Les substances pharmaceutiques dans les milieux aquatiques. Niveaux d'exposition et effet biologique : que savons nous?

Nous présentons ici une revue synthétique des récents résultats disponibles sur la présence, le devenir et les effets des principales familles thérapeutiques de médicaments à usage principalement humain, détectées dans les milieux aquatiques. Un exemple d'illustration du risque d'effet biologique, lié à la présence d'un ß-bloquant, le propranolol est présenté.This paper reviews the recent data available on the exposure, fate and effects of human pharmaceuticals in aquatic ecosystems. Since the 1980s, pharmaceuticals have been detected in urban wastewater and receiving waters. More recently, some events have stressed the issue of the continuous presence of such compounds in the aquatic environment. Indeed, it is now well established that veterinary and human pharmaceuticals are widely measured in effluents, surface and ground water, and more rarely, in tap water. Measured concentrations normally vary in the µg/L to ng/L range. Some of these pharmaceuticals, such as steroidal hormones used as oral contraceptives, can be toxic at very low concentrations (ng/L) in several organisms (such as fish, amphibians or molluscs). Recent European regulations dealing with pharmaceutical environmental risk assessment, as well as the Water Framework Directive, have stimulated research on the issue of the pharmaceuticals in the environment.Most available data deal with the occurrence of pharmaceuticals in various aquatic settings, but fewer data are available on the fate of these compounds, in particular in aquatic ecosystems, sediments and biota, or their toxic effects. Much of the latter information concerns acute lethal toxicity, as determined from acute testing on algae, invertebrates and fish in laboratory studies. These results tend to show that effects are most often detected at concentrations above 1 mg/L, i.e., higher than environmental exposure concentrations. Nevertheless, for some pharmaceuticals, recent ecotoxicological findings have shown a range of acute to chronic ratios (i.e., acute toxicant concentration divided by the no-effect concentration) covering several orders of magnitude. Indeed, recent results on sublethal toxic effects, such as the modification of reproduction or growth rates, or perturbations of fish metabolism, indicate that these effects can occur at much lower concentrations. Therefore, due to the continuous release of a mixture of numerous pharmaceuticals into aquatic ecosystems, and considering that these are biologically active compounds, possible long-term environmental effects cannot be excluded, even at low concentrations of exposure. Moreover, few data are currently available concerning the fate of pharmaceuticals, such as their ability to accumulate in sediment or to bioaccumulate in aquatic organisms.A cumulative frequency distribution of surface water concentrations of carbamazepine, diclofenac, clofibric acid, propranolol and sulfamethoxazole shows that 90% of the available data exceed 10 ng/L, the threshold concentration above which an environmental risk assessment is required for human and veterinary pharmaceuticals. As an example, we present here a probabilistic risk assessment carried out for the widely detected ß-blocker propranolol. This assessment is based on the comparison between the exposure concentrations in surface water and the toxic effect concentrations, gathered from a literature survey. The results indicate that chronic toxic effects are likely to arise in aquatic species. They also highlight the need to improve the knowledge base, both for the behaviour and the fate of pharmaceuticals in wastewater treatment plants and the receiving aquatic ecosystems (e.g., sorption on particles, accumulation in sediment, biotic and abiotic degradation), and for toxic effects at low levels of exposure, using several levels of biological organisation, to improve the environmental risk assessment of pharmaceuticals