PRIO – A tool for Risk Reduction of Chemicals

Criteria for assessing whether the substance is a priority risk-reduction substance – Potential PBT/vPvB

  Criteria
Potential PBT Persistence Bioaccumulation Toxicity
 Where data on half-lives from a simulation test are lacking, other information on degradability can be used.

Log Kow > 4.5
High bioaccumulation in other than aquatic organisms.

L(E)C50 < 0.1 mg/L

LD50<200 mg/kg body weight/d and toxicity is expected to be systemic (H301 and H300 or R25 and R28) respectively  

Potential vPvB  As above As above  Not applicable

The potential PBT/vPvB criteria of the PRIO tool are to a large extent equal to the PBT screening criteria in Reach which is published in Echa:s Guidance Document for risk assessment,  PBT assessment.

Data for assessing whether the criteria for potential P/vP are fulfilled


Where data on half-lives from a simulation test are lacking, other information on degradability can be used. The following criteria can be used as a guide in assessing whether the substance is potentially P:

– Readily biodegradable substances (*29) (regardless whether within the 10-day window or not) are regarded as non-persistent in the PBT assessment.
– Substances that do not fulfil the criteria for ready biodegradability are regarded as potentially persistent.
– Substances that do not fulfil the criteria for structurally induced degradability (inherent degradability) (*30) are regarded as potentially persistent.
– Substances that fulfil the criteria for inherent degradability are not automatically regarded as persistent. Two specific tests can, however, be considered to point to non-persistence if certain criteria are fulfilled:

  1. Zahn-Wellens test (OECD 302B). 70% mineralisation must be achieved within seven days, the log phase must not be more than three days, the percentage disappearing in the test before degradation starts must be less than 15%, and the test must be performed without pre-adapted microorganisms;
  2. MITI II-test (OECD 302C). The level for inherent must be reached within 14 days, the log phase must not be more than three days, the test must be performed without pre-adapted microorganisms.

If there are several items of contradictory data, an assessment is made on a case-by-case basis, weighing in all available information on the degradability properties of the substance (weight of evidence) in order to ascertain whether the substance should be considered to have the potential to be persistent.

– For many substances there are no data or else available data are difficult to interpret. Models can be useful in estimating the potential for degradation in the environment for these substances. In a preliminary assessment, it is proposed that three out of six models in the BIOWIN programme are used according to:

  1. Non-linear model prediction: not degraded rapidly (<0.5) or
  2. MITI non-linear model prediction: not readily degradable (<0.5) and
  3. Ultimate biodegradation timeframe prediction: ³ months (<2.2)

When these three models are combined, relatively few non-readily biodegradable substance will avoid being identified, and a significant increase in the number of incorrectly included actually readily biodegradable substances will be avoided. The BIOWIN programme is available from the website of the US Environmental Protection Agency (EPA).

Data for assessing whether the criteria for potential B/vB are fulfilled

When measured BCF values are lacking, Kow or BCF can be calculated using QSAR (*31) models to assess the potential of a substance to bioaccumulate. For very fat-soluble substances, with log Kow >6, an expert assessment must be made on a case-by-case basis to assess whether the substance is potentially bioaccumulating.

Other information such as demonstrated high bioaccumulation in species other than aquatic organisms and measured concentrations in biota (*32) can also be used to assess whether the substance fulfils the criterion. Measures concentrations in biota show that the substance can be taken up in the organism, but not to what extent it is bioaccumulated or bioconcentrated. This type of information must therefore be assessed on a case-by-case basis.

Data for assessing whether the criteria for potentially T are fulfilled

Where data from long-term studies are lacking to assess whether a substance is a PBT substance, results from short-term studies can be used to assess whether it is potentially toxic (T). A substance is considered to be potentially toxic (T) when it has an experimentally determined L(E)C50 <0.1 mg/l for aquatic organisms (*33).

Data from short-term studies on mammals are not normally used to assess possible chronic effects. A substance that is classified as toxic or very toxic by swallowing (LD50<200 mg/kg body weight/d), i.e. classified R25 or R28 according to KIFS 2005:7, may, however, be regarded as potentially toxic. It is required that the toxicity in this context can be expected to be systemic for the sub-criterion to be fulfilled.

Where no data are available on the toxicity of a substance, the assessment can be based on model calculations on the basis of the structure of the substance using QSAR models



*29 Ready biodegradability test, e.g. according to guidelines for test methods OECD no. 301.

*30 Inherent degradability e.g. according to OECD Guideline 302.

*31 QSAR - Quantitative Structure Activity Relationships – is a collective name for various models that calculate the properties of a substance on the basis of its structure.

*32 Biota = living animals and plants

*33 L(E)C50 (Lethal (Effect)Concentration) is the concentration at which 50% of the test organisms die or are seriously affected in some other way.