Contribution of terrestrial processes in reducing environmental mycotoxin levels: a review on mycotoxin-soil interactions

TL;DR

This paper reviews how soil processes help reduce mycotoxin levels in the environment, highlighting the role of microbial activity and soil interactions.

Contribution

The paper provides a new interpretation of mycotoxin fate in soils, emphasizing microbial degradation and soil-based strategies for environmental monitoring.

Findings

Microbial transformation is the main process for mycotoxin dissipation in soils, especially when bacteria are dominant.

Adsorption to soil particles, influenced by mycotoxin chemical properties, reduces their availability for degradation.

Soil acts as a mediator of mycotoxin levels rather than a source, with plant uptake being a minor contamination pathway.

Abstract

Mycotoxins are fungal metabolites that can harm humans and animals. They occur primarily in infected crops, with higher levels under environmental stress. Their origin in contaminated crops is the main contributor to soil contamination. Although high levels can be detected in soils, these are transitory and in average far lower than in contaminated crops, indicating a key role of functioning soils in down-regulating environmental mycotoxin levels. This review examines mycotoxin-soil interactions in terms of four terrestrial processes: (i) adsorption to soil fractions, (ii) microbial transformation and mineralisation (iii) transport/mobilization with water, (iv) plant uptake and response. Results show that the main process for dissipation in soils is microbial, improved by biomass and activity and by a narrow fungi-to-bacteria ratio. This aligns with incubation studies suggesting a key role of bacteria in the degradation of mycotoxins. This path is favoured by the availability of the mycotoxins, that can be reduced by the adsorption to soil particles: the aromatic character and the carbonyl functions are decisive for adsorption to soil organic matter and clay particles, respectively. Consequently, mycotoxin levels in environmental compartments can be interpreted as the (net) result of entry and dissipation processes mediated through the soil, rather than the soil acting as a source of them. Plant uptake represents a minor pathway of contamination compared to the in situ production. In soil-plant systems, suboptimal nitrogen (N) and pesticide management are factors triggering fungal infestation and mycotoxins levels. Fungal infestation and mycotoxin can induce the polyphenolic response of the plant, along with mycotoxin metabolization as reported for DON. Based on this newly-made interpretation, this review provides future perspectives on mycotoxin occurrence and fate under climate change and intensive agriculture and proposes soil-based strategies for an integral environmental monitoring.

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