Dioxins and furans:
Dioxins are a group of polychlorinated aromatic compounds arising either naturally or as by-products of industrial activities e.g. metal smelting, molding or burning of chlorine-containing organic chemicals such as plastics. It is toxic and stable. Once produced, it tends to persist in the environment and concentrates in the food chain.
Different dioxin compounds have different degree of toxicity. Of all types of dioxin-related compounds that have been identified, the most toxic one is 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD).
Some dioxin-related food crises occurred in overseas countries have raised considerable public attention and concern.
Dioxins dissolve in fat in nature and are not easily broken down. They tend to accumulate in fatty tissues and are passed up the food chain from plants to animals to humans.
Sources of human exposure to dioxins include food intake, drinking water, air inhalation and skin contact. Dietary intake is by far the most important and accounts for over 90% of dioxins exposure. Fatty foods such as meat, poultry, seafood, milk, egg and their products are the major dietary sources of dioxins.
Accidental exposure to large amount of dioxins could lead to the development of chloracne, a skin condition, excessive body hair and other skin lesions such as skin rashes and skin discolouration.
The International Agency for Research on Cancer (IARC) has classified the TCDD congener as human carcinogen. Long-term exposure to dioxins is linked to impairment of the immune system, reproductive function, endocrine system and the developing nervous system. Associations with diabetes, thyroid dysfunction and heart diseases in humans have been reported in some studies. WHO has recommended that the tolerable daily intake for dioxins and dioxine like PCB should be below 2pgTEQ/Kg body weight.
Furan is a heterocyclic compound and potential carcinogen that has been identified in a number of foodstuffs that undergo thermal treatment such as bottled, canned and jarred food products. Some amino acids and sugars break down into furans when thermally treated. Other food components such as Vitamin C and polyunsaturated fatty acids may also produce furans as an unwanted byproduct of food processing. Ionizing radiation is also known to induce the formation of furan in solutions of simple sugars and ascorbic acid with where sugar content is high and pH is low, for example canned fruits and vegetables.
Polychlorinated Biphenyls (PCBs) occur in food as the result of environmental contamination leading to accumulation in the food chain, direct contact with food or animal feeds, or contact with food packaging materials made from recycled paper containing PCBs.
Dermatologic signs are the most persistent indicator of a considerable uptake. Neurological symptoms, respiratory findings and impairment of liver function are further aspects of the contamination. Skin manifestations have been observed also in the newborn infants from mothers exposed to high levels of the substances.
Mercury:
Sea foods are the major source of contamination. The most toxic mercury compounds are those that are fat soluble, because this property assists in their distribution throughout the body. Methyl mercury compounds, such as dimethyl mercury, are among the most dangerous.
In humans, the most widely reported fetal risk associated with maternal exposure to mercury is brain damage. The placental transfer of mercury and its effects on the human fetus were first recognized in the 1950’s with the well-known outbreak of congenital Minamata disease in the towns of Minamata and Niigata, Japan.
In 1959, 23 infants suffering from mental retardation and motor disturbances had been born to mothers exposed to methyl mercury during their pregnancies.
The clinical symptoms of the infants resembled those of severe cerebral palsy or cerebral dysfunction syndrome
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