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(597) The effect of black carbon on equilibrium partitioning in PAH-contaminated marine sediments.
Vinturella, Amy*,1, Shine, James1, 1 Harvard School of Public Health, Boston, MA, USA
ABSTRACT- We have developed a method using polyethylene devices (PEDs) to determine the freely dissolved polycyclic aromatic hydrocarbon (PAH) concentrations in the porewater of contaminated marine sediments and to estimate equilibrium partitioning (EqP) among different sediment phases. Standard bioaccumulation tests using the polychaete Nereis virens along with the PEDs were run with sediments collected at various locations in Boston Harbor. Both natural organic carbon (NOC) and black carbon (BC) were considered as possible sorption phases in these sediments. Predicted freely dissolved porewater concentrations were calculated using two models: (i) traditional EqP models using NOC only and (ii) newer models that consider both NOC & BC. These predicted freely dissolved porewater concentrations were compared to measured concentrations (from PED calculations) to test the ability of each model to predict partitioning behavior. For the sites studied here, EqP with both NOC & BC predicted porewater PAH concentrations better than EqP with NOC only. The observed freely dissolved porewater PAH concentrations as measured with the PEDs were much lower than would be predicted from traditional EqP modeling using NOC only. In addition, the observed uptake of PAHs into Nereis virens was much lower than would be predicted by traditional EqP modeling. Estimates of the partition coefficient for PAH sorption to BC (KBC ) are generally 2 orders of magnitude higher than partition coefficients to natural organic carbon (KOC ). Although only about 10% of the total organic carbon in these sediments was BC, a thermodynamic model of PAH partitioning shows that the majority ( 95%) of the mass of PAHs are contained in the black carbon phase of the sediments. Traditional EqP models using NOC only may not always provide accurate estimates of PAH partitioning. Our results indicate that inclusion of BC as a separate phase in EqP models may be essential.
Key words: black carbon, equilibrium partitioning, sediments, porewater
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