Heavy Metals and Fluoride

Aluminium

Aluminium is the third most common element in the earth’s crust so is widespread in the environment. The main route of exposure to humans is through food but exposure can also occur via medicines which contain aluminium and from drinking water if aluminium compounds have been used in water treatment plants. Aluminium is also found in some additives used in bakery products and confectionery and via aluminium containing food packaging materials and aluminium containing cooking equipment, especially if used for storing acidic or salty foods. There has long been discussion of aluminium toxicity in humans related to the development of dementia and this is discussed further following the link above.

Arsenic

Arsenic is found in varying quantities in food and water around the world in both organic and inorganic forms. Organic arsenic is sometimes called organoarsenic species and includes arsenobetaine, arsenolipids, arsenocholine, and arsensugars, with arsenobetaine being the most prevalent in fish and crustaceans. 

Arsenic concentrations in water can vary from below 10ug/litre to higher than 5000ug/litre in certain regions. The biggest source of total dietary arsenic comes from fish and seafood, but it is mainly present in an organic form. Rice often contains inorganic arsenic at concentrations of 0.1-0.4mg/kg dry weight or higher as it has the ability to accumulate arsenic than other cereals. Arsenic is absorbed via the roots of the plant so contamination depends heavily on the amount of arsenic in irrigation water. In areas of the world where rice is cultivated and the environmental levels are high, dietary exposure can be sufficiently high to be a cause of toxicological concern in terms of cancer incidence. Inorganic arsenic is classified as a category 1 carcinogen by IARC.

Cereal-linked arsenic consumption (from rice, rice products and rice milk alternative) can be a risk, particularly for infants and children. 

Antimony

Antimony is a metal which is found in enamel and can migrate into food from chipped enamel, especially when used to store acidic food. Antimony can accumulate in the body and cause damage to the nervous system.

Cadmium

Cadmium is a natural element in the earth’s crust, but is also distributed through cadmium containing phosphate fertilizers and sewage sludge and smokers are exposed to cadmium from inhalation. Cadmium is widely found in soils and so is therefore present in all foods of plant origin. Most foods have a low content but foods particularly rich in cadmium include mushrooms, oilseeds and cocoa beans. How much is found in foodstuffs of animal origin depends on the cadmium in the animal feed, but it does accumulate in the liver and kidneys. Cadmium is also found in relatively high amounts in crustaceans and bivalve molluscs. Another source of possible exposure is from the use of glazed ceramic vessels for the storage or preparation of foods. Acute toxicity is rare in humans, but intake of food with high cadmium levels leads to gastrointestinal symptoms. Toxicity caused by chronic exposure can lead to renal dysfunction and cardiovascular and bone effects. Cadmium is classified as a carcinogen to humans after chronic inhalation and there is some evidence of an association between cadmium exposure and an increased risk of cancer.

Chromium

Chromium is a metal widely distributed in the environment occurring in rocks, soil and volcanic dust and gases. Chromium can exist in a variety of oxidation states and is a natural dietary constituent present in a variety of foods and also in dietary supplements. Chromium can also be present in drinking water usually as a consequence of industrial pollution. The International Agency for Research on Cancer (IARC) has classified Cr(VI) compounds as carcinogenic to humans (Group 1) with respect to the cancer of the lung and also cancer of the nose and nasal sinuses based on evidence from occupational studies.

Copper

Copper is an essential trace element in the diet but can also have toxic effects. Copper is involved in electron transfer reactions in cellular energy metabolism and other processes. Relatively high copper levels are detected in cereal products, legumes, nuts, cocoa, chocolate, coffee, tea and some green vegetables. Particularly high copper levels may be present in the liver and kidneys of ruminants as well as in fish and shellfish. Drinking water may also be a route of exposure and may be increased by the use of copper pipes and acidic pH in the drinking water.  Whilst the body has a well-regulated system for controlling copper balance in the body (homeostasis) there can be health damage associated with copper in some disease states where copper excretion is disturbed (e.g. Wilson’s disease) and infants are particularly sensitive to an increased copper supply since the capacity of biliary copper excretion by the liver develops fully over the course of the first few years of life.  Early childhood liver cirrhosis may result if infant food is prepared with water contaminated with copper. 

Lead

Lead is everywhere in the environment and exists in compounds in oxidation states +2 and +4. The use of tetraethyl lead in petrol resulted in relatively high concentrations of lead in the blood of the general population through exposure to car exhaust fumes. This has reduced since lead free petrol is now the main fuel used. Food grown near very busy roads is also likely to be contaminated with lead. A further source of substantial exposure may be drinking water in older houses that still contain lead pipes and cases of acute lead poisoning are possible in children from lead containing paint on toys or other objects that peels off and can be orally absorbed with dust.

Lead concentrations are typically between 10-200ug/kg, with food of plant origin containing less lead than food of animal origin. Higher levels of 1mg/kg are sometimes found in offal, mussels, mushrooms and spices. The most important contributors to dietary lead exposure are cereals, vegetables and tap water. If ceramic vessels are filled with acidic food such as fruit juice this may also contribute. Lead causes toxic effects on various organs and lead exposure has been shown to lead to impaired learning and memory functions as well as effects on the kidneys and blood. Lead is classified as a carcinogen.

Children are particularly sensitive to lead exposure and there are known serious consequences to physical and mental development.

Mercury

Mercury is a rare earth element and is the only metal that is liquid at room temperature. Inorganic mercury is transformed into organic mercury compounds by aquatic microorganisms and accumulates in the food chain. Methylmercury is the most serious in terms of toxicity. The most important source of exposure for the general population is the diet, in particular the consumption of fish and other marine organisms. Predatory fish such as tuna fish have the highest amounts of mercury. Acute poisoning with inorganic mercury compounds causes damage to the kidneys and gastrointestinal tracts and there have been examples of acute poisoning of a general population in Japan after inorganic mercury was discharged into an estuary and the fish became contaminated, and in Iraq where grain was contaminated by methylmercury and this le to bread contamination.  Symptoms of mercury poisoning includes effects on the cardiovascular system, kidney toxicity and effects on the nervous system. Effects on the foetus and newborn can be extensive.

There have been recommendations to limit the intake of some fish by pregnant or breastfeeding women, infants and children and these can be found at https://www.nhs.uk/live-well/eat-well/food-types/fish-and-shellfish-nutrition/

Nickel

Nickel is a widely distributed element in nature, occurring in soil and drinking water both naturally and from pollution, from which it enters the food supply. Although nickel is ubiquitous in the environment, its effects on the human body are not fully understood. According to the European Food Safety Authority (EFSA), there is a risk of exceeding the tolerable daily intake of nickel in some infants and children, especially through the consumption of nickel rich foods, including cocoa, chocolate, nuts, and legumes.

Currently, there is a lack of studies assessing the impact of dietary nickel intake on children’s health. EFSA evaluated the risk to health from nickel in food and water in 2020 and highlighted the particular risk to nickel-sensitised individuals and reported that current acceptable limits can be exceeded by infants and toddlers. There is some evidence of developmental toxicity in animal studies and impacts on fertility. 

Tin

Tin is a trace metal that has not been shown to have any essential functions in humans. Its concentration in foods is generally low but tin can be absorbed when foods are canned. The release of tin into a product is reduced if the can is lacquered. Some bioaccumulation has been found in fish and seafood. Humans have reported gastrointestinal symptoms such as pain, diarrhoea and vomiting after consumption of tin contaminated food but generally the risk associated with normal food intakes is considered to be low.

Uranium

Uranium is naturally present in low concentrations in soil, rocks, and water. This means it can be found in food and drinking water, with plants, particularly root vegetables, absorbing it from the soil. Some human activities, like mining and industrial processes, can also contribute to uranium in the environment and subsequently in food and water. Risks associated with uranium in food and water were evaluated by EFSA in 2009. There has been some concern that infant formula made up with some waters could contain high levels of uranium, which is thought to have potential toxic effects on kidney function. The World Health Organization (WHO) has set a guideline maximum level of 15µg/litre for uranium in water, but there is some concern that giving infants infant formula made up with water that has 15µg/litre could result in infants under 6 months consuming up to four times the tolerable dietary intake (TDI) also set by WHO. At the present time there are not thought to be any health concerns to infants related to uranium in infant milk, but the UK COT (the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment) acknowledges that it has little data in this area and the impact of these intakes is uncertain. Some bottled waters may have high levels of uranium and so it is important that, if a bottled water is used to make up a feed, the bottled water should specify that it is suitable for infant formula.

Fluoride

Fluoride is not a heavy metal but is a naturally occurring mineral in the environment which is beneficial to human populations for preventing tooth decay in small amounts, but which can become a contaminant when levels are too high. There has long been controversy about fluoride addition to public water supplies and the evidence related to benefits and potential risks of fluoridation and risks of fluoride contamination.