Cadmium persistence

Cadmium is a silver-white metal with an atomic weight of 112.4 and a low melting point of 321 °C. It is malleable and can be rolled out into sheets. The metal unites with the majority of the heavy metals to form alloys. It is readily oxidized to the +2 oxidation state, giving the colorless Cd2+ ion. Cadmium persists in the environment its biological half-life is 10 to 25 years. 

Air-poUutant effects on neural and sensory functions in humans vary widely. Odorous pollutants cause only minor annoyance yet, if persistent, they can lead to irritation, emotional upset, anorexia, and mental depression. Carbon monoxide can cause death secondary to the depression of the respiratory centers of the central nervous system. Short of death, repeated and prolonged exposure to carbon monoxide can alter sensory protection, temporal perception, and higher mental functions. Lipid-soluble aerosols can enter the body and be absorbed in the lipids of the central nervous system. Once there, their effects may persist long after the initial contact has been removed. Examples of agents of long-term chronic effects are organic phosphate pesticides and aerosols carrying the metals lead, mercury, and cadmium. 

Into a conical flask, pipette a 50.0 or 100.0 mL aliquot of the solution and adjust the pH to 1-2 with aqueous ammonia solution (use pH test-paper). Add five drops of xylenol orange indicator and titrate with additional 0.05 M EDTA until the colour changes sharply from red to yellow. This gives the bismuth content. Record the total (combined) volume of EDTA solution used. Now add small amounts of hexamine (ca 5g) until an intense red-violet coloration persists, and titrate with the standard EDTA to a yellow end point the further consumption of EDTA corresponds to the lead-plus-cadmium content. 

In adults, a study of 75 autopsies of persons who had resided in a soft-water, leached soil region of North Carolina found a positive correlation between lead level in the aorta and death from heart-related disease (Voors et al. 1982). The association persisted after adjustment for the effect of age. A similar correlation was found between cadmium levels in the liver and death from heart-related disease. (Aortic lead and liver cadmium levels were considered to be suitable indices of exposure.) The effects of the two metals appeared to be additive. Potential confounding variables other than age were not included in the analysis. The investigators stated that fatty liver (indicative of alcohol consumption) and cigarette smoking did not account for the correlations between lead, cadmium and heart-disease death. 

Two species of freshwater aquatic mosses (Fontinalis dalecarlica, Platyhypnidium riparoides) exposed to concentrations between 0.5 and 6.5 pg Cd/L for 28 days had accumulation factors as high as 137,000 and 158,000, respectively (Gagnon etal. 1998). Accumulations increased with increasing cadmium concentration and decreasing water hardness. Cadmium tended to persist in these mosses. During a depuration period of 28 days following the 28-day exposure, only 37 to 48% of the accumulated cadmium was eliminated (Gagnon et al. 1998). 

The reproductive systems of both males and females can be harmed by particular chemicals. In males certain chemicals cause the testes to atrophy and reduce or eliminate their capacity to produce sperm. Particularly striking in this regard is a now banned but once widely used pesticide called DBCP, residues of which persist in ground water supplies in a few regions of the country. Its pronounced impact on spermatogenesis is readily detectable in experimental animals and, unfortunately, has also been observed in some men once occupation-ally exposed to large amounts. The heavy metal cadmium is another substance effective at reducing sperm production. 

Metals frequently occurring in the state s waste streams include cadmium, chromium, lead, arsenic, zinc, copper, barium, nickel, antimony, beryllium, mercury, vanadium, cobalt, silver, and selenium. These metals are toxic to humans and other organisms, are persistent in the environment, and can bioaccumulate in food chains. They are typically used by businesses in many industrial categories, as shown in Table 2.1-1. 

A classic example of essential metal deficiency resulting from nonessential metal exposure is Itai itai disease. Cadmium pollution in the Jinzu River basin in Japan resulted in severe nephrotoxicity in approximately 184 people. Renal tubule damage caused excessive loss of electrolytes and small proteins from the urine. In severe cases, urinary Ca loss was so severe that bone Ca was mobilized, resulting in osteomalacia. Renal tubular defects persisted for life and induced hypophosphatemia, hyperuricemia, and hyperchloremia, which are characteristic biochemical features of Itai-itai disease (see Section 21.6.1). 

The APDC—MIBK extraction system is widely used to determine a variety of metals in water. In both the U.K. [6, 7] and the U.S.A. [8] it is the standard method for the determination of lead and cadmium in water. It is also used as a standard method [8] in the determination of hexavalent chromium. In order to determine total chromium, trivalent chromium is oxidised to hexavalent chromium by bringing the sample to the boil and adding sufficient potassium permanganate solution (0.1 N) dropwise to give a persistent pink colour while the solution is boiled for 10 min. 

Apart from mercury and cadmium. List I refers to families or groups of substances rather than to individual substances identified on the basis of toxicity, persistence, and bioaccumulation. 

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