The purpose of this communication is to address how substances are classified for effects in the aquatic environment.

The first step in building a registration dossier (to fulfil the ‘R’ part of REACH) is to carry out lab testing on the substance in a GLP environment. Annex VII of REACH lists the twenty two lab tests (known as endpoints) that must be carried out if you are manufacturing a substance in quantities greater than one metric tonne per annum (TPA) within the EU; or else importing that substance into the EU in the same quantity. These lab tests are split into physical wet chemistry tests, toxicology tests and ecotoxicology tests (effects on the environment). Many of the twenty two tests can be waived if not applicable, or if test data already exists for the endpoint (REACH aims to lessen duplication and encourages data sharing amongst companies).

When all endpoints are complete, toxicologists have a conference to see if the substance will be classified as hazardous. Perhaps the substance was an organic liquid with a boiling point of 60°C – this would make it Flammable. Perhaps the substance had a low LD50 – this would affect Acute Toxicity.

Classification for environmental effects depends on a complicated interaction between the following parameters:

  • Acute toxicity in three food-chain levels of aqueous organisms: Fish>Daphnia Magna> Algae, along with chronic toxicity in aquatic organisms (Algae)
  • Bioconcentration factor, estimated using the octanol–water partition coefficient (Log Kow); and
  • Biodegradation

The figure obtained for Log Kow is very important for toxicologists. The higher this is, the more likely the substance is to dissolve in the skin of animals or stick to sludge; and thus the more likely it is to bioaccumulate and be a persistent chemical that does not readily biodegrade.

Acute Toxicity

Acute toxicity testing in the lab lasts a few days and uses high chemical concentrations, simulating the threat to aquatic life from a chemical spill. The lab quantifies the toxicity either:

  • as an LC50 (for fish), which is the “lethal concentration” that kills 50% of the population, or
  • as an EC50 for Daphnia and Algae, which is the “effect concentration” causing the effect of immobilisation in Daphnia or the growth-rate inhibition in Algae; in 50% of the population

Classification for environmental hazards is possible if either the LC50 or the EC50 is < 100 mg L-1. The toxicologist needs results from testing in all three food-chain levels, because the lowest LC50 or EC50 value is required for correct classification.

No observed concentration

Chronic tests in aquatic species determine the No-Observed Effect Concentration (Noec), which is the max substance concentration that does not produce adverse effects in tests over a couple of weeks. This is another important parameter for classification of the substance.

The “effects” usually refer to any impaired growth of Fish or Algal population; or impaired reproduction in Daphnia. The three or four day Algal growth inhibition test can be considered to be a chronic test; and the Noec obtained can be used for classification purposes. Noec values of < 1 mg L-1 may lead to hazardous classification.

Bioconcentration factor

The bioconcentration factor (BCF) indicates a substance’s propensity to concentrate in an aquatic organism. The organism (usually fish) is placed in water containing the substance. If the substance accumulates, then it is more likely to cause toxicity, either in the organism itself or in hierarchical organisms that eat it. A BCF of ≥500 is a concern, and may result in a more severe classification. The full test to assess the BCF (EU Method C13) can be very expensive. Fortunately, the BCF is often estimated from the octanol–water partition coefficient (Log Kow), which is derived from a simple laboratory test that does not rely on animals (it can also be modelled using software programmes if the chemical structure is known). A Log Kow ≥4 may lead to a more severe classification.

Rapid biodegradation

Biodegradation is the ability of an organic (carbon-containing) substance to be converted into simple inorganic substances, such as CO2 and water (mineralisation) by micro-organisms. Substances that rapidly degrade are less likely to produce long-term effects in the environment. Rapid degradation is usually measured in the “Ready Biodegradability” test. The basic criterion of mineralisation of >60% under a test duration of 28 days is stringent, and most substances with a reasonably large molecular structure (e.g. many pharmaceuticals) are considered “not rapidly degradable”.

The EU CLP Regulation gives the method by which these three parameters are used for classification of substances, as shown in table 4.1 of Annex 1.

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