Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

In the exposure section of the Effects of the Proposed Action we also present more recent
unpublished data on the chemicals and degradates addressed in this Opinion from the
NAWQA program and state databases maintained by California and Washington. As far
as NMFS was able to ascertain, neither Oregon nor Idaho maintain publically available
state-wide water quality databases. The California and Washington databases include
some data from the NAWQA, but mostly the data are from more localized studies.
Overall, data from those databases are relatively consistent in regards to pesticides
addressed in this Opinion, with carbaryl generally being the most frequently quantifiable
parent compound. Carbaryl and carbofuran were measured in concentrations ranging
from 0.0001-33.5 μg/L. Methomyl generally was measured at slightly lower
concentrations, ranging from 0.004-5.4 μg/L. Methomyl is also detected less frequently
in some monitoring datasets, as it dissipates rapidly in aquatic systems, and non-targeted
monitoring does not necessarily coincide with applications. Both 1-napthol (methomyl
degradate) and 3-hydroxycarbofuran (carbofuran degradate) were detected in slightly
lower concentrations, ranging from 0.0007-0.64 μg/L, than any of the parent compounds.
According to Gilliom et al.(2006), the distributions of the most prevalent pesticides in
streams and ground water correlate with land use patterns and associated present or past
pesticide use. When pesticides are released into the environment, they frequently end up
as contaminants in aquatic environments. Depending on their physical properties some
are rapidly transformed via chemical, photochemical, and biologically mediated reactions
into other compounds, known as degradates. These degradates may become as prevalent
as the parent pesticides depending on their rate of formation and their relative persistence.
National Water­Quality Assessment Program.
From 1992-2001, the USGS sampled water from 186 stream sites within 51 study units;
bed-sediment samples from 1,052 stream sites, and fish from 700 stream sites across the
continental U.S. Concentrations of pesticides were detected in streams and groundwater
within most areas sampled with substantial agricultural or urban land uses. NAWQA
results further detected at least one pesticide or degradate more than 90% of the time in
water, in more than 80% in fish samples, and greater than 50% of bed-sediment samples
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