Mitigating potential of polystyrene microplastics on bioavailability, uptake, and toxicity of micronutrients in Zea mays L.

Abstract

Microplastics (MPs) are widespread in agroecosystems, while the coexistence of MPs and Copper (Cu) contamination in agricultural soils is increasing dramatically with time, thus posing a serious risk to soil-crop interaction. However, little is known about how MPs interact with essential micronutrients in Cu-contaminated soils and their impact on crop growth. To fill this gap, we analyzed the immobilization potential of polystyrene microplastics (PSMPs) for micronutrient bioavailability in soil and assessed Cu uptake, and its toxicity in maize under different Cu and PSMPs concentration. To test the hypothesis, a pot experiment was carried out where maize (Zea mays L.), variety (Islamabad gold) grown in Cu spiked soil with concentrations (0, 50, 100, 200, and 400 mg/kg) and PSMPs (150-250µm) at the concentration (0%, 1%, and 3% w/w) for 60 days. Maize growth indicators consist of height, chlorophyll, fresh and dry weight, while biochemical parameters include antioxidant enzymes (SOD, POD, CAT and APX) activity and oxidative damage (MDA content) was measured in maize root and shoot. Micronutrients in soil and maize tissues were analyzed by atomic absorption spectrophotometry. Results showed that PSMPs positively while Cu application impact negatively on soil pH and other micronutrients (Mn, Zn, and Fe) concentration in post-harvesting soil. The reduction of micronutrients (Cu, Mn, Zn, and Fe) in soil decreased with increasing PSMPs in soil. Morpho-physiological traits showed that maize growth improved at Cu50, and Cu100 mg/kg then declined significantly with further increase in soil Cu concentration as compared to control. Growth traits of maize were enhanced with 3%PSMPs application. PSMPs significantly reduced the uptake of Cu and other micronutrients, while reduced the Cu-induced oxidative stress (MDA) by increasing SOD, POD, CAT, and APX activity in root and shoot particularly at higher Cu concentrations. These findings suggest that PSMPs application in soil can improve maize growth and alleviate Cu-stress, in pot experiment however, their long-term impacts can be focused in the future on soil biota and plant growth performance under field conditions.