Impacts of biochar materials on copper speciation, bioavailability, and toxicity in chromated copper arsenate polluted soil

Trace element polluted soils pose risks to human and environmental health. Biochar can decrease trace element bioavailability in soils, but their resulting ability to reduce soil toxicity may vary significantly depending on feedstocks used, pyrolysis conditions, and the target pollutants. Chromated copper arsenate (CCA) polluted sites are common, but only very few types of biochar have been tested for these sites. Hence, we tested fourteen well-characterized biochar materials for their ability to bind Cu and reduce toxicity in a CCA polluted soil in a 56-day experiment. Biochar (1%, wt/wt) increased plant (wheat, Triticum aestivum L.) shoot and root growth by 6–58% and 0–73%, reduced soil toxicity to Arthrobacter globiformis by 7–55%, decreased bioavailable Cu (Pseudomonas fluorescens bioreporter) by 5–65%, and decreased free Cu2+ ion activities by 27–89%. The A. globiformis solid-contact test constituted a sensitive ecotoxicological endpoint and deserves further attention for assessment of soil quality. Oil seed rape straw biochar generally performed better than other tested biochar materials. Biochar performance was positively correlated with its high cation exchange capacity, multiple surface functional groups, and high nitrogen and phosphorus content. Our results pave the way for future selection of feedstocks for creation of modified biochar materials with optimal performance in CCA polluted soil. [Display omitted] •Fourteen biochars reduced toxicity of chromated copper arsenate polluted soil.•Arthrobacter globiformis solid-contact test was superior to seed germination test.•Soil toxicity could be explained by the free Cu2+ ion activity.•Biochar performance was attributed to its CEC, functional groups, N and P content.•Oilseed rape straw biochar was effective for decreasing soil toxicity.