PRIO – A tool for Risk Reduction of Chemicals

Why are PBT/vPvB substance phase-out substances?

Footprints in sand

PBT/vPvB substances are persistent, bioaccumulating and toxic or very persistent and very bioaccumulating. A substance is persistent if it is stable in the environment, in the sense that to a great extent, it resists breakdown (*9).

The basic principle is that organic substances that are persistent and bioaccumulating pose a potential risk to human health and to the environment, and when the substances are found to have adverse effects a long time passes before measures/restrictions that are implemented produce results. A persistent substance, which at the same time is bioaccumulating, may be available for uptake in organisms over a long period. This may lead to overlooked or unpredictable adverse effects, even for substances that in various tests have not been shown to have a toxic effect. The reason for this may be additive or synergistic effects (*10), chronic low-dose effects (*11) and the risk of the substance being dispersed to more sensitive environments or of more sensitive groups being exposed being greater for persistent substances. For substances that are very persistent (vP) and very bioaccumulating (vB), the difficulty in assessing the risks is even greater and the uncertainty of future harmful effects is so great that some form of adverse effects is assumed despite no such effects having been demonstrated in toxicity tests.

There are several historical examples of exposure situations and effects that were not predicted on the basis of available data, e.g. for DDT and PCBs. The present-day increase in levels of brominated flame retardants in humans and other organisms is a current example [de Wit, 1999 (*12)].


 *9 Chemical substances may be long-lasting in the environment even if they are readily biodegradable. For example, the presence of a substance may be due to a constant inflow from the technosphere, e.g. from vehicle exhausts. Such persistence is not included in what is meant here by persistent substances.

*10 Additive or synergistic effects may mean that a substance, when it is present in the environment together with other substances, has a higher toxic effect.

*11 Chronic low-dose effects means that exposure over a long period may cause adverse effects at very low levels that are difficult to predict from tests on the acute toxicity of the substance. However, data from short-term tests, known as acute toxicity tests, are the type of data most often available.

*12 de Wit, C. A. (1999) Brominated flame retardants in the environment – an overview. Organohalogen Compounds, 40:329-332.