Significant Levels of Mercury in Autistic Kids

Wecker, L; Miller, SB; Cochran, SR; Dugger, DL; Johnson, WD. Trace element
concentrations in hair from autistic children. Journal of Mental Deficiency
Research, 1985 Mar, 29 ( Pt 1):15-22. (UI: 85237449)
Language: English; Pub type: JOURNAL ARTICLE

      Abstract: The concentrations of 14 elements were determined in scalp
hair samples from control, autistic and autistic-like children. Significant
differences were noted between normal males and females for calcium,
magnesium and mercury. The autistic population had significantly lower
levels of calcium, magnesium, copper, manganese and chromium and higher
levels of lithium as compared to sex- and age-matched controls.
      Children with autistic features (autistic-like), classified as having
childhood-onset pervasive disorder, had lower levels of magnesium, cadmium,
cobalt and manganese as compared to controls. Discriminant function analysis
using the 14 trace elements correctly classified 90.5% of the normal and
100% of the autistic population. Using a stepwise procedure, the five
elements with the greatest discriminatory power were calcium, copper, zinc,
chromium and lithium.
      Analysis based on these five trace elements led to the correct
classification of 85.7% of the normal and 91.7% of the autistic group.
Results indicate that the concentrations of trace elements in hair from
normal children differ from patterns observed in both autistic and
autistic-like children. Furthermore, evidence suggests that hair analysis
may have potential use as a diagnostic tool for autism.
Robert Byrd, MD, MPH
UC Davis Medical Center
Department of Pediatrics
Section of General Pediatrics
2516 Stockton Blvd., Ticon II, Suite 337
Sacramento, CA 95817
916-734-4128 office
916-456-2236 fax
916-762-6926 beeper
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Limiting Infant Exposure to Thimerosal in Vaccines and Other Sources of

      [JAMA editorial from the November 10, 1999 issue by Neal A. Halsey,

      In late June of 1999, the Food and Drug Administration (FDA) revealed
that some infants who receive multiple doses of vaccines containing
thimerosal could be exposed to total amounts of mercury that exceed some
federal guidelines.1 Thimerosal is a mercury-containing preservative used in
some Haemophilus influenzae type b (Hib), diphtheria and tetanus toxoids
with acellular pertussis (DTaP), hepatitis B, influenza, and other
vaccines.2 Federal agencies, the American Academy of Pediatrics (AAP),
international agencies, and vaccine manufacturers have responded quickly to
address the concern.1, 3, 5 However, more can be done to maintain public
confidence in vaccines and to reduce childhood exposures to mercury from all
      Some confusion has occurred because of uncertainty regarding the
applicability of guidelines for long-term exposures to methylmercury from
environmental sources to intermittent exposures to ethylmercury, a breakdown
product from thimerosal. Based on the limited data available, experts have
concluded that the toxicity of ethylmercury may be similar to methylmercury.
Guidelines for limiting exposure to methylmercury in foods (primarily fish)
are based on the assumption that exposure will continue over long periods of
time. The long half-life of methylmercury (average, 50 days) results in
accumulation that could be harmful to the developing fetal brain, which is
much more susceptible to organomercurial compounds than the adult brain.2
The doses thought to be able to be consumed on a daily basis without harm
vary among agencies: 0.1 g/kg per day for the Environmental Protection
Agency (EPA),6 0.3 g/kg per day for the Agency for Toxic Substances Disease
Registry,7 and 0.4 g/kg per day for the FDA.8 The World Health Organization
provides a provisional tolerable weekly intake of 3.3 g/kg for the general
population, but the dose for pregnant women and infants would be smaller.9
The EPA estimates that 7% of women of childbearing age in the United States
consume 0.1 g/kg per day or more of mercury from fish harvested in high
risk areas, and 1% of women consume 0.37 g/kg per day or more.6 Mercury
accumulated in these women is transferred to their children prenatally and
in breast milk; subsequent exposures to organomercurials from other sources,
including biologic products, are presumed to be additive to their baseline
body loads.
      Exposure to ethylmercury from vaccines containing thimerosal in the
first 6 months of life ranges from 0 to 187 g based on which vaccines are
administered.2 Since many vaccines do not contain thimerosal, most children
receive less than the total amount of mercury indicated in the guidelines
during the first 6 months of life. If all thimerosal-containing vaccines are
given, the total exposures exceed the EPA guidelines, and possibly other
guidelines, for the smallest infants. There are safety or uncertainty
factors (10-fold for the EPA) built into the guidelines, and experts believe
there is no evidence of harm from exposure to thimerosal in vaccines.1, 2
However, clinicians are uncertain as to how much mercury can be safely given
at 1 time when multiple thimerosal-containing vaccines are administered
      Data from 2 recent studies examining the relationship between
methylmercury exposure and neuropsychological outcome in children suggest
that intermittent large exposures may pose more risk than small daily doses.
Faeroese children at age 7 years who had been exposed in utero to
intermittent bolus doses of methylmercury were found to have subtle
neurologic impairments based on domain-specific neuropsychological
testing.10 The total exposures during pregnancy were in the range that was
not associated with impairments by global IQ testing in Seychelloises
children aged 5.5 years who had been exposed to smaller daily doses.11 The
investigators from the 2 studies disagree over what exposures are safe, but
a review by a panel of independent scientists found no major methodological
problems in either of the studies.12-14 Differences in testing methods and
age at evaluation might explain some of the differences; follow-up studies
will provide more information. The controversy resembles that in studies of
lead toxicity where sequential studies over many years provided evidence for
subtle effects with progressively lower exposures and resulted in
increasingly lower acceptable limits of exposure.15 Additional studies are
being planned to evaluate the possible effects of mercury exposure from
      The FDA sent a letter to vaccine manufacturers on July 1, 1999,
requesting plans to remove thimerosal from vaccines or justify the continued
use of this preservative.1 The AAP and the US Public Health Service issued a
statement on July 7 calling for elimination or reduction of thimerosal in
vaccines for children and recommending deferral of the first dose of
hepatitis B vaccine for infants born to hepatitis B virus surface antigen
(HBsAg) negative women until age 2 to 6 months.1 A parallel review of these
issues in Europe resulted in the European Agency for the Evaluation of
Medicinal Products issuing a statement on July 8 promoting the use of
vaccines without thimerosal for infants and toddlers within the shortest
possible time frame.3 The AAP issued a more detailed statement on July 144
that provided physicians with the mercury content in vaccines, background
information on mercury toxicity, advice for reducing mercury exposures from
all sources, and specific guidelines for the use of hepatitis B vaccines.
The AAP also urged the FDA and manufacturers to rapidly reduce the mercury
content of vaccines.2 In a remarkably short time, the FDA approved a request
from Merck on August 27 to market a thimerosal-free hepatitis B vaccine for
use in infants. SmithKline Beecham also has submitted a request for approval
of products with little or no thimerosal.5 The Centers for Disease Control
and Prevention (CDC) and the AAP have strongly encouraged physicians to
resume neonatal hepatitis B vaccination of infants born to HBsAg negative
women with products that have reduced or no thimerosal.2, 5
      Some clinicians apparently were confused by the rapid changes in
hepatitis B guidelines. Infants born to women who are HBsAg positive or
whose hepatitis status is unknown should be vaccinated at birth regardless
of the availability of thimerosal-free vaccines because the high risk of
acquiring hepatitis B infection and increased likelihood of becoming a
carrier far outweigh theoretical concerns about the amount of mercury in a
single dose of this vaccine.1-5 The CDC has emphasized the need for
immunization of all newborns in populations at increased risk for hepatitis
B infections from contacts early in life.5 Most countries have initiated
programs to administer hepatitis B immunization at birth or in the first few
weeks of life because this is the optimal strategy for preventing hepatitis
B transmission.16, 17 Immunization at birth provides early and long-term
protection of neonates against infection by HBsAg positive mothers who were
missed by screening programs and HBsAg carriers among families, friends, and
other contacts.18
      Are preservatives like thimerosal necessary in vaccines? The FDA
regulations require preservatives in multidose vials of most vaccines (with
the exception of certain live viral vaccines) to protect against inadvertent
contamination from repeated puncture of the seal.20 Thimerosal does not
prevent all bacterial contamination, as evidenced by clusters of disease
from group A streptococcus infections traced to multidose diphtheria toxoid,
tetanus toxoid, and pertussis (DTP) vaccine vials that were contaminated
after opening.21 The use of single-dose vials or prefilled syringes for
vaccines should be encouraged because this eliminates errors in preparation
as well as the need for preservatives for most vaccines. Thimerosal is used
during production of some vaccines and in many cases can be removed leaving
trace amounts (<0.3 g) of mercury that have no biologic effect.22 Such
products should be considered equivalent to thimerosal-free products.
Alternative preservatives are one option for multidose vials, especially in
developing countries where the need to keep costs low is an essential
component of the success of the World Health Organization's Expanded Program
on Immunization. The use of new combination products will reduce exposure to
preservatives by decreasing the number of injections needed to deliver
recommended vaccines.
      How should physicians deal with the uncertainties during the
transition to the elimination or reduction of thimerosal in vaccines? On
October 20, 1999, the Advisory Committee on Imunization Practices of the CDC
decided not to give a general preference for thimerosal-free vaccines for
administration to infants. The CDC and AAP have indicated that hepatitis B
vaccines containing no or trace amounts of thimerosal should be
preferentially used for infants during the first 6 months of life. I believe
that this preference should be extended to Hib and DTaP vaccines for infants
(especially premature infants) whenever possible. The list of mercury
content in vaccines is kept up-to-date on the Institute for Vaccine Safety
Web site ( to assist physicians in vaccine
choices. If supplies are limited, exposure to no more than 1
thimerosal-containing vaccine at each visit would reduce exposures while
ensuring that infants are fully protected against diseases, including
influenza in high-risk infants. Elimination of thimerosal or other
preservatives will be more difficult for influenza vaccines produced in eggs
because a preservative helps ensure protection against contamination. The
small amount of thimerosal in influenza vaccines does not constitute an
undue risk for older children and adults, especially for high-risk
individuals in whom complications from influenza constitute a major health
      The AAP encourages parents to follow local fish advisories to reduce
children's exposure to mercury.2 Since mercury exposures from other sources
may be additive, special care should be taken not to administer additional
mercury from vaccines to small infants in populations in which pregnant
women may consume more than the maximum recommended amounts of mercury.
Thimerosal has been eliminated from latex paints, and merthiolate, a
concentrated form of thimerosal used as an antiseptic, is no longer used
because of serious toxic effects from these products in infants.23 Congress
deserves credit for mandating the review of thimerosal in biological
products, but needs to ensure that the agencies responsible for vaccine
safety have the resources and freedom from undue regulation to allow them to
carry out their mandates. The FDA needs highly qualified scientists and
resources to address the increasingly complex scientific issues involved in
vaccine production. Therefore, health care professionals should be concerned
that the research budget for the Center for Biologics and Evaluation
Research has been reduced to one third the level that it was in 1994.24
Availability of the safest vaccines now and in the future requires support
for scientists working at federal agencies responsible for vaccine safety.
In late June and early July, when decisions needed to be made rapidly,
officials from the CDC could not officially consult with the Advisory
Committee on Immunization Practices because statutes prevent such meetings
without posting a notice in the Federal Register.25 Exceptions should be
made to allow the CDC and other agencies to address urgent situations.
      The public has become intolerant of unnecessary exposure to real and
theoretical risks for children from all sources as evidenced by demands to
make food products, toys, seat belts, and air bags as safe as possible.26
Reducing or eliminating exposure to mercury from all sources, including
industrial contamination of waterways that leads to accumulation of mercury
in fish, should be a national priority.27 Further reductions or elimination
of mercury in vaccines will help maintain public confidence by demonstrating
a commitment to provide the safest vaccines possible for protecting children
against disease.
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