Elsevier

Pedosphere

Volume 32, Issue 2, April 2022, Pages 307-316
Pedosphere

Evaluation of immobilizing agents as soil quality conditioners in addition to their metal(loid) immobilizing effect

https://doi.org/10.1016/S1002-0160(21)60075-9Get rights and content

ABSTRACT

In trace metal (TM)-contaminated agricultural soils, management of TM availability is important for safe crop production. In addition, maintenance or improvement of soil quality is vital for sustainable crop cultivation. Decreased TM phytoavailability and increased soil quality can be achieved by the application of various immobilizing agents to soil, which can supply both macronutrients and organic matter. This study investigated the long-term influences of four common immobilizing agents on soil biogeochemical properties and the phytoavailability of TMs in mixed metal-contaminated soil from a cultivated upland near an abandoned mining site. Lime (L), gypsum (G), fly ash (F), and animal manure-based compost (C) were applied to pots containing contaminated soil, either individually or in combination. After incubation for three years under sequential cultivation of two crops and fallow, soil biogeochemical properties were determined, and Brassica rapa plant bioassay was performed. The phytoavailability of all TMs (both cationic metals and anionic metalloids) remained significantly lower in soils treated with immobilizing agents even after three years, when compared with the no-agent control (CK) soil. In addition, the soil quality was significantly improved by treatment with immobilizing agents. For instance, the C and L + C treatments were the most effective in improving soil physical (bulk density, porosity, and water-resistant aggregate stability), chemical (pH, organic matter, total nitrogen, cation exchange capacity, and plant-available phosphorus, magnesium, and potassium), and biological (microbial biomass carbon and dehydrogenase activity) properties. The improvement of soil properties and lowering of TM bioavailability were also consistent with the most significant increase in B. rapa biomass production observed in the C treatment, followed by the L + C, G + F, L, G, F, and L + G treatments, as compared with that in CK. These results indicate that the function of the TM-immobilizing agent as a soil quality conditioner, in addition to its TM immobilizing effect, should be considered when selecting such agents for agricultural or ecological applications.

Section snippets

INTRODUCTION

Soil contamination by trace metal (TM) poses potential risks to humans, directly through ingestion and indirectly through contact with contaminated soils, the food chain (soil-plant-human or soil-plant-animal-human), and consumption of contaminated groundwater (McLaughlin et al., 2000a). Soil contamination by toxic TMs also threatens food safety and decreases land usability for agricultural production (McLaughlin et al., 2000b; Ling et al., 2007). In addition, TMs affect the soil's ability to

Soil and immobilizing agents

The soil used in this experiment was sampled from a cultivated upland near an abandoned mining site in Gongju, Korea. Topsoil (0–25 cm) was collected and mixed homogeneously prior to pot incubation. The soil texture was sandy loam, and soil concentrations of arsenic (As), cadmium (Cd), and lead (Pb) (Table I) were high, greatly exceeding the local environmental guideline values outlined in the Soil Environmental Conservation Act 2010 (Ministry of Environment, Korea) of 25 mg kg-1 for As, 4 mg kg

Variations in TM phytoavailability

It was observed that all immobilizing agents were effective for at least three years, as evidenced by the significantly lower (P < 0.05) concentrations of As, Cd, Cu, Pb, and Zn in the leaves of B. rapa plants grown in the treatments with immobilizing agent(s) when compared with those in CK (Fig. 1). In particular, gypsum, as a DOC coagulator, was the most effective in metalloid (As) immobilization, whereas lime and fly ash, as pH change-inducing agents, and compost, as a TM sorption agent,

CONCLUSIONS

The role of immobilizing agents in improving soil quality, in addition to their TM immobilization efficiency, must be considered during selection for practical remediation of metal(loid)-contaminated soil. This is because proper soil function is not only influenced by metal(loid) toxicity, but also by other physicochemical and biological properties of soil. Soil quality parameters can directly influence soil productivity, as evidenced by the variation in the biomass of B. rapa plants in

ACKNOWLEDGEMENT

This work was supported by Gyeongsang National University Grant in 2020–2021.

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