An evaluation of current methods for developing sediment quality guidelines for 2,3,7,8-tetrachlorodibenzo-p-dioxin

Abstract

There are currently few proposed sediment quality guidelines and no promulgated regulatory criteria for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in sediments. Among the eight major approaches used to develop sediment quality guidelines, only three have been used to date in developing proposed guidelines for TCDD: the background method, the equilibrium partitioning (EqP) method, and the tissue-residue based (TRB) method. At present, nineteen proposed sediment quality guidelines for TCDD have been proposed in the U.S. and other countries, including seven derived exclusively for the protection of human health, seven derived exclusively for the protection of aquatic organisms and/or wildlife, and five that were derived for the protection of both human and ecological receptors. In this paper, the technical basis and proposed regulatory objectives of these guidelines were evaluated in an effort to assess the feasibility of deriving a national sediment quality guideline for TCDD. Guidelines derived from the background method inferred that TCDD concentrations in sediments should not exceed the detection limit (1 to 10 parts per trillion; pg/g) of the currently accepted high resolution gas chromatography/mass spectroscopy analytical method, and for one guideline, an outdated analytical detection limit of 1,000 parts per trillion. Guidelines developed by the EqP and TRB methods varied over several orders of magnitude (0.014 to 210 parts per trillion, dry weight basis; and 200 to 1×107 pg/gOC). These large variations are the result of data gaps in our knowledge of TCDD toxicity, and the physical and chemical parameters that govern its fate and transport in aquatic systems.