An Assessment of the Potential Environmental Risks Posed by Phthalates in Soil and Sediment

Abstract

To assess the potential environmental concerns associated with phthalate esters (PEs) in sediments and native- as well as sludge-amended soils a screening risk assessment was performed using the risk quotient paradigm. Five single isomers, dimethyl, diethyl, di-n-butyl, butylbenzyl and di-2-ethylhexyl, and two commercial mixed isomers, di-isononyl and di-isodecyl, were specifically investigated. Application of statistical extrapolation techniques to aquatic effects data coupled with Equilibrium Partitioning (EqP) theory were used to derive Predicted No Effect Concentrations (PNECs) intended to protect terrestrial and benthic organisms from direct toxicity posed by PEs in soil or sediment. The resultant PNECs were found to be protective when compared to the wealth of available soil and sediment toxicity data for these compounds. PNECs intended to protect wildlife consumers from indirect effects associated with exposure via the terrestrial/benthic food chain were also calculated for each PE. Comparison of risk-based criteria revealed that direct toxicity to soil or sediment-dwelling organisms dictates PNEC derivation for low molecular weight PEs while potential indirect effects on wildlife consumers via food chain exposure determine PNECs for higher molecular weight PEs. A comprehensive literature review indicated extensive field monitoring data are available characterizing PE concentrations in sediments from Europe, North America and Japan. While less exposure data were available for characterizing the soil compartment, predicted and observed concentrations were lower than in sediments. Results of the screening risk assessment found that for all PEs investigated, none of the observed soil concentrations exceeded risk-based limits even in the case of soils that were heavily amended with sewage sludge. Similarly, no study reported concentrations in field sediments that exceeded the PNEC for either BBP or DINP. For the remaining PEs, at least one study indicated a maximum sediment concentration above the PNEC. However, the number of sediment samples exceeding the PNEC was typically less than 1% of the available monitoring database. It is concluded that the environmental concerns posed by soil and sediment-associated PEs are at worst, restricted to infrequent, localized hot spots of contaminated sediment. The conservative assumptions invoked in this screening risk analysis and implications of this work in future regulatory decision-making are also discussed.