The Influence of Biomass on the Toxicity of Hydrophobic Organic Contaminants

Abstract

Hydrophobic organic contaminants (HOCs) enter the marine environment through several means, including industrial, urban, and agricultural runoff, and accumulate in sediments. Methods for measurement of sediment toxicity include porewater tests using sea urchin (Arbacia punctulata) fertilization and embryological development assessments. Previous studies investigating sediments from Boston Harbor determined that significant binding of contaminants to organic matter led to insufficient evidence of the bioavailability of HOCs in porewater toxicity tests. It was hypothesized that excessive biomass in testing systems prevents a critical body residue of HOCs from forming, thus curbing toxic effects. In this study, the effect of biomass on the toxicity of phenanthrene (a polycyclic aromatic hydrocarbon) and lindane (an organochlorine pesticide) were assessed individually and combined in a mixture. The fertilization toxicity test for phenanthrene and mixture solutions containing both compounds revealed less biomass in the test vial caused higher toxicity levels, the fact of which was enhanced with increased hydrophobicity. The 50% inhibition concentration (IC(50)) of phenanthrene to sea urchin fertilization success in test vials with 50 eggs/mL (lowest biomass concentration tested) was 3.72 micromol/L, but in vials with 100 to 400 eggs/mL, the IC(50) was >4.12 micromol/L. Toxicity of several concentrations of the phenanthrene and lindane mixture to sea urchin fertilization success and embryological development was significantly higher at lower biomasses (50 and 100 eggs or embryos/mL) than with biomasses > or =200 eggs or embryos/mL. The results suggest that when testing environmental samples that may contain HOCs, lowering the biomass can help better estimate sediment toxicity using porewater tests.