Geology topics

Kelly L. Smalling

Publications and source records attributed to Kelly L. Smalling.

111 records · Page 7Linked to original sources

USGS2008

Pesticides in Water and Suspended Sediment of the Alamo and New Rivers, Imperial Valley/Salton Sea Basin, California, 2006-2007

Water and suspended-sediment samples were collected at eight sites on the Alamo and New Rivers in the Imperial Valley/Salton Sea Basin of California and analyzed for both current-use and organochlorine pesticides by the U.S. Geological Survey. Samples were collected in the fall of 2006 and spring of 2007, corresponding to the seasons of greatest pesticide use in the basin. Large-volume water samples (up to 650 liters) were collected at each site and processed using a flow-through centrifuge to isolate suspended sediments. One-liter water samples were collected from the effluent of the centrifuge for the analysis of dissolved pesticides. Additional samples were collected for analysis of dissolved organic carbon and for suspended-sediment concentrations. Water samples were analyzed for a suite of 61 current-use and organochlorine pesticides using gas chromatography/mass spectrometry. A total of 25 pesticides were detected in the water samples, with seven pesticides detected in more than half of the samples. Dissolved concentrations of pesticides observed in this study ranged from below their respective method detection limits to 8,940 nanograms per liter (EPTC). The most frequently detected compounds in the water samples were chlorpyrifos, DCPA, EPTC, and trifluralin, which were observed in more than 75 percent of the samples. The maximum concentrations of most pesticides were detected in samples from the Alamo River. Maximum dissolved concentrations of carbofuran, chlorpyrifos, diazinon, and malathion exceeded aquatic life benchmarks established by the U.S. Environmental Protection Agency for these pesticides. Suspended sediments were analyzed for 87 current-use and organochlorine pesticides using microwave-assisted extraction, gel permeation chromatography for sulfur removal, and either carbon/alumina stacked solid-phase extraction cartridges or deactivated Florisil for removal of matrix interferences. Twenty current-use pesticides were detected in the suspended-sediment samples, including pyrethroid insecticides and fungicides. Fourteen legacy organochlorine pesticides also were detected in the suspended-sediment samples. Greater numbers of current-use and organochlorine pesticides were observed in the Alamo River samples in comparison with the New River samples. Maximum concentrations of current-use pesticides in suspended-sediment samples ranged from below their method detection limits to 174 micrograms per kilogram (pendimethalin). Most organochlorine pesticides were detected at or below their method detection limits, with the exception of p,p'-DDE, which had a maximum concentration of 54.2 micrograms per kilogram. The most frequently detected current-use pesticides in the suspended-sediment samples were chlorpyrifos, permethrin, tetraconazole, and trifluralin, which were observed in more than 83 percent of the samples. The organochlorine degradates p,p'-DDD and p,p'-DDE were detected in all suspended-sediment samples.

Data Series↗

USGS2007

Occurrence of pesticides in water, sediment, and soil from the Yolo Bypass, California

The objective of this study was to evaluate the potential sources of pesticides to the Yolo Bypass, including those that could potentially impact critical life stages of resident fish. To assess direct inputs during inundation, pesticide concentrations were analyzed in water and suspended and bed sediment samples collected from source watersheds during high-flow events. To understand inputs from direct application on fields, pesticides were also measured in soils collected from several sites within the Bypass. Thirteen current-use pesticides were detected in water samples collected in 2004 with the highest pesticide concentrations observed at the input sites to the Bypass during high-flow. Hexazinone and simazine were detected at all sites and at some of the highest concentrations. In bed and suspended sediments collected in 2004 and 2005, thirteen current-use pesticides were detected along with DDT and its metabolites. Trifluralin, DDE, and DDT were highest in the bed sediments, whereas oxyfluorfen and thiobencarb were highest in the suspended sediments. With the exception of the three organochlorine insecticides, suspended sediments had higher pesticide concentrations compared to bed sediments, indicating the potential for pesticide transport especially during high-flow events. Soil samples were dominated by DDT and its degradates but also contained a variety of current-use pesticides typically at lower concentrations. The types of pesticides detected in water and sediments were correlated with agricultural application in each watershed. Understanding the distribution of pesticides between the water and sediment is important in assessing their fate and transport within the Bypass, and in evaluating the exposure and potential effects to resident fish.

California↗

USGS2005

Analysis of pesticides in surface water and sediment from Yolo Bypass, California, 2004-2005

Inputs to the Yolo Bypass are potential sources of pesticides that could impact critical life stages of native fish. To assess the direct inputs during inundation, pesticide concentrations were analyzed in water, in suspended and bed-sediment samples collected from six source watersheds to the Yolo Bypass, and from three sites within the Bypass in 2004 and 2005. Water samples were collected in February 2004 from the six input sites to the Bypass during the first flood event of the year representing pesticide inputs during high-flow events. Samples were also collected along a transect across the Bypass in early March 2004 and from three sites within the Bypass in the spring of 2004 under low-flow conditions. Low-flow data were used to understand potential pesticide contamination and its effects on native fish if water from these areas were used to flood the Bypass in dry years. To assess loads of pesticides to the Bypass associated with suspended sediments, large-volume water samples were collected during high flows in 2004 and 2005 from three sites, whereas bed sediments were collected from six sites in the fall of 2004 during the dry season. Thirteen current-use pesticides were detected in surface water samples collected during the study. The highest pesticide concentrations detected at the input sites to the Bypass corresponded to the first high-flow event of the year. The highest pesticide concentrations at the two sites sampled within the Bypass during the early spring were detected in mid-April following a major flood event as the water began to subside. The pesticides detected and their concentrations in the surface waters varied by site; however, hexazinone and simazine were detected at all sites and at some of the highest concentrations. Thirteen current-use pesticides and three organochlorine insecticides were detected in bed and suspended sediments collected in 2004 and 2005. The pesticides detected and their concentrations varied by site and sediment sample type. Trifluralin, p,p'-DDE, and p,p'-DDT were highest in the bed sediments, whereas oxyfluorfen and thiobencarb were highest in the suspended sediments. With the exception of the three organochlorine insecticides, suspended sediments had higher pesticide concentrations compared with bed sediments, indicating the potential for pesticide transport throughout the Bypass, especially during high-flow events. Understanding the distribution of pesticides between the water and sediment is needed to assess fate and transport within the Bypass and to evaluate the potential effects on native fish.

Scientific Investigations Report↗