Long term urban wastewater irrigation drives zinc bioaccumulation and health risks in contaminated vegetables

Summary

This field study compared zinc accumulation in vegetables irrigated with tap water, canal water, or untreated urban wastewater in Pakistan. Wastewater irrigation led to significantly higher soil and vegetable zinc concentrations, with bioaccumulation factors indicating variable uptake across crops (notably high in Spinacia oleracea). Although current health risk quotients remained below established toxic thresholds, the authors caution that continuous wastewater irrigation drives progressive zinc buildup in soils, posing a long-term food-chain risk requiring regular monitoring and mixed irrigation strategies.

Regional applicability

This study was conducted in Pakistan and reflects irrigation practices and soil conditions in South Asian arid regions. The findings may have limited direct applicability to the United Kingdom, where wastewater irrigation of vegetables is heavily regulated and less common; however, the bioaccumulation mechanisms and monitoring approaches are relevant to UK food safety policy and may inform assessments of any localised wastewater reuse schemes in agriculture.

Key measures

Zinc concentrations in soil and vegetables; transfer factor (TF) values (0.46–1.21); single pollution index (SPI) (0.12–0.93); enrichment factor (EF) (0.2–0.54); geoaccumulation index (Igeo) (−3.628–0.692); health risk index (HRI) (0.06–0.38); target hazard quotient (THQ) (0.014–0.085)

Outcomes reported

The study measured zinc concentrations in soils and vegetables under three irrigation treatments (tap water, canal water, and wastewater), and assessed bioaccumulation through transfer factors and health risk indices. Zinc concentrations differed significantly across irrigation types, with wastewater-irrigated sites showing moderate soil pollution and elevated vegetable contamination, though calculated health risk indices remained below toxic thresholds.

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