Pesticide Registration Toolkit

Hazard identification & characterization.

Relevant documents

 Hazard Assessment Table - Human Health


Human health hazard identification is the identification of the type and nature of adverse effects that a pesticide may cause in an organism. Human health hazard characterization is the qualitative and, wherever possible, quantitative description of the inherent property of a pesticide having the potential to cause adverse effects. This should, where possible, include a description of its mode of action, a dose–response assessment and the establishment of a threshold dose below which the toxic effects are no longer observed.

Hazard assessment includes both hazard identification and hazard characterization. It is the process designed to determine the possible adverse effects of a pesticide to which human beings could be exposed. The purpose of human health hazard assessment is to identify:

  • whether an agent may pose a hazard to human health; and
  • the circumstances in which the hazard may be expressed.

A hazard assessment is based on the intrinsic toxicity of the product and does not take into account the degree of exposure of the person to the pesticide. Note that exposure to a product with a relatively high hazard does not necessarily result a high risk, if the degree of exposure is low. Alternatively, high exposure to a pesticide with a low hazard may well result in adverse health effects. By drawing conclusions about the risk of pesticide based only on a hazard assessment, one implicitly assumes that any exposure to the pesticide, irrespective of magnitude, will lead to the toxic effect identified in the hazard assessment. This may be valid for certain pesticides under certain circumstances, but is not generally the case. In many instances, the degree of exposure does determine risk (i.e. “the dose makes the poison”). A hazard assessment is often done as a first step in a more elaborate risk assessment. Moreover, a hazard assessment is also done as a basis for hazard classification of the product.

Data required

The data required for human health hazard identification and characterization of a pesticide can be searched in the Data Requirements Tool. These are mainly animal toxicity studies and in-vitro studies, but may also include quantitive structure activity relationships (QSARS) and human data, used to assess both acute and chronic effects of the pesticide. The toxicity data used to asses hazard may be different, depending on the pesticide group and the intended use of the product.


1. Data evaluation

If the registration authority employs experienced toxicologist(s), it can evaluate the range and quality of human and animal toxicity information itself. The following points are of particular importance in evaluating the relevance of toxicological studies to hazard identification and risk assessment (see guidelines cited below for further information):

  • Experimental design and quality of the critical study or studies. This includes, for example, purity of the active ingredient tested, physicochemical properties (stability, etc.), size of the study (number of exposure groups, group sizes, sex, etc.), suitability of the exposure levels used, duration of exposure, extent of toxicological and statistical evaluation, relevancy of the route of exposure to humans, and whether the study adhered to established guidelines and GLP.
  • Nature of the effects seen; their severity and sites, and whether they would be reversible on cessation of exposure.
  • Is it possible to identify a dose–response relationship, no-observed-adverse-effect-level (NOAEL) and lowest-observed-adverse-effect-level (LOAEL)?

The final outcome of this evaluation is often summarized in a so-called “list of endpoints”. This is a summary of all aspects of the evaluation including the agreed critical value for each aspect (e.g. Rat oral LD50 = xxx mg/kg bw; eye irritation = irritant/non-irritant; relevant No Observed Adverse Effect Concentration (NOAEL) = type of study: yyy mg/kg bw per day).

A template for the list of toxicological and hazard endpoints, as used in the European Union, can be found here (see Section 2 of this document for the toxicological endpoints). .

2. Hazard classification

The outcome of the hazard assessment is also used to classify hazards. Hazard classification is used to communicate, in a simple and clear manner, the dangers of a pesticide to its users or handlers, for instance in transport, storage, use and disposal. The two most used hazard classification systems for pesticides are the GHS (Globally harmonized system for the classification and labelling of chemicals) and the WHO Classification of pesticides by hazard. These systems provide the criteria needed to classify the health hazards of a pesticide on the basis of the outcome of the toxicological studies mentioned under Data evaluation above. However, GHS and WHO do not provide the actual hazard classifications of the formulated pesticide products that have to be registered (though WHO classifies pesticide active ingredients). Such classification still needs to be conducted by national or regional regulatory authorities. Since the GHS is now the international standard for the classification of chemicals, it is recommended that the registration authority classifies the formulated pesticide product according the GHS. If capacity is lacking for complete GHS classification, to the WHO classification may be used as an alternative, though it is less complete. On the other hand, the registration authority may choose to follow international or regional authorities that classify individual pesticides, such as the ILO/WHO International Chemical Safety Cards (ICSC) or the European Chemicals Agency (ECHA). Further information on the classification systems can be found in the Hazard Classification Tool, which also provides links to authorities that classify individual pesticide active ingredients.

3. Circumstances in which the hazard may be expressed

The circumstances in which the identified hazards of the pesticide may be expressed should be identified. This involves questions such as: Who may be exposed to the pesticide (operators, workers, residents, consumers, etc.)? When will this occur (during pesticide application, when harvesting the crop, if living close to the treated location, during transport and storage, when consuming treated commodities, if sleeping in a treated room, etc.)? What is (are) the route(s) of exposure (oral, dermal, inhalation)? Will exposure likely be short-term or long-term?

4. Potential hazard concerns

On the basis of the list of toxicological endpoints, the hazard classification and the identification of circumstances in which the hazard may be expressed, the registration authority should identify which hazards may be of concern for the handling and use of the pesticide under local conditions of use. In principle, any pesticide product that is classified with the GHS signal words “Danger” or “Warning”, and to which persons may be exposed, may be of concern. Furthermore, the International Code of Conduct on Pesticide Management defines Highly Hazardous Pesticides (HHPs) as:

 pesticides that are acknowledged to present particularly high levels of acute or chronic hazards to health or environment according to internationally accepted classification systems such as WHO or GHS or their listing in relevant binding international agreements or conventions. In addition, pesticides that appear to cause severe or irreversible harm to health or the environment under conditions of use in a country may be considered to be and treated as highly hazardous.

The FAO/WHO Joint Meeting on Pesticide Management (JMPM) defined criteria to identify Highly Hazardous Pesticides (HHPs). If the pesticide to be registered is classified as an HHP, it is likely to be high concern to registration authorities. However, pesticides that are not HHPs may still be of concern under local conditions of use (see above).

Outcome of the hazard assessment

  1. List of endpoints of the toxicological evaluation
  2. Hazard classification for human health aspects
  3. List of circumstances in which the hazard may be expressed
  4. List of potential human health hazard concerns

An Hazard Assessment Table - Human Health  can be used to summarize the data.

Interpretation of the outcome

When interpreting the data, one should be mindful of the fact that the hazard of a pesticide product does not necessarily represent its risk, because exposure has not been taken into account. Therefore, in principle, a risk assessment should be conducted (at least) of all pesticides that pose human health hazards that are of concern. The risk assessment will show the level of risk of the pesticide under the proposed use conditions (see the various human health risk assessment methods presented under the Assessment Methods Tool). If no human health risk assessment can be conducted, the registration authority may decide on the acceptability of the pesticide on the basis of a hazard assessment alone. This is not recommended, but may be a necessity due to limited resources at the registration authority or the absence of appropriate risk assessment models. If, in such a case, high human health hazards have been identified, the registration authority may decide to severely restrict the pesticide, or even not to register it. This is because pesticide products posing a high health hazard may also pose a high health risk, in particular in situations where judicious application practices are not respected or appropriate personal protective equipment is not being used. In this respect, the International Code of Conduct stipulates in its Article 7.5 that:

Prohibition of the importation, distribution, sale and purchase of highly hazardous pesticides may be considered if, based on risk assessment, risk mitigation measures or good marketing practices are insufficient to ensure that the product can be handled without unacceptable risk to humans and the environment.

FAO does not set criteria on the acceptability of human health hazards; this is the final responsibility of the registration authority. 


Further practical guidance on human health hazard assessment can be found in: