Screening of accumulating plants in farmland surrounding typical lead and zinc smelting enterprises

As one of the most important lead (Pb) and zinc (Zn) smelting production bases in China, the heavy metal content in the farmland surrounding the enterprises in Jiyuan City of Henan Province seriously exceeded the national standard due to the backward technology and large pollutant discharge. In order to explore the characteristics of heavy metal contamination in farmland around Pb and Zn smelting enterprises in Jiyuan City, select the dominant plants for remediation and safe utilization of heavy metal-contaminated farmland, and establish a preliminary remediation model, field experiments were conducted on farmland surrounding Pb and Zn smelting enterprises in Jiyuan City. The study included investigating the characteristics of cadmium (Cd), Pb, and arsenic (As) pollution in soil, analyzing the heavy metal content in main agricultural products, selecting 17 kinds of heavy metal-accumulating plants for field cultivation, and studying their biomass, heavy metal contents, bioconcentration factor, extraction amount, and remediation efficiency. The results showed that the average content of Cd, Pb, and As in soil was 2.22 mg·kg⁻¹, 173.1 mg·kg⁻¹ and 18.38 mg∙kg⁻¹, respectively, which were mainly distributed in the cultivated layer. Among them, the content of Cd and Pb exceeded the risk screening values in the Environmental Quality Standard for Soils (GB 15618—2018), and the single factor pollution index reached 3.71 and 1.02, respectively. In terms of the wheat and maize cultivated on the contaminated farmland, the content of Cd, Pb, and As in maize seeds did not exceed the values in the National Food Safety Standards (GB 2762—2022), but the Cd and Pb content in wheat seeds exceeded the standards, while the exceeding rates both reached 100%. In plant cultivation experiments, the biomass and heavy metal enrichment capacities of the 17 kinds of accumulating plants differed significantly. The biomass of Amaranthus hypochondriacus was the highest, reaching 29 598 kg·hm⁻², which was 46.61 times that of Noccaea caerulescens (635 kg·hm⁻²). The contents of Cd, Pb, and As in the 17 plant species were 2.90−30.90 mg·kg⁻¹, 7.81−93.07 mg·kg⁻¹, and 3.76−22.90 mg·kg⁻¹, respectively. The bioconcentration factors of Cd, Pb, and As were 1.31 to 13.92, 0.05 to 0.54, and 0.20 to 1.24, respectively. Helianthus annuus ‘S606’ had the largest Cd, Pb, and As comprehensive bio-concentration index of 2.3. Combining plant biomass and enrichment capacity, 17 plant species showed clear differences in the removal efficiency of contaminated soil. Cluster analysis showed that Amaranthus hypochondriacus, Brassica napus ‘Zhongyou 1000’, and Helianthus annuus ‘S606’ had higher Cd and Pb accumulation and remediation capacities in soil. The removal efficiency of these three species was higher than 1.90% for Cd and 0.07% for Pb, showing a promising potential for remediation of Cd and Pb-contaminated soils. In addition, Brassica napus and Helianthus annuus can be further processed to produce edible oil, feed, or fertilizer, which can bring economic benefits while remediating soil. In conclusion, the farmland surrounding the Pb and Zn smelting enterprise in Jiyuan City was typically light to moderately contaminated with Cd and Pb. In response to this situation, two technical modes of heavy metals-contaminated farmland remediation were proposed: Amaranthus hypochondriacus-Brassica napus rotation remediation mode and Helianthus annuus monoculture remediation mode. Both modes can achieve high remediation efficiency and were viable and extendable.