Food Toxicology 2(2+0)

Lesson 18 : Food Contamination and Safety

Classification

1. Insecticides:
   DDT (dichloro diphenyl trichloroethane), aldrin, dieldrin, and chlordane.
• Chlorinated hydrocarbons: parathion, diazinon, mevinphos, chlorpyrifos, and azinphos-methyl ( The uses of most chlorinated hydrocarbon insecticides were replaced byt he organophosphate and carbamate insecticides.)
• Carbamate insecticides: carbaryl, aldicarb, methomyl, and carbofuran.
  
• Pyrethroids: Pyrethroids are synthetic derivatives of pyrethrins


2. DDT: DDT was heralded as one of the most important disease preventing agents known to humans, highly lethal to insects and protecting field crops but remarkably harmless to human beings. DDT was used to dust people to kill lice, for which it was very effective. Sri Lanka, provides examples of the positive impact of DDT on human health. Before the use of DDT, nearly 3 million cases of malaria were reported yearly in Sri Lanka. DDT compounds were extensively used in the U.S. as pesticides before they were banned in 1973. There is no evidence from human studies that DDT causes cancer. Individuals who have been occupationally exposed to high levels of DDT have been reported to only have transient effects such as tingling of the extremities.


3. Organophosphates
   Organophosphates (OPs) are the oldest of the synthetic pesticides. OPs have several commonly used names: organic phosphates, phosphorus insecticides, nerve gas relatives, phosphate, phosphate insecticides, and phosphorus esters or phosphoric acid esters. All compounds are derived from phosphoric acid, and, generally speaking, are the most toxic to vertebrate animals. OPs are rapidly metabolized and excreted and do not accumulate in the body.
   
   Signs and symptoms of organ phosphorus insecticide poisoning include tightness in the chest and wheezing expiration due to broncho constriction and increased bronchial secretions, and increased salivation and lacrimation. Sweating, increased gastrointestinal tone and peristalsis with nausea, vomiting, abdominal cramps, diarrhea, bardycardia, and contraction of smooth muscles of the bladder are other symptoms. The immediate cause of death in fatal organophosphate poisoning is asphyxia resulting from respiratory failure.
   
   The key to the usefulness of OPs is that residues on food products do not normally result in exposures sufficient to lead to health problems in humans.


4. Carbamates
   These compounds are toxic alkaloids. Carbonates are quite water soluble and can accumulate to dangerous levels in foods with high water content. Thus, carbonates are not registered for use in food with high water contents, but their wide use makes contamination possible, as in the watermelon case.
   
   Typical symptoms of poisoning include lacrimation, salivation, miosis, convulsion, and death. Carbonates are not considered broad-spectrum insecticides because some of the common household insects are relatively immune.


5. Cyclodiene insecticides
   This is an important group of chlorohydrocarbons, such as aldrin and dieldrin. The mode of action is neurotoxicity. Their toxicity increases with increase in the surrounding temperature. They, like DDT, are highly lipid soluble and quite stable and accumulate in animal tissues.