60 research outputs found
Polychlorinated Biphenyl Sorption and Availability in Field-Contaminated Sedimentsâ
Traditional and new relationships of polychlorinated biphenyl (PCB) distribution among the solid phases, the free aqueous phase, and biolipids are comprehensively reviewed using seven well-characterized freshwater and marine sediments polluted with PCBs. The traditional relationship relating free aqueous concentration and biolipid concentration to sediment total organic carbon, compound octanolâwater partitioning coefficient, and solid-phase contaminant concentration overestimates measured free aqueous concentrations and biolipid concentrations by mean factors of 8 and 33, respectively. By contrast, relationships based on measured free aqueous phase concentrations or the PCB mass fraction desorbed from sediment provide reasonable predictions of biolipid concentrations. Solid-phase concentration-based predictions perform better when sorption to amorphous organic matter and black carbon (BC) is distinguished. Contrary to previously published relationships, BC sorption appears to be linear for free aqueous PCB-congener concentrations in the picogram to microgram per liter range
Absorption of the and Mesons in Nuclei
Due to their long lifetimes, the and mesons are the ideal
candidates for the study of possible modifications of the in-medium
meson-nucleon interaction through their absorption inside the nucleus. During
the E01-112 experiment at the Thomas Jefferson National Accelerator Facility,
the mesons were photoproduced from H, C, Ti, Fe, and Pb targets. This
paper reports the first measurement of the ratio of nuclear transparencies for
the channel. The ratios indicate larger in-medium widths compared
with what have been reported in other reaction channels.Comment: 6 pages, 4 figure
Equilibrium Sampling to Determine the Thermodynamic Potential for Bioaccumulation of Persistent Organic Pollutants from Sediment
Equilibrium
partitioning (EqP) theory is currently the most widely
used approach for linking sediment pollution by persistent hydrophobic
organic chemicals to bioaccumulation. Most applications of the EqP
approach assume (I) a generic relationship between organic carbon-normalized
chemical concentrations in sediments and lipid-normalized concentrations
in biota and (II) that bioaccumulation does not induce levels exceeding
those expected from equilibrium partitioning. Here, we demonstrate
that assumption I can be obviated by equilibrating a silicone sampler
with chemicals in sediment, measuring chemical concentrations in the
silicone, and applying lipid/silicone partition ratios to yield concentrations
in lipid at thermodynamic equilibrium with the sediment (<i>C</i><sub>LipâSed</sub>). Furthermore, we evaluated the validity
of assumption II by comparing <i>C</i><sub>LipâSed</sub> of selected persistent, bioaccumulative and toxic pollutants (polychlorinated
biphenyls (PCBs) and hexachlorobenzene (HCB)) to lipid-normalized
concentrations for a range of biota from a Swedish background lake.
PCBs in duck mussels, roach, eel, pikeperch, perch and pike were mostly
below the equilibrium partitioning level relative to the sediment,
i.e., lipid-normalized concentrations were â€<i>C</i><sub>LipâSed</sub>, whereas HCB was near equilibrium between
biota and sediment. Equilibrium sampling allows straightforward, sensitive
and precise measurement of <i>C</i><sub>LipâSed</sub>. We propose <i>C</i><sub>LipâSed</sub> as a metric
of the thermodynamic potential for bioaccumulation of persistent organic
chemicals from sediment useful to prioritize management actions to
remediate contaminated sites
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