Page 175 - Soil Degradation, Conservation and Remediation

164 6 Soil Pollution

Fig. 6.4 Carbamate
pesticides

acid moiety alcohol moiety

O H O H

O O
O
O O
Pyrethrin I Pyrethrin II
O
O H O H
O O
O
O O
Cinerin I Cinerin II
O

O H O H

O O
O
O O
Jasmolin I Jasmolin II
O

Fig. 6.5 Molecular structures of six natural pyrethrins

permethrin, and fenvalerate groups. Pyrethroids are used in many household
insecticides. They provide quick “knockdown” action and rapidly degrade in heat
and sunlight. This eliminates their usefulness in agricultural pest control. Pyrethroids
are relatively nontoxic to mammals and birds. However, they are highly toxic to aquatic
organisms and bees.

6.2.6.2 Herbicides

Herbicides are chemical substances used to control weeds. It has become an essential
management practice in conservation tillage systems, because no till and minimum
tillage cannot eradicate weeds. A few hundreds of organic and inorganic substances
of more than 50 chemical groups are used as herbicides. The following are some