Cadmium in Food: Common Sources, Risks, and Regulations

Cadmium is a toxic heavy metal that accumulates in the body over time, potentially leading to kidney damage, weakened bones, and other health issues. Unlike some metals, it has no biological function in humans, making dietary exposure a concern, particularly for those with high intake or prolonged exposure.

Understanding how cadmium enters the food supply can help consumers make informed choices and highlight the role of environmental and regulatory measures in reducing risks.

Food Categories With Elevated Cadmium Levels

Cadmium enters food primarily through plant uptake from contaminated soil and water, as well as bioaccumulation in certain animal-based foods. Some food groups accumulate higher levels due to their growing conditions and biological characteristics.

Leafy Greens

Leafy vegetables such as spinach, lettuce, and kale absorb cadmium from the soil through their shallow root systems. A study in Environmental Science & Technology (2021) found that cadmium concentrations in leafy greens are higher in areas using phosphate-based fertilizers, which often contain cadmium as an impurity. Proximity to industrial zones or polluted irrigation water further increases contamination.

A 2022 European Food Safety Authority (EFSA) survey reported that spinach contained cadmium levels averaging 0.2 mg/kg, contributing significantly to dietary intake in populations consuming large quantities of greens. Washing and peeling do little to reduce cadmium content, as it is absorbed systemically by the plant. Choosing produce from less contaminated regions and diversifying vegetable consumption can help reduce exposure.

Grains And Cereals

Staple grains such as rice, wheat, and oats absorb cadmium from soil and water. Rice, grown in flooded fields, is particularly vulnerable, as anaerobic conditions make cadmium more bioavailable. A 2023 study in Science of the Total Environment found that rice from contaminated areas in China exceeded 0.4 mg/kg, surpassing the Codex Alimentarius limit of 0.2 mg/kg for polished rice.

Wheat and oats can also accumulate cadmium, especially in soils with high phosphate fertilizer use. The EFSA estimates that cereals contribute up to 30% of total cadmium intake in European populations. Choosing grains from regions with stringent agricultural monitoring and incorporating diverse carbohydrate sources can help mitigate exposure.

Seafood

Mollusks such as oysters, mussels, and scallops accumulate cadmium due to their filter-feeding nature, absorbing metals from water and sediment. A 2022 Food and Agriculture Organization (FAO) report found cadmium levels in bivalves ranging from 0.5 to 2.0 mg/kg, significantly higher than most other foods.

Crustaceans like crabs and lobsters also accumulate cadmium, particularly in their hepatopancreas, the detoxification organ. Regular consumption of cadmium-rich seafood can lead to excessive intake, particularly in coastal communities. Regulatory agencies set limits on cadmium levels in seafood, but consumers can reduce exposure by moderating intake and opting for species with lower concentrations, such as salmon or cod.

Nuts And Seeds

Sunflower seeds and flaxseeds are notable sources of dietary cadmium due to their deep root systems, which extract metals from the soil. A 2021 study in Food and Chemical Toxicology found that sunflower seeds can contain cadmium levels exceeding 1.5 mg/kg, significantly higher than most plant-based foods. Sunflowers are sometimes used in phytoremediation efforts to clean contaminated soils, which contributes to their high cadmium uptake.

Other seeds, such as flaxseeds and chia seeds, also accumulate cadmium, though typically at lower levels. A 2020 EFSA dietary exposure study found that frequent consumption of sunflower-based products can significantly contribute to total cadmium intake. Consumers can reduce risk by moderating intake and sourcing products from regions with lower soil contamination.

Soil And Water Characteristics Affecting Uptake

Cadmium accumulation in crops is influenced by soil and water chemistry, which affect its bioavailability. Soil pH plays a key role, with acidic soils (pH < 6) increasing cadmium solubility and making it more accessible to plant roots. A 2022 study in Environmental Pollution found that cadmium uptake in wheat and rice was nearly 50% higher in soils with a pH of 5.5 compared to neutral soils. Liming acidic soils with calcium carbonate can reduce cadmium bioavailability by promoting the formation of insoluble cadmium compounds. Soil organic matter also affects cadmium uptake. Some organic compounds reduce cadmium availability by forming stable complexes, while others enhance mobility. A 2023 meta-analysis in Science of the Total Environment found that soils rich in decomposed plant material had lower cadmium bioavailability, whereas those with high fulvic acid content showed increased solubility. The presence of competing cations, such as zinc, also influences cadmium absorption. Since cadmium and zinc share uptake pathways, higher zinc concentrations in soil can reduce cadmium accumulation in crops. A 2021 study in Plant and Soil found that increasing zinc fertilization in contaminated fields reduced cadmium uptake in rice by 30%. Water quality is another factor, particularly in irrigated agricultural systems. Contaminated irrigation sources, such as those affected by mining runoff or industrial discharge, introduce cadmium directly to crops. A 2022 investigation in Water Research found that rice paddies irrigated with wastewater in parts of South Asia contained cadmium concentrations exceeding 0.3 mg/kg, far above safety limits. The study emphasized the need for stringent monitoring of irrigation water, as heavy metal contamination can persist in sediments.

Industrial Sources Influencing Food Contamination

Industrial activities have led to persistent cadmium contamination in agricultural regions. Mining, metal refining, and manufacturing release cadmium into the environment, with emissions from zinc, lead, and copper smelting contributing significantly to soil and water pollution. A United Nations Environment Programme assessment found that areas near smelters in Eastern Europe and East Asia had topsoil cadmium levels exceeding 5 mg/kg, leading to increased plant uptake. Cadmium persists in soil for decades due to its low mobility under natural degradation processes.

Phosphate-based fertilizers are another major source of cadmium contamination. Phosphate rock, used in fertilizer production, naturally contains cadmium. A 2022 Environmental Science & Technology analysis found cadmium levels in commercial fertilizers ranging from 5 to 100 mg/kg, with higher concentrations in products sourced from North African phosphate deposits. Over time, repeated fertilizer applications increase cadmium bioavailability, particularly in acidic soils. Countries such as Sweden and the Netherlands have set strict cadmium limits in fertilizers, capping concentrations at 20 mg/kg to minimize contamination, though global regulations vary.

Industrial production of batteries, pigments, and plastics also contributes to cadmium pollution through wastewater discharge. Nickel-cadmium battery factories release cadmium-laden effluents into nearby water bodies, where the metal accumulates in sediments and enters irrigation systems. A 2023 case study in the Journal of Hazardous Materials documented cadmium concentrations exceeding 0.8 mg/L in river systems near battery plants in South Asia, far above the World Health Organization’s recommended limit of 0.003 mg/L for drinking water. Contaminated waterways used for irrigation introduce cadmium directly to crops, bypassing soil interactions and increasing uptake in rice and leafy vegetables. Industrial wastewater regulations vary widely, with some regions lacking strict enforcement, exacerbating contamination risks.

Regulatory Guidance For Cadmium Levels

To mitigate health risks, international and national agencies have set maximum allowable cadmium levels in food. The Codex Alimentarius, a global food safety standard-setting body under the World Health Organization (WHO) and the Food and Agriculture Organization (FAO), has established limits such as 0.2 mg/kg for polished rice and 0.3 mg/kg for wheat. These standards guide national policies, though enforcement varies. The European Union imposes lower cadmium limits for infant food products due to children’s heightened vulnerability.

Regulatory agencies monitor cadmium intake by assessing food contamination levels and consumption patterns. The U.S. Food and Drug Administration (FDA) conducts Total Diet Studies to estimate exposure across different age groups, refining risk assessments and informing policy. Similarly, Japan’s Ministry of Health, Labour and Welfare mandates periodic soil and crop testing in regions with a history of cadmium contamination. Some countries require labeling for cadmium-heavy foods, particularly seafood and seeds, to enhance consumer awareness and promote informed choices.