The understanding that some pesticides are more hazardous than others is well established. Recognition of this is reflected by the World Health Organization (WHO) Recommended Classification of Pesticides by Hazard, which was first published in 1975. The document classifies pesticides in one of five hazard classes according to their acute toxicity. In 2002, the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) was introduced, which in addition to acute toxicity also provides classification of chemicals according to their chronic health hazards and environmental hazards.