 

December 13, 2006

MEMORANDUM

SUBJECT:	The Health Effects Division’s Review of California’s Methyl
Parathion Risk Characterization Document on Dietary and Ambient Air
Exposures (dated 10/26/2004)

PC Code: 053501 (Methyl Parathion)

DP Barcode: D329321

FROM:	Charles Smith, Environmental Scientist/Risk Assessor

Reregistration Branch II

Health Effects Division (7509P)

THRU:	William J. Hazel, Ph.D., Branch Chief

Reregistration Branch II

Health Effects Division (7509P)

TO:	John Pates, Chemical Review Manager

Reregistration Branch I

Special Review and Reregistration Division (7508P)

CC:	Laura Parsons, Team Leader

	Susan Lewis, Branch Chief

		Reregistration Branch I

		Special Review and Reregistration Division (7508P)

The attached document entitled, “The Health Effects Division’s
Review of California’s Methyl Parathion Risk Characterization Document
on Dietary and Ambient Air Exposures” was generated in the post-Phase
6 period of the Proposed Public Participation Process (FR Notice
03/15/00) to address the October 26, 2004 California methyl parathion
risk characterization document.  The main focus of this memo is to
discuss the differences in California’s risk characterization document
and HED’s Interim Reregistration Eligibility Decision (IRED) which was
completed in May of 2003.  This review includes input from Sherrie
Kinard (Residue Chemistry and Dietary Exposure) and Charles Smith
(Occupational and Residential Exposure/Risk Assessment).

Health Effects Division’s Review of California’s Methyl Parathion
Risk Characterization Document on Dietary and Ambient Air Exposures

I. Introduction

	The following is HED’s review of California’s methyl parathion risk
characterization document (dated October 26, 2004) generated in the
post-Phase 6 period of the Proposed Public Participation Process.  The
main focus of this review is to discuss the differences in
California’s risk characterization document and HED’s IRED which was
completed in May of 2003.  The main differences involve the dietary and
ambient air assessments.

II. Dietary Assessment

HED has the following comments on the dietary portion of the California
methyl parathion characterization document.

HED does not usually present screening level assessments if a more
refined assessment has been done.  HED only presents the more refined
assessment.

HED used an acute endpoint of 0.11 mg/kg/day (with an uncertainty factor
of 100 and a FQPA safety factor of 10) and a chronic endpoint of 0.02
mg/kg/day (with an uncertainty factor of 100 and a FQPA safety factor of
10).  CA used an acute endpoint of 0.025 mg/kg/day and the same 0.02
mg/kg/day chronic endpoint that HED used.

HED could not find a reference to the specific version of DEEM that was
used in the CA methyl parathion assessment.  The version of DEEM is
necessary to determine if the recipes and age groupings are the same as
those used by HED.  In other words, an assessment done with an old
version of DEEM cannot be directly compared to an assessment done with a
new version of DEEM and expect to get the same results.

The CA methyl parathion assessment used newer consumption data compared
to the older consumption data that were used in the HED risk assessment.
 At the time the most recent HED risk assessment was completed (Interim
Reregistration Eligibility Decision for Methyl Parathion; May 2003), the
newer data set had not been thoroughly reviewed.

The CA assessment expresses the dose in ug/kg/day; however, these units
need to be converted to mg/kg/day since those are the units used in
DEEM.

It appears that the CA assessment included p-nitrophenol for risk
assessment purposes.  In the HED risk assessment it was included for
tolerance assessment, but not for risk assessment purposes.

The HED risk assessment used the older PDP data since the assessment was
done in the 98-99 time-frame; however, that would be inappropriate to do
now since use patterns have changed drastically.  The CA assessment used
old (93-98) and new PDP data.  HED typically uses the most recent 5
years of monitoring data and the assessments are supposed to be updated
using anticipated residues every 5 years.

FDA data for dried beans were used in the HED risk assessment but the CA
assessment translated PDP data for succulent beans to dried beans.  HED
believes that it is more appropriate to use FDA data for dried beans
since the variation in detectable residues is great.  Succulent beans
had many detectable residues, where as dried beans did not.

PDP did not analyze for methyl paraoxon.  There were not detectable
residues of methyl paraoxon in field trial studies; therefore, HED would
not expect PDP to find detectable residues.  However, HED accounted for
the paraoxon in our assessment as 1/2 LOD for all treated samples.

HED used weighted averages of the LOD in the dietary risk assessment
while CA used the highest LOD, which is more conservative.

The CA assessment discusses populations that HED does not normally base
regulatory decisions on (non-hispanic/non-white/non-black).

It appears that CA performed probabilistic assessments with and without
%CT estimates.  HED does not do probabilistic assessments without using
%CT.

The CA assessment used 500 iterations while HED used 1000 iterations.

III. Ambient Air Assessment

The CA risk characterization document includes an assessment of the
risks resulting from individuals exposed to methyl parathion and methyl
paraoxon in ambient air.  The ambient air assessment was expressed in
three separate ways, as an absorbed daily dose (ADD), as a seasonal
average daily dose (SADD), and as an Annual Average Daily Dosage (AADD).
 The exposures to ambient air concentrations of methyl parathion and
methyl paraoxon were estimated using two air monitoring studies which
looked at 4 outdoor sites in Colusa and Sutter counties in CA (Seiber et
al., 1987).  This monitoring was performed during the high season of use
on rice fields.

In the CA risk characterization document, the total (methyl parathion
and methyl paraoxon) ADDs for a 6 year old child, a male adult, and a
female adult were estimated as 64.55 ng/kg/day, 24.27 ng/kg/day and
15.93 ng/kg/day, respectively (Reed, 1999).  The ambient air ADDs result
in acute MOE s ranging from 390-1,600.  The SADDs were 19.64 ng/kg/day
(a 6 years old child), 7.45 ng/kg/day (a male adult) and 4.84 ng/kg/day
(a female adult).  The ambient air SADDs result in ambient seasonal MOEs
ranging from 1,500-6,300.  The AADDs were 14.78 ng/kg/day (a 6 year old
child); 5.56 ng/kg/day (a male adult) and 3.56 ng/kg/day (a female
adult).  The ambient air AADDs result in chronic MOEs ranging from
1,300-5,400.  These exposure estimates and calculations were based on
the following default breathing rates (BR): 0.74 m3/kg/day for a 6 year
old child; 0.28 m3/kg/day for a male adult and 0.18 m3/kg/day for a
female adult (Reed, 1999).

HED did not perform an ambient air assessment in the IRED for Methyl
Parathion dated May 2003.  HED believes the risks to residential
bystanders from methyl parathion in ambient air are limited in scope. 
When the ambient air concentrations for methyl parathion are compared to
the inhalation endpoints used in the IRED, all resulting MOEs are above
HED’s level of concern.  Also, the ambient air studies that are used
to define risks in the CA risk characterization document were performed
in 1987 and the use patterns for methyl parathion have changed
significantly since that time.

References

Reed, N. R. 1999. Evaluation of methyl parathion as a toxic air
contaminant. Human Health Assessment, Part C. Medical Toxicology Branch.
Department of Pesticide Regulation (DPR), California Environmental
Protection Agency, Sacramento, CA

(  HYPERLINK
"http://www.cdpr.ca.gov/docs/empm/pubs/methylpa/mppartc.pdf" 
www.cdpr.ca.gov/docs/empm/pubs/methylpa/mppartc.pdf ).

Seiber, J. M. and McChesney, M. M. 1987. Measurement and computer model
simulation of the volatilization flux of molinate and methyl parathion
from a flooded rice field. California Department of Food and
Agriculture. Sacramento, CA. Contract #6854.

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

