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Atrazine Updates

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Atrazine is a herbicide for controlling weeds that compete with desirable plants such as food crops, pasture, and other types of agriculture, as well as golf course turf and residential lawns. Go to more information about atrazine.

This page provides initial results from the programs, activities, and studies required by EPA's Atrazine Reregistration Eligibility Decision of 2003, including:

EPA considered the combined effects of atrazine and simazine, two closely related triazine herbicides, and concluded that the cumulative risks associated with these pesticides are below the Food Quality Protection Act (FQPA) level of concern. EPA is reviewing public comments received on the triazine cumulative risk assessment released in June 2006. Upon completion of that review, EPA will post its response to comments and revise the cumulative assessment, if necessary.

Pesticide Program's Monitoring in Community Water Systems

Status Update - December 2007

An intensive monitoring program to look for atrazine residues in 128 community water systems (CWS) is underway. These systems, located primarily in the Midwest, appear to be the most vulnerable to atrazine contamination. Results for 2003, 2004, and 2005 (PDF) (6 pp, 319 KB, about PDF) show no exceedances of the EPA Office of Pesticide Programs' (OPP's) level of concern for atrazine plus its chlorinated metabolites. Results for 2006 will be posted in early 2008.

Background on CWS Monitoring Program

The January 2003 Atrazine Interim Reregistration Eligibility Decision (IRED) and subsequent Memorandum of Agreement (MOA) between EPA and the atrazine registrants initiated a monitoring program to focus on the most significant exposures associated with agricultural and residential uses -- exposures through drinking water. To this point, levels found in CWS have been low. 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. The potential risk is for delayed development in children if atrazine levels of concern were reached consistently in CWS over a period of several months.

How CWS were Chosen - Of the approximately 50,000 CWS in the US, 40,000 are served by ground water and 10,000 are served by surface 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. In 128 of these CWS, detections had approached or exceeded the Maximum Contaminant Level (MCL) for atrazine. Of the 128, eight CWS had annual average readings that significantly exceeded the MCL. These eight CWS may be especially vulnerable to atrazine contamination.

Under conditions of the Atrazine RED (PDF) (12 pp, 108 KB, about PDF) and MOA (PDF) (36 pp, 132 KB, about PDF), EPA required an intensive drinking water monitoring program in CWS. This monitoring program began in 2003. Information developed by EPA's Office of Water under the Safe Drinking Water Act (SDWA) is used in conducting this program. For example, since 2003, 13 more CWS have been added to the monitoring program based on Safe Drinking Water Act (SDWA) monitoring data collected for compliance with the Office of Water's Maximum Contaminant Level (MCL).

CWS Monitoring - Since 2003, raw water at the 128 CWS has been monitored under the atrazine MOA to ensure that levels of atrazine and its chlorinated degradates or Total Chlorotriazines (TCTs) do not reach the performance standard level of concern, 37.5 ppb, which represents a 90-day average of atrazine plus TCTs. These CWS are monitored on a weekly basis during the peak atrazine use season and biweekly during the rest of the year.

In the eight especially vulnerable CWS, one exceedance of OPP's level of concern over a five-year period will result in prohibition of any further use of atrazine in the watershed.

In the other 120 CWS, two exceedances in different years in a five-year period will result in prohibition of further atrazine use in the watershed. Monitoring under the atrazine MOA will be conducted for at least five years. If a CWS does not have exceedances during five years of monitoring, it will be released from this monitoring program.

However, existing monitoring requirements under the SDWA will continue. For all watersheds where atrazine is used, the SDWA typically requires quarterly samples be taken to test for atrazine in finished drinking water. The pesticide program uses these data to screen CWS nationwide to see which ones might be more likely to have higher seasonal atrazine contamination. These CWS will enter the weekly/biweekly monitoring program under the atrazine MOA. For these systems, detections approaching the MCL for atrazine will trigger additional monitoring and regulatory oversight.

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Ecological Watershed Monitoring Program

Status Update - December 2007

Consistent with a March 2006 Settlement Agreement between EPA and the Natural Resources Defense Council (NRDC), in late January 2007, EPA released atrazine ecological watershed monitoring program data for 2004, 2005, and 2006. Information on how to obtain these data is available on the Agency's Endangered Species Protection Program web page under Release of Atrazine Ecological Watershed Monitoring Data. Information about the Settlement Agreement is available on EPA's Endangered Species Protection Program web page.

Background on Ecological Watershed Monitoring Program

In its October 2003 Atrazine Interim Reregistration Eligibility Decision (IRED), EPA required the registrants to conduct a watershed monitoring program to confirm the Agency's conclusion that use of this herbicide is not likely to result in unreasonable risk to freshwater aquatic ecosystems. To gather the necessary data, EPA worked with the registrants to develop an innovative, intensive ecological watershed monitoring program, as well as a mitigation process to implement if atrazine water concentrations exceed the Agency's levels of concern. This program is detailed in the October 2003 Revised Atrazine IRED (PDF) (12 pp, 108 KB, about PDF).

Corn and Sorghum - The ecological watershed monitoring program was designed to focus initially on flowing water bodies in the most vulnerable watersheds associated with corn and sorghum production. Monitoring was to occur over a three-year period (2004 through 2006), with each site having two years of monitoring data. Over the three years, 40 watersheds, which are statistically representative of 1,172 watersheds identified as potentially vulnerable to atrazine exposure, have been monitored. The results of this survey will inform a decision on the extent to which additional water bodies may need to be surveyed. The study design and results will also aid the states in developing any atrazine monitoring they may wish to undertake. A list of the 40 watersheds (PDF) (2 pp, 125 KB, about PDF) included in the ecological monitoring program is provided on the atrazine web page.

Based on results from aquatic ecological effects testing in 25 microcosm and mesocosm studies with atrazine, changes in aquatic plant communities were found to be the most sensitive endpoint. By focusing on protection of aquatic plant communities, EPA intends to protect fish and invertebrates from direct effects of atrazine, as well as the effects that atrazine could have on the habitat and food sources of aquatic animals.

For the aquatic ecosystem monitoring program, the level of concern is approximately 10 to 20 parts per billion (ppb) for atrazine over a prolonged period of time (approximately two weeks to three months). This level of concern is consistent with the Office of Water's draft aquatic life criteria.

As mentioned in the October 2003 IRED, the effects of atrazine on aquatic community structure are highly dependent on the duration and frequency of atrazine exposure, as well as the magnitude of exposure. It is highly unlikely that atrazine would cause significant adverse effects in freshwater stream ecosystems if atrazine concentrations did not exceed the following levels of concern:

If atrazine monitoring data exceed any of the screening-level values, a more refined analytical procedure is employed to determine if the measured levels are associated with significant effects on aquatic communities. If any of the watersheds show levels of atrazine above the level of concern, the registrants must initiate watershed management activities in concert with any state or local watershed teams. These remedies must be consistent with the EPA Office of Water's Total Maximum Daily Load (TMDL) program requirements but are enforceable under FIFRA.

As of early 2007, two Missouri monitoring sites have exceeded the screening trigger, although neither exceeds a level that would require immediate mitigation. The two sites are in the South Fabius River and Youngs Creek watersheds. The atrazine registrant Syngenta has collected detailed soil, slope and cropping maps, model runs, rainfall measurements, crop rotation patterns, and other useful information about these two sites. In 2005, they began discussions with stakeholders to determine atrazine use patterns in these watersheds. Syngenta is now conducting TMDL-like stewardship and outreach activities with growers and other stakeholders in these areas, including a series of label education and best management practice (BMP) meetings. Through these meetings, growers will learn how best to use atrazine effectively while protecting local water quality. To evaluate the progress of this outreach, Syngenta will continue to monitor the two Missouri sites while adding others in these watersheds. This further monitoring will help assess the effectiveness of the BMP and label education programs.

In a public peer review meeting on December 4-6, 2007, EPA consulted with the FIFRA Scientific Advisory Panel (SAP) on the approaches and methodologies of the atrazine ecological monitoring program, and the Agency's preliminary interpretations of monitoring results. As a body of independent scientific experts, the SAP provides advice and recommendations to the Agency on important scientific issues. The Agency is looking forward to receiving the SAP's final report and recommendations, which will be posted to the public docket (EPA-HQ-OPP-2007-0934 at Regulations.gov), by early March 2008. Feedback from the SAP in this area will guide on-going EPA work and will help determine to what extent additional monitoring is needed in other watersheds.

Sugarcane - 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. Results from the monitoring program are anticipated in early 2008.

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Cancer

Status Update - December 2007

EPA is reviewing several epidemiological cancer studies for atrazine and expects to review others after they are completed.

EPA has received and is reviewing three studies, including:

EPA expects to receive two additional epidemiological studies and analyses concerning atrazine and cancer from NCI's Agricultural Health Study during 2008, including:

After receiving and reviewing the two pending studies, EPA plans to convene another SAP meeting concerning atrazine and its possible association with carcinogenic effects. The Agency will present its assessment of all available data about the potential carcinogenicity of atrazine - both epidemiology studies and laboratory animal studies - and reconsider whether the totality of the data suggests that the Agency should revise its determination that atrazine is not likely to cause cancer in humans.

EPA will continue to review all new data submissions. If at any time results from any new data raise significant questions, the Agency will convene another SAP meeting before all of the anticipated NCI Agricultural Health Study results concerning atrazine become available.

Background

Based on available scientific studies, EPA believes that atrazine is not likely to cause cancer in humans.

EPA's January 2003 Atrazine IRED did not include a quantitative risk assessment for cancer due to the Agency's determination that it is unlikely that atrazine's cancer mode of action in the rat is operative in humans. This position is consistent with June 2000 conclusions by the FIFRA Scientific Advisory Panel (SAP), a group of non-EPA scientists with expertise in this field. Considering the animal data and human epidemiological data, EPA concluded that atrazine is "not likely to be carcinogenic to humans." Results of recent epidemiological studies regarding atrazine's potential link to prostate cancer taken to the SAP in July 2003 did not alter that conclusion. Accordingly, the Agency concluded in the October 2003 revised IRED that atrazine is not likely to be a human carcinogen.

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Amphibians

Status Update - December 2007

EPA has concluded that atrazine does not adversely affect amphibian gonadal development based on a thorough review of 19 laboratory and field studies, including studies submitted by the registrant and others in the public literature.  At this time, EPA believes that no additional testing is warranted to address this issue.

To ensure the quality and transparency of its assessment of atrazine’s potential to affect amphibian gonadal development, EPA solicited advice from the FIFRA Scientific Advisory Panel (SAP) at a public peer review meeting on October 9 - 11, 2007.  As a body of independent scientific experts, the SAP provides advice and recommendations to the Agency on important scientific issues.  EPA’s assessment of new studies regarding the potential effects of atrazine on amphibian gonadal development, as well as supporting documents and a list of specific questions directed to the SAP (charge questions), are available in the public docket (EPA-HQ-OPP-2007-0498 at Regulations.gov). The SAP's final report and recommendations, which will also be made publically available, is expected in January 2008.

Background

In June 2003, after evaluating the available literature on the potential effects of atrazine on amphibian gonadal development, EPA concluded that while there was sufficient information to formulate a hypothesis that atrazine exposure can affect amphibian gonadal development, 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 critically 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 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 alone on amphibian gonadal development, and conducted two studies consistent with the first tier of testing described in the 2003 White Paper.  In June 2007, Syngenta submitted to EPA its final report regarding the potential effects of atrazine on gonadal development of amphibians.

As of late September 2007, EPA has reviewed 19 laboratory and field studies, including registrant-submitted studies and studies available in the public literature.  Only the two DCI studies submitted by the registrant incorporated all of the design elements recommended by the Agency and the SAP to address uncertainties identified in the 2003 White Paper.  These studies were conducted separately in two independent laboratories.  Although both studies contain limitations, the overall design and conduct of the studies reflect a high degree of quality control that allows them to be used to test the hypothesis that atrazine exposure affects amphibian gonadal development.  Other laboratory and field studies reviewed by the Agency did not fully account for experimental and environmental conditions that could influence relevant endpoints.

Based on a thorough examination of these studies and their results, EPA finds that atrazine does not adversely affect amphibian gonadal development, and believes there is no compelling reason to pursue additional testing of atrazine for amphibian gonadal effects.

This decision does not preclude EPA from examining other atrazine issues.  As discussed earlier on this web page, EPA also is awaiting the results of atrazine human cancer studies, 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 risk management decisions for atrazine as appropriate.

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