Tissues organic mercury

Mercury will cross the placental barrier. In mammalian tissue, organic mercury, especially alkyl mercury, is converted to inorganic forms but not vice versa. Inorganic forms of mercury (not organic forms) induce a metallothionein. Inorganic mercury concentrates mainly in the kidney. Organic mercury compounds, being lipid soluble, concentrate in adipose tissue and the brain. Elimination is primarily in the urine and the feces, with small amounts in breath, sweat, and saliva. 

Concentrations of V, Mn, Fe, Cr, Co, Cu, Zn, As, Se, Mo, Ag, Cd, Tl, Hg, Pb, and organic mercury (Org-Hg) were determined in liver, kidney, and muscle of healthy Caspian seals (Phoca caspica) collected in 1998. These concentrations were compared with those of seals infected with canine distemper virus (CDV) found stranded along the coastal areas in 2000 (Table 1). Concentrations of toxic elements (As, Ag, Cd, Tl, Hg, Pb, and Org-Hg) in Caspian seals stranded in 2000 were comparable or lower than those of samples collected in 1998 and in other pinnipeds. Thus it may be inferred that these elements were not the causative agents in the deaths of the seals. In contrast, concentrations of Zn and Fe were much higher in diseased Caspian seals than those in other pinnipeds. Zinc concentrations in all tissues of Caspian seals also increased during 1993-2000. Furthermore, negative correlations were found between blubber thickness and hepatic and renal Zn concentrations. These results imply the disturbance... 

Unithiol and succimer increase urine mercury excretion following acute or chronic elemental mercury inhalation, but the impact of such treatment on clinical outcome is unknown. Dimercaprol has been shown to redistribute mercury to the central nervous system from other tissue sites, and since the brain is a key target organ, dimercaprol should not be used in treatment of exposure to elemental or organic mercury. Limited data suggest that succimer, unithiol, and N- acetyl-L-cysteine (NAC) may enhance body clearance of methylmercury. 

An understanding of the environmental fate of these elements is necessary in the total assessment of associated health risks. Mercury is known to cycle between the geosphere and biosphere (35). Once in the hydrosphere, it can be converted by sediment flora into highly toxic methylmercury whereupon it is incorporated into aquatic life and ultimately accumulates in human food chains (31). Limited bacterial conversion of inorganic to organic mercury has been shown to occur in soil humus (36) and in animal tissue as well (37). There is no evidence that alkylated mercury is generated from coal combustion directly if it did it would probably be dissociated to the elemental form (14). 

Any one of a series of physiological, biochemical, behavioural or metrics measurements reflecting an interaction between a living system (tissue, organ, cell, etc.) and an environmental agent, which may be chemical, physical or biological. For example, the induction of metallothionein, a heavy metal biomarker of defense, is activated in fish hepatic tissue exposed to metals such as cadmium or mercury. Volume 1(14), Volume 2(1,10). 

FIGURE 6.3 Mercury concentrations (mg kg-1) and organic mercury percentages in the different tissues and genders of 1+, 2+, and 3+ year old Carcinus maenas. (After Coelho et al. 2008. Mar. Pollut. Bull. 56 1104-1110. With permission.)... 

R. Wagemann, E. Trebacz, R. Hunt, G. Boila, Percent methylmercury and organic mercury in tissues of marine mammals and fish using different experimental and calculation methods, Environ. Toxicol. Chem., 16 (1997), 1859-1866. 

The extensive lipophilicity of DMM allows the substance to pass readily through biological membranes. This chemical property facilitates its near instantaneous absorption by the skin, lungs, and gastrointestinal tract, and results in its accumulation in depots of adipose tissue, plasma proteins, and brain. Approximately 10% of the body burden of organic mercury is localized in the brain. 

Organic Mercury. Distribution of organic mercury compounds in humans and animals is similar to that of metallic mercury. Methylmercury distributes readily to all tissues, including the brain and fetus, after absorption from the gastrointestinal tract. The uniform tissue distribution is due to methylmercury s ability to cross diffusion barriers and penetrate all membranes without difficulty (Aberg et al. 1969 Miettinen 1973). Thus, tissue concentrations tend to remain constant relative to blood levels. About 90% of the methylmercury in blood is found in the red blood cells (Kershaw et al. 1980). The mean mercury concentrations in red blood cells were 27.5 ng/g and 20.4 ng/g in males and females, respectively, exposed to mercury, primarily from mercury-contaminated fish (Sakamoto et al. 1991). Because of this uniform distribution in tissues, blood levels are a good indicator of tissue concentrations independent of dose (Nordberg 1976). 

Mechanisms for the toxic effects of inorganic and organic mercury are believed to be similar. It has been suggested that the relative toxicities of the different forms of mercury (e g., metallic, monovalent, and divalent cations and methyl- and phenylmercury compounds) are related, in part, to its differential accumulation in sensitive tissues. This theory is supported by the observation that mercury rapidly accumulates in the kidneys and specific areas of the central nervous system (Rothstein and Hayes 1960 Somjenetal. 1973). 

Organic mercury is the most readily absorbed (90-95% from the gastrointestinal tract), and after absorption distributes especially to the brain, particularly the posterior cortex. All the forms of mercury will cross the placenta and gain access to the foetus, although elemental mercury and organic mercury show greater uptake. The concentrations in certain foetal tissues, such as red blood cells, are greater than in maternal tissue. 

GC/AFS (gas chromatography/atomic fluorescence spectrometry) can be used to separate individual mercury species so that the relative contributions of metallic, inorganic and organic mercury in tissues can be established. 

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