On 15 June 2018, new regulations were published in the Government Gazette regarding the maximum levels of metals (often referred to as heavy metals) and other elements found in foodstuffs. These regulations will come into effect on 15 September this year and will replace all previous regulations on maximum levels of metals in foodstuffs.

The presence of metals in our food is a reality, but how does it get there and when does it become dangerous?

Why are there metals in food?

Answering this question is not easy. Metals can enter the food supply chain at farm level, during processing or packaging, or even during cooking. Metals naturally occur in the earth’s crust and are present in the soil. In this way, it can enter produce on a primary production level. Post-harvest handling could also play a role.

Further down the food supply chain metals can enter food when it’s processed by metal machinery, or it can be contaminated by packaging after it has been processed. Lastly, it can enter food in the home when using cookware made of metals that could be harmful to human health.

Other factors can play an indirect role. If water is contaminated with metals, it can enter the food supply chain through irrigation, or post-harvest activities such as washing or processing food. Manure contaminated by toxic metals is another possible consideration. Furthermore, the way food is stored could be considered a possible source of contamination.  

According to the European Food Safety Authority (EFSA), elements such as arsenic, cadmium, lead and mercury are naturally occurring chemical compounds. They are present at various levels in the environment (soil, water and atmosphere). Any vegetation, fruit, vegetables, grains or legumes grown directly in contaminated soil or surrounding water bodies will absorb these naturally occurring metals just as they would other nutrients, such as zinc or iron.

Heavy metals in the earth’s soil are thus not solely caused by pollution or industrial activity. Metals can, however, also occur as residues in food due to farming and industry practices, as well as other human activities such as car exhaust pollution.

Recent cases

There are several examples of cases where metals were found in food at levels much higher than the permissible maximum.

In 2015, the Food Safety and Standards Authority of India (FSSAI) withdrew millions of rands worth of Maggi 2-minute noodles in India after test results showed that it was contaminated with lead at levels higher that those allowed. The brand put consumers’ health at risk and was consequently banned. The website www.foodsafetyhelpline.com attributes the high levels of lead found in the noodles to wheat (the main raw material) grown in lead-contaminated soil.

In 2011, Chinese government scientists reported that large areas of China’s agricultural land were contaminated with heavy metals. This is according to an article published on www.science.times.com. Over twelve million tons of Chinese grain was contaminated and 10% of rice contained the carcinogenic heavy metal cadmium. Cadmium and lead are two of the most toxic metals commonly found in foodstuffs.

Other elements such as metalloids, which have some qualities that make them metal-like, frequently contaminate food and water. For example, West Bengal in India has large areas where contaminated groundwater is used in villages for drinking purposes. High amounts of arsenic have also been found in apple juice in the United States (US).

Types of metals and metalloids

Heavy metals are defined as metallic elements that have a relatively high density compared to water. With the assumption that heaviness and toxicity are interrelated, heavy metals also include metalloids, such as arsenic, that can induce toxicity at low levels of exposure. The following is a brief overview of each of the elements listed in the new regulations that have been published in South Africa.

Table 1: Maximum levels for metals in foodstuffs. (Source: Government Gazette)
Metal Foodstuff ML (mg/kg or mg/ℓ)
Arsenic, total (As-tot) Edible fats and oils 0,1
  Fat spreads and blended spreads 0,1
  Rice, husked* 0,35
  Rice, polished* 0,2
Arsenic, inorganic (As-in) Rice, polished (*follow up analysis if As-tot exceed ML) 0,2
  Rice, husked (*follow up analysis if As-tot exceed ML) 0,35
Lead (Pb) Berries and other small fruit (excluding cranberry, currant and elderberry) 0,1
  Cranberry, currant and elderberry 0,2
  Brassica vegetables 0,1
  Bulb vegetables 0,1
  Fruiting vegetables (excluding fungi and mushrooms) 0,05
  Leafy vegetables 0,3
  Pulses 0,1
  Table olives 0,4
  Cereal grains (excluding buckwheat, canihua and quinoa) 0,2
  Meat and fat of cattle, pigs and sheep (without bones) 0,1
  Meat and fat of poultry 0,1
  Fish (whole or portions, without viscera) 0,3
  Edible fats and oils 0,1
  Natural mineral water 0,01
  Milk 0,02
  Wine 0,2
Mercury (Hg) Natural mineral water 0,001
  Salt, food grade 0,1
Methylmercury Fish (whole or portions, without viscera; except predatory fish) 0,5
  Predatory fish, such as tuna, pike, swordfish and others (whole or portions, without viscera) 1,0

This list has been shortened for publication. The full report can be viewed here.

Lead

Chronic exposure to lead through contaminated food affects the central nervous system (CNS) and the gastrointestinal (GI) system. Chronic exposure results in loss of concentration, confusion, depression, headaches, etc. GI symptoms include stomach cramps, nausea and vomiting. It causes in utero toxicity to developing foetuses, leading to premature and low birth weight babies.

Lead interferes with iodine uptake by the thyroid and can inactivate the thyroid hormone thyroxin. It displaces and causes deficiency in or bio-unavailability of calcium, zinc, manganese, copper and iron (South African Grain Laboratory, SAGL).

Cadmium

It is a group one human carcinogen and is an extremely toxic metal that has no known necessary function in the body. Cadmium concentrates in the kidneys, liver and various other organs. Its toxicity contributes to many health conditions, including heart disease, cancer and diabetes. It displaces zinc in several metallo-enzymes and many of the toxicity symptoms can be traced to cadmium-induced zinc deficiency (SAGL).

Arsenic

According to the US Food and Drug Administration (FDA), arsenic is present in the environment as a naturally occurring substance or because of contamination from human activity. It is found in water, air, soil and food. In food, arsenic may be present as inorganic arsenic (the most toxic form) or organic arsenic.

It can enter the food supply chain through consumption of shellfish, as well as through vegetables grown in fields where fertilisers or pesticides containing arsenic had been applied decades ago. Chronic exposure to arsenic through contaminated drinking water can cause dermatitis and various types of cancer. It may affect memory, reproductive function, and cause cardiovascular diseases.

Tin

The use of tin cans as packaging for food and beverages can lead to tin contamination. It may enter food through the use of tin-containing pesticides. Chronic exposure to tin can cause GI problems, liver damage, reproductive issues, developmental defects, as well as cancer.

Mercury

Mercury can enter the body through food in the form of methylmercury, which may accumulate in large sea fish, such as swordfish. Reducing intake of sea fish is an effective way to reduce mercury exposure. It has toxic effects on the GI system, CNS, immune system, and respiratory and renal systems, as well as the eyes and skin.

Copper

Although copper is an essential element, it may be toxic to humans at high levels. Copper contamination of food can occur if the cooking utensils, including pots and pans, are made of uncoated copper, especially if acidic foods are cooked. Copper also enters the human food chain when copper-containing fungicides are used. Chronic exposure can cause liver failure.

Threatening levels

South African regulations concerned with acceptable levels of metals in foodstuffs measure each metal on the list in milligrams (mg) per kilogram (kg) or mg per litre (ℓ), i.e. mg/kg or mg/ℓ. Each metal, and food type, has its own criteria for acceptable levels of metals. For example, the acceptable cadmium levels for brassica, bulbous and fruiting vegetables are 0,05mg/kg and 0,2mg/kg for leafy vegetables.

Understanding the risk these metals pose in our food supply is complicated by the fact that no single food source accounts for people’s exposure to metals. Exposure to these metals comes from many different food sources, which may contain low levels of metals. If all the food we eat are combined, these low levels can sometimes add up to a level of concern (FDA).

Mercury and lead are often referred to as heavy metals. The toxicity of these metals is partly due to their tendency to accumulate in biological tissues – a process known as bioaccumulation. The process of bioaccumulation of metals occurs in all living organisms, resulting from exposure to metals in food and the environment.

How it is measured

The universally used analytical technique to test the concentration of metals in foodstuffs is Atomic Absorption Spectrometry (AAS). According to www.foodsafetyhelpline.com, the technique is so sensitive that it can measure parts per billion (ppb). The technique uses wavelengths of light that are specifically absorbed by an element.

A variation of AAS, called vapour generation AAS, can detect miniscule levels of mercury, including methylmercury in fish. An even more sensitive analytical method is the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), which measures parts per quadrillion (ppq) – a million times more sensitive than AAS. Another method is Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES).

Besides these highly sensitive methods, conventional colorimetric methods that measure single elements are also available. – Ursula Human, FarmBiz

For more information, visit www.foodsafetyhelpline.com, www.fda.gov, or read the South African Government Gazette vol 636, no 41704.