Safe utilization of heavy-metal-contaminated farmland by mulberry tree cultivation and silk production

Heavy-metal-contaminated soil threatens human health and environmental safety. Complete remediation of contaminated soil is expensive; therefore, phytomanagement has emerged as a cost-effective alternative. The current study investigated mulberry tree (Morus alba) plantation, silkworm cultivation, and silk production as phytomanagement options. Results defined the safety of planting mulberry trees in soils with lead (Pb) and arsenic (As) concentrations lower than 369 and 180mgkg^-1, respectively. Silkworms fed with mulberry leaves collected from slightly contaminated soil exhibited productive growth and normal silk production. The silk, silkworm chrysalis, and silkworm fecal matter reached the national standards for textiles, feed, and agricultural sludge, respectively. Based on risk assessment, planting mulberry trees instead of rice significantly decreased the human health risk from contaminated soil. The total carcinogenic risk (Risk_d) and noncarcinogenic risk (HQ_d) derived from mulberry tree plantation and textile production were 2.4×10^-8 and 6.7×10^-5, respectively, whereas those derived from rice plantation and ingestion were 0.44 and 18.4, respectively. Cost-benefit analysis showed that a mulberry tree plantation can yield $25,675 for every 1ha soil, whereas a rice plantation can yield $8409 for the same area. Moreover, phytoextraction requires $50,000-$150,000 to remediate 1ha of soil. Therefore, constructing a mulberry tree plantation with silkworm culture and silk production is a safe means to utilize slightly contaminated soil.