Feasibility of Chinese cabbage (Brassica bara) and lettuce (Lactuca sativa) cultivation in heavily metals−contaminated soil after washing with biodegradable chelators

Abstract

Soil washing with biodegradable chelator is a promising technique for treating metal-contaminated soil. However, limited information is available on the effects of such treatments on plant growth and the accumulation of residual metals from remediated soil. Four biodegradable chelators including glutamate–N,N–diacetic acid (GLDA), iminodisuccinic acid (ISA), polyaspartic acid (PASP), and glucomonocarbonic acid (GCA) were employed to remove Cd, Pb, and Zn from polluted soils, and two common vegetables (Brassica bara and Lactuca sativa) were used to verify the fitness of plants grown on the washed soil. The ISA and GLDA demonstrated excellent Cd, Pb, and Zn removal efficiencies (25–85%) compared with GCA and PASP. Moreover, the phytoavailability of soil Cd, Pb, and Zn decreased after washing, and this effect was more pronounced for GLDA than ISA. B. bara and L. sativa grew well in the washed soils but considerably less biomass was produced than by plants grown in unwashed soil. Their photosynthetic capacities, oxidation defense abilities, and nutritional qualities were improved, compared with plants cultivated in the original soils. The ISA and GLDA treatments decreased the Cd, Pb, and Zn concentrations in B. bara and L. sativa shoots but the GCA and PASP treatments had no effect or increased the metal concentrations. B. bara and L. sativa grown in remediated soils were unacceptable for human consumption because the Cd and Pb concentrations in the edible parts were higher than the European legal limits. Soil washing with biodegradable chelators especially ISA and GLDA successfully removed toxic metals and allowed the plants to grow well while decreasing the uptake of metals remaining in the remediated soil.