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Posted by on Nov 18, 2008 in Neuropsychiatry, Toxicology

Chelation Challenge for Mercury Toxicity Is “A Scam”

Chelation Challenge for Mercury Toxicity Is “A Scam”


Among those who maintain that autism is the consequence of environmental mercury poisoning, the use of “provocation” or “challenge” doses of chelators (eg, a “Kelmer challenge test”) is frequently proposed as a legitimate diagnostic maneuver. For instance, Mark and David Geier implied that the urinary or fecal excretion of mercury after the administration of DMSA (succimer) or DMPS in children with autism is evidence of mercury overload. But is this conclusion valid?

Over at Quackwatch, dentist and physician Robert Baratz reminds us that, because mercury is a ubiquitous element, it will be detected in anyone’s blood or urine at some low, steady-state level (eg, <10 ug/L in urine). He advises, however,

Urine mercury levels can be artificially raised by administering a mercury scavenger (chelating agent) such as DMPS or DMSA, which collect the small amounts of mercury from the body, concentrate them, and then force them to be excreted…The urine level under such circumstances is artificially raised above the steady-state level [emphasis added].

Baratz cites a 2001 study by Frumkin et al, who found no association between a history of occupational mercury exposure and the urinary excretion of mercury either before or after DMSA (10 mg/kg) in former employees at a chloralkali plant or in an unexposed control population. The investigators concluded that a DMSA chelation challenge is not a useful diagnostic test for prior mercury exposure. Baratz writes more emphatically,

The use of a chelating agent before testing“provoked testing”should be considered a scam. Anyone told that a urine-mercury level produced after DMPS represents a toxic state is being misled.

Baratz also maintains that mercury levels in stool or hair samples are not accurate indicators of mercury exposure, and that such tests have not been standardized.

In 2004, Archbold et al assessed the urinary excretion of mercury in 13 healthy adult volunteers with dental fillings,* before and after the administration of DMSA 30 mg/kg. These results were compared with the mercury-excretion patterns of patients who claimed to have symptoms caused by mercury-containing dental fillings (Hibberd et al. J Nutr Environ Med. 1998;8:219-231 [no PMID]).


Urinary Mercury, μg/L
(uncorrected for creatinine)

Archbold et al
(N = 13)

Hibberd et al
(N = 65)

Before chelation dose

2.2 ± 1.9

5.0 ± 3.5

After chelation dose

13.7 ± 13.6

13.1 ± 9.0

Archbold et al found that the incremental increase in mercury excretion after the DMSA challenge in asymptomatic volunteers was comparable to that in previously reported symptomatic individuals. They concluded, therefore, that the validity of a chelation challenge test is diagnostically misleading. Their results are consistent with those of Vamnes et al, who also concluded that symptomatic individuals with dental fillings could not be differentiated from asymptomatic persons on the basis of a DMPS challenge test.

In a more recent, pilot study, Soden et al did not find evidence of “an excess chelatable body burden” of arsenic, cadmium, lead, or mercury in the urine samples of 15 autistic children after provocation doses of DMSA. Their study also evaluated 5 neurotypical control children. The authors acknowledge that their study was complicated by the fact that there are no normal references for provoked levels of urinary metalswhich is the crux of the problem in general when assessing the level of urinary mercury after a chelation challenge.

DMPS = 2,3-dimercapto-1-propanesulfonic acid; DMSA = dimercaptosuccinic acid.

* One excluded volunteer suffered a severe reaction to DMSA, requiring emergency care.

bmartin (1130 Posts)

A native East Tennessean, Barbara Martin is a formerly practicing, board-certified neurologist who received her BS (psychology, summa cum laude) and MD from Duke University before completing her postgraduate training (internship, residency, fellowship) at the Hospital of the University of Pennsylvania in Philadelphia. She has worked in academia, private practice, medical publishing, drug market research, and continuing medical education (CME). For the last 3 years, she has worked in a freelance capacity as a medical writer, analyst, and consultant. Follow Dr. Barbara Martin on and Twitter.