Cadmium sorption in biosolids amended soils: results from a field trial

The effect of biosolids amendment on cadmium sorption coefficient (Kd) was determined for soils in a biosolids field trial. The sorptive properties of biosolids are thought to have a significant controlling effect upon the availability/uptake and mobility of potentially toxic metals. Kd values for the three biosolids were 10–30 times greater than those for unamended soil. Elevated Kd values were still apparent 1 and 2 years after biosolids amendment (100 t ha−1) for two of the three biosolids. Chemical extractants (sodium hypochlorite and hydrofluoric acid, respectively) were used in an attempt to determine Kd values of isolated inorganic and organic fractions. For both biosolids amended soils and unamended controls, Cd sorption appeared to be dominated by the inorganic fraction, potentially indicating the overriding importance of this fraction in controlling metal mobility. However, for the biosolids themselves, the sum of inorganic and organic fraction contributions to Kd accounted for less than half the Kd of the whole biosolids. This discrepancy was attributed to the loss of highly sorptive water soluble species in both chemical extractions.