Most of the major world governments and organisations, such as the World Health Organisation1 have studied the effects of heavy metals, primarily lead, cadmium, mercury and arsenic on human health. Adverse human health from these compounds is well documented but still ongoing. Whilst heavy metals can be found in nature, the increase of these substances in food can be found through industrial and environmental pollutants.
Naturally Occurring Substances
Lead (Pb), cadmium (Cd), mercury (Hg) and arsenic (As) can be found naturally occurring in soil and can leach into water. Humans have used, and still use these heavy metals in manufacturing:
- Lead was used in petrol, batteries, paints, water pipes and the soldered seams of tin cans.
- Cadmium can be found in batteries, plasticisers, electroplating and pigments.
- Arsenic can be found in arsenic based pesticides, wood preservatives, feed additives and silicon based computer chips.
- Mercury can be found in thermometers, barometers and dental amalgam fillings.
Lead, cadmium and mercury are discharged into the atmosphere by the burning of fossil fuels and other industrial emissions2. Cigarettes provide another airborne source of heavy metals. Once in the air, water and soil, heavy metals are taken up by plants and animals, and into the food chain for humans.
Heavy Metals in the Food Chain
Heavy metals come in elemental, organic and inorganic forms. Some forms are more stable, and/or more soluble, will uptake into food more readily and are more or less toxic than other forms. Some leave the body quicker than others. For example, inorganic arsenic As3+ is soluble and more toxic, than inorganic arsenic As5+. This in turn is also more toxic and soluble than organic arsenic, which has a low solubility, low human intestinal intake and lower toxicity. Humans obtain most of their inorganic arsenic from beverages and rice. The major source of organic arsenic is seafood3.
Mercury comes in elemental, inorganic and organic forms. Inorganic mercury is converted to organic forms in nature. Methylmercury, the most common organic form, is easily absorbed into the intestinal system and readily enters the brain, especially the brain of a developing foetus. Methylmercury is found in fish and other marine animals and in higher amounts in long-lived predator fish4.
Cadmium in food is found in grains, cereals and leafy vegetables, but there is a low absorption rate of about 5% through those sources. Inhalation of cadmium from fumes, dust and cigarettes is absorbed at a rate of greater than 90%.
Methylmercury is excreted from the body at a half-life of 50 days, while cadmium is poorly excreted and suspected to have a half-life of 25 to 30 years. Lead, because of prior use in various substances and as a pollutant, can possibly be found in almost every food product.
Adverse Effects on Human Health
These heavy metals create adverse health effects. Exposure to large concentrations of lead can affect the central nervous system, the kidneys and the immune system. In children, even at low levels, lead is associated with impaired cognitive function, including reduced IQ, behaviour difficulties and other problems.
Ingested cadmium can cause nausea, vomiting, abdominal pain, diarrhoea and haemorrhagic gastroenteritis. Cadmium is a known human carcinogenic. Arsenic can cause constriction of the throat, difficultly in swallowing, severe intestinal pain, vomiting, diarrhoea, muscle cramps, cardiac arrhythmias, cancer, gangrene of feet and coma. 70 to 180 mg or 2 mg/kg of As3+ in a child can be fatal.
Methylmercury’s primary effect is impaired neurological development in foetuses, infants and children. Other possible symptoms are impairment of peripheral vision, speech, hearing, walking and muscle weakness5.
Continuous Standards Reevaluation
Due to the adverse effects of these heavy metals on humans, the regulatory agencies have established maximum standards and guidance to the industry and public. Additionally, these standards are in a constant state of revision because of ongoing studies.
Examples of these standards are:
- Codex Standard 193-19956 revised 2013, which lists maximum levels for lead, cadmium, mercury, arsenic and tin in various food products.
- European Commission Regulation (EC) No. 1881/20067 which establishes maximum levels of cadmium, lead, mercury and tin in various foodstuffs.
- Australian New Zealand Food Standards Code – Standard 1.4.1 – Contaminants and Natural Toxicants8 which establishes maximum tolerances for arsenic, cadmium, lead, mercury and tin in various foods.
Testing for low levels of heavy metals is easy using Inductively Coupled Plasma either coupled with a Mass Spectrometer (ICP-MS) or not. An atomic absorption spectrometer (AAS) test can also be performed at most SGS food laboratories. High Performance Liquid Chromatography (HPLC) with ICP-MS can be used to determine the amount of inorganic or organic heavy metals.
For more information, please visit: SGS Foodsafety
Food Scientific and Regulatory Affairs Manager
SGS North America, Inc.
t: +1 973 461 1493
- WHO - Adverse Health Effects of Heavy Metals in Children
- WHO Europe - Health risks of heavy metals from long-range transboundary air pollution
- EFSA - Scientific Opinion on Arsenic in Food
- FDA - Exposure to Methylmercury in the United States
- US EPA - Mercury Health Effects
- Codex Alimentarius - International Food Standards
- EU Commission Regulation setting maximum levels for certain contaminants in foodstuffs
Australia New Zealand Food Standards Code - Standard 1.4.1 - Contaminants and Natural Toxicants