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The Arizona Department of Environmental Quality (ADEQ) issued a fish consumption advisory in 1991 for the lower Gila River. Fish, along with turtles, frogs, and crayfish, were included in the advisory. This advisory was issued for the organochlorine pesticide DDT and its metabolites DDE and DDD (DDTr), toxaphene, dieldrin, and chlordane.

ADEQ and the Arizona Game and Fish Department (AGFD) conducted confirmatory fish sampling and tissue analysis in 1999. The fish consumption advisory was reissued in April 2000 for DDTr and toxaphene based on the 1999 sampling. In 2001, ADEQ posted 72 new signs to replace the 1991 fish advisory signs because most of the original signs had been removed or destroyed.

Estrella Regional Park rangers have observed individuals fishing along this stretch of the Gila River. Park staff asked the Arizona Department of Health Services to re-evaluate the data from the 1999 fish tissue analysis and to determine what additional measures may be necessary to reduce consumption of contaminated fish taken from the Park.

The objective of this health consultation is to review recent fish sampling data, evaluate the extent of fishing activity, and determine whether additional public education is necessary to inform the public about the fish advisory.


The lower Gila River is southwest of Phoenix, in southwestern Arizona. The watershed extends 88 miles from 59th Avenue in Phoenix to the Painted Rocks Lake, which is approximately 18 miles northwest of Gila Bend, Arizona. (Figure 1 - Map of Arizona Watersheds). 1

This portion of the river is dominated by effluent flows with the exception of significant rainfall events. During normal flow periods, almost all water in the river originates as discharges from wastewater treatment plants. Perennial flows begin in metropolitan Phoenix at the 23rd Avenue Wastewater Treatment Plant, and additional effluent is received from the 91st Avenue Wastewater Treatment Plant. Agricultural drain water canals supplement the river system.2

Use of organochlorine pesticides

DDT was first applied experimentally in Arizona in 1943. Commercial use began in 1945. Within a year, DDT was in general use against the cotton bollworm.3 The development of a cotton monoculture during the 1950s in the lower Gila River Valley resulted in infestations of the pink bollworm (Pectinophora gossypiella). By the late 1950s, the bollworms threatened to severely decimate the Valley's cotton crop.1 Cotton farmers frequently used DDT to control the pink bollworms because of DDT's low cost and long-term effectiveness.1 Twenty-three pounds per acre of DDT were applied per year from multiple applications throughout the growing season.2 Use restrictions were placed on DDT in Arizona in 1968. DDT was banned in 1969 due to the contamination of dairy products.3

Toxaphene was used as a broad-spectrum agricultural insecticide. Its use increased significantly following the national suspension of DDT. Toxaphene applications averaged 7.6 pounds per acre in 1965. Most domestic use of toxaphene and DDT was on cotton crops. Before the suspension of both products, toxaphene-DDT mixtures were frequently used to control insect pests.

The total farmland irrigated by DDT- and toxaphene-contaminated drain water exceeded 100,400 acres. Agricultural drain water canals have transported an estimated 4,917 tons of DDT to the river.2 In the 1970s, authors Johnson and Lew concluded that, "the Gila River appears to be the most DDT-burdened stream of 20 streams sampled in the Western United States." 2 The U. S. Fish and Wildlife Service (USFWS) said in 1982 that DDE residues in birds collected in the Goodyear-Avondale area were among the highest in the nation.1 The University of Arizona conducted soil sampling in 1985 that revealed 1.5 micrograms per gram (µg/g) DDE and 0.4 µg/g DDT extended to 18 inches below the soil surface. These levels were 20 times the background concentrations. Based on that report, and those of the Arizona Game and Fish Department (AGFD) and ADHS, fish consumption advisory signs were posted in 1991 from 59th Avenue in Phoenix to Painted Rocks Lake for DDTr and toxaphene.2

The Arizona Priority Pollutant Sampling Program (APPSP) and the ADEQ Water Quality Assurance Revolving Fund (WQARF) conducted confirmatory sampling at three sites within the Gila drainage system in 1999. Sampling sites were at Estrella Regional Park and Gillespie Dam. Samples of largemouth bass, common carp, channel catfish, and tilapia were collected. DDTr residues found in these fish exceeded the ADEQ's state screening concentrations in 72% of the samples. The mean concentration of DDTr was 0.48 milligrams per kilogram (mg/kg) wet weight, and the maximum level found was 4.5 mg/kg wet weight in a channel catfish. These levels of DDTr were lower than the levels found in previous studies.

Toxaphene was found in high concentrations in several of the samples. The mean was 2.45 mg/kg wet weight, and the maximum level found was 5.8 mg/kg wet weight in a channel catfish. Dieldrin and chlordane were also named in the original 1991 fish advisory. In the 1999 study, levels of dieldrin were below detection levels. Analyses for chlordane were not conducted because of interference from the other constituents, including components of toxaphene. The possibility of a large terrestrial reservoir and the transport of DDTr to the Gila drainage during runoff events and agricultural canal return flows may help to renew the aquatic reservoir of these pesticides.3

The 1999 ADEQ report recommended that the fish consumption advisory remain in effect for DDTr and toxaphene.3 The advisory also included turtles, crayfish, and frogs. The ADEQ estimated that persons should not consume more than one 8-ounce meal from these areas every 7.2 weeks.


The sampling results collected in 1999 by ADEQ were used to determine maximum recommended consumption rates for fish. DDTr and toxaphene are identified as the contaminants of concern for the Gila River fish advisory. The average levels of DDTr and toxaphene were compared to the risk-based consumption limits calculated by the U.S. Environmental Protection Agency (USEPA). USEPA's risk-based approach is protective of recreational fishers and subsistence fishers within the general population.5

The risk-based maximum recommended consumption limits were calculated as the number of allowable fish meals per month, based on the ranges of DDTr and toxaphene in the consumed fish tissue. Table 1 provides the assumptions USEPA used to calculate the consumption limits. Table 2 provides a comparison of the 1999 sampling results to the risk-based consumption limits.3,4,6

Table 1.

USEPA Assumptions Used To Determine Risk-Based Consumption Limits.
Variable DDTr Toxaphene
Adult body weight 70 kilograms (kg) 70 kilograms (kg)
Average fish meal size 0.227 kilograms (8 ounces) 0.227 kilograms (8 ounces)
Time-averaging period 1 month (30.44 days) 1 month (30.44 days)
Reference dose (USEPA) 5 x 10-4 milligrams/kilograms-day 2.5 x 10-4 milligrams/kilograms-day
Cancer slope factor (IRIS) 0.34 (milligrams/kilograms-day)-1 1.1 per milligrams/kilograms-day
Maximum acceptable cancer risk level 10-5 over 70-year lifetime 10-5 over 70-year lifetime

Table 2.

1999 Fish sampling Results and Corresponding USEPA fish Consumption limits
Chemical Mean Milligrams per kilogram of wet weight Allowable Fish Meals per Month
DDTr 0.48 0.5 meals
Toxaphene 2.45 0 meals

Organochlorine Pesticides.

Both DDTr and toxaphene are organochlorine pesticides. They are readily absorbed through the digestive system. DDTr and toxaphene accumulate in fatty tissue, including brain and adipose tissue, and may be found in human milk because of their high lipid content. The neurological effects of organochlorine exposure are based upon interference with axonic transmission of nerve impulses. This causes altered functioning of the nervous system, primarily the brain.6

DDT (1,1,1 -trichloro-2,2-bis (p-chlorophenyl)ethane)

DDT is an organochlorine pesticide that was banned for use in the United States in 1972; however, it is ubiquitous because of its widespread use in previous decades and its relatively long half-life. DDT has been reported to persist for at least 30 years in the environment. Heavy agricultural applications may cause accumulations of DDTr in the top layers of the soil. DDT and its metabolites (DDTr) are immobile in most soils and are relatively insoluble in water. Loss and degradation in soils of DDTr include runoff, volatilization, photolysis, and biodegradation (aerobic and anaerobic). These processes occur very slowly. The main pathways for loss in water are volatilization, photodegradation, adsorption to particulates in the water, bioaccumulation, and sedimentation.2

DDTr is particularly hazardous in the environment because of its high bioconcentration factor of 53,600. This is the highest of any priority pollutant. Bioconcentration factors are a measure of a chemical's probable propensity to build up in animal tissues. Bioconcentration may cause almost undetectable amounts of DDTr in the water of aquatic ecosystems to be concentrated to extreme levels in top predators such as largemouth bass (Micropterus salmoides) and black crappie (Promoxis nigromaculatius).

DDTr is stored in fat, liver, kidney, and brain tissue, and trace amounts can be found in all tissues. DDE is stored more readily than DDT. DDT is eliminated through first-order reduction to DDD and, to a lesser extent, to DDE. DDE is eliminated much more slowly, with a biological half-life of 8 years. Because elimination occurs slowly, ongoing exposure may lead to an increase in the body burden over time.6

The main exposure route for DDTr is the consumption of foods from areas of the world where DDT is still used or areas that contain bioaccumulated residues of DDTr.7 Upon ingestion, DDT is readily absorbed through the gastrointestinal tract, with increased absorption in the presence of fats. Acute health effects in humans may include nausea, diarrhea, increased liver enzyme activity, irritation of the eyes, nose or throat, disturbed gait, malaise and excitability; at higher doses, tremors and convulsions are possible. Moderate to high ingested doses of up to 280 mg/kg may be tolerated by adults although one ounce of 5% DDT in a kerosene solution was reported to have caused a fatal poisoning in a child.2

Chronic effects have been observed on the nervous system, liver, kidneys, and immune systems in experimental animals. Effects on the nervous system have been observed in both humans and animals and can vary from mild altered sensations to tremors and convulsions.7 Localized liver damage was the main effect on the liver seen in animal studies. Subtle changes in liver cell physiology, increased liver weight, and increased liver enzyme activity were observed at low doses. Kidney effects observed were adrenal gland damage and adrenal gland hemorrhage.2 USEPA classified DDTr as a B2, or probable, human carcinogen on the strength of animal trials on DDT. Eight of nine studies conducted using mice showed indications of tumorgenicity. Doses of 0.15 - 37.7 mg/kg-day showed an increase of liver and lung tumors in mice. 2


Toxaphene is the trade name for an organochlorine pesticide that is a mixture of at least 670 chlorinated camphenes. Toxaphene was first introduced in 1947 and was probably the most heavily used pesticide on cotton and other crops in the United States during the 1970s after DDT was banned.4 Toxaphene was banned for most uses in 1982 and banned completely in 1990. Toxaphene has a relatively long half-life of 1 to 14 years. Toxaphene can enter waters from agricultural runoff or might volatilize and be transported through the atmosphere. Toxaphene bioconcentrates in the tissues of aquatic organisms and is biomagnified in the aquatic food chain.4

Toxaphene exposures may occur in the general population through ingestion of contaminated food. The advisories recommending reduced fish consumption are based on an acceptable daily intake (ADI) level for toxaphene. The EPA's ADI for toxaphene is 0.2 micrograms per kilogram. Persons who consume large quantities of fish contaminated with toxaphene may be at greater risk than the general population because toxaphene bioaccumulates in fish.

Toxaphene primarily targets the nervous system. Individuals with latent or clinical neurological diseases, such as epilepsy or behavioral disorders, may be at higher risk. Infants and the fetus with developing nerve systems are also vulnerable to the harmful effect of potential toxaphene exposure.

Toxaphene is rapidly conveyed into breast milk after maternal exposure to the chemical. The half-life of toxaphene in milk has been estimated at 9 days.4 Chronic exposure to toxaphene may result in damage to the liver, kidney, adrenal, immunological, and neurological systems as indicated by animal studies. No information was available about the long term effects on humans. 8

Developmental toxicity associated with toxaphene is based on effects observed in adult individuals. Children are at greater risk. Embryos, fetuses, and neonates up to age 2 to 3 months may be at increased risk of adverse effects because their enzyme detoxification systems are immature. Infants and children are especially susceptible to immunosuppression because their immune systems do not reach maturity until 10 to 12 years of age. Animal studies suggest that the detoxification of toxaphene mixture in the immature human may be less efficient than the metabolism and detoxification of the single components.

Individuals who may be at greater risk from toxaphene are those with diseases of the renal, nervous, cardiac, adrenal, and respiratory systems. Individuals using certain medications are also at potential risk because of induction of hepatic microsomal enzymes by toxaphene. Hepatic microsomal enzymes affect the metabolism of some drugs and alcohol. This was observed in a man using warfarin as an anticoagulant while he used toxaphene as an insecticide. The effectiveness of the drug was reduced due to its increased metabolism arising from toxaphene's induction of microsomal enzymes.8

USEPA has classified toxaphene as a probable human carcinogen (Group B2) based on oral studies in animals. No conclusive human epidemiological studies are available on the carcinogenic effects of toxaphene.4


ADHS staff made site visits in August and September 2003 to the stretch of river near and in the Estrella Regional Park. This stretch of river is largely inaccessible by vehicle. These visits were made very early in the morning on weekends to observe compliance with the posted fish advisory. ADHS staff had initially intended to interview persons that were actively fishing along the river to collect information on consumption rates. However, almost all of the persons fishing along the river either moved away or declined attempts to conduct a conversation. Attempts were made in English and Spanish languages because the vast majority of fishermen encountered were Hispanic males. The presence of alcohol and firearms also were a deterrent to approaching some groups. The fishermen appeared to be keeping fish that they caught instead of releasing the fish back into the river.

It is likely that rural and urban residents fishing at the river are aware of the fish advisory. Large, yellow conspicuous fish advisory signs in both English and Spanish have been posted since 2000 (Appendix 2). Personal conversations in August 2003 with an Estrella Park ranger indicated that fishing was a regular activity along the river inside and nearby the park despite the posted signs. Park rangers routinely advise fishermen about the fish advisory and to remove trash left behind that includes bait and other items used during fishing. The rangers also said fishermen will hide in the vegetation along the riverbank to avoid contact with the rangers. Some of the fish advisory signs around and inside the park have been removed or heavily damaged by vandals. County park personnel have requested the Arizona Department of Environmental Quality replace the missing and damaged signs.

River flows were negligible west of the Estrella Parkway, which precluded anyone fishing past this point. This road is the western boundary of Estrella Regional Park. ADHS also observed people fishing below the 91st Avenue wastewater treatment facility.

Subsistence fishers consume fish as a major staple of their diet. These fishermen rely on fish to meet nutritional needs, as an inexpensive food source, and in some cases, because of their cultural traditions. Subsistence fishermen often have higher consumption rates than other groups; however, consumption rates vary considerably among subsistence fishermen. Other fish surveys in the nation have raised concerns that minority or low-income populations may be exposed to contaminant concentrations over a long period. These groups, while not composed entirely of fishers, may have exposure levels as high as those for subsistence fishers. Another exposed group may not be well-characterized is made up of fishermens' family members, including extended families to whom fish is supplied. Those consuming the fish may be unaware of the fish advisories, even if the actual fishermen are aware.6


Whether fishermen along this region of the Gila River are bringing home fish and preparing them for their family and children is unknown. The presence of tackle, including ice chests and buckets, suggest that at least some fish are being prepared at home. It is reasonable to assume that at least fishermen's children are consuming some fish despite the current fish advisory of no consumption of fish from this stretch of the river.

A child's exposure may differ from an adult's exposure in many ways. Children drink more fluids; and eat more food per kilogram of body weight. The greatest dietary intake of organochlorine pesticides is from meat, poultry, dairy products, and fish. Infants and young children for whom a substantial part of their food is breast milk may be exposed to DDTr and toxaphene. Both selectively partition in fatty tissues and into human breast milk. Children may be at greater risk for toxic effects caused by toxaphene because their immune systems are not fully developed until 10 to 12 years of age. Immunosuppressive effects have been demonstrated in animals after chronic exposure to toxaphene. These studies have also suggested that immature animals cannot detoxify a toxaphene mixture as efficiently as they can the single components of the mixture.4


  • Following the fish advisory issued for the middle Gila River poses no public health hazard. However, consumption of fish from this part of the river more often can increase the risk that people could develop adverse health effects. The risk is greatest for those who subsistence fish and for the developing fetus and nursing child.

  • ADHS staff observed a subpopulation of Hispanics obtaining fish from the river. Because of the equipment the people had, ADHS believes the people fish there often and take at least some of the fish home for consumption.

  • Additional educational efforts in Spanish are needed to inform the Hispanic community of the fish advisory. The recipients of fish taken from the Gila River may not be aware of the advisory. Public awareness of the fish consumption advisory needs to be increased among the Hispanic community who consume fish from the middle Gila River. Family members and others may be consuming fish obtained from these areas without any knowledge of the fish advisory, even though the fisher is aware of the existing advisory. Fish, turtles, and frogs obtained from this area should not be eaten.


  • Replace vandalized or missing warning signs. The Arizona Department of Environmental Quality has posted fish advisory signs in English and Spanish along the river. The Arizona Department of Health Services will continue to notify the Arizona Department of Environmental Quality when the public and other government agencies report signs that are missing or vandalized.

  • Ensure that community leaders within the neighboring Hispanic community understand the fish advisory and that consumption of fish from the river should be avoided.


  1. The Arizona Department of Health Services will provide flyers in English and Spanish for retail businesses and grocery stores in the areas of the river explaining why fish and other wildlife from the lower Gila River should not be consumed. These flyers will provide information for the public who may fish in this stretch of the Gila River and for families who may consume fish caught by someone else.

  2. The Arizona Department of Health Services will provide information to the local Hispanic media. The goal of this information will be to increase awareness of the fish advisory along the lower Gila River. This will be done in August 2004 when water flows in this part of the river increase and fishing activity increases.


  1. Earth Technology Corporation. 1993. Lower/Middle Gila River Study and Painted Rocks Lake Phase 1 Diagnostic/Feasibility Study. Maricopa County, Arizona. Volume 1 of 2. Tempe, Arizona.

  2. U.S. Fish and Wildlife Service. 1997. Region 2 Contaminants Program. Environmental Contaminants in fish and wildlife of the lower Gila River, Arizona.

  3. Arizona Department of Environmental Quality and Arizona Game and Fish Department. 1999. A fish consumption advisory investigation for the Middle Gila River: Patterns and Trends. Phoenix, Arizona.

  4. U.S. Environmental Protection Agency. Office of Water. 1999. Toxaphene Update: Impact on Fish Advisories. EPA-823-F-99-018.

  5. U.S. Environmental Protection Agency. Office of Water. 2000. Volume 1: Fish Sampling and Analysis. EPA-823-B-00-007.

  6. U.S. Environmental Protection Agency. Office of Water. 1997. Guidance for Assessing Chemical Contamination Data for Use in Fish Advisories. Volume 2. Risk Assessment and Fish Consumption Limits. Second Edition. EPA-823-B-97-009.

  7. Agency for Toxic Substances and Disease Registry. 2002. Toxicological Profile for DDT/DDD/DDE (Update). Atlanta, Georgia. U.S. Department of Health and Human Services, Public Health Service.

  8. Agency for Toxic Substances and Disease Registry (ATSDR). 1996. Toxicological Profile for toxaphene. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.


Arizona Watersheds


Arizona Department of Health Services, Office of Environmental Health

Kristina Schaller, Office of Environmental Health
Will Humble, Bureau Chief, Epidemiology and Disease Control, Principal Investigator

ATSDR Regional Representative

William Nelson
Office of Regional Operations, Region IX
Office of the Assistant Administrator

ATSDR Technical Project Officer

Gail Godfrey
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
State Programs Section


This Health Consultation for the Gila River Fish Advisory, Phoenix, Maricopa County, Arizona, was prepared by the Arizona Department of Health Services under cooperative agreement with the Agency for Toxic Substances and Disease Registry. It is in accordance with approved methodology and procedures existing at the time the exposure investigation report was begun.

Gail Godfrey
Technical Project Officer

The Division of Health Assessment and Consultation, ATSDR, has reviewed this health consultation and concurs with the findings.

Richard Gillig
Team Leader-Cooperative Agreement Program

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

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