Peak centiles of chlorpyrifos surface-water concentrations in the NAWQA and NASQAN programs.

We provide upper bound estimates for peak centiles of surface water chlorpyrifos concentration readings within spatial, temporal, and land-use domains of the United States Geological Survey (USGS) National Water-Quality Assessment (NAWQA) and National Stream Quality Accounting Network (NASQAN) programs. These datasets have large overall sample sizes but variable sampling frequencies and, for chlorpyrifos, extremely high levels of non-detections. Point and interval estimates are provided for the 90th, 95th, 99th, and the 99.

A spatially and temporally explicit risk assessment for salmon from a prey base exposed to agricultural insecticides.

This risk assessment applied a framework for determining probable co-occurrence of juvenile spring Chinook salmon (Oncorhynchus tshawytscha) with agricultural pesticides in the Willamette Basin, Oregon (Teply et al. this issue) to characterize risk to the threatened population. The assessment accounted for spatial and temporal distribution of 6 acetylcholinesterase-inhibiting insecticides in salmonid habitat within the basin and their relative contributions to mixture toxicity estimated from chemical monitoring data.

A spatially and temporally explicit model for determining the exposure of juvenile salmon to agricultural pesticides in freshwater.

In this paper, we present a novel approach for determining the probable co-occurrence of juvenile salmon or steelhead with agricultural pesticides and apply it to spring Chinook (Oncorhynchus tshawytscha) salmon in the Willamette Basin, Oregon. We adapted a published exposure analysis framework by explicitly considering fish migration among habitat units and assuming that habitat use is proportional to habitat quality. Temporal variability in habitat use was accounted for via biweekly time steps over the entire period when a single brood was expected to spawn until the last juvenile migrated to sea.

An ecological risk assessment for chlorpyrifos in an agriculturally dominated tributary of the San Joaquin River.

Single-species toxicity testing of ambient water samples and national-scale probabilistic risk assessment have implicated the organophosphorous (OP) insecticide chlorpyrifos (O, O-diethyl O-(3,5,6-trichloro-2-pyridyl)-phosphorothioate) as a potential chemical stressor of aquatic organisms residing in the lower San Joaquin River basin. This site-specific aquatic ecological risk assessment was conducted to determine the probability of adverse effects occurring from exposure to chlorpyrifos in an agriculturally dominated tributary of the San Joaquin River and to assess the ecological significance of such effects. Assessment endpoints were fish population persistence and invertebrate community productivity.