Absorption, distribution and excretion of phenylmercuric acetate

Toxic and essential elements changed in black-legged kittiwakes (Rissa tridactyla) during their stay in an Arctic breeding area

Seasonal fluctuations in mercury (Hg), cadmium (Cd), zinc (Zn), copper (Cu) and selenium (Se) concentrations were studied in black-legged kittiwakes (Rissa tridactyla) from Kongsfjorden, Svalbard (79°57'N, 12°12'E). Element concentrations were determined in muscle and liver tissue in kittiwakes collected in May, July and October 2007. Stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N) were analysed in muscle tissue to calculate trophic position (TP) and examine the possible influence of carbon source on element accumulation. Metallothionein (MT) concentrations in liver, as well as Hg and Cd concentration in size-fractionated liver supernatant were determined to evaluate the association between elements and MT. Mercury concentrations declined from May through July to October in both tissues, while concentrations of Cd were similar in May and July and lower in October. A decline in TP between May and July, indicating a shift from fish-based diet towards an invertebrate-based diet explains the declining Hg concentration. The low Hg and Cd concentrations in October may be a result of an increased elimination, probably related to moulting. Selenium decreased in the same manner as Hg in liver and muscle, possibly related to the formation of Se-Hg complexes. Zinc and Cu did not fluctuate in muscle tissue, whereas hepatic Zn concentrations where highest in May. Hepatic Zn concentrations were higher in females compared to males in May, possibly related to egg production. Hepatic MT concentrations were lower in October compared to July, following the same trend as Hg and Cd. Cadmium was predominantly bound to the MT fraction of proteins in liver tissue, whereas Hg was associated with the larger proteins, indicating that MT was not sequestering Hg in the kittiwakes.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

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.

The role of eggs in mercury excretion by Quail Coturnix coturnix and the implications for monitoring mercury pollution by analysis of feathers

: This paper describes differences in the excretion of methyl mercury between male and female Quail Coturnix coturnix after a single dose. Since feathers are often used to monitor mercury pollution it is important to take into account biases in feather mercury levels that may arise as a result of mercury loss through egg-laying. Evidence is presented to support the use of bird eggs to sample for environmental mercury contamination. Birds were monitored up to twelve weeks after administration. Mercury concentrations in the kidney exceeded those in the liver which exceeded those in the pectoral muscle. Significant differences in mercury levels between male and female birds were found up to eight weeks after administration. Mercury was initially distributed through most of the internal tissues and was lost relatively slowly in a negative exponential manner. Mercury loss through excretion differed between the sexes for the first eight weeks after mercury administration. Initial mercury concentration in eggs was 3.5 μg g(-1) but no mercury was detected in eggs five weeks after the dose was administered. At this point over 40% of the females' intake had been lost into the eggs.

The chronic toxicity of aluminium, cadmium, mercury, and lead in birds: a review

The toxicity of chronic dietary metal exposure in birds is reviewed. It is concluded that significant physiological and biochemical responses to such exposure conditions occur at dietary metal concentrations insufficient to cause signs of overt toxicity. Particularly important are reproductive effects which include decreased egg production, decreased hatchability, and increased hatchling mortality. Young, growing birds are typically more sensitive to the toxic effects of chronic metal exposure than adults, and altricial species are often more sensitive than precocial species. Factors which modify the absorption and toxicity of heavy metals, such as Se for the case of Hg, and Ca for the case of Pb and Cd, are discussed. Monitoring strategies for assessing environmental metal exposure in birds are evaluated.

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.

Preliminary study of the effects of feeding ethyl mercury chloride on four breeds of chickens

Different breeds of chickens namely Single Comb White Leghorn (S.C.W.L.), New Hamsphire (N.H.), Iraqi (IRQ) and a cross (CRS.) S.C.W.L. X N.H. X IRQ. were housed in small pens (20 females and 2 males each) and given, in the diet, 40% wheat treatmed with ethyl mercury chloride, for 88 days. Throughout the whole experiment all birds remained active and showed no symptoms of toxicity. The Iraqi breed was significantly higher than the other breeds with respect to egg production. The results also indicated that mercury in egg white is almost three times as much as that in the yolk, although there was no significant difference between the breeds. The liver and kidney of the four breeds tended to accumulate the highest amount of mercury. Significant differences appeared between sexes according to liver and kidney. White Leghorn and local breeds behaved the same, but N.H. had the highest concentration of mercury in most tissues.

Heavy metal toxicities

Several reviews have been published recently on the toxicity of heavy metals, but few of these have made any reference to the influence of the nutritional state of animals upon their tolerance of heavy metals. Furthermore, the clinical and metabolic changes occurring as a consequence of increased dietary intake of heavy metals are extremely dependent on factors such as the mineral composition of the diet and nature of the protein source. These aspects will be given particular attention in this review.

The metabolism of phenylmercury by the rat

The metabolism of [U-(14)C]phenylmercury acetate was studied in the rat. After a single subcutaneous dose a small proportion is excreted unchanged in urine, and a larger amount in bile with some resorption from the gut. The greater part of the dose is broken down in the tissues to yield inorganic mercury which is excreted mainly in faeces, and conjugates of phenol and quinol are excreted in urine. In experiments in vitro phenylmercury is broken down by liver homogenates to release inorganic mercury and benzene; this reaction is effected by the soluble, but not the microsomal, fraction and does not require NADPH or NADH. No elemental mercury is formed under these conditions. It is probable that this reaction occurs in vivo and the benzene produced is rapidly converted into phenol and quinol by microsomal enzymes.

Six cases of poisoning after a parenteral organic mercurial compound (Merthiolate)

The case histories of four children and two adults who were accidentally given toxic amounts of Merthiolate are recorded. The possible modes of action of Merthiolate in causing symptoms are discussed.

Five out of the six patients died, and necropsy showed extensive renal tubular necrosis in each case, and in two, evidence of diffuse intravascular coagulation.

DISTRIBUTION AND EXCRETION OF METHYL AND PHENYL MERCURY SALTS

The distribution, metabolism, and excretion of phenyl mercury acetate (P.M.A.) and of methyl mercury dicyanidiamide (M.M.D.) has been studied in the rat during the repeated subcutaneous administration of small doses over a period of six weeks, and for several weeks after a single dose. The results indicate that P.M.A. is absorbed unchanged into the circulation from which it is mainly removed by the liver and kidneys where it is metabolized and excreted in the faeces and urine mostly as inorganic mercury. During repeated dosage the rats reached a steady state by the end of the second week when excretion approximately balanced intake. No measurable amount of mercury was found in the central nervous system. After repeated dosage with M.M.D. there is no clear indication of a steady state being reached after six weeks. There is an accumulation of organic mercury in all tissues, particularly in the red cells, and a progressive increase in the brain concentration. M.M.D. is more slowly released from the tissues than P.M.A. and the breakdown to inorganic mercury is low. The control of human exposure to alkyl and aryl mercury salts is considered in the light of these experimental observations. The recommendation that the concentration of alkyl mercury salts in the atmosphere should not exceed 0·01 mg./m.³ seems justifiable, but there appears to be no reason to establish the figure for aryl mercury salts below the 0·1 mg./m.³ recommended for inorganic mercury vapour.