Developmental changes in the biliary excretion of methylmercury and glutathione

The long half-time for methylmercury in the neonatal rats is explained by the neonatal liver's inability to secrete the toxin into bile, which in adults is the main route of elimination. The ability to secrete mercury into bile develops between 2 and 4 weeks of age and is correlated with the increasing ability of the developing liver to secrete glutathione into bile.

Dose-response relationship for human fetal exposure to methylmercury

Eighty-four Iraqi mothers and their infants had been exposed to methylmercury during pregnancy. The methylmercury had been ingested as a fungicide. Peak maternal hair mercury concentrations were related to the frequency of maternal symptoms during pregnancy and to neurological effects in the infants. These include various degrees of psychomotor retardation. Severe neurological deficits were observed in five children whose maternal peak hair mercury concentrations were 165 to 320 ppm. Minimal symptoms were reported for mothers and children when peak maternal hair levels were below 68 ppm. Minimal clinical neurological signs occurred in children when peak maternal hair mercury concentrations were at an undetermined point between 68 and 180 ppm. Greater fetal risk appears to be associated with exposure during the second trimester. This exposure to methylmercury was acute and the results may not be extrapolated to a constant level of exposure throughout pregnancy. The effects of fetal exposure to methylmercury in marine fish may differ.

Ethanol reveals novel mercury detoxification step in tissues

Volatile mercury was produced de novo by mouse tissue homogenates that contained mercuric ions. Ethanol stimulated the release of tissue mercury into the vapor phase, and the mechanism appears to be an inhibition of reoxidation of volatile mercury. Components responsible for mercury volatilization are heat-labile. The highest volatilizing activity in the liver is associated with the soluble fraction obtained after centrifugation at 105,000g.

Comparative study of the sensitivity of male and female rats to methylmercury

Male and female rats were dosed daily by gastric gavage four or five times with 8.0 mg/kg Hg as methylmercury. Treatment lowered the body weight in relation to the body weight of untreated rats to the same extent in male and female rats but when body weight was related to the initial body weight, the effect of methylmercury was more pronounced in females than in males. The important of differences in growth or loss of body weight is that in spite of the similar whole body clearance mercury concentrations were higher in females than in males. After identical doses the brains of females always contained more mercury than those of males and in both sexes the brain concentration of mercury showed a disproportionate elevation when the number of doses was increased from four to five. However, weight change alone does not explain the sex related difference in the brain concentration of mercury as this was evident even 72 h after a single dose. In agreement with the brain concentration of mercury, female rats developed more intensive co-ordination disorders and after five doses they had more extensive damage in the granular layer of the cerebellum than males.

Methylmercury poisoning in the Iraqi suckling infant: a longitudinal study over five years

In a five-year longitudinal study of mothers and infants exposed to methylmercury during the Iraq epidemic of 1972, the frequencies of signs and symptoms exhibited by the mothers were typical of methylmercury poisoning. When blood concentrations of mercury are corrected to 1 March 1972, mothers with the most severe signs and symptoms had an average blood mercury concentration significantly higher (p less than 0.01) than either the milder or asymptomatic groups. Analytical data indicate that the predominant route of exposure for the infant was through breast milk in which approximately 60% of total mercury was determined, by cold vapor atomic absorption, to be organic mercury. Abnormal neurological signs in these infants became more obvious with time: hyperreflexia was observed in 8 of 22 infants at first examination, and in 17 of 22 at second examination. Delayed motor development became evident at the second and third examinations. The frequency of pathological reflexes and delayed motor developmental milestones was so high as to be considered significant even in the absence of a controlled study. There was no increase in mortality as compared to a control group.

Tests of efficacy of antidotes for removal of methylmercury in human poisoning during the Iraq outbreak

Three complexing agents and a thiolated resin were tested for their ability to reduce the T 1/2 of methylmercury in blood during an outbreak of human poisoning. The slope of the line relating the natural logarithm of the blood concentration to time during treatment was calculated by a parametric (linear regression) and a nonparametric (two-point) method. The mean slope for each treatment group was calculated and the T 1/2 was calculated from the mean slope. Both the linear regression and two-point methods yield similar mean values. The "two-point" T 1/2 will be quoted here. The mean T 1/2 in six patients receiving no specific treatment was 65 days and in 10 patients receiving placebo was 61 days, and these values did not differ from those reported in the literature. All four treatments significantly reduced the mean T 1/2 values below the mean for the combined placebo and no treatment groups. Sodium 2,3-dimercaptopropane-1-sulfonate was the most effective agent, reducing the mean T 1/2 in 10 patients to 10 days. The thiolated resin given to eight patients produced a mean T 1/2 of 20 days. The penicillamines also produced a significant reduction in T 1/2 values; the mean T 1/2 for D-penicillamine in 12 patients was 26 days and N-acetyl-DL-penicillamine in 17 patients yielded a mean T 1/2 of 24 days. This is the first report of the effects of sodium 2,3-dimercaptopropane-1-sulfonate and resin in human subjects exposed to methylmercury. No adverse effects were observed in any of the treatment groups. A clinical trial was not possible but it is concluded that agents that reduce blood levels and accelerate excretion are probably clinically useful if given before irreversible damage has occurred.

Selective determination of elemental mercury in blood and urine exposed to mercury vapor in vitro

A method is described to ensure quantitative measurement of dissolved mercury vapor (Hg0) in blood and urine. Room air passed through samples of blood and urine carries with it all the dissolved Hg0 but leaves behind all the ionic mercury (Hg++). Oxidation of Hg0 to Hg++ in blood samples is completely inhibited by addition of ethanol (0.5% v/v). To minimize error due to evaporation of Hg0, it is suggested that samples should be stored at 0 degree C and Hg0 should be determined within 60 min of collection of blood samples and within 10 min of urine samples.

Interaction of ethanol and inorganic mercury: generation of mercury vapor in vivo

Mercury exhalation increased after parenteral administration of ethanol to mice injected with a single dose of mercuric chloride (0.5 mg of Hg/Kg). Increased output of the metal was ethanol dose-dependent (blood EC50 = 215 mg/dl) and maximal rates (0.2% of the body burden per 30 min) were about 10-fold higher than controls. The chemical form of exhaled mercury was determined to be the elemental vapor (Hg degrees) indicating an ethanol-sensitive reduction pathway for ionic mercury (Hg++) in the body. Ethanol appeared to selectively affect mercury exhalation inasmuch as no large differences in whole-body mercury retention times or in the distribution of the metal in organs could be detected even after repeated daily doses of ethanol. The results show that at least a portion of the ionic mercury in the body can be mobilized via reduction and Hg++ in tissues is more labile than generally recognized.

Methylmercury in populations eating large quantities of marine fish

A Peruvian population was identified that was chronically exposed to methylmercury from the long-term consumption of ocean fish. The weekly fish intake averaged 10.1 kg per average family of 6.2 persons. Blood methylmercury concentrations ranged from 11 to 275 ng/ml, with a mean of 82 ng/ml. Paresthesias were reported by 29.5% of the population. In contrast, a nearby control population had a mean weekly fish consumption of 1.9 kg per average family of 6.4 persons. Their blood methylmercury levels were 3.3-25.1 ng/ml, with a mean of 9.9 ng/ml. Paresthesias were reported by 49.5% of this control group. No individual was identified with symptoms or signs that could be attributed to methylmercury intoxication.

The effect of ethanol on the fate of mercury vapor inhaled by man

Three human subjects ingested 1065 ml of beer equivalent to 65 ml of ethanol 30 min before exposure (12-20 min) to mercury vapor. An additional two subjects were exposed to mercury vapor without ethanol pretreatment. The results show that alcohol brings about: 1) reduced mercury retention, 2) an increase in the rapid phase of vapor loss by expiration, 3) an increased mercury storage in the liver, 4) a marked reduction in mercury uptake by the red blood cells and 5) the abolition of vapor exposure experiments were performed by using control and ethanol-pretreated mice and rats. Sacrifice occurred at 1 hr and 3 days. The results support and extend the human data.

The effect of lactation on methylmercury intoxication

Four days after parturition 17 weeks old rats of Porton Wistar strain were given 8 mg/kg mercury as methylmercury chloride for 5 days. Virgin females or mothers separated from their offspring immediately after delivery received the same treatment and served as controls. Compared with these controls, lactation delayed the onset of weight loss, shortened the time between the end of treatment and the onset of weight gain, accelerated the elimination of mercury from the whole body and prevented the development of severe co-ordination disorders. However, lactation had no detectable effect on the elimination of mercury from the brain. Moreover control and lactating females had the same degree of histological abnormalities both in the granular layer of the cerebellum and in the dorsal root ganglion cells.

Organic mercury exposure from fungicide-contaminated eggs

During a period of 50 to 55 days from early January to March 2, 1979, 14 members of an extended family in Yakima, Washington, ate eggs contaminated with organic mercury. Seed grain which had been treated with a mercurial fungicide and fed to chickens in a home flock was the source of exposure. Blood mercury levels in family members ranged from 0.9 to 20.2 ppb and correlated positively with average daily egg consumption (r = 0.92). There were no symptoms or physical signs of organic mercury intoxication. Prompt confiscation of the contaminated grain, eggs, and chicken flock terminated the exposure and may have prevented the development of serious illness.

Interrelationships of blood and hair mercury concentrations in a North American population exposed to methylmercury

Samples of blood and head hair were analyzed for organic and inorganic mercury from a population which consumed large amounts of fish contaminated with methylmercury. Mercury levels in newly formed hair were found to reflect those in blood with the concentration in hair being approximately 300 times that in blood. Organic and inorganic mercury levels were linearly related in both hair and blood samples, with a mean inorganic/organic ration of 0.05 in blood and 0.21 in hair, but individual differences were found to exist. In addition, the total mercury concentration and inorganic/organic ratio in hair remained constant with time. Thus, longitudinal analysis of hair samples can provide a simple and accurate method of monitoring continuing exposure and an estimation of peak blood levels months to years after exposure.

Fetal methylmercury poisoning: clinical and toxicological data on 29 cases

This report describes psychomotor retardation in infants caused by prenatal exposure to methylmercury. A study of 29 mother-infant pairs established a relationship between maximum maternal hair mercury concentration during pregnancy and the frequency of neurological effects in the infants. The latter included delayed achievement of developmental milestones with or without neurological signs. The infants were 4 1/2 to 5 years of age on last examination. Ten infants of mothers who had maximum hair concentrations in the range of 99 to 384 pars per million (ppm) had a significantly higher frequency of abnormal findings than those in two groups having lower maternal hair mercury concentrations (12 to 85 and 0 to 11 ppm). The group sizes were too small to allow identification of a specific "threshold" maternal hair concentration above which such effects can be expected. Transient paresthesias during pregnancy occurred in 80% of the mothers in the higher concentration group (99 to 384 ppm) as compared with 30% and 22% in the lower groups. Neurological abnormalities were found in some children whose mothers had been asymptomatic during pregnancy.

Comparative study of the sensitivity of virgin and pregnant rats to methylmercury

Pregnant and virgin female rats were dosed by gastric lavage 10 times or 5 times with 5 mg/kg mercury as methylmercury. Treatment of pregnant animals started on day 3 of gestation and ended on day 14 of gestation with two days break between the 5th and the 6th doses. In Group B, treatment lasted from day 10 to day 14 of gestation. Pregnant and virgin rats responded identically to methylmercury in terms of body weight changes, coordination disorders, and cerebellar histological changes. Furthermore, the brain, liver and kidney concentrations and the rates of methylmercury elimination in the post-treatment period were identical. Thus the results indicate no difference in sensitivity of pregnant versus non-pregnant animals.

The relationship between blood levels and dose of methylmercury in man

The kinetics of blood deposition and clearance of methylmercury were measured in volunteers given a single meal of fish containing 18 to 22 microgram mercury/kg body weight. Peak blood concentrations were achieved within 4 to 14 hr. Disappearance from blood was biphasic, with average half-times of 7.6 hr and 52 days, respectively. The fraction of the dose deposited in the blood volume after completion of tissue distribution was 5.9%. Blood concentrations of total mercury reached as high as 60 ng mercury/ml, whereas inorganic mercury did not exceed 2 ng mercury/ml. The average red blood cell to plasma concentration ratio was 21 and the hair to blood ratio was 292. The kinetic parameters relating to blood deposition and clearance were used to calculate the expected relationship between average long-term daily intake of methylmercury and steady state blood concentration.

Methylmercury poisoning in Canadian Indians--the elusive diagnosis

A World Health Organization Expert Committee has concluded that symptoms of methylmercury poisoning may appear at blood concentrations of 200-500 ng Hg/ml. Blood levels in this range have been found in several Indian and Inuit communities in Canada. The syndrome of severe methylmercury poisoning (Hunter-Russell syndrome) is well described. However, diagnosis of less severe cases is difficult. This paper review the present situation in Canada. The problems of diagnosis currently being encountered are discussed and are illustrated by the case of an individual who had one of the highest blood concentrations (551 ng Hg/ml) ever described in fish-eating populations outside of the outbreaks in Minamata and Niigata in Japan. Although mercury concentrations in brain were estimated to have been in the "symptomatic" range at least once in the two years prior to his death, neurohistological examination was normal. Detailed examination by two teams of neurologists revealed effects that may be associated with methylmercury poisoning but a definitive diagnosis remained elusive.

The effects of bromosulphophthalein, indocyanine green and bilirubin on the biliary excretion of methylmercury

The effects of three ligands for ligandin on the biliary excretion of methylmercury were investigated in male rats injected intravenously with 1.0 mg/kg Hg as Me203 HgCl. Bromosulphophthalein and indocyanine green inhibited the biliary excretion of methylmercury, while bilirubin had no such effect. None of the compounds tested which inhibited the biliary excretion of methylmercury decreased bile flow or changed the hepatic concentration of mercury of non-protein thiols. The possibility of the involvement of ligandin in the biliary excretion of methylmercury is discussed.

Prenatal methylmercury poisoning. Clinical observations over five years

Thirty-two infants prenatally exposed to methylmercury and their mothers were examined over a five-year period after the Iraqi methylmercury epidemic. Severity of poisoning in mothers was related to the peak mercury concentration in their hair and in the infants to the maximum concentration in maternal hair during pregnancy. In nine cases of cerebral palsy, methylmercury exposure occurred only during the last trimester. All infants except three (two were orphaned soon after birth and one was bottle-fed) were exposed postnatally via suckling. Whereas the mother's symptoms usually improved, the damage to the fetal nervous system appears to be permanent. Milder cases previously not identified in other studies are reported. The syndrome consists of varying degrees of developmental retardation in addition to exaggerated tendon reflexes and the pathologic extensor plantar reflex (minimal brain damage syndrome).

Ethanol-increased exhalation of mercury in mice

CBA/J mice injected three days beforehand with 203HgCl2 were given ethanol or water by gavage and placed in a chamber designed to collect exhaled mercury. Ethanol treatment led to an eight-fold increase of counts accumulated on a filter over a four-hour period, compared with water-treated mice. The mercury-collection apparatus tested for extracorporeal contribution of volatilised mercury indicated that the counts originated from the air exhaled by the mice.