Sorption properties for black carbon (wood char) after long term exposure in soils

Amending soil with black carbon (BC) can change the sorption properties of the soil. However, there is some concern based on studies that deal with newly produced BC and barely consider the possible changes in sorption properties for BC after being amended in soil. This study uses newly produced BC and historical BC samples, along with soils containing high levels of historical BC and adjacent soils without visible BC, to compare their diuron, atrazine and Cu2+ sorption properties. Compared with newly produced BC, historical BC exhibited reduced (56-91%) sorption capacity for diuron and atrazine but 2-5 times enhanced sorption capacity of Cu2+. These changes in sorption properties can be interpreted via the formation of surface functional groups in BC. Whereas the sorption capacity for diuron and atrazine was reduced with historical BC, the sorption capacity of BC-containing soils was higher than for the adjacent soils, indicating that BC possessed stronger sorption capacity than non-BC material. A biological assay revealed reduced herbicide efficiency for the newly produced BC, and even the historical BC still exerted an influence on reducing herbicide efficiency. Along with its recalcitrance in environments, BC has a significant long term effect on the toxicity of contaminants and soil fertility.