Re: Wall Effect on metals in solution

[c0etxlim@mrd42.mrd.usace.army.mil (Luke I. McCormick)]

I talked with our HTRW chemists and their report is that the Wall effect is 
alive and well.  Metals will oxidize on the surface of glass and precipitate
on polyethylene.  Metals, (Uranium and Plutonium) are generally more soluble
in acidic solutions so lowering the pH will help keep them in solution.
Salts will have a maybe and maybe not effect. (I'm just quoting that) 
The time for acidification should be when the sample is initially procured.
Holding the sample for 15 days will generally csuse plate out if it is going 
to happen.   
Our chemists felt that if the sample is for determining regulatory compliance,
It shouldn't be acceptable, but that in the pCi/L range that most of the 
samples are measured in, the plate out would probably not exceed 10% of the 

sample value, which will probably be within the margin of error for the 
measurement. 
My interpretation of what they said is that the reading is in the ballpark 
even including wall effect for most the stuff i deal with, but its not what
I would want to present to a regulator to sign off that the water is clean 
enough for free release, if I am anywhere above background.
Luke McCormick c0etxlim@mrd42.mrd.usace.army.mil
--------------------------------------------------------------------------------> 
> 
> From:          "Webb, Jim" <jwebb@health.ohio.gov>
>    
>      Fellow Radsafers
>      
>      We were reviewing environmental water sample data that was analyzed 
>      for Iso U and Iso Pu. It was learned that the sample contained no 
>      preservatives and the samples had sat in the laboratory for 15 days 
>      before being analyzed.  
>      
>      We would like to know if you would reject or accept the data. A brief 
>      explanation for your answers would be appreciated. 
>      
>      JWEBB@HEALTH.OHIO.GOV
> 
> We too have been wrestling with concern about a " wall effect" -- 
> ions in solution plating out on the inner surface of a container.  
> Our lab has usually insisted on acidification of the sample with 
> nitric acid to a pH of 2.  When pressed the lab indicated that the 
> sample could be acidified when brought back to the office, as long as 
> it sat for around 48 hours before being tested.   I contacted the EPA 
> labs and inquired how samples were handled there, pointing out that 
> samples which were acidified with nitric acid could not legally be 
> transported by commercial aircraft.  They indicated that they did not 
> acidify samples which they took to their lab.  Several questions 
> which have arisen out of our experiences are as follows:
> 
> 1. Does a sample which is to be analyzed for certain metals have to 
> be acidified as soon as possible after being taken?
> 
> 2.  If you can wait until you return to your main office, but still 
> have to acidify the sample, how long must it sit before you can rely 
> on the ions being returned to solution?
> 
> 3.  Does the materials of construction of the container, have any 
> effect on whether or not ions will plate out?  We use polyethylene 
> cubitainers nowadays.
> 
> 4.  Will insoluble oxides behave like soluble salts and exhibit the " 
> wall effect " phenomenon?  Or more to the point does the " wall 
> effect" truly exist, and should we be concerned with sample 
> acidification for that purpose?
> 
> 5.  Is there literature on sampling procedures, which give guidance 
> on sample prep in the field specifically for radionuclides which take 
> chemical reactions into account?  I remember back in the '50's some 
> discussion in the literature regarding the " wall effect"  but can 
> find nothing about it now. Could I be using the wrong terminology?
> 
>              ***************************************
>                Russ Meyer                            
>                Internet: cmeyer@brc1.tdh.state.tx.us 
>                tel: 512/834-6688                                                    
>                fax: 512/834-6654
>              ***************************************     
>