At what level does mercury become harmful?
The World Health Organization's guidelines maintain that the lowest level that could possibly be harmful to humans is 5 parts per million (ppm). This level is based on scientific results from the 1960s that placed the level at which risk begins at 50 ppm for most people; WHO then applied a safety factor of 10, deciding that a level of 5 or less is safe for even the most vulnerable populations.
Now the University of Rochester team has conducted an extensive study in
the Seychelles Islands of the most sensitive population -- young
children -- where the average level is about 7 ppm, about 10 times the
level of the U.S. population. The scientists found no harm from mercury
at levels up to 15 ppm, nearly twice the average Seychelles level and
about 20 times higher than the average U.S. level.
Despite those reports, hair analysis laboratories in the U.S. continue to report of toxicity at only 1 ppm.
Hair mercury is considered a valid test if properly performed. The recent Seychelles Island study showed that hair mercury below 15 µg/g (mean 6.9 ppm, SD 4.5 ppm) did not cause any problems in pregnant mothers or their newborn infants, who were followed with extensive neurological testing for many years from birth onwards. The diet contained ocean fish 12 meals per week. The fish contained the same amount of methyl mercury as found elsewhere in the world.
Laboratory Reference Ranges for Toxic Metals in Blood and Urine
Random urine < 5 µg/g creatinine (Not provoked with a chelator).
Occupational limit in urine of exposed workers < 35 µg/g creatinine (Not provoked with a chelator)
Whole blood < 8.0 µg/L
Occupational limit in exposed workers < 15.0 µg/L.
Hair <15 µg/g (µg/g = ppm)
Environmental exposure: < 8.0 µg/L, individuals consuming large quantities of seafood may have values as high as 200.0 µg/L.
Occupational exposure: BEI®: inorganic mercury (sampling time is end of shift at end of work week): <15.0 µg/L1
Some Common Mistakes
Reference ranges for upper safe limits for metals, including mercury in urine, are often printed on laboratory report forms with ranges that apply only to urine collected without first giving a chelator. The safe upper limit on the report form will thus be much higher after a chelator. If proper procedures are followed, a large majority of people tested will be in the nontoxic range.
By provoking urine excretion with a chelator, metals in urine will always increase, by up to 1,000% or more, even if levels in the body are at quite safe and low levels. The result therefore, usually appears deceptively high. That type of report is meaningless and can frighten patients into thinking they are toxic when their levels are actually quite safe.
What does the Latest Researches says
Methyl mercury and HgS was orally administrated to mice for five
The present study suggests that the insoluble HgS (the main constituent of a Chinese mineral drug, cinnabar, used as a sedative) can still be absorbed from gastrointestinal tract and distributed to various tissues including the brain.
• As compared with methyl mercury, the total amount of HgS accumulated in the tissues ranging is about one five-thousandth of methyl mercury, which is well correlated with the biological activity of HgS reported previously.
• (Tissue distribution of different mercurial compounds analyzed by the
improved FI-CVAAS. Yen CC, Liu SH, Chen WK, Lin RH, Lin-Shiau SY.
Institute of Toxicology, College of Medicine, National Taiwan
PMID: 12166816 [PubMed - indexed for MEDLINE]
HgS or cinnabar was administered orally (1.0 g/kg) to Hartley-strain guinea pigs once daily for 7 consecutive days. A battery of electrophysiological, biochemical, and histopathological examinations were performed
The increased Hg contents in the cerebellum following oral administration of HgS and cinnabar were responsible, at least in part, for the detrimental neurotoxic effect on the VOR (vestibular ocular reflex system)
• Young YH, Chuu JJ, Liu SH, Lin-Shiau SY.
• Neurotoxic mechanism of cinnabar and mercuric sulfide on the vestibulo-ocular
reflex system of guinea pigs. Department of Otolaryngology, National
Taiwan University Hospital, No. 1 Section 1, Jen-Ai Road, Taipei,
PMID: 12011485 [PubMed - indexed for MEDLINE]
This study compared the neurobehavioral toxicities of three mercurial
compounds: Methyl mercury (MeHg) which is soluble and organic. Mercuric
sulfide (HgS) and Cinnabar (naturally occurring HgS), which are
insoluble and inorganic. Cinnabar, a Chinese mineral medicine, is still
used as a sedative in some Asian countries, but there is relatively
little toxicological information about it. These mercurial compounds
were administered intra peritoneal (MeHg, 2 mg/ kg) or orally (HgS and
cinnabar, 1.0 g/kg) to male rats once every day for 13 consecutive days
with assays conducted during or after discontinuous administration for 1
h, 2, 8 and 33 weeks. Neurotoxicity was assessed based on the active
avoid-ance response and locomotor activity. The results obtained showed
that MeHg and cinnabar prominently and irreversibly caused a decrease in
body weight, prolongation of latency for escape from electric shock, a
decrease in the percentage for the conditioned avoidance response (CAR)
to electric shock, impairment of spontaneous locomotion and inhibition
of Na+/K+-ATPase activity of the cerebral cortex. In contrast. HgS
reversibly inhibited spontaneous locomotion and Na+/K+-ATPase activity.
It was noted that HgS significantly decreased the latency of escape from
electric shock during the ad-ministration period, which lasted for 33
weeks after discontinuous administration.
These findings suggests that insoluble HgS and cinnabar can be absorbed from the G-I tract and distributed to the brain.
The possibility that contamination due to other minerals in the cinnabar is responsible for the greater neurotoxic effects compared to HgS is under investigation.
Chuu JJ, Liu SH, Lin-Shiau SY.
Insitutes of Toxicology, College of Medicine, National Taiwan University, Taipei, ROC.
PMID: 11370760 [PubMed – indexed for MEDLINE]