Trace elements are usually naturally present in low concentrations in the environment and in our diet. Some of them are essential to man, i.e. they are needed (in low concentrations) for good health. Excessive exposure to both essential and non-essential elements may cause adverse health effects.
Trace elements are chemical elements that are naturally most commonly found in low concentrations (traces) in the environment, our food and in all living organisms. Often the term “heavy metals” is used to refer to these types of elements but, as explained below, this is not always correct.
For some trace elements, it has been demonstrated that they are essential for living organisms, including man. This means that they perform a function that is necessary for the organism to function properly. A deficiency in a daily intake of an essential element causes (illness) symptoms. When the daily intake of this element is sufficient, these symptoms will disappear again. Examples of essential elements for man are cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), iodine (I), molybdenum (Mo), selenium (Se), and zinc (Zn).
A number of other trace elements are not essential and therefore have no (known) biological function, such as aluminum (Al), arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb). It is important to note that both non-essential and essential elements may be toxic when they occur at a too high concentration.
Through the environment, trace elements can enter food and feed, thus increasing exposure in man. Where health effects occur as a result of increased exposure to trace elements, these are usually the result of chronic (i.e. prolonged) exposure. Acute damage is rather rare and usually associated with accidental exposure in a work environment (e.g. inhalation of metal fumes).
Although the term heavy metals is often used as a synonym for trace elements, this is not scientifically correct. Many trace elements do not possess the typical properties of metals (e.g. high electrical and thermal conductivity, luster, etc.) and are chemically speaking metalloids, such as arsenic (As) or selenium (Se).
In addition, “heavy metals” in the strict sense of the word are metals with a high specific gravity (i.e. a high mass density), and in principle their specific gravity must exceed a limit value in order to qualify them as “heavy”. However, this limit differs from source to source and can range from >3 g cm-3 to >7 g cm-3 and higher, making it difficult to determine whether a metal is “heavy” or not. At Sciensano, we therefore prefer the use of the term “trace elements” to the term “heavy metals”. The group of trace elements therefore includes both:
The term trace elements is based on the distinction between macro-elements and micro-elements (trace elements) as used in many scientific disciplines.
Trace elements are those elements that are usually present in low concentrations (traces) in the environment, in our food and in all living organisms. They contrast with macro-elements, which occur in much higher concentrations.
Depending on the scientific discipline, other elements are involved.
In earth sciences, for example, the macro-elements are the 8 rock-forming elements (O, Si, Al, Fe, Na, Mg, Ca and K) which together make up more than 90% of the earth’s crust. The other naturally occurring elements each make up <0.1% of the total and are considered as trace elements.
In life sciences, on the other hand, trace elements are those present in living organisms in concentrations < 0.01% or < 100 mg kg-1. Here, macro-elements are the main components of biomolecules, namely C, O, H, N, P, S, Mg, Ca and K, and are present in concentrations that depend on the organism studied.
Trace elements are natural constituents of the earth’s crust. As a result, they are present (usually in low concentrations) everywhere in the environment, in living organisms and in our diet.
Man is mainly exposed to trace elements through food intake, inhalation or skin contact. The extent to which someone is exposed via one or more of these roads depends on the element in question and the circumstances: for example, someone can be exposed in the workplace or simply through environmental pollution. In the case of cadmium (Cd), smoking behavior can also help to determine exposure, as this element is present in tobacco in high concentrations.
One undesirable side effect of our industrialized society, in which trace elements are used in all kinds of useful applications (such as lead in water pipes, copper in electrical wiring, arsenic compounds in pesticides or wood preservatives, cadmium and nickel in Ni-Cd batteries), is the contamination of soils, sediments, water and food with trace elements.
Primary sources of contamination are mining and smelting activities, fossil fuel combustion and volcanic eruptions. Additional contaminants include motorized traffic, certain agricultural activities (e.g. pesticides, wood preservatives, impurities in fertilizers, intensive animal production manure from pigs and chickens in particular), the chemical industry (e.g. batteries, pigments and paints), electricity and electronics (e.g. cables, connectors and semiconductors). In addition, the landfilling of waste (in which trace elements are present) and the use of sewage sludge can cause the dispersal of trace elements in the environment.
The usefulness of the numerous applications of trace elements, and the use of products containing trace elements, therefore go hand in hand with potentially increased human exposure (e.g. by drinking contaminated water or eating vegetable or animal products in which these elements have accumulated). Locally, naturally occurring concentrations of certain elements can also reach harmful levels.
Due to increased concerns about the possible health risks posed by certain trace elements, the use of some of these elements is now more strictly regulated and possible alternatives are being sought (e.g. the use of plastic instead of lead for water pipes, replacing mercury thermometers with digital thermometers).
In order to protect consumer health, maximum levels have been set at European level for certain trace elements in certain foodstuffs. The maximum levels are laid down in COMMISSION REGULATION (EC) No 1881/ 2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs (with several amendments: EU 488/2014 (Cd), EU 2015/1005 (Pb), EU 2015/1006 (Asi)).
In Belgium, the Federal Agency for the Safety of the Food Chain (FASFC), together with a network of accredited laboratories, ensures that the maximum permitted levels are not exceeded.
