Immobilization of hexavalent chromium in contaminated soil by nano-sized layered double hydroxide intercalated with diethyldithiocarbamate: Fraction distribution, plant growth, and microbial evolution.

Soil contamination by hexavalent chromium (Cr(VI)) poses great risks to human health and ecosystem safety. We introduced a new cheap and efficient layered double hydroxide intercalated with diethyldithiocarbamate (DDTC-LDH) for in-situ remediation of Cr(VI)-contaminated soil. The content of Cr(VI) in contaminated soil (134.26 mg kg) was rapidly reduced to 1.39 mg kg within 10 days by 0.5% of DDTC-LDH. This result attains to or even exceeds the effectiveness of most of reported soil amendments for Cr(VI) removal in soils. The production cost of DDTC-LDH ($4.02 kg) was relatively low than some common materials, such as nano zero-valent iron ($22.80-140.84 kg). The growth of water spinach became better with the increase of DDTC-LDH dose from 0% to 0.5%, suggesting the recovery of soil function. DDTC-LDH significantly altered the structure and function of soil microbial communities. The species that have Cr(VI)-resistant or Cr(VI)-reductive ability were enriched in DDTC-LDH remediated soils. Network analysis revealed a significant functional niche differentiation of soil microbial communities. In addition to the enhancement of Cr(VI) reduction, the stimulation of plant growth promoting traits, including siderophore biosynthesis, oxidation resistance to reactive oxygen species, and phosphorus availability by DDTC-LDH was another essential mechanism for the immediate remediation of Cr(VI)-contaminated soil.