Ecotoxicological assessment of aflatoxin in soil under different temperature and moisture conditions utilising earthworms
Fouché, Tanya Christina
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Aflatoxins are secondary metabolites produced by specific strains of fungi. These natural toxins are mainly found in soil, decaying vegetation, and food storage systems and are particularly abundant during drought stress. Aflatoxin contamination is one of the most important threats to food safety and human health, however, limited information about its toxicological consequences in the soil ecosystem is available. Recent studies suggest that aflatoxin contamination might become a bigger problem if the climate continues to change. This research aimed to define the risk of aflatoxin contamination in the soil ecosystem by investigating the toxicological consequences of aflatoxins to earthworms (Eisenia andrei) under different temperature and moisture conditions. Further, the biological control of aflatoxins by earthworms were investigated. The review concluded that many aspects of aflatoxin occurrence, degradation, and the effects of its transformation products in the soil environment are still unknown and remain an important area of research for soil health and productivity. Standard toxicity tests with different combinations of air temperature (21 and 26 °C) and soil moisture (30 and 50% of the soil water holding capacity- WHC) were used to investigate aflatoxins’ toxicological consequences to earthworms in a soil medium. Sublethal endpoints, including growth, reproductive success and genotoxicity, were monitored. Additionally, aflatoxin concentrations in the soil were monitored over four weeks in the presence and absence of earthworms to establish earthworms’ role in aflatoxin degradation. Negligible effects on earthworm survival, growth, and reproduction were observed at aflatoxin concentrations between 10 – 100 μg/kg, but a concentration-dependent increase in DNA damage at standard testing conditions was observed. The influence of temperature and moisture changed the exposure effect outcomes of aflatoxin in soil. Drought conditions (30% WHC) resulted in significantly more negative effects on earthworm reproductive and genetic status under increasing aflatoxin concentrations. The research highlighted the possible risk of environmentally relevant aflatoxin levels to the functional ability of important soil organisms for providing essential ecosystem services under changing climate conditions. However, it also highlighted the potential of earthworms to contribute to the biological control of aflatoxins under favourable environmental conditions.