Page 2 of 10 SAP CHARGE

As part of the re

- evaluation of the health effects of atrazine, three meetings of the FIFRA Scientific Advisory Panel (SAP) are scheduled in 2010. The first two meetings were held i n February and April

. The purpose of the September meeting is to solicit feedback from the SAP on the status and overall scientific

direction of the Agency’s re

- evaluation on several topics in cluding our preliminary

conclusions regarding the non

- cancer epidemiology literature o n atrazine, as well as the human health risk implications of the experimental toxicology data

. The Agency is also seeking the Panel’s feedback on the proposed updates to the

dose

- response assessment including the use of an internal dose metric and

EPA’s b enchmark dose analysis. With respect to drinking water exposure, the Agency is seeking the Panel’s feedback on a general framework for designing monitoring studies along with basic approaches for analyzing sampling strategies

and other methods for estimat ing exposures from less frequent existing monitoring data

. Finally, the SAP is being asked to consider and comment on the implications of atrazine’s toxicity profile and it ’ s MOA on the development of a

w ater monitoring strategy.

Question 1.0 : Non

- canc er Epidemiology

Section 3.0 and Appendix B of the draft Issue Paper provide the Agency reviews and synthesis of the non

- cancer epidemiology studies available for atrazine. These include studies on a variety of topics, notably female and male reproductive outcomes and birth outcomes in addition to other topics. Section 4.0 integrates the findings of the epidemiology and experimental toxicology

studies.

Question 1.1 Please comment on the sufficiency of the Agency’s non

- cancer epidemiology

reviews with r espect to identifying the major strengths and limitations of each study.

Question 1.2

A t this time, atrazine’s non

- cancer epidemiologic database is not robust enough for inclusion in quantitative risk assessment and does not support the ability to

determi ne causal associations

. There are several limitations present in the current database, and the quality of atrazine exposure assessment is paramount among the limitations. In Section 4.0 of the draft Issue Paper, the Agency describes the qualitative simila rities and differences between the epidemiologic findings and the experimental toxicology database. In short, the observational

studies

– particularly those related to reproductive effects in adult females, as well as small for gestational age in newborns

– lend further support for the human relevance of the laboratory animal findings.Page 3 of 10 a. Please comment on the scientific information that does and does not support the Agency’s conclusions ( as described in Section 3.0 ) with respect to the characterizati on of quality, and limitations of the non

cancer epidemiologic database and its utility in hazard characterization, dose response analysis, and quantitative risk

assessment.

b. Please comment on scientific information that does and does not support the integrative analysis and conclusions

, contained in
Section 4.0

, with respect to the similarities

, differences

, and

uncertainties of the experimental toxicology and epidemiologic findings.

Question 2.0: Review of Studies on Mammary Gland Development

A t the April SAP, the Agency evaluated effects of atrazine on a number of apical endpoints including neuroendocrine, neurotoxicity, and immunotoxicity effects

. At that time, the Agency deferred review of experimental toxicology studies on mammary gland dev elopment to the September SAP meeting. Development of mammary tissue occurs in defined stages linked to sexual maturation and reproduction including embryonic, pre

- and peripubertal periods, as well as pregnancy and lactation. Given that atrazine a ffects the hormonal environment and reproductive system, it is not unreasonable to hypothesize that it may also affect mammary gland development. The database of mammary gland development studies includes four studies

--- three from same the research group (Rayne r et al. , 2004; Rayner et al. , 2005; Enoch et al. , 2007) in addition to one conducted by Coder (2010). It is important to note that the key events leading to reported delays in mammary gland development in the young following gestational exposure to atraz ine are not known and none of these studies propose a mechanism/mode of action.

Question 2.1

The studies from the two different research groups yield ed different results regarding the impact of atrazine on mammary gland development. While the Rayner and Enoch studies report delays in mammary gland development, the Coder study does not. The basis of these different findings is unknown. However, one notable difference in the study design used by the two research groups is the scoring system. The Ray ner et al . and Enoch et al. studies used a subjective scoring scale with a 1

- 4 scoring system (1 = poor development/structure; 4 = normal development/structure ) with criteria which

vary depending on the age of the pups. In contrast, Coder employed a quanti tative morphometric analysis to evaluate mammary gland development

. In addition, the Coder study also included the use of BrDU labeling to assess cell proliferation in the mammary tissue.Page 4 of 10

Please comment on the quality, strengths, and limitations of the mammary gland development studies by Rayner et al

. (2004, 2005) and Coder (2010) studies

. Please discuss in your comments factors which could lead to different findings. Please comment on the Agency’s conclusions regarding these studies on

atrazine.

Qu estion 2.2.

In three of the studies considered in Question 2.1 (Rayner et al., 20 04 and 20 05 ; Coder, 2010), effects have only been observed at a n atrazine dose of 100 mg/kg/day. In contrast

, E noch et al

. ( 2007) report delays in mammary gland development as low as 0.09 mg/kg/day following exposure to atrazine and a

mixture of several metabolites/degradates (DEA, DIA, DACT, hydroxy

- atrazine ). The Agency’s review of this mixture study is provided in Appendix A (Section A.10) Please comment on the Enoch et al

. ( 2007) study and the degree to which the Agency’s review accurately reflects the strengths and limitations of the study . Please include in your comments a consideration of the study design of the mixtures experiment and how this design impacts the interpretation of the

results

.

Question 2.3

. As described in the Introduction of the draft Issue Paper (Section 1.0), the Agency’s problem formulation is being conducted in a step

- wise manner. One important component of this problem formulation is the evaluation of the overall

database and the quality of the available experimental toxicology studies . In the case of mammary gland development, the Agency is proposing to acknowledge

these four studies (Rayner et al. , 2004; Rayner et al. , 2005; Enoch et al

. , 2007 ; Coder, 2010) in the hazard characterization but place little emphasis on them in its proposed updates to the dose

- response assessment for atrazine. The only findings reported in the Rayner et al.

, ( 2004 ), Rayner et al.

, ( 2005 )

, and Coder (2010) s tudies , occurred at a high dose ( 100 mg/kg/day ) which is approximately

50

- fold higher than the PoD of 1.86 for LH attenuation being proposed by the Agency. In the Enoch et al

. ( 2007) study, t here are significant limitations with the conduct and reporting the Agency believes which preclude the study from use in quantitative risk assessment.

In light of Panel discussion on Questions 2.1 and 2.2, please comment on the manner in which the Agency has proposed to use the mammary gland development studies in t he hazard assessment for atrazine.Page 5 of 10

Question 3 .0: Proposed Updates to the Dose

- Response Assessment

At the April, 2010 SAP, the Panel made two key recommendations related to

dose

- response assessment: 1) consider pursuing a dose

- response analysis

based o n an internal dose metric, as an alternative to the administered dose metric used in the previous risk assessment; and 2) identify the sensitive endpoint associated with functional impairment and perform benchmark dose (BMD) modeling. The Agency conducted both recommended analyses (Section

5.0 of the draft Issue Paper ) in response to these recommendations. LH attenuation, as a key event in atrazine’s MoA, is the most sensitive internal dose

metric that is assoc iated with a number of endocrino pathies

Ques tion 3 .1
Given that there is no robust pharmacokinetic model yet available, a non

compartmental analysis of the existing pharmacokinetic data was conducted and
described in Section 5.2 of the draft Issue Paper

. EPA thinks t his r epresents the

best method t o estimate an internal dose metric without exceeding the limits of

the available data.

a. Please comment on the Agency’s analysis of the pharmacokinetic data

contained in Thede ( 1987) to estimate internal dose reflective of atrazine

and its metabolite s in rat plasma

.

b. Based on Figure 5.5 in the draft Issue Paper , t he Agency has preliminarily

concluded that plasma levels of atrazine and its metabolites reach (or nearly reach) pharmacokinetic pseudo

- steady state in the rat plasma afte r approximately fo ur daily oral exposures over a wide range of doses

. Please comment on the extent to which the data do and do not support this finding.

c. Figure 5.8 of the draft Issue Paper shows a plot of LH attenuation data versus administered atrazine across a range of exposure durations (i.e., four days up to six months). The data contained on this figure were

collected from several different laboratorie s and involved two modes of oral administration (dietary, oral gavage) and two different rat strains.

Attenuation o f LH

, as measured by percent of control, is remarkably similar across studies, strains, laboratories, and most notably duration of

exposure. The Agency has preliminarily concluded that the findings on Figure 5.8 strongly support the hypothesis that pseudo

- steady state is

achieved (or nearly achieved) in adult rats after four daily consecutive oral

exposures

. T he Agency also believes that pseudo

- steady state is strongly associated with the attenuation of the LH surge following atrazine exposure in rats. Pl ease comment on the analysis shown in Figure 5.8 and the Agency’s preliminary conclusions related to these findings in rats

.Page 6 of 10

Question 3 .2

In Section 5.3, the Agency describes a benchmark ( BMD ) analysis conducted for

LH attenuation studies. As describe d in the draft Issue Paper, the Agency initially considered a wide range of toxicological endpoints for inclusion in the BMD analysis. In considering all of the data, this analysis focused on studies measuring LH attenuation where female rats were exposed orally for four days and/or longer. This was not only the most sensitive endpoint but i t’s temporal and dose response are well defined experimentally. The LH effect originates from atrazine’s effect on the hypothalamic control of pituitary function throug h its interference with GnRH neurotransmitters. Thus, protection from LH attenuation as a precursor event to several functional impairments would be protective of

atrazine’s neuroendocrine effects.

a. Please comment on the BMD analysis summarized in Sect ion 5.3 of the draft Issue Paper with details provided in Appendix C.

b. The selection of a suitable benchmark response (BMR) is an important component of conducting a BMD analysis. As described in Section 5.3,

for continuous endpoints, like LH attenuatio n, the BMR most often represents an X% change from background levels (or untreated controls). Typically, the BMR is selected on the basis of a combination of biological (mode of action, quantitative link between key events and adverse

outcomes , historica l/concurrent controls) and statistical considerations (sample size, variability, etc). LH attenuation may be potentially

associated with several adverse outcomes and the level of attenuation of the LH surge considered to be adverse is a function of several factors including the functional outcome and the life

- stage. There is an absence of information concerning the level of response (or % change) associated

with the various functional impairments. Also , the differences in reproductive cycles/aging between rodents and humans add an additional level of complexity to establishing a specific BMR value. When an X% change can not be defined, the Agency’s draft BMD guidance suggests that the BMD and BMDL corresponding to a change in the mean response equal to one standard deviation from the control mean be used as the

BMR. This approach was applied to atrazine. Please comment on the scientific factors important for establishing a BMR for LH attenuation as part of the BMD analysis for atrazine.Page 7 of 10

Question 4 .0: Approaches To Evaluating Water Sampling Strategies And Frequency Of Monitoring

The ultimate utility of pesticide monitoring data for drinking water exposure estimations in human health risk assessments depends on how well the monitoring data characterize the spatial and temporal variability of pesticide concentrations in drinking water, with an emphasis on the upper end of the exposure distribution. In addition, t he method used to estimate concentrations from monitoring data depends on the duration of co ncern and how critical it is to estimate peak concentrations.

Question 4 .1

A well

- designed drinking water monitoring study takes into account both spatial and temporal patterns of exposure. Please comment on the USEPA’s recommended framework for designi ng a monitoring study by targeting the most vulnerable areas, targeting seasonal times for more intensive sampling, basing sampling frequency on the toxicological exposure duration of concern, and using autosamplers to supplement monitoring data (see Secti on 7.2 of the draft Issue Paper ).

Question 4 .2

The April 2010 SAP recommended that simulations of candidate monitoring strategies and evaluations of the utility of different exposure estimation methods be benchmarked against intensive empirical data that cover a representative range of sites. In response, the USEPA proposes using more intensively sampled ambient water monitoring for flowing waters and PRZM/EXAMS modeling for static water bodies, matching them to the CWS based on similar chemograph shapes (see Section 7.3).

a. Please comment on the Agency’s proposal to use chemograph shapes (number, duration, and magnitude of peaks) to match CWS with more intensively monitored datasets. In particular, the Agency is interested in recommendations on approach es for matching chemograph shapes given

the loss of short

- duration peaks that occurs with less frequent sampling.

b. Please comment on the strengths and weaknesses of using more intensively sampled datasets from Heidelberg and AEEMP for analysis o f flowing w ater and PRZM/EXAMS for lakes and reservoirs.Page 8 of 10

Question 4.3

Once the magnitude and duration of exposure of toxicological concern are identified, the USEPA will determine which method(s) to use to analyze the existing atrazine CWS monitoring data for us e in drinking water exposure

estimates. Based on t he April 2010 SAP recommend ations, the Agency is focusing on regression

- based modeling combined with random function modeling (for example, a revised WARP model coupled with kriging or the USGS

SEAWAVE

- Q m odel).

Please comment on the strengths and weaknesses of these proposed approaches and provide any recommendations for improving the model applications.

Question 5 .0: Scientific Considerations in Potential Sensitivity of Infants &

Children

As describ ed in Section 6.0 in the draft Issue Paper, t he FFDCA, as amended by the FQPA (1996), requires the Agency to give special attention to infants and

children by placing emphasis on the availability of toxicology and exposure information to estimate the poten tial risk to these age groups. The 2003 Registration Eligibility Decision (RED) notes that the Agency reduced the FQPA Safety Factor for those localities which are part of the drinking water monitoring program conducted by Syngenta, as required by EPA. T his reduction in the Safety Factor was based on more intensive monitoring required in the monitoring program that reduced the uncertainty for estimating concentrations of atrazine and its metabolites in drinking water for the 90

- day rolling average identif ied in the previous risk assessment as the appropriate duration of concern. Based on the newest studies, our understanding of atrazine’s temporal pharmacokinetic and pharmacodynamic characteristics has changed and it appears that shorter durations may be appropriate. In light of the potential need to shorten the critical duration of exposure and as discussed by the Panel in Questions 4.1

- 4.3, the Agency is evaluating appropriate methods for assessing the drinking water monitoring data.

Previously, th e Agency noted data gaps related to “ information on Atrazine concerning exposure throughout all critical developmental periods (i.e., gestation through puberty in both sexes), in particular, early in development

... . ( emphasis added, FQPA memo, 2002).” At t he time of the previous risk assessment, there were only a few available studies which included measures sensitive to endocrine disruption on specific early life exposure periods (e.g., peripubertal). Since that time new studies have become available (Sec tion 6.0) which add to the existing database and support the findings of the older studies. In addition, new tissue dosimetry studies provide information on the transfer of atrazine and its chlorinated metabolites to the fetus and to the lactating pup.

F urther, a study evaluating exposure to atrazine from multiple criticalPage 9 of 10

developmental periods identified previously by the Agency as a data gap is on

going. The results of this research will inform our understanding of the potential

for differential life stage sensitivity.

In the coming months, as the drinking water exposure analysis develops further

and the on

- going toxicology studies become available, the Agency will work towards completing the scientific analysis that will inform whether or not a new

F QPA Safety Factor should be applied in the atrazine risk assessment.

The Agency requests the Panel to comment on important scientific factors for the Agency to consider in its analysis. Please include in your comments specific

consideration of uncertai nties in estimating drinking water exposures and remaining uncertainties in atrazine’s toxicological profile across life stages, particularly as they pertain to assessing risk to infants and children.

Question 6.0: Implications of MOA & Toxicity Profile on Water Monitoring

As described in the I ntroduction of the draft issue Paper (Section 1), the goals of

the current atrazine re

- evaluation are : 1) to determine the extent to which new science indicates a need for the Agency to develop a revised human hea lth risk assessment for atrazine and 2) to re

- consider, as appropriate, the frequency of drinking water monitoring needed . Two important issues related to achieving these goals are determining the point of departure and identifying the critical

effect and its associated duration of exposure. Proposed updates to the point of departure are considered in Questions 3.1 and 3.2. With respect to the critical duration of concern, th e frequency of drinking water monitoring is related to the temporal pattern of t he toxicological endpoint of concern used for the risk assessment. Generally, longer durations of toxicological concern (e.g., a long

term chronic effect) require a less frequent drinking water sampling design to approximate longer term exposures. Howeve r, as the duration of concern shortens, the frequency and timing of sampling become more important in determining how well the sample data capture short

- duration exposures. Observation epidemiology studies raise hypotheses and suggest possible links

betwe en atrazine exposure and reproductive and developmental outcomes

, but these epidemiology studies suffer from limitations which prevent firm conclusions. Although certain studies some provide qualitative support for the human relevance of the endpoints ide ntified through the experimental toxicological database, they provide little to no information on the critical duration of exposure. In addition, the MOA and PK database are also lacking in human specific information on the effects of atrazine which could be used to quantitatively extrapolate between species. As such, the information available to evaluate the critical duration of exposure lacks quantitative precision . Thus, the critical duration of exposure is instead derived by inferring generic knowledg e from a variety of scientific disciplines.Page 10 of 10

The Agency has used a variety of approaches to extrapolate findings from experimental animal data to humans including allometric scaling and human

specific information on the physiology of the menstrual cycle inferred from the

IVF literature. A ccording to the Agency’s analysis of the pharmaceutical data and allometric scaling of the rodent pharmacokinetics data

, the potential

durations of human exposure that would correspond to the exposure period of

interest in rats lie between a few days to approximately 4 weeks of exposure.

Please comment on the Agency’s analysis and prelim i nary conclusions contained
in Section 8.0 of the draft I ssue P aper as it relates to the potential critical windows of exposure. Pleas e include in your comments additional or alternative approaches or data that may inform this issue.