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    Aquatic Safety Assessment of Chemicals Sorbed to Sediments

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    Chemical safety is assessed by the relationship of toxic effects to exposure concentrations, that is, by defining the margin of safety. To date, however, these principles have been applied only to organisms in the water column of aquatic ecosystems. A deficiency exists in our ability to understand the aquatic hazard of chemicals that are sorbed to sediment.

    Studies to define the key route of exposure (interstitial water, water column water, sediment or food) were conducted with Kepone and the midge, Chironomus tentans, in partial life cycle static and flow-through tests. The endpoints measured were survival, growth, and bioaccumulation. Seven separate 14-day partial life cycle tests were conducted.

    The no effect-effect concentrations for midges exposed to Kepone in the water were >5.4 <11.8 ppb. No effects were observed when the midges were fed food containing up to 17 900 ppb Kepone. In the sediment exposure studies, the no-effect concentrations varied from 3000 to 36 000 ppb depending upon the organic carbon content of the sediment. In all the sediment exposure studies, water column concentrations were below the water exposure chronic effect levels (11.8 ppb), and effects were observed only when the sediment interstitial column concentrations exceeded the 11.8 ppb water column exposure chronic effect level. Measured bioaccumulation factors for each study showed little variability when the midge tissue concentrations were divided by the sediment interstitial water concentrations. Calculations of the bioaccumulation factors based on water column concentrations or sediment concentrations were highly variable.

    It can be concluded from our studies with Kepone and C. tentans that the key route of exposure is from the interstitial water and/or the water at the sediment/water interface. Toxic effects can be expected to occur in benthic invertebrates only if the chemical concentration is high enough in the sediments such that the equilibrium interstitial water concentration reached by desorption is equal to or higher than the concentration demonstrated to cause an effect in a water exposure test. Interpretation of aquatic hazard and calculation of safety factors for nonionic organic chemicals sorbed to sediments should be based on the concentration of the chemical in the sediment interstitial water, which is a function of the chemical's sediment partition coefficient (Kp), concentration of chemical on the sediment, and the organic carbon content of the sediment.


    midge, Chironomus tentans, Kepone, sediment, hazard assessment, safety factor, partition coefficient, K, oc, K, p, chronic toxicity, bioaccumulation

    Author Information:

    Adams, WJ
    Monsanto Company, St. Louis, Mo

    Kimerle, RA
    Monsanto Company, St. Louis, Mo

    Mosher, RG
    Monsanto Company, St. Louis, Mo

    Committee/Subcommittee: E47.01

    DOI: 10.1520/STP36282S