UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

June 24, 2015 

PC de: 116001,116002,116004 

DP Barcode: 426692 

Larry Liu, PhD, Chemist ~ Brian Montague, Fishery Biologist d _ - ~ :..;:~ Environmental Risk Branch 5 ~ ~"'f! 

Environmental Fate and Effects Division (7507P) 

Mah Shamim, Branch Chief 

Environmental Risk Branch 5 

Environmental Fate and Effects Division (7507P) 

Brittany Pruitt, Chemical Review Manager 

Avivah Jacob, Team Leader, RMIB3 

Pesticide Re-evaluation Division (7508P) 

EFED Triclopyr team has reviewed comments received from the California Stormwater Quality 

Association (CASQA), the San Francisco Bay Regional Water Quality Control Board (a CASQA 

member), Dow AgroSciences LLC, and the Physicians Committee for Responsible Medicine. 

The team recognizes that though some of the comments made by CASQA are specific to 

Triclopyr uses and detections in California, many of the comments are not chemically specific, 

but do indicate the importance of considering urban use scenarios in future risk assessments for 

any chemicals undergoing registration review. In that context the Triclopyr Ecological Risk 

team will make attempts to better characterize these use pattenw where current modeling 

scenarios can be applied or modified. In addition, urban incidents and monitoring data for all 

U.S. states, including California, will be assessed as part of the registration review process. Both 

CASQA and the San Francisco Bay Regional Water Quality Control Board have also cited 

additional information regarding the toxicity of the TCP degradate to the freshwater invertebrate, 

Daphnia carinata which will be evaluated along with the current aquatic data set for this 

degradate. Dow AgroSciences has commented on issues related to a soil photolysis review 

(MRID 44329901) as well as requirements for Honeybee 10 day chronic and larval testing 

currently required for outdoor use chemicals. The Physicians Committee has cited existence of a 

European test for Oral Toxicity to Passerine species with Triclopyr butoxyethyl ester and 

recommended that this study be used to fulfill the 850.2100 FIFRA data requirement. EFED has 

responded below to the individual comments by category and source for the comment. 
Comments Regarding Monitoring, Exposure Modeling and Environmental Fate

CASQA and SFB Comment regarding Urban Runoff: Submitters (CASQA and SFB) 

indicated that the risk hypothesis and conceptual model do not recognize triclopyr application to 

impervious surfaces and storm drainage system design. Also, CASQA requested clarification 

regarding how the E-FAST and the Surface Water Concentration Calculator (SWCC) would be 

used and/or modified for modeling urban use and subsequent run-off from pervious 

(turf/landscape) and impervious surfaces (around buildings and throughout rights-of-way) in the 

measures of exposure. CASQA cited an article (M.P. Ensminger, et. al. 2013) 1 in which 

triclopyr and other 63 pesticides or associated degradates were examined between 2008 and 2011 

in urban surface waters and sediments in three urban areas in California. As reported, these three 

areas (i.e., Sacramento, San Francisco Bay, and Orange County) were not affected by 

agricultural inputs. Results indicated that triclopyr was one of the three most frequently detected 

herbicides in surface water (the other two herbicides were 2,4-D and dicamba). Triclorpyr was 

found more frequently in southern California (Orange County with 82% detection frequency) 

than in northern California (Sacramento with 62% detection frequency and San Francisco Bay 

with 40% detection frequency). They also stated that more monitoring information could be 

obtained from California Department of Pesticide Regulation.

EFED Response: EFED will consider relevant submitted routes of exposure, including 

applications on impervious surfaces, in the revised risk hypothesis and conceptual model. The 

article by M.P. Ensminger, et. al. (2013) will be included and considered in making decisions on 

the registration review for this chemical. 

At the present time, EFED considers the use of the impervious scenario (a PRZM modeling 

scenario) as the most suitable available modeling approach for impervious runoff. The PRZM 

impervious scenario may be used in the tier 2 coupled aquatic models SWCC along with a 

residential or other suitable scenario such as rights-of-way (ROW) to obtain 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 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 should be copied from the times series file (NAME_TS.out) 

 1 Ensminger MJ.P. R. Budd, K.C. Kelley, K.S. Goh. 2013. Pesticide occurrence and aquatic benchmark 

exceedances in urban surface waters and sediments in three urban areas of California, USA, 2008–2011 (Urban and 

Agricultural Sources of Pyrethroid Insecticides to the Sacramento-San Joaquin Delta of California). Environ Monit 

Assess (2013) 185:3697–3710.
generated from the PRZM graphical user interface (PE5.pl) into the spreadsheet provided. The 

time series data are then 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 return 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 (the most current database includes 2012 use 

information), and the Residential Joint Venture Task Force homeowner survey data, to make 

certain reasonable assumptions regarding various applications and information related to 

urban/residential use. Due to the limited data available, exposure to the environment and 

uncertainties will be characterized. Detailed information on non-agricultural use and usage of 

triclopyr products, specifically triclopyr BEE, would be useful in order to reduce those 

uncertainties for the final environmental risk assessment for triclopyr

.

Dow AgriSciences Comment: Dow indicated that TCP (a minor degradate) cited in the PF was 

for dark control in the soil photolysis study (MRID 44329901) and less TCP was detected in the 

sunlight-exposed samples. In dark control samples, TCP reached a maximum of 5.1% AR (19 

DAT) and levels at study termination (31 DAT) were 4.6% AR. In sunlight-exposed samples,

TCP reached a maximum of 1.9% AR (3 DAT) and levels at study termination were 1.2% AR. 

EFED Response: Since the levels of TCP detected in the sunlight-exposed samples were lower 

than those in the dark control in the soil photolysis study, it appears that natural sunlight has no 

direct effects on the formation of TCP. EFED will revisit the endpoints cited in the Problem 

Formulation and make corrections as needed.
Comments Regarding Effects Studies: 

CASQA Comment: Though CASQA generally supports the fate and toxicity assessments, some

minor modifications were suggested. CASQA has cited a study for TCP with Daphnia carinata

(Caceres, T. 2007. Water Research, Nov;41(19):4497-503) that shows it to be more toxic than 

the tested parent (which in this case was Chlorpyrifos). 

EPA Response: This open literature study, which investigates the potential synergistically 

additive toxicity of Chlorpyrifos and TCP together, will be requested for review. This study 

citation has also been provided to the Chlorpyrifos Registration Review team. The Agency has 

evaluated laboratory data for Daphnia magna with the TCP degradate (MRID 41829005) and 

this study already shows TCP to be more toxic than the TEA salt and Triclopyr Acid, but less 

toxic than the Butoxyethyl ester. However, no data has been reviewed to show the potential for 

synergistic increase in toxicity when both triclopyr and TCP are present together.

CASQA Comment: CASQA is requesting that a cumulative aquatic TCP risk assessment be 

done for chlorpyrifos to allow for a more accurate and separate aquatic benchmark for this 

degradate. 

EPA Response: In general, OPP has not done separate risk assessments for metabolites, even 

though they may be common to multiple parent actives. We do combine the toxicity and fate 

data for a single degradate from all data submitted by registrants for support of their actives, but 

use patterns, use sites and application rates may differ and therefore alter the exposure levels for 

the degradate under the criteria specific to these uses. 

CASQA Comment: Expand the data requirements for TCP to include chronic testing with 

Daphnia carinata in addition to Fish Early Lifestage testing.

EFED Response: The Agency has already received a TCP chronic toxicity study with Daphnia 

magna (458861301) to support Triclopyr actives and this study is under review. If acceptable 

this study should provide an adequate set of endpoints for assessment of freshwater invertebrate 

hazard potential for any active ingredient for which TCP is a degradate of concern.

Dow AgroSciences Comment regarding Honeybee Larval Chronic Toxicity Testing 

requirement with Triclopyr Acid technical.

Comment: As triclopyr is an herbicide, does not have an insecticidal mode of action, and is not 

an insect growth regulator, it is not expected to impact terrestrial invertebrates such as 

honeybees. This is further corroborated by the following:

1. Triclopyr acid is practically non-toxic to honeybees based on acute oral and contact

toxicity tests (see comment below).

2. Once plant uptake occurs, triclopyr acid is quickly conjugated and forms polar acid

labile conjugates. Research demonstrated that < 0.06% applied dose was detected in fruit 

(Yackovich and Lardie 1996) and 0.006% of triclopyr’s applied dose was detected in ryegrass 

seed (Yackovich et al. 1993). Based on this evidence, triclopyr acid does NOT preferentially 

translocate to plant flowers, seeds, and/or fruit. Since triclopyr does not preferentially move to 
untreated plant areas as well as its rapid conjugation, the likelihood of adult honeybees 

transporting triclopyr residues to the hive via contaminated nectar and pollen is negligible thus 

eliminating potential larval exposure. Furthermore, since triclopyr acid is practically non-toxic to 

adult honeybees, it is feasible that triclopyr acid would have minimal, if any, impact on larval 

development or survival.

3. Finally, triclopyr is primarily used in rice, rangeland and pasture, rights-of-way, forestry, and 

turf for the control of broadleaf and woody plants. Herbicide applications rarely occur during 

flowering growth stages due to grazing and other mechanical inputs and, therefore, foraging 

worker bees would have minimal, if any, exposure to triclopyr residues from treated crops thus 

reducing the probability of transporting contaminated nectar and pollen back to the hive. 

DAS disagrees that an acute and chronic larval toxicity tests are necessary based on the

available information.

EFED Response: Dow has cited what appear to be residue tolerance studies in fruit and seeds 

as well as previously evaluated honeybee acute studies, as a basis to dismiss the requirement as 

being unnecessary. The Pollinator Protection Policy currently being implemented for pesticides

is not promulgated entirely for systemically acting chemicals, though this could be one criteria of 

concern. The policy states, “In general, outdoor spray applications are assumed to have a 

reasonable potential to result in exposure of adult bees and their brood (eggs, larvae, pupae) to 

pesticides if they are applied to pollinator attractive crops or drift to pollinator attractive plants 

during periods when bees are likely to be foraging.” Exposure to residues in flowering plants 

(invasive or native) is a criteria and direct spraying of Triclopyr products in rights of way, 

pastureland, forests, and rangeland could certainly present the potential for food source 

contamination for wild or commercially provided pollinators. To our knowledge there are no 

current label restrictions on applying Triclopyr products when target or non-target plants are 

blooming. It is assumed that nectar or pollen could also be exposed to residues of triclopyr under 

these circumstances. In addition, acute contact and oral toxicity testing with adult bees do not 

necessarily reflect potential toxicity to developing larvae. In order to conduct Tier I assessment 

of pollinator risk, chronic effects to adults and larval bees are considered. The registrant may 

wish to consult the Office of Pesticide Programs Guidance for Assessing Pesticide Risks to Bees 

implemented June 23, 2014 regarding determination for testing needs and assessment of 

exposure potential currently used by the Agency.

Dow AgroSciences comment regarding Honeybee Adult 10 Day Oral Chronic Toxicity 

Testing requirement with Triclopyr Acid technical.

Dow Comment: An adult honey bee acute oral and contact toxicity studies were conducted 

according to OECD guidelines 213 and 214 [Hahne 2001; Dingledine and Jaber 1985].

Overall, results from these tests indicate that triclopyr acid is practically non-toxic to bees

based on the acute oral and contact 48-hour LD50 values of > 100 μg a.i./bee and > 100

μg a.i./bee, respectively. Furthermore, since acute effects were not observed, chronic

effects would not be expected due to the absence of acute toxicity. These endpoints

provide evidence that triclopyr is practically non-toxic to adult honey bees thus chronic
effects are not anticipated. Therefore, DAS disagrees that the chronic adult oral tests are

necessary based on the information provided. Studies can be provided to the EPA upon

request.

EFED Response: The current 48 hour acute contact and oral toxicity testing using Triclopyr 

acid with adult bees may not reflect potential chronic toxicity to adult bees from longer term 

exposure to residues via ingestion of pollen or nectar. In order to conduct Tier I assessment of 

pollinator risk, chronic effects to adults and larval bees are considered. The registrant may wish 

to consult the Office of Pesticide Programs Guidance for Assessing Pesticide Risks to Bees 

implemented June 23, 2014 regarding determination for testing needs and assessment of 

exposure potential currently used by the Agency.

Physicians Committee for Responsible Medicine comment regarding Oral Toxicity 

Requirement for Passerine species 850.2100.

Comment: We have found existing data for the avian oral toxicity endpoint in passerines 

(850.2100). This study used 12 birds in each of the 5 concentrations, in addition to the control.

Citation: Holmes, SB, et al. “Effects of lethal and sublethal concentrations of the herbicide, triclopyr butoxyethyl 

ester, in the diet of zebra finches.” J Wildl Dis. 1994 Jul; 30(3):319-27.

“The 8-day median lethal dietary concentration, LC50 (95% confidence interval), of TBEE to 

zebra finches was 1,923 (1,627 to 2,277) mg/kg.” 

If this data is not accepted by the Agency then we recommend that OECD Test Guideline 223, 

Avian Acute Oral Toxicity Test, be used as the protocol instead of EPA Guideline 850.2100 in 

the interest of reducing the numbers of animals used by up to 61%. We also refer the registrant to 

the “Guidance for Classifying Studies Conducted Using the OECD Test Guideline 223 (TG223) 

(Acute Avian Oral Sequential Dose Study)” available on the Agency’s website.

EFED Response: The study cited as an oral study appears to be a dietary study. The Agency 

does accept dietary studies as a substitute for guideline 850.2100 when oral studies are found to 

be impractical due to regurgitation issues or other problems encountered during the study.

Though there is guidance available regarding classification of OECD 223 studies, EFED 

generally recommends against reliance on TG 223 for passerine species since this guideline was 

not tested or validated for passerines.