Calculating
the Diffusive Flux of Persistent Organic
Pollutants between Sediments and the Water Column on the Palos Verdes
Shelf Superfund Site Using Polymeric Passive Samplers
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Abstract
Passive samplers were deployed to
the seafloor at a marine Superfund
site on the Palos Verdes Shelf, California, USA, and used to determine
water concentrations of persistent organic pollutants (POPs) in the
surface sediments and near-bottom water. A model of Fickian diffusion
across a thin water boundary layer at the sediment-water interface
was used to calculate flux of contaminants due to molecular diffusion.
Concentrations at four stations were used to calculate the flux of
DDE, DDD, DDMU, and selected PCB congeners from sediments to the water
column. Three passive sampling materials were compared: PE strips,
POM strips, and SPME fibers. Performance reference compounds (PRCs)
were used with PE and POM to correct for incomplete equilibration,
and the resulting POP concentrations, determined by each material,
agreed within 1 order of magnitude. SPME fibers, without PRC corrections,
produced values that were generally much lower (1 to 2 orders of magnitude)
than those measured using PE and POM, indicating that SPME may not
have been fully equilibrated with waters being sampled. In addition,
diffusive fluxes measured using PE strips at stations outside of a
pilot remedial sand cap area were similar to those measured at a station
inside the capped area: 240 to 260 ng cm<sup>–2</sup> y<sup>–1</sup> for <i>p,p</i>′-DDE. The largest
diffusive fluxes of POPs were calculated at station 8C, the site where
the highest sediment concentrations have been measured in the past,
1100 ng cm<sup>–2</sup> y<sup>–1</sup> for <i>p,p</i>′-DDE