RE: Tritium Therapy & Beer Drinking

["Weiner, Ruth" <rfweine@sandia.gov>]

"Chelation" is the formation of a chelate, a type of coordination compound
(molecule) in which a central metal ion is attached by coordinate links
(ligands) to two or more non-metallic atoms. Typically the non-metallic
components are heterocyclic rings.  The non-metallic components form a cage
around the metal ion; hence the term "chelate" from the Greek for cage.
Chelation with the appropriate ligands often enhances solubility of metal
ions.  A typical example of a chelating agent is EDTA (the active agent in
the cleaner Fantastik).  EDTA, which has four ligation sites, is used to
clean or decontaminate because it readily forms chelates with transition
metal, lanthanide, and actinide ions.  Citrate  and oxalate (among others)
also form chelates, though they have less affinity for metal ions than EDTA
because the molecules have fewer ligand sites.

Chelation enhances solubility.  It is not the same thing as solubility, and
I don't think anyone ever implied that it was.

Ruth F. Weiner, Ph. D.
Sandia National Laboratories 
MS 0718, POB 5800
Albuquerque, NM 87185-0718
505-844-4791; fax 505-844-0244
rfweine@sandia.gov


-----Original Message-----
From: Potter, Charles [mailto:capotte@sandia.gov]
Sent: Thursday, April 29, 1999 11:13 AM
To: Multiple recipients of list
Subject: RE: Tritium Therapy & Beer Drinking


Since the term "chelation" has been used in this thread, I feel the need to
point out that forcing fluids to increase the elimination of tritium is not,
strictly speaking, "chelation".  This term has, unfortunately, been used by
some to be synonymous with medical intervention for internal contamination.
NCRP-65 describes four different treatment scenarios for internal
contamination.  

The first are "procedures to reduce gastrointestinal absorption."  This
includes stomach-lavage, emetics (for induction of vomiting), purgatives,
aluminum-containing antacids, etc.  The second are "blocking and diluting
agents."  These block metabolic processes in a specific tissue, such as
potassium iodide.  "Forced fluids" for increased elimination of tritium is
included in the blocking/diluting agent category.  

The third category is "mobilizing agents" that increase the natural turnover
of the substance from body tissues.  This category includes diuretics for
sodium and other electrolytes and ammonium chloride for strontium.  The
fourth and last category is "chelating agents."  this refers specifically to
chemical compounds that enhance the excretion of metals by bonding with
them.

I hate to be nit-picky, but I think proper use of terms is the best way to
ensure that people know what we're talking about.

Gus

C. A. Gus Potter
Sandia National Laboratories
Albuquerque, New Mexico
(505) 844-2750
capotte@sandia.gov
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