Characterization of heavy metal in soils as affected by long-term irrigation with industrial wastewater

Investigation of heavy metals (HM) fractions in soils irrigated with wastewater (WW) would ascertain their bioavailability and contamination level in soils. This study investigated HM fractions in soils after long-term WW irrigation. WW irrigation profoundly affected HM fractions in soil. The ranges of HM concentrations in soils irrigated with WW were apparently wide. All fractions were significantly higher in the fields irrigated with industrial WW than rain-fed fields. HM concentrations varied in the soils as Pb > Cu > Ni > Zn > Fe > Cd > Mn after WW irrigation. In rainfed fields, HM concentrations differed in soils as Fe > Zn > Mn > Pb > Cd > Cu > Ni. The HM fractions were dominant in the residual form followed by oxides bound and carbonate associated fractions in WW-irrigated soils. Lower contents of HM in the soil were obtained in the exchangeable fraction. WW irrigation resulted in the transformation of HM into different fractions as residual > oxide associated > carbonate associated > organically bound > exchangeable form. Repeated WW irrigation increased pH values of the soils. The higher EC of soil indicated an accumulation of salts in the soils due to WW irrigation. Mitigation of HM contamination in Hattar industrial effluent is required before irrigation.