IUBio

FW: Intraspecies Variability

Lisek, Beata Lisek.Beata at nrc.ca
Tue May 25 10:37:48 EST 1999



-----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




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