Synergistic effect of arsenate and microplastics and its toxicity mechanism on lettuce

Abstract

Arsenate (As(V)) and polystyrene microplastics (PS MPs) in irrigation water have become significant environmental concerns. This study investigates the combined effects of PS MPs and As(V) and its toxicity mechanism on lettuce (Lactuca sativa). The adsorption experiments showed that As(V) was adsorbed by PS MPs, which enhanced its uptake by lettuce. The adsorption capacity decreased by 4.6 % as the temperature increased from 15 °C to 35 °C, with the highest adsorption occurring at 15 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed reduced binding energy of carboxyl (-COOH) groups on PS MP surfaces after As(V) adsorption, indicating that carboxyl groups are key sites for As(V) binding and accumulation. In the V1P30 and V10P30 treatment groups, co-exposure to As(V) and PS MPs significantly reduced lettuce root length (by 42.8 %) and leaf weight (by 56.2 %) compared to the V1 and V10 groups exposed to As(V) alone. Catalase (CAT) activity in the V10P30 group increased by 203.7 %, reflecting a marked increase in oxidative stress due to the combined exposure. Nutrient analysis showed that As(V) exposure in the V10 group increased magnesium (Mg) content by 50 % and calcium (Ca) content by 240 %. In contrast, in the V1P10 group, potassium (K) content increased by 65 %, while iron (Fe) content decreased by 58.8 %, indicating a significant nutrient imbalance caused by the presence of PS MPs. Nitrite content in the V10P10 group increased by 1.52 times, while soluble protein and vitamin C contents decreased by 36.2 % and 24.3 %, respectively, pointing to a reduction in the plant's nutritional quality due to co-exposure. Metabolomic analysis revealed that co-exposure to As(V) and PS MPs enhanced glutathione (GSH) synthesis and improved membrane stability by upregulating metabolites involved in antioxidant defense and osmotic regulation. This study demonstrates that PS MPs enhance the toxicity of As(V) in lettuce by facilitating its uptake and disrupting nutrient balance, leading to increased oxidative stress and alterations in metabolic pathways. These findings provide new insights into the environmental risks of contaminated systems and offer implications for future pollution management strategies.