Determination of heavy metal concentrations and metal fingerprints of sewage sludge from Eastern Cape province, South Africa by inductively coupled plasma - Mass spectrometry (ICP-MS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)

Sewage sludge from Schornville, Zwelitsha and Dimbaza Sewage Treatment Plants (STPs) in the Eastern Cape province, South Africa were analyzed for the heavy metal contents by inductively coupled plasma-mass spectrometry (ICP) while metal fingerprints of the sludge were determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Levels of Cd ranged from 1.1 mg kg^-1 at Zwelitsha STP to 1.9 mg kg^-1 at Shornville STP while the levels of Zn varied between 1600 mg kg^-1 also at Zwelitsha STP and 4100 mg kg^-1 at Dimbaza STP. The levels of Ni also ranged from 37 mg kg^-1 again at Zwelitsha STP to 86 mg kg^-1 at Dimbaza STP while the levels of Cr varied between 70 mg kg^-1 at Zwelitsha. STP) and 120 mg kg^-1 at Dimbaza. STP). The levels of Cu varied between 245 mg kg^-1 at Zwelitsha STP and 441 mg kg^-1 at Dimbaza STP while the levels of Pb ranged from 69 mg kg^-1 at Zwelitsha STP and 365 mg kg^-1 at Dimbaza STP. The fingerprint studies showed that metals like Si, K, Cu, Pt, Ni and Ag probably have natural bedrock sources from the study area while others like Zn, Pb and Cd may have anthropogenic sources in addition to natural sources. Generally, sludge from Zwelitsha STP has the lowest concentration of heavy metals and has the greatest potential for agricultural use while sludge from Dimbaza STP has the highest concentration of heavy metals with the least potential for agricultural use.