Results from wetted stream-bed mapping at randomly selected sites in four California streams were summarized to determine the spatial extent of depositional areas (fine grain areas where hydrophobic chemicals may accumulate) and non-depositional areas. In some cases, concentrations of pyrethroids from both depositional and non-depositional stream areas were also measured concurrently. The spatial extent of depositional areas was low for all streams with values ranging from 5 to 24 % of the wetted area. A comparison of sediment concentrations of 8 pyrethroids from depositional and non-depositional areas in three of these streams showed that pyrethroid concentrations were substantially lower in non-depositional areas compared with depositional areas. In two cases, the mean sediment pyrethroid concentrations  for non-depositional areas were either below or near the level of detection.  These non-depositional areas, the preferred habitat for most benthic taxa, are not suspected to be at risk from pyrethroid exposure in sediment. Therefore, care must be taken when considering the significance of sediment residue data reported for streams when sampling protocol has required only depositional areas to be sampled.

Summary of sediment mapping studies with concurrent pyrethroid measurements in depositional and non-depositional areas in California streams

248th National Meeting (2014)

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