Pesticide Safety, Toxicity, and Human Health Protection
Measuring toxicity
Toxicity is described by LD50 (dose lethal to 50% of test animals, usually mg per kg of body weight) or LC50 (concentration in air or water). Lower numbers mean a more toxic product. Know that LD50 is acute, single-dose toxicity; chronic effects (cancer, birth defects, nerve damage, reproductive harm) appear on the label as precautionary statements and in the Safety Data Sheet. Also know that dermal and inhalation LD50 values can drive the signal word just as oral values do.
Signal words
Category I: DANGER, plus the skull-and-crossbones and the word POISON when the oral, dermal, or inhalation toxicity falls in Category I. DANGER alone (no skull) signals severe eye or skin irritation/corrosivity. Category II: WARNING. Category III: CAUTION. Category IV: CAUTION or no signal word, only "Keep Out of Reach of Children." A common trap is assuming the skull always appears with DANGER - it does not.
Exposure and protection
The four exposure routes are dermal, inhalation, oral, and ocular; dermal is the most common for applicators. PPE statements on the label are the minimum legal requirement: gloves, coveralls, respirator, eyewear, boots, apron. Respect the restricted-entry interval for workers and the handler rules for mixing and loading. Organophosphates and carbamates depress cholinesterase; early poisoning looks like flu - headache, nausea, sweating, blurred vision, muscle twitching - and is easily confused with heat stress, which causes heavy sweating with cool, clammy skin and no pinpoint pupils. Remove contaminated clothing, wash with soap and water, and get medical help with the label in hand.
Worked example
A product has an oral LD50 of 5 mg/kg. For a 70 kg (154 lb) applicator, 5 × 70 = 350 mg of active ingredient could be a lethal dose - a few drops of a concentrated formulation. That arithmetic, not the smell or the color, is why label PPE is non-negotiable.