5.1.1 Acute Hazards and Operator Safety
The World Health Organisation (WHO) provides an internationally recognised system for classifying the acute hazard of pesticides.
They are grouped in terms of their median lethal dose (LD50) from Class I (most toxic) to Unclassified (unlikely to cause harm) with each class bounded by a 10-fold range of dose (in mg/kg body weight).
The WHO system recognises a 4-fold reduced hazard with solid formulations, in comparison with liquids. The classification was further developed by the US Environmental Protection Agency (EPA), which also recognises inhalation, eye and skin sensitisation effects.
Both classifications should be based on formulations (where such information is available), but unfortunately, detailed information on individual products is often difficult to obtain, and many entries in the Pesticide Manual [5] are estimated from AI values.
Member countries of the EU evaluate each product on a case-by-case basis and, if necessary, assign one of nine risk symbols and a large number of associated risk phrases [1]; this scheme also has been adopted by the International Labour Organization.
i. The World Health Organisation (WHO) classification
| Class | Solids Oral | Dermal | Liquids Oral | Dermal | |
|---|---|---|---|---|---|
| Ia | Extremely Hazardous | <= 5 | <= 10 | 1.75 (1.71) | III |
| Ib | Highly Hazardous | 6-50 | 11-100 | 21-200 | 41-400 |
| II | Moderately Hazardous | 51-500 | 101-1000 | 201-2000 | 401-4000 |
| III | Slightly Hazardous | >= 501 | >= 1001 | >= 2001 | >= 4001 |
| (U) | Unlikely to present acute hazard in normal use | >= 2000 | - | > 3000 | - |
(LD50 to rats mg/kg body weight: of formulations where information is available)
ii. The US Environmental Protection Agency (EPA) system
| Class |
All formulations LD50 (mg/kg) |
All formulations LD50 (mg/kg) |
Inhalation LC50 (mg/l) |
Eye effects | Skin effects |
|---|---|---|---|---|---|
| ORAL | DERMAL | ||||
| I | <= 50 | <= 200 | <= 2 | Corrosive, corneal opacity not reversible within 7 days | Corrosive |
| II | 51-500 | 201-2000 | 0.2-2 | Corneal opacity not reversible within 7 days, irritation persisting for 7 days | Severe irritation at 72 hours |
| III | 501-5000 | 2001-20,000 | 2-20 | No corneal opacity, irritation reversible within 7 days | Moderate irritation at 72 hours |
| IV | > 5000 | > 20,000 | > 20 | No irritation | Mild or slight irritation at 72 hours |
In some countries, toxicity classification is illustrated by a colour coded stripe or triangle indicating the hazard of the product. This is excellent, but unfortunately not universal.
To summarise, for farmers and operators that do not have access to good protective equipment, the guiding rule should be:
| Class | hazardous | handling |
|---|---|---|
| Class I pesticides | extremely / highly hazardous | DO NOT USE |
| Class II pesticides | moderately hazardous | take great care |
| Class III pesticides | slightly hazardous | take care |
| Unclassified / Class IV pesticides | unlikely to be hazardous | still take care |
Certain pressure groups, including the Global IPM Facility (supported by FAO and other organisations working with Farmer Field Schools) have suggested that Class I and II products should be withdrawn from general use, since smallholder farmers are unlikely to use appropriate personal protective equipment (PPE).
With the development of new insecticide products, there are now only a very few cases where Class I pesticides can be justified at all, let alone for smallholder agricultural problems. However, complications could occur if all Class II products were to be withdrawn immediately.
The problem here is especially with insecticides, where there is often a need for resistance management strategies involving alternations in the use of different groups of compounds.
Therefore, a phased restriction / withdrawal of the more hazardous compounds may be more appropriate, before safer products become available.
EC Regulation No 1272/2008 [2], of the European Parliament and Council, provides a harmonised basis classification, labelling and packaging of substances and mixtures: including for example, such aspects as pictograms as discussed elsewhere.
The original Directives it replaced: 67/548/EEC and 1999/45/EC were repealed on 1 June 2015 and Regulation (EC) No 1907/2006 [3], concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) and which established a European Chemicals Agency, was also amended.
As with AI, REACH restricted substance lists are regularly updated with adjustments made to the Annexes: a recent revision occurred in 2021. [4]
