Correlation between chemical fractionation of heavy metals and their toxicity in the contaminated soils

One of the major environmental problems is to accumulate heavy metals in the soil, which can be hazardous while transferring the heavy metals to plants or water. The study aims in understanding fractionation, distribution, mobility as well as the toxicity of lead (Pb), nickel(Ni), cadmium(Cd), copper (Cu) and zinc (Zn) in contaminated soils of Tehran province, Iran. The total concentrations of Pb, Ni, Cd, Cu and Zn in the 18 samples were determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The fractionation of Pb, Ni, Cd, Cu and Zn in these soils have also been ivistigated using a sequential extraction method to assess their possible mobility, bioavailability and toxicity. Accordingly, five chemical fractions of heavy metals under study have been described, including exchangeable (F-1), carbonate (F-2), organic (F-3), Fe-Mn oxide (F-4) as well as residual (F-5). The highest Pb, Ni, Cd, Cu and Zn concentrations were found in the residual fraction. Actually, the distribution and fractionation of Zn and Cu were same in this study. The distribution pattern of Cd and Pb indicated theses heavy metals are strongly associated with the Fe-Mn oxide fraction in all soils. Our results indicated significant correlations between Eh, pH, clay, silt content, and organic matter and retention of all heavy metals. Then, microbial and enzymatic toxicity experiments have been performed to evaluate heavy metal toxicity in the environment (MetPLATE (TM)); a correlation (r(2) = 0.991) was obtained between toxicity and total heavy metal concentration in this research. The recovery percent of the all heavy metals studied were above 90. The highest and lowest mobility factor values were calculated to be 23.8 and 4.4 percent for Cd and Zn, respectively. These findings, therefore, show the highest risk of mobilization of heavy metals and their potential toxicity. They could represent risk of pollution of ground water, influenced food chain and become an environmental risk.

Automated summary

The study focused on fractionation, distribution, mobility, and toxicity of lead, nickel, cadmium, copper, and zinc in contaminated soils in Tehran province, Iran. Results showed correlations between soil factors such as Eh, pH, clay, silt content, and organic matter with heavy metal retention. Heavy metals were strongly associated with the Fe-Mn oxide fraction, indicating potential risk of pollution of groundwater and food chain contamination.