Evaluating the emerging environmental risks of mycotoxins in freshwater ecosystems.

Abstract

Deoxynivalenol (DON) and zearalenone (ZON) are two of the prominent mycotoxins which regularly contaminate food, both of these natural toxins are produced by fungi within the Fusarium genus. With the known widespread occurrence of these toxins in cereal crops there has been rising interest into the potential transference into freshwaters. Multiple reports of mycotoxin occurrence in freshwater samples have led to their consideration as natural chemicals of emerging concern, particularly with ZON seen to act in an oestrogenic nature, yet the ecotoxicological data to support analysis of risk to freshwater ecosystems is lacking. The main aim of this work was to determine the hazard posed by DON and ZON to freshwater plants and invertebrates in laboratory exposures in order to perform a freshwater environmental risk assessment. The acute response was measured in various groups of freshwater organisms including macrophytes Lemna minor, microalgae Pseudokirchneriella subcapitata, rotifers Brachionus calyciflorus, insects Chironomus riparius (larvae), crustaceans Daphnia pulex and Thamnocephalus platyurus, cnidarians Hydra vulgaris, molluscs Lymnaea stagnalis (embryos) and Protozoa Tetrahymena thermophila. The resulting inhibition values in terms of growth, immobilisation survival or reproduction demonstrated DON poses the greater toxic hazard to crustaceans, whereas ZON was most toxic to mollusc embryos and cnidarians. The overall hazard posed to freshwater ecosystems was considered for each mycotoxin using species sensitivity distributions, generated with the plant and invertebrate data along with additional plant and fish data available in literature. These provided freshwater HC5 values of 5.2 μg DON/L and 43 μg ZON/L, respectively. Global freshwater exposure concentration data was reviewed for comparison with the hazard concentrations, resulting risk ratios indicated no immediate risk in terms of acute toxicity, posed by DON and ZON. Agricultural streams were highlighted for further consideration in terms of DON loads received as this is where the highest reported concentration of DON was sourced, which was exceptionally high causing it to be the only instance where a measured concentration exceeded the predicted no effect level in terms of acute toxicity. For ZON lethal effects are not predicted to be of a concern but it may contribute to the overall oestrogenic load in freshwaters.