Various studies highlighting the potential hazards posed by modern society’s industrial over-reliance on heavy metals have led to an important public and scientific debate on their use in numerous different sectors. Heavy metals can accumulate both in the environment and living organisms, and some can pose a significant public health risk. Once again under the spotlight, legislators are responding in turn.
A 2019 report by the European Environmental Agency entitled the “Contaminants in Europe’s Seas” underscored the growing environmental threat posed by artificial contaminants and their ubiquity in natural environments due to the consumptive demands of modern society. The report highlights in particular the threat of heavy metals as potentially hazardous substances. Two years on, and the European Commission’s ‘Farm To Fork’ strategy, at the heart of the European Green Deal, pays particular attention to heavy metals as potentially dangerous Food Contact Materials (FCMs).
But what, in fact, are heavy metals? What risks do they pose to our health? And how are governments legislating to protect citizens from possible health risks? This article aims to summarise the main factors to consider regarding heavy metals and take a look at current political responses to their use and potential dangers.
About Heavy Metals: Origins and Toxicity
Heavy metals are elements that occur naturally all around us that have a high atomic weight and a density at least five times that of water. Heavy metal use is widespread in industrial, domestic, agricultural, medical and technological theatres. This has long raised alarm bells regarding the potential risk they pose not only to the environment but to public health in general.
The concept of heavy metals is primarily empirical in nature and does not have a precise scientific definition. Depending on the density threshold used, the list of elements considered heavy metals is rather long. In addition, this category often includes certain toxic elements that are not strictly speaking heavy metals, such as arsenic (a metalloid) or methylmercury (an organometallic compound). The term ‘trace metals’ is often used where the definition of the element is more ambiguous.
The definition for heavy metals outlined in a Decision published by the European Commission on 3 May, 2000, states that “a heavy metal means any compound of antimony, arsenic, cadmium, chromium (VI), copper, lead, mercury, nickel, selenium, tellurium, thallium and tin, including these metals in metallic form, as far as these are classified as dangerous substances.”
Some heavy metals have a higher level of toxicity to others (toxicity depends on several environmental, climatic and biological factors), these include chromium, cadmium, lead and mercury. Many of these have a known or probable carcinogenic risk, according to the U.S. Environmental Protection Agency, and the International Agency for Research on Cancer, and have been linked to numerous diseases.
Although all of these elements are present to varying degrees in trace amounts in nature, and can be released into the atmosphere via volcanic eruptions and the weathering of metal-baring rocks, their increased abundance is the direct result of anthropogenic industrial and agricultural activity.
Cadmium, for example, is a prime example of a heavy metal found in excessive levels due to industrial activity. Its use in refining, other industry, burning coal and other fossil fuels and from household wastes poses a significant environmental threat.
Impact on Public Health
Heavy metals enter the body through inhalation, ingestion or skin exposure. They are stored mainly in the bones, liver, kidneys and brain. In humans, they can affect the nervous system, kidney, liver, respiratory and cardiovascular functions…. Exposure to high doses of heavy metals is implicated in several chronic diseases and severe pathologies such as multiple sclerosis, neurodegenerative diseases (Alzheimer’s and Parkinson’s), and kidney failure. Some, such as arsenic, cadmium, chromium and nickel, are considered carcinogenic. It is generally considered that the most toxic of the heavy metals for humans are arsenic, cadmium, lead and mercury.
According to the World Health Organisation, mercury “is considered as one of the top ten chemicals or groups of chemicals of major public health concern.” It is a neurotoxin, or a substance that is known to pose a threat to the human nerve tissue. Found in the soil, in water and in the air, mercury is known to exist is various different forms: elemental (or metallic), inorganic (to which people may be exposed through their occupation); and organic (e.g., methylmercury, to which people may be exposed through their diet), the WHO outlines.
The extensive use of lead has likewise led to widespread environmental contamination that poses a serious threat to public health, especially among young children, according to the WHO. Overexposure can result in attacks on the brain and the central nervous system, behavioural changes, comas, convulsions, intellectual disabilities and death. A shocking 2020 report led by UNICEF and Pure Earth suggested that up to 1 in 3 children – up to 800 million – are suffering from lead poisoning. The report was undertaken by the Institute of Health Metrics Evaluation (IHME) also estimated that lead exposure resulted in up to 900,000 deaths worldwide in 2019.
Apart from certain specific diseases such as the aforementioned lead poisoning, macrophagic myofasciitis (aluminium), hydrargyrism (mercury) or Itai-itai disease (cadmium), which are directly caused by a single metal, pathologies induced by metals are probably most often multifactorial, as several elements may act in synergy. This would be the case for mercury and lead, in particular, in the induction of neurodegenerative diseases.
Regulation
In the framework of commitments under the Air Convention, heavy metal emissions in Europe have been in decline over the last decades. According to the EEA, “between 2005 and 2019 lead emissions decreased by 44%, mercury emissions by 45% and cadmium emissions by 33% across the EU-27 Member States. In 2019, Germany, Italy and Poland contributed most to heavy metal emissions in the EU.”
Furthermore, the EU “is a party to the Convention on Long-range Transboundary Air Pollution (LRTAP Convention), a pan-European framework for reducing air pollution including heavy metals (under the Aarhus Protocol) (UNECE, 2021a, 2021b). Releases of Hg are also controlled by the United Nations Environment Programme Minamata Convention (UNEP, 2021).
Regarding heavy metal levels in foodstuffs, the The Contaminants in Food (England) Regulations 2013 make ‘enforcement measures’ for the European Commission. This led to maximum levels for certain contaminants in food, including lead, mercury, cadmium, tin and arsenic being set in a 2006 regulation: “To ensure high levels of public health, in this law, the European Union sets maximum levels for certain contaminants in food. Contaminants are substances that have not been intentionally added to food but have arrived in it in the course of its production, packaging, transport, etc.” Similar regulations are being called for in the United States.
While the EU has highlighted the presence of contaminants in the seas (see EEA report mentioned above) and therefore in the food that comes from them, it has taken very strict regulations on the presence of heavy metals in fertilisers. For Cadmium, for example, the new European regulation on fertilisers of 5 June 2019 has lowered the maximum cadmium content allowed in phosphate fertilisers from 90 to 60 mg/kg. This tightening of standards that were already the most demanding in the world (compared to 889mg in Canada or even 131mg in Australia), is based more on the precautionary principle than on irrefutable scientific evidence.
Regulations are being put in place, with the most demanding countries pulling the others towards a more dynamic approach. However, it is vital to adapt and maintain a reasonable approach, as in an industrialised and globalised world, avoiding any form of contamination at all i practically impossible. The main thing is to ensure that we stay below the toxicity thresholds, which requires vigilance from all stakeholders.
