Impact of Sorption to Dissolved Organic Matter on the Bioavailability of Organic Chemicals

Dissolved organic matter (DOM) is ubiquitously present in the aquatic environment as well as in soil and sediment pore water. Partitioning-based techniques have generated better insights into the influence of different DOM structural features on sorption for hydrophobic chemicals, but the prediction of pH-dependent sorption for polar and ionisable chemicals remains problematic. Sorption to DOM can reduce the apparent rate of uptake and extent of accumulation of hydrophobic chemicals, although sorption to DOM may in some cases enhance diffusive transport of the contaminants and thereby increase uptake rates during bioaccumulation. Similarly, DOM can act as a surfactant to increase the rate of solubilisation and microbial uptake of soil-sorbed chemicals and therefore their rates of biodegradation. The impact of DOM structure is, however, more complex than can be captured by simple organic carbon-based approaches. In particular, exploration of the influence of condensed aromatic structures in DOM, often referred to as dissolved black carbon, would probably yield better insights into their impact on the bioavailability of high molecular weight PAHs and other hydrophobic compounds. More studies of the sorption of polar and ionisable chemicals to DOM would also increase our understanding of its potential impact on the bioavailability of such chemicals.