The contents and speciation of heavy metals in sewage sludge from 10 wastewater treatment plants in the cities of Changsha

Zhuzhou and Changde of Hu＇nan Province were addressed. The potential ecological risk index(IR) was used to evaluate the ecological risk of heavy metals in the sludge intended for agriculture. The results showed that the sewage sludge was rich in organic matter

nitrogen

phosphorous

and potassi-um. As sewage sludge could potentially cause multi-metal contamination

especially Cd

sewage sludge should not be directly used for agriculture. The total content of Cd in sewage sludge ranged from 1.43 to 260 mg/kg and the major speciation of Cd was in reducible form with percentage as high as 28.9%. The major speciations of As and Pb in sludge were also in reducible form

those of Ni and Zn were in acid soluble and re-ducible forms

while those of Cu were in reducible and oxidizable forms

respectively. The results demon-strated that the environmental availability of heavy metals in sewage sludge was high. Based on the results of IR

Cd and As in the sewage sludge imposed a potentially severe risk. Both the single and comprehensive po-tential ecological risks of the heavy metals in the sewage sludge from the industrial areas were extremely seri-ous.