Weight Of Evidence Dominates PBT Expert Group Meeting

« Parties try to reach common ground on flexible WoE approach.
The challenge of how to use weight of evidence (WoE) in assessing possible persistent, bioaccumulative and toxic (PBT) compounds featured heavily, during Echa’s PBT expert group meeting on 29-30 September.

“The WoE approach needs to remain flexible and should not be too prescriptive because we always have a case-by-case assessment,” said Peter Lepper, chair of the expert group.

“Potential guidance on WoE should be more on how to describe systematically what has been done rather than be prescriptive on a particular approach or methodology to be applied,” he added.

“We are not too far away from reaching common ground on WoE,” said expert group participant, Björn Hidding, from BASF and Cefic. “We are dealing with very complex endpoints and WoE applied to PBT can be very challenging, depending on the data.”

A defined WoE approach is particularly important for assessing complex PBT cases, said Eric Verbruggen, expert group participant from The Netherlands. “A conclusion might be very difficult to draw because the data may not match the criteria. You really need to [give] weight to each piece of information and to look at how it contributes to persistence, bioaccumulation, or toxicity,” he said.

Mark Bonnell from Environment Canada presented the organisation’s WoE approach; his visit follows a memorandum of understanding to increase cooperation and exchange of information between Environment Canada and Echa. There are “no major differences” between the Canadian approach and how Echa has been applying WoE, said Dr Lepper.

At its tenth meeting, the group discussed a number of substances, covering assessment strategies, data requirements and testing needs. For the first time, the group did not reach final conclusions on PBT/vPvB properties for any of the substances.

Participants discussed at length the type of simulation tests that should be used to assess persistence. “The group is considering drafting guidance on how to apply the tests in different situations, depending on the physico-chemical properties of a substance and the environmental compartments of concern,” said Milagros Vega, from the Spanish competent authority.

Echa is currently running a project to explore whether toxicokinetics data can be used to assess the bioaccumulation potential of substances that do not accumulate in aquatic species – commonly used in environmental assessments – but do build up in “air-breathing species”.

The project’s results will first be used for perfluorinated chemicals, to compare mammalian toxicokinetics data with information on known PBT substances to determine whether the chemicals are bioaccumulative or “very bioaccumulative”.

In its first ten meetings, the PBT expert group has discussed 148 substances. Of these, it considered that sufficient information is available to identify seven as PBT or vPvB, while 31 are “not PBT”, based on current data. For the remaining 110 substances, the expert group has decided that there is not currently enough information for assessment.

With some of the required extra tests taking as long as two to three years, a delay is expected before any of these substances can be placed in a PBT or non-PBT group. »

Article by Emma Davies

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