Sampling water contaminants

Chauncey W. Anderson chauncey at usgs.gov
Fri Feb 16 12:50:13 EST 1996


In article <4g1asn$2d5 at ionews.io.org>, Byron Bodo <bodo at io.org> writes:
> Louise Lapierre <74267.2135 at CompuServe.COM> wrote:
> >I would like to know the relative advantages and disadvantages of 
> >large volume sampling of water and the differences of 
> >centrifugation vs filtration on the detectability of substances.
> >Please forward me any thoughts or references.
> >I am presently preparing sampling of rivers and would like to 
> >choose between different matrices.
> >
> 

I agree with Byron's comments, with the added caveats:

> It will depend very much on the chemicals / substances that you
> want to detect & their ambient concentrations.  

And the levels you feel you wish to detect, and the laboratory
procedures you are working with.  As Byron states below,
non-detects are not very useful...


...snip...

> If you're after low level contaminants, eg, PCBs, TCDD/PCDF, etc,
> you may little choice but to go high volume if you want to obtain
> quantifiable lab measurements.  A data base full of non-detections
> doesn't give you much information other than an upper limit on potential
> concentrations.
> 
> As for filtration versus centrifugation, both have been used.  I've
> not seen a good discussion of the relative merits of the two. 

Take a look at:

Howrowitz, A. J., 1986, Comparison of metods for the concentration of
suspended sediment in river water for subsequent chemical analysis,
Environ. Sci. & Technol. 20, 155-160.

One major factor to keep in mind is that filtration of too much
sediment can actually change the effective pore size of your filter as
the sediments build up (otherwise known as "sediment loading"). You
may need to change your filters frequently.  The USGS has done a lot
of thinking about this in the last few years since it was discovered
that there were some problems with the way we'd done things in the
past.
...snip...

> 
> While you're at it don't forget to get the basic ancillary data,
> i.e., suspended solids, DOC, TOC (or POC on the particles).  I
> just waded through extensive literature on global organochlorine
> levels, and the majority of investigators have failed to collect
> or report SS, DOC, POC which severely limits the use of the data for
> comparative study and extrapolation.

Very important -- I agree wholeheartedly.. Also, if you're measuring
trace metals, don't forget to measure hardness if you want to relate
the concentrations to water-quality criteria

> 
> Keep in mind that the lower the ambient concentrations of the target
> substance, the greater the risks of sample contamination in the field
> and the lab. Stringent QC/QA procedures may be required. 

Absitively.

Chauncey Anderson, Hydrologist 	      e-mail:chauncey at usgs.gov
USGS-WRD			      tel: (503) 251 - 3206
10615 SE Cherry Blossom Dr.           FAX: (503) 251 - 3470
Portland, OR  97216                   http://wwworegon.wr.usgs.gov/index.html




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