Over the past fifteen years there has been increasing interest in the environmental occurrence, fate and effects of substances used as pharmaceuticals or personal care products. While the understanding of the environmental fate and ecotoxicity of pharmaceuticals is now well developed, less information is available on the uptake of pharmaceuticals and personal care products into aquatic organisms and, in particular, into sediment-dwelling organisms. This study was therefore performed to develop an understanding of the factors and processes affecting the uptake of pharmaceuticals and personal care products into the sediment dwelling oligochaete worm, Lumbriculus variegatus. The study combined experimental studies into the distribution of a range of pharmaceuticals and personal care products in sediment-water systems and studies into the uptake of the study compounds under a range of conditions. The results were used to parameterize and evaluate a model for estimating uptake of pharmaceuticals and personal care products into benthic organisms.
Adsorption of the study compounds from water to sediment solids increased in the order diclofenac < chloramphenicol < salicylic acid < naproxen < caffeine < sulfamethazine < triclosan < fluoxetine. Comparison of the sorption results with estimations from available models for predicting sorption from chemical properties indicated that relationships developed for neutral organic chemicals were not appropriate for use on ionisable pharmaceuticals and personal care products. While predictive models, developed specifically for ionisable chemicals, produced improved predictions of sorption, even these predictions were not perfect.
Bioconcentration factors for the study compounds from water into L. variegatus were found to increase in the order chloramphenicol < diclofenac < salicylic acid < fluoxetine < naproxen < triclosan. The differences in bioconcentration factors could not be explained by differences in log Kow and log Dow which are descriptors that have previously been used to predict the uptake of neutral organic substances and ionisable substances in other species of invertebrates. There was also disagreement between the uptake measurements and predictions obtained from models developed for estimating the uptake of ionisable chemicals into aquatic organisms.
The uptake of four of the study compounds (caffeine, diclofenac, fluoxetine and triclosan) was further evaluated at different water pH values. For three of these compounds (diclofenac, fluoxetine and triclosan), the potential for metabolism by L. variegatus was also assessed as was the uptake and route of uptake from whole sediments. Uptake of diclofenac and fluoxetine was found to be highly sensitive to changes in pH with bioconcentration factors varying by over two orders of magnitude (diclofenac) and four orders of magnitude (fluoxetine) across three pH units. Tissue analysis indicated that while diclofenac is not metabolized by the worms, fluoxetine and triclosan are heavily metabolized. The whole sediment studies demonstrated that uptake of diclofenac and fluoxetine occurs primarily from the sediment pore-water whereas for triclosan, sediment ingestion provides a small contribution to the uptake.
Results from the different components of the study were used to parameterize and evaluate a model for estimating uptake of pharmaceuticals and personal care products from sediments into benthic organisms. Comparison of predictions from this model for diclofenac, fluoxetine and triclosan were compared to measurements from whole sediment studies. While the model was found to under-predict the uptake of triclosan, good predictions were obtained for diclofenac and fluoxetine. With further development and evaluation, the uptake modeling approach could provide a valuable tool for use in the risk assessment of ionisable compounds such as many pharmaceuticals and personal care products
