Development and evaluation of consensus-based sediment effect concentrations for polychlorinated biphenyls

Sediment-quality guidelines (SQGs) have been published for polychlorinated biphenyls (PCBs) using both empirical and theoretical approaches. Empirical ly based guidelines have been developed using the screening-level concentra tion, effects range, effects level, and apparent effects threshold approach es. Theoretically based guidelines have been developed using the equilibriu m-partitioning approach. Empirically-based guidelines were classified into three general categories. in accordance with their original narrative inten ts, and used to develop three consensus-based sediment effect concentration s (SECs) for total PCBs (tPCBs), including a threshold effect concentration , a midrange effect concentration, and an extreme effect concentration. Con sensus-based SECs were derived because they estimate the central tendency o f the published SQGs and, thus, reconcile the guidance values that have bee n derived using various approaches. Initially, consensus-based SECs for tPC Bs were developed separately for freshwater sediments and fur marine and es tuarine sediments. Because the respective SECs were statistically similar, the underlying SQGs were subsequently merged and used to formulate more gen erally applicable SECs. The three consensus-based SECs were then evaluated for reliability using matching sediment chemistry and toxicity data from fi eld studies, dose-response data from spiked-sediment toxicity tests, and SQ Gs derived from the equilibrium-partitioning approach. The results of this evaluation demonstrated that the consensus-based SECs can accurately predic t both the presence and absence of toxicity in field-collected sediments. I mportantly, the incidence of toxicity increases incrementally with increasi ng concentrations of tPCBs. Moreover, the consensus-based SECs are comparab le to the chronic toxicity thresholds that have been estimated from dose-re sponse data and equilibrium-partitioning models. Therefore, consensus-based SECs provide a unifying synthesis of existing SQGs, reflect causal rather than correlative effects, and accurately predict sediment toxicity in PCB-c ontaminated sediments.