Influence of different organic geo-sorbents on Spinacia oleracea grown in chromite mine-degraded soil: a greenhouse study

Abstract

Purpose

Potentially toxic element (PTE) concentrations in mine-degraded soil and their bioaccumulation in food crops is a public health concern worldwide. The current study investigates the influence of organic geo-sorbents including biochar (B), farmyard manure (FYM), and peat moss (PTM) on PTE in chromite mine-degraded soil and their subsequent effects on spinach biomass, PTE uptake, average dietary intake (ADI), and health risk (HRI) associated with PTE via spinach consumption.

Materials and methods

Chromite mine-degraded soil samples were collected from different mining sites in Kohistan region. Pot experiments were carried out in the greenhouse environment. The selected geo-sorbents (B, FYM and PTM) were mixed at application rates of 1%, 2%, and 5%. Contaminated soil without geo-sorbents (control treatment) was also included in each batch of the experiments. Local FYM and PTM were used in this experiment, while B was provided by the Institute of Urban Environment (CAS) Xiamen, China. The total carbon (C), total nitrogen (N), and total sulfur (S) contents in mine-degraded soil and organic geo-sorbents were measured using a macro-elementor (VarioMax CNS, Germany). Total (acid digestion) and bioavailable PTE (As, Cd, Cr, Ni, Zn, and Pb) concentrations in mine-degraded soil and spinach were determined using inductive coupled plasma mass spectrophotometer (ICP-MS 7500 CX, Agilent Technologies, USA).

Results and discussion

The addition of organic geo-sorbents effectively immobilized the PTE concentrations in mine-degraded soil, and increased the major nutrient contents and thereby reduced the bioaccumulation of PTE (Cr, As, Ni, Cd, Zn, and Pb) in spinach. Consequently, B2, B5, FYM2, FYM5, PTM2, and PTM5 amendments significantly (p < 0.001) increased the biomass, whereas the B1, FYM1, and PTM1 addition showed no significant increase in spinach biomass as compared to the control treatment. The results showed that all the organic geo-sorbents had significantly (p < 0.001) reduced the As uptake in spinach, while B2, B5, FYM2, FYM5, and PTM5 significantly (p < 0.001) decreased PTE bioaccumulation as compared to the control treatment.

Conclusions

The highest application rate (5%) showed the best result in increasing the spinach growth and biomass as well as reducing the PTE mobility in soil, and their bioaccumulation in spinach, as compared to 1% and 2% application rates and also with the control treatment. Furthermore, the average dietary intake (ADI) of PTE and health risk indices (HRIs) reduced via spinach consumption for both the children and adults, due to the addition of selected organic geo-sorbents used for soil amendments.

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