Toxicology, Human Health Protection and Personal Safety
Toxicity is not the same as hazard
Toxicity is a product's capacity to injure; hazard is toxicity multiplied by exposure. Routes of exposure are dermal (the main route for applicators), inhalation, oral and ocular. Acute effects appear soon after exposure; chronic effects follow repeated exposure over time.
LD50 (mg/kg) and LC50 (mg/L or ppm in air) express acute toxicity: the lower the value, the more toxic the product. Signal words and hazard symbols on the label reflect this acute picture.
Know the signature effects: organophosphates and carbamates inhibit cholinesterase, producing cholinergic signs (salivation, lacrimation, urination, defecation, GI cramps, emesis, plus pinpoint pupils and slow heart rate); pyrethrins and pyrethroids cause tingling or numbness (paresthesia) and tremors; anticoagulant rodenticides cause bleeding and respond to vitamin K1; fumigants act on the central nervous system and respiratory tract.
PPE selection starts with the label: gloves matched to the formulation (nitrile versus butyl), coveralls, boots, eye protection and respirators, which must be fit-tested and cartridge-matched. Never eat, drink or smoke while handling; wash before breaks; change contaminated clothing; watch for heat stress under impermeable PPE. Read SDS Section 4 for first aid and call Poison Control for advice.
Traps: assuming "natural" or "organic" means low hazard; thinking a higher LD50 means more toxic; ignoring dermal absorption; assuming mixing two products is safer than one; underestimating heat stress.
Rule of thumb: a tenfold lower LD50 means roughly ten times more toxic - compare numbers by ratio, not by the size of the figure.