Pesticide Registration Toolkit

Hazard assessment for soil organisms

Relevant documents
Hazard Assessment Table for Soil organisms

 

Principle

A hazard assessment is based on the intrinsic properties of the product and does not take into account the degree of exposure of the soil organisms to the pesticide. Note that exposure to a product with a relatively high hazard does not necessarily result in a high risk, if the level of exposure is low. Alternatively, high exposure to a pesticide with a low hazard may well result in adverse effects on soil organisms.
A hazard assessment is often done as a first step in a more elaborate risk assessment. The objective of a hazard assessment is:

  • to evaluate which soil organisms are likely to be exposed by the pesticide and under which circumstances;
  • to identify the various routes of exposure of the soil organisms to the pesticide;
  • to compile the relevant environmental fate and toxicity data;
  • to decide which risk assessments need to be conducted;
  • (optional) to classify the pesticide product according to persistence in soil and toxicity.

By drawing conclusions about the risk of a pesticide based only on a hazard assessment, one implicitly assumes that any exposure to the pesticide, irrespective of its magnitude, will lead to the toxic effect identified in the hazard assessment. This may be valid for certain pesticides under certain circumstances. However, since the degree of pesticide exposure of soil organisms in the field tends to be very variable, it is generally not possible to draw a conclusion about risks to soil organisms only based on the hazard of a pesticide product.

 

Data required

The following data can be used for a hazard assessment for soil organisms:

  • Application methods, expected crop cover (crop interception) at the time of treatment (i.e. how much of the pesticide will reach the soil?)
  • Soil organisms (which groups of soil organisms are present in the soil?)
  • Persistence of the active ingredient in soil (endpoints e.g. DT50 and/or DT90)
  • Effects on earthworms – Earthworm reproduction test (endpoint e.g. NOEC)
  • Effects on springtails – Collembola reproduction test (endpoints e.g. LC50, NOEC)
  • Effects on soil microbial activity – Nitrogen turnover test (endpoints e.g. EC25, EC10, NOEC)

More information on data requirements and testing guidelines for soil organisms can be found in the Data Requirements module in the Toolkit.

 

Procedure

Evaluate possible route(s) and likelihood of exposure

Investigate if the directions for use of the active ingredient are likely to contaminate the soil. For example, for the following applications methods soil organisms are normally not exposed: e.g. treatment of food storage in enclosed spaces, wound sealing or healing treatments of trees, enclosed spaces with rodenticidal baits. It is also important to evaluate at which plant growth stage the pesticide will be applied, because depending on the crop cover (crop interception), more or less of the pesticide will reach the soil. For example, if the pesticide is to be applied at a late stage of crop production, the crop interception can be up to 80-90%, meaning that only 10-20% of the pesticide may reach the soil.

Assess the persistence of the active ingredient

Persistence of the active ingredient(s) is of special concern because persistent pesticides may have effects on several generations of soil organisms and any population recovery could take a long time. The degradation of the pesticide in soil is described by its degradation half-life (DT50 or DegT50), or other measures of degradation (e.g. DT90).

Various hazard-based criteria that include the persistence of a pesticide in soil are presently used. These include the Persistent Organic Pollutant (POP) criteria of the Stockholm Convention, the Persistent Bioaccumulative and Toxic (PBT) criteria used in the USA and the EU, and the very Persistent, very Bioaccumulative (vPvB) criteria used in the EU.

In all three cases, pesticides are classified on the basis of persistence and bioaccumulation potential, either in water, sediment or soil (and in some cases also based on toxicity and long-range transport capacity). Explicit criteria for persistence in soil are provided, but bioaccumulation of pesticides in soil organisms is only rarely studied and no international soil bioaccumulation criteria have been set so far. Therefore, a hazard assessment or classification of pesticides only on the basis of POP/PBT/vPvB criteria is presently not feasible for soils. However, an overall persistence assessment – not just for soils – is useful as part of initial screening of the pesticide by a registrar, as it may guide further risk assessment. Furthermore, some countries may decide that a pesticide classified as a POP/PBT/vPvB cannot be registered, not necessarily for the immediate risks that the pesticide poses, but because of the uncertainty of possible long-term effects.

Obtain relevant toxicity data.

Toxicity data for soil organisms can be obtained from the pesticide registration dossier (see Data Required, above).

Toxicity data supplied by the applicant may be compared with validated (inter)national data available from reputable sources, which can be found in the Information Sources Module (check Pesticide Properties and/or Scientific Reviews)
 

Classify acute and chronic hazard
There is currently no international acknowledged hazard classification of pesticide toxicity of soil organisms.

 

Outcome of the hazard assessment

The outcome of the hazard assessment focusses on:

  • List of endpoints of the toxicity studies
  • Classification of the persistence of the pesticide
  • Description of potential hazards of the pesticide to soil organisms
  • List of circumstances in which the hazard may be expressed and the likelihood of exposure to soil organisms
  • List of hazard concerns for soil organisms

A Hazard Assessment Table for Soil organisms can be used to summarize these data.

 

Interpretation of the outcome

The outcome of the hazard assessment should help to identify whether a risk assessment is warranted, and which exposure and toxicity parameters are important to include in the risk assessment.

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. Since an international acknowledged hazard classification for soil organisms does currently not exist, decision making solely based on hazard criteria for soil organisms and functions is not recommended. Furthermore, the degree of exposure of soil organisms to a pesticide is very variable but plays an important, often overriding, role in the determination of risk in soils. Since relatively simple and robust exposure models are available for soil organisms, basic risk assessment is considered feasible with limited resources.

Therefore, in principle, a risk assessment should be conducted if the pesticide poses a hazard of concern to soil organisms. The risk assessment will show the level of risk of the pesticide under the proposed use conditions. Risk assessment methods, either based on bridging of an existing assessment or a local risk assessment, are presented under the Assessment Methods Tool.