Assessment of the interaction of copper and zinc with cadmium to reduce its toxicity in heavy metal-contaminated river basin soils

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Copper (Cu) and zinc (Zn) serve a dual purpose by providing essential nutrients to plants and reducing cadmium (Cd) toxicity in the soil–plant system. Using Cu and Zn to alleviate Cd toxicity could be an effective and low-cost method for rehabilitating contaminated soils. Two laboratory incubation experiments were conducted to study the interaction mechanisms between Cd and Cu, and Cd and Zn at different application levels in metal-contaminated Typic Haplaquept soil. In the first experiment, 2 g of soil were placed in wide-mouthed test tubes in duplicate, with four levels of Cd (0, 1, 2, and 5 mg kg−1) and four levels of Cu (0, 5, 10, and 20 mg kg−1) added simultaneously. The second experiment used the same levels of Cd with four levels of Zn (0, 5, 10, and 20 mg kg−1). The samples were kept at 50% field water holding capacity and incubated for 0, 7, 15, 30, and 60 days at room temperature (26 ± 1 °C). The study results showed that increasing doses of Cu or Zn significantly and consistently reduced the extractable Cd and increased the soil Cu or Zn content. Over time, a significant reduction in extractable Cd and Zn and an increase in Cu in the soil were observed. Cd concentrations exhibited a gradual decline of 71.8%, 70.2%, 69.8%, and 73.5% at Cu levels of 0, 5, 10, and 20 mg kg⁻1, and 69.2%, 69.6%, 68.0%, and 70.1% at Zn levels of 0, 5, 10, and 20 mg kg⁻1, respectively, averaging a 71.3% and 69.2% reduction over an incubation period from 0 to 60 days. The interactions of Cd with Cu, Cd with Zn, Cu with days, Zn with days, and Cd with days significantly decreased Cd and Zn and increased Cu contents in the soil. The interactions between Cd and Cu, and Cd and Zn in the soil were antagonistic, demonstrating that applying Cu and Zn to the soil effectively counteracted Cd toxicity, supporting healthy plant growth in Cd-contaminated soil. It can be useful in reducing heavy metal pollution in the soils providing a sustainable and economical approach with ramifications for the environment. Using antagonistic interaction of Cd with essential micronutrients such as Cu and Zn, it contributed to soil restoration, diminished bioavailability of toxic metals and further raised the potential for safer agricultural practices in contaminated locations.