Bioavailability and toxicokinetics of hydrophobic aromatic compounds in benthic and terrestrial invertebrates

Uptake and accumulation of persistent hydrophobic chemicals by benthic and terrestrial invertebrates in water, sediment, and soil depends on the hydrophobicity of the compound (log Kow) and the lipid content of the organism. Several methods exist to determine the route of uptake. Their advantages and drawbacks are discussed. The route of uptake of hydrophobic contaminants is mainly via interstitial water, but for compounds with log Kow > 5 uptake from soil and sediment particles becomes important. In the presence of sediment or soil, the bulk of hydrophobic contaminants is sorbed to sediment/soil particles. Accumulation is, therefore, also controlled by sorption-related factors, such as the organic matter content and composition of sediment/soil, the presence of oil, particle size distribution, and the residence time of the contaminant. Other factors may be clay content and the presence of metals. It is shown that organic matter is the most important factor controlling accumulation in benthic and terrestrial organisms, while residence time of the contaminant and composition of organic matter seem to be of next importance. Also animal behaviour influences uptake and accumulation, such as size of the organism, avoidance of highly contaminated sites, burrowing behaviour, biotransformation, density of the organism population, and bioturbation. The influence of above mentioned factors on the equilibrium partitioning theory and related models for estimating accumulation levels was examined. The omittance of uptake from soil and sediment particles, the normalization on lipid content irrespective of other animal characteristics, biotransformation, organic matter composition, residence time of the contaminant, and the presence of oil are major factors interfering. As a result, a discrepancy between equilibrium partitioning theory estimated and actual accumulation levels of persistent hydrophobic compounds in benthic and terrestrial organisms exist.Key words: hydrophobic chemicals, accumulation, bioavailability, terrestrial organisms, benthic organisms, equilibrium partitioning theory.