Perinatal multiple exposure to neurotoxic (lead, methylmercury, ethylmercury, and aluminum) substances and neurodevelopment at six and 24 months of age

We studied neurodevelopment in infants from two communities. Children living in the vicinity of tin-ore kilns and smelters - TOKS; n = 51) were compared to children from a fishing village (Itapuã; n = 45). Mean hair-Hg (HHg) concentrations were significantly higher in Itapuã children which received significantly (p = 0.0000001) less mean ethylmercury (88.6 μg) from Thimerosal-containing vaccines (TCV) than the TOKS children (120 μg). Breast-milk Pb concentrations were significantly higher in the TOKS mothers (p = 0.000017; 10.04 vs. 3.9 μg L(-1)). Bayley mental development index (MDI) and psychomotor development index (PDI) were statistically significant (respectively p < 0.0000001, p = 0.000007) lower for the TOKS children only at 24 months of age. Multivariate regression analysis showed that MDI was negatively affected by breast-milk Pb and by HHg. PDI was positively affected by breastfeeding and negatively affected by ethylmercury. Milestone achievements were negatively affected by breast-milk Pb (age of walking) and by HHg (age of talking).

A review of Thimerosal (Merthiolate) and its ethylmercury breakdown product: specific historical considerations regarding safety and effectiveness

Thimerosal (Merthiolate) is an ethylmercury-containing pharmaceutical compound that is 49.55% mercury and that was developed in 1927. Thimerosal has been marketed as an antimicrobial agent in a range of products, including topical antiseptic solutions and antiseptic ointments for treating cuts, nasal sprays, eye solutions, vaginal spermicides, diaper rash treatments, and perhaps most importantly as a preservative in vaccines and other injectable biological products, including Rho(D)-immune globulin preparations, despite evidence, dating to the early 1930s, indicating Thimerosal to be potentially hazardous to humans and ineffective as an antimicrobial agent. Despite this, Thimerosal was not scrutinized as part of U.S. pharmaceutical products until the 1980s, when the U.S. Food and Drug Administration finally recognized its demonstrated ineffectiveness and toxicity in topical pharmaceutical products, and began to eliminate it from these. Ironically, while Thimerosal was being eliminated from topicals, it was becoming more and more ubiquitous in the recommended immunization schedule for infants and pregnant women. Furthermore, Thimerosal continues to be administered, as part of mandated immunizations and other pharmaceutical products, in the United States and globally. The ubiquitous and largely unchecked place of Thimerosal in pharmaceuticals, therefore, represents a medical crisis.

Hair mercury in breast-fed infants exposed to thimerosal-preserved vaccines

Because of uncertainties associated with a possible rise in neuro-developmental deficits among vaccinated children, thimerosal-preserved vaccines have not been used since 2004 in the USA (with the exception of thimerosal-containing influenza vaccines which are routinely recommended for administration to pregnant women and children), and the EU but are widely produced and used in other countries. We investigated the impact of thimerosal on the total Hg in hair of 82 breast-fed infants during the first 6 months of life. The infants received three doses of the hepatitis-B vaccine (at birth, 1 and 6 months) and three DTP (diphtheria, tetanus, and pertussis) doses at 2, 4 and 6 months, according to the immunization schedule recommended by the Ministry of Health of Brazil. The thimerosal in vaccines provided an ethylmercury (EtHg) exposure of 25 microgHg at birth, 30, 60 and 120 days, and 50 microgHg at 180 days. The exposure to vaccine-EtHg represents 80% of that expected from total breast milk-Hg in the first month but only 40% of the expected exposure integrated in the 6 months of breastfeeding. However, the Hg exposure corrected for body weight at the day of immunization was much higher from thimerosal- EtHg (5.7 to 11.3 microgHg/kg b.w.) than from breastfeeding (0.266 microgHg/kg b.w.). While mothers showed a relative decrease (-57%) in total hair-Hg during the 6 months lactation there was substantial increase in the infant's hair-Hg (446%). We speculate that dose and parenteral mode of thimerosal-EtHg exposure modulated the relative increase in hair-Hg of breast-fed infants at 6 months of age.

Degradation of methyl and ethyl mercury into inorganic mercury by oxygen free radical-producing systems: involvement of hydroxyl radical

Degradation of methyl mercury (MeHg) and ethyl Hg (EtHg) with oxygen free radicals was studied in vitro by using three well-known hydroxyl radical (.OH)-producing systems, namely Cu2(+)-ascorbate, xanthine oxidase (XOD)-hypoxanthine (HPX)-Fe(III)EDTA and hydrogen peroxide (H2O2)-ultraviolet light B. For this purpose, the direct determination method for inorganic Hg was employed. MeHg and EtHg were readily degraded by these three systems, though the amounts of inorganic Hg generated from MeHg were one half to one third those from EtHg. Degradation activity of XOD-HPX-Fe(III)EDTA system was inhibited by superoxide dismutase, catalase and the .OH scavengers and stimulated by H2O2. Deletion of the .OH formation promoter Fe(III)EDTA from XOD-HPX-Fe(III)EDTA system resulted in the decreased degradation of MeHg and EtHg, which was enhanced by further addition of the iron chelator diethylenetriamine pentaacetic acid. In all these cases, a good correlation was observed between alkyl Hg degradation and deoxyribose oxidation determining .OH. By contrast, their degradation appeared to be unrelated to either superoxide anion (O2-) production or H2O2 production alone. We further confirmed that H2O2 (below 2 mM) itself did not cause significant degradation of MeHg and EtHg. These results suggested that .OH, but not O2- and H2O2, might be the oxygen free radical mainly responsible for the degradation of MeHg and EtHg.

The comparative toxicology of ethyl- and methylmercury

Neurotoxicity and renotoxicity were compared in rats given by gastric gavage five daily doses of 8.0 mg Hg/kg methyl- or ethylmercuric chloride or 9.6 mg Hg/kg ethylmercuric chloride. Three or 10 days after the last treatment day rats treated with either 8.0 or 9.6 mg Hg/kg ethylmercury had higher total or organic mercury concentrations in blood and lower concentrations in kidneys and brain than methylmercury-treated rats. In each of these tissues the inorganic mercury concentration was higher after ethyl- than after methylmercury. Weight loss relative to the expected body weight and renal damage was higher in ethylmercury-treated rats than in rats given equimolar doses of methylmercury. These effects became more severe when the dose of ethylmercury was increased by 20%. Thus in renotoxicity the renal concentration of inorganic mercury seems to be more important than the concentration of organic or total mercury. In methylmercury-treated rats damage and inorganic mercury deposits were restricted to the P2 region of the proximal tubules, while in ethylmercury-treated rats the distribution of mercury and damage was more widespread. There was little difference in the neurotoxicities of methylmercury and ethylmercury when effects on the dorsal root ganglia or coordination disorders were compared. Based on both criteria, an equimolar dose of ethylmercury was less neurotoxic than methylmercury, but a 20% increase in the dose of ethylmercury was enough to raise the sum of coordination disorder scores slightly and ganglion damage significantly above those in methylmercury-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Octanol/water partition coefficients as a model system for assessing antidotes for methylmercury(II) poisoning, and for studying mercurials with medicinal applications

1-Octanol/water partition coefficients, [HgII]octanol/[HgII]water, provide a simple but limited model system for aspects of the biological behavior of methylmercury(II) and commonly used organomercury(II) medicinal compounds. In an octanol/water system some widely studied antidotes for mercury poisoning at least partly displace the biological thiols L-cysteine and glutathione from binding to MeHgII at pH 6.9. Addition of the antidote meso-dimercaptosuccinic acid to MeHgII in the presence of glutathione results in formation of metallic mercury. For RHgII derivatives of L-cysteine and glutathione, octanol/water partition coefficients follow the order Ph greater than Et greater than Me. An exceptionally high value for diphenylmercury, compared with PhHgII derivatives of L-cysteine and glutathione, is consistent with reported results of the distribution of mercury compounds in rats. Ethylmercury(II) is partly displaced from thimerosal by L-cysteine and glutathione in the octanol/water system, indicating that the active form of thimerosal in vivo may involve binding of EtHgII to biological ligands.

Interaction of alkylmercuric compounds with sodium selenite. I. Metabolism of ethylmercuric chloride administered alone and in combination with sodium selenite in rats

The effect of sodium selenite administered intragastrically in repeated doses to rats receiving ethylmercuric chloride po in various repeated doses (0.25 or 2.5 mg Hg/kg) on the excretion, whole-body retention, and organ distribution of mercury was studied. Selenium was found to affect the distribution of ethylmercury among tissues and subcellular fractions of the kidneys and liver as well as its binding to proteins of soluble fractions in these organs. Similarities and differences between the effect of interaction of sodium selenite with ethylmercuric chloride and methylmercury as well as inorganic mercury are also discussed.

Toxicokinetics

The absorption, distribution and elimination of toxic compounds can be described by means of kinetic parameters such as used in pharmacology. Administration of toxic doses may lead to changes in some of the parameters. The toxic effect may further influence the known parameters of some test substances. Toxicokinetic parameters will be described using examples from two groups of compounds 1) naturally occurring toxic compounds and 2) synthetic compounds. Changes in elimination parameters caused by toxic substances will be demonstrated a.o. the effect of long term intake of ochratoxin A and methoxyethyl mercury on the kidney function in swine. In both examples are demonstrated a pronounced reduction in the clearances of inulin and para-amino-hippuric acid. Furthermore, an elucidation of concentration dependent change in enzyme activity and changes in metabolism of pesticides will be given. As examples alkylphosphates and dinitrophenols in domestic animals will be used.

[The tissue distribution and the effect of mercury on the hepatic cholesterol biosynthesis following the oral administration of methyl- and ethylmercurial compounds (author's transl)]

Hepatic cholesterol biosynthesis from acetate-1-14C, hepatic cholesterol level and accumulation of mercury into various tissues were examined following oral administration of methyl- or ethyl-mercury to mice (or rat) at next dosage levels, 80 ppm for 10-19 days, 50 ppm for 30 days and 100 ppm for 15 days. The results obtained were as follows. 1. Hepatic cholesterol biosynthesis was elevated at a dose of 80 ppm and decreased at a dose of 50 and 100 ppm. The change of hepatic cholesterol biosynthesis showed the negative correlation with that of cholesterol level. 2. In comparison between methyl-and ethylmercury, the latter accumulated more than the former in liver and spleen, while the former accumulated more than the latter in kidney, cerebum and skeletal muscle. The administration of ethylmercury caused more decrease of body weight, increase of hepatic cholesterol biosynthesis and hepatic cholesterol level than the administration of methylmercury.

Tissue concentrations of mercury after chronic dosing of squirrel monkeys with thiomersal

Squirrel monkeys were dosed intranasally with saline or thiomersal (sodium ethylmercurithiosalicylate, 0.002 percent w/v) daily for six months. The total amounts of thiomersal given during the six months period were 418 mug (low dose group) and 2280 mug (high dose group). This was equivalent to 207 and 1125 mug mercury. The dose differential was achieved by more frequent administration to the high dose group. Mercury concentrations were significantly raised over control values in brain (high dose group only), liver, muscle and kidney, but not in blood. Concentrations were highest in the kidney, moderate in liver and lowest in brain and muscle. Much of the mercury was present in the inorganic form (37-91 percent). No evidence of toxicity due to thiomersal was seen in any animal. Nevertheless accumulation of mercury from chronic use of thiomersal-preserved medicines is viewed as a potential health hazard for man.

Teratogenicities of ophthalmic drugs. II. Teratogenicities and tissue accumulation of thimerosal

Under the conditions of this study, systemically or topically applied thimerosal was found to have no teratogenic effect even when given in concentrations approaching the 50% lethal dose of these compounds. A comparison of topical and subcutaneous administration of thimerosal to rabbits shows that a substantial concentration of mercury was present in blood and tissues of the treated animals and their offspring. Thimerosal was found to cross the blood-brain and placenta barriers.

Chemical assay of merthiolate after incubation with serum from subjects with positive patch tests to merthiolate

A method for quantitative and qualitative determination of merthiolate (thimerosal) is presented. Merthiolate is chemically assayed by spectrophotometry and thin-layer chromatography following ether extraction of acidified solutions. Serum from subjects with positive patch tests to merthiolate does not affect merthiolate differently than serum from control subjects.