The GHS describes in detail how hazard categories should be assigned for each environmental hazard class. A summary of these methods can be found by clicking on the entries below. More detail is provided in the GHS document.

• Hazardous to the aquatic environment
• Hazardous to the ozone layer

 Back to: Classification of Environmental Hazards

The basic elements for classification of aquatic hazards are:

• Acute aquatic toxicity
• Chronic aquatic toxicity
• Degradation (biotic or abiotic) of organic chemicals
• Potential for or actual bioaccumulation

Toxicity data is normally needed on three trophic levels (i.e. algae, aquatic invertebrates and fish). 

For packaged substances, like formulated pesticides, it is considered that the principal hazard is defined by chronic toxicity. For acute toxicity, only Category Acute 1 is therefore considered hazardous; at toxicity levels above this, it is considered that the acute toxicity itself does not describe the principal hazard, which arises from low concentrations causing effects over a longer time scale (see Table 4.1.1 (a) and (b) in Part 4 of the GHS)

Acute aquatic toxicity

Short-term hazard is determined by acute toxicity.

The intrinsic property of a pesticide to be harmful after short-term exposure (hours to days) is generally expressed in terms of the LC₅₀ (50% lethal concentration), or the EC₅₀ (50% effect concentration), e.g. immobilization of daphnids or reduction in growth rate of algae.

The criteria for classification of a substance in acute category 1 is defined based on the acute toxicity data only, expressed as LC₅₀ or EC₅₀.

Chronic aquatic toxicity

Long-term hazard is determined by chronic toxicity. 

Chronic toxicity is an intrinsic property of the pesticide being harmful during exposures which are determined in relation to the life cycle of the organism (i.e. days to weeks). These are generally expressed in terms of: NOEC (no observed effect concentration), LOEC (lowest observed effect concentration) or EC_x (x% effect concentration). These are sublethal endpoints, e.g., survival, growth or reproduction.

Substances are classified in the various chronic categories unless the chronic NOEC that is available for all three trophic levels exceeds water solubility or is above 1 mg/l. Part 4 of the GHS provides further guidance in case adequate chronic toxicity data is not available.

The studies on aquatic chronic toxicity are required for pesticide registration. In case such data is not available the following information on degradability and bioaccumulation potential could be used for classification.

Rapid degradability

Substances that rapidly degrade can be quickly removed from the environment. While effects can occur, particularly in the event of a spillage or accident, they will be localized and of short duration. The absence of rapid degradation in the environment can mean that a substance in the water has the potential to exert toxicity over a wide temporal and spatial scale.

Criteria for rapid degradability are if in 28-day ready biodegradation studies, the following levels of degradation are achieved:

• tests based on dissolved organic carbon: 70% degradation
• tests based on oxygen depletion or carbon dioxide generation: 60% degradation of theoretical maxima.

The decision scheme below may be used as a general guidance to facilitate decisions in relation to rapid degradability in the aquatic environment and classification of chemicals hazardous to the aquatic environment (EU, 2017) 

A substance is considered to be “not rapidly degradable” unless at least one of the following is fulfilled:

• The substance is demonstrated to be readily biodegradable in a 28-day test for ready biodegradability. The pass level of the test (70 % DOC removal or 60 % theoretical oxygen demand) must be achieved within 10 days from the onset of biodegradation, if it is possible to evaluate this according to the available test data (the ten-day window condition may be waived for complex multi-component substances and the pass level applied at 28 days. If this is not possible, then the pass level should be evaluated within a 14 days’ time window if possible, or after the end of the test; or
• The substance is demonstrated to be ultimately degraded in a surface water simulation test with a half-life of < 16 days (corresponding to a degradation of >70 % within 28 days); or
• The substance is demonstrated to be primarily degraded biotically or abiotically e.g. via hydrolysis, in the aquatic environment with a half-life <16 days (corresponding to a degradation of > 70 % within 28 days), and it can be demonstrated that the degradation products do not fulfill the criteria for classification as hazardous to the aquatic environment.

Bioaccumulation

Bioaccumulation is one of the important intrinsic properties of substances that determine the potential environmental hazard. Bioaccumulation of a substance into an organism is not a hazard in itself, but bioconcentration and bioaccumulation will result in a body burden, which may or may not lead to toxic effects. A distinction should, however, be drawn between bioconcentration and bioaccumulation.

The bioaccumulation potential is applied in the GHS system to establish criteria for long term toxicity in cases where no long- term data is available. This is normally not relevant for pesticides since data on long-term effects is required in the registration process for pesticides. However, in cases where long-term data is not available, data on bioaccumulation is necessary.

Classification of mixtures (i.e. pesticide products)

In general, the approach used is dependent upon the type of information available for the pesticide formulation itself and for its components. Testing of mixtures should generally be avoided. It is highly complex, both to conduct the test and to interpret the data. Degradability and bioaccumulation tests for mixtures are never used as they are usually difficult to interpret.

Hence, classification of pesticide products is based on the hazards of the components of the product (active ingredient(s) and co-formulants). This is done by applying “bridging principles” or the “summation method”. (GHS chapter 4.1.3)

To be able to do so, it is important to get a clear picture about the components of the pesticide product. Basic information includes:

• the identity of the components,
• their classification,
• any applied M-factor, and
• concentrations of the components in the mixture.

Application of the M-factor:

When a mixture contains ingredients classified as Acute 1 or Chronic 1, attention should be paid to the fact that such ingredients, when their acute toxicity is well below 1 mg/L and/or chronic toxicity is well below 0.1 mg/L, contribute to the toxicity of the mixture even at a low concentration. Active ingredients in pesticides often possess such high aquatic toxicity. Under these circumstances the application of the normal cut-off values/concentration limits may lead to an “under-classification” of the mixture. Therefore, multiplying factors should be applied to account for highly toxic ingredients.

* Under development *