Fabrication of Multifunctional Starch Mulch Film for Remediation of Pb(II)/Cr(VI) and Slow Release of NH ₄ ⁺ in Soil

White pollution, excessive heavy metals, and fertilizer leaching have become key issues restricting the development of agriculture. In this work, we prepared multifunctional starch mulch film (SMF/MAP/FeS) by loading ferrous sulfide (FeS) and monoammonium phosphate (MAP) onto commercial starch mulch film using poly(vinyl alcohol) for bonding. The removal efficiencies of Pb(II)/Cr(VI) for SMF/MAP/FeS could reach 97% and 93% in the aqueous solution. The adsorption isotherm, thermodynamic, and kinetics studies indicated that the adsorption process was an endothermic multimolecular-layer chemisorption. The main removal mechanisms for Pb(II)/Cr(VI) of SMF/MAP/FeS were precipitation and redox reactions. In addition, SMF/MAP/FeS not only possessed great thermal insulation and moisturizing properties but also could realize the slow release of NH₄⁺. Furthermore, the maximum release rate of NH₄⁺ for SMF/MAP/FeS could reach 93.4% during Pb(II)/Cr(VI) removal. At the same time, SMF/MAP/FeS has a good degradability at 50 d. A pot experiment indicated that SMF/MAP/FeS had a detoxifying effect on the Pb(II)/Cr(VI)-contaminated soil to promote the growth of pakchoi. Therefore, this study not only solves the problem of plastic and heavy metal pollution but also realizes the slow release of nutrients.