Metals and other elements can be naturally present in food or can enter food as a result of human activities such as industrial and agricultural processes. The metals of particular concern in relation to harmful effects on health are mercury, lead, cadmium, tin and arsenic. Mercury and lead are often referred to as “heavy metals”. The toxicity of these metals is in part due to the fact that they accumulate in biological tissues, a process known as bio accumulation. This process of bio accumulation of metals occurs in all living organisms as a result of exposure to metals in food and the environment, including food animals such as fish and cattle as well as humans

The main concern in relation to the toxicity of mercury in the general population is the potential effect of organic forms of mercury, e.g. methyl mercury, on the brain and intellectual development in young children. Lead also has an effect on brain and intellectual development in young children, while long-term exposure in both children and adults can cause damage to the kidneys, reproductive and immune systems in addition to effects on the nervous system. Cadmium is toxic to the kidney, while exposure to high levels of tin from, e.g. canned food in incorrectly manufactured tins can cause gastrointestinal irritation and upsets. Exposure to inorganic arsenic is of concern because of its cancer-causing properties. Given the wide spectrum of effects on health and the fact that these toxic metals accumulate in the body, it is essential to control levels in foodstuffs in order to protect human health.

Maximum levels for mercury, lead, cadmium and tin in foodstuffs have been set by Commission Regulation No 1881/2006, the framework EU legislation which sets maximum levels for chemical contaminants in foodstuffs. This Regulation establishes maximum levels (MLs) for these metals in a wide range of foodstuffs including milk, meat, fish, cereals, vegetables, fruit and fruit juices, and also sets a maximum level for mercury in fish and fish products

Introduction

Food contains a wide range of metallic elements (metals) such as sodium, potassium, iron, calcium, boron, magnesium, selenium, copper and zinc. These elements are essential in trace quantities for maintenance of cellular processes. Other metallic elements have no functional effects in the body and can be harmful to health if foodstuffs containing them are consumed regularly in the diet. The majority of metals are natural components of the earth’s crust. Metals and other elements can be naturally present in food or can enter food as a result of human activities such as industrial and agricultural processes. Chemically, metallic elements can exist as the pure metal, e.g. tin or lead, or compounds formed by combination of a metallic element with a non-metallic element such as the combination of sodium with chlorine (giving a salt such as sodium chloride, common salt) or oxygen (giving an oxide)

The metals of particular concern in relation to harmful effects on health are: mercury (Hg), lead (Pb), cadmium (Cd), tin (Sn) and arsenic (As), mercury and lead often being referred to as “heavy metals” because of their high atomic weight. Other potentially toxic metals such as chromium and uranium have been also reported to be present as contaminants in food or water, while a number of metals have been associated with health effects in individuals exposed to them in the workplace, for example beryllium and nickel. The harmful effects of the latter group of metals are associated with the inhalation of metal dusts, causing lung injury, and these elements are not normally found in food at levels that could c

Toxicity of mercury, lead, cadmium, tin and arsenic

The toxicity of these metals has two main aspects: (a) the fact that they have no known metabolic function, but when present in the body they disrupt normal cellular processes, leading to toxicity in a number of organs; (b) the potential, particularly of the so-called heavy metals mercury and lead, to accumulate in biological tissues, a process known as bio accumulation. This occurs because the metal, once taken up into the body, is stored in particular organs, for example the liver or the kidney, and is excreted at a slow rate compared with its uptake. This process of bio accumulation of metals occurs in all animals, including food animals such as fish and cattle as well as humans. It is therefore necessary to control the levels of these toxic metals in foodstuffs in order to protect human health.

Excessive exposure to mercury is associated with a wide spectrum of adverse health effects including damage to the central nervous system (neurotoxicity) and the kidney. Different forms of mercury (i.e. mercury metal, inorganic mercury salts such as mercuric chloride and organic forms of mercury such as methylmercury) produce different patterns of toxicity. The main concern in relation to the toxicity of mercury in the general population exposed to low levels of mercury in their diet relates to the potential neurotoxicity of organic forms of mercury, e.g. methylmercury, in young children. Organic forms of mercury can cross the placental barrier between the mother and the unborn baby, and epidemiological studies in exposed populations of humans and toxicological studies in animals have shown that this can result in a range of neurological disturbances from impaired learning to obvious brain damage.