PBT, Persistent Bioaccumulative and Toxic Substances

Persistent, bio-accumulative and toxic substances, PBT, is a new type of hazard which was brought into the EU in 2001 , and it has since been brought into the scope of the REACH regulation.

The idea is to try to identify materials which are classified as toxic under CLP, and which can build up in animals over time and poison them through the substance which has accumulated in their bodies.

A classic example of this type of effect was noticed in the 1960s in the UK, when DDT (and other chlorinated pesticides such as Dieldrin) were discovered to be affecting kestrels.  The kestrels themselves were not killed, but the chlorinate pesticides caused thinning of their eggshells, so that many eggs never hatched, and the kestrel population dropped significantly.  These effects were reversed when some chlorinated pesticides were banned, and more careful use of pesticides was encouraged.

At the time of writing, there is no specific test or suite of tests to identify PBTs, which are identified in two ways:

  • by comparison with the list of properties in Annex XIII of REACH, which indicates whether a substance is potentially PBT or is not PBT
  • if the substance is potentially PBT, an emissions assessment has to be carried out for REACH registration purposes

As well as industry-classified PBT substances, there is also an EU process for formally identifying PBT substances relies on expert opinions and interpretations of available data, using experts from the various European competent authorities.

It is understandable that Europe, with its desire to apply the “precautionary principle” would try to take a lead on identifying PBT substances, but historically these effects have only ever been identified in ecosystems, leading to a response to ban or reduce the chemicals concerned, and the benefits of this type of “expert opinion” system are currently unclear.

There is also a danger that over-precaution may have very real adverse effects in removing chemicals which are beneficial to humans from the supply chain.

The only other jurisdiction to include PBT as a hazard in their chemical control systems is the USA, and it is possible that the EU and the USA, by adopting this approach first, will simply “move the problem” from chemicals identified as PBT being made and used in a well-controlled way in Europe and the USA, offshore to e.g. India, China or Vietnam, where pollution rates and exposure to humans are typically much higher.

Substances which are identified as PBT do not have any labelling requirements under CLP, but it does trigger the requirement for an SDS for a substance or mixture (down to 0.1% w/w PBT content), even where the product is not classified under CLP (this is on request of a recipient, rather than automatic provision of an SDS, although most companies issue all their SDSs on or before the date of first supply).  There are also information requirements for the SDS , in section 2.3, other hazards, and section 12.5, where the results of any PBT testing and evaluation should be listed.

The Indian Vulture crisis – is Diclofenac classed as PBT or not?

A more recent experience of ecosystem effects from hazardous chemicals is the inadvertent poisoning of Indian vultures by a vet medicine, diclofenac, which is used to treat inflammation and pain in animals, but which has turned out to be very toxic to these birds when they feed on an animal carcass which contains it.

Diclofenac is classified as acutely toxic (actually Acute tox. 4 oral, H302) under CLP, see https://echa.europa.eu/registration-dossier/-/registered-dossier/13096/2/1 , and its effects on Indian vultures are summarised by https://en.wikipedia.org/wiki/Indian_vulture_crisis .  The answer to the crisis has been to ban diclofenac for veterinary use, and a replacement drug for cattle, meloxicam, has been developed which is harmless to vultures. However, it is likely to take some time for the vulture population to be restored to pre-diclofenac levels.

The fact that diclofenac is toxic means it would theoretically come under the PBT category.  However, a PBT assessment has not been published in the REACH dossier, which may mean that it is not strictly a PBT, as it is not necessarily bio-accumulative.  PBT assessments are not straightforward, and if you are having difficulty with this area, it may be necessary to use the services of a reputable consultant with experience in this area.

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