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Atrazine Interim Reregistration Eligibility Decision (IRED) Addendum Q&A’s - October 2003

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EPA issued an addendum on October 31, 2003 that updates the Interim Reregistration Eligibility Decision (IRED) that the Agency issued on January 31, 2003. This addendum describes new scientific developments pertaining to: ecological monitoring and mitigation of watersheds; potential effects of atrazine on amphibian endocrinology and development; and the potential association between atrazine exposure and the incidence of prostate cancer and other cancers in humans. The addendum also identifies the following next steps:

On This Page:

  1. Why is the Agency releasing this component of the assessment today?
  2. What are these new requirements for ecological monitoring?
  3. What is a TMDL?
  4. What does it mean to exceed a level of concern?
  5. How do I know if my watershed was selected for monitoring?
  6. How were the 40 watersheds chosen?
  7. Why is this additional monitoring necessary?
  8. How does the IRED promote flexibility to enable a localized watershed approach while also ensuring consistent standards are met across the country?
  9. Are amphibians (frogs, toads, and salamanders) at risk from atrazine exposure?
  10. What is the Agency doing to implement the SAP recommendations and other comments on ecological effects, including those related to amphibians?
  11. What is the Agency doing to assess impacts to endangered species?
  12. What is EPA's view of the potential for atrazine to cause cancer?
  13. What are the next steps for the atrazine human health reassessment?
  14. What is the status of the recent NRDC lawsuit on atrazine's potential to cause cancer?
  15. How is EPA’s Drinking Water Standard for atrazine impacted by the IRED addendum
  16. What requirements has EPA put in place to monitor the nation's water supply for atrazine?
  17. How has the registrant been involved?

  1. Why is the Agency releasing this component of the assessment today?

    2. Under terms of the September 26, 2001, Consent Decree between the Natural Resources Defense Council (NRDC) and EPA (as amended on August 8, 2002), the Agency committed to completing a revision to the January 2003 IRED by October 31, 2003, to consider several new studies on potential amphibian risk and the potential association between atrazine exposure and the incidence of prostate cancer or other cancers in humans. The document includes specific plans for aquatic monitoring related to potential ecological effects, in accordance with the January 2003 IRED.

  2. What are these new requirements for ecological monitoring?

    3. EPA and Syngenta have developed a monitoring protocol that identifies 40 indicator watersheds in the United States. These 40 are representative of more than 1,100 other indicator watersheds across the nation. Syngenta will monitor at key sites within these watersheds over a two-year period to determine if a level of concern is exceeded. If the level is exceeded, the watershed will be subject to remedies consistent with EPA’s Total maximum daily load (TMDL) program and the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). EPA’s Office of Water, Office of Pesticide Programs, and Office of Research and Development worked together to ensure that their levels of concern (aquatic life criteria and ecological level of concern) are identical. This will ensure consistency of action on this issue to states and other stakeholders.

  3. What is a TMDL?

    4. Total Maximum Daily Load (TMDL) is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards. The Clean Water Act requires states to identify waters not meeting water quality standards and to establish TMDLs that describe reductions in loadings necessary to meet these water quality standards. TMDLs identify sources of the pollution and the reductions needed to achieve state water quality standards. In essence, TMDLs establish “pollution budgets” that allocate the load among the sources of the pollutant. These pollution budgets are translated into permit requirements for point sources. For other pollution sources, the program relies on local, state and federal watershed plans and programs to determine priorities for implementation. More information about the Office of Water's TMDL program can be found at: http://www.epa.gov/owow/tmdl/.

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  4. What does it mean to exceed a level of concern?

    5. The atrazine level of concern was determined as the concentration of atrazine that if not exceeded should not cause significant effects to the structure and function of plants in aquatic communities. Maintaining the health of aquatic plants ensures adequate habitat and food for fish and invertebrates. Because atrazine concentrations in streams can vary during the growing season due to rainfall, soil conditions, and time of application, etc. the atrazine level of concern was derived in such a way that it can evaluate complex atrazine exposure patterns. The atrazine level of concern is derived in a manner identical to the draft atrazine aquatic life criterion that is being issued for public comment at the same time the addendum to the IRED is being released.

  5. How do I know if my watershed was selected for monitoring?

    6. A total of 40 watersheds will be sampled. At this point in the monitoring study design, the watersheds are likely to be in the following 10 states: Ohio, Indiana, Kentucky, Illinois, Iowa, Missouri, Nebraska, Minnesota, Tennessee, and Louisiana. Once the monitoring protocols are finalized, the specific watersheds will be provided.

  6. How were the 40 watersheds chosen?

    7. The watersheds were chosen from a group of 1,172 watersheds in the country that are associated with atrazine in corn and sorghum production and considered to be among the most potentially vulnerable to atrazine runoff. The 40 watersheds are randomly selected from this group.

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  7. Why is this additional monitoring necessary?

    8. The monitoring program is designed to ascertain whether or not atrazine concentrations in streams could be causing ecological effects. While the likelihood appears low that atrazine concentrations are currently occurring at levels sufficient to cause such effects, the monitoring program will help determine the extent to which any such levels of exposure are occurring. If levels of concern are exceeded, meaning significant atrazine concentrations are detected, then a watershed-based mitigation program will be initiated. As part of the Agency’s January 2003 decision on atrazine, the registrant initiated a monitoring program on community drinking systems. This study is in progress.

  8. How does the IRED promote flexibility to enable a localized watershed approach while also ensuring consistent standards are met across the country?

    9. The IRED allows the registrant to work with local stakeholders (e.g., growers) to address any problems in that watershed first using whatever tools or best management practices are appropriate. This is a hallmark of the Clean Water Act total maximum daily load (TMDL) process. Ultimately, to ensure consistency, more monitoring needs to be done to confirm that the watershed is not exceeding the level of concern. EPA can always pursue additional steps to address whatever potential risks remain, consistent with FIFRA's requirements.

  9. Are amphibians (frogs, toads, and salamanders) at risk from atrazine exposure?

    10. EPA has carefully reviewed available studies regarding the effects of atrazine on amphibians. These data do not produce consistent, reproducible effects on amphibians. Based on this assessment, the Agency concluded, and the SAP agreed, the data currently available are insufficient to make a scientifically sound determination on the potential for atrazine to impair gonadal development in amphibians.

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  10. What is the Agency doing to implement the SAP recommendations and other comments on ecological effects, including those related to amphibians?

    11. The SAP supported EPA in seeking additional data to reduce uncertainty about potential risk to amphibians. The data collection will follow the multi-tiered process outlined in the Agency’s white paper presented to the SAP. In addition to addressing uncertainty regarding the potential of atrazine to cause these effects, the studies will be helpful in characterizing the nature of any potential dose-response relationship.

  11. What is the Agency doing to assess impacts to endangered species?

    12. The ecological assessment is the baseline of information from which we conduct our assessment specific to threatened and endangered species. Although some uses of atrazine have been assessed and consulted on in the past, an updated endangered species assessment will follow completion of the ecological assessment. The measures in the IRED will serve as protective measures in the interim.

    There are two lawsuits that are pertinent to the atrazine IRED addendum, one brought by Washington Toxics Coalition (WTC), the other by NRDC. As a matter of long-standing policy, EPA does not comment on pending litigation.

  12. What is EPA's view of the potential for atrazine to cause cancer?

    13. Based on the available scientific work on the potential association between atrazine and cancer, the Agency does not at this time find compelling data that would lead the Agency to conclude that potential cancer risk is likely from exposure to atrazine. However, EPA will continue to review new studies on this issue as they become available, and plans to convene another independent Scientific Advisory Panel (SAP) meeting concerning atrazine and its potential association with carcinogenic effects in light of any new data.

    EPA recognizes that another SAP meeting addressing the existing and new data on atrazine (and other triazines) and cancer would be beneficial and the Agency believes that this future meeting should be held after EPA has received and reviewed the results of the National Cancer Institute’s Agricultural Health Study in 2005. Waiting for the data from that study will give the SAP the most comprehensive picture of the issue and will make the most efficient use of SAP and EPA resources. We believe this is a reasonable approach given that, to date, we have no clear indication that atrazine is carcinogenic in humans, and we know that more robust data will be available in the near future. In the meantime, EPA will continue its review of all newly available data. If, at any time, results from any of the new data raise significant questions that would benefit substantially from SAP review prior to submission of all of the data, the Agency will hold a SAP meeting before all aspects of the Agricultural Health Study are completed.

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  13. What are the next steps for the atrazine human health reassessment?

    14. EPA must consider the cumulative effects of the triazine pesticides atrazine, simazine, and propazine, and their common chlorinated degradates, which share a common mechanism of toxicity. When the Agency completes its cumulative assessment of the triazine pesticides, final tolerance reassessment and reregistration eligibility decisions for atrazine and the other triazines will be issued. At that time, EPA may need to pursue further risk mitigation for atrazine to address any risks identified in the triazine cumulative assessment.

  14. What is the status of the recent NRDC lawsuit on atrazine's potential to cause cancer?

    15. EPA's response to the motion is due in mid-November. A hearing is scheduled for December 4, 2003.

  15. How is EPA’s Drinking Water Standard for atrazine impacted by the IRED addendum

    16. The October 31, 2003 addendum focuses on ecological issues, so drinking water standards are unaffected by today’s action. The maximum contaminant level for atrazine is 3.0 µg/l as established under EPA's National Primary Drinking Water Rules. EPA will review the adequacy of this standard and its associated monitoring requirements in light of the new information and science provided by the current atrazine IRED. EPA will also continue to evaluate new and ongoing human health research for atrazine to determine what if any modifications are necessary. Today’s revision to the IRED for atrazine does not change the Agency’s position in the January 2003 IRED that the registrant must perform intensive monitoring of drinking water systems that may be sensitive to atrazine. The Agency also continues to require source water controls or possible prohibition of atrazine use in watersheds for drinking water supplies where atrazine levels exceed levels of concern. These measures in combination with the current drinking water standard provide additional protection of public health as the Agency reviews its drinking water standard.

  16. What requirements has EPA put in place to monitor the nation's water supply for atrazine?

    17. The January IRED for atrazine described drinking water monitoring in surface water. This action is similar in that EPA is now requiring monitoring of flowing bodies of water to determine if levels of concern are exceeded for ecological effects. If they are, actions need to be taken to determine what can be done to remedy the problem in the watershed. Subsequently, EPA will also get data on static water bodies (lakes and reservoirs) and look into a similar program for estuaries and areas where sugarcane is grown.

  17. How has the registrant been involved?

    18. In consultation with EPA’s Office of Pesticide Programs, Office of Water, Office of Research and Development, USDA, growers groups, and Syngenta, a program has been developed to monitor for atrazine concentrations and mitigate environmental exposures if the Agency determines that mitigation is necessary. Additionally, Syngenta is conducting a specialized testing program in indicator watersheds to monitor "raw" drinking water for atrazine during high-use periods. If Agency standards are exceeded, atrazine use may be cancelled in that geographic area. This stringent approach augments monitoring of "finished" drinking water under the Safe Drinking Water Act (SDWA). For these systems, detections approaching the Maximum Contaminant Level (MCL) for atrazine will trigger additional monitoring and regulatory oversight. If the MCL is violated, Syngenta will take steps to assist the community water system in returning to compliance. This flexible program accounts for local conditions while assuring that EPA's safety standards are met. The costs of these monitoring programs are borne by Syngenta and other atrazine registrants as part of their product stewardship.

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