Heavy metals in the industrial sludge and their ecological risk: A case study for a developing country

Heavy metals in the industrial sludges were investigated to assess ecological risk using inductively coupled plasma mass spectrometer (ICP-MS). The ranges of Cr, Ni, Cu, As, Cd, and Pb in the samples were 1.4-9469.7, 4.8-993.8, 12.8-444.4, 2.2-223.8, 1.9-46.0 and 1.3-87.0 mg/kg, respectively. Statistically significant difference (P < 0.05) was observed for metal concentration in sludge of the studied industries. As a whole, the average concentrations of heavy metals were in the decreasing order of Cr > Ni > Cu > As > Pb > Cd. The results of the Community Bureau of Reference (BCR) sequential extraction showed that the studied metals were predominantly associated with the residual fraction followed by the oxidizable fraction. The values of pollution load index (PLI) were higher than one (> 1), indicating progressive deterioration of sludge due to metal contamination. The contamination factor (Cfi) of Cd ranged from 11.2 to 28.9 revealed that the examined sludges were strongly impacted by Cd. The Cfi value demonstrated that sludges from tannery, dye, metal processing and battery manufacturing industries were moderately to very high contamination by Cr, Ni, Cu and As. In view of the potential ecological risk (PER), sludges from all industries showed very high ecological risk.