Blood molybdenum

Proposed criteria for human health protection include drinking water concentrations less than 50 pg Mo/L, and daily dietary intakes less than 7 pg Mo/kg food — based on a 70-kg adult (Table 30.5). Molybdenum concentrations in blood of healthy people averaged 14.7 pg Mo/L, distributed between the plasma and erythrocytes. Anemic people had significantly lower blood molybdenum levels. In leukemia patients, molybdenum levels increased significantly in whole blood and erythrocytes but not in plasma (Shamberger 1979). Additional work is recommended on the use of blood in fish and wildlife as an indicator of molybdenum stress and metabolism (Eisler 1989). 

Deficiency or Toxicity in Humans. Molybdenum deficiency in humans results in deranged metaboHsm of sulfur and purines and symptoms of mental disturbances (130). Toxic levels produce elevated uric acid in blood, gout, anemia, and growth depression. Faulty utiH2ation results in sulfite oxidase deficiency, a lethal inborn error. 

It appears that chromium(III) is an essential trace element in mammalian metabolism and, together with insulin, is responsible for the clearance of glucose from the blood-stream. Tungsten too has been found to have a role in some enzymes converting CO2 into formic acid but, from the point of view of biological activity, the focus of interest in this group is unquestionably on molybdenum. 

The compounds of the t/block elements show a wide range of interesting properties. Some are vital to life. Iron is an essential component of mammalian blood. Compounds of cobalt, molybdenum, and zinc are found in vitamins and essential enzymes. Other compounds simply make life more interesting and colorful. The beautiful color of cobalt blue glass, the brilliant greens and blues of kiln-baked pottery, and many pigments used by artists make use of d-block compounds. 

Devoto 115)has described an indirect procedure for the determination of 0.1 ppm arsenic in urine. The arsenomolybdic acid complex is formed and extracted from 1 ml of urine at pH 2 into 10 ml of cyclohexanone. The molybdenum in the complex is then measured. Before extracting the arsenic, phosphate in the urine is separated by extracting the phosphomolybdic acid complex at pH 1 into isobutyl acetate. The direct determination of arsenic in biological material and blood and urine is best done using a nitrous oxide-acetylene flame 116>. The background absorption by this flame is low at 1937 A, and interferences are minimized due to the high temperature of the flame. 

As some other sugars are also present in blood sample, and besides the above reaction not being absolutely stoichiometric, it has become necessary in actual practice to establish an emperical calibration curve using known concentrations of glucose. The above reaction is allowed to proceed for exactly 8 minutes at 100°C. To the resulting solution phosphomolybdic acid is added, which is subsequently reduced by Cu20 to give rise to an intensely coloured molybdenum blue that is measured at 420 nm accurately. 

The best colour contrast of red blood cells is achieved on mono- and polycrystalline silicon, and monocrystalline surfaces of refractory metals molybdenum and tungsten, which possess maximal reflectivity. 

As indicated in Fig. 25-18, free adenine released from catabolism of nucleic acids can be deaminated hydrolytically to hypoxanthine, and guanine can be deaminated to xanthine.328 The molybdenum-containing xanthine oxidase (Chapter 16) oxidizes hypoxanthine to xanthine and the latter on to uric acid. Some Clostridia convert purine or hypoxanthine to xanthine by the action of a selenium-containing purine hydroxylase.3283 Another reaction of xanthine occurring in some plants is conversion to the trimethylated derivative caffeine. 328b One of the physiological effects of caffeine in animals is inhibition of pyrimidine synthesis.329 However, the effect most sought by coffee drinkers may be an increase in blood pressure caused by occupancy of adenosine receptors by caffeine.330... 

Iron (Fe) Iron is arguably the most important construction metal. In addition to buildings and cars, iron alloyed with chromium, molybdenum, nickel, and carbon form surgical stainless steel. Each hemoglobin molecule, the protein that transports oxygen in the blood, contains four ferrous (Fe+2) ions, each of which serve as a point of attachment for an oxygen molecule. 

Elevated levels of chromium in blood, serum, urine, and other tissues and organs have been observed in patients with cobalt-chromium knee and hip arthroplasts (Michel et al. 1987 Sunderman et al. 1989). Whether corrosion or wear of the implant can release chromium (or other metal components) into the systemic circulation depends on the nature of the device. In one study, the mean postoperative blood and urine levels of chromium of nine patients with total hip replacements made from a cast cobalt-chromium-molybdenum alloy were 3.9 and 6.2 pg/F, respectively, compared with preoperative blood and urine levels of 1.4 and 0.4 pg/F, respectively. High blood and urinary levels of chromium persisted when measured at intervals over a year or more after surgery. These data suggest significant wear or corrosion... 

Burguera, J.L., Burguera, M. Molybdenum in human whole blood of adult residents of the Merida State (Venezuela). J. Trace Elem. Med. Biol. 21, 178-183 (2007)... 

A procedure for the determination of molybdenum in serum, red blood cells, and urine is described. The low concentration of molybdenum in most unexposed individuals requires the sensitivity obtained using atomic absorption spectrophotometry and electrothermal atomization. Spike recovery tests indicate that low temperature ashing is required for accuracy. Severe matrix interferences preclude wet ashing or high-temperature ashing as sample pretreatments. Using the method described, it is possible to distinguish between industrially exposed and unexposed individuals. 

Biological fluids such as serum or plasma, red blood cells, and urine are particularly diflBcult to analyze. The low molybdenum concentrations found in normal human samples are below the detection limit of the thiocyanate colorimetric method (100 ng) and much below conventional flame absorption spectroscopy (1 /xg). Normal blood levels of molybdenum are about 10 /xg/L and sample volume is usually < 1 mL. The low concentration and limited sample size preclude direct analysis or sample preconcentration for analysis by the conventional analytical methods. 

In summary, a method for the analysis of molybdenum in biological fluids has been presented. The method requires the destruction of the organic materials in the sample by low-temperature ashing. Detection was accomplished by using a graphite furnace—atomic absorption technique and the standard additions method. The method is sufficiently sensitive to distinguish between molybdenum levels in the blood, serum, and urine from exposed and unexposed individuals. 

Molybdenum is efficiently absorbed over a wide range of dietary intakes mainly as molybdate, although competitive inhibition of absorption by sulfate reduces intestinal uptake. Concentrations in whole blood are about l.Opg/L (10 nmol/L) and some 80% to 90% or more of molybdenum in whole blood is bound to red cell proteins. Transport of the smaller amount in blood plasma may involve a2-macroglobulin. Urine output directly reflects the... 

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