Pesticide Safety, Toxicology, and Human Health
Dose makes the poison
Toxicity is expressed as LD50 (mg/kg body weight) or LC50 (mg/L of air or water), the dose killing 50% of test animals. Lower numbers mean greater toxicity. Acute effects appear soon after a single exposure; chronic effects (cancer, birth defects, nerve damage) follow repeated low doses over time.
Signal words follow the worst route
Category I: oral at or below 50 mg/kg, dermal at or below 200, inhalation at or below 0.05 mg/L - DANGER. Category II: 50-500, 200-2000, 0.05-0.5 - WARNING. Category III: 500-5000, 2000-5000, 0.5-2 - CAUTION. Category IV: above those values - CAUTION.
Exposure routes
Dermal is the most common route for applicators. Skin absorbs best where it is thin, warm, and moist - scalp, neck, groin, under a watchband. Inhalation matters with fumigants, dusts, and mists; oral exposure comes from hand-to-mouth contact, smoking, or storing pesticides in drink containers.
Poisoning and first aid
Organophosphates and carbamates inhibit cholinesterase; signs include headache, blurred vision, pinpoint pupils, sweating, salivation, vomiting, cramps, and muscle twitching. Stop exposure, remove contaminated clothing, wash with soap and water, and call the poison center plus the label's emergency number. Never induce vomiting unless the label says to.
Worked example
A product has oral LD50 320 mg/kg, dermal LD50 4,000 mg/kg, and inhalation LC50 0.03 mg/L. Inhalation falls in Category I, so the label carries DANGER despite the moderate oral value.