Environmentally hazardous substances include, inter alia, liquid or solid substances pollutant to the
aquatic environment and solutions and mixtures of such substances (such as preparations and wastes).
For the purposes of 126.96.36.199.10, "substance" means chemical elements and their compounds in the
natural state or obtained by any production process, including any additive necessary to preserve the
stability of the product and any impurities deriving from the process used, but excluding any solvent
which may be separated without affecting the stability of the substance or changing its composition.
The aquatic environment may be considered in terms of the aquatic organisms that live in the water,
and the aquatic ecosystem of which they are part9. The basis, therefore, of the identification of hazard
is the aquatic toxicity of the substance or mixture, although this may be modified by further
information on the degradation and bioaccumulation behaviour.
While the following classification procedure is intended to apply to all substances and mixtures, it is
recognised that in some cases, e.g. metals or poorly soluble inorganic compounds, special guidance
will be necessary10.
9 This does not address aquatic pollutants for which there may be a need to consider effects beyond the aquatic
environment such as the impacts on human health etc.
10 This can be found in Annex 10 of the GHS.
The following definitions apply for acronyms or terms used in this section:
- BCF: Bioconcentration Factor;
- BOD: Biochemical Oxygen Demand;
- COD: Chemical Oxygen Demand;
- GLP: Good Laboratory Practices;
- ECx: the concentration associated with x% response;
- EC50: the effective concentration of substance that causes 50% of the maximum response;
- ErC50: EC50 in terms of reduction of growth;
- Kow: octanol/water partition coefficient;
- LC50 (50% lethal concentration): the concentration of a substance in water which causes the
death of 50% (one half) in a group of test animals;
- L(E)C50: LC50 or EC50;
- NOEC (No Observed Effect Concentration): the test concentration immediately below the
lowest tested concentration with statistically significant adverse effect. The NOEC has no
statistically significant adverse effect compared to the control;
- OECD Test Guidelines: Test guidelines published by the Organization for Economic
Cooperation and Development (OECD).
Definitions and data requirements
The basic elements for classification of environmentally hazardous substances (aquatic environment)
(a) Acute aquatic toxicity;
(b) Chronic aquatic toxicity;
(c) Potential for or actual bioaccumulation; and
(d) Degradation (biotic or abiotic) for organic chemicals.
While data from internationally harmonised test methods are preferred, in practice, data from national
methods may also be used where they are considered as equivalent. In general, it has been agreed that
freshwater and marine species toxicity data can be considered as equivalent data and are preferably to
be derived using OECD Test Guidelines or equivalent according to the principles of Good Laboratory
Practices (GLP). Where such data are not available, classification shall be based on the best available
Acute aquatic toxicity means the intrinsic property of a substance to be injurious to an organism in a
short-term aquatic exposure to that substance.
Acute (short-term) hazard, for classification purposes, means the hazard of a chemical caused by its
acute toxicity to an organism during short-term aquatic exposure to that chemical.
Acute aquatic toxicity shall normally be determined using a fish 96 hour LC50 (OECD Test Guideline
203 or equivalent), a crustacea species 48 hour EC50 (OECD Test Guideline 202 or equivalent) and/or
an algal species 72 or 96 hour EC50 (OECD Test Guideline 201 or equivalent). These species are
considered as surrogate for all aquatic organisms and data on other species such as Lemna may also be
considered if the test methodology is suitable.
Chronic aquatic toxicity means the intrinsic property of a substance to cause adverse effects to aquatic
organisms during aquatic exposures which are determined in relation to the life-cycle of the organism.
Long-term hazard, for classification purposes, means the hazard of a chemical caused by its chronic
toxicity following long-term exposure in the aquatic environment.
Chronic toxicity data are less available than acute data and the range of testing procedures less
standardised. Data generated according to the OECD Test Guidelines 210 (Fish Early Life Stage) or
211 (Daphnia Reproduction) and 201 (Algal Growth Inhibition) may be accepted. Other validated and
internationally accepted tests may also be used. The NOECs or other equivalent ECx shall be used.
Bioaccumulation means net result of uptake, transformation and elimination of a substance in an
organism due to all routes of exposure (i.e. air, water, sediment/soil and food).
The potential for bioaccumulation shall normally be determined by using the octanol/water partition
coefficient, usually reported as a log Kow determined according to OECD Test Guideline 107 or 117.
While this represents a potential to bioaccumulate, an experimentally determined Bioconcentration
Factor (BCF) provides a better measure and shall be used in preference when available. A BCF shall
be determined according to OECD Test Guideline 107, 117 or 123.
Degradation means the decomposition of organic molecules to smaller molecules and eventually to
carbon dioxide, water and salts.
Environmental degradation may be biotic or abiotic (e.g. hydrolysis) and the criteria used reflect this
fact. Ready biodegradation is most easily defined using the biodegradability tests (A-F) of OECD Test
Guideline 301. A pass level in these tests may be considered as indicative of rapid degradation in most
environments. These are freshwater tests and thus the use of the results from OECD Test Guideline
306, which is more suitable for marine environments, has also been included. Where such data are not
available, a BOD(5 days)/COD ratio ≥ 0.5 is considered as indicative of rapid degradation.
Abiotic degradation such as hydrolysis, primary degradation, both abiotic and biotic, degradation in
non-aquatic media and proven rapid degradation in the environment may all be considered in defining
Substances are considered rapidly degradable in the environment if the following criteria are met:
(a) In 28-day ready biodegradation studies, 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
These levels of biodegradation shall 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 a complex, multi-component 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 days12; or
(b) In those cases where only BOD and COD data are available, when the ratio of BOD5/COD is ≥
(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 above 70% within
a 28 day period.
Substance classification categories and criteria
Substances shall be classified as "environmentally hazardous substances (aquatic environment)", if
they satisfy the criteria for Acute 1, Chronic 1 or Chronic 2, according to Table 188.8.131.52.10.3.1. These
criteria describe in detail the classification categories. They are diagrammatically summarized in
11 Special guidance on data interpretation is provided in Chapter 4.1 and Annex 9 of the GHS.
12 See Chapter 4.1 and Annex 9, paragraph A184.108.40.206.3 of the GHS.
Table 220.127.116.11.10.3.1: Categories for substances hazardous to the aquatic environment (see Note 1)
(a) Acute (short-term) aquatic hazard
NOTE 1: The organisms fish, crustacea and algae are tested as surrogate species covering a range of
trophic levels and taxa, and the test methods are highly standardized. Data on other organisms may
also be considered, however, provided they represent equivalent species and test endpoints.
NOTE 2: When classifying substances as Acute 1 and/or Chronic 1 it is necessary at the same time to
indicate an appropriate M factor (see 18.104.22.168.10.4.6.4 ) to apply the summation method.
NOTE 3: Where the algal toxicity ErC50 (= EC50 (growth rate)) falls more than 100 times below the
next most sensitive species and results in a classification based solely on this effect, consideration
shall be given to whether this toxicity is representative of the toxicity to aquatic plants. Where it can
be shown that this is not the case, professional judgment shall be used in deciding if classification
shall be applied. Classification shall be based on the ErC50. In circumstances where the basis of the
EC50 is not specified and no ErC50 is recorded, classification shall be based on the lowest EC50
NOTE 4: Lack of rapid degradability is based on either a lack of ready biodegradability or other
evidence of lack of rapid degradation. When no useful data on degradability are available, either
experimentally determined or estimated data, the substance shall be regarded as not rapidly
NOTE 5: Potential to bioaccumulate, based on an experimentally derived BCF ≥ 500 or, if absent,
a log Kow ≥ 4 provided log Kow is an appropriate descriptor for the bioaccumulation potential of the
substance. Measured log Kow values take precedence over estimated values and measured BCF values
take precedence over log Kow values.
Figure 22.214.171.124.10.3.1: Categories for substances long-term hazardous to the aquatic environment
The classification scheme in Table 126.96.36.199.10.3.2 below summarizes the classification criteria for
Table 188.8.131.52.10.3.2: Classification scheme for substances hazardous to the aquatic environment
NOTE 1: Acute toxicity band based on L(E)C50 values in mg/l for fish, crustacea and/or algae or
other aquatic plants (or Quantitative Structure Activity Relationships (QSAR) estimation if no
NOTE 2: Substances are classified in the various chronic categories unless there are adequate
chronic toxicity data available for all three trophic levels above the water solubility or above 1 mg/l.
("Adequate" means that the data sufficiently cover the endpoint of concern. Generally this would
mean measured test data, but in order to avoid unnecessary testing it can on a case by case basis also
be estimated data, e.g. (Q)SAR, or for obvious cases expert judgment).
NOTE 3: Chronic toxicity band based on NOEC or equivalent ECx values in mg/l for fish or
crustacea or other recognized measures for chronic toxicity.