Using phosphorus-rich biochars to remediate lead-contaminated soil: Influence on soil enzymes and extractable P

In recent times, there has been increased focus on a holistic approach to soil remediation with consideration of social, economic and environmental factors. Consequently, there is a demand from practitioners and regulators alike for suitable ways to measure ancillary outcomes, for example, effects on soil quality. Here we show that biochar, when applied to land to remediate lead (Pb)-contaminated soils, can lead to environmental improvements not realized by adding mined or manufactured phosphates. Here, we study a Pb-contaminated soil amended with two phosphate fertilizers (slow- and fast-release) and with biochars produced from poultry litter and from biosolids at three temperatures (300 °C, 400 °C and 500 °C). The results show that, unlike the fast-release P fertilizer, biochars did not result in an increase in the amount of leachable P that could be released into the environment. Biochars prepared at 500 °C presented a higher value of the integrative geometric mean of soil enzyme activity, compared to the P fertilizers. Overall, our research shows that biochars, particularly those prepared at the higher temperature tested, are a suitable alternative to P fertilizers as an integrative remediation strategy in Pb-contaminated soils, enabling soil biological restoration