Chromium contamination in paddy soil-rice systems and associated human health risks in Pakistan Original paper

What was issued?

Researchers reported a national assessment of chromium contamination in paddy soil–rice systems in Pakistan and linked the findings to human health risk from rice intake. I review this as policy-ready evidence on chromium contamination in paddy rice and show how plants, certifiers, and regulators can act on it. The team collected 500 paired soil and plant samples across Punjab and Sindh, modeled drivers of grain chromium with geographically weighted regression, and set site-specific soil “critical thresholds” that keep grain below the allowable limit. The work benchmarked rice grain against the China National Food Standard limit of 1.0 mg/kg and benchmarked soils against China’s agricultural soil standard GB 15618-2018, which sets pH-based screening values near 250–350 mg/kg and a natural background value of 90 mg/kg. Pakistan lacks its own chromium limits for rice and paddy soils, so the authors used these external cutoffs to frame risk and to guide control points for growers, mills, and public agencies.

Who is affected?

Growers in Punjab and Sindh face the highest near-term exposure through crop uptake. Rice mills, packers, exporters, and certification bodies face specification risk when grain chromium exceeds 1.0 mg/kg. Urban and peri-urban consumers who rely on rice as a staple face long-term intake exposure, though current hazard quotients indicate low non-cancer risk. Provincial agriculture and environment agencies, food safety authorities, and third-party certifiers that audit GAP, HACCP, and GFSI schemes also face alignment needs because national limits remain absent while international buyers enforce strict specifications at import.

Most important findings

The study measured widespread elevation of chromium in the rice chain and mapped strong spatial heterogeneity that hinges on soil pH, soil organic matter, and plant tissue chromium. Ninety-seven point four percent of rice grain samples exceeded 1.0 mg/kg, while 62.6% of soils exceeded the 90 mg/kg background value but stayed below the pH-dependent 350 mg/kg screening value. The model set site-level soil critical thresholds that keep grain at or below 1.0 mg/kg and showed that 38.4% of soils already exceed those thresholds, which signals direct crop risk in many Punjab districts. The loading-capacity analysis flagged very high risk in 38.4% of sampled locations where soils provide no remaining buffer to prevent grain exceedances. Despite those exceedances, the calculated average daily dose and total hazard quotient for adults and children stayed well below one, which signals low non-cancer risk at current rice consumption rates in Pakistan; the exceedances still matter for trade compliance and for cumulative exposure control. The analysis also showed stronger grain sensitivity where pH trends lower and where shoots carry higher chromium, which points to practical controls that raise soil pH and limit plant translocation.

Key implications

Growers and mills should set chromium as a critical hazard in rice HACCP plans, test polished rice lots for chromium against a 1.0 mg/kg internal action level, and segregate or reject grain that fails. Agronomy teams should raise soil pH toward neutral with liming where feasible, manage organic matter to reduce chromium mobility, adjust irrigation to support reducing conditions that favor Cr(III) over Cr(VI), and favor cultivars with lower translocation to grain. Buyers should embed farm-origin mapping and simple pH screening into supplier approval so they avoid very high-risk zones. Regulators should publish national rice and soil limits that align with trading partner standards, adopt a surveillance plan that targets Punjab hot spots, and publish a soil guideline that mirrors the study’s critical-threshold approach. Certification bodies should reference the model’s drivers in auditor checklists, require proof of grain testing where local soils exceed the background value, and verify pH management practices. These steps cut grain exceedances now, protect market access, and prepare for future cross-border harmonization.

Citation

Ali, W., Zhang, H., Mao, K., Shafeeque, M., Aslam, M. W., Yang, X., Zhong, L., Feng, X., & Podgorski, J. (2022). Chromium contamination in paddy soil-rice systems and associated human health risks in Pakistan. Science of The Total Environment, 826, 153910. https://doi.org/10.1016/j.scitotenv.2022.153910