UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

				

MEMORANDUM

September 5, 2006

							

SUBJECT:	Trifluralin:  Revised Dietary Risk Estimates Based on the
Addition of Mung Bean Sprouts.  

		PC Code:	036101

		DP Barcode:	332202

FROM:	Richard Griffin, Risk Assessor

		Reregistration Branch II

Health Effects Division (HED)

THROUGH:	William Hazel, Branch Chief

		Reregistration Action Branch II

Health Effects Division (7509P)

			

TO:		John Pates, Chemical Review Manager

		Reregistration Branch II

		Special Review and Reregistration Division (7508P)

The human health risk assessment for trifluralin was completed on May 7,
2004 (R. Griffin memo) for the Tolerance Reassessment Eligibility
Decision (TRED) process.  At that time it was believed that the
tolerance for mung bean sprouts, specifically, was not supported by the
registrant, and the use was deleted from the risk assessment.  

The primary registrant for trifluralin, Dow AgroSciences, has
subsequently made it clear to the Agency that this use is, in fact,
still supported and should be included in the dietary risk assessment
for trifluralin.  Although mung bean sprouts are not a significant
consumption item, this memo amends the previous dietary exposure
estimates for trifluralin to fulfill the requirements of FQPA.

Endpoint / Dose 

The toxicological endpoints and dose levels that the risk assessment for
trifluralin is based on have not changed since the 5/7/04 risk
assessment.  For clarity, the endpoints/doses are summarized below.

An acute Population Adjusted Dose (aPAD) of 1.0 mg/kg/day was
established for females of child-bearing age based on the No Observable
Adverse Effect Level (NOAEL) of 100 mg/kg/day observed in a rat
developmental study.  A chronic Population Adjusted Dose (cPAD) of 0.024
mg/kg/day was established based on the NOAEL (2.4 mg/kg/day) of a
chronic toxicity study in dogs.  The endpoint(s) of concern are
increased frequency of abnormal stool, decreased body weights, decreased
body weight gains, decreased erythrocytes and hemoglobin, and increased
thrombocytes in males at the study LOAEL.  The Uncertainty Factor is
100x, based on 10x for inter-species extrapolation, 10x for
intra-species variability, and 1x for FQPA considerations.  

Trifluralin is classified as a Group C (“possible”) human
carcinogen, and a low dose extrapolation model (Q1*) is applied to the
animal tumor data for quantification of human risk.  The upper-bound
potency factor (Q1*) for trifluralin is 5.8 x 10-3 (mg/kg/day)-1.  

Exposure  

Trifluralin is a selective pre-emergence herbicide primarily used on
soybean and cotton, but it is also used on many other food commodities. 
Tolerances range from 0.05 ppm to 2.0 ppm.  Tolerances for livestock
commodities are not required.  Dietary exposure estimates are refined
based on field trial data, monitoring data (Pesticide Data Program), and
estimates of actual use, or “percent crop treated” estimates.

Non-agricultural uses include turf, ornamentals, and vegetable gardens. 


Contamination estimates (EECs) for drinking water were refined by the
use of PRZM-EXAMS modeling, incorporating Percent Cropped Area (PCA)
data.  Dietary exposure estimates for drinking water are based on the
estimates of 7.0 ppb for acute exposure, 0.4 ppb for chronic (cPAD)
exposure, and 0.3 for carcinogenic risk estimates.  EEC estimates are
based on the use parameters of soybean, since soybean is the major use
for trifluralin (and somewhat higher than cotton EECs).

Most of trifluralin’s food tolerances are 0.05 ppm, denoting the
enforcement

method’s Level of Quantitation, or LOQ.  Mung bean sprouts, however,
have a tolerance of 2.0 ppm, which is due to the unique use as a seed
soak versus the typical pre-plant use.  The following risk estimates for
all commodities, including mung bean sprouts, are based on the mung bean
sprout tolerance of 2.0 ppm.

Risk Estimates

 Summary of Dietary Exposure and Risk for Trifluralin

Population Subgroup	Acute Dietary

(99.9 Percentile)	Chronic Dietary	Cancer

	Dietary Exposure (mg/kg/day)	% aPAD	Dietary Exposure

(mg/kg/day)	% cPAD	Dietary Exposure

(mg/kg/day)	Risk

General U.S. Population	--	--	0.000032	0.1	0.000029	1.7E-07

All Infants (< 1 year old)

--	0.000063	0.3	--	--

Children 1-2 years old

--	0.000076	0.3



Children 3-5 years old

--	0.000063	0.3



Children 6-12 years old

--	0.000043	0.2



Youth 13-19 years old

--	0.000026	0.1



Adults 20-49 years old

--	0.000026	0.1



Adults 50+ years old



--	0.000026	0.1



Females 13-49 years old	0.001110	0.1	0.000026	0.1





  

  

