REACH European Chemicals Agency (ECHA) – Regulatory Guidance on use of Radiolabelled Compounds

Information requirements under (REACH Regulation (EC) No 1907/2006) are generated using technical guidance approved by the OECD and EU for conducting Chemical Safety Assessments  to prepare Chemical Safety Reports which may be required as part of a registration dossier.

Due to scientific and regulatory developments, test guidelines are updated and the ECHA issues Endpoint Specific Guidance such as Chapter R.7b: Version 4.0, June 2016

Specific reference, made by ECHA, to guidance where radiolabelled compounds are employed, includes Environmental Fate; Degradation and Bioaccumulation:

OECD 314 Simulation Tests to assess biodegradability of chemicals in discharged water (Note: OECD 303A is judged as complimentary to the OECD 314B)
OECD 315 Bioaccumulation in Sediment-dwelling Benthic Oligochaetes, 2008
OECD 317 Bioaccumulation in Terrestrial Oligochaetes, 2010
OECD 305 Bioaccumulation in Fish: Aqueous and Dietary Exposure, 2012

Of special interest is chapter R.7.9: Degradation/Biodegradation

Degradation of organic chemicals in the environment influences exposure and, hence, it is a key parameter for estimating the risk of long-term adverse effects on biota. Degradation rates, or half-lives, are determined in, or default rates assigned from, laboratory-based degradation tests. These tests can be simple screening tests (e.g. the OECD 301 ready biodegradability tests and the OECD 111 hydrolysis as a function of pH test), or relatively complex higher tiered simulation types of tests (e.g. the OECD 308 aerobic and anaerobic transformation in aquatic sediment systems, OECD 309 aerobic and anaerobic transformation in surface water and the OECD 303 aerobic sewage treatment).

There are also two draft OECD guidelines considering photolysis. These are (1) Phototransformation of chemicals on soil surfaces and (2) Phototransformation of chemicals in water-direct and indirect photolysis.

More specifically, Guidance on Information Requirements and Chemical Safety Assessment where radiochemicals may be required include:

OECD 302A Inherent Biodegradability: A: Modified SCAS Test
OECD 303A Simulation Test - Aerobic Sewage Treatment A: Activated Sludge Units B: Biofilms
OECD 304A Inherent Biodegradability in Soil
OECD 306 Biodegradability in Seawater
OECD 307 Aerobic and Anaerobic Transformation in Soil
OECD 308 Aerobic and Anaerobic Transformation in Aquatic Sediment Systems
OECD 309 Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test
OECD 311  Anaerobic Biodegradation of Organic Compounds in Digested Sludge - Method by Measurement of Gas Production
OECD 314 Simulation Tests to Assess the Biodegradability of Chemicals Discharged in Wastewater

Testing data on degradation/biodegradation is subject to more detailed guidance and reference to radiochemicals includes:

Sewage treatment

The fate of chemicals in sewage treatment plants can be studied in the laboratory by using the Simulation Test.

Aerobic Sewage Treatment: Activated Sludge Units (OECD 303 A). Many chemicals are normally present at very low concentrations, even in waste water, and procedures for testing the biodegradation at suitably low concentrations (<100 μg/L) are presented in Annex 7 to the TG 303 A (OECD, 2006).

If a radiolabelled conventional activated sludge study (CAS) is performed and a mass balance is done on the effluent and solids, it is possible to determine biodegradation for any type of non-volatile compound.

Marine Biodegradability

Degradation of chemicals in seawater has generally been found to be slower than that in freshwater tests inoculated with activated sludge and sewage effluent, and, therefore, a positive result obtained during 28 (Closed Bottle Method) or 60 days (Shake Flask Method) in the biodegradability in Seawater test can be regarded as evidence of a chemical’s potential for biodegradation in the marine environment. When a chemical attains >60% ThOD (theoretical oxygen demand) or >70% DOC (dissolved organic carbon) removal in a Biodegradability in Seawater test (OECD 306), it can also be expected to fulfil the criteria for ready biodegradability.

Modified Ready Biodegradability Tests

These consider biodegradability testing at low test substance concentrations and assessing the biodegradation of poorly water soluble chemicals. Provided that all other conditions in the Ready Biodegradability Tests are fulfilled, these tests are regarded as Ready Biodegradability Tests and the results can be used directly in classification.

Testing at low test substance concentrations due to inoculum toxicity

Conducting studies at low concentrations may only be possible if the test chemical is available containing an appropriate radioisotope. If this is not possible then the primary biodegradability of the test chemical should be measured using specific chemical analysis. If primary degradation is being measured then an attempt should be made to identify any major degradation products.

Soil, sediment and water

The following tests can be used to simulate the biodegradation of organic chemicals under environmentally realistic conditions in soil, sediment or surface water: Aerobic and Anaerobic Transformation in Soil (OECD 307); Aerobic and Anaerobic Transformation in Aquatic Sediment Systems (OECD 308); and Aerobic Mineralisation in Surface Water – Simulation Biodegradation Test (OECD 309).

When using radiolabelled chemicals, the label should be located in the most recalcitrant part of the molecule when total mineralisation is assessed.

R. Remaining uncertainty for degradation/biodegradation

Chemicals that fulfil the criteria for ready biodegradability are likely to undergo rapid degradation in the environment under most conditions (OECD, 2006). However, it must be recognised that these tests are very stringent and most chemicals will not fulfil the pass criteria for ready biodegradability. For chemicals that exhibit between 40 and 60% mineralisation in ready biodegradability test, extensive primary biodegradation would have occurred even though the use of non-specific endpoints such as DOC and BOD do not directly measure this. Therefore there will remain a large degree of uncertainty about the biodegradability of many chemicals and testing at higher levels or tiers will be required.

Relevant environmental compartment Recommended biodegradation studies
Freshwater Freshwater simulation test (e.g. OECD 309) and/or CAS test (OECD 303)  
Freshwater sediment Freshwater water/sediment simulation test (e.g. OECD 308) and/or CAS test (OECD 303)  
Marine water Marine water simulation test (e.g. OECD TG 309) and/or CAS test (OECD 303)  
Marine water sediment Marine water sediment simulation test (e.g. OECD 308) and/or CAS test (OECD 303)  
Soil Soil simulation test (e.g. OECD 307)

In 2008, the OECD published OECD TG 314. This test guideline aims to allow checking of the fate of a substance on its way through the sewer system and sewage treatment plant to the mixing zone in surface water. It comprises the following five different component guidelines:

  • Sewer System, OECD 314A
  • Activated Sludge, OECD 314B
  • Anaerobic Digester Sludge, OECD 314C
  • Mixing Zone for Treated Effluent and Surface Water, OECD 314D
  • Mixing Zone for Untreated Wastewater and Surface Water, OECD 314E

Up to now OECD 314 has seldom been used and so there is little regulatory experience of it under REACH.