[Catalist] A Study in Environmental Chemistry: Lead in portable Drinking Water

Fri Apr 21 13:46:56 AEST 2017

A couple of issues with this:
1) Lead has its greatest effect on the developing brain - there are a 
number of epidemiological studies that correlate blood lead and decline 
in IQ, and that is very significant.

2) The greatest relative effects occur at low levels of dosage, so this 
means it is desirable to push the limits as low as attainable.

3) It is a children's hospital - hard to imagine a worse-case scenario, 
especially hard on chronic childhood diseases. In other words, the most 
vulnerable (sickest) are likely to have the greatest exposure (longest 
time in residence). When kids get sick, they (hopefully) have a longer 
remaining life, and hence cost more to compensate. ("Kids brains are 
worth more than yours or mine" - at least in litigation !)

4) Adult brains don't seem to be as badly affected.

5) The insolubility is a red herring: toxic levels in blood are 100ug 
per litre or 100ppm. Most "insoluble" salts are less than 100mg/l. 
Calcium easily reaches this at 25C, there is upwards of 2.4mg /l of 
calcium dissolved. Lead solubility in the presence of hard water 
(carbonates) still gives about 56mg per litre - easily enough to 
absorb!  (based on ksp of 7.4 x 10^-14, 25 degrees C, m(r) 207 for 
lead). Lead is likely to be grabbed by the general divalent ion 
transporter protein / calcium system in your gut, so there is a 
mechanism for absorption.

Now the interesting thing is the remediation. These guys are looking at 
phosphate treatment. At first sight this looks good as the Ksp of lead 
phosphate is around 44, ie [Pb]3[PO4 3-]2 = 10^-44 (ish, - try measuring 
that sucker!).

But note that the equilibrium expression is [Pb]^3[PO4]^2= 10^-44 - 
those powers really stuff things up.
If we solve for the Pb concentration, we can set the PO4 concentration 
as x, and therefore the Pb concentration as 3x/2 or 1.5x.
Then we find we can rewrite out equilibrium expression as 1.5x^3 times 
x^2 = 10^-44, and then the concentration of Pb can be found to be 1.46 x 
10^-9 Molar, or 0.3 micrograms per liter, which is ok, but in fact only 
a couple of orders of magnitude less soluble that the carbonate!

So is the hope is to cover the surface of the pipes with a phosphate 
coat that is insoluble? Just of lead and other metals? How often will it 
need to be re-flushed? I can't believe that they only want to treat the 
lead already in the water. What about a plasticiser?

But I reckon it gets worse. To keep the lead in the really insoluble 
phosphate form (as distict from the considerably more soluble hydrogen 
phosphate HPO4- form, you are going to have to have burn-your-mouth-out 
pH of above 10. So there is no way it can be drunk like that! And, given 
that there is a dodgy alloy in there somewhere, of unknown composition, 
it may be that the high pH may even make the lead problem worse (by 
accelerating the bulk corrosion of the metal, thereby freeing a greater 
mass of Pb. How much zinc is in that unknown dodgy metal (Zn(OH)4 2- 
being both soluble and amphoteric ). Who knows! Certainly I am not brave 
enough to buy a lottery ticket in that one.

So if it all goes pear shaped, tell your kids this: If the WA government 
had properly studied their Y12 equilibrium chemistry, (and if our course 
had just taught that little bit further, and required numerical answers 
for problems to equilibrium expressions), they could have saved the 
state a motza, which could have been spent on the pensions of worthy and 
deserving science teachers!

Have fun now Roy! This has distracted me from writing my course manual 
of stem/robotics (which is looking suspiciously like physical sciences 
with robots added in). Ah well, it was a pleasant hour and a half. 
Please point out any errors in my reasoning - I have not spent a huge 
amount of time thinking/reworking this.

Cheers,
Leon

https://www.ncbi.nlm.nih.gov/pubmed/27837574

https://books.google.com.au/books?id=SToDhE40GhYC&pg=PA92&lpg=PA92&dq=distance+from+road+iq+lead&source=bl&ots=w5zrOxEqXS&sig=DQ8FHG3zXQAUN5E5A9XDtqTzeEM&hl=en&sa=X&ved=0ahUKEwiH6daFv7TTAhXFybwKHRV6BbwQ6AEITTAJ#v=onepage&q=distance%20from%20road%20iq%20lead&f=false

and numerous others.

On 21/04/2017 9:45 AM, Roy Skinner wrote:
>
> I find it strange that suddenly minute amounts of lead in water is a 
> problem.
>
> I lived in a house in UK for 20 years where waste pipes were all lead 
> and water pipes were all soldered with lead. The Romans had water 
> pipes made of lead also.
>
> I always understood that lead itself is not poisonous as it is not 
> soluble in water so it cannot get into the bloodstream unless 
> converted to a soluble salt. I have also had mercury fillings since I 
> as a child which, my dentist assures me is no problem for the same 
> reason – mercury compounds are mostly insoluble. If you drank mercury 
> it would actually do you no harm but pass straight through.
>
> I suppose the problem might come if there was a bacterium that 
> converted lead or mercury into soluble compounds such as methyl 
> mercury, but I very much doubt this.
>
> I have lived for over 60 years with mercury in my mouth and I think I 
> am getting ever more intelligent – so what exactly is the problem with 
> small amounts of lead in water?
>
> Roy
>
> *From:*Catalist [mailto:catalist-bounces at lists.stawa.net] *On Behalf 
> Of *Michael McGarry
> *Sent:* Friday, 21 April 2017 7:50 AM
> *To:* catalist at lists.stawa.net
> *Subject:* [Catalist] A Study in Environmental Chemistry: Lead in 
> portable Drinking Water
>
> Greetings Science Colleagues,
>
> ABC URL: 
> http://www.abc.net.au/news/2017-04-20/govt-to-pay-lead-contamination-fix-perth-childrens-hospital/8457388
>
> The above ABC online news report motivated me to conduct www research 
> into the causes, distribution and degree of lead contamination in 
> Australian drinking water. [There is a serious lack of Australian 
> webpages informing lead in drinking water.]
>
> *Dosing of portable water with Phosphates*
>
> The dosing of portable water with phosphates can reduce lead 
> contamination.
>
> URL: 
> http://orendatech.com/wp-content/uploads/2014/02/Potable-Water-Treatment-phosphates.pdf
>
> Does phosphate dosing provide a long-term solution to lead 
> contamination of portable drinking water?
>
> “*Brass fittings to blame for lead scare: Government*” [ABC news story]
>
> “Mr Wyatt [WA State Treasurer] said it was the Government's view the 
> lead contamination was a *result of the de-zincification of brass 
> fittings in the pipes*.”
>
> Given that the alloy brass is mainly a solid, blended mixture of 
> copper and zinc metals surely manufacturers of brass would never 
> attempt to de-zincify brass?
>
> *Lead content in Brass*
>
> Brass can be lead free or leaded brass. Lead metal is added to brass 
> to increase the machinability of the brass during manufacture of 
> plumbing fittings, e.g., taps.
>
> During machining of leaded brass for taps, patches of lead metal 
> concentrate on the surface of the leaded brass. These patches of lead 
> on the inside of the leaded brass taps, especially hot water taps, 
> leach into the water.
>
> Were lead-free brass plumbing fittings used in the building of the 
> Perth Children’s Hospital? Do Australian Federal and State government 
> regulations require the installation of lead-free brass fittings in 
> the pluming of Hospitals? [Stainless steel taps do not contain lead 
> metal!]
>
> *Lead affects brain development in children resulting in learning 
> difficulty.*
>
> Mayo Clinic URL: 
> http://www.mayoclinic.org/diseases-conditions/lead-poisoning/symptoms-causes/dxc-20275054
>
> *Additional URL’s that inform causes and distribution of lead 
> contamination in water.*
>
> URL 4: 
> https://www.newscientist.com/article/2100806-lead-in-australias-drinking-water-is-leaching-from-brass-taps/
>
> URL 5: https://www.sciencedaily.com/releases/2010/11/101111141849.htm
>
> URL 6: 
> http://dwi.defra.gov.uk/research/completed-research/reports/DWI70-2-287exsum.pdf
>
> URL 7: 
> http://vtnews.vt.edu/articles/2010/11/111710-engineering-edwardsunc.html
>
> URL 8: http://www.tandfonline.com/doi/full/10.1080/02670836.2016.1220906
>
> Best Wishes,
>
> Michael John McGarry
>
>
>
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