Dissolved pesticides, dissolved organic carbon, and water-quality characteristics in selected Idaho streams, April--December 2010

Abstract

Water-quality samples were collected from April through December 2010 from four streams in Idaho and analyzed for a suite of pesticides, including fungicides, by the U.S. Geological Survey. Water samples were collected from two agricultural and two nonagricultural (control) streams approximately biweekly from the beginning of the growing season (April) through the end of the calendar year (December). Samples were analyzed for 90 pesticides using gas chromatography/mass spectrometry. Twenty-three pesticides, including 8 fungicides, 10 herbicides, 3 insecticides, and 2 pesticide degradates, were detected in 45 water samples. The most frequently detected compounds in the two agricultural streams and their detection frequencies were metolachlor, 96 percent; azoxystrobin, 79 percent; boscalid, 79 percent; atrazine, 46 percent; pendimethalin, 33 percent; and trifluralin, 33 percent. Dissolved-pesticide concentrations ranged from below instrumental limits of detection (0.5-1.0 nanograms per liter) to 771 nanograms per liter (hexazinone). The total number of pesticides detected in any given water sample ranged from 0 to 11. Only three pesticides (atrazine, fipronil, and simazine) were detected in samples from the control streams during the sampling period.

Assessing the Potential Effects of Fungicides on Nontarget Gut Fungi (Trichomycetes) and Their Associated Larval Black Fly Hosts

“…Agricultural sites: Sand Run Gulch and Wanstad Ditch. For watershed characteristics refer to Table (Reilly et al ., ).…”

“…Site descriptions, watershed characteristics, and water sampling techniques are further detailed in Reilly et al . ().…”

“…Samples were collected approximately biweekly starting in April for the two agricultural streams and Cottonwood Creek and starting in June for Dry Creek. This spans the typical growing season in Idaho (Reilly et al ., , b). Sample collection did not target runoff events or other specific hydrologic conditions.…”

“…The four selected study sites in Idaho (Figure , Table ) included two agricultural streams (Sand Run Gulch and Wanstad Ditch) and two reference streams (Cottonwood Creek and Dry Creek). The former were selected because they drain high use agricultural areas (Table ) and fungicides have been detected in each stream throughout the growing season (Reilly et al ., , b). The latter were selected because they are known to contain insect larvae with robust and well‐characterized populations of gut fungi (Bench and White, ; Kandel and White, ).…”

“…Thawed composite black fly larvae samples (0.12‐2.5 g), containing between 70 and 1,500 individuals from each site, were analyzed for a suite of 12 current‐use pesticides. In total, 17 composite larval tissue samples were analyzed based on the compounds historically detected in the water column (Reilly et al ., ). Prior to extraction, tissue samples were spiked with trifluralin‐d 10 , ring‐ 13 C‐ p,p ′‐DDE and phenoxy‐ 13 C‐ cis ‐permethrin (Cambridge Isotopes, Andover, Massachusetts) as recovery surrogates.…”