Abstract
In China, 1/5 of the total farmland area is Cd-enriched; the wide occurrence of Cd-contaminated soil in China has already posed significant public health risk and deserves immediate action. In situ immobilization has been regarded as one of the most promising agricultural extension-technologies for remediating low-to-medium levels of heavy metal contaminated land in China. Although extensive research has been conducted to examine the effectiveness of different amendments on remediation of Cd-contaminated soils, the influence of changed soil properties on secondary release of Cd from Cd-amendment to soil is rarely known. The objective of this study was to evaluate the effectiveness of four soil amendments (denoted as Ad1, Ad2, Ad3 and Ad4, their main components being clay mineral, base mineral, humus and biochar, respectively) on reducing Cd availability and increasing Cd stability in soil. The maximum adsorption capacity of test amendments on Cd ranged from 7.47 to 17.67 mg g−1. The characterizations of test amendments before and after Cd loading provided the evidence that surface precipitation and ion exchange were the main reasons for Ad1 and Ad2 to adsorb Cd, and complexation was for Ad3 and Ad4. In addition, there was significant increase in the desorption percentages of Cd from amendments as pH decreased (from 7 to 1) or ion strength increased (from 0 to 0.2 M). Comparatively, Ad3 and Ad4 could be more effective for in situ immobilization of Cd in contaminated soils, due to their high adsorption capacities (12.82 and 17.67 mg g−1, respectively) and low desorption percentages (4.46–6.23%) at pH from 5 to 7 and ion strengths from 0.01 to 0.1 mol L−1. The results obtained in this study could provide a guideline for in-situ remediation of Cd polluted field-soil in China.
Highlights
Soil heavy metal contamination is regarded as one of the most severe environmental issues globally due to its elusive invisibility, persistence and irreversibility, as well as high-toxicity [1,2,3,4,5]
In China, more than 100 million ha of land are contaminated by heavy metal, and, among all inorganic pollutants, the over-standard rate of Cd is up to 7.0% [2,3]
A total of 13,300 ha arable land in China was found to be polluted with Cd, leading to a decline of 1000 tons crop yield every year, resulting in potential pollution of grains and a high health risk [12,13]
Summary
Soil heavy metal contamination is regarded as one of the most severe environmental issues globally due to its elusive invisibility, persistence and irreversibility, as well as high-toxicity [1,2,3,4,5]. In China, more than 100 million ha of land are contaminated by heavy metal, and, among all inorganic pollutants, the over-standard rate of Cd is up to 7.0% [2,3]. After its import into agro-ecosystems, it affects the agricultural environment quality, and the yield and safety of rice, vegetables and fish, and it threatens the health of animals and humans through the food chain [7,8,9,10]. A total of 13,300 ha arable land in China was found to be polluted with Cd, leading to a decline of 1000 tons crop yield every year, resulting in potential pollution of grains and a high health risk [12,13]
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