Bioavailability of microcystin-LR in two different soil types to the legume Alfalfa Medicago sativa L.

Abstract

The adverse effects of exposure to microcystins in terrestrial crops have been well documented. However, the retention and bioavailability of microcystin-LR, one of the most prevalent cyanotoxins, from soil to plants, is poorly understood. In the present study, the amount of free microcystin-LR from two soil types, a silty sand and clayey loam, with exposure to three toxin concentrations and time was investigated. Using the two soil types, the effects on Medicago sativa (Alfalfa) growth after microcystin-LR exposure via irrigation with spiked water and pre-spiked soil was investigated and the amount of microcystin-LR taken up by the plant quantified. After 3 weeks of growth, the amount of free microcystin-LR remaining in the two soil types with each treatment was quantified. The results indicated that in clayey loam more microcystin-LR is bound to the soil. However, the growth of Alfalfa was only affected in the clayey loam with microcystin/LR exposure via irrigation. Nevertheless, microcystin-LR was detected in Alfalfa grown in both soil types exposed by both irrigation and via pre-spiked soil. Interestingly, more microcystin-LR remained in the silty sand after 3 weeks; yet, more microcystin-LR was taken up by the Alfalfa grown in the silty sand, with a larger concentration in the roots compared to the shoots. The results indicate that the soil type substantially influences the bioavailability and uptake of microcystin-LR and present some insight into the ecological risk posed by microcystin-LR.