The Effects Of Different Types Of Biochar On Ecotoxicity Of Persistent Toxic Substances In Sediments

Biochar,due to its good adsorption capacity to pollutants,has recently become a focused issue in the fields of contaminated soil and water remediation.Because of the complexity of environmental media,it is not enough to evaluate the efficacy of biochar for the remediation of contaminated environment only by the change of bioavailability of pollutants,and the biological effects of pollutants should be considered.At present,little is known about the potential ecological toxicity risk of biochar itself and the interaction between biochar with pollutants.To evaluate the ecotoxicity of different types of biochar and their effects on the ecotoxicity of typical persistent toxic substances in sediments,in this study,the effects of activated-sludge-derived biochar(ASB)and corn-straw-derived biochar(CSB)with different particle size and different dosage on Cd or BDE-47 in sediments were investigated following 28-day chronic bioassay with sediment-dwelling benthic macroinvertebrate Bellamya aeruginosa.This study will be of important scientific significance for understanding remediation efficacy of biochar to polluted sediments and potential ecological risks,and further providing scientific basis for the setting of long-term application to the environment.The results indicated that,Cd accumulation in the visceral mass of B.aeruginosa exposed to ASB-only-amended sediments was found,and the accumulation was related to the percent of ASB,but not to particle size.The resulted Cd accumulation did not cause DNA damage and oxidative stress of hepatopancreas.No Cd accumulation in the visceral mass of B.aeruginosa exposed to CSB-only-amended sediments was found,DNA damage and oxidative stress of hepatopancreas were not observed.The above results showed that ASB has relatively lower ecotoxicity risk,and CSB has no ecotoxicity risk.As for Cd,1% of 40#ASB did not reduce Cd toxicity,4% and 7% of 40#ASB could significantly reduce Cd toxicity,but the increase of percent of ASB did not further reduce Cd toxicity.100#ASB could significantly reduce Cd toxicity,the increase of percent of ASB did also not reduce Cd the toxicity.Comparatively,the fine particles were better than the coarse particles.The efficacy of CSB to decrease Cd toxicity was slightly better than ASB.After 28-day exposure,both ASB and CSB did not remove Cd toxicity.As for BDE-47,1% of ASB did not reduce the toxicity of BDE-47.4% and 7% of ASB could reduce the toxicity of BDE-47,but the increase of percent of ASB did not further reduce the toxicity of BDE-47.100#CSB with varied percent could significantly reduce the toxicity of BDE-47,and a higher percent(4% and 7%)of 100#CSB showed more pronounced efficacy.After 28-day exposure,both ASB and CSB could not remove the toxicity of BDE-47 thoroughly.When comparing bioaccumulation of Cd or BDE-47 after biochar amendment,it can be found that higher proportion of ASB and CSB might reduce the oxidative stress of Cd or BDE-47 on hepatopancreas by reducing its bioaccumulation,thus resulting in a decline in the toxicity of the Cd or BDE-47.The increased proportion of biochar amendment could not further Cd or BDE-47 toxicity.When taking into consideration of the potential ecological toxicity risks of two kinds of biochar,the efficacy of biochar to reduce toxicity of Cd and BDE-47 in sediments,and the cost of biochar production,it was estimated that the appropriate addition levels of ASB and CSB for the remediation of contaminated sediments are 4~5% and 7~8%,respectively,and the fine-sized biochar is recommended.