Trace Metals in Surface Soil Contaminated by Release of Phosphate Industry in the Surroundings of Sfax-Tunisia

Abstract

There is a worldwide growing concern about soil pollution caused by phosphate industry creating thus large amounts of phosphogypsum slurry. This slurry is piped from the processing facilities up into acidic wastewater ponds that sit atop the mountainous waste piles known as gypsum stacks. This issue is of special interest because of toxic metals threats to groundwater tables as well as to the surrounding environment.

There is a worldwide growing concern about soil pollution caused by phosphate industry creating thus large amounts of phosphogypsum slurry. This slurry is piped from the processing facilities up into acidic wastewater ponds that sit atop the mountainous waste piles known as gypsum stacks. This issue is of special interest because of toxic metals threats to groundwater tables as well as to the surrounding environment.

The aim of the present work is to assess the level of trace elements content in soil around stocked solid waste “a phosphogypsum” derived from a former phosphate fertilizers factory and to investigate their factors of variation. Twenty soil samples were collected at the depths of 20 cm and analyzed for their physicochemical properties, the content of their major elements (Ca, Mg, K, Na, Al, Fe, Mn), and some trace elements such as Zn, Pb, Cr, Cu, Co and Ni. Data were processed with multivariate statistical analysis in order to investigate relationships among the trace elements and the factors controlling their distribution in the phosphogypsum surrounding environment. Enrichment factors (EF) were calculated to assess either natural and/or anthropogenic origins. The results indicate moderate levels of contamination and big differences in variability among elements. The maximal and mean concentrations found in soil, except the soil sample S5.1, were 95.2 and 36.5 mg Kg^-1 for Zn, 75.2 and 30.23 mg Kg^-1 for Pb, 28.4 and 17.5 mg Kg^-1 for Cr, 61.9 and 15.6 mg Kg^-1 for Cu, 5.28 and 2.7 mg Kg^-1 for Co, and 13.2 and 6.4 mg Kg^-1 for Ni.  Most of the elements were positively correlated with pH and cation-exchange capacity, and no correlation with total organic carbon  and electrical conductivity except for Cu, Zn and Pb was found. The EF values of the most trace metals were higher than 1.5 indicating that the phosphate fertilizer industry had an anthropogenic effect causing a negative impact on the environment. The relatively increased amount of toxic metals in the examined soils requires the area to be controlled since a variety of agricultural activities are conducted nearby moreover the surroundings are programmed to be residential zones.

DOI: http://dx.doi.org/10.5755/j01.erem.65.3.4865