Bioavailability Of Hydrophobic Contaminants Research Articles

Application of isotope dilution method for measuring bioavailability of organic contaminants sorbed to dissolved organic matter (DOM)

Natural waters such as surface water and sediment porewater invariably contain dissolved organic matter (DOM). Association of strongly hydrophobic contaminants (HOCs) with DOM leads to decreased toxicity and bioavailability, but bioavailability of DOM-sorbed HOCs is difficult to measure. Current methods to estimate bioavailability of HOCs in water are based on only the freely dissolved concentration (Cfree). The ignorance of the exchangeable fraction of HOCs sorbed on DOM may result in an underestimation of the toxicity potential of HOCs to aquatic organisms. Here we explore the applicability of an isotope dilution method (IDM) to measuring the desorption fraction of DOM-sorbed pyrene and bifenthrin and determining their exchangeable pool (E) as an approximation of bioavailability. E values, expressed as percentage of the total concentration, ranged between 0.80 and 0.92% for pyrene and 0.74 and 0.85% for bifenthrin, depending primarily on the amount of chemical in the freely dissolved form. However, between 34 and 78% of the DOM-sorbed pyrene was exchangeable. This fraction ranged between 23% and 82% for bifenthrin. The ability of IDM to predict bioavailability was further shown from a significant relationship (r2>0.72, P<0.0001) between E and bioaccumulation into Daphnia magna. Therefore, IDM may be used to improve the bioavailability measurement and risk assessment of HOCs in aquatic systems.

Tenax extraction of sediments to estimate desorption and bioavailability of hydrophobic contaminants: a literature review.

Characterizing sediment-associated hydrophobic contaminants is problematic, because assessing the total amount of a compound available for chemical exchange with an organism is difficult. To address this, contaminant concentrations have been normalized for specific sediment characteristics (including organic C content) or the chemical activity has been estimated using passive samplers. Another approach to assess compound availability is to determine the extent of readily desorbed compound using resin extractions of sediment slurries. The present paper reviews the literature that uses Tenax® TA, a 2,6-diphenylene-oxide polymer as an extraction tool to measure bioavailability of hydrophobic organic contaminants in sediment. Some work has assessed the extent of desorption with sequential extractions to characterize the maximum rate and pool sizes for different desorbing fractions of bound contaminant. As such, the rapidly desorbing fraction has been well correlated with the extent of degradation, bioaccumulation, and toxicity of hydrophobic contaminants. A shortcut to measuring the full desorption curve to determine the rapidly desorbing compound is to use a single-point extraction, with 6 h or 24 h extractions being the most common. The Tenax extraction has been shown to be effective with laboratory-spiked sediments, field-collected sediments, laboratory-exposed organisms, field-collected organisms, and studies among laboratories. Furthermore, a literature-based model has described the bioaccumulation of polychlorinated biphenyls from independently measured field-collected sediments. Despite the success of this approach, applying the Tenax method to manage contaminated sediments is limited by the absence of a standard set of conditions to perform the extractions, as well as standard methods for using field sediments.