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The influence of sediment and colloidal material on the bioavailability of a quaternary ammonium surfactant.

The bioaccumulation and tissue distribution of a quaternary ammonium surfactant (hexadecylpyridinium bromide, HPB) in aquatic organisms was assessed under a variety of exposure conditions. Tadpoles, clams, and minnows were exposed simultaneously to sublethal levels of [3H]HPB under flowthrough conditions for a period of 7 days. Four exposure conditions were studied: water-borne HPB alone, water-borne HPB flowed over a natural sediment, waterborne HPB mixed in a suspension of bentonite clay, and HPB sorbed to a natural sediment. In addition, the significance of ingestion as an exposure pathway for HPB was assessed in a series of oral-dosing experiments conducted with tadpoles. Gill tissues accumulated the highest HPB residues for organisms exposed to the chemical in the absence of sediment or clay. The accumulation of HPB in all tissues, but especially in gills, was reduced significantly in the presence of sediment or clay. This finding is important because gill tissue is a primary site of toxic action for quaternary ammonium compounds. Tadpoles ingested HPB-contaminated sediment and clay, which became a source of exposure for GI-tract tissues. The results of oral-dosing experiments confirmed that sorbed HPB did contribute to the accumulation of this compound in intestinal tissues.