Dear Chuck,
1. the old "dosis venenum facit" (The dose makes the poison) is not
ALLWAYS true. There is, as far as i remember, one mechanism where there
are no safe limits: If genes are affected, the repair mechanisms as well
as the damaging mechanisms are stochastic. That means that even one
molecule of the substance can cause damage, and the safe level is 0.
Probability of effect is of course lower with lower doses.
MERIAN ("Metals and their compounds in the environment", VCH, 1991)
(this one is in english ;-) mentions some evidence for genotoxic effects
of lead and several compounds. 

2. Just to mention it: Lead is not essential (see MERIAN). At least not
for biology...

It is an interesting thing that copper, which is also quite toxic to
many organisms including humans, is essential. There are some
cu-detoxification mechanisms in cells that anyway allow copper uptake
without harm. For lead, this specialized mechanisms do not exist,
because it is not essential to take up lead. I think i read that
somewhere in MERIAN, too.

3. One more from MERIAN: The increase of lead in sediments during the
last 150 yrs was up to 20-fold, 4-fold in south pole snow. Of course
that is due to atmospheric pollution, gasoline etc. and not to
electronics, but it means that anthropogenic lead is not in principle
negligible, as you implied.

4. It is a good idea to include "other living creatures" as well in the
considerations. If you do that, you could end up with extremely low
acceptable doses for certain soil bacteria. (Dont laugh, they provide
our food)

That's why i dont think that Keith's post was so extremely meaningless
and untrue.

Best regards, 
khz


-----Ursprüngliche Nachricht-----
Von: Leadfree [mailto:[log in to unmask]] Im Auftrag von Chuck Dolci
Gesendet: Mittwoch, 5. Mai 2004 21:51
An: [log in to unmask]
Betreff: Re: [LF] the tiny amount of lead in electronic assemblies is
irreleva...


In Keith's post he says:
"An underlying premise is that lead is indeed as dangerous to health and
well being as
is claimed by the toxicologists. The key point on lead toxicology seems
to be that there
is no safe lower limit. It is always the case of less is better. "

The problem with this statement is that it is 1) meaningless and 2) not
true.  You can
not say lead (or anything else for that matter) is "dangerous to health"
unless you talk
about dose. There are, in fact, safe lower limits, because there are
(and for millenia,
have been) exposures to lead that produce no discernible harm. Less
always being better
is also not true. There are many chemicals, minerals and elements that
are absolutely
essential to normal body functions and good health, at certain doses.
But at higher
doses would be lethal.

Keith goes on to say "The fact that there is already a lot of lead
scattered around the
earth as a result of the use of lead in paint, gasoline, car batteries
etc does not
necessarily mean that it does not matter whether more is scattered."

I thought lead (Pb) was scattered around the earth as a result of
nature. Man is not
scattering any more lead (Pb) around than existed a billion years ago.
Granted, not all
lead in the world is found as pure, refined Pb. But then we are not
really talking about
Pb in electronics, are we? We are talking about solder and CRT glass.
What is it about
solder that makes its lead so mobile while lead in other materials is
not so mobile?  If
lead leaches out of solder does it also leach out of lead sulphide?

Granted that impermeable liners are not absolutely impermeable. But, in
the real world,
do the laws of physics and chemistry allow for conditions in a landfill
to cause lead to
be leached out of solder, for lead to be transported to adjacent soil
and then migrate
to water sources (or other sources that might lead to human exposures),
in such
quantities as will be harmful to man and other living creatures?

That is the relevant question.


Chuck Dolci



[log in to unmask] wrote:
> Robin,
>
> There may be a lot of technically plausible reasons why leaching of
lead from
> scrapped electronics in landfill does not by itself provide sufficient
> grounds for eliminating lead from solder.    However, I feel that
there is more to
> the case for lead-free solder than simply that it is too late to stop
the
> consequences of some misguided European legislation.
>
> I believe that there are two more general grounds that might be
considered
> justification for the move to lead-free.     An underlying premise is
that lead
> is indeed as dangerous to health and well being as is claimed by the
> toxicologists.   The key point on lead toxicology seems to be that
there is no safe
> lower limit.   It is always the case of less is better.
>
> The first is that, given that lead is a toxic material, it seems
unwise to
> continue to use it in an application which virtually ensures that it
will be
> scattered widely around the world.    Electronic circuitry is becoming
> ubiquitous.    Even many of the very poor of this world have a radio
and the middle
> class, whose numbers are growing rapidly around the world, typically
own 5 - 50
> items which contain some sort of electronics.  And apart from private
ownership
> electronics are being scattered around the earth in communication,
control and
> monitoring equipment.   All of this electronics is eventually
discarded and
> may not necessarily end up in a recycling program or in managed
landfill.   It
> is as if someone were firing a shot gun  from space scattering tiny
pellets of
> lead nearly everywhere.    The fact that there is already a lot of
lead
> scattered around the earth as a result of the use of lead in paint,
gasoline, car
> batteries etc does not necessarily mean that it does not matter
whether more is
> scattered.   Lead has been largely eliminated from paint and gasoline
and car
> batteries are largely recycled.   It may be argued that there are
technical
> grounds for believing that those tiny pellets of lead are just going
to lie
> there, largely inert with none of the lead finding its way into the
water supply
> or food chain.   However, is it worth taking a risk when it is
avoidable?
>
> The second is occupational health and safety.   In this forum the
point has
> been made recently that at normal soldering temperatures the vapour
pressure of
> lead is not high enough for its fumes to create a significant problem.
> However, it is my personal experience that if you are exposed to
lead-containing
> solder it is likely that your blood lead level will increase.   Blood
lead
> levels in most industrialised countries might already be elevated
because there
> is still quite a lot of lead from other sources about but that does
not
> necessarily mean that a further increase is of no consequence.   In
electronics
> assembly the greatest risk is for people working with processes
involving pots of
> molten solder, not because of lead vapour but because of the fine lead
oxide
> dust that is inevitably generated.    For those working with solder
paste there
> is always a small risk of ingesting the fine particles of solder
powder on
> which this product is based as residues of paste dry out and
disintegrate.
> Even for those handling solder wire, the lead oxide on the surface
rubs off onto
> the fingers and can find its way into the body by ingestion or, more
> dangerously if the worker is smoker, by inhalation.   Of course
precautions are
> normally taken to ensure that blood lead levels of people working with
solder stay
> below the legislated limit.    Masks are worn when skimming dross off
a solder
> bath.  Strict hand washing procedures are followed before eating or
smoking
> and for people with the greatest risk of exposure there are periodic
checks of
> blood lead.    However, there can be no guarantee that such
precautions are
> always followed perfectly so the risk remains.   As contributors to
this forum
> have pointed out recently there are other health risks associated with
> soldering, e.g flux fumes, but that does not necessarily mean that it
is not worthwhile
> eliminating this lead risk from the work environment.
>
> It is true that the effects of the foregoing are small and so the
question
> remains as to whether they justify causing such great inconvenience to
the
> electronics industry.
>
> Some years ago there was concern that a change to lead-free solder was
not
> technically possible.    There are certainly some challenges in making
the
> change but it does seem that it is technically possible.    There are
already
> hundreds of millions of printed board assemblies in service that have
been made
> with lead-free solder over the past five years.   The question of
reliability
> will remain at least partly unanswered until lead-free solders have
been in
> service as long as tin-lead solder has been but so far no problems
have emerged
> that seem to be beyond a technical solution.
>
> Is the change to lead-free justified?
>
> Since I am associated with a solder maker who might be considered to
benefit
> from a change to lead-free I cannot make that call.   All that solder
makers
> can ethically do is offer assistance to customers who find themselves
obliged
> to make the change to lead-free.
>
> As a final comment, from my personal experience with Japanese I would
say
> that it would be unfair to suggest that their leadership in the change
to
> lead-free solder has been motivated by some devious commercial
strategy.    Living as
> they do on a small crowded island the Japanese are very conscious of
> environmental issues.   And because of the Minamata disaster
(thousands of people
> suffering from severe mercury poisoning as a result of industrial
pollution) they
> have been acutely sensitised to the potential dangers of toxic metals
in the
> environment.    Perhaps the Japanese should be given the benefit of
the doubt
> that they are motivated by a genuine concern for the environment.
>
> Keith Sweatman
> Nihon Superior Co., Ltd.
>
>
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