Assessment of phthalic acid esters plasticizers in sediments of coastal Alabama, USA: Occurrence, source, and ecological risk.

Considering the ubiquitous occurrences and ecotoxicity of phthalates (PAEs), it is essential to understand their sources, distribution, and associated ecological risks of PAEs in sediments to assess the environmental health of estuaries and support effective management practices. This study provides the first comprehensive dataset on the occurrence, spatial variation, inventory, and potential ecological risk assessment of PAEs in surface sediments of commercially and ecologically significant estuaries in the southeastern United States, Mobile Bay and adjoining eastern Mississippi Sound. Fifteen PAEs were widely detected in the sediments of the study region, with total concentrations varying between 0.02 and 3.37 µg/g. The dominance of low-molecular-weight (LMW) PAEs (DEP, DBP and DiBP) relative to high-molecular-weight (HMW) PAEs (DEHP, DOP, DNP) indicates that residential activities have stronger impacts than industrial activities on PAE distributions. The total PAE concentrations displayed an overall decreasing trend with increasing bottom water salinity, with the maximum concentrations occurring near river mouths. These observations suggest that river inputs were an important pathway by which PAEs were transported to the estuary. Linear regression models identified sediment adsorption (measured by total organic carbon and median grain size) and riverine inputs (measured by bottom water salinity) as significant predictors for the concentrations of LMW and HMW PAEs. Estimated 5-year total inventories of sedimentary PAEs in Mobile Bay and the eastern Mississippi Sound were 13.82 tons and 1.16 tons, respectively. Risk assessment calculations suggest that LMW PAEs posed a medium-to-high risk to sensitive aquatic organisms, and DEHP posed a low or negligible risk to the aquatic organisms. The results of this study provide important information needed for establishing and implementing effective practices for monitoring and regulating plasticizer pollutants in estuaries.

Sources and composition of natural and anthropogenic hydrocarbons in sediments from an impacted estuary.

Hydrocarbons in estuarine sediments provide information on sources of sedimentary organic matter (OM), and they are thus useful for tracing natural and anthropogenic OM inputs to the estuary. Here, we assessed the amounts, compositions and sources of natural and anthropogenic hydrocarbons from the sediments of a large, ecologically important estuary, Mobile Bay in Southeast USA. TOC/TN ratios and δ13C of organic carbon suggest that the bulk natural OM was sourced from marine phytoplankton and bacteria mixed with marsh and terrigenous C3 plants. Normal alkanes show high proportions of long-chain compounds with a high Carbon Preference Index, indicating the importance of C3 plants-derived OM in Mobile Bay. High concentrations of biogenic hopanes and perylene indicate microbial sources and degradation played an important role in shaping OM compositions. Anthropogenic hydrocarbons, αß-hopanes and polycyclic aromatic hydrocarbons (PAHs), were widely detected in Mobile Bay sediments. The source diagnostic ratios of hopanes and steranes suggest they were sourced from coal and diesel combustions. The source diagnostic ratios of PAHs, together with a positive correlation between PAHs and total mercury, suggests that PAHs originated primarily from coal combustion. We proposed two ratios, αß-hopanes/(ßß-hopanes+hopenes) and 16 PAHs/perylene, to evaluate anthropogenic versus natural contributions of hydrocarbons. These ratios were higher in the western estuary than in the eastern estuary, suggesting elevated anthropogenic hydrocarbon inputs to the western estuary. Correspondingly, the toxic equivalent quantity (TEQBaQ) of PAHs showed a higher ecological risk for the western estuary. This spatially uneven distribution of hydrocarbon pollutants can be attributed to more concentrated urban and industrial areas on the western shore, suggesting the importance of adjacent pollution sources. Collectively, our results provide new insights into the origins and dynamics of natural and anthropogenic OM and highlight the significance of coal combustion in contributing hydrocarbon pollutants in Mobile Bay sediments.