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The Concentrations of Heavy Metals and Their Potential Environmental Risks of Sludges from 15 Cities in Yangtze River Delta Region

The presence of heavy metals in the sludge produced in wastewater treatment plants restricts the application of sludges in agriculture. Forty-four sludge samples were collected from 15 cities within Yangtze River Delta region, and the total contents of heavy metals (Cu, Zn, Pb, Cd, Cr, Ni) were investigated. The results demonstrated that the contents of heavy metals in sludge samples varied significantly. The average contents of heavy metals followed an order of Zn>Cu>Ni>Cr>Pb>Cd. Industrial sludges were more polluted than domestic sludge and mixed flow sludge, according to pollutant indexes. The extracted three principal components (PC
 1
, PC
 2
 and PC
 3
, ranked by contribution) indicated good expressions to the initial 6 variables. The cumulative proportion of the three principal components was 82.0%. PCi represented nearly 50% of information of initial variables and mainly contributed to the enrichment of heavy metals. Heavy metals content and measurement should be considered to reduce the potential eco-environmental safety and public health risk associated with the application of sewage sludge.