Influences of binding to dissolved organic matter on hydrophobic organic compounds in a multi-contaminant system: Coefficients, mechanisms and ecological risks

The complexation flocculation (CF) method was successfully employed to identify binding coefficients (K_doc) of specific organic contaminants to dissolved organic matter (DOM, often indicated by dissolved organic carbon, DOC) in a multi-contaminant hydrophobic organic contaminant (HOC) system. K_doc values were obtained for most of the evaluated 33 HOCs, indicating the feasibility and applicability of the CF method in a multi-contaminant system. Significant positive correlations were observed between binding coefficients and octanol–water partition coefficients (K_ow) for organic halogen compounds, such as polybrominated diphenyl ethers (PBDEs) (R² = 0.95, p < 0.05) and organic chlorine pesticides (OCPs) (methoxychlor excluded, R² = 0.82, p < 0.05). The positive correlations identified between the lgK_doc and lgBCF (bioconcentration factor) for PBDEs and OCPs, as well as the negative correlation observed for polycyclic aromatic hydrocarbons (PAHs), indicated that different binding or partition mechanisms between PAHs and organic halogen compounds exist. These differences further result in discriminative competition partitions of HOCs between DOM and organisms. Assuming that only freely dissolved HOCs are bioconcentrative, the results of DOM-influenced bioconcentration factor (BCF_DOM) and DOM-influenced lowest observed effect level (LOEL_DOM) indicate that the ecological risk of HOCs is decreased by DOM. - Highlights: • Complexing-flocculation is viable in measuring K_doc in a multi-polluted system. • The binding mechanisms between PAHs and organic halogens were different. • DOM should be considered when assessing ecological risk of HOCs in natural ecosystem. - Assuming only freely dissolved HOCs are effective, bioconcentration factors and ecological risks of HOCs are decreased by dissolved organic matter via binding.