Effects of biowaste-derived biochar on the dynamic behavior of cadmium fractions in soils

As a commonly used amendment to soil contaminated by heavy metals, biochar has attracted great attention and has been applied for decades due to the benefits to the soil. However, the effects of biochar on the dynamic behavior of soil properties and metal fractions are still unclear. Here, we used two biochars, derived from biowastes (reed and bamboo willow), to treat two cadmium (Cd)-contaminated soils, S1 (loamy sand) and S2 (sandy loam), and determined the dynamic effects. The incubation experiments were designed to investigate the effects of biochar on the dynamic behavior of soil pH, dissolved organic matter (DOM), bioavailable Cd, and the transformation of Cd fractions for 270 days. The results showed that the soil pH, DOM, and bioavailable Cd initially increased and then decreased with incubation time, and the soil pH and DOM were higher, but bioavailable Cd content was lower than the original value. The transformation of the metal fractions changed dynamically, and the exchangeable fraction of Cd decreased with incubation time. Furthermore, the correlation results showed that the DOM can directly control the redistribution of Cd fractions, while soil pH can control it indirectly by regulating the DOM. This study highlighted that biochar can affect soil pH and DOM, redistribute Cd fractions, decrease bioavailable Cd content, and lower the potential risk of heavy metals. This study suggests ways to immobilize heavy metals in contaminated soils using biochar.