Naturally occurring or anthropogenic heavy metals are known to accumulate in the human body and can reach toxic levels. Sources and concentrations of heavy metals in the food chain have been a topic of scientific interest for many years, as has the question of where the elements ultimately end up. The presence of heavy metals and other trace elements in phosphate rock and phosphate-based fertilizers has long been known, and is a cause for concern. Around sixteen elements that are potentially hazardous for human health are known to be associated with phosphate rock and phosphate-based fertilizers [1]. Cadmium (Cd) has been the source of greatest concern, followed by arsenic, lead and chromium. These elements may enter the food chain when fertilizers are applied to the soil, and have the potential to create risks to human health.

Human health risks

For non-smokers, the area of greatest concern in terms of long-term exposure to elevated levels of Cd is from dietary intake. An increase in consumption of crops grown in Cd-contaminated soils or drinking water may lead to accumulation of toxic levels in the body. Human Cd toxicity was first reported in the 1950s in Japan. The health hazard became known as Itai-Itai disease and resulted from the consumption of rice grown in a contaminated floodplain downstream of lead-zinc mining activities.

Cadmium in soils may come from a number of different sources, including high naturally-occurring background levels, atmospheric deposition, sewage sludge or phosphate-based mineral fertilizers (see environmental/or what are fertilizer section). It has been argued that, depending on the region, increasing Cd levels in soils may be primarily related to the application of high-Cd phosphate-based mineral fertilizers. Monitoring Cd content in soils and water, as well as in input sources, are thus an important step to determine whether adverse health effects may occur. The most relevant factor for Cd uptake in plants is soil pH. Established agricultural management practices include liming, which increases Cd adsorption in soil and thus reduces its bioavailability for uptake by plants.

Dietary exposure to cadmium

Food products have been found to contain different levels of Cd. More recent assessments by the European Food Safety Authority show that milk contains the smallest amount of cadmium (1 mg/kg) [2]. Meat, fish and fruit can contain from 1 to 50 mg/kg, whereas wheat, rice and potatoes from 10 to 300 mg/kg. The highest cadmium content (100-1000 mg/kg) is found in the inner organs of animals (kidneys and liver), in certain types of mussels as well as in deep-sea scallops and oysters. Certain crops, such as rice, can accumulate over 1000 mg/kg of cadmium when cultivated on contaminated soil.

Table 1: Key sources of cadmium in food products, by countries, according to Chunhabundit (2016) [4]
Country No. 1 No. 2 No. 3
USA Deep-sea scallops and other seafood (15%) Bread and foods that contain wheat (11%) Potatoes (5%)
Korea Rice (31%) Fruits (28%) Vegetables except potatoes and legumes (18%)
Europe Grain crops (27%) Vegetables (16%) Meat and meat products (8%)
Sweden Bread (33%) Potatoes (18%) Grain crop foods, except bread (15%)
Hong-Kong Vegetables (31%) Fish and seafood (26%) Grain crop foods (21%)
Vietnam Rice (90%) - -
India (Vadodara, Gujarat state) Grain crop foods (31%) Curd [3] (20%) Fruits (17%)
China Meat (33-41%) Rice (27-41%) Vegetables (12-16%)

For the European Union, the European Food Safety Authority (EFSA) has established a guideline value for weekly Cd intake of 2.5 μg Cd/kg b.w. (body weight), which is lower than the WHO/FAO provisional health-based guidance value for tolerable monthly intake level of 25 μg Cd/kg b.w. [5, 4]. EU-wide risk assessments found that highly exposed groups of the population such as children, vegetarians or smokers may exceed this level by up to two-fold [5, 6]. Because the mean dietary exposure in the EU is close to or slightly exceeding the tolerable weekly intake level, EFSA recommends reducing exposure.

It has been suggested that the most efficient measure to deal with hazardous contents of phosphate-based mineral fertilizers such as Cd would be to implement technologies that exist today in order to purify the fertilizers during the production process. This would prevent them from being widely dispersed into the environment in concentrations that can negatively affect soil fertility, water quality and eventually human health.

  1. Van Kauwenbergh, S. (2009). Heavy metals and radioactive elements in phosphate rock and in fertilizer processing, p. 1-58. [return]
  2. EFSA (2009). Cadmium in food. Scientific opinion of the Panel on Contaminants in the Food Chain (CONTAM). European Food Safety Authority. EFSA Journal 980, 1-139. Available online: http://www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/980.pdf [return]
  3. Indian dairy product [return]
  4. Chunhabundit, R. (2016). Cadmium Exposure and Potential Health Risk from Foods in Contaminated Area, Thailand. Toxicological Research 2016;32:65−72. Available online: https://doi.org/10.5487/TR.2016.32.1.065 [return]
  5. EFSA (2012). Cadmium dietary exposure in the European population. European Food Safety Authority. EFSA Journal 2012;10(1):2551. http://www.efsa.europa.eu/en/efsajournal/doc/2551.pdf [return]
  6. ECB (2007). European Union Risk Assessment Report. Cadmium Metal. Part II Human Health. European Chemicals Bureau, p. 1-705. Available online: https://echa.europa.eu/documents/10162/4ea8883d-bd43-45fb-86a3-14fa6fa9e6f3 [return]

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