Though the general perception is that heavy metals like mercury, lead and arsenic have very little chance to enter human bodies, the fact is that these can be easily absorbed into the body through elements like earth, water, and air, as well as sources as varied as food, cosmetics and kitchen appliances. The causes of contamination could be manufacturing process, raw materials used and chemicals released from many types of factories.
Heavy metals can be described as metals that have a density of more than five gram per cubic centimetre namely mercury, lead and arsenic. These toxins, when collected in the body to a certain level, will show their effect. The results of toxicity of heavy metals to cell mechanisms can be categorised into five types as follows; Causing cells to die; Changing the structure and functions of cells; Causing cancer; Causing genetic disorders; and Causing damages to chromosome which is a genetic factor.
Mercury
This metal is mostly found in air, water and soil, caused by fuel combustion, incineration, waste of household products and factories using mercury as its raw material such as paper pulp plant, plastic factory, pharmaceuticals factory and coal-fired power plant.
Furthermore, mercury is often found in cosmetics and food especially seafood and big aquatic animals such as sharks, tuna, dolphins and whales as they live longer lives and feed on small fish, which results in having more mercury in their bodies (called biomagnification). The belief that shark fins are rich in nutrition may not always be correct. The contamination of mercury in natural water resources is caused by factories releasing mercury with its wastewater.
The most severe incident regarding mercury happened in Minamata, Japan, in 1953, causing “Minamata disease.” It is caused by eating fish caught in Minamata bay which was contaminated with mercury. While many people were afflicted with central nervous system problems, many children suffered brain problems.
Lead
An individual may absorb lead directly from food, water or even breathing. People with risk of lead poisoning are workers in lead mines, battery factory, electronic and computer parts factory, paint factory, herbicide factory and people residing near lead melting factory or factories using lead as its raw material, traffic police and people in the traffic jam area.
Arsenic
It is mostly found in vegetables, fruits, water, seafood, cosmetics and traditional drugs and is an important component of herbicide factory, leather tanning industry and iron smelting factory. When arsenic is absorbed into body through breathing or consuming contaminated food, it will enter various parts of the body like blood, urine, hair and other tissues in different amounts. Arsenic will become toxic when being absorbed into body for a long time.
The causes of metal contamination in food are a natural cycle of food chain, cycle of industrial waste and cycle of food production. Therefore, it shows that no matter what kind of packages food comes in, if the ingredients are contaminated with heavy metals since cultivation, that product will always contain heavy metals. Meanwhile, if the ingredients are clean but production and packaging processes are not up to the standard, the products will be contaminated with heavy metals as well. Therefore, every agency responsible for consumer protection has issued a law to control the safety of products for consumers. To know whether food is contaminated with heavy metals, the analysis from the lab specialising in heavy metals must be conducted.
For the test to find the amount of lead and heavy metals, the appropriate and nationally and internationally accepted analysis methods must be carried out. The National Food Institute (NFI) implements AOAC to test lead and heavy metals in food which is an internal standard method, certified by ISO/IEC 17025 by the department of medical sciences.
The equipment used in the analysis process of lead and heavy metals has been maintained and calibrated according to the plan at least once a year to prepare the equipment for effective use. The equipment NFI uses to analyse are as follows:
1. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES): It is a technique that can analyse many types of heavy metals at a time by using plasma to dissolve the sample into atoms or ions. The sample will be stimulated until reaching the stage of emitting the light at the specific wavelength of each type of metals. The light emitted will relate to the density of each metal. This technique can test at the lowest level of part-per-billion (ppb).
2. Atomic Absorption Spectroscopy (AAS): It is a technique that can analyse only one kind of heavy metals at a time. This technique uses fire to dissolve the sample into an independent atom. When the light with the specific wavelength of each type of metals is shone to a group of independent atom, the atom will absorb the light. The absorption light will relate to each metal. Flame AAS can test at the lowest level of part-per-million (ppm).
3. Inductively Coupled Plasma Mass Spectrometry (ICP-MS): It is a technique that uses plasma as well to dissolve the sample into atoms and ions like ICP-OES but the detector is different. ICP-MS does not detect the amount of light but rather the ions. The ions will be sorted out from the difference of mass to charge ratio of each type of ion. This technique can test at the lowest level of part-per-trillion (ppt)
The analysis of heavy metals in each type of food is conducted with different methods. The test of contaminants and the standard criteria are proved to be a challenge for every lab. No matter how low the criteria is, the method must comply with laws. Therefore, since every type of food is important to analysts, they need to apply the right and most appropriate method. For example, if you must conduct a test on amount of copper in good at ppm level in one time before the results are submitted to clients, the AAS tool is therefore the most appropriate for the work. But if you want to test 23 types of heavy metals in drinking water, the technique that can analyse many types of heavy metals at once must be applied like ICP-OES and so on. The tool used to test lead and heavy metals in the food sample is AOAC (2012). The sample must be dissolved by acid to turn it into a solution before being analysed with ICP-OES or AAS. The analysis of heavy metals in a water sample must use AWWA (2012) method and ICP-OES tool.
Testing methods that cover the national and international criteria are Codex EU, Ministry of Public Health, The National Bureau of Agricultural Commodity and Food Standards, Thai Industrial Standards Institute etc.
The limit of detection (LOD) of the National Food Institute’s lab can be measured by an analysis method that has been approved with the limit in accordance with contaminant provisions of The National Bureau of Agricultural Commodity and Food Standards 9007-2005, Ministry of Public Health and EU as shown in the table.
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