990b). Toxicological Profile for Heptachlor/Heptachlor Epoxide. TP-90/26. U.S. Dept. of Health & Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. December, 1990.

PREPARERS OF REPORT 

Maureen Kolasa, R.N., M.P.H.
Environmental Health Scientist
Petition Response Branch
Division of Health Assessment and Consultation

Lourdes Ortiz, B.S.
Oak Ridge Fellow
Petition Response Branch
Division of Health Assessment and Consultation

Frank Schnell, Ph.D.
Toxicologist
Petition Response Branch
Division of Health Assessment and Consultation

ATSDR Regional Representative:

William Nelson
Senior Public Health Adviser
EPA Region IX

APPENDIX A

Figure 1: Salton Sea and Imperial Valley Area Map
Figure 2: Imperial Valley Canal Map
[These figures are not included in this website version. They show little more than locations of towns, cities and rivers in the region, and high quality copies of them are not available to us.]

APPENDIX B

Table 1. Contaminants in On-Site Surface Water At New River
1 = Most Probable Number per 100 milliliter
2 = colonies per liter
3 = surface water designated for water contact recreation
4 = parts per billion
5 = reference dose media evaluation guide
6 = environmental media evaluation guide
7 = U.S. EPA secondary maximum contaminant limit
8 = U.S. EPA primary maximum contaminant level
9 = U.S. EPA lifetime health advisory for drinking water
10 = cancer risk evaluation guide
11 = volatile organic chemical
12 = pico Curie per liter
* = no comparison value is available
** = no data is available
IB = International Boundary
 
Table 2. Pesticides and PCBs in Fish at New River Summary of 1978-1987 & 1990 Data (PPB, wet weight)
 
Table 3. Metals in Fish at New River Summary of 1978-1987& 1990 Data (PPM, wet weight)
 
Table 4. Pesticides and PCBs in Fish at New RiverSummary of 1978-1987 & 1990 Data. (PPB, wet weight)
 
Table 5. Volatile Organic Chemicals Detected in New River Fish. (PPM, wet weight)
 
Table 6. Organic and Inorganic Chemicals detected in New River Sediments. (Dry weight in PPM)
 
Table 7. Contaminants in Soft Shelled Turtle Tissue at New River. (wet weight)
Table 8. Organic and Inorganic Chemicals in Fish at the Salton Sea. (PPB, wet weight)
 
Table 9. Organic Chemicals in Fish at Salton Sea. Summary of 1978-1987 & 1990 Data (PPB, lipid weight)
  

 

APPENDIX C - COMPARISON VALUES

Comparison Values

Comparison values used in ATSDR public health assessments are contaminant concentrations in specific media used to select contaminants for further evaluation. The values provide guidelines for estimating a dose at which no adverse health effects would be expected. When more than one comparison value exists for a contaminant in a particular medium, ATSDR uses the most conservative (lowest) value. Comparison values and units of measure used in the Environmental Contamination and Other Hazards and the Public Health Implications sections of this public health assessment are described in the following paragraphs.

* CLHA = Child Longer-Term Health Advisory
* CREG = Cancer Risk Evaluation Guide
* EMEG = Environmental Media Evaluation Guide
* LTHA = Lifetime Health Advisory
* MCL = Maximum Contaminant Level
* MCLG = Maximum Contaminant Level Goal
* MRL = Minimal Risk Level (mg/kg/day)
* RfD = Reference Dose (mg/kg/day)
* RBCs = Risk-Based Concentrations
* ppm = milligrams per liter (mg/L water) milligrams per kilogram (mg/kg soil)
* ppb = micrograms per liter (mg/L water) micrograms per kilogram (mg/kg soil)
* kg = kilogram
* mg = milligram
* mg = microgram
* L = liter

Child Longer-Term Health Advisories (CLHAs) are contaminant concentrations that the Environmental Protection Agency (EPA) believes will protect public health (taking into consideration the availability and economics of water treatment technology) using a child's weight and ingestion rate.

Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million persons exposed over a lifetime (70 years). CREGs are calculated from EPA's cancer slope factors and therefore reflect estimates of risk based on the assumption of zero threshold and lifetime exposure. The true risk is unknown and could be as low as zero.

Environmental Media Evaluation Guides (EMEGs) are media-specific comparison values used to select contaminants of concern at hazardous waste sites. They are calculated using ATSDR minimal risk levels (MRLs) and factor in body weight and ingestion rates. 

Lifetime Health Advisories (LTHAs) are contaminant concentrations that the Environmental Protection Agency (EPA) believes will protect public health (taking into consideration the availability and economics of water treatment technology) over a lifetime (70 years) at an ingestion rate of 2 liters of water per day. 

Maximum Contaminant Levels (MCLs) are maximum permissible contaminant concentrations in drinking water that EPA believes will protect public health (considering the availability and economics of water treatment technology) over a lifetime (70 years) at an exposure rate of 2 liters per day (for an adult).

Maximum Contaminant Level Goals (MCLGs) are drinking water health goals set at levels at which no known or anticipated adverse health effect occurs and which allow an adequate margin of safety. Such levels consider the possible impact of synergistic effects, long-term and multi-stage exposures, and the existence of susceptible groups in the population. When there is no safe threshold for a contaminant, the MCLG should be set at zero.

A Minimal Risk Level (MRL) is an estimate of daily human exposure to a chemical (in mg/kg/day) that is likely to be without an appreciable risk of deleterious effects (noncancer) over a specified duration of exposure. MRLs are calculated using data from human and animal studies, and are reported for acute (ē 14 days), intermediate (15-364 days), and chronic (ģ 365 days) exposures. MRLs for specific chemicals are published in ATSDR Toxicological Profiles. 

EPA's Reference Dose (RfD) is an estimate of the lifetime daily exposure to a contaminant that is unlikely to cause adverse (noncancer) health effects.

Risk-Based concentrations (RBCs) are calculated by EPA Region III for contaminants in air, water, soil, and fish. ATSDR uses RBCs primarily for the values in fish, because ATSDR has no comparison values for contaminants in fish. However, like ATSDR's comparison values, RBCs are screening values only, and do not constitute regulation or official guidance.

Comparison Value References

1. Agency for Toxic Substances and Disease Registry. Health Assessment Guidance Manual. Atlanta: ATSDR, March 1992.