Human Health Effects, Toxicity, Exposure Routes and PPE
Toxicity is measured by LD50 - the single dose (mg per kg body weight) that kills 50% of test animals; the lower the number, the more toxic. Always note the route (oral, dermal, inhalation): a product with a high oral LD50 can still be very hazardous through skin. Federal labels carry signal words and symbols: Danger with a skull and crossbones means very toxic; Warning means moderately toxic; Caution means slightly toxic. Separate acute effects (hours to days) from chronic effects (cancer, reproductive, neurological - after repeated exposure), and remember "organic" or "natural" does not mean low hazard.
Exposure routes: dermal (by far the most common for handlers - hands, forearms, neck), inhalation (vapours, mists, dusts - worst in enclosed spaces), oral (eating, drinking, smoking, poor hand washing) and ocular (splashes, rubbing eyes with contaminated gloves).
PPE comes from the label and SDS and is task-specific: mixing/loading generally requires more protection than applying. Use chemical-resistant gloves (butyl, nitrile, neoprene) - never leather or cotton, which soak and hold product against the skin; check the SDS for the glove material matched to that active ingredient. Coveralls, boots, goggles or face shield, and a properly fit-tested respirator with the right cartridge; cartridges have finite service life and must be changed on schedule.
Traps: assuming dilute spray needs the same PPE as concentrate (read the label); treating a hat and sunglasses as eye protection; and arguing that dizziness and sweating prove heat stress rather than poisoning - or the reverse. Suspicion of poisoning should always be managed as poisoning.
Rule of thumb: PPE goes on before any container is opened; remove outer gloves last, then wash hands before touching your face, food or phone.