Fish consumption, methylmercury and child neurodevelopment.

PURPOSE OF REVIEW: To summarize recent evidence regarding associations of early life exposure to mercury from maternal fish consumption during pregnancy, thimerosal in vaccines and dental amalgam with child neurodevelopment. RECENT FINDINGS: Recent publications have built upon previous evidence demonstrating mild detrimental neurocognitive effects from prenatal methylmercury exposure from maternal fish consumption during pregnancy. New studies examining the effects of prenatal fish consumption as well as methylmercury suggest there are benefits from prenatal fish consumption, but also that consumption of fish high in mercury should be avoided. Future studies incorporating information on both the methylmercury and the docosahexaenoic acid contained within fish will help to refine recommendations to optimize outcomes for mothers and children. Additional recent studies have supported the safety of vaccines containing thimerosal and of dental amalgam for repair of dental caries in children. SUMMARY: Exposure to mercury may harm child development. Interventions intended to reduce exposure to low levels of mercury in early life must, however, be carefully evaluated in consideration of the potential attendant harm from resultant behavior changes, such as reduced docosahexaenoic acid exposure from lower seafood intake, reduced uptake of childhood vaccinations and suboptimal dental care.

Mercury exposure and public health.

Mercury is a metal that is a liquid at room temperature. Mercury has a long and interesting history deriving from its use in medicine and industry, with the resultant toxicity produced. In high enough doses, all forms of mercury can produce toxicity. The most devastating tragedies related to mercury toxicity in recent history include Minamata Bay and Niagata, Japan in the 1950s, and Iraq in the 1970s. More recent mercury toxicity issues include the extreme toxicity of the dimethylmercury compound noted in 1998, the possible toxicity related to dental amalgams, and the disproved relationship between vaccines and autism related to the presence of the mercury-containing preservative, thimerosal.

A case series of children with apparent mercury toxic encephalopathies manifesting with clinical symptoms of regressive autistic disorders.

Impairments in social relatedness and communication, repetitive behaviors, and stereotypic abnormal movement patterns characterize autism spectrum disorders (ASDs). It is clear that while genetic factors are important to the pathogenesis of ASDs, mercury exposure can induce immune, sensory, neurological, motor, and behavioral dysfunctions similar to traits defining or associated with ASDs. The Institutional Review Board of the Institute for Chronic Illnesses (Office for Human Research Protections, U.S. Department of Health and Human Services, IRB number IRB00005375) approved the present study. A case series of nine patients who presented to the Genetic Centers of America for a genetic/developmental evaluation are discussed. Eight of nine patients (one patient was found to have an ASD due to Rett's syndrome) (a) had regressive ASDs; (b) had elevated levels of androgens; (c) excreted significant amounts of mercury post chelation challenge; (d) had biochemical evidence of decreased function in their glutathione pathways; (e) had no known significant mercury exposure except from Thimerosal-containing vaccines/Rho(D)-immune globulin preparations; and (f) had alternate causes for their regressive ASDs ruled out. There was a significant dose-response relationship between the severity of the regressive ASDs observed and the total mercury dose children received from Thimerosal-containing vaccines/Rho (D)-immune globulin preparations. Based upon differential diagnoses, 8 of 9 patients examined were exposed to significant mercury from Thimerosal-containing biologic/vaccine preparations during their fetal/infant developmental periods, and subsequently, between 12 and 24 mo of age, these previously normally developing children suffered mercury toxic encephalopathies that manifested with clinical symptoms consistent with regressive ASDs. Evidence for mercury intoxication should be considered in the differential diagnosis as contributing to some regressive ASDs.

Ethyl mercury poisoning during a protein A immunoadsorption treatment.

We describe the case of a 38-year-old woman with Guillain-Barré syndrome who was accidentally intoxicated with thimerosal, a column disinfectant containing ethyl mercury, during a protein A immunoadsorption treatment. The 1-time overdose caused by an equipment handling error led to a maximum blood serum mercury level of 2,250 microg/L, thus exceeding the normal blood reference range by a factor of approximately 200. Although the patient did not show short-or long-term clinical signs of mercury intoxication, she was treated with chelation therapy, and we replaced thimerosal with a commercially available mercury-free disinfectant, suggesting that thimerosal is no longer indicated for preservation of protein A columns.

Thimerosal and autism? A plausible hypothesis that should not be dismissed.

The autism-mercury hypothesis first described by Bernard et al. has generated much interest and controversy. The Institute of Medicine (IOM) reviewed the connection between mercury-containing vaccines and neurodevelopmental disorders, including autism. They concluded that the hypothesis was biologically plausible but that there was insufficient evidence to accept or reject a causal connection and recommended a comprehensive research program. Without citing new experimental evidence, a number of observers have offered opinions on the subject, some of which reject the IOM's conclusions. In a recent review, Nelson and Bauman argue that a link between the preservative thimerosal, the source of the mercury in childhood vaccines, is improbable. In their defense of thimerosal, these authors take a narrow view of the original hypothesis, provide no new evidence, and rely on selective citations and flawed reasoning. We provide evidence here to refute the Nelson and Bauman critique and to defend the autism-mercury hypothesis.

Autism and thimerosal-containing vaccines: lack of consistent evidence for an association.

BACKGROUND: In 1999, concerns were raised that vaccines containing the preservative Thimerosal might increase the risk of autism and/or other neurodevelopmental disorders. METHODS: Between the mid-1980s through the late-1990s, we compared the prevalence/incidence of autism in California, Sweden, and Denmark with average exposures to Thimerosal-containing vaccines. Graphic ecologic analyses were used to examine population-based data from the United States (national immunization coverage surveys and counts of children diagnosed with autism-like disorders seeking special education services in California); Sweden (national inpatient data on autism cases, national vaccination coverage levels, and information on use of all vaccines and vaccine-specific amounts of Thimerosal); and Denmark (national registry of inpatient/outpatient-diagnosed autism cases, national vaccination coverage levels, and information on use of all vaccines and vaccine-specific amounts of Thimerosal). RESULTS: In all three countries, the incidence and prevalence of autism-like disorders began to rise in the 1985-1989 period, and the rate of increase accelerated in the early 1990s. However, in contrast to the situation in the United States, where the average Thimerosal dose from vaccines increased throughout the 1990s, Thimerosal exposures from vaccines in both Sweden and Denmark-already low throughout the 1970s and 1980s-began to decrease in the late 1980s and were eliminated in the early 1990s. CONCLUSIONS: The body of existing data, including the ecologic data presented herein, is not consistent with the hypothesis that increased exposure to Thimerosal-containing vaccines is responsible for the apparent increase in the rates of autism in young children being observed worldwide.

Clinical course of severe poisoning with thiomersal.

CASE REPORT: A 44-year-old man ingested 83 mg/kg Thiomersal. He developed gastritis, renal tubular failure, dermatitis, gingivitis, delirium, coma, polyneuropathy and respiratory failure. Treatment was symptomatic plus gastric lavage and the oral chelating agents dimercaptopropane sulfonate and dimercaptosuccinic acid. The patient recovered completely. Maximum mercury concentrations were blood 14 mg/L, serum 1.7 mg/L, urine 10.7 mg/L, and cerebrospinal fluid 0.025 mg/L. Mercury concentration in blood declined with two velocities: first with half-time 2.2 days, then with half-time 40.5 days. The decline of mercury concentration in blood, urinary mercury excretion, and renal mercury clearance were not substantially influenced by chelation therapy.

Intoxicaçäo letal por mercúrio através da ingestäo de merthiolate / Lethal mercury poisoning due to ingestion of merthiolate

Descrevemos uma intoxicaçäo grave por ingestäo crônica de composto mercurial orgânico usado como antisséptico "merthiolate". O paciente desenvolveu quadro neurológico grave e irreversível, apesar do tratamento com penicilamina e resina ter reduzido rapidamente os níveis plasmáticos e a concentraçäo de mercúrio nos cabelos. Apesar da intoxicaçäo por ingestäo de antissépticos mercuriais ser raramente descrita, chamamos a atençäo para essa possibilidade frente ao largo uso caseiro desses antissépticos contendo mercúrio e álcool, que podem ser ingeridos por crianças e alcoólatras

[Lethal mercury poisoning due to ingestion of merthiolate]. / Intoxicação letal por mercúrio através da ingestão de "merthiolate".

A case of mercurial poisoning caused by ingestion of an organic mercurial compound, thimerosal, found in local antiseptic solutions. The clinical picture consisted of grave neurological symptoms which were not reversed by penicillamine and resin administration despite rapid plasma level reduction of mercury. We call attention to this case because of the widespread availability of antiseptic solutions containing mercurial compounds and alcohol.

Organ mercury levels in infants with omphaloceles treated with organic mercurial antiseptic.

Samples of fresh and fixed tissues from infants with exomphalos treated by thiomersal application were analysed for mercury content. The results showed that thiomersal can induce blood and organ levels of organic mercury which are well in excess of the minimum toxic level in adults and fetuses. The analysis of fresh and fixed tissues must be carefully controlled against normal tissues in order to interpret mercury levels accurately.