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aamerraza <[log in to unmask]> Sent by: Contaminated Land Management Discussion List <[log in to unmask]> 14/01/2009 10:53 Please respond to aamerraza <[log in to unmask]>

To [log in to unmask] cc Subject Re: Toxcic Equivalency Factors

I’d agree with the other comments below regarding uncertainties in using TEFs. I also agree that the FSA has rejected their use for the assessment of PAH risk in foods, as it stands (I also thought a re-assessment of this position was due from the FSA, but I am not aware if this was released). However  it is probably worth considering the following in the context of contaminated land assessment:
 
The use of TEFs and additivity assumptions for chlorinated dioxins and furans is widely considered to be acceptable, and is largely based on a peer reviewed scientific consensus on their use. The same uncertainties related to synergistic effects etc. apply to dioxins. For PAHs, the data is less rigorous, and there is less consensus on the use of TEFs. For threshold PAHs, we can use US EPA RfD, for example. However, for most PAHs (non-threshold) unless a TEF or other relative potency approach is used, the PAHs are simply not assessed. Application of TEFs, while uncertain, is more conservative and health protective than not assessing the other PAHs at all. The FSA approach is to use BaP as an indicator of risk. To assume that other PAHs are equipotent to BaP would be overly conservative, and lead to impracticable remediation requirements. I’d also note that, while the uncertainties associated with TEFs are valid points, they have been applied by credible international organizations such as WHO and USEPA.
 
 
An alternative to the TEF method is the Whole Mixture Model approach. The model assumes that the potency of the PAH mixture is proportional to the B[a]P) content of the mixture. B[a]P serves as a surrogate for all other PAHs and B[a]Psurrogate assumes the potency of the entire PAH mixture. The Ontario Ministry of Environment  assign B[a]P surrogate a potency 16 times greater than the potency of B[a]P on the assumption that this represents the potency of the entire PAH mixture. The risks assigned to the PAH mixture are then given by the product of the B[a]P content and the toxic potency of B[a]Psurrogate. I believe the FSA also recommend a BaP surrogate approach, except that they suggest that the BaP surrogate potency should be 10 rather than 16. In any event, if this method is applied, an SSAC for total PAHs (other than threshold PAHs) would need to be derived, based on the suitable BaP surrogate potency.
 
Also, we should note that the uncertainties related to synergistic affects etc. are not unique to PAHs – this could apply to other combinations of chemicals as well. However, even additivity of toxic effects, let alone potentiation of these effects are typically not assessed as practiced in the UK. At least the TEF approach addresses the issue of additivity, albeit adjusted for somewhat uncertain relative potency estimates.
 
In any event, it should be noted that the TEF, or other relative potency approach, is more conservative than the default which is currently applied i.e. other than BaP and threshold PAHs, the PAH levels are simply not assessed.
 
I’d appreciate any thoughts.
 
 
Aamer Raza
Associate Director
Harrison Group Environmental
Kimberley Street,
Norwich, Norfolk, NR2 2RJ
Phone: 01603-613-111
Email [log in to unmask]
 
 
 
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Jonathan Parr
Sent: 13 January 2009 15:40
To: [log in to unmask]
Subject: Re: Toxcic Equivalency Factors
 
TEFs also doesn't model the synergistic effects PAHs have on one another either.
 
Jon
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]]On Behalf Of John Allison
Sent: 13 January 2009 15:31
To: [log in to unmask]
Subject: Re: Toxcic Equivalency Factors

Simon
It's also worth remembering it's not only the toxicology which may be different but also the fate and transport of the individual chemicals may be significantly different, for example contrast the physical properties of naphthalene with one of the heavier PAH. the approach may overestimate or underestimate the risks posed by individual PAH depending on the parameters selected as representative of all PAH.
John Allison BSc(Hons) CSci CChem MRSC SiLC
Principal Land Quality Consultant



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Ben Rees <[log in to unmask]> Sent by: Contaminated Land Management Discussion List <[log in to unmask]> 13/01/2009 14:42 Please respond to Ben Rees <[log in to unmask]>

To [log in to unmask] cc Subject Re: Toxcic Equivalency Factors

TEF are briefly mentioned in the latest SR2 publication from the EA (see pg 41). As you point out. TEF  are used for groups of compounds such as PAHs, dioxins etc. Significant caution should be applied in using TEFs as there each PAH may have a different toxicological mode of action and there is not likely to be sufficient toxicological data available to assess each compound.  As a consequence, the approach could under estimate the actual risks posed.

In a recent review of the use of TEF for the intake of PAHs in food the European Food Standard Agency rejected the use of TEF.

Let me know if you want the document.


Ben Rees MSc CGeol
Environmental Geoscientist
Geotechnology Limited
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