Climate change and heavy metal contamination of food

By Linda Jackson on 21 October 2020

It is clear that food security has been highlighted by the current COVID 19 pandemic with supply chain disruptions, the impact of the economic slowdown resulting in millions of people going below the breadline and becoming food insecure. The pandemic also highlighted the negative effects of our normal economic activities on the environment with lockdown images contrasting starkly with normal emissions.

It is interesting therefore that the FAO (Food & Agricultural Organisation) would launch its latest publication in the Food safety and quality series, Climate change: Unpacking the burden on food safety, this year.

While the topic of climate change and global warming may be contentious, the problem of increased levels of heavy metals due to our impact on the planet cannot be ignored - for food safety reasons.

What are heavy metals?

Metals such as arsenic, cadmium, lead and mercury are naturally occurring chemical substances. They can be naturally present at various levels in the environment in soil, water, and the atmosphere. Heavy metal pollution has spread broadly over the globe posing serious health hazards to humans. The root causes of this problem are generally held to be because of human activities such as farming, industry, or car exhausts or from contamination during food processing and storage. The concern is that these metals can also occur as residues in food because of their presence in the environment.

The bad

The heavy metals that are of major public health concern are lead (Pb), chromium (Cr), cadmium (Cd), mercury (Hg) and arsenic (As). These are considered toxic to our bodies even at low levels of exposure.

  • 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 emissions
  • Cigarettes provide another airborne source of heavy metals.

Sources of heavy metals

The good

Other metals such as cobalt (Co), copper (Cu), iron (Fe), nickel (Ni), magnesium (Mg), manganese (Mn), zinc (Zn) and selenium (Se) are considered to be micronutrients as they have essential biological functions.

The ugly?

Heavy metals enter the human body mainly through diet, and some harmful metals may concentrate in the body if certain food items, such as seafood, are consumed regularly.
The effects of harmful heavy metals varies. 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. Exceptionally low levels can be fatal to children.

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 weakness.

How do we control levels of heavy metal in foods?

The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has established tolerable daily intake (TDI) levels for different metals (FAO and WHO, 2007; 2011a; 2011b; 2013). In addition, there is South African legislation that governs the maximum levels of heavy metals in foods, Regulation R 588 of June 2018.

What do we do in the food industry to protect consumer health?

Our legislation makes it the responsibility of the food business operator (FBO) for the safety of food and feed which they produce, import, transport, store or sell. They must also ensure that their products comply with the legislative limits for heavy metals. It is important that FBOs identify CCPs in their processes such as lead in the water supply; the identification of appropriate CCPs along their process chain will enable them to develop and apply proper HACCP systems which will ensure that there are no unforeseen sources of metal contamination in the food. It is the responsibility of the FBO to test his products for content of mercury, lead, cadmium, tin, or arsenic at the point of sale and this should be done using internationally recognised, validated methods by an accredited laboratory.

We should heed the FAO’s warning: “Heavy metal pollution and its effects on public health are a neglected area that requires urgent attention at regional and national levels, especially in the context of climate change.”

While curbing the increase in heavy metal pollution may be complex, the FAO are urging prioritization of controls and remediation practices. As the levels of heavy metals increase due to man’s activities, so must our vigilance in food safety.