UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE  OF 

PREVENTION, PESTICIDES AND 

TOXIC SUBSTANCES

								PC Code: 080103

DP Barcode: D252840

Date: 13 September 2007

MEMORANDUM

SUBJECT:	Ammonium Thiosulfate 

CAS Reg. No.   HYPERLINK
"http://www.sigmaaldrich.com/catalog/search/SearchResultsPage?Query=7783
-18-8&Scope=CASSearch&btnSearch.x=1"  7783-18-8  (Solution); 7664-41-7
(Anhydrous)

Ecological Risk Assessment 

FROM:	Colleen Flaherty, M.S., Biologist

			James A. Hetrick, Ph.D., Senior Scientist

			Silvia Carlota Termes, Ph.D., Chemist

		Ecological Risk Branch III

		Environmental Fate and Effects Division (7505-P)

TO:		Katie Hall

		Special Review and Reregistration Division (7508-P)

	THRU:	Karen Whitby, Ph.D., Branch Chief

		Ecological Risk Branch III

		Environmental Fate and Effects Division (7505-P)

Ammonium thiosulfate (CAS No.   HYPERLINK
"http://www.sigmaaldrich.com/catalog/search/SearchResultsPage?Query=7783
-18-8&Scope=CASSearch&btnSearch.x=1"  7783-18-8 ), an inorganic
compound, is the chemical stressor considered in the attached ecological
risk assessment. Ammonium thiosulfate dissociates completely in water.
The dissociation products are the thiosulfate anion and its ammonium
counter cation, and both are considered in this risk assessment.

Risk Summary

This ecological risk assessment considers the limited use of ammonium
thiosulfate as an herbicide on dichondra lawns in residential/homeowner
settings in California. This assessment is qualitative in nature; that
is, the risk quotient approach is not utilized.  The nature of ammonium
thiosulfate and its predicted behavior in the environment make it
difficult to provide meaningful quantitative exposure estimates for
aquatic and terrestrial systems.  Since ammonium thiosulfate is being
used as an herbicide, there is a possibility that non-target plants may
be at risk; however, given that it is only used in residential/homeowner
settings in California, the potential for adverse effects to non-target
plants seems highly unlikely.  Based on this qualitative assessment for
the pesticidal use of ammonium thiosulfate, risk to non-target aquatic
and terrestrial organisms (including Federally-listed species) is
presumed to be negligible.  

Uncertainties and Data Gaps

No acceptable environmental fate or ecotoxicity guideline studies are
available for ammonium thiosulfate.  However, given the nature of the
chemical and its predicted behavior in the environment, this was not an
impediment to the risk assessment. At this time, the EFED is not
requesting any environmental fate or ecotoxicity studies to be submitted
for ammonium thiosulfate.

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