Effectiveness of Toxicity Characteristics Leaching Procedure for Assessing Metal Hazards of Polluted Soils in Relation to Human Health

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Abstract
In view of scarcity of information, effectiveness of toxicity characteristics leaching procedure (TCLP) in assessing metal hazards of polluted soils was evaluated in relation to human health. Total metal content in the soils studied were 1657 ± 2335 mg kg−1 for Zn, 351 ± 180 mg kg−1 for Cu, 166 ± 79.9 mg kg−1 for Ni, 249 ± 269 mg kg−1 for Pb and 18.6 ± 23.2 mg kg−1 for Cd. The TCLP requires a buffering of acidic leaching extraction based on the soil reaction. The TCLP extractable (reagent 1) metal content was varied as 177 ± 376 mg kg−1 for Zn, 10.9 ± 28.5 mg kg−1 for Cu, 23.1 ± 67.2 mg kg−1 for Ni, 2.79 ± 10.3 mg kg−1 for Pb and 4.92 ± 16.3 mg kg−1 for Cd across the experimental soils. Reagent 2 extractable Zn, Cu, Ni, Pb and Cd were recorded as 136 ± 364, 3.16 ± 1.79, 1.49 ± 2.73, 0.57 ± 2.20 and 1.95 ± 6.92 mg kg−1, respectively. In case of spinach, the values of hazard quotient (HQ) varied from 0.055 to 0.972, 0.002 to 0.019, 0.008 to 0.181, 0.066 to 5.489 and 0.044 to 11.32 in respect of Zn, Cu, Ni, Pb and Cd, respectively. The ranges of HQ for intake of Zn, Cu, Ni, Pb and Cd through consumption of wheat grain were 0.36–1.88, 0.02–0.12, 0.05–0.80, 0.13–1.21 and 0.10–59.5, respectively. While comparing the effectiveness of assessing metal hazard of TCLP with that assessed in terms of HQ, it is clear that in some soil samples the critical value of HQ (>0.5) exceeded for Pb (spinach), whereas TCLP extractable Pb content in those soils were within the safe limit i.e. −1. It appears that TCLP method is not only useful for judging the ecological risk of metal polluted soil but also assessing the suitability of soil for crop production, provided permissible limit of TCLP should be revised.

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