Fire effects on the distribution and bioavailability of potentially toxic elements (PTEs) in agricultural soils

In the last years, uncontrolled fires are frequently occurring in forest and agricultural areas as an indirect effect of the rising aridity and global warming or caused by intentional illegal burnings. In addition, controlled burning is still largely used by farmers as an agricultural practice in many parts of the world. During fire events, soil can reach very high temperatures at the soil surface, causing dramatic changes of soil properties and elements biogeochemistry. Among soil elements, also potentially toxic elements (PTEs) can be affected by fires, becoming more or less mobile and bioavailable, depending on fire severity and soil characteristics. Such transformations could be particularly relevant in agricultural soils used for crop productions since fire events could modify PTEs speciation and uptake by plants and associated (micro)organisms thus endangering the whole food-chain. In this review, after describing the effects of fire on soil minerals and organic matter, the impact of fires on PTEs distribution and speciation in soils is presented, as well as their influence on soil microorganisms and plants uptake. The most common experimental methods used to simulate fires at the laboratory and field scale are briefly illustrated, and finally the impact that traditional and innovative agricultural practices can have on PTEs availability in burned agricultural soils is discussed in a future research perspective.