Concentration dependency of biota-sediment accumulation factors for chlorinated dibenzo-p-dioxins and dibenzofurans in Dungeness crab (Cancer magister) at marine pulp mill sites in British Columbia, Canada

Biota-sediment accumulation factors (BSAFs) for some chlorinated dibenzo-p- dioxin and dibenzofuran congeners (PCDD/Fs) in Dungeness crab (Cancer magis ter) hepatopancreas and associated sediments are concentration independent as required by equilibrium partition models. In particular 2,3,7,8-tetrachl orodibenzo-p-dioxin (2,3,7,8-TCDD), 2,3,7,8-tetrachlorodibenzofuran, the 2, 3,7,8-substituted pentachlorodibenzofurans, and the non-2,3,7,8-hexachlorod ibenzofurans (HxCDFs) seem to fall into this group. The BSAFs for other iso mers exhibit significant, nonlinear variations with sediment or crab PCDD/F concentrations. For some of these other isomers (e.g., the non-2,3,7,8 TCD Ds and possibility the 2,3,7,8-substituted HxCDFs), association of a variab le fraction of the total present with soot carbon may provide a satisfactor y explanation for the concentration behavior. For the HxCDDs we propose tha t the nonlinear concentration behavior may arise from the thermodynamic pro perties of fluids confined in hydrophobic voids within particulate and coll oidal material produced by the pulp mills. The nonlinear relationship betwe en BSAFs and PCDD/F concentrations greatly complicates prediction of the po tential for dioxin and furan bioaccumulation in crabs and the formulation o f sediment quality criteria. We provide a nonlinear equation relating toxic equivalency and sediment concentrations.