Fragility of multixenobiotic resistance in aquatic organisms enhances the complexity of risk assessment

The protective function of multixenobiotic resistance (MXR) mechanism in aquatic organisms can be inhibited by many chemical compounds, the chemosensitizers. The presence of these MXR-inhibitors has important implications on environmental parameters like exposure, uptake, internal dose, bioaccumulation, response, synergism or toxicity, enhancing thereby the complexity of assessment of risks caused by pollution. The concentration of MXR-inhibitors was significantly higher in samples of water concentrates, sediment extracts, and native waters from polluted marine sites, or from polluted rivers, than in samples from corresponding unpolluted sites. In this paper we demonstrate that even nontoxic lipophilic agents from household waste or from communal waste-waters may be recognised and processed by this molecular mechanism, and, at high concentrations, might saturate the system and thereby reverse MXR. These findings stress why it is important not to burden the environment unnecessary with our waste: it is better to save the capacity of the MXR for pumping out toxic substances, natural or artificial. The discovery of MXR and the identification of a new class of hazardous chemical, the chemosensitizers, offer a scientific proof for the necessity of the zero-emission strategy.