Elemental mercury, toxic effects

The association between metal exposure and renal failure can be approached from two points of view. On the one hand environmental/industrial exposure to heavy metals, more particularly, lead, cadmium and mercury and other inorganic substances such as silicon has been linked to a reduced renal function and/or the development of acute or chronic renal failure [1]. This issue has been dealt with in other chapters of this book. On the other hand patients with chronic renal failure, especially those treated by dialysis are at an increased risk for trace element disturbances (Figure 1). Indeed in these subjects the reduced renal function, the presence of proteinuria, metabolic alterations associated with renal insufficiency, the dialysis treatment, medication etc. all may contribute to either accumulation or deficiency of trace metals. With regard to aluminum intensive research on the element s toxic effects has been performed in the past. Recently, new metal-containing medications have been introduced of which the potential toxic effects should be considered and put in a justified context. 

Elemental Mercury Vapor. Although there may be toxic effects to the respiratory system from the inhalation of mercury vapor, the major toxic effect is to the CNS. This is especially true after chronic exposure. There are a variety of symptoms such as muscle tremors, personality changes, delirium, hallucination, and gingivitis. 

Mercury exists in three forms elemental, inorganic, and organic with different toxic effects. Elemental mercury is absorbed as a vapor and may enter the CNS and cause toxicity there. Inorganic mercury is poorly absorbed, but the cysteine conjugate of mercury is concentrated in the kidney by active transport. The kidney is the main target organ (also gastrointestinal tract if exposure by that route). 

Mercury is unique among the heavy metals in that it can exist in several physical and chemical forms, including elemental mercury, which is a liquid at room temperature. All forms of mercury have toxic effects in a number of organs, especially in the kidneys [188]. 

Bluhm RE, Bobbit RG, Welch LW, Wood AJ. Elemental mercury vapour toxicity, treatment and prognosis after acute, intensive exposure in chloralkali plant workers. Part I History, neuropsychological findings and chelator effects. Human ExpToxicol 1992 11 201-10. 

The mechanisms by which metals induce toxic effects or diseases are not well understood. The most toxic heavy metal ions, cadmium, lead, mercury, are potent enzyme inhibitors because the ions are readily polarizable and bind to donor groups in the enzyme, the binding strengths decreasing in the electron-donor element order S > N > O. In-vivo, phosphate and chloride ions are ubiquitous and these may lead to the formation of insoluble species such as lead hydroxophosphate or only slightly soluble mercuric chloride. 

Weihe P, Grandjean P, Debes F, et al Health implications for Faroe Islanders of heavy metals and PCBs from pilot whales. Sci Total Environ 186 141-148,1996 West I, Lim J Mercury poisoning among workers in California s mercury mills a preliminary report. J Occup Med 10 697-701,1968 White RF, Feldman RG, Travers PH Neurobehavioral effects of toxicity due to metals, solvents and insecticides. Clin Neuropharmacol 13 392-412,1990 Williamson AM, Teo RKC, Sanderson J Occupational mercury exposure and its consequences for behavior. Int Arch Occup Environ Health 50 273-286,1982 Yang Y-J, Huang C-C, Shih T-S, et al Chronic elemental mercury intoxication clinical and field studies in lampsocket manufacturers. Occup Environ Med 51 267-270, 1994... 

Once inhaled, mercury vapour is relatively lipid soluble and crosses the lung alveoli into the bloodstream and red blood cells. Here, it is largely converted to an inorganic divalent (mercuric, Hg ) form by the enzyme catalase which is present in the red blood cells. However, small amounts of non-oxidised elemental mercury continue to persist and readily cross the blood/brain barrier into the central nervous system, where toxic effects are caused. These may reflect the subsequent conversion of mercury into ionised forms which are then trapped in the tissues. The characteristic symptoms are of tremor, especially in activities requiring fine... 

Although Lewis Carroll s famed hatter is the most notorious literary character thought inflicted by mercury poisoning, the phrase mad as a hatter is known to predate Alice in Wonderland by over fifty years. Despite the fact that the toxic effects of mercurials have been known for at least two hundred years, this element still remains a concern in modem society. Chief among the culprits... 

Selenium may be a problem in the freshwater environment 5 pg/1 is the criterion for protection of aquatic life at chronic exposure and modifications of this criterion have been proposed recently [90]. A similar situation apparently does not exist in the marine environment. Selenium is a relatively abundant trace element in the marine environment and seems to counteract the toxic effects of mercury. 

Mercury is a fairly common heavy metal. Its elemental form at room temperature is that of a liquid that is volatile with the characteristic shininess of a metal. Mercury atoms are readily oxidized to Hg [mercury(I) ion] and Hg + [mercury (11) ion]. Both of these ionic forms are toxic, and their effects can be cumulative (i.e., repeated exposures will increase the toxic effects because the body does not easily rid itself of the element). 

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