Chapter 66 - Symmetrical and Asymmetrical Triazine Herbicides

Abstract

This chapter explores triazines chemistry and formulation, uses, and risk characterization. Triazines have been used extensively as selective herbicides in agriculture in the United States and other parts of the world for more than 35 years. The triazines inhibit photosynthesis. These inhibitors of photosynthesis include the asymmetrical triazines or triazinones, such as metribuzin and the symmetrical triazine herbicides. Mode of action of the triazine and triazinones herbicides is inhibition of photosynthetic electron transport in most plants and generally has low toxicity to animals. The chapter presents, in tabular form, the modes of action and the uses of various triazine and triazinone based chemicals. Evaluation of hazard profiles of the triazine herbicides revealed that these products are relatively nontoxic, well tolerated when administered to animals over a long duration of time, not developmental or reproductive toxins, and are neither mutagenic nor carcinogenic in mice or male rats. The chloro-s-triazines appear to produce an earlier onset or an excess of mammary tumors in female S-D rats at high doses. Because of the unique nature of reproductive aging in female S-D rats, the carcinogenic response in this strain of rat is not considered relevant for human risk assessment.