Toxicity of hydroxylated polychlorinated biphenyls (HO-PCBs) using the bioluminescent assay Microtox®

Hydroxylated polychlorinated biphenyls (HO-PCBs) are toxic contaminants which are produced in the environment by biological or abiotic oxidation of PCBs. The toxicity of a suite of 23 mono-hydroxylated derivatives of PCBs and 12 parent PCBs was determined using the bacterial bioluminescent assay Microtox(A (R)). All HO-PCBs tested exhibited higher toxicity than the corresponding parent PCB, with effect concentration 50 % (EC50) ranging from 0.07 to 133 mg L-1. The highest toxicities were recorded with 4-hydroxylated derivatives of di-chlorinated biphenyls (EC50 = 0.07-0.36 mg L-1) and 2-hydroxylated derivatives of tri-chlorinated biphenyls carrying a chlorine substituent on the phenolic ring (EC50 = 0.34-0.48 mg L-1). The toxicity of HO-PCBs generally decreased when the degree of chlorination increased. Consistently with this observation, a significant positive correlation was measured between toxicity (measured by EC50) and octanol-water partition coefficient (pK (ow)) for the HO-PCBs under study (Pearson's correlation coefficient, r = 0.74), which may be explained by the lower solubility and bioavailability generally associated with higher hydrophobicity. This study is the first one which assessed the toxicity of a suite of PCBs and HO-PCBs using the bioluminescent assay Microtox(A (R)), showing an inverse correlation between toxicity and hydrophobicity.