. Author manuscript; available in PMC: 2006 Dec 8.

Published in final edited form as: Bull World Health Organ. 2004 Jan 20;81(11):789–798.

Box 3.

WHO classification of pesticide toxicity (48).

Class	oral		dermal
	solid	liquid	solid	liquid
Ia - extremely hazardous	≤5	<20	<10	<40
Ib - highly hazardous	5-50	20-200	10-100	40-400
II - moderately hazardous	50-500	200-2000	100-1000	400-4000
III - slightly hazardous	>500	>2000	>1000	>4000
Active ingredients unlikely to present acute hazard

Toxicity of pesticides is classified using animal LD50s (mg/kg of toxicant required to kill 50% of a large population of test animals) of the technical compound and formulations. The relative toxicity of compounds in human poisoning is complicated by the ease of treatment – for example Class I OP pesticides can be treated with atropine and oximes with some effect while self-poisoning with Class II organochlorines is practically untreatable in some locations.