Richard Denison, Ph.D., is a Senior Scientist.
I want to clarify and expand on the discussion in my last post on ACC’s selection of criteria for persistence (P) and bioaccumulation (B). The bottom line remains the same: ACC selected the least conservative values proposed by any authoritative body for these parameters.
I want here to give a fuller picture of available P and B criteria. It should be noted that there can be multiple types of measures of both P and B, but so as not to overly complicate the discussion, and for comparative purposes, I’m focusing here on:
- Values for transformation half-lives for P
- Values for fish bioaccumulation factors (BAF) or fish bioconcentration factors (BCF) for B
As a reminder, here’s what ACC proposed for these values:
- Half-life < 180 days = non-persistent
- BAF/BCF > 5,000 = bioaccumulative
So how do those compare to cut-offs established by authoritative bodies?
- For P, GHS doesn’t use transformation half-life values.
- For B, GHS indicates that a fish BCF < 500 is “considered as indicative of a low level of bioconcentration.”
- For P:
- a half-life > 60 days in water is deemed persistent and triggers imposition of testing requirements and controls via a consent order (if B and T criteria are also met)
- a half-life > 180 days is deemed highly persistent and triggers a presumptive ban unless demonstrated to be incorrect (if B and T criteria are also met)
- For B:
- a fish BAF/BCF > 1,000 is deemed bioaccumulative and triggers imposition of testing requirements and controls via a consent order (if P and T criteria are also met)
- a fish BAF/BCF > 5,000 is deemed highly bioaccumulative and triggers a presumptive ban unless demonstrated to be incorrect (if P and T criteria are also met)
EPA’s Design for Environment (DfE) Program: These are the values that I cited in my last post; they were developed by DfE staff in consultation with other EPA experts and consideration of relevant literature. They were designed to provide greater granularity in P and B rankings to reflect the continuous nature of these chemical properties.
- For P:
- a half-life > 40 days in fresh water is deemed persistent
- a half-life > 60 days in fresh water is deemed very persistent (vP)
- For B:
- a fish BAF/BCF > 2,000 is deemed bioaccumulative
- a fish BAF/BCF > 5,000 is deemed very bioaccumulative (vB)
Finally, it’s worth noting that the Stockholm Convention on Persistent Organic Pollutants (POPs) also has criteria to identify P and B for chemicals for which international bans on production and use are warranted (when they also meet toxicity criteria) – which of course goes far beyond mere criteria for prioritizing chemicals for further scrutiny. Here are the POPs criteria:
- For P: a half-life > 60 days in fresh water
- For B: a fish BAF/BCF > 5,000
It’s clear that ACC’s P and B cut-off values are those representing the most extreme level of concern for these parameters across a range of authoritative U.S. and international bodies.