Multi-ratio equilibrium passive sampling method to estimate accessible and pore water concentrations of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in sediment.

The freely dissolved concentration (C(w,0)) in the pore water and the accessible (releasable) concentration in the sediment (C(as,0)) are important parameters for risk assessment. These parameters were determined by equilibrating contaminated sediments and passive samplers using largely differing sampler­sediment ratios. This method is based on the principle that incubations at low sampler/sediment ratios yield the concentration in the pore water (minor depletion of the sediment phase) and incubations at high sampler/sediment ratios yield the accessible concentration in the sediment (maximum depletion of the sediment phase). It is shown that equilibration was faster in dense suspensions and at high sampler/sediment ratios when compared to low sampler/sediment ratios. An equilibrium distribution model was used to estimate C(w,0) and C(as,0) by nonlinear least-squares regression. The method was evaluated for three sediments (harbor, estuarine, marine). Accessible concentrations of 13 PAHs were 2 (low K(ow)) to 10 (high K(ow)) times lower than the total concentrations (three sediments). By contrast, the accessible concentrations of 15 PCBs were about 1.2 times lower than the total concentrations and displayed no trend with K(ow) (one sediment). Implications for risk assessment and considerations for application of multi-ratio equilibrium passive sampling with other sediments are discussed.

Development of a polydimethylsiloxane film-based passive dosing method in the in vitro DR-CALUX® assay.

In bioassays, exposure concentrations of test compounds are usually expressed as nominal concentrations. As a result of various processes, such as adsorption, degradation, or uptake, the actual freely dissolved concentration of the test compound may differ from the nominal concentration. The goal of the present study was to develop a method to dose passively the freely dissolved fraction of organic chemicals in an in vitro bioassay with adherent cells. To this end, a polydimethylsiloxane (PDMS) film-based method was developed for a reporter gene assay for dioxin-like compounds in a rat liver cell line. Polydimethylsiloxane films loaded with test compounds ensure that the concentration during exposure is in equilibrium and that the ratio between the concentration on the film and the concentration in medium is constant. Benzo[k]fluoranthene (BkF) was used as a model compound to develop the passive dosing method in transwell plates, which was further tested with a complex mixture, i.e., an extract prepared from a contaminated sediment. A higher dioxin-like activity was found when extracts were dosed by passive dosing with PDMS than when directly added to medium. Comparison with analysis of the concentration of BkF in medium shows that passive dosing of individual chemicals may not be necessary if freely dissolved concentrations are known. Use of PDMS for passive dosing of complex samples may represent a more realistic method for exposure in in vitro bioassays.