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[en] More than 2300 sediment pore water distribution coefficients (KPCBids) of 93 polychlorinated biphenyls (PCBs) were measured and modeled from sediments from Indiana Harbor and Ship Canal. KPCBids were calculated from previously reported bulk sediment values and newly analyzed pore water. PCBs in pore waters were measured using SPME PDMS-fiber and ∑PCB ranged from 41 to 1500 ng L−1. The resulting KPCBids were ∼1 log unit lower in comparison to other reported values. A simple model for the KPCBid consisted of the product of the organic carbon fraction and the octanol–water partition coefficient and provided an excellent prediction for the measured values, with a mean square error of 0.09 ± 0.06. Although black carbon content is very high in these sediments and was expected to play an important role in the distribution of PCBs, no improvement was obtained when a two-carbon model was used. -- Highlights: •PCB sediment-pore water distribution coefficients were measured and modeled. •Distribution coefficients were lower in comparison to other reported values. •Organic carbon fraction times the KOW yielded the best prediction model. •The incorporation of black carbon into a model did not improve the results. -- The organic carbon fraction times the octanol–water partition coefficient yielded the best prediction model for the sediment pore water distribution coefficient of PCBs
[en] We quantified internal processes that supply methylmercury from hypolimnetic reducing zones to the upper waters of a Hg-contaminated lake, Onondaga Lake, NY, USA. Diffusive transport continuously supplied methylmercury to the epilimnion under summer stratification, while fall mixing resulted in a pulsed release of methylmercury to the upper mixed waters. These processes were the main internal sources of methylmercury to the epilimnion, and together almost equaled the total external supply. The wind-driven entrainment represented an additional stochastic internal supply of methylmercury of approximately 9% in 2006. Considering more than 15 years of data, we estimate 1.8 wind-driven events occur per year. The mass of methylmercury inputs to the epilimnion exceeded the measured increase, suggesting that loss processes are important in regulating methylmercury accumulation. The relative contribution of internal sources of methylmercury to the epilimnion has decreased in recent years, shifting the importance to the external inputs. Highlights: • Internal mercury cycling was equally important to external inputs in a polluted lake. • Diffusive mixing was a critical source of methylmercury under stratified conditions. • Entrainment-based transport of methylmercury detected under sustained wind conditions. • Lake-wide mixing provided the single largest internal input of MeHg to the epilimnion. -- Capsule: Internal cycling of legacy mercury deposits constitutes a substantial source of methylmercury to the epilimnion of a stratified polluted lake
[en] Groundwater is a globally important, valuable resource for human life and economic development. Despite its importance, it is often misused and rarely well managed. Delineation of polluted zone attains significance especially when the pollution affects the human health. Delineation can be done by many approaches: process based, statistical and overlay and index methods. Overlay and index methods are relatively simpler and are based on hydrogeological settings and other factors which are considered to control the groundwater quality in a region. Groundwater vulnerability to contamination due to anthropogenic as well as seawater intrusion in an unconfined aquifer spread over the watershed areas of Kazhakkoottam, Kulathoor and Menamkulam regions of Thiruvananthapuram District, Kerala, India, was carried out using both susceptibility index (SI) method and modified GALDIT index method. Majority of the region selected was categorised as moderately vulnerable by both indices. The cause of groundwater vulnerability to contamination was found using factor analysis. The factor score map of the study area also shows that majority of the study area is moderately affected by contamination. Hence, the area requires continuous monitoring of groundwater quality to prevent the contamination of groundwater resources for future generations.