The toxicity classes of insecticides are classified based on the acute oral and dermal LD50 (the dose that is lethal to 50% of test animals, expressed in mg/kg body weight) and the inhalation LC50 (lethal concentration).
The World Health Organization updated its pesticide hazard classification system in 2009, dividing products into five main classes.
Class Ia — Extremely Hazardous: oral LD50 <5 mg/kg.
Class Ia products are banned or restricted from household use in the vast majority of countries and may only be used by licensed professionals.
Class Ib — Highly Hazardous: LD50 5–50 mg/kg.
Many organophosphate insecticides (e.
, dichlorvos, parathion) fall into this category — most countries have restricted or phased out their household use.
Class II — Moderately Hazardous: LD50 50–2000 mg/kg.
Many organophosphate and carbamate products fall into this category.
Class III — Slightly Hazardous: LD50 >2000 mg/kg.
Most pyrethroid and neonicotinoid household insecticides fall into this category — their acute mammalian toxicity is low.
Class U — Unlikely to present acute hazard in normal use.
Within this classification system — household insecticides should always be Class III (Slightly Hazardous) or Class U products.
The term "non-toxic" is not permitted on pesticide product labels in China's pesticide registration system — even low-toxicity products must bear a toxicity class identifier.