help: PCDD/F non-detect may equal a WQS violation

[ttweed@wildrockies.org (Tony Tweedale)]

Does anyone know any other responses to that old industry complaint, that
the standard is lower than current analytical detection abilities, possibly
resulting in a violation when there is none present?  Specifically, MT has
proposed changing its 2,3,7,8-TCDD ambient water quality standard to a TEq
basis (leaving the concentration not to be exceeded unchanged).
Smurfit-Stone Container Corp and NCASI have submitted comments that include
the above complaint.  I don't know the dl's for EPA's ambient water PCDD/F
method, but it seems possible that the common procedure for
non-detects--assume it to be present at a concentration that is the median
between zero and the d.l. for the congener-- could result in a violation of
the standard even when many of the congeners are not detected (and even tho
the MT legislature weakened their WQS for carcinogens, incl. dioxins,  by
10-fold a few years ago).

I know the "it's a health based standard, so the d.l's are irrelvant"
argument, but that is weak against such a concrete scenario.  Does the
analytical compliance method specify that nd's be treated as zero, or as
half the PQL or dl, or some other way?

They are also arguing that since different congeners have different
degradation and (especially) accumulation factors, compliance analysis
based on all congeners (weighted by TEq's), rather than compliance measured
on 2,3,8,8-TCDD alone, is bad science, therefore a bad regulation.  Any
insights on this broad argument?  Also, is the EPA dioxin WQS for
2,3,7,8-TCDD alone, or does EPA have ambient water limits for PCDD/F?

Enviros have already commented that a TEq based standad is appropriate as
it can reflect advances in toxicity knowledge of the different congeners
(such as the recent WHO 1.0(!) TEF for one of the penta 2,3,7,8-substituted
congeners.  Just because the expopsure (env fate & uptake) parts of the
risk equation are less characterized than the health effects portion, that
doesn't mean  having WQS for other congeners is inappropriate!

Tony Tweedale, Montana-CHEER
(Coalition for Health, Environmental & Economic Rights)
224 E. Pine (2)
Missoula, MT 59802-4541
406-542-1709 tel. [& Fax--must call me 1st)]
ttweed@wildrockies.org

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