Dear Brian
I would just like to clear up some of the points you make on toxicity of tin. It is inaccurate to say that many tin compounds are toxic as distinction should always be made between organo-tin compounds and all other forms of tin. It is also inaccurate to generalise and claim all organotins are toxic. The toxicity is not specifically related to the tin, but to the nature and number of the organo- groups attached. See the paragraph below.
As far as the comment on cans is concerned the lacquer coating is in fact there to prevent corrosion. In some cases a lacquer coating is deliberately not used in order for the tin to dissolve to a small extent in the acid food juice and stabilise colour and (apparently) taste. Take a look at your cans of tomatoes/beans etc and you will find that they are unlacquered, or only partially lacquered.
The effect of distribution of tin metal in the environment has been well examined. In particular, the US Fish and Wildlife service made an extensive study on tin toxicity during approval of tin as lead-free shot. Data on the behaviour of tin in soils, water, wildlife, livestock and man was examined with tin succesfully passing this stage of the approval process.
Kay
ITRI
Organotins: toxicity is related to the precise nature of the organo-moiety. Essentially, there are four basic types: mono- (with one organic group attached to the tin), di- (with two), tri- (three) and tetra- (four). As a generalisation, toxicity is greater for tetra- and tri- types than for di-, which in turn is greater than for mono-. However, within each type, it is the nature of the organo- groups attached to the tin that is important. With regard to mammalian toxicity, methyl- and ethyl- groups generally give the highest toxicity, whereas larger alkyl groups (e.g butyl-, octyl-) are less toxic to mammals, but are often more toxic to other species. For example, tributyltin compounds (e.g. TBTO) are particularly toxic to marine organisms, and are therefore used in antifouling paints to prevent barnacle growth on boat hulls. This is the application that TBTO was developed for. However, it is important to note that most of the di- and mono- organotin compounds used commercially (e.g. in PVC stabilisers, catalysts, tin oxide film precursors) are of low toxicity, and some are approved for food contact applications (as in PVC packaging). The main message is that it is wrong to generalise and say that all organotins (or, indeed, all tin compounds) are toxic.
-----Original Message-----
From: Brian Ellis [SMTP:[log in to unmask]]
Sent: 05 November 1999 10:35
To: [log in to unmask]
Subject: Re: [LF] Long-term solutions
I agree, but tin is also a severe issue which has not been sufficiently
addressed. Many tin compounds are toxic (some organotin compounds are
used as wood preservatives, fungicides, algicides etc.). Who knows what
reactions may occur in a landfill? Anyway, tin is (or at least was) not
federally regulated in waste water in the USA, although I believe some
States may cap it at 5 - 10 ppm. However, in Europe, the levels are set,
mostly at 1 - 5 ppm (copper at 0,5 - 2 ppm in many countries as a
comparison). I won't discuss Malaysia's limit at 0,1 ppm, because this
is a special case. Anyway, tin is considered about half as toxic as
copper, so don't consider it as being exempt from all future regulation.
Note that many tin-plate cans for acid foods are now polymer-coated as
additional protection against the ingestion of tin salts.
I think the crux of the matter is that ALL metals can be shown to be
toxic in some form or another. Lead is just a technocrat's buzz-word and
should not be treated differently from any other metal. When these guys
cotton on to these facts, all metals will be banned, as will also
bromo-bisphenols used for fire-retarding PCB laminates. There is only
one logical solution: obligatory recycling of all metals. The sooner
this fact is realised, the better: then we can get on with our business
of soldering boards with tin/lead solders to our heart's content. AND I
say this as one much and actively concerned with the protection of our
environment.
Brian
"Bernier, Dennis" wrote:
>
> Though I am not an advocate of rapid changeover to lead-free solder alloys
> without more reliability testing, I can see the lead-free alloys might be a
> future environmental problem. However, the amount of silver and copper
> combined in the solder will only be about 10% of the amount of lead in
> Sn63Pb37 solder alloy used now. This will be a very small amount of metal
> contamination due to the solder in the electronic product. It seems then
> the copper may become the issue because there will be 20-50 times as much
> copper in the assembly than silver.
>
> -----Original Message-----
> From: Carol Handwerker [mailto:[log in to unmask]]
> Sent: Wednesday, November 03, 1999 5:56 AM
> To: [log in to unmask]
> Subject: Re: [LF] Long-term solutions
>
> In the Assembly Processing group working on the Lead-Free Solder Roadmap at
> the IPC meeting, the highest priority item from the group was to ensure
> that the new alloys are viable in the long term from a toxicology and
> environmental life cycle point of view. Having to change alloys again in
> three years would be a waste of resources if we can formulate a proper
> solution now.
>
> At 07:06 PM 11/02/1999 -0800, you wrote:
> >All,
> >
> >As I read the debates ongoing, it strikes me that there are 2 major focus
> >areas right now:
> >
> >1) Technical solutions to Pb-free solders
> >2) Is the decision environmentally correct?
> >
> >Are we missing a 3rd item?
> >
> >Regardless of what solder we end up with, how does the industry position a
> >long term, environmentally sound policy that will forestall future green
> >initiatives from causing such upsets?
> >
> >The history of Pb is rife with abuses -- Workers not following safe
> >practices, employers not requiring or implementing safe practices, emission
> >controls not being in place on smelters, .... This is in addition to Pb
> >being used without a full understanding of the toxicology and exposure
> risks
> >(Paint, gasoline, plumbing The point is, past uses (and abuses) and
> >handling of Pb has created the situation we are in now.
> >
> >I have not seen/heard any discussion on establishing practices and
> protocols
> >that will foster responsible use of any solder -- Both safe working
> >practices on the production end, and End of Life management. Should this be
> >part of the overall strategy, or a recommended best known method? How does
> >this link into product takeback requirements that are gaining popularity in
> >the EU and Japan?
> >
> >Regards,
> >Paul Wermer
> >(Whose opinions are his own and do not necessarily reflect those of his
> >employer)
> >
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> Carol A. Handwerker
> Chief, Metallurgy Division
> NIST
> 100 Bureau Drive Stop 8550
> Gaithersburg MD 20899-8550
> Office:(301) 975-6158
> Fax:(301) 975-4553
> e-mail:[log in to unmask]
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Please visit IPC's Center for Lead-Free Electronics Assembly
(http://www.leadfree.org ) for additional information.
For technical support contact Gayatri Sardeshpande [log in to unmask] or 847-790-5365.
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