Effect of Sewage Sludge Compost Products Application on Total Mercury and Methylmercury in Soil and Plants

Abstract

Two different sludge composting products (with and without biochar) were applied in field to study the variations of total mercury (THg) and methylmercury (MeHg) in soil and plants,as well as their migration in the soil-plant system and accumulation ability in plants during the sludge compost land use process.The results indicated that the concentrations THg and MeHg in soil increased after applying sewage sludge compost products,while the THg level was still lower than the secondary standard of national soil environmental quality.Biochar was speculated to probably promote the soil mercury methylation with lower MeHg/THg ratios in different soil treatments.THg concentrations in mature plants were significantly lower than those in seedling stage,but MeHg levels were higher than those in seedling stage.An obvious influence of composting on MeHg enrichment in plants was observed,and this similar effect was not found for THg enrichment.MeHg concentration in the soils applied with biochar compost was significantly higher than that without applying biochar compost soil,while MeHg in plant presented a contrary trend with higher level observed in no-biochar compost soil,suggesting that the addition of biochar could be in favour of soil MeHg formation and inhibit the MeHg accumulation in plants by influencing its migration.Since a strong MeHg accumulation ability with BCF of 1.24-14.63 was present in plant,the mercury ecological risk in soil environment caused by long-term fertilizing should be noticed.