Biochar in soil mitigates dimethoate hazard to soil pore water exposed biota

Soil contamination is a worldwide problem urging for mitigation. Biochar is a carbonaceous material used as soil amendment that can immobilize chemical compounds, potentially turning them unavailable for soil biota. The aim of our study was to evaluate biochar's capacity to immobilize dimethoate in soil and, therefore, decreasing the toxicity to soil organisms. Two biochar application rates (2.5% and 5% w/w) were chosen to assess dimethoate potential immobilization, looking at changes in its toxicity to the collembolan Folsomia candida and the plant Brassica rapa upon soil amendment. Complementarily, chemical analyses were performed on soil pore water. Results showed that biochar may sorb and decrease dimethoate concentrations in soil pore water, influencing dimethoate bioavailability and consequent toxicity. Contrary to dimethoate solo impact on collembolans (LC₅₀ 0.69 mg kg^-1, EC₅₀ 0.46 mg kg^-1), their survival rate and offspring production were not affected by dimethoate when biochar was applied, regardless of application rate (LC₅₀ and EC₅₀ > 1.6 mg kg^-1). Shoot length, fresh and dry weights of B. rapa were less affected by dimethoate upon biochar addition (EC₅₀ values increase for all endpoints). Our study shows that biochar may contribute to decrease dimethoate bioavailability and toxicity to soil porewater exposed organisms.