January 1999


WHAT IS ATRAZINE? Atrazine is an herbicide (pesticide). It is the most widely used herbicide in Texas corn and grain sorghum production, and one of the most widely used herbicides in the U.S. Atrazine is also used on sugarcane and on fallow wheat fields, in pine plantations and is found in some products available for use on home lawns, commercial turf grass and golf courses.


WHO MAKES ATRAZINE? Atrazine is primarily manufactured and marketed by Novartis Crop Protection, Inc. This company was formed through a 1996 merger of two chemical production companies: Ciba-Geigy and Sandoz. Novartis is based in Switzerland, with some facilities in the U.S..


HOW MUCH ATRAZINE IS USED IN TEXAS? There no precise information on how much atrazine is used in Texas, though general estimates based on surveys of agricultural operations are available. The most recent data indicate that an estimated 3. 2 million lbs. of atrazine is used annually in Texas agricultural operations, making atrazine the second most widely used herbicide in Texas agriculture. There is no readily available information on the amount of atrazine used for non-agricultural purposes. There is very little information available on exactly where atrazine is being used or how much is being applied in particular locations, in either agricultural or non-agricultural applications.


WHAT DO WE KNOW ABOUT ATRAZINE IN TEXANS’ TAP WATER? We know that atrazine is the pesticide most frequently detected in the tap water provided to Texans from public drinking water supply systems. Atrazine can reach water supplies through run-off from fields and other application areas near lakes, streams or rivers. It also leaches through soils into groundwater aquifers. Atrazine is not removed from the water by conventional drinking water treatment systems. To remove atrazine from the water supply, a system would have to use expensive powdered or granulated activated carbon filtration units. Most public water supply systems in Texas do not have these type of filtration units.

The Texas Natural Resource Conservation Commission has reported that in the first eight months of 1997 alone atrazine was detected in the quarterly monitoring samples in over 60 public water supply systems. Together, these systems, serve at least 4 million Texans, ranging from large cities like Fort Worth, Dallas and Arlington, to mid-size cities like Denton, Corsicana and Midlothian to a host of small towns across the state. Much of the contamination is found in the Trinity River basin. In about 10% of the samples, atrazine exceeded the federal drinking water standard. Other TNRCC data indicate that in 1,350 tests of public drinking water, atrazine was detected in 318 of the tests (almost 25%). Table 1 lists those public water supply systems where atrazine detections were reported between 1996 and the first quarter of 1998.

It is important to note also that, according to TNRCC staff:

Public drinking water sampling is conducted quarterly at the convenience of the inspector’s schedules and is not conducted during periods of greatest vulnerability within the quarter. Many peak concentrations may be missed. (Source: TNRCC Executive Management Briefing Paper: Atrazine Occurrence in Public Drinking Water, August 1997).

In Aquilla, Texas, drinking water is supplied by a small reservoir. During 1997, atrazine was repeatedly detected in the tap water being provided through the Aquilla system, at levels exceeding the federal drinking water standard. Between April 30, 1997 and February 3, 1998, atrazine was detected in quarterly samples at levels ranging from 3.1 to 10.5 ppb. The safe drinking water standard is set by the U.S. Environmental Protection Agency and is known as an MCL (maximum contaminant level). The MCL for atrazine is 3 parts per billion. The regulations provide that formal "violation" of the standard occurs if the average level of atrazine in samples from four consecutive quarterly tests exceeds the MCL. State regulators have not been able to determine the source of atrazine contamination of the Aquilla Reservoir.

In Friona, Texas, drinking water is supplied from the Ogallala aquifer. A portion of the aquifer, and, thus, Friona’s drinking water has also been contaminated by atrazine, though levels have not exceeded the MCL for four consecutive quarters. Atrazine in the Friona system, however, has reached 5.4 ppb in at least one quarterly test. State regulators have also been unable to determine the source of atrazine contamination in this area of the Ogallala aquifer.

Many of the drinking water systems in which atrazine contamination has been detected draw their water from large reservoirs such as Lake Tawakoni, Richland-Chambers and Lake Lewisville. In fact, TNRCC has declared nine surface water bodies as "threatened" because of atrazine contamination of drinking water provided from those supply sources. The nine water bodies are:


  • Big Creek Lake
  • Lake Tawakoni
  • Bardwell Reservoir
  • Lake Waxahachie
  • Lake Lavon
  • Richland-Chambers Reservoir
  • Joe Pool Lake
  • Aquilla Lake
  • Marlin City Lake System


SHOULD WE BE CONCERNED ABOUT ATRAZINE IN TAP WATER? Yes. The potential health threats from atrazine–as well as its widespread use and mobility in the environment--have been sufficient to warrant its listing as a contaminant for which drinking water must be monitored. This list contains only 33 the hundreds of pesticides in use today. The 3 parts per billion MCL level for atrazine in drinking water, shows that exposure to only very small amounts, especially over the long-term, has potential to cause adverse health effects. The 3 ppb MCL is about 30 times higher than the European standard for atrazine of 0.1 ppb.

A recent "fact sheet" on atrazine developed by the "Weed Specialist" and other personnel at Texas A&M University implies that atrazine is safer than caffeine or aspirin, since the "lethal dose" of either of these common substances is lower than the lethal dose for atrazine. This approach confuses acute effects of toxic chemicals, such as atrazine, with longer-term chronic health effects associated with very low dose exposures over a long period of time. The focus of concern over atrazine is not acute effects from a one-time high dose, rather it is the potential of atrazine to cause, over the longer-term, chronic effects such as cancer or disruption of the hormone system.

Cancer: Atrazine is currently classified as a "possible human carcinogen" by the U.S. Environmental Protection Agency. In 1994, EPA began a "Special Review" of atrazine in an attempt to understand more fully the cancer risks associated with exposure to atrazine through drinking water or other routes. A Special Review can result in a decision to cancel, restrict or continue uses of the pesticide. Due, in part, to intense scientific controversy over atrazine, the EPA has still not yet issued the results of this Special Review.

Studies commissioned by Novartis (the manufacturer) and the International Agency for Cancer Research (IARC) both show that atrazine causes mammary gland (breast) cancer in female rats, and that it causes these tumors to occur earlier in life than they would without exposure to the herbicide, a condition known as "early onset" (Source: International Agency for Research on Cancer. 1991. World Health Organization. IARC Monographs on the Evaluation of Cancer Risk to Humans. Vol. 53.) The study conducted for IARC also showed that atrazine caused a statistically significant increase in combined lymphomas and leukemia, and extremely rare mammary tumors in male rats. In sum, these two studies show that atrazine causes tumors, including extremely rare tumors, in two species of rats, at multiple sites, and with early onset. All but the male mammary tumors were malignant. Only just recently, however, has EPA indicated that it will consider the IARC study, along with the Novartis study, in the Special Review decision.

While not denying that atrazine may cause cancer, Novartis nevertheless argues that there is a "safe threshold" exposure level for atrazine, below which there is no risk of cancer at all. This argument is at the heart of Special Review controversy. Public interest groups have argued that: (1) when the results of the IARC study are considered, the validity of the "safe threshold" argument evaporates and (2) there are no studies that indicate there is any kind of "safe threshold" for exposure to atrazine during the human equivalent of fetal development or the first 5 years of life, precisely the time when atrazine exposures are proportionately highest in the exposed population.

In essence, then, we know that atrazine is at least a "possible human" carcinogen and would be classified as a "probable carcinogen" when considering the IARC study. We also know that there is serious scientific dispute over whether there is any "safe threshold" exposure level for atrazine, especially for developing fetuses, infants and children.

Hormone disruption. Hormones regulate a vast array of physiologic and developmental processes, from sexual development to the "fear and flight" response. Many organ systems are extremely vulnerable to even tiny does of hormones, particularly during critical periods of fetal and infant development. Extremely small doses of hormonally active substances at the right moment in development can cause serious and permanent damage later in life.

For example, the free estrogen–the estrogen that is available to cells in the human body–is active at 0.1 parts per trillion (ppt). Atrazine has been shown to be hormonally active and toxic to the endocrine system, but the mechanisms are not yet well-understood by scientists. Is atrazine as potent as free estrogen? No. But the dose of atrazine in some Texas tap water has been found to be as much as 10,000 times this 0.1 ppt level. Thus, at these levels of exposure to atrazine, toxic effects on the endocrine system could be possible. EPA’s animal testing requirements for atrazine (and other pesticides) currently do not require study of the long-term endocrine system effects of exposure, so scientists cannot yet evaluate fully its potential effect on humans.

Special concerns for infants and children. The current federal drinking water standard for atrazine was not set at a level designed to make sure infants and children are fully protected. Instead, like federal drinking water standards for other pollutants, it is based on a population-wide average of water consumption, averaged over a lifetime exposure. While this population average includes children, averaging infant and children exposure with adult exposure does not constitute adequate protection for infants and children. The National Research Council (NRC) made precisely this point in its landmark study, Pesticides in the Diets of Infants and Children.  (Source: National Research Council. 1993. Commission on Life Sciences. Committee on Pesticide in the Diets of Infants and Children. Pesticides in the Diets of Infants and Children. Washington, D.C. National Academy Press.) This study recommended that the regulatory process be changed to account for the fact that infants and children are more vulnerable than adults to adverse effects from pesticides, including cancer risks, nervous system toxicity and reproductive and hormonal disorders later in life. (Note: these recommendations were largely adopted in the 1996 federal Food Quality Protection Act, which is designed to reduce risks from pesticides in food, especially for infants and children).

Infants drink about 3 times more fluids relative to their size than adults. This means that a disproportionate percentage of total lifetime exposure occurs in the first five years of life, precisely when the body is most vulnerable to toxic substances like atrazine. This is especially true if tap water is being used to reconstitute infant formula.

Cumulative and synergistic effects. "Cumulative" effects generally refer to the situation where people are exposed to a pesticide through more than one route–e.g. through drinking water, food consumption and/or workplace exposure. Though atrazine is not widely used directly on crops destined for human consumption, with the exception of sugar cane, it can find its way into the food chain, as feed corn and grain sorghum are feed to dairy or beef cattle. "Cumulative" effects can also refer to a situation where a person is exposed to multiple pesticides, especially when the pesticides have similar toxic effects. Infants and children are especially vulnerable to these additive effects, according to the NRC report.

This is of concern for atrazine, which is sometimes found in drinking water along with simazine, another herbicide. When EPA initiated its special review of atrazine in 1994, it included simazine and cyanazine in the review (In August 1995, EPA and DuPont announced the phase-out and eventual ban of cyanazine. Registrations for the use of cyanazine were to be cancelled by December 31, 1996). These herbicides (known as chlorotriazines) have similar chemical structures, similar health risks and similar degradation and metabolization products.

WHAT CAN BE DONE TO ADDRESS ATRAZINE POLLUTION OF TEXAS DRINKING WATER SOURCES? There are many reasonable, cost-effective actions that can be undertaken to reduce atrazine contamination of the ground water and surface water we depend on for drinking water supply. First and foremost, all users of atrazine can undertake to reduce their use and make sure that any applications are done in a way that reduces the potential for the atrazine to reach groundwater or surface water. Because the state does not collect data on when and where atrazine is being used, it is difficult to identify which atrazine applications may be resulting in contamination of drinking water supplies, and which public water systems are most vulnerable to contamination.

  • To address these problems, the state should develop a high-profile program to provide all atrazine users, but especially farmers, with access to information and, if necessary, funding to reduce their atrazine use and adopt better application practices to reduce the possibility of contamination.
  • The state should also require all users of atrazine to report when, where and how much atrazine they use, on an annual or more frequent basis. This information can then be used by TNRCC and drinking water supply systems to identify and remedy sources of contamination if atrazine is detected in tap water.

In some areas of the state, atrazine use may be so widespread and surface water and/or groundwater may be so vulnerable to contamination that use of atrazine needs to be restricted or even banned. This has been the approach adopted by Wisconsin, where atrazine had contaminated hundreds of shallow groundwater wells. Dane County, Wisconsin, has an atrazine ban over most of its area, yet it is still the leading corn-producing county in the state. In Texas, several state agencies are working together through the State Groundwater Protection Committee to develop a "management plan" for atrazine. This plan is supposed to be designed to prevent atrazine contamination of groundwater, and it may need to include recommendations for use restrictions or bans, especially if the two measures identified above are not effective.


The only other option would be for most cities, towns and rural water supply systems to increase their testing for atrazine and/or add expensive activated carbon filtration systems in to remove atrazine from the drinking water before it is distributed to the public. These options could significantly increase water costs for drinking water systems and their consumers. And, as noted by TNRCC staff::

Public health protection is best exercised at the point of application of atrazine versus millions of dollars of public water supplier expenditures on powdered activated carbon and granular activated carbon facilities for atrazine removal. (Source: TNRCC Executive Management Briefing Paper: Atrazine Occurrence in Public Drinking Water, August 1997).


Copley, Marion P. 1988. Third Peer Review of Atrazine–Re-evaluation Following the September 7, 1988 Scientific Advisory Panel Review. U.S. Environmental Protection Agency, Washington, D.C.

Copley, Marion P. 1989. Follow-up to Third Peer Review of Atrazine. U.S. Environmental Protection Agency, Washington, D.C.

Hauswirth, Judith W. 1988. Peer Review of Atrazine. U.S. Environmental Protection Agency, Washington, D.C.

Hauswirth, Judith W. 1988a. Peer Review of Atrazine. U.S. Environmental Protection Agency, Washington, D.C.

International Agency for Research on Cancer. 1991. World Health Organization. IARC Monographs on the Evaluation of Cancer Risk to Humans. Vol. 53.

Pinter, A., et al. 1990. Long-term Carcinogenicity Bioassay of the Herbicide Atrazine in F344 Rats. Neoplasma 37:5.

Spencer, Henry. 1987. Twenty-Four Month Combined Chronic Oral Toxicity and Oncogenicity Study in Rats Utilizing Atrazine 98.9 Technical. U.S. Environmental Protection Agency, Washington, D.C.

U.S. Environmental Protection Agency (Office of Pesticide Programs). 1997. Questions and Answers: The Triazine Pesticides. Available at:

U.S. Environmental Protection Agency (Office of Ground Water and Drinking Water). 1998. National Primary Drinking Water Regulations, Technical Fact Sheet on Atrazine. Available at:




Texas Public Water Supply Systems


With Atrazine Detections: 1996 through first quarter 1998


(from TNRCC Database)

System # Detections* Range (ppb) MCL is 3 ppb
    Minimum Maximum
Anahuac 2 0.11  
Aquilla 9 0.56 10.5
Arlington 10 0.15 1.8
Baytown Area Water Authority 2 0.29 0.4
Bell County WCID No. 1 4 0.11 0.16
Big Cedar Golf Club 1 1.8  
Bistone Municipal Water Supply 3 0.13 0.29
Bluebonnet Water Supply Corp. 2 0.1 0.13
Brazosport Water Authority 1 0.26  
City of Cameron 3 0.11 2.2
Cash Water Supply Corporation 7 0.21 0.8
Chocolate Bayou Plant 1 0.11  
Cleburne 4 0.16 1.1
Combined Water Supply Corp. (Lake Tawakoni) 11 0.15 4
Commerce 7 0.35 0.78
Cooper 3 0.6 2.2
Corsicana 6 0.66 1.6
Crosby Municipal Utility District 2 0.14 0.22
Dallas County Park Cities MUD 4 0.41 0.78
Dallas Water Utility 15 0.21 1.1
Dawson 5 0.87 3.9
Deer Park 18 0.18 0.54
Denton 4 0.41 1.2
Dianal America Inc. 1 0.31  
Dow Chemical Plant A 2 0.43 0.53
East Cedar Creek FWS District 8 0.11 0.19
Emory 7 0.31 0.63
Ennis 6 0.81 2.4
Friona Municipal Water Supply System 5 0.42 3.3
Fort Worth 16 0.56 3.1
Gatesville 2 0.12 0.15
GBRA-Port Lavaca 2 0.11 0.14
Grapevine 11 0.13 0.46
Greenville 14 0.24 0.78
Gulf Coast Water Authority 3 0.19 0.49
Houston 11 0.16 0.5
Huntsville 1 1  
International Paper Company 4 0.17 0.92
Kemp 3 0.12 0.24
Lajitas on the Rio Grande 1 0.06  
Lewisville 6 0.55 1.5
Livingston Regional Water Supply 4 0.21 0.71
Lubbock 4 0.11 0.14
Lyford 1 0.41  
Mabank 7 0.12 0.3
Mac Bee Water Supply Corporation 4 0.48 0.72
Mackenzie Municipal Water Authority 3 0.2 0.28
Mansfield 12 0.19 2.6
Marlin 9 0.3 9.6
Midlothian 9 0.75 2.28
North Texas Municipal Water District 7 0.6 2.5
Pampa 3 0.1 0.12
Paris 8 0.27 0.45
Phillips 66 Company-Houston 6 0.45 0.5
Point 1 1.53  
Point Comfort 2 0.11 0.25
Rio Hondo 1 0.13  
Robinson 10 0.2 3.7
SLC Water Supply Corporation 3 0.1 0.84
Sagemeadow Municipal Utility District 10 0.23 8.83
San Patricio Municipal Utility District 2 0.17  
Sherman 1 0.1  
Star Harbor 1 0.14  
Sterling Chemicals, Inc., Texas City 8 0.18 1.2
Tarrant County Regional Water District 1 1 1.2
Taylor 3 0.52 0.7
TBCD-HEW 3 0.17 0.18
TBCD-Oak Island and Double Bayou 4 0.11 0.35
Temple 3 0.11  
Terrell 1 0.12  
Texarkana Water Utilities 1 0.22  
Trinity River Authority-Tarrant Co. Water Project 7 0.31 0.56
Trinity River Authority-Huntsville 5 0.13 0.38
Tulia 7 0.2 1.6
Upper Leon River Municipal Water District 1 0.16  
Waco 4 0.1 0.65
Waterwood Municipal Utility District 3 0.18 0.43
Waxahachie 12 0.77 2.7
West Cedar Creek Municipal Utility District 5 0.1 0.2
West Tawakoni 2 0.63 2
White River Municipal Utility District 4 0.12 0.5
Wills Point 6 0.4 0.6
Wortham 2 0.3  


* Does not include multiple detects on same day, unless different water supply source listed for each detection.


How to Contact TCPS:                                                                                             

Mailing Address: Texas Center for Policy Studies, PO Box 2618, Austin, Tx. 78768;  

Physical Address: Texas Center for Policy Studies, 44 East Avenue, Suite 306, Austin TX 78701;                                                                                         

Phone/Fax: (512) 474-0811/(512) 474-7846


5 June 1998
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