Abstract
Scarce management of solid wastes, excessive wastewater discharge and irrigation with noxious water are among the main causes of heavy metal contamination in agricultural soils. The soils of upper Litani basin in Lebanon are subjected to these sources, beside soil irrigation by Litani river water, contaminated by wastewater. However, the metal mobility, bioavailability, or potential risk can be elucidated by metal soil and water chemical speciation. This study involved the metal speciation in soils of the upper Litani basin, and computation of pollution indices for risk assessment. A modified BCR sequential extraction technique was implemented to soil samples that operationally extract metals sequentially from fractions termed as acid soluble, reducible, oxidizing, and residual. Beside, soil pH, Eh and TOC, macro-water parameters, and metal water content were measured. The geochemical computer model PHREEQC was used to predict water metal species. Data indicated that Mn, Zn, Cr, and As had their highest average percentage from total metal in the reducible and acid soluble soil fractions, while Cu, Ni, Cd, Hg were in the oxidizing and acid soluble soil fractions. Metal speciation was related to TOC, Eh and water BOD. The average values for the indices indicated: enrichment factor and geo-accumulation of severe enrichment and very strong contamination for Cd and Hg; risk assessment high risk for Cr, Ni, and Cd; and 50% of sites suffered from considerable contamination according to the global contamination factor. The highest percentage of water species were for Mn, Zn, Ni, and Cd, the free metal aqua ion.
Published Version
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