Heavy metals in wastewater-irrigated vegetables are widely above safety limits in Asian hotspots; leafy crops and roots carry the highest burdens, elevating child risk. This review guides HMTC on testing, crop choices, and regulatory alignment.
Authors
- Kaur N, Singh J, Sharma NR, Natt SK, Mohan A, Malik T, Girdhar M. , Environ Sci Process Impacts. 2025
What was reviewed
Heavy metals in wastewater irrigated vegetables were critically reviewed to map contamination patterns, exposure risks, and regulatory relevance for developing Asian countries. Drawing on multi-country studies from India, Bangladesh, Pakistan, and China, the authors compile reported concentrations for cadmium, lead, chromium, arsenic, nickel,mercury, copper, zinc, iron, and manganese in edible tissues, and relate them to international limits and health risk indices.
Who was reviewed
The review compiles populations indirectly through food systems in peri-urban and industrially influenced agricultural zones across South and East Asia. Vegetables most frequently assessed include spinach, amaranth, lettuce, mustard greens, coriander, okra, tomato, brinjal, radish, cabbage, and cauliflower reflecting common market baskets. Exposure modeling repeatedly identifies children as the highest-risk group due to body-weight–adjusted intake. Regional hotspots include the Yamuna floodplain and Lucknow peri-urban belt (India), Dhaka Export Processing Zone and Tangail (Bangladesh), Vehari/Bhakkar and Dera Ghazi Khan (Pakistan), and Suxian and Baiyin (China), where reported levels for Cd, Pb, Cr, As, Ni, Fe, and Mn frequently exceed permissible limits.
Most important findings
| Critical point | Details |
|---|---|
| Leafy vegetables accumulate more metals | Across countries, leafy species (spinach, amaranth, coriander, lettuce, mustards) show the highest edible-tissue burdens; visualizes this gradient (leafy > stalk/root > fruiting types). Brassicaceae often behave as hyperaccumulators, elevating dietary exposure. |
| Roots retain higher totals than edible parts | It demonstrates root>shoot metal totals for As, Cd, Cr, Pb, Fe, Ni, Mn, implying fruiting crops may pose comparatively lower risk than root or leafy vegetables when soils are contaminated. |
| Widespread exceedances of safety limits | Documents numerous exceedances versus Codex/WHO/FAO benchmarks: e.g., Cd often above 0.2 mg/kg; Pb frequently >0.3 mg/kg; Cr above 2.3 mg/kg in many Indian/Bangladeshi sites; Ni >10 mg/kg and Zn >99.4 mg/kg in several locations. Lucknow showed extreme Fe and Mn ranges, with repeated multi-metal exceedances across sites. |
| Source and practice drivers | Irrigating with untreated/industrial effluent, long irrigation duration, acidic soils, high bioavailable fractions, and peri-urban nutrient-rich wastewater use all heighten bioaccumulation; leafy tissue’s larger surface area and high transpiration intensify uptake and deposition. |
| Measurement comparability & targets | It shows the dominant use of AAS/ICP-OES/ICP-MS with nitric-acid digestions, enabling certification schemes to anchor detection limits and method performance requirements for HMTC audits. |
| Site-specific hotspots to prioritize | Consistent hotspots include Delhi–Yamuna floodplain, peri-urban Lucknow (India), Tangail and Dhaka EPZ (Bangladesh), Vehari/Bhakkar and Dera Ghazi Khan (Pakistan), and Suxian/Baiyin (China), where multi-metal exceedances and elevated risk metrics recur. |
| Crop-selection as risk control | Evidence supports risk reduction by favoring lower-accumulating species (e.g., tomatoes, kidney beans, potatoes, cabbage) over high-accumulating leafy types when contamination cannot be fully remediated. |
Key implications
For regulators, aligning national maximum levels with Codex and enforcing effluent limits is primary; HMTC certification should require verified water source quality, soil testing, method-validated product testing, and crop-selection controls. Industry can apply safer crop portfolios, soil pH management, organic amendments, and treated water use. Research gaps include chronic low-dose mixtures and low-cost remediation. Practically, mandate incoming-water audits, quarterly composite produce testing, and hotspot traceability.
Citation
Kaur N, Singh J, Sharma NR, Natt SK, Mohan A, Malik T, Girdhar M. Heavy metal contamination in wastewater-irrigated vegetables: assessing food safety challenges in developing Asian countries. Environ Sci Process Impacts. 2025;27:1747-1767. doi:10.1039/d4em00565a
Heavy metals are high-density elements that accumulate in the body and environment, disrupting biological processes. Lead, cadmium, arsenic, mercury, nickel, tin, aluminum, and chromium are of greatest concern due to persistence, bioaccumulation, and health risks, making them central to the HMTC program’s safety standards.
Cadmium is a persistent heavy metal that accumulates in kidneys and bones. Dietary sources include cereals, cocoa, shellfish and vegetables, while smokers and industrial workers receive higher exposures. Studies link cadmium to kidney dysfunction, bone fractures and cancer.
Lead is a neurotoxic heavy metal for which no safe blood lead level in children has been identified. It contaminates food, consumer goods and drinking water, and exposure is linked to cognitive deficits in children, adverse pregnancy outcomes such as preterm birth and low birth weight, and cardiovascular disease. HMTC’s rigorous lead testing applies ALARA principles to protect infants and consumers and to prepare brands for tightening regulations.
Chromium (Cr) is a widely used metal with significant public health implications, especially in its toxic hexavalent form. The HMTC program’s stricter regulations ensure that chromium exposure is minimized, safeguarding consumer health, particularly for vulnerable populations.
Arsenic is a naturally occurring metalloid that ranks first on the ATSDR toxic substances list. Inorganic arsenic contaminates water, rice and consumer products, and exposure is linked to cardiovascular disease, cognitive deficits, low birth weight and cancer. HMTC’s stringent certification applies ALARA principles to protect vulnerable populations.
Nickel is a widely used transition metal found in alloys, batteries, and consumer products that also contaminates food and water. Oral nickel can trigger eczema flare-ups in people already sensitised to nickel, and EFSA has set a tolerable daily intake of 13 μg/kg body weight based on developmental effects seen in animal studies. EFSA found that high-consuming toddlers and other children generally exceed this intake. Nickel has been measured in placental and umbilical cord blood, and its links to pregnancy outcomes are still being studied, which is why HMTC applies stricter limits to protect vulnerable populations.
Mercury (Hg) is a neurotoxic heavy metal found in various consumer products and environmental sources, making it a major public health concern. Its regulation is critical to protect vulnerable populations from long-term health effects, such as neurological impairment and cardiovascular disease. The HMTC program ensures that products meet the highest standards for mercury safety.