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Spatial insights into microplastics and heavy metals levels, and risks in wastewater irrigated surface soils of Okara, Pakistan: Microplastics sizes impacts on heavy metals distribution using structure equation model
Summary
Researchers mapped microplastic and heavy metal contamination in wastewater-irrigated farm soils in Okara, Pakistan, finding 1,850 to 5,300 microplastic particles per kilogram of soil. Statistical modeling showed that microplastic levels significantly influenced how heavy metals were distributed in the soil. While current health risks were estimated to be low, the study highlights that using wastewater for irrigation introduces both microplastics and heavy metals into agricultural soil, where they could eventually affect food safety.
Pakistan's freshwater shortage and climate events have caused soil nutrient leaching, prompting cities to adopt wastewater irrigation. This study investigates wastewater as a potential source of microplastics (MPs) and heavy metals (HMs), assessing contaminant levels in wastewater-irrigated surface soils (WISS) in district Okara, Pakistan. It further explores potential ecological and human health risks associated with HMs in soil and the impact of MPs on HMs distribution and physicochemical properties. The concentrations of HMs in WISS were within permissible limits (Cd: 0.48, Cu: 17.99, Zn: 29.73, Pb: 19.65, Fe: 8559.5), except for Mn, which was 182.94 mg/kg. MPs abundance ranged from 1850 to 5300 particles/kg, with the most common physical characteristics being fragment shapes (49.6%); black color (40.1%), and small sizes (<500 μm) many physical properties depicted association with HMs and MPs sizes. The structural equation model (SEM) showed a significant impact of MPs on HMs distribution, risk index, and pollution load index, but no significant relationship with physicochemical properties. The pollution indices for HMs in WISS indicated low ecological risk and negligible non-carcinogenic health risks were predicted for both adults and children. However, regular monitoring, enforcement of management and implementation plans, and remediation strategies for HMs and MPs in WISS are highly recommended.