The role of biochar in modifying the environmental fate, bioavailability, and efficacy of pesticides in soils: a review

The role of biochar in sequestration of carbon, reducing the emission of greenhouse gases, and improving the soil fertility is increasingly being recognised and is leading to the recommendations of biochar amendment of soils. However, the implications of such amendments to the environmental fate and efficacy of pesticides are not well understood. The published work on the role of black carbon (which includes charcoal, soot, and other pyrolytic carbon materials) in the environmental fate and effect of organic contaminants is reviewed here, together with the studies on bioavailability and efficacy of some herbicides in soils amended with freshly produced biochars. Biochars, due to their unique properties especially their highly carbonaceous and aromatic nature and high specific surface area, have been reported to be up to >2000 times more effective than soil in sorbing pesticides. The incorporation of relatively small amounts of fresh biochars in soil (0.05% by wt) has also been shown to inhibit the microbial degradation of organic compounds including pesticides as well as reduce their plant availability and efficacy. Based on limited published research on biochars and related research on black carbon reviewed here, biochar amendments to soils are likely to reduce the bioavailability and efficacy of pesticides. Furthermore, these amendments can influence the potential accumulation and ecotoxicological impact of pesticides and other organic contaminants in the soil environment. The implications of heterogeneity and ageing of biochars applied to soils for sorption and desorption processes and in turn for other environmental fate processes need to be understood to seek the appropriate balance between carbon sequestration and pesticide efficacy. While biochar amendment of soil holds appeal from a carbon accounting and soil conditioning perspective, further research is urgently required to determine how biochar influences the efficacy and environmental fate of agrochemicals such as pesticides.