Page 173 - Soil Degradation, Conservation and Remediation

162 6 Soil Pollution

Fig. 6.2 Two
organophosphorus pesticides

Pesticides applied to plants or harmful organisms (plant, microorganism, insects)
undergo repeated dissolution, adsorption, and elution with the soil solution and
colloidal phases and spread to all directions within soil, water, and atmosphere
systems. This mobility depends on solubility, adsorbability, and volatility.

6.2.6.1 Insecticides

The use of insecticides has been increasing after the end of World War II. There are

a great number of substances classified as insecticides, but they can belong to any
of the four groups of organic compounds: the organophosphorus compounds, the
organochlorines, the carbamates, and the pyrethroids.

Organophosphorus Compounds

Organophosphorus compounds are technically nerve poisons because they act on
the central nervous systems. Developed during World War II, they are used in many
different ways in agriculture. They can be used as fumigants, some as contact poisons,
and others as systemic pesticides. The most important members of the group are
tetraethyl pyrophosphate (TEPP) and sarin (Fig. 6.2 ). Sarin is also used in warfare.
Many organophosphates are highly toxic to nontarget organisms.
Organophosphates manufactured latter are less toxic to mammals but toxic to target
organisms, such as insects. Malathion, Dibrom, chlorpyrifos, temephos, diazinon,
and terbufos are organophosphates.

Organochlorines

Some organochlorine compounds, also developed during World War II, were found
to be very effective in controlling pests responsible for diseases such as malaria and
yellow fever. These compounds were cheap and easily available, and they were thought
to be safe for humans. They belonged to the three families: the DDT (dichlorodiphe-
nyltrichloroethane) family, the BHC family, and the cyclodiene family (Fig. 6.3 ). The
principal representative of the BHC family is called lindane. Aldrin, dieldrin, and
heptachlor are stereochemically related compounds and belong to the cyclodiene