Validating
the Use of Performance Reference Compounds
in Passive Samplers to Assess Porewater Concentrations in Sediment
Beds
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Abstract
Hydrophobic organic compounds (HOCs)
like polycyclic aromatic hydrocarbons
(PAHs) and polychlorinated biphenyls (PCBs) tend to accumulate in
sediment beds when they are released into aquatic environments. Due
to this buildup of HOCs in the sediment, the highest water concentrations
are often in the pore water. Passive samplers can be used in the field
(i.e., in situ) to measure freely dissolved porewater concentrations
if target contaminants diffusing through the sediment and into the
sampler exhibit the same diffusive retardation factors as performance
reference compounds (PRCs) that are diffusing out of the sampler and
into the sediment. To test this assumption, polyethylene (PE) passive
samplers were placed in an organic- and black- carbon-rich sediment
bed in the laboratory with samplers removed every 30 days for 4 months.
The concentrations of target contaminants in the PE at each time point,
corrected using measures of the losses of PRCs, were in good agreement
with separately measured equilibrium concentrations in a well-mixed
system. Concentrations in the PE passive samplers, normalized by their
polyethylene-water partition coefficients, were also in good agreement
with directly measured porewater concentrations. Finally, PE-deduced
porewater concentrations were compared with the traditional equilibrium
partitioning models and showed that considering sorption to only organic
carbon substantially overestimated porewater concentrations. However,
predictions improved greatly if sorption to black carbon was also
considered