# Abiotic Degradation of the Toxin Simplexin by Soil Collected from a Pimelea-Infested Paddock

## TL;DR

This study shows that the toxin simplexin can break down in soil when exposed to high temperatures, without needing microbes.

## Contribution

The study demonstrates that abiotic, heat-induced degradation of simplexin occurs in soil, independent of microbial activity.

## Key findings

- Soil from Pimelea-infested paddocks did not degrade simplexin at 22 °C, indicating no microbial metabolism.
- High temperature (100 °C) caused significant abiotic degradation of simplexin with three breakdown products identified.
- Simplexin degradation in soil was attributed to heat-promoted acid hydrolysis/elimination, not microbial activity.

## Abstract

Pimelea poisoning of cattle is caused by the toxin simplexin present in native Pimelea plant species. Surface weathering and burial of Pimelea plant material under soil in Pimelea-infested pastures previously showed simplexin degradation, suggesting soil microbial metabolism and/or abiotic degradation of simplexin in the field. This current study investigated whether soil from a Pimelea-infested paddock was capable of simplexin degradation in the laboratory. The effects of temperature on isolated simplexin levels and simplexin levels in Pimelea plant material treated with field-collected soil, acid-washed sand or bentonite were determined. Pimelea plant material incubated in field-collected soil at 22 °C for seven days did not show any simplexin degradation. Isolated simplexin preadsorbed to field-collected soil, acid-washed sand or bentonite showed simplexin decrease after one hour of incubation at 100 °C with three breakdown products identified by UPLC-MS/MS, indicating that toxin breakdown can be a heat-induced process rather than a microbial-based metabolism. Decreased simplexin levels were observed in Pimelea plant material mixed with acid-washed sand under similar incubation conditions. Overall, the study showed the field-collected soil did not contain soil microorganisms capable of simplexin metabolism within a short period of time. However, the co-exposure to high temperature resulted in significant abiotic simplexin breakdown, without microorganism involvement, with the product structures suggesting that the degradation was a heat promoted acid hydrolysis/elimination process. Overall, this study demonstrated that simplexin breakdown in the field could be a thermal abiotic process with no indication of microbial involvement.