Chemical Hazards

()Map FOOD DERIVED HAZARDS TO HUMAN HEALTH (Map)

Chemical contamination of foodstuffs can be due to their presence in the environment, or their intentional or unintentional application somewhere along the food chain. Some chemical toxins may occur naturally. Controlling chemicals which are only unintentionally present in the food chain is obviously difficult. Foodborne Chemical Hazards may be from the following categories:

Drug Residues

This category consists of:

1. Veterinary Medicines.
   Veterinary Medicines, after being administered to an animal, will still be present in the animal's tissues (or food products) for a variable ammount of time depending on the drug & the species amongst other things. Drugs given to treat animals intended for food production, if licienced, will have a minimum withdrawal period which must be observed before the animal can go for slaughter (for meat withdrawal). Withdrawal periods also exist for other animal products, e.g. egg withdrawal, milk withdrawal, etc...This is to allow enough time for the drug to be excreted or metabolised sufficiently so that no drug or only insignificant ammounts will be present in any food derived from that animal.
   If a Veterinary Medicine is not Licienced for use in a particular species for treating a particular condition then (having observed the Cascade System) the standard withdrawal period of 7 days for meat & 28 days for milk should be observed. Some drugs are specifically prohibited from use in all food animals (e.g. Phenylbutazone, Lignocaine to name two) and some drugs are prohibited in specific types of food producing animal (e.g. Tilmicosin is prohibited in Dairy cows but not beef cows).
   Veterianry Medicines whose use are widespread in food producing animals are Antimicrobial & Antiparasitic drugs. Residues of ranquilizers are also of concern.
   Organic producers ofen have to observe much longer withdrawal periods and can only administer drugs when the use has been specifically approved by a vet. Use of drugs other than to treat sick animals is generally not approved (although welfare should not be compromised).
   
   
2. Agricultural Chemicals.
   As the use of these substances is generally intentional they can be applied well in advance of harvesting in a controlled manner (this is the case for herbicides, fungicides, fertilizers & rodenticides), thus limiting their presence in feeds then given to animals. Some insecticides may be used nearer to harvest or on animals & their environments.
   1. Insecticides-As the most widely used agricultural chemicals represent the greatest risk to food contamination of this category. Some are extremely environmentally stable & toxic.
      1. Chlorinated Hydrocarbons
         DDT (Dichloro-Diphenyl-Trichloroethane) is th most well known. It is very durable, accumulates in tissues & persists in the environment. Chlorinated Hydrocarbons are CNS stimulants & cause congestion of internal organs & focal centrilobular necrosis of the liver.
      2. Organophosphates
         The most widely used insecticides, are much less persistant in the environment & body tissues than Chlorinated Hydrocarbons and hence, present less of a risk. They can however, be extremely toxic to mammals causing non-specific acute signs or chronic lung congestion. They may be an Occupational Hazard.
   2. Herbicides-Are not usually used on animal food crops but may sometimes be used for plants used for animal bedding causing residue problems. Some may contain Dioxins.
   3. Fungicides-(e.g. dicloran & folpet) Do not usually cause residue problems. They may contain heavy metals. They are often dyed to allow identification of treated crops, however, accidental feeding of treated crops to animals or use in cereal foods has led to poisonings.
   4. Fertilizers-Can cause significant environmental problems, particularly if they contaminate run-off waters. Algal blooms may result aswell as the growth of toxic algae that may contaminate shellfish.
   5. Rodenticides- (e.g. Warfarin & Antu) although widely used should not contaminate foodstuffs.
      
      
3. Growth Promoters
   Growth Promoters are used amongst other things to increase production performance of animals and not for a health benefit to the animal or consumer. Commonly used Growth Promoters are Hormone-like compounds & antimicrobials. Growth Promoters Growth Promoters are not allowed in the EU but are in the USA & other countries. This has important trade implications.
   1. Hormone-like growth promoters
      These include synthetic hormones (e.g.Diethylsibestrol), natural hormones (e.g. estradiol, Progesterone, Testosterone), fungal oestrogens (Zearalenone), Beta-agonists (Trenbolone) and thyreostatics. Risk associated with these compunds can be difficult to evaluate as administered natural hormones may be dificult to distinguish from endogenous hormones in animals & people. Also synthetic hormones given to young animals may not be detectable at time of slaughter.
   2. Antimicrobial Growth Promoters
      Fed are low but continuous doses in feed they have been observed to cause increased growth rates. Although not understood the mechanism of action could be via suppressing disadvantagous intestinal microflora or direct anabolic effects of the drugs themselves. Virginamycin, bacitracin, polymyxin B & sulphonamides are commonly used. There used is strongly suspected of causing Antimicrobial Resistance.

Environmental Chemical Hazards

Often from an industrial source they include:

1. Heavy Metals
   (e.g. Lead, Arsenic, Mercury, Cadmium, Fluorine &Selenium)
   1. Lead-Lead can occur in animals grazing near smelting plants or from animals licking lead based paints or old car batteries. Lead then accumulates in the bones. Acute poisoning may result in high levels in the liver & kidneys. Chronic exposure may cause softening & cavitation of the CNS.
   2. Arsenic-Contamination of food animals with arsenic is typically due to exposure to arsenical herbicides, rodenticides or insecticides. Its accumulation in the liver & kidneys can lead to fatty degeneration. It also accumulates in the bones.
   3. Mercury-Rare cases of mercury poisoning have been due to animals being fed with grain treated with mercury-based anti-fungicides. The result is enlarged internal organs & petechiation). Inorganic mercury is also stored in the liver & kidneys, whereas organic mercury is more widely distributed. See Minamata disease
   4. Cadmium-An increasing problem, high cadmium levels occur in animals grazing pasture irregated with aerobically digested sludge. Contamination of shell fish & fish also occur as cadmium may contaminate water. It accumulates in the bidy tissues & may cause kidney failure. Prolonged accumulation is required to reach toxic levels.