Analysis of Urea derivative herbicides in water and soil

Herbicides derived from urea form a large group of chemical compounds widely used in agriculture to control weeds in cereal, vegetable, and fruit tree crops. On the basis of their chemical natures, use, and mode of action, substituted urea herbicides can be divided into two main groups phenylureas and sulfonylureas. Although phenylurea herbicides (PUHs) were introduced more than 40 years ago, they are still widely used. Phenylureas can be divided into three subgroups: 1. N-phenyl-N0 N0-dialkylureas, such as, chlorotoluron, isoproturon, and diuron 2. N-phenyl-N0-alkyl-N0-methoxyureas, such as, linuron, monolinuron, and metobromuron 3. Phenylureas containing a heterocyclic group, the major exponent being methabenzthiazuron. The chemical structures of the main representatives of the three phenylurea subgroups are depicted in Figure 25.l. The common names, water solubility, half-life in soil, and leaching potential through the soil (when available) of the most widely used phenylureas are presented in Table 25.1. PUHs are generally absorbed through the roots of plants and transported via the transpiration system. The mode of action of PUHs seems to be due to the combined effects of the inhibition of photosynthesis and the irreversible injury of the plant photosynthesis system via inhibition of NADPH2.1