The role of various dissolved organic matter forms on chlorpyrifos bioavailability to the estuarine bivalve Mercenaria mercenaria

In 14C-CHPY uptake and elimination experiments, juvenile bivalves were exposed to uniformly-labeled 14C-CHPY and collected at time intervals during 48 h. The remaining bivalves were transferred to 14C-CHPY-free elimination chambers with bivalve collection at time intervals over 144 h. Total uptake of 14C-CHPY by bivalves in DOM-free seawater was >40% greater than in bivalves exposed to 14C-CHPY in the presence of most DOM forms. These results are consistent with much faster 14C-CHPY uptake rates estimated using a simple two parameter model. After the elimination period, bivalves exposed to DOM-free seawater had 14C-CHPY body residue concentrations between 25% and 86% greater than bivalves in the presence of DOM forms. Experiments with larger bivalves showed that pulse-chase exposures with a 1.5 h exposure period to 14C-CHPY was not long enough to detect differences in 14C-CHPY tissue accumulation efficiencies across treatments. Our findings suggest that natural forms of DOM, at environmentally realistic organic carbon concentrations, reduced pesticide uptake and bioconcentration, consistent with much lower uptake rates relative to bivalves exposed to 14C-CHPY in the absence of DOM. Interestingly, at the tested organic carbon concentrations CD-α and CD-β did not reduce 14C-CHPY bioconcentration in M. mercenaria.