Chapter 92 - Inhibitors of Aromatic Acid Biosynthesis

Abstract

This chapter presents a brief overview of the toxicity of a broad-spectrum, postemergent systemic herbicide known as glyphosate. It is typically referred to as the technical grade material and has the empirical formula C3H8NO5P. It is a white, odorless, crystalline powder with a melting point of 184.5 °C, a molecular weight of 169.1, and a specific gravity of 1.704. The initial uses for glyphosate were for preplanting or preemergence applications and resulted in negligible residues in the crops. Later uses have included applications when the crops are present, either using directed spray techniques, applications close to harvest, or herbicide-tolerant crops. Due to low solubility in water, glyphosate is typically formulated into commercial products in the form of a salt. It is poorly absorbed both dermally and via oral exposure and it is not biotransformed. In repeated dose studies in laboratory animals, treatment-related effects included reduced body weight gain, increased liver weights, degenerative ocular lens changes, and microscopic liver changes but only at very high dose levels. Large amounts of glyphosate-based herbicides are occasionally deliberately ingested to attempt suicide and may result in serious gastrointestinal, cardiovascular, pulmonary, and renal effects and possibly death. Accidental exposures to small volumes of glyphosate have not produced serious effects. In spite of this experience, it has been stated that glyphosate is a leading cause of pesticide poisoning in California.