Wastewater irrigation effects on contaminant fate soil quality nutritional traits and human health risks in rice agroecosystems with emphasis on microplastics

Freshwater scarcity, rapid urbanization, and rising agricultural demand have increased interest in wastewater irrigation, especially in water-intensive rice systems. Wastewater reuse can support crop production through nutrient recycling and reduced fertilizer dependence, yet it also introduces a persistent mixture of contaminants into soil–plant systems. This review synthesizes evidence on contaminant fate, soil quality changes, nutritional effects, and human health risks associated with wastewater irrigation in rice agroecosystems, with particular emphasis on microplastics as an emerging pollutant. The reviewed literature shows that wastewater can improve soil fertility, increase nitrogen availability, and increase rice grain protein concentration and, in some systems, yield when wastewater supplies additional plant-available nutrients without excessive salinity or toxic-element loading. However, long-term use may also increase the accumulation of heavy metals, persistent organic pollutants, pathogens, salts, and microplastics. These contaminants can alter soil physical structure, nutrient cycling, and microbial activity, and may eventually enter edible rice tissues. Recent studies have detected microplastic particles in both raw and cooked rice and have identified polymers such as polyethylene (PE) and polyethylene terephthalate (PET), indicating that rice may represent a dietary exposure pathway; however, current evidence remains limited and does not yet establish the contribution of field irrigation relative to processing and packaging. This review adopts a global perspective while using Pakistan and other water-scarce regions as illustrative examples where wastewater irrigation is particularly relevant because of freshwater constraints, limited treatment infrastructure, and growing agricultural demand. The key challenge is not whether wastewater should be reused, but how to make its reuse safer through treatment, monitoring, and crop-specific management. The review concludes that sustainable wastewater irrigation requires stronger treatment infrastructure, standardized analytical methods, field-scale validation, and targeted risk assessment for both contaminants and nutritional benefits.