Concentrations of Pesticides and Pesticide Degradates in the Croton
River Watershed in Southeastern New York, July-September 2000
by Patrick J. Phillips and Robert W. Bode
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 02-4063
ABSTRACT
Thirty-seven pesticides and (or) pesticide
degradates were detected in baseflow samples collected from 47 stream sites
in the Croton River Watershed (374 square miles) in southeastern New York in
the summer of 2000. The Croton Reservoir provides about 10 percent of New
York City's water supply. Maximum concentrations of most pesticides detected
did not exceed 0.1 μg/L (micrograms per liter). This study, by the U.S.
Geological Survey in cooperation with the New York State Department of
Environmental Conservation, was conducted from July through September 2000
and entailed analysis of the samples for more than 150 pesticides and their
degradates. Nine compounds were detected at a concentration greater than
0.10 μg/L; three of these were insecticides (diazinon, carbaryl, and
imidacloprid), one was a fungicide (mycobutanil), and five were herbicides
(simazine, 2,4-D, diuron, hexazinone, and 2,4-D methyl esther). Only two of
these compounds (simazine and 2,4-D) were detected at a concentration
exceeding 1 μg/L; the simazine concentration exceeded the
New York State surface-water standard of 0.5 μg/L. Two
insecticides (diazinon and azinphos-methyl) exceeded aquatic-life-protection
standard in one sample each. Concentrations of three insecticides
(chlorpyrifos, carbaryl, and malathion) were more than 50 percent of the
aquatic-life-protection standards in one sample each.
Total concentrations of insecticides and herbicides (the sum of the
concentrations, whereby all concentrations below the detection limit were
set to zero), and the concentrations of the herbicide prometon and the
insecticide diazinon, were highest in samples from watersheds with
population densities greater than 510 per square mile (21 sites); therefore,
the presence of these compounds is attributable to urban, residential, and
other developed land uses.
The data obtained in this study are useful for making general comparisons
among watersheds with differing land uses, but the concentrations represent
baseflow conditions and, thus, are probably lower than the annual maximum
concentrations in these streams. A July baseflow sample had total insecticide
and fungicide concentrations of less than 0.03 μg/L, whereas
a stormflow sample collected at the same site 2 weeks later had a
corresponding concentration greater than 0.10 μg/L. Total
herbicide concentrations for the July baseflow and stormflow samples were
around 0.03 μg/L, but that for a stormflow sample collected
at the same site 2 months later was greater than 20 μg/L.
Citation: Phillips, P.J., and Bode, R.W., 2002, Concentrations of
Pesticides and Pesticide Degradates in the Croton River Watershed in
Southeastern New York, July-September 2000: U.S. Geological Survey
Water-Resources Investigations Report 02-4063, 20 p.
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