Several organic and inorganic compounds can find their way into fish and seafood. These compounds can be divided into three major groups: - Inorganic chemicals: arsenic, cadmium, lead, mercury, selenium, copper, zinc and iron. (for detailed info click here)
- Organic compounds: polychlorinated biphenyls (PCBs), dioxins and insecticides (chlorinated hydrocarbons). This is a very diverse group with a wide range of industrial uses and a chemical stability that allows them to accumulate and persist in the environment.
- Processing-related compounds: sulphites (used in shrimp processing), polyphosphates, nitrosamines and residues of drugs used in aquaculture (e.g. antibiotics or hormones).
Many of the inorganic chemicals are essential for life at low concentration but become toxic at high concentration. While minerals such as copper, selenium, iron and zinc are essential micronutrients for fish and shellfish, other elements such as mercury, cadmium and lead show no known essential function in life and are toxic even at low concentrations when ingested over a long period. These elements are present in the aquatic environment as a result of natural phenomena such as marine volcanism and geological and geothermal events, but are also caused by anthropogenic pollution arising from intensive metallurgy and mining, waste disposal and incineration, and acidic rain caused by industrial pollution. This is in contrast with organic compounds, most of which are of anthropogenic origin brought to the aquatic environment by humans.
| Increasing amounts of chemicals may also be found in predatory species as a result of biomagnification, which is the concentration of the chemicals in higher levels of the food chain. Similarly, they may be present as a result of bioaccumulation, when chemicals in the body tissues accumulate over the life span of the individual. In this case, a large (i.e. older) fish will have a higher content of the chemical concerned than a small (younger) fish of the same species. The presence of chemical contaminants in seafood is therefore highly dependent on geographic location, species and fish size, feeding patterns, solubility of chemicals and their persistence in the environment.
Source FAO "The State of World Fisheries and Aquaculture, 2004"
Source Photo: European Commission |  |
EU - Maximum levels for contaminants in food Legislation related to food safety in Europe is based primarily on risk assessments made by the European Food Safety Authority.
In setting maximum permitted levels of contaminants in food, the background levels of contaminants in different food items from unpolluted areas have to be considered. Maximum levels exist for a number of “undesirable substances” in feeds and also, to a lesser extent, for several chemical contaminants in human food. A prerequisite for establishing maximum levels in feed and food is knowledge of the health effects of the chemical in question, as well as knowledge on its transfer from feed to the edible product (in the case of food of animal origin) and the risks vs. benefits of consuming food with a certain background level of contamination.Furthermore, sensitive and reliable analytical methods are required to measure the substance in question and, for control purposes, to document that the level is below the maximum permitted in a given food item.A tolerable (daily) intake (TDI) level is set to provide protection againts toxic effects in the most susceptible subgroups of the population, taking into account human variability; the TDI is defined as an amount that can be consumed daily - over an entire lifetime - without appreciable risk to health. It is not a threshold for risk and there is uncertainty about the degree of risk incurred if consumption exceeds the tolerable intake levels established. Moreover, it should be emphasised that exceeding the tolerable intake levels does not mean that there will be direct effects on health effects arise. Rather, it means that the safety margin is lessened.
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Last Updated ( Thursday, 12 August 2010 )
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Human health 
