change specific parts of the Registration Review Problem Formulation. This document contains 

responses only to those comments submitted related to the ecological risk assessment or the drinking 

water exposure assessment outlined in the problem formulation. Given the large number of comments 

and the similarity between comments, comments have been grouped together and summarized by 

common topic. 

2
OPP RESPONSE TO PUBLIC COMMENTS: 

1. Comment Summary: Chlorothalonil drift from treated fields to areas where bystanders 

(including frogs) may live, work or frequently visit should be considered as part of the 

registration review process.

ID Number: EPA-HQ-OPP-2011-0840-0010; Commenter: Carol Ashley; Organization: none

OPP RESPONSE: Potential chlorothalonil spray drift will be assessed during the registration 

review process. In addition, data on the potential volatilization of chlorothalonil following 

application has been requested. The potential risks associated with drift and volatilization will be 

assessed as part of the registration review process. 

2. Comment Summary: Based on the cited reference (Holt et al., 2010) the levels found should be 

expressed as 39 ng ΣPCDD/F g-1 AI. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta

OPP RESPONSE: As stated in the problem formulation, “(t)hese chemicals have been found in 

technical grade chlorothalonil, as well as formulated chlorothalonil products; however, the levels 

are low (39 ng DF/g a.i.).1

” The unit/term “DF” was defined as “polychlorinated dioxins (D) and 

dibenzofurans (F)” in the same paragraph as the quoted text. The difference in the expressions 

used by EPA in the problem formulation and that suggested by Syngenta does not impact data 

requirements or the conceptual model for conducting risk assessment. 

3. Comment Summary: The correct chemical name for R419492 is 4-amido-2,5-dichloro-6-

cyanobenze. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: The typo has been corrected. 

4. Comment Summary: Chlorothalonil application rate corrections were provided for several 

crops: banana, cherry, filbert (hazelnut), golf course, papaya, passion fruit, plantain, squash, and 

stone fruits.

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: EFED confirmed that the use (application rates) information provided by 

Syngenta is correct. During the registration review process EFED will assess all uses as specified 

on the registered labels current at the time of the assessment is completed. 

5. Comment Summary: The studies given as the source for several environmental fate studies 

(00071625, 00071627, 00087369, 00087301 and 00087332) could not be confirmed or located in 

either the Syngenta electronic or hard-copy archives. MRID 00087332 presents data for both a 

laboratory study, which provided the product identification, and a field study, which quantified 

the environmental concentrations of the identified products. 

 

1

 Holt. E.; Weber, R.; Stevenson, G.; Gaur, C. Environ. Sci. Technol. 2010, 44, 5409-5415. 

3
ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

EFED RESPONSE: The listed environmental fate MRID references (00071625, 00071627, 

00087369, 00087301 and 00087332) are correct, and are studies previously submitted to support 

chlorothalonil. The information provided for MRID 00087332 is correct. This study is classified 

as supplemental as stated in the problem formulation. 

6. Comment Summary: The referenced studies presented monitoring data from the Central Valley 

of California and surrounding areas (EPA footnotes 19, 20 and 21, Pages 46-47), which indicated 

the potential for long-range atmospheric transport of pesticides. Sparling et al. (2001) and Fellers 

et al. (2004) provided data for several organophosphorous and organochlorine pesticides, but did 

not provide monitoring data specific to chlorothalonil (EPA footnotes 20 and 19, respectively). 

Lenoir et al. (1999), EPA footnote 21, did present chlorothalonil monitoring data but a 

mechanism for transport was not identified. The statement should be clarified to reflect that only 

LeNoir et al. (1999), EPA footnote 21, presented information on chlorothalonil. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta

OPP RESPONSE: The referenced literature articles (Sparling, et al.

2

 and Fellers et al.

3

) were 

used in general terms as a means to highlight the potential for pesticide volatilization and 

subsequent off site transport. These two articles did not specifically look for chlorothalonil; 

therefore, the presence or absence of the chemical cannot be confirmed. One of the referenced 

articles (Lenoir et al.

4

) includes detections of chlorothalonil. While this study does not suggest a 

transport mechanism, the detection of chlorothalonil in air cannot be dismissed. Furthermore, 

additional citations were provided that suggest chlorothalonil is getting into the air following 

application and may be transported offsite. This suggests that chlorothalonil may volatilize from 

treated field. 

7. Comment Summary: As part of the response to Chlorothalonil Salmonid BiOP, Syngenta 

reviewed the available monitoring data (Syngenta Report TK0026829). Details are available in 

the report, but in general, water monitoring data collected across 18 years, including multi-year 

national surveys (NAWQA), targeted state surveys (WSDA and USGS) and academic surveys 

and upwards of 10,00 collective samples indicate no residues in water above 0.71 ppb. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: OPP uses mathematical models as well as monitoring data to generate 

exposure estimates for drinking water and aquatic exposure assessments. Modeling and 

monitoring data are both important tools that by and large provide different types of information 

that can be used for assessing pesticide concentrations in water. 

Mathematical models are used to generate exposure estimates for drinking water and aquatic 

environments to better understand the extent to which monitoring data may underestimate 

 

2

 Sparling, D.W., Fellers, G.M., McConnell, L.L., 2001. Pesticides and amphibian population declines in 

California USA. Environ. Tox. Chem. 20: 1591-1595. 

3

 Fellers, G.M, L.L. McConnell, D. Pratt, S. Datta. 2004. Pesticides in Mountain Yellow-Legged Frogs (Rana 

Mucosa) from the Sierra Nevada Mountains of California, USA. Environ. Tox. Chem. 23 (9):2170-2177. 

4

 LeNoir, J.S., L.L. McConnell, G.M. Fellers, T.M. Cahill, J.N. Seiber. 1999. Summertime Transport of 

Current-use pesticides from California’s Central Valley to the Sierra Nevada Mountain Range, USA. 

Environmental Toxicology & Chemistry 18(12): 2715-2722. 

4
exposures, both spatially and temporally. Models, specifically PRZM-EXAMS, calculate EDWCs 

using laboratory data that describe how fast a pesticide breaks down to other chemicals and how 

it moves in the environment. In addition, modeling provides an efficient tool for exploring the 

impact of different environmental factors such as soil type and meteorological conditions on 

estimated pesticide concentrations in water. Although computer modeling provides an indirect 

estimate of pesticide concentrations, these concentrations can be estimated continuously over 

long periods of time, and for places that are of most interest for a particular pesticide. Modeling is 

a useful tool for characterizing vulnerable sites, and can be used to estimate peak concentrations 

from infrequent, large storms. 

Monitoring data can elucidate what is happening under current use practices and under typical 

conditions. Although monitoring data can provide a direct estimate of the concentration of a 

pesticide in water, it does not always provide a reliable estimate of peak exposures because 

sampling may not occur where the highest pesticide concentrations are found and/or sampling 

may not occur when the pesticide concentrations are the highest. It is also important to consider 

the design of the monitoring program where there is use information available and where it was 

targeted to chemical specific use areas. 

EFED will evaluate all available monitoring data for chlorothalonil during the registration review 

process. Monitoring data and modeling estimates will be used together to characterize the 

potential exposure to chlorothalonil. It would not be appropriate to rely solely on monitoring data; 

for the reasons explained above, not to mention the fact that it would be inefficient and 

ineffective, if not impossible, to capture all relevant scenarios, site and meteorological conditions, 

soil types, etc., in a monitoring program. 

8. Comment Summary: The final report [for the PGW study] was submitted February 9, 1998 

(MRID 44483401). 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: This study will be reviewed as part of the registration review process. Thank 

you for providing the MRID. 

9. Comment Summary: The final report [for the PGW study] was submitted February 9, 1998 

(MRID 44483401). Field dissipation data for SDS-3701 can be obtained from the submitted PGW 

study (MRID 44483401). 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: This study will be reviewed as part of the registration review process and 

may provide useful information on the dissipation of SDS-3701 in the environment. The 

acceptability of these data (PGW study) are not expected to impact the risk assessment approach 

explained in the problem formation

10. Comment Summary: Syngenta provided additional information relating to the deficiencies 

identified in the terrestrial field dissipation study. “Syngenta Comment: Several points can be 

addressed: (1) a final report for the freezer-storage stability study conducted over 4 years was 

submitted (MRID No. 44483402); (2) and (3) the PGW study (MRID No. 44483401) presented 

the results of shallow- and deep-core sampling conducted from 0 to 24 MAA from which rates of 

dissipation for chlorothalonil and SDS-3701 could be derived. During the conduct of the PGW 

5
study, (4) analytical methods for determination of residues of chlorothalonil, SDS-3701, SDS19221, SDS-47525 and SDS-46851 were developed.” 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: (1) MRID 44483402 will be reviewed as part of the registration review 

process. Thank you for providing the MRID. The acceptability of these data (storage stability) are 

not expected to impact the risk assessment approach explained in the problem formation nor does 

it change the data requirements. (2) and (3) the design of a PGW study is to examine the leaching 

potential of a pesticide and its transformation products through a vertical soil profile in a soil 

highly vulnerable to leaching; however, it is not a terrestrial field dissipation study and does not 

consider other dissipation routes and site conditions that should be considered in a terrestrial field 

dissipation study. (4) If the analytical methods used in the PGW are representative suitable 

environmental chemistry methods and have been independently validated, then a waiver for the 

environmental chemistry methods requirement should be submitted to EPA that includes the 

reports and methods along with the independent lab validation. 

11. Comment Summary: A field volatility study is not triggered per EPA guidance and; therefore, 

the study should not be required. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: There are monitoring data available that suggest that chlorothalonil is present 

in air as well as precipitation samples. These real world data suggest that chlorothalonil may be 

volatilizing off treated fields. In order to account for this dissipation route and the potential 

exposure to chlorothalonil as a result of volatilization a field study is needed. 

This study (field volatilization) may be combined with a standard terrestrial field dissipation 

study. 

12. Comment Summary: Urban exposure and runoff of chlorothalonil was overlooked. 

ID Number: EPA-HQ-OPP-2011-0840-0021; Commenter: Janet B. O’Hara; Organization: San 

Francisco Bay Regional Water Control Board 

ID Number: EPA-HQ-OPP-2011-0840-0015; Commenter: Sipcam Agro USA, Inc.; 

Organization: Sipcam Agro USA, Inc. 

OPP RESPONSE: EFED is currently further exploring methods to assess urban and residential 

uses on a national basis. EFED will consider comments regarding the need to include models that 

consider transport of runoff from impervious surfaces and stormwater drainage systems while it 

develops these methodologies. At the present time, EFED considers the use of the impervious 

scenario (a Pesticide Root Zone Model (PRZM) modeling scenario) as the most suitable available 

modeling approach for impervious runoff and has used this approach for some assessments 

completed for Endangered Species in California. The PRZM impervious scenario may be used in 

the Tier 2 coupled aquatic models PRZM/Exposure Analysis Modeling System (EXAMS) along 

with a residential or other suitable scenario such as rights-of-way (ROW) to obtain Estimated 

Environmental Concentrations (EECs). The conceptual model for the residential scenario 

integrates simultaneous modeling of the individual use scenario with an impervious scenario. 

This approach assumes that no watershed is completely covered by either the 1⁄4 acre lot (the basis 

6
for the residential scenario) or undeveloped land (the basis for the ROW scenario) for residential 

and ROW use patterns; therefore, differential amounts of runoff will occur within the watershed. 

The impervious scenario was developed to represent the paved areas within a watershed not 

including roads, parking lots, sidewalks, and buildings outside the 1⁄4 acre lot (the 1⁄4 acre lot 

scenario accounts for impervious surfaces such as buildings within the represented area). By 

modeling a separate scenario for impervious surfaces, it is also possible to estimate that amount 

of exposure that could occur when the pesticide is oversprayed onto this surface. Using two 

scenarios in tandem requires post-processing of the modeled output in order to derive a weighted 

EEC that represents the contribution of both the pervious (i.e., residential and ROW scenarios) 

and the impervious surfaces. Exposure from both scenarios can also be weighted and aggregated. 

The daily time series from each model run from the times series file (NAME_TS.out) generated 

from the PRZM graphical user interface (PE5.pl) residential and impervious surface scenarios are 

combined using Microsoft EXCEL. The time series data are weighted based on percentage of 

impervious surface, the percentage of the pervious surface treated, and an adjusted time series is 

created. Rolling averages for the relevant durations of exposure (e.g., 21-day and 60-day 

averages) are calculated, and the relevant one-in-ten year EEC is generated from these 

distributions. 

The Agency intends to use available non-agricultural use and usage data, such as the Kline 

database, the California Department of Pesticide Regulation’s (CDPR) Pesticide Use Reporting 

Data and Pest Control Operator’s usage survey, and the Residential Joint Venture Task Force 

homeowner survey data (2003), to make certain reasonable assumptions regarding various 

applications and information related to urban/residential use are made. Due to the limited data 

available, exposure to the environment and uncertainties will be characterized. Detailed 

information on non-agricultural use and usage of chlorothalonil would be useful in order to 

reduce those uncertainties for the final environmental risk assessment for chlorothalonil. 

As stated in the problem formulation, AD anticipates requiring data on the leaching of 

chlorothalonil from treated wood. The leach rate from other material preservative uses (e.g., 

stucco, paint, coating, and caulk) is desired but in the absence of leaching data, the wood leaching 

results will be used to assess all of the outdoor antimicrobial uses. When the registered 

antimicrobial chlorothalonil products are used in urban settings, AD will consider using the 

approach outlined above. Please see the conceptual models outlined in the problem formulation 

for more information. 

13. Comment Summary: The risk assessment must include analysis of products contaminants 

including dioxins, furans, and hexachlorobenzene) and transformation products (particularly 

SDS-3701). 

ID Number: EPA-HQ-OPP-2011-0840-0021; Commenter: Janet B. O’Hara; Organization: San 

Francisco Bay Regional Water Control Board 

OPP RESPONSE: The problem formulation identified stressors of concern including 

contaminants and transformation products (including SDS-3701) and how they will be assessed in 

the final risk assessment. 

14. Comment Summary: In the problem formulation EFED recommends that the Agency work with 

registrants to establish the level of known impurities. Sipcam comments that “The levels of 

HCB in currently registered technical products are well established: current technical 

products are produced to a specification of <40ppm HCB. Sipcam Agro USA, Inc. has 

7
ID Number: EPA-HQ-OPP-2011-0840-0015; Commenter: Sipcam Agro USA, Inc.; 

Organization: Sipcam Agro USA, Inc. 

OPP RESPONSE: The Agency encourages the registrants to submit relevant information at 

any time or, at the very latest, at the time of the data call-in associated with this registration 

review. 

15. Comment Summary: The identified NOEC (1.3 μg a.i./L) for the chronic fish toxicity study 

(MRID 00030391) in the problem formulation is not supported by the cited study as the NOEL 

was calculated to be 3 μg a.i./L based on significant effects on reproduction and hatchability. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: There was a 79% and 88% decrease in the mean number of eggs per female 

in the 3.0 and 6.5 μg/L treatment groups, respectively, compared to the negative control group. 

However, due to inherent variability in egg production and that the study only utilized two 

replicates per treatment, the statistical analysis could only detect a 110% difference from the 

control. Therefore, the 79% and 88% decreases were not statistically significant (p>0.05, 

Dunnett’s). EFED considers these decreases to be biologically significant and a NOEC of 1.3 μg 

a.i./L will be used in the risk estimation of the risk assessment. If the registrant has evidence or 

information that demonstrates that decreases of these magnitudes do not have an impact on the 

fitness of the fish population, then EFED will consider such information. 

16. Comment Summary: The chronic NOEC for freshwater invertebrates is identified as 0.6 μg 

a.i./L (MRID 45710222) which is classified as supplemental and was not included in the RED 

(U.S. EPA 1999) for chlorothalonil. This endpoint is not consistent with the core chronic 

invertebrate study (MRID 00115107) which demonstrated a NOEC of 39 μg/L. The registrant 

considers the study with the NOEC of 39 μg/L the best available data. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: EFED has re-evaluated the toxicity data for MRID 45710222. This study 

was not included in the 1999 RED as it was not submitted to the Agency until June 20, 2002 

(however, it has been used in subsequent risk assessments). In the study report, the 

estimated ‘no observed effect concentration’ value was 0.6 μg/L, based on direct lethal effects 

(≤20% immobility). Although the test concentrations dissipated between renewal periods 

thereby, introducing uncertainty into the actual exposure concentrations, EFED considers the 

immobilization toxicity observed to be treatment-related based on: 1) a decreasing trend 

(monotonic response) in survival as the concentration increased; 2) the effect was consistent 

between replicates within test concentrations; and 3) survival in both controls (negative and 

solvent) was 93%. Survival in the treatment groups ranged from 95% at the lowest treatment (0.6 

μg/L) to 40% at the highest (75 μg/L). Immobilization of the parental generation was statistically 

significantly (p<0.05, using Dunnett’s and William’s test) at concentrations ≥ 1.8 μg/L (75% 

survival); therefore, the NOAEC value is 0.6 μg/L based on immobilization. Significant effects 

(p<0.05) on reproduction (number of live young per adult) were also reported for the 75 μg/L 

treatment group. The NOAEC value of 0.6 μg/L is considered to be adequate for quantitative 

use. EFED uses the lowest effect value observed from all available studies that have been 

8
deemed appropriate for quantitative use, which may include studies that have an overall study 

classification of core (acceptable) or supplemental, for calculating risk quotients (RQs) in a risk 

assessment. Therefore, the NOAEC value of 0.6 μg/L will be used in calculating the RQ value 

while the NOAEC value of 39 μg/L observed in study MRID 00115107 will be used in 

characterizing risk. 

17. Comment Summary: The chronic NOEC for birds is identified as 153 mg/kg-diet (MRID 

45710218) in the problem formulation. This study was not included in the RED (U.S. EPA 1999) 

for chlorothalonil and is not statistically supported. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: The results of this study (MRID 45710218) were not included in the 

chlorothalonil RED, because it was not submitted to the Agency until after the RED was 

completed (submitted on June 20, 2002 and it has been used in subsequent risk assessments). A 

NOAEC of 153 mg a.i./kg-diet and a LOAEC of 624 mg a.i./kg-diet were based on a reduced 

number of egg laid per hen. Although the endpoints were not statistically significantly different 

than the controls (p>0.05), the differences were considered biologically significant (there was an 

18% reduction in the number of eggs laid/hen at the 624 mg a.i./mg-diet concentration when 

compared to the controls). The NOAEC value of 153 mg/kg-diet was used in the chronic avian 

RQ calculations (using the T-REX model) for the California red-legged frog risk assessment 

(CRLF RA) (EPA 2007). If the registrant has evidence or information that demonstrates that a 

decrease of this magnitude does not have an impact on the fitness of the bird population, then 

EFED will consider such information. 

18. Comment Summary: Syngenta previously submitted 16 studies with formulation specific 

toxicity data for fish (rainbow trout) and invertebrates (Daphnia) for consideration. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: The Agency has received the data and will consider the information as part 

of the risk assessment for the registration review of chlorothalonil. 

19. Comment Summary: A formation rate of 34% of SDS-3701 was assumed based on formation 

observed in soil metabolism studies (MRIDs 00040547 and 00087351). The available data 

demonstrate that residue levels on plant foliage do not support the highly conservative formation 

rate of 34% on potential food items. 

ID Number: EPA-HQ-OPP-2011-0840-0016; Commenter: Syngenta; Organization: Syngenta 

OPP RESPONSE: A discussion about the formation of SDS-3701 on avian and mammalian 

food items is presented in the 1999 RED and 2007 CRLF risk assessment. Studies that evaluated 

the amount of SDS-3701 that may form after chlorothalonil application to peanut hay, turf, and 

grass grown for seed are available. However, these studies do not provide a dependable basis for 

estimating the amount of SDS-3701 that may form on avian and mammalian food items as 

described in the 1999 U.S. EPA RED. In a peanut hay study (MRID 43843601), SDS-3701 

residues were reported at a maximum of 24% of the parent chlorothalonil residues. The 1999 

RED reported that use of a 10% formation rate would be conservative; however, it also stated that 

due to the observed formation of 24% in the peanut hay study, it is conceivable that under 

different conditions, residues of SDS-3701 could reach higher levels. 

9
10

As previously stated in these documents, there are insufficient residue study data to characterize 

with certainty how much SDS-3701 will form on avian and mammalian food items. Most of the 

available residue studies were designed to measure the amount of SDS-3701 that is taken up by 

crops and how much accumulates in vegetable items associated with human consumption such as 

beans and fruits. Unfortunately, most of these studies do not provide a dependable basis for 

estimating how much SDS-3701 will form on avian and mammalian food items in the days 

immediately following treatment with chlorothalonil, as measurement of chlorothalonil and its 

degradates generally occur days up to months after the last chlorothalonil application (RED, EPA 

1999). Typically, a minimum of three reliable residue studies which measure residues 

immediately after application are needed to adequately evaluate potential magnitude of formation. 

As the residue data was deemed to not be sufficient, the available laboratory data were used to 

estimate the amount of SDS-3701 that may form on terrestrial organism food items. Soil 

metabolism studies suggest that SDS-3701 could form at levels of approximately 34% of applied 

parent material. SDS-3701 was observed in several of the submitted aerobic soil metabolism 

studies (MRIDs 00087351/00040547, 4387960, 47207702, and 47207703. The maximum 

concentration ranged from <10% to 34.1% (n=14) in various soils and time points. In four of the 

test systems the concentration of SDS-3701 was >20%. The second highest concentration of 

SDS-3701 observed was 28.4%, thereby, suggesting that 34% is an appropriate maximum 

formation value. 

20. Comment Summary: Sipcam provided citations for existing public literature studies on the 

leaching of chlorothalonil from treated wood and requested guidance with regards on the methods 

and substrates that should be used to conduct the leaching studies anticipated to be required. 

ID Number: EPA-HQ-OPP-2011-0840-0015; Commenter: Sipcam Agro USA, Inc.; 

Organization: Sipcam Agro USA, Inc. 

OPP RESPONSE: The Agency encourages the registrants to submit relevant studies and 

applicable waivers in response to the data call-in associated with this registration review. At that 

time, the Agency will review the information to determine if the wood leaching data requirement 

is adequately met and can be waived. In the event the literature studies are not sufficient, the 

Agency recommends that the registrant conduct the study according to the AWPA E11-06 

method for addressing leaching from wood submerged in water. As stated in the problem 

formulation, the Agency anticipates utilizing these data “to determine the leach rate of 

chlorothalonil and its major toxic transformation products, and impurities of concern out of 

preserved wood for use in modeling loading to soil from rain washoff of antimicrobial applied 

wood preservatives.”