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4.1.2.: Classification criteria for substances

4.1.2.1.

►M12 The system for classification recognises that the intrinsic hazard to aquatic organisms is represented by both the acute and chronic toxicity of a substance. For the long-term (chronic) hazard, separate hazard categories are defined representing a gradation in the level of hazard identified. ◄ The lowest of the available toxicity values between and within the different trophic levels (fish, crustacean, algae/aquatic plants) shall normally be used to define the appropriate hazard category(ies). There are circumstances, however, when a weight of evidence approach is appropriate.

4.1.2.2.

►M12 The core classification system for substances consists of one short-term (acute) hazard classification category and three long-term (chronic) hazard classification categories. The short-term (acute) and long-term (chronic) classification categories are applied independently. ◄

4.1.2.3.

►M12 The criteria for classification of a substance in Acute 1 are defined on the basis of acute aquatic toxicity data only (EC50 or LC 50). The criteria for classification of a substance into Chronic 1 to 3 follow a tiered approach where the first step is to see if available information on chronic toxicity merits long-term (chronic) hazard classification. In absence of adequate chronic toxicity data, the subsequent step is to combine two types of information, i.e. acute aquatic toxicity data and environmental fate data (degradability and bioaccumulation data) (see Figure 4.1.1). ◄

Figure 4.1.1

▼M12

Categories for substances long-term (chronic) hazardous to the aquatic environment

▼M2

4.1.2.4.

►M12 The system also introduces a ‘safety net’ classification (referred to as Chronic 4) for use when the data available do not allow classification under the formal criteria for Acute 1 or Chronic 1 to 3 but there are nevertheless some grounds for concern (see example Table 4.1.0). ◄

4.1.2.5.

Substances with acute toxicities below 1 mg/l or chronic toxicities below 0,1 mg/l (if non-rapidly degradable) and 0,01 mg/l (if rapidly degradable) contribute as components of a mixture to the toxicity of the mixture even at a low concentration and shall normally be given increased weight in applying the summation of classification approach (see note 1 of Table 4.1.0 and section 4.1.3.5.5).

4.1.2.6.

The criteria for classifying and categorising substances as ‘hazardous to the aquatic environment’ are summarised in Table 4.1.0.

▼M12

Table 4.1.0

Classification categories for substances hazardous to the aquatic environment

(a) Short-term (acute) aquatic hazard
Category Acute 1:	(Note 1)
96 hr LC50 (for fish)	≤ 1 mg/l and/or
48 hr EC50 (for crustacea)	≤ 1 mg/l and/or
72 or 96 hr ErC50 (for algae or other aquatic plants)	≤ 1 mg/l.	(Note 2)
(b) Long-term (chronic) aquatic hazard
(i) Non-rapidly degradable substances (Note 3) for which there are adequate chronic toxicity data available
Category Chronic 1:	(Note 1)
Chronic NOEC or ECx (for fish)	≤ 0,1 mg/l and/or
Chronic NOEC or ECx (for crustacea)	≤ 0,1 mg/l and/or
Chronic NOEC or ECx (for algae or other aquatic plants)	≤ 0,1 mg/l.
Category Chronic 2:
Chronic NOEC or ECx (for fish)	≤ 1 mg/l and/or
Chronic NOEC or ECx (for crustacea)	≤ 1 mg/l and/or
Chronic NOEC or ECx (for algae or other aquatic plants)	≤ 1 mg/l.
(ii) Rapidly degradable substances (Note 3) for which there are adequate chronic toxicity data available
Category Chronic 1:	(Note 1)
Chronic NOEC or ECx (for fish)	≤ 0,01 mg/l and/or
Chronic NOEC or ECx (for crustacea)	≤ 0,01 mg/l and/or
Chronic NOEC or ECx (for algae or other aquatic plants)	≤ 0,01 mg/l.
Category Chronic 2:
Chronic NOEC or ECx (for fish)	≤ 0,1 mg/l and/or
Chronic NOEC or ECx (for crustacea)	≤ 0,1 mg/l and/or
Chronic NOEC or ECx (for algae or other aquatic plants)	≤ 0,1 mg/l.
Category Chronic 3:
Chronic NOEC or ECx (for fish)	≤ 1 mg/l and/or
Chronic NOEC or ECx (for crustacea)	≤ 1 mg/l and/or
Chronic NOEC or ECx (for algae or other aquatic plants)	≤ 1 mg/l.
(iii) Substances for which adequate chronic toxicity data are not available
Category Chronic 1:	(Note 1)
96 hr LC50 (for fish)	≤ 1 mg/l and/or
48 hr EC50 (for crustacea)	≤ 1 mg/l and/or
72 or 96 hr ErC50 (for algae or other aquatic plants)	≤ 1 mg/l.	(Note 2)
and the substance is not rapidly degradable and/or the experimentally determined BCF ≥ 500
(or, if absent, the log Kow ≥ 4).	(Note 3).
Category Chronic 2:
96 hr LC50 (for fish)	> 1 to ≤ 10 mg/l and/or
48 hr EC50 (for crustacea)	> 1 to ≤ 10 mg/l and/or
72 or 96 hr ErC50 (for algae or other aquatic plants)	> 1 to ≤ 10 mg/l.	(Note 2)
and the substance is not rapidly degradable and/or the experimentally determined BCF ≥ 500
(or, if absent, the log Kow ≥ 4).	(Note 3).
Category Chronic 3:
96 hr LC50 (for fish)	> 10 to ≤ 100 mg/l and/or
48 hr EC50 (for crustacea)	> 10 to ≤ 100 mg/l and/or
72 or 96 hr ErC50 (for algae or other aquatic plants)	> 10 to ≤ 100 mg/l.	(Note 2)
and the substance is not rapidly degradable and/or the experimentally determined BCF ≥ 500
(or, if absent, the log Kow ≥ 4).	(Note 3).
‘Safety net’ classification Category Chronic 4 Cases when data do not allow classification under the above criteria but there are nevertheless some grounds for concern. This includes, for example, poorly soluble substances for which no acute toxicity is recorded at levels up to the water solubility (note 4), and which are not rapidly degradable in accordance with Section 4.1.2.9.5 and have an experimentally determined BCF ≥ 500 (or, if absent, a log Kow ≥ 4), indicating a potential to bioaccumulate, which will be classified in this category unless other scientific evidence exists showing classification to be unnecessary. Such evidence includes chronic toxicity NOECs > water solubility or > 1 mg/l, or other evidence of rapid degradation in the environment than the ones provided by any of the methods listed in Section 4.1.2.9.5.

▼M2

Note 1:

When classifying substances as Acute Category 1 and/or Chronic Category 1 it is necessary at the same time to indicate the appropriate M-factor(s) (see Table 4.1.3).

Note 2:

Classification shall be based on the ErC50 [= EC50 (growth rate)]. In circumstances where the basis of the EC50 is not specified or no ErC50 is recorded, classification shall be based on the lowest EC50 available.

Note 3:

When no useful data on degradability are available, either experimentally determined or estimated data, the substance should be regarded as not rapidly degradable.

Note 4:

‘No acute toxicity’ is taken to mean that the L(E)C50(s) is/are above the water solubility. Also for poorly soluble substances, (water solubility < 1 mg/l), where there is evidence that the acute test does not provide a true measure of the intrinsic toxicity.

4.1.2.7. Aquatic toxicity

4.1.2.7.1.

Acute aquatic toxicity is normally determined using a fish 96-hour LC50, a crustacea species 48-hour EC50 and/or an algal species 72- or 96-hour EC50. These species cover a range of trophic levels and taxa and are considered as surrogate for all aquatic organisms. Data on other species (e.g. Lemna spp.) shall also be considered if the test methodology is suitable. The aquatic plant growth inhibition tests are normally considered as chronic tests but the EC50s are treated as acute values for classification purposes (see note 2).

4.1.2.7.2.

For determining chronic aquatic toxicity for classification purposes data generated according to the standardised test methods referred to in Article 8(3) shall be accepted, as well as results obtained from other validated and internationally accepted test methods. The NOECs or other equivalent ECx (e.g. EC10) shall be used.

4.1.2.8. Bioaccumulation

4.1.2.8.1.

Bioaccumulation of substances within aquatic organisms can give rise to toxic effects over longer time scales even when actual water concentrations are low. For organic substances the potential for bioaccumulation shall normally be determined by using the octanol/water partition coefficient, usually reported as a log Kow. The relationship between the log Kow of an organic substance and its bioconcentration as measured by the bioconcentration factor (BCF) in fish has considerable scientific literature support. Using a cut-off value of log Kow ≥ 4 is intended to identify only those substances with a real potential to bioconcentrate. While this represents a potential to bioaccumulate, an experimentally determined BCF provides a better measure and shall be used in preference if available. A BCF in fish of ≥ 500 is indicative of the potential to bioconcentrate for classification purposes. Some relationships can be observed between chronic toxicity and bioaccumulation potential, as toxicity is related to the body burden.

4.1.2.9. Rapid degradability of organic substances

4.1.2.9.1.

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

4.1.2.9.2.

One way of demonstrating rapid degradation utilises the biodegradation screening tests designed to determine whether an organic substance is ‘readily biodegradable’. Where such data are not available, a BOD(5 days)/COD ratio ≥ 0,5 is considered as indicative of rapid degradation. Thus, a substance which passes this screening test is considered likely to biodegrade ‘rapidly’ in the aquatic environment, and is thus unlikely to be persistent. However, a fail in the screening test does not necessarily mean that the substance will not degrade rapidly in the environment. Other evidence of rapid degradation in the environment may therefore also be considered and are of particular importance where the substances are inhibitory to microbial activity at the concentration levels used in standard testing. Thus, a further classification criterion is included which allows the use of data to show that the substance did actually degrade biotically or abiotically in the aquatic environment by > 70 % in 28 days. Thus, if degradation is demonstrated under environmentally realistic conditions, then the criterion of ‘rapid degradability’ is met.

4.1.2.9.3.

Many degradation data are available in the form of degradation half-lives and these can be used in defining rapid degradation provided that ultimate biodegradation of the substance, i.e. full mineralisation, is achieved. Primary biodegradation does not normally suffice in the assessment of rapid degradability unless it can be demonstrated that the degradation products do not fulfil the criteria for classification as hazardous to the aquatic environment.

4.1.2.9.4.

The criteria used reflect the fact that environmental degradation may be biotic or abiotic. Hydrolysis can be considered if the hydrolysis products do not fulfil the criteria for classification as hazardous to the aquatic environment.

4.1.2.9.5.

Substances are considered rapidly degradable in the environment if one of the following criteria holds true:

(a) if, in 28-day ready biodegradation studies, at least the following levels of degradation are achieved:

(i) tests based on dissolved organic carbon: 70 %;

(ii) tests based on oxygen depletion or carbon dioxide generation: 60 % of theoretical maximum.

These levels of biodegradation must be achieved within 10 days of the start of degradation which point is taken as the time when 10 % of the substance has been degraded, unless the substance is identified as an UVCB or as a complex, multi-constituent substance with structurally similar constituents. In this case, and where there is sufficient justification, the 10-day window condition may be waived and the pass level applied at 28 days; or

(b) if, in those cases where only BOD and COD data are available, when the ratio of BOD5/COD is ≥ 0,5; or

(c) if other convincing scientific evidence is available to demonstrate that the substance can be degraded (biotically and/or abiotically) in the aquatic environment to a level > 70 % within a 28-day period.

4.1.2.10. Inorganic compounds and metals

4.1.2.10.1.

For inorganic compounds and metals, the concept of degradability as applied to organic compounds has limited or no meaning. Rather, such substances may be transformed by normal environmental processes to either increase or decrease the bioavailability of the toxic species. Equally the use of bioaccumulation data shall be treated with care ( 14 ).

4.1.2.10.2.

Poorly soluble inorganic compounds and metals may be acutely or chronically toxic in the aquatic environment depending on the intrinsic toxicity of the bioavailable inorganic species and the rate and amount of this species which enter solution. All evidence must be weighed in a classification decision. This would be especially true for metals showing borderline results in the Transformation/Dissolution Protocol.

4.1.1.

4.1.3.

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4.1.2.: Classification criteria for substances