Cadmium beneficial effect

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

Agencies will need to accept the possibility (actually, the likelihood) that toxic substances, even the most highly toxic (e g., cadmium, lead, mercury, dioxin, PCBs, etc.) can cause beneficial effects at low doses. 

Zinc is relatively nontoxic but, if present in the diet at high concentration and in readily available form, it can interfere with the absorption of calcium, copper, iron, and cadmium and can produce anemia. These elements, in turn, can decrease zinc absorption if present in sufficient quantities. Use of zinc salt lozenges has been claimed to reduce the duration of the common cold. However, many randomized, double-bind, placebo-controlled trials have failed to show any beneficial effects of zinc lozenges in reducing the duration of upper respiratory tract viral infections. 

Some of them, such as arsenic, lead, cadmium and mercury are frequently classified as toxic elements because their toxicity to man and animals is relatively high and their biological activity is largely confined to toxic reactions. However, all the trace elements can be toxic if consumed in sufficiently large quantities or for protracted periods of time, as we will learn this afternoon from Dr. Mertz, who will dis-curse on "essentiality and toxicity of heavy metals". I am sure that he will be able to supply us with further evidence that the toxicity or beneficial effect of a particular element can be greatly influenced by the extent to which other elements or compounds present in the diet affect its absorption, excretion, or metabolism. 

Effects of Cadmium on Phytoplankton Growth 3.1 Beneficial Effect... 

Chromium has proved effective in counteracting the deleterious effects of cadmium in rats and of vanadium in chickens. High mortality rates and testicular atrophy occurred in rats subjected to an intraperitoneal injection of cadmium salts however, pretreatment with chromium ameliorated these effects (Stacey et al. 1983). The Cr-Cd relationship is not simple. In some cases, cadmium is known to suppress adverse effects induced in Chinese hamster (Cricetus spp.) ovary cells by Cr (Shimada et al. 1998). In southwestern Sweden, there was an 80% decline in chromium burdens in liver of the moose (Alces alces) between 1982 and 1992 from 0.21 to 0.07 mg Cr/kg FW (Frank et al. 1994). During this same period in this locale, moose experienced an unknown disease caused by a secondary copper deficiency due to elevated molybdenum levels as well as chromium deficiency and trace element imbalance (Frank et al. 1994). In chickens (Gallus sp.), 10 mg/kg of dietary chromium counteracted adverse effects on albumin metabolism and egg shell quality induced by 10 mg/kg of vanadium salts (Jensen and Maurice 1980). Additional research on the beneficial aspects of chromium in living resources appears warranted, especially where the organism is subjected to complex mixtures containing chromium and other potentially toxic heavy metals. 

Coloring agents can be either organic or inorganic, but the former can adversely affect heat stability. Examples of suitable inorganic colorants are oxides and salts of iron, chromium, cobalt, titanium, and cadmium. Some not only provide color, but can also have some beneficial heat-aging effects. 

It should be noted that in the majority of the above mentioned studies, metal-induced renal injury was considered as if exposure occurred to only one metal at a time. In reality it is clear that environmental and occupational exposure may involve several metals at the same time and in varying concentrations [34]. It has been shown that with combined exposure various metals may interact with each other and that one metal may alter the potential toxicity of another in either a beneficial or deleterious way. As an example, whilst arsenic has been shown to worsen cadmium-induced nephrotoxicity, data from experimental studies have shown that selenium may protect against the renal effects induced by cadmium [52]. Other studies have shown that the iron status may alter the toxic effects of aluminium at the level of the bone and the parathyroid gland [53,54], whilst in a recent increased lead accumulation was associated with disturbances in the concentration of a number of essential trace elements [55]. 

More than 15 additional trace elements are considered by some investigators to have a potentially important role in human medicine. A review by Nielsen considers these in detail and discusses emerging concepts of essentiality. For some such as lead, cadmium, arsenic, aluminum, and nickel, the clinical laboratory will primarily consider them as toxic elements (see Chapter 35). Others, such as lithium and fluoride, are classified as pharmacologically beneficial and monitoring of dosage may be required. Some elements can be considered nutritionally beneficial and are reported to produce restorative health effects at lower dosages. Evidence comes mainly from animal studies when dietary depletion of the element is combined with other metabohc, hormonal, or physiological stressors. ... 

The first evidence that cadmium had a beneficial biological function came from growth data in laboratory cultures of the diatom Thalassiosira weissflogii [43,45]. As shown in Fig. 10, cultures of this coastal diatom grow slowly when the unchelated Zn concentration in the medium is reduced to about Zn = 3 pM. pM. These same cultures grow much faster when Cd is added to the medium at unchelated concentrations >5 pM [46]. This effect, which is particularly obvious at low Co concentrations, has now been observed in other families of marine phytoplankton. For example, Cd enhances the growth rate of the cosmopolitan coccolithophore Emiliana huxleyi when the unchelated Zn and Co concentrations in the medium are below 1 pM (Fig. 10) [42]. From similar laboratory studies, it appears that Zn, Cd, and Co can substitute for each other in many marine eukaryotic phytoplankton [47-51]. 

Adsorption of metal cations is one of the most beneficial functions of chitin and chitosan. An extensive review has been made by Muzzarelli (1973, 1976). Marucca et al. (1982) examined adsorption of chromium under various conditions. Koyama and Taniguchi (1986) studied the effect of deacetylation of chitin on adsorption and the importance of high hy-drophilicity. Eiden et al. (1980) reviewed the uptake of lead (II) and chromium (HI) by chitin and chitosan as a function of concentration. Hexavalent chromium interaction with chitosan has also been studied by Onsoyen and Skavgrud (1990). Other recent studies on adsorption include iodine, nickel, copper, zinc, and cadmium. 

---