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Atrazine Updates

Current as of September 2011

One of the most widely used agricultural pesticides in the U.S., atrazine may be applied before and after planting to control broadleaf and grassy weeds. It is used primarily on corn, sorghum, and sugarcane, and is applied most heavily in the Midwest. Atrazine is used to a lesser extent on residential lawns, particularly in Florida and the Southeast. Go to more information about atrazine.

On this page you will find:

Atrazine SAP Meetings
Atrazine Evaluation

Atrazine Evaluation Process

Since EPA concluded its last evaluation of atrazine in 2003, the Agency has evaluated close to 150 published studies investigating a wide array of effects potentially relevant to human health risk assessment. Given this significant new body of scientific information as well as the documented presence of atrazine in both drinking water sources and other bodies of water, EPA determined it appropriate to review the state of the science in light of the new research and to ensure that the Agency’s regulatory decisions continue to protect public health. This review is based on transparency and sound science, including independent scientific peer review. Since 2003 EPA’s oversight of atrazine has always been dynamic, not static, to ensure continued safety.

To be certain that the best available science is used to inform its atrazine human health risk assessment, and to ensure transparency, EPA has sought advice on key aspects of the science evaluation from the independent FIFRA Scientific Advisory Panel (SAP).

EPA’s human health evaluation considers atrazine’s potential for cancer and non-cancer effects. The data generated from laboratory animal and human epidemiology studies since the Agency 2003 Human Health Risk Assessment were reviewed by the SAP in 2010. In general, the SAP concurred with the Agency’s evaluation of these new data.

Specifically, the SAP supported the conclusions reached by the Agency on the reproductive and developmental effects in the 2003 risk assessment, as well as the Agency’s conclusions on the new animal data concerning effects on the immune and nervous systems. The Agency also evaluated new epidemiology studies on non-cancer effects, and the SAP agreed with the Agency’s conclusion that while these studies were generally supportive of the animal findings, they could not be used as the basis for the risk assessment. Furthermore, the SAP agreed that even in light of new information on other effects, the Agency should continue to use atrazine’s effects on hormone levels as the basis for the atrazine risk assessment because this effect continues to be the most sensitive. By using the most sensitive effect in its regulatory decisions on atrazine, EPA protects human health against other effects that have been identified in the newly published studies.

Consistent with the SAP recommendations, EPA will continue to analyze dose-response relationships presented in the new atrazine animal toxicity studies to more precisely refine the levels and duration of exposure to atrazine in drinking water that could cause changes in hormone levels. In 2011 the SAP will review this analysis and also provide advice to EPA on whether – and to what extent – the frequency and duration of sampling in the atrazine drinking water monitoring program should be increased, or otherwise adjusted to guard against atrazine levels that are of concern.

As part of the 2010 SAP reviews, EPA also presented its evaluation of new studies relevant to evaluating potential sensitivity to infants and children. EPA is expecting additional data, to be submitted this spring, that will be evaluated and presented to the SAP in 2011.

Additionally as part of the SAP review in 2011, EPA will present its evaluations of the relevant cancer epidemiology studies published since 2003, including data from the National Cancer Institute’s Agricultural Health Study. EPA will seek the SAP’s advice on its evaluation of these data. The SAP agrees with the Agency that mammary tumors, observed in rats following atrazine exposure, are not expected to occur in humans because of differences in species physiology between humans and rats. Due to these differences, the events (including hormonal changes) leading to mammary tumors in rats do not occur in humans.

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Triazine Cumulative Risk Assessment

EPA’s triazine cumulative risk assessment considered the combined effects of atrazine and simazine, two closely related triazine herbicides. In 2006, EPA concluded that cumulative exposures to these pesticides through food and drinking water are safe and meet the rigorous human health standards set forth in the Food Quality Protection Act (FQPA). This assessment showed that the levels of atrazine and simazine that Americans are exposed to in their food and drinking water, combined, are below the level that would potentially cause health effects.

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Atrazine Post-RED Results

Quick Resources
This section provides results to date from the programs, activities, and studies required by EPA’s Atrazine Reregistration Eligibility Decision (RED) (PDF) (323 pp, 187M, about PDF) of 2003, including:

Pesticide Programs' Monitoring in Community Water Systems

Status Update - March 2011

Atrazine Monitoring Data

Currently, an intensive monitoring program to look for atrazine residues in drinking water from approximately 100 community water systems (CWS) is ongoing. These systems, located primarily in the Midwest, are among the most vulnerable to atrazine exposure.

Through its review of these data, the Agency has confirmed that none of the systems have exceeded OPP's level of concern, a 90-day average of 37.5 parts per billion (ppb) of atrazine and its degradates. The program is dynamic in nature; the Agency released 51 CWS from the program because these systems have had no exceedences of EPA’s level of concern after five years of monitoring. Conversely, EPA has added over 25 CWS into the program based on data gathered under the Safe Drinking Water Act (SDWA), suggesting these systems may approach levels of concern.

The data available are the following:

The following data complement the summary listed above. These nine spreadsheets present atrazine drinking water monitoring data that are required under the Agency’s 2003 Atrazine Reregistration Eligibility Decision (RED) and subsequent Memorandum of Agreement (MOA) with the atrazine registrants. These Atrazine Monitoring Program (AMP) data files contain the results of the required sampling, by year, for all CWS that have been monitored over an 8-year period from 2003 to 2010.

Each data file includes a “ReadMe” worksheet that explains the data contained in the file. AMP data for 2003 and 2004 do not contain simazine data. AMP data from the latter half of 2005 onward contain data for all triazine residues, including simazine.

If you need these data in a different format than the Excel spreadsheets for accessibility or other reasons, please contact Melanie Biscoe (biscoe.melanie@epa.gov) or 703-305-7106.

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Interpreting the Atrazine Drinking Water Monitoring Data

An EPA level of concern is specific to a particular issue (human health, for example) and an exposure period. For example, a long-term (or chronic) level of exposure would be associated with an exposure over many months or years, whereas an intermediate level of exposure would be looking at potential health effects over a three-month period. Through the atrazine monitoring programs in place, EPA can evaluate all these potential exposures.

Atrazine potential risk and how it is evaluated

Change in hormone levels is the most sensitive health effect observed in an extensive battery of atrazine toxicity tests. In other words, if the Agency’s standard is protective of hormonal effects, it will protect against all other effects that occur at higher levels. The Agency’s 2003 risk assessment supporting the re-registration of atrazine incorporates standard safety factors to ensure protection of public health, as well as an additional safety factor to ensure further protection for children.

As a result, EPA’s risk assessment includes a 300-fold margin of safety to help ensure that an exposure will not affect hormone levels, and a 1000-fold margin of safety to help protect against long-term or chronic effects. In other words, the exposure that the Agency allows is at least 300 to 1000 times more protective than the level where the Agency saw no adverse effects in the most sensitive animal species tested. EPA applies these additional safety factors as a precaution to protect the public health of all consumers in the United States.

Based on this risk analysis, the Agency determined that concentrations of atrazine and its degradates in raw water below an average of 37.5 ppb over a 90-day period ensures protection of pregnant women and all others, and concentrations of atrazine in finished water that do not exceed 3 ppb as an annual average to protect consumers from longer term chronic effects.

The following paragraphs describe the short-, intermediate-, and long-term exposure levels that EPA has evaluated and found to be protective of human health.

Short-term exposure - Based on the Agency’s screening-level assessment conducted for the Atrazine Interim Reregistration Eligibility Decision (IRED) from 2003, one-day concentrations less than the Drinking Water Level of Concern (DWLOC) of 298 ppb do not exceed the Agency’s level of concern for acute effects. In other words, occasional readings of atrazine that are below 298 ppb in water treated by municipalities do not pose a risk to human health.

Intermediate-term exposure -- The Office of Pesticide Programs’ level of concern for drinking water is an intermediate level of exposure where the level is exceeded if, in a 90-day rolling average, the concentration exceeds 37.5 ppb for atrazine and its degradates in raw water.  After seven years of monitoring, although some amount of atrazine may be detected in community water systems, none of the CWS in the monitoring program have exceeded the 37.5 ppb level of concern as a 90-day rolling average in raw water. This suggests that the more stringent restrictions and use practices required by the Agency in 2003 are working to reduce the amount of atrazine reaching water bodies, thereby protecting public health. If any CWS were to exceed this level twice within a five-year period, EPA would prohibit atrazine use in the watershed associated with the CWS.

Long-term exposure - Under the Safe Drinking Water Act (SDWA), the atrazine Maximum Contaminant Level (MCL) is intended to prevent longer-term, or chronic, health concerns from occurring even after years of exposure and is calculated against a running average from four quarterly samples. An occasional peak concentration above 3 ppb is, therefore, not cause for concern. Rather, a long-term, consistent value above a yearly average of 3 ppb would be of concern. The MCL is designed to protect all population subgroups.

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Background on CWS Monitoring Program

The January 2003 Atrazine Interim Reregistration Eligibility Decision (IRED) (323 pp, 1.87 MB) about PDF)and subsequent Memorandum of Agreement (MOA) (36 pp, 132k, about PDF)between EPA and the atrazine registrants initiated a monitoring program to focus on the most significant human health exposures associated with agricultural and residential uses -- exposures through drinking water. Through the CWS monitoring program, EPA is ensuring that exposures to atrazine in drinking water do not reach levels that pose a risk to public health. EPA’s regulatory program for atrazine ensures drinking water concentrations are below a level that could potentially cause changes in hormone levels, which is the most sensitive health effect observed in an extensive battery of toxicity tests. The Agency’s level of concern ensures protection of children and adults, including women of child-bearing age.

How CWS were Chosen - Of the approximately 50,000 CWS in the United States, 40,000 are served by ground water and 10,000 are served by surface water. Because atrazine levels in surface water tend to be higher than those in ground water, surface water is EPA's focus for this monitoring program. In 2003, the Agency identified 3,600 systems where atrazine was used and monitoring information was available. OPP used Safe Drinking Water Act (SDWA) data to screen CWS nationwide to see which systems might be more likely to have higher seasonal atrazine contamination. An initial group of CWS was identified for more intensive monitoring based upon the Agency's review of data submitted voluntarily by the registrant. Under conditions of the Atrazine RED and MOA, EPA required an intensive drinking water monitoring program in these CWS. This monitoring program began in 2003.

Information developed by EPA's Office of Water under the SDWA is continually reviewed to determine whether additional CWS should be monitored more intensively through OPP’s required atrazine monitoring program. Since 2003, a number of CWS have been added to OPP’s monitoring program based on SDWA monitoring data as detections approached or exceeded the Office of Water's Maximum Contaminant Level (MCL) for atrazine as an average of four quarterly samples.

CWS Monitoring - Since 2003, raw and finished water at approximately 150 CWS has been monitored under the atrazine MOA to ensure that levels of atrazine and its chlorinated degradates do not reach the level of concern of 37.5 ppb. Because CWS enter and exit the program on an ongoing basis, the number of systems that have taken part in this program varies from year to year. These CWS have been monitored on a weekly basis during the peak atrazine use season and biweekly during the rest of the year.

Under the MOA, monitoring is conducted for at least five years. Two exceedances in raw water at a CWS in different years over a five-year period will result in prohibition of further atrazine use in the associated watershed. If a CWS does not have exceedances during five years of monitoring, it may be released from this monitoring program. To date, 51 systems have been released from the program, and no system has had two exceedances. Over 25 CWS have been added to program.

EPA will continue to review monitoring data under the SDWA. If any CWS in the future have detections approaching the MCL, then the intensive monitoring requirements and regulatory oversight of the Pesticide Program will be invoked.

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Ecological Watershed Monitoring Program

Background

During atrazine’s reregistration in 2003, EPA established a framework for developing an aquatic ecosystem level of concern (LOC) that ensures atrazine concentrations in watersheds will not cause significant changes in aquatic plant community structure and productivity, the most sensitive effect of concern. Concentrations of atrazine that affect aquatic plant community structure and productivity typically occur at levels lower than those that directly affect fish and aquatic invertebrates. By focusing on aquatic plant community structural and productivity changes, the EPA intends to protect invertebrates, fish, and amphibians from the direct effects of atrazine as well as the effects that atrazine could have on the habitat and food sources of aquatic animals.

To that end, in its October 2003 Atrazine Interim Reregistration Eligibility Decision (IRED) (323 pp, 1.87 MB, about PDF), EPA required atrazine registrants to implement an innovative, intensive ecological watershed monitoring program, as well as a risk mitigation process if atrazine water concentrations exceed the Agency's levels of concern for aquatic ecosystems.

Aquatic Ecosystem Level of Concern

Level of Concern Development

When atrazine is applied during the growing season, water bodies receive episodic and highly variable amounts of atrazine runoff from agricultural fields. Since 2003, EPA has been working to develop a level of concern (LOC) that is based on the numerous studies (microcosm and mesocosm studies, which are studies designed to mimic conditions in natural communities and ecosystems) where effects on aquatic plants have been measured at constant atrazine concentrations. This analysis allows the Agency to better understand and evaluate the varied concentrations and durations of exposures monitored in natural systems.

To address this fundamental challenge of applying experimental toxicity information to natural systems, the EPA developed a tool called the “Plant Assemblage Toxicity Index” (PATI) to estimate the LOC.The PATI methodology uses single-species plant toxicity data and microcosm/mesocosm studies to discern what atrazine exposure patterns and concentrations can cause adverse effects on aquatic plant communities. We use these data to develop a level of concern, which together with monitoring data can be used to identify watersheds where atrazine levels are too high and need to be mitigated consistent with the 2003 IRED and Memorandum of Agreement (MOA) (36 pp, 132 KB, about PDF) signed by the Agency and Syngenta.

In public peer review meetings in 2007 and 2009, EPA consulted with the FIFRA Scientific Advisory Panel (SAP) on its general approach and the specific methodologies that could be used in developing the LOC. As a body of independent scientific experts, the SAP provides advice and recommendations to the Agency on important scientific issues. EPA first presented the PATI methodology at the 2009 SAP meeting and has since incorporated many of the Panel’s recommendations concerning this methodology, including additional evaluations of the PATI index, further development of the microcosm/mesocosm dataset, and development of a new method for determining LOCPATI (see Update and Next Steps) . The 2007 SAP report can be found in docket EPA-HQ-OPP-2007-0934 and the 2009 SAP's final report can be found in docket EPA-HQ-OPP-2009-0104.

The Current Aquatic Ecosystem Level of Concern

EPA is currently estimating the aquatic ecosystem level of concern as approximately 10 parts per billion (ppb) for atrazine over a 60-day period. We developed this estimate using the PATI model described in EPA’s issue paper that we presented to the 2009 SAP, available at www.regulations.gov in docket number EPA-HQ-OPP-2009-0104-0006.

If a watershed shows levels of atrazine above this level of concern in any two years of monitoring, atrazine registrants must initiate watershed-based management activities in concert with state or local watershed programs to reduce atrazine exposure. These remedies will be consistent with the approaches used in the EPA Office of Water's Total Maximum Daily Load (TMDL) program but are enforceable under FIFRA through the 2003 Atrazine IRED and Memorandum of Agreement.

Monitoring Results in Areas of Corn, Sorghum, and Sugarcane Production

With regard to corn and sorghum producing areas, the ecological watershed monitoring program was designed to focus initially on flowing water bodies in the most vulnerable watersheds in the Midwest. Monitoring occurred over a three-year period (2004 through 2006), and certain sites have had additional monitoring conducted from 2007-2011. During the sampling timeframe, 40 watersheds were monitored for at least two years. These initial 40 were selected to be representative of watersheds potentially vulnerable to atrazine runoff.

The results of this survey informed the Agency’s decision to sample an additional 25 sites (1 pp, 73k, about PDF) across the Midwest starting in 2010. These sites appear to have characteristics similar to the most vulnerable of the original 40 sites and thus were expected to be prone to atrazine runoff resulting in water concentrations that exceed the Agency's levels of concern. The 2010 monitoring results for these new sites, as well as the existing sites, are available at public docket number EPA-HQ-OPP-2003-0367-0206.

A pilot atrazine monitoring program in water bodies associated with sugarcane crop production was initiated in 2005. Monitoring began in Louisiana in March 2005 and Florida in December 2005. However, the monitoring effort in Louisiana was delayed in the latter half of 2005 because of Hurricane Katrina.

In March 2011, EPA released monitoring data collected in 2009-2010 from Midwestern streams and sugarcane-growing areas that are part of EPA’s atrazine ecological watershed monitoring program. These data are available in public docket EPA-HQ-OPP-2003-0367.

Monitoring Sites that Exceed the Level of Concern

Two Missouri ecological watershed monitoring sites and two Nebraska sites have exceeded the Agency’s level of concern based on the draft methodology presented to the 2009 FIFRA SAP. The two Missouri sites are in the South Fabius River and Youngs Creek watersheds. The Nebraska sites are in the Big Blue River (Upper Gage) and Muddy Creek watersheds.

The atrazine registrant, Syngenta, has collected detailed soil, slope and cropping maps, rainfall measurements, crop rotation patterns, and other information about the sites, and continues monitoring in these watersheds. Syngenta is also conducting watershed stewardship and outreach activities with growers and other stakeholders.

Despite these efforts, all four sites remain of high priority for mitigation, with three of these sites having repeatedly exceeded EPA’s level of concern:

As a result, the Agency is working with atrazine registrants to ensure additional mitigation steps are taken consistent with requirements of the 2003 IRED (323 pp, 1.87 MB, about PDF) and Memorandum of Agreement (36 pp, 132 KB, about PDF).

One Louisiana monitoring site has exceeded the Agency’s level of concern based on the draft methodology presented to the 2009 FIFRA SAP. Advice from that SAP meeting is helping the Agency interpret these data to determine whether additional monitoring and/or mitigation is needed.

Update and Next Steps – September 2011

In September 2011 EPA released the revised methodology it intends to present to the FIFRA SAP in 2012 as part of its atrazine evaluation process. This revised methodology would update the current aquatic ecosystem level of concern and would be used to analyze monitoring data from water bodies in the U.S. to determine which water bodies exceed that level of concern.

EPA describes this revised methodology in more detail in the following documents:

Additionally, the following software can be used to evaluate and apply this methodology:

EPA believes that establishing a level of concern with a fixed atrazine concentration and exposure duration will be more useful for state officials and the general public. Therefore, rather than evaluating monitoring sites routinely based on PATI and LOCPATI, EPA intends to use the software listed here to examine data from several intensive watershed monitoring programs (including those conducted by Heidelberg University, states, the U.S. Department of Agriculture and atrazine registrants) to establish a concentration-equivalent level of concern that effectively discriminates between exposures that exceed LOCPATI and those that do not. EPA will present the derivation of this “concentration-equivalent” level of concern to the 2012 SAP.

For More Information


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Cancer

Status Update - June 2011

Based on the review of available scientific studies, EPA determined in 2000 that atrazine is not likely to cause cancer in humans. This determination was the result of a transparent process that invited public participation, solicited development and submission of the best available scientific data, and allowed preeminent independent scientists to ensure that the Agency was using the highest quality data in its regulatory decision-making process. This determination was based on results from the full spectrum of animal test data that the Agency requires, as well as numerous research studies on atrazine’s mechanism of action.

Since the mid-1990’s, EPA has been co-sponsoring epidemiological studies through the National Cancer Institute (NCI) to evaluate the potential for any association between atrazine exposure, as well as other pesticides, to people and cancer, even though rigorously conducted animal studies show that this result is unlikely. In 2011, updated Agricultural Heath Study (AHS) analyses were published that will inform our risk assessment process.

Background

The EPA has identified several epidemiological cancer studies for atrazine. Specifically, the Agency has received the following studies noted by the 2003 FIFRA SAP as particularly important to this question:

The EPA has also received an updated epidemiological study comparing specific cancer types between atrazine-exposed and atrazine non-exposed pesticide applicators from the NCI’s AHS. So far, the results of the completed Agricultural Health Studies have shown no relationship between atrazine and prostate cancer or non-Hodgkin’s lymphoma.

The SAP agrees with the agency that mammary tumors, observed in rats following atrazine exposure, are not expected to occur in humans because of differences in species physiology between humans and rats. Due to these differences, the events (including hormonal changes) leading to mammary tumors in rats do not occur in humans.

The EPA is convening a SAP from July 26-29, 2011, where it will present its assessment of all available epidemiology data about the potential carcinogenicity of atrazine, including its review of the most recent results from the AHS. Members of the public interested in obtaining the analytic data set used in this study for the purpose of contributing to the SAP deliberations should follow these instructions (4 pp, 53.14k, about PDF).

 

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Amphibians

Status Update - April 2010

EPA concluded in 2007 that atrazine does not adversely affect amphibian gonadal development based on a review of laboratory and field studies, including studies submitted by the registrant and studies published in the scientific literature. At this time, EPA believes that no additional testing is warranted to address this issue.

Background

In June 2003, after evaluating the available literature on the potential effects of atrazine on amphibian gonadal development, EPA concluded that there was sufficient information to formulate a hypothesis that atrazine exposure can affect amphibian gonadal development; however, there was insufficient information to refute or confirm that hypothesis, mainly because of the limitations of the study designs and uncertainties in the data. The Agency’s 2003 White Paper (PDF) (8 pp, 62k, about PDF) carefully evaluated the data from 17 laboratory and field studies, discussed remaining uncertainties in evaluating the potential effects of atrazine on amphibian development, and outlined future studies that could address these uncertainties. The FIFRA Scientific Advisory Panel (SAP) reviewed EPA’s White Paper and concluded that the Agency’s review was thorough, the conclusions were valid, and the approaches and criteria for new studies were appropriate. The SAP also agreed that additional studies were warranted and that a tiered testing approach was appropriate.

In response to a November 2004 Data Call-In (DCI) Notice from EPA, Syngenta, the principal atrazine registrant, developed a testing protocol for determining the effects of atrazine on amphibian gonadal development, and conducted two studies consistent with the first tier of testing described in the 2003 White Paper and the SAP review. In June 2007, Syngenta submitted to EPA its final report regarding the potential effects of atrazine on gonadal development of amphibians.

To ensure the quality and transparency of its assessment of atrazine’s potential to affect amphibian gonadal development, EPA solicited advice from the SAP at a second public peer review meeting on October 9 - 11, 2007. During this meeting, EPA presented its assessment of 19 laboratory and field studies, including the registrant-submitted studies and additional studies available in the public literature since the 2003 SAP. Of the 19 studies, only the two DCI studies submitted by the registrant incorporated all of the design elements recommended by the Agency and the 2003 SAP to address uncertainties identified in the 2003 White Paper. The 2007 SAP agreed with the Agency that, although both DCI studies contained some limitations, the overall design and conduct of the studies reflected a high degree of quality control that allowed them to be used to evaluate whether or not atrazine exposure affects amphibian gonadal development. The 2007 SAP also agreed with the Agency that other laboratory and field studies reviewed by the Agency did not fully account for experimental and environmental conditions that could influence relevant endpoints. The SAP Panel concluded at that time that atrazine does not produce consistent, reproducible effects on the gonadal development of amphibians; however, the Panel recommended that EPA continue to be apprised of ongoing research and review any new data. The 2007 SAP's final report and recommendations are available in public docket EPA-HQ-OPP-2007-0498.

Based on the Agency’s thorough examination of the 19 studies and the 2007 SAP’s subsequent concurrence with the Agency’s assessment of those studies, EPA finds that atrazine does not adversely affect amphibian gonadal development. If new papers in the scientific literature regarding the potential effects of atrazine on amphibians become available, the Agency will review the information as part of its ongoing atrazine program.

Although EPA is not currently requiring additional testing of atrazine on amphibians, as discussed earlier on this Web page, EPA has begun a comprehensive reevaluation of atrazine’s ecological effects, including potential effects on amphibians, based on data generated since 2007. The Agency also is awaiting the results of studies examining the potential for any association between atrazine exposure to people and cancer, and has received and is analyzing additional monitoring data from community water systems and data from an ecological watershed monitoring program. If at any time atrazine data raise new risk concerns, EPA will modify its regulation of atrazine as appropriate.

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