Page 176 - Soil Degradation, Conservation and Remediation

6.2 Sources of Soil Pollutants 165

Fig. 6.6 Organochlorine
herbicides

Fig. 6.7 Aniline derivatives

used as herbicides

Fig. 6.8 Structures of
glycine and glyphosates

popular examples. A classification of herbicides may be obtained from the web page
http://www.alanwood.net/pesticides/class_herbicides.html .
Organochlorine compounds contain derivatives of phenoxyacetic acid, such as
2,4-dichlorophenoxyacetic acid known as 2,4-D and 2,4,5-trichlorophenoxyacetic
acid 2,4,5-T or 2-methyl-4,6-dichlorophenoxyacetic acid, known as MPCA (Fig. 6.6 ).
An equal mixture of 2,4-D and 2,4,5-T is known in the code name Agent Orange. The
US Army sprayed millions of hectares of woodlands during their war against Vietnam.
Vietnamese still suffer from damages caused by the substance. Besides derivatives of
phenoxyacetic acid, there are derivatives of aniline among organochlorine herbicides.
Two aniline derivatives are propanil and alachlor (Fig. 6.7 ).
Organophosphorus herbicides (known as glyphosates) are widely used in

agriculture for their weed killing efficiency and noncarcinogenic nature. Glyphosate
is a modified glycine (Fig. 6.8 ).