Use of sewage sludge as secondary fuel in a cement plant: human health risks.

Since 2008, sewage sludge is being used as alternative fuel in a cement plant placed in Vallcarca (Catalonia, Spain). To evaluate the temporal trend of the environmental levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and a number of metals (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, Tl, V, and Zn), as well as the potentially associated human health risks, samples of soil, herbage, and air were collected around the facility, after approximately one year of the permanent partial substitution of fuel. The temporal evolution of the pollutant levels was assessed by comparing the measured concentrations (2009) with those from samples collected in previous surveys (2003 and 2006) at the same sampling sites. The concentrations of PCDD/Fs in herbage and soil were 0.10 and 1.11 ng I-TEQ·kg⁻¹ dw, respectively, values very similar to those found in our previous surveys. For metals, although a clear tendency could not be observed, there were fluctuations through time. In this study, the levels of metals, which had not been analyzed in previous campaigns, were also determined in air, additionally to soil and vegetation. Airborne metal concentrations were similar to those found in other industrial areas worldwide. The human health risks for the population living around the cement plant were comparable to those obtained in previous studies, when petroleum coke was exclusively used as combustible, being in both cases tolerable according to the international standards.