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

detected in samples from all sites, except for the Palouse River at Laird Park (a
headwaters site in a forested area). Many pesticides were detected in surface water at
very low concentrations. Concentrations of six pesticides exceeded freshwater-chronic
criteria for the protection of aquatic life in one or more surface-water samples. They
include the herbicide triallate and five insecticides (azinphos-methyl, chlorpyrifos,
diazinon, gamma-HCH, and parathion). Carbaryl and carbofuran were detected in 6%
and 5% of samples, respectively. Methomyl was screened for, but not detected in any
samples (Williamson et al. 1998).
Detections at four sites were high, ranging from 12 to 45 pesticides. The two sites with
the highest detection frequencies are in the Quincy-Pasco subunit, where irrigation and
high chemical use combine to increase transport of pesticides to surface waters. Pesticide
detection frequencies at sites in the dryland farming (non-irrigated) areas of the North-
Central and Palouse subunits are below the national median for NAWQA sites. All four
of the sites had at least one pesticide concentration that exceeded a water-quality standard
or guideline.
Concentrations of organochlorine pesticides and PCBs are higher than the national
median (50 th percentile) at seven of 11 sites; four sites were in the upper 25% of all
NAWQA sites. Although most of these compounds have been banned, they still persist
in the environment. Elevated concentrations were observed in dryland farming areas as
well as in irrigated areas.
Urban and Industrial Development
The largest urban area in the basin is the greater Portland metropolitan area, located at the
mouth of the Willamette River. Portland’s population exceeds 500,000 (Hinck, Schmitt
et al. 2004). Although the basin’s land cover is about 8% of the U.S. total land mass, its
human population is one-third the national average (about 1.2% of the U.S. population)
(Hinck, Schmitt et al. 2004).
Discharges from sewage treatment plants, paper manufacturing, and chemical and metal
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