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Identification and evaluation of pyrethroid insecticide mixtures in urban sediments

Authors

  • Andrew J. Trimble,

    1. Fisheries and Illinois Aquaculture Center and Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901–4306, USA
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  • Donald P. Weston,

    1. Department of Integrative Biology, University of California, 3060 Valley Life Sciences Building, Berkeley, California 94720–3140, USA
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  • Jason B. Belden,

    1. Department of Zoology, Oklahoma State University, Stillwater, Oklahoma 74078–0002, USA
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  • Michael J. Lydy

    Corresponding author
    1. Fisheries and Illinois Aquaculture Center and Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901–4306, USA
    • Fisheries and Illinois Aquaculture Center and Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901–4306, USA
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  • Published on the Web 2/26/2009.

  • The U.S. Environmental Protection Agency has not officially en-dorsed this publication, and the views expressed herein may not reflect the views of the U.S. EPA.

Abstract

Organochlorine, organophosphorous, and pyrethroid insecticides frequently have been detected together as mixtures in stream sediments. To simplify mixture analyses, additive toxic responses usually are assumed but rarely are confirmed, especially for compounds with similar modes of action. The first objective of the present study was to screen a database of 24 different pesticides and 94 urban-stream sediment samples collected throughout central and northern California (USA) to identify compounds and partial mixtures that dominated sample toxicity to Hyalella azteca. Pyrethroids and chlorpyrifos were the most toxicologically relevant compounds in terms of detection frequency, contribution to overall sample toxicity, and co-occurrence in the most common mixture patterns. Organochlorine insecticides were the least toxicologically relevant compounds, with only a small percentage of samples exceeding predefined screening values. The second objective was to confirm that mixtures of type I and type II pyrethroids display additive responses. Ten-day sediment toxicity tests of binary pesticide mixtures were conducted using H. azteca as the test organism. Observed dose-response curves were compared to those predicted from concentration-addition and independent-action models. Model deviation ratios (MDRs) were calculated at the median effect level to quantify the magnitudes of deviation between observed and predicted curves. Whereas the concentration-addition model adequately predicted toxicity for all the pyrethroid mixtures (MDRs within a factor of two), dose-response values deviated from additivity enough to warrant further investigation.

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