CHARGE QUESTIONS CHARGE QUESTIONS
Charge Question 1

1. One approach for evaluating the performance of monitoring sampling desigdifferent sampling frequency strategies using robust (daily or near-daily samhigh use/runoff use/runoff period) period) monitoring monitoring data. As noted in previous previous SAPs (April 2010 2010), Heidelberg University’s National Center for Water Quality Resemonitoring of selected watersheds in Ohio and the Atrazine Ecological ExpoProgram (AEEMP) monitoring of headwater streams in the corn belt provide datasets datasets for atrazine atrazine. Using examples examples from these datasets datasets, the USEPA pre

pre

approach for deriving a bias factor for different sampling frequencies (e.g., 4intervals) for use in estimating concentrations for different exposure durations 4, 14, 28, 90 day durations).

a) Given that the factors are likely to vary based on watershed size and 

comment on the level of detail we would need to develop (e.g., fl

reservoir; small vs. medium vs. large watershed area). How many da

need to analyze to provide a reasonable representation of a bias 

category?

b) Please comment comment on the advantages advantages and disadvantages disadvantages of deriving deriving bi

based on analyses of individual sites and years compared to taking pof averages across sites/years.
Charg Qeuestion 2

2. The September 2010 FIFRA SAP on atrazine recommended combining model such as WARP with either a deterministic deterministic model such as PRZM or a approach in order to estimate a time series of atrazine concentrations from monitoring. In developing methods based on the SAP’s recommendationwas able to derive reasonable estimations of the time series for sampling days or shorter shorter using conditional conditional simulations simulations of variogram variogram models withou

withou

additional models. Although the simulations underestimated the 1-day maappeared to provide reasonable bounds for rolling average concentrations days.

a) Please comment on the Agency’s method of estimating time 

conditional simulations of variograms for monitoring data sets sucCWS monitoring that have 7-day sampling frequencies.

b) Based on the USEPA’s analysis using WARP with longer dura

intervals (Appendix D.1), what advantages does the SAP see of inmodeling in this approach (i.e., better estimation of the daily maximu
Charge Question 3 Charge Question

3

3. Given that most monitoring data for pesticides are basfrequent frequent sampling sampling intervals intervals (e.g., bi

-weekly, monthly) monthly), the U

explored additional approaches that combined variogram mcovariate approaches – in particular, correlation with flow withwindow

– or with WARP. We also considered considered methods methods of fil

fil

series concentrations using a deterministic model such as Pmass balance model, although such approaches would resource/data intensive.

a) Please comment on these additional modeling appr

interpreting interpreting sparse (less frequently frequently sampled) sampled) monitoring monitoring 
Charge Question 4

4. In characterizing overall uncertainty in exposure estimates from monito

USEPA must also consider how many years of monitoring are necessar

reasonable bound on the year-to-year variability or, alternatively, developlacing the existing monitoring data in context of likely exposures that matime period of interest (for instance, 15 year cycles for registration review).

a) Please comment on the sufficiency of existing atrazine/triazine m

available to the Agency – in particular the Atrazine Monitoring Pcoupled with the earlier Voluntary Monitoring Program (VMP), whi

span from 1993 to the present present for some CWS – for use in characte

characte

range in year-to-year variability in atrazine/TCT concentrations.

b) Please comment on the Agency’s suggestion for using a PRZM 

calibrated on the current years of monitoring, to provide estimates f

frame by modeling additional years using weather data that span a period.

c) What other possible approaches can the SAP recommend for cap

year variability? 
Charg Qeuestion uestion uestion uestion 5

5. In 2000, the SAP agreed with the Agency’s proposal neuroendocrine MOA, and they further concluded that it is unlikely thaction by which atrazine atrazine induces induces mammary mammary tumors in adult female Sp

Sp

rats could be operational in humans. The SAP further concluded unreasonable to expect, however, that atrazine might cause advehypothalamic-pituitary-gonadal (HPG) function in humans if exsufficiently high and that perturbation of the HPG axis was developmental and reproductive effects (FIFRA SAP, 2000). In the 2Agency identified perturbations of the neuroendocrine system (pregulation) regulation) leading leading to reproductive reproductive toxicity toxicity as the most biologically biologically sensitive effects attributable to atrazine exposure. The adveoccurring as a consequence of disruptions to the HPG axis in disruption of estrous cyclicity and delays in puberty onset (males An additi l dditional eff t ec – not di tl rec y li k d n e to LH di ti srup on – is tsuckling-induced prolactin release in milk early in life (perinatally), increased incidence of prostatitis in young adult rats. All of these linked to and/or occur at higher doses than the atrazine atrazine-induced induced c

c

secretion.
ChargQ ( 

e Question 5 uestion 5 uestion 5 uestion 5 (Co

Research conducted since the 2003 IRED continues to point to LH suas the most sensitive effect in the atrazine database. Consequently, continue to use changes in LH secretion as a senti l ne end 

p

perturbations and the basis of the atrazine risk assessment. The SSAP “ agreed with the Agency's conclusion that, based on the avbe c a n hm rk dose ( ) BMD mode ed l from da at on supp ess o r i n of the LH to be protective for other endpoints, since this phenomenon occurs than for the wide range of effects identified in a rather extensivdatabase.”

a) Currently available data show that in the rat a brief exposure 

days) to low levels of atrazine can elicit decreases in LH. Pon the biological biological plausibility plausibility of these brief changes changes leading leading outcome taking into account typical variability and how long aLH surge reduction is needed to cause the observed adverdisruptions in cyclicity, delayed puberty, and prostatitis).
Charg Qeuestion 6

6. During the September 2010 SAP, the Panel raised the issue of singatrazine exposure effects on the LH surge. In their report to the Ag commented:“Data are clear in identifying that a greater-than-one pulse of exposurnecessary for attenuation of the LH surge. For example, single high do

mg/kg) administered on the morning of proestrus did not alter characLH surge occurring later the same day. Additional data clearly demo

daily dose for 4 days and beginning beginning on estrus can induce significant significant i

i

LH surge peak. In this instance, a dose response is observed. Howevclear is if less than 4, but greater than 1 days’ exposure is sufficient surge. Further complicating the matter, it is not clear if a 4-day exposon a diff t eren day of the cycle, will result in changes in the LH surge s

when dosing begins on the morning of proestrus. Understanding of tbetween duration of exposure and phase of the cycle will be key in tradata to humans for risk assessment p p ur oses.”
ChargQ ( 

e Question 6 uestion 6 uestion 6 uestion 6 (Con

In response to the Panel’s comments, EPA scientists in thResearch Research and Development Development have undertaken undertaken a series of exp

exp

try to elucidate the nexus between phase of the cycle and exposure. This research is in the early stages. Initial resuthat a single high dose of atrazine (100 mg/kg bw) can affsurge. However, the effect seen was an increase in LH rathdecrease observed after 4 days of exposure.

a) Please comment on the potential relevance of one da

to elicit an adverse outcome(s) and the significance of vs. a decrease in LH.
Charg Qeuestion 7

7. An increased incidence of prostatitis has been observed in of rats exposed to atrazine from PND 1 to 4. This effect was an LH alteration, but rather the atrazine related suppression 

induced prolactin release in the lactating dams. Prolactin plarole in the neonatal brain for normal TIDA neuron developm

ad lt u off i spr ng, the i id mpa red TIDA regul ti a on is refl t d ec e prolactin levels (hyperprolactinemia). It is this elevated level oprolactin in the adult male rats that has been linked to aincidence incidence of prostatitis prostatitis. It is unknown unknown when the TIDA neuron

neuron

the human fetus or whether this development is dependmaternal prolactin concentrations.

a) Given the biological processes involved in the atrazi

prostatitis in rats, please comment on the human releva

findings findings in rats for the overall overall hazard characterization characterization for 
Charge Question 8

8. When evaluating the data on mammary gland development, the Septemreport concluded that the “use of the existing data on rat mammary gland assess the potential potential human risk of atrazine atrazine is not warranted warranted at the present present timthe methodological differences between the Rayner et al., and the Coder stu

commented that “it is surprising that they did not employ both qualitative ascoring measures of mammary gland development, which would have provi

inter-study comparison comparison.” In response response to this comment comment, the Agency has con

con

experiments investigating the potential impact of in utero atrazine exposur

gland development (MGD) in Sprague Dawley rats using both the submethodology described by Rayner et al. and a computer-based quantitativ

(morphometric morphometric analysis) analysis). Using either quantitative quantitative or subjective subjective measur

measur

mammary gland development, no differences in MGD were found betwatrazine-exposed rats indicating that gestational atrazine exposure had no effect on normal mammary gland development.

a) Please comment on the Agency’s findings in addressing the issues rai

during the September 2010 meeting. Please comment on whether th

with the negative studies by Coder) adds to the weight of evidence t

that atrazine impacts mammary gland development.
Charg Qeuestion 9 

9. In 2003, an FQPA Safety Factor was retained in part to addof data evaluating the potential for differences in sensitivitstages. Since then, multiple studies evaluating atrazine’s potfollowing exposure during the prenatal, perinatal, prepubertstages of life have been cond td uc e to address these d t a a gathe new studies has identified an enhanced sensitivity in the yLH surge attenuation observed in females of reproductive age be the most sensitive endpoint.

a) Please comment on the weight of the evidence analys

by the Agency and the ext t en to whi hc the uncert i ti a n 

the potential for differential sensitivity of the young arwith the additional data.
Charg Qeuestion 10

10. Section 3.0 and Appendices B-3 through B-5 of the drafprovide the Agency’s reviews and synthesis of the atrepidemiology studies. These studies examine a variety of cancnotably reproductive and endocrine system tumors includb t reas , ovarian and th id yro tumors, cancers of the l h 

lympho

system including non-Hodgkin lymphoma (NHL), and other including glioma, pediatric cancers and colon cancer. Section 

the findings findings of the epidemiology epidemiology and experimental experimental toxicology toxicology st

st

a) Please comment on the sufficiency of the Age

epid i l em o ogy reviews with respect to id tif i identifying the m

and limitations of each study, and overall synthesis cancer types.
Charg Qeuestion 11

11. There is no compelling evidence in the available experimedatabase database that atrazine atrazine may be carcinogenic carcinogenic in humans. This database database by the SAP in April 2010. Briefly, the results of both guideline and nvivo as well as in vitro studies do not suggest atrazine has 

carcinogenic properties. With regard to mammary tumors, severa

external peer reviews have concluded that the mode of action atrazine influences mammary tumor development is not operationFurther, EPA’s current review of the atrazine cancer epidemiology daidentify identify evidence evidence across any of the cancer-specific specific databases databases evalu

evalu

carcinogenic potential of atrazine that EPA finds sufficiently convincinconclusions. Therefore, in view of the evidence in the experimental epidemiologic databases, EPA concludes atrazine is not likely to be the human population. The observational data lend further support 

relevance of the laboratory rodent tumor findings, i.e., the databases 

of an association between atrazine and cancer in the human populatio
Charge Question 11 (Co

a) Please comment on the extent to which the scientifi

supports the integrative analysis contained in Sectrespect to the similarities, differences of the experimen

an

d epid i l i idemiologic fi di n ngs. Please commen

t on an

uncertainties in the epidemiologic findings.

b) Please comment on whether the epidemiology literatu

since the last SAP review including the AHS findings i

justify changing the Agency’s conclusions that atrazin

to be carcinogenic to humans.
Charg Qeuestion 12

12. The proposed refined dose response assessment for atrazine will be bmeasures of exposure. At the St b ep em er 2010 SAP meeting, the Agestimates of area under the concentration-time curve (AUC) for plasma triazrat [14C]-atrazine study (i.e., Thede 1987). The Panel concluded that “...on 

currently available data, plasma appears to be a reasonable biological com

refl ti ec ve of tissue dose, and th t a use of area under the plasma concent 

r

(AUC) provides an appropriate measure of internal exposure.” The Panel alsuse of total chlorotriazine based on total 14C-compounds is a reaso

(particularly in the absence of information on the pharmacodynamic activi

compound and i di id l individual met b lit ) tabolites). However, the P l ane b li d e eve th t a thdata, had limitations, and should be interpreted with caution.” In response tby the Panel, the Agency has evaluated additional pharmacokinetic studies inspecies including humans and two additional rat14C-atrazine studies that supclearance esti t ma es obt i d a ne from the Th de e 1987 st du y. B d ase on the pharmacokinetic behavior of plasma triazines resulting from orally adminiatrazine across the different studies, the Agency proposes to use an interim modeling approach based on a one-compartment linear model to inform inth t a seems to ad tl equa ely d ib escr e the ph ki ti harmacokinetics of plasma ti i r az n

orally administered atrazine.
Charge Question 12 (Co

a) Please comment on the strengths and limitations associated with 

pharmacokinetic pharmacokinetic modeling modeling approach approach for human extrapolation extrapolation.

b) Compare and contrast the strengths and weaknesses of using total ra

pharmacokinetic analysis (as presented in the Agency’s issue paper) 

using available pharmacokinetic data for the parent and the c

metabolites that have similar toxicological properties to the parent?

c) A

s

pointed out in the Ag y enc

y issue

pp , a

per, we are still reviewin

g 

submitted by Syngenta. As we complete our review of the Syngenta comment on key aspects that EPA should be considering concerning including model credibility (e.g., structure, parameter values, documereliabilit

y (e.

g., how well does the model simulate the dose metrics 

mode of action), and model applicability (e.g., does the model have esfor intended application).

d) Please comment comment on the extent to which the one-compartment compartment linea

plasma radioactivity derived from 14C labeled atrazine may account 

differences in pharmacokinetics. 
Charge Question 13

13. Any risk assessment of atrazine ideally should account for the temporal reex

posure and toxicolo

gical end

point (i.e., LH attenuation). The Ag y enc

y is rel

y 

involving constant dosing frequency and dose level to elucidate this relationship. in rats appears to be based on the build-up of plasma triazines to pseudo steady triazine levels stay within a constant range). The Agency is using this informatallometricall

y scaled e

quivalent human time-topseudo stead

y state

plasm

However, the Agency is cognizant that human exposure is different from contrthat both the dose level and the frequency of exposure through drinking water the Agency has identified several possible durations of human exposure, which the ex

posure intervals of concern for LH attenuation in humans:

• 28 days: a duration predicted by allometrically scaling the rat plasma elimination 

and humans, the time estimated to reach pseudo steady state plasma triazineres

pective len

gth of their ovarian c

ycles (i.e., 4 and 28 da

ys, res

p y) ectively).

• 14 days: Proposed to serve as a midpoint between the other two durations for bet

water monitoring frequencies.

• 4 days: the duration of exposure needed to reach pseudo steady state in rats and 

follicular phase in the human menstrual cycle. 
ChargQ ( 

e Question 13 uestion 13 uestion 13 uestion 13 (Co

a) Please comment on the rationale used by the Ag y enc for s

exposure duration options. Please discuss the rationale for otdurations of concern, if any.

b) Please comment on which exposure duration in humans 

corresponds to the exposure duration found to cause adverse 

c) Please comment on the approach used by the Agency 

compartment linear model) to relate atrazine levels frochemographs to predict corresponding human plasma triazine 

proposed proposed durations durations of concern concern. In particular, particular, please com

com

Agency’s proposed approach to use water AUC estimates time-weighted daily average of atrazine exposure for a givconcern. Please suggest alternative approaches as appropriat
Charge Question 14

14. For the case study, the Agency used the 95th and 5th pconditional conditional simulations simulations of daily concentrations concentrations from variog

variog

based on 7-day sampling intervals to predict human plasmtriazines. The estimations of daily concentrations from weekwere used to calculate calculate the rolling rolling average average concentrations concentrations for critical window of exposure from 4 to 28 days. The simulaunderestimated a single day peak concentration but appeareasonable approximations o

f rollin

g avera

ge concentr

durations as short as 4 days as well as the length of time of exceedance.

a) Please comment on the use of a 95th percentile of the 

simulations for providing an upper bound on rolliconcentrations in the case stud

y.