A field study of nano-FeS loaded lignin hydrogel application for Cd reduction, nutrient enhancement, and microbiological shift in a polluted paddy soil

Cadmium (Cd) pollution in paddy soil has caused serious harm to human health. Nano-ferrous sulfide@lignin hydrogel (FeS@LH) composites could be an ideal material for paddy soil Cd removal due to the excellent adsorption performance and mechanical strength. But the FeS@LH’s performance in a paddy field remains unclear. In this study, FeS@LH was applied to a Cd-contaminated paddy field when planting water spinach (Ipomoea aquatica Forssk). The results showed that FeS@LH effectively removed Cd from the soil (37.6 %) and water spinach (34.5 %) after 30 days. The concentrations of Pb, Zn, Cu, and other metals in soil and water spinach were co-reduced. When the FeS@LH dosage was 30 g·m−2, the effective functional distance was within 30 cm. FeS@LH application had a positive effect on soil nutrients. The soil nitrogen and organic matter contents increased by 16.1 % and 13.8 %, respectively. No significant effect on soil total phosphorus and potassium contents was presented. The survival rate of zebrafish in the acute toxicity test of FeS@LH was 98.9 %, indicating its biosafety. In addition, FeS@LH application decreased soil microbial community diversity probably due to the decreased pH. The microbial metabolism tended to enhance, suggesting a restoration of soil microbial community function after Cd removal.