FW: Intraspecies Variability

James Stanley Smith, Jr., Ph.D. jssmith at oak-creek.net
Wed May 26 08:40:18 EST 1999

Your post is quite intriguing.  Can you supply me with a reference(s) to your
statement that "exposure to mercury from amalgams can be a lot higher than the
amount that corresponds to 0.3 ug/m^3?"

For comparison purposes, only 0.01 percent of elemental mercury is absorbed in
the gut following oral ingestion (US EPA Mercury Study Report to Congress,
1996).  In contrast, nearly all (100 percent) of the inhaled elemental mercury
is thought to be absorbed in the lung.  Combine this with an assumed respiration
rate of 20 m^3/day (US EPA default value used in risk assessment, 1989) and one
would have to ingest 600 ug/day (0.3 ug/m^3 x 20 m^3/day = amount absorbed via
inhalation, then multiply by 100 to get the presumed equivalent oral dose
ingested) to have an equivalent exposure to 0.3 ug/m^3.  This calculation is, of
course, crude and may not represent any particular reality, but it does provide
a point of departure for discussing the relative exposure to mercury in dental

I hope that you will respond similarly, by sharing your knowledge in this area.
I look forward to a meaningful discussion of this issue.

"Lisek, Beata" wrote:

> -----Original Message-----
> From: arie at no.mail.thanks.nl [mailto:arie at no.mail.thanks.nl]
> Sent: Wednesday, May 19, 1999 6:42 PM
> To: toxicol at net.bio.net
> Subject: Re: Intraspecies Variability
> What do you mean to say? That the US EPA lowest allowable dose of
> mercury intake is in every individual larger than the real intake of
> mercury from amalgams? So that health problems due to amalgam are
> impossible? Is this what you suggest by
> "however, even this small population's sensitivity is limited" and
> "as you can see there can be a lot of additional uncertainty taken
> into account in the derivation of the level of a compound that is
> deemed "safe" and thought to be unlikely to cause adverse effects over
> a lifetime of exposure."
> ?
> The exposure to mercury from amalgams can be a lot higher than the
> amount that corresponds to 0.3 ug/m^3, for instance by ingestion.
> kind regards,
> arie
> On Wed, 19 May 1999 09:26:24 -0400, "James Stanley Smith, Jr., Ph.D."
> <jssmith at oak-creek.net> wrote:
> >You are correct to assume that a small percentage of the populace may be
> more
> >sensitive to mercury intoxication than the general populace, however, even
> >this small population's sensitivity is limited.  US EPA and other human
> health
> >organizations typically use an uncertainty factor (UF) of 10 (no
> information)
> >or 3 (limited information) to account for variability in human sensitivity.
> >This UF is in addition to UFs that are typically used to account for a
> limited
> >data base (10), interspecies extrapolation (10), extrapolation from
> subchronic
> >to chronic study results (10), and extrapolation from a low observed
> adverse
> >effect level (LOAEL) to a no observed adverse effect level (NOAEL).  When
> >appropriate, these UFs are multiplied together (UF product) and used to
> lower
> >the lowest amount of mercury shown to have an effect in the most sensitive
> >animal species (LOAEL) or to lower the NOAEL, defined as the dose below a
> >LOAEL at which no adverse effect occurs.  As you can see there can be a lot
> of
> >additional uncertainty taken into account in the derivation of the level of
> a
> >compound that is deemed "safe" and thought to be unlikely to cause adverse
> >effects over a lifetime of exposure.
> >
> >For elemental mercury such as that used in amalgam, the US EPA
> ><http://www.epa.gov/ngispgm3/iris/subst/0370.htm> uses a UF product of 30;
> 10
> >was used for the protection of sensitive human subpopulations (including
> >concern for acrodynia) and 3 was used for the lack of a sufficent data
> base,
> >particularly developmental and reproductive studies.
> >
> >Current scientific studies suggest that an UF of 10 is adequate and in fact
> >very likely to be overprotective of the most sensitive human population.
> >Consequently, there is little concern for adverse health effects developing
> in
> >humans from chronic exposure to elemental mercury vapor that does not
> exceed
> >0.3 micrograms per cubic meter air (ug/m3).
> >
> >Finally, I do not want to suggest absolutely that some people are not
> affected
> >by chronic exposure to lower concentrations of elemental mercury vapor, but
> I
> >am not aware of any scientific evidence in support of their health claims.
> >
> >arie at no.mail.thanks.nl wrote:
> >
> >> I wonder if this would apply to mercury.
> >> It's often said that only a small portion of the population (2 - 3 %)
> >> suffers from detrimental health effects due to the chronical low dose
> >> intoxication from mercury leaking from amalgam fillings. This could
> >> mean that the other part has much more resistance.
> >>
> >> arie
> >>
> >> On Mon, 17 May 1999 11:52:46 -0400, toddh at brownvm.brown.edu (Todd)
> >> wrote:
> >>
> >> >We often use a 10-fold uncertainty factor when considering the
> >> >intraspecies variability in reactions to a particular chemical.  I am
> >> >currently interested in looking at cases where that 10-fold factor may
> >> >understate the true variability in the population.  I would be greatly
> >> >appreciative if somebody could either give me examples or point me in
> the
> >> >direction of a good resource to find examples where this may be the
> case.
> >> >Human variation in reactions to Prozac would be one example.  Again, I'd
> >> >appreciate any help that you could lend.  Thank you very much!
> >> >
> >> >Todd


James S. Smith, Jr., Ph.D.
President & Toxicologist

Toxicology & Risk Assessment Consulting
     RR 3  Box 246B
     Route 22
     Gorham, Maine  04038-9428

     Voice      : 207.929.6375
     Facsimile: 207.929.6474
     E-mail     : jssmith at oak-creek.net
     WWW    : http://www.oak-creek.net

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