SEDIMENT CONTAMINANTS AND MICROTOX TOXICITY TESTED IN A DIRECT-CONTACT EXPOSURE TEST

Limnic and brackish water sediments were tested in a modified contact exposure bioluminescence test, the Microtox test. A variety of chemica l constituents were analyzed in the sediments such as metals, chlorina ted pesticides, and polychlorinated biphenyls. Sulfur in the common el emental form and pore water hydrogen sulfide were also analyzed. The m easured effect in the Microtox toxicity test was correlated with the v arious chemical parameters to determine the origin of the toxic effect . Based on multivariate data anlaysis, a group of metals including Cu, Zn, Pb, and Cd were correlated positively with the Microtox toxicity tested in the direct contact test. Similarly, but to a lesser extent s ulfur, hydrogen sulfide, and the pesticides p,p'-DDT and p,p'-DDD were also correlated. Other pesticides and all the analyzed polychlorinate d biphenyls were poorly, if at all, correlated with the toxicity of th e samples. In a comparison with the Microtox toxicity of the pure comp ounds, it was found that, of the analyzed and tested compounds, Zn, Pb , Cu, and elemental sulfur were present in amounts high enough to prod uce an effect in the test system. This calculation was, however, based on the assumption (unrealistic) that the total amount of a compound i n the sediment was available in the test. On the other hand, the metal s Cd, Cr, and Ni were found at concentrations of a few percent or less of their EC(50) concentrations in the Microtox test of the sediment. gamma-Hexachlorocyclohexane and p,p'-DDT were also far less than the c oncentration required to give an effect in the test system. The pore w ater content of hydrogen sulfide was also too small to affect the test organism at the EC(50) dilution and, similarly, the fraction of the t oxicant in the remaining aqueous phase in the sediment after separatio n of the pore water. Thus only the three metals Zn, Pb, and Cu, and el emental sulfur, were found in concentrations that would give an effect in the test system (0.68-398 times the effect), provided that the sub stances were available for the organisms. Consequently, elemental sulf ur, Zn, Pb, and Cu were indicated as causing the effect in the Microto x test of sediments and not a series of other metal ions, nor tested c hloropesticides or chlorinated biphenyls. (C) 1996 by John Wiley & Son s, Inc.