Aquatic Pollution and Coastal Zone Managememnt (2+1)

Unit 4 : Pesticide pollution

4.9.1.Chemical Properties
Some of their chemical characteristics include low water solubility, high lipid solubility, high molecular masses and low volatility. One important factor of their chemical properties results in the ability to accumulate in the fatty tissue of living organisms.

The mechanism of toxicity of the organophosphate pesticides is inhibition of acetylcholinesterase, which catalyzes the deacetylation of acetylcholine. Acetylcholine helps transfer nerve impulses between nerve cells or from a nerve cell to other types of cells, such as muscle cells. The inhibition of the enzyme acetylcholinesterase leads to the build-up of acetylcholine, which then over-stimulates muscles, causing symptoms such as weakness and sometimes paralysis.

When a crop is treated with a pesticide, a very small amount of the pesticide, or indeed what it changes to in the plant (its ‘metabolites’ or ‘degradation products’), can remain in the crop until after it is harvested. This is known as the ‘residue’.

The POPs include three groups of chemicals,

• Pesticides/insecticides: which were once commonly used to control pests in agriculture and to protect public health. eg. aldrin, chlordance, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene, polychlorinated camphenes
• Industrial chemicals
• Chemical byproducts