VPT 421: Veterinary Toxicology (2+0)

PROPERTIES OF TOXICOLOGICAL IMPORTANCE

• There is great variation in toxicity between the compounds.
• Most organophosphorous compounds are not persistent in the environment and dissipate in 2 – 4 weeks.
• They are poorly soluble in water and so they may be used as dusts, wettable powders or emulsions.
• Improper formulation of a pesticide vehicle mixture can lead to under exposure or over exposure. These compounds are soluble in organic solvents, fats and oils. Hence they can penetrate waxy coatings o f leaves or fruits or directly absorbed through the skin.
• Oily vehicles or solvents can facilitate passage of organophosphorous pesticides through the skin.
• Toxicity of the OPC decrease as they are degraded by sun, water, microbes, alkali or metal ions.
• Highly toxic isomers can be formed spontaneously in poor solvents or water. So increase in toxicity occurs during storage.
• Ambient temperature affects toxicity.
• High temperature increases toxicity of parathion in mice and low temperature increases toxicity of malathion in mice.
• Nature of the vehicle used also affects toxicity.
• Cattle are more sensitive to sheep for a few compounds.
• Many of the species differences are caused by differences in enzymatic activation or degradation of various pesticides.
• Compounds that do not require enzymatic activation are more toxic in very young animals.
• Dichlorvos, dioxathion and parathion are more toxic to female, while fenithion and dimethoate are less toxic to female compared to male.