• Acute toxicity;
  • Sediment quality criteria;
  • Geochemistry;
  • Amphipod;
  • PAH


Organic matter in sediment is derived from many sources, including dead plants and animals, fecal matter, and flocculated colloidal organic matter. Chemical partitioning and toxicity of nonpolar organic contaminants is strongly affected by the quantity of sediment organic matter. The purpose of this study was to determine whether the quality of sediment organic matter affects partitioning and bioavailability of such contaminants.

A base substrate, amended to a consistent organic carbon level (nominally 0.4%, measured 0.35% ± 0.11 sd POC [particulate organic carbon]) with five types of organic matter (a macrophyte, fecal matter of two invertebrate species, suspended particulate organic matter, and an organic-rich mud), was spiked with serial concentrations of the polynuclear aromatic hydrocarbon, fluoranthene. After a five-week equilibration period, the toxicity of the spiked substrates to an infaunal amphipod, Rhepoxynius abronius, was measured, and the distribution of fluoranthene between particulate and interstitial water phases (including total and freely dissolved interstitial water phases) was determined.

The range of acute toxicity among organic matter–source treatments was small when based on total sediment concentrations (11.1–19.1 mg fluoranthene per kilogram dry sediment, nominal). Partitioning of fluoranthene between particulate-sorbed and interstitial water phases was not affected by organic matter quality, except when the source was fresh plant material. This variability may have been due to qualitative differences in the particulate/interstitial water partitioning in plant material as a source of sedimentary organic matter or an artifact in the method used to determine freely dissolved, interstitial water fluoranthene concentrations. Equilibrium partitioning models accurately predicted interstitial water concentrations of fluoranthene for the nonplant substrates once corrections were made for the solubility of fluoranthene in seawater. Our data suggest that equilibrium partitioning–based sediment quality criteria for fluoranthene may not need to correct for the quality of organic carbon in sediments and that these criteria can be applied to sediments with a particulate organic carbon content as low as 0.3%.