Sensitivity toxic metal

Some microbes are able to decrease the permeability of their membranes to prevent toxic metals from entering. If the toxic metals are not able to physically enter the cell, they will not be able to affect vital metal-sensitive structures, such as proteins. One way to prevent heavy metals from entering is by decreasing the production of membrane channel proteins.18 It is also possible for the metal-binding sites in the membrane and periplasm to be saturated with nontoxic metals.37 A third possibility is the formation of an extracellular polysaccharide coat, which binds and prevents metals from reaching the surface of the cell.24,38... 

Moving from single microorganisms to microbial communities, metals create selection pressure for microbes with cell structures that are less sensitive to metals. For example, mutations may occur that alter metal-binding sites of proteins without rendering the enzyme inactive. Another method for preventing metal toxicity is to produce excess amounts of the target so that there is an insufficient amount of metal to bind to all of the cellular molecules.4 35 53... 

The immunotoxicology of metals in fishes has been reviewed elsewhere [74-76, 45], Overall, the immune systems of fishes are highly sensitive to metals, although the effects are not always suppression of immune functions. Burnett [76] demonstrated that low levels of metals increased intracellular calcium, increased protein phosphorylation, and stimulated lymphocyte proliferation in fish. Since most metals are toxic to both the nervous system and the immune system, a neuroendocrine-immune link to immuno-toxicity from metal exposure is likely. 

The results of the investigation of 58 adult persons who live on industry territory of North Crimea and 60 male teenagers at age 15 years and 84 children (2-14 years) in the Simferopol city showed that the children are more sensitive to the relatively low level of heavy metal concentrations than the adult (Evstafyeva et al., 2002). It is known that many toxic metals have neurotoxic effects (Arezzo et al., 1985). It was also shown that the effects of central and autonomous nervous systems of different... 

It is known that zinc and cooper play an important role in immune system functioning (Kelley et al., 1995 Skalny and Rudakov, 2004 Zinc, 2001). Deficiency of these metals causes immune system dysfunctions. Recently these dysfunctions are seen to be widely distributed, especially in children. It is known also that sensitivity of the immune system to external influences differs in different age periods and it was found (Evstafyeva et al., 2002) that the influence of toxic metals is more significant in 7-11-year-old urbanized children. At the same time zinc and cooper deficiency was found in 1-6-year-old children, zinc deficiency and copper lowered contents, in... 

P25 Each of these [previous methods] involves one or more of the following drawbacks uses expensive and toxic metals, demonstrates severe water sensitivity, or produces hydrazoic acid, which is highly toxic and explosive as well as volatile. The few methods that seek to avoid hydrazoic acid liberation during the reaction, by avoiding acidic conditions, require a very large excess of sodium azide. In addition, ah of the known methods use organic solvents, in particular, dipolar aprotic solvents such as DMF. This is one of the solvent classes that process chemists would rather not use. (Adapted from Demko and Sharpless, 2001)... 

The Julia - Colonna asymmetric epoxidation of electron-deficient unsaturated ketones to the corresponding epoxides with high yields and high ee is well known. This technique produces chiral chemical entities from the clean oxidant, hydrogen peroxide, without the use of a toxic or water sensitive transition metal additive. 

These proteins are important for binding potentially toxic metals such as cadmium, mercury, and lead, which all bind to sulfydryl groups. Consequently, the binding and removal of these metals are protective functions. Metallothioneins are markedly induced by cadmium exposure and the small protein, rich in SH groups, can then sequester the metal. They also may have a protective role in oxidative stress and protect redox-sensitive processes. The protein also has a role in cadmium nephrotoxicity (see chap. 7). 

The case study presented here was conducted by the Environmental Research Centre, CIMA, Faculty of Sciences, of the University of La Plata. The more frequently applied tests were those conducted with the Lactuca sativa seed germination assay, followed by the Hydra, Daphnia and Selenastrum tests. They were used for the assessment of toxicity from hazardous wastes and waste leachates, sediment pore water and sediment leachates, surface waters and groundwater. An additional test based on (3-galactosidase (in vitro-free enzyme test) inhibition, known for its sensitivity to metals (Apartin and Ronco, 2001), was also incorporated in the battery. 

There is another important determinant of which species do and can evolve tolerance and those that do not. Symeonidis et al. (1985) screened cultivars of Agrostis capillaris for metal tolerances and demonstrated differential sensitivities to metals, suggesting the existence of non-specific low level tolerances to metals other than those present at toxic levels in soils from which they were derived. Other screening experiments have implicated such constitutive properties in the ability to evolve... 

Although photophosphorylation was reported to be very sensitive to metals in vitro, the reduction of photosynthetic ATP production was shown to be related to an inhibition of the electron flow rate in Euglena gracilis treated with toxic concentrations of zinc, cadmium and mercury (De Filippis et al., 1981 b), in cadmium-treated Lycoper-sicon esculentum (Bazinsky et al., 1980) and in zinc-treated Phaseolus vulgaris (Van Assche and Clijsters, 1986a). 

Me tals and metallic compounds are among the toxic substances most often found in workplace environments (1,2), Industrial hygienists and hygiene chemists must accurately determine the presence and amount of toxic metals and their compounds in the industrial environment. Accurate methods for the quantification of metals in biological and atmospheric samples are required for the industrial hygienist to properly evaluate the environment. Atomic absorption spectroscopy (AAS) has been the primary method of analysis for toxic metals because AAS is sensitive, specific, and rapid especially compared to colorimetric analysis. 

Field and laboratory studies were conducted to determine the levels of Cd, Pb, and HCBD in various samples collected from a swamp environment in Louisiana and to assess the toxicities of As, Cd, and Hg to two species of aquatic organisms (bluegills and crawfish) indigenous to this swamp [18]. Cadmium and Pb were present in almost all collected samples. Their concentrations in fish were below the action levels set by EPA for the protection of human health. However, hazardous levels of these two elements were found in samples of crawfish, vegetation, soil, sediment, and water to some extent. Low levels of HCBD were recorded in water and sediment samples. In bioassay studies, Hg was found to be the most toxic metal, while As was the least toxic. Between the two test organisms, blue-gills appeared to be more sensitive than crawfish. Mixtures of Cd with As or Hg resulted in a combined toxic effect which was simply additive. However, a synergistic effect was recorded with the mixtures of As and Hg. 

The quality control of pharmaceuticals is particularly important. Care must be taken to limit the levels of toxic metals in the final product. The acid dissolution. procedures described above (e.g. 6 M hydrochloric acid) are often equally applicable for the determination of impurities. Complete destruction of the matrix by wet oxidation or dry ashing may be necessary to obtain a completely independent method. Raw materials, catalysts, preparative equipment and containers are all possible sources of contamination. Lead, arsenic, mercury, copper, iron, zinc and several other metals may be subject to prescribed limits. Greater sensitivity is often required for lead and arsenic determinations and this can be achieved by electrothermal atomisation. Kovar etal. [112] brought samples into solution using 65% nitric acid under pressure at 170—180° C and, after adding ammonium and lanthanum nitrate, determined arsenic in the range 10—200 ng in a graphite... 

Group 4 poisons should be checked as a matter of routine if vomiting and diarrhoea are noted as symptoms, no matter what other poisons may be suggested by medical opinion or circumstantial evidence. Although the Reinsch Test (p. 57) will detect only seven of the twenty potentially toxic metals, it can be applied to almost any material (body fluids, slmried tissue, food Mid (hinks) without Miy elaborate prepM ation, and it is sensitive enou to detect toxic concentrations of tiie most common poisonous metals in a few minutes. However, it misses too many metals for it to be considered as a complete group exclusion test. 

An intriguing problem about which we know very little is the mechanism of metal identification by the body that triggers Its response, as in the case of the huild-up of metallothioneins upon exposure to toxic metals. Perhaps the best understood of the metalloregulatory proteins is MerR that protects bacteria from mercurial toxicity. It is extremely sensitive to Hg, and distinguishes it from its congeners Zn and Cd. There is good evidence that the mercury receptor forms three-coordinate mercury(II) complexes (see Fig. 12.1c), making possible this specificity. ... 

A number of different factors can influence the toxicity of heavy metal (metalloid) elements, including chemical structure, physical properties, mode of administration and the nature of the species affected. The toxic effects of the elements on organisms are very complicated. Some organisms are very sensitive to one chemical compound of an element, but have high resistance to another compound of the same element or to other toxic metals. 

Aquatic organisms, especially those at the top of the food chain, such as fish-eating birds, are much more sensitive to toxic metals in their habitat than are terrestrial biota. There is some circumstantial evidence to suggest that the noeffect thresholds for some metals is fairly close to their current levels in natural waters (see Table 6.1). 

The ultra-sensitive technique of LEAFS was developed and exploited for the analysis of snow and ice to be carried out at the Institute of Spectroscopy of the Russian Academy of Science (ISAN) (46). This technique allows the direct determination of toxic metals in polar snow and ice to be carried out at and below the pg/g level in sample volumes of less than 100 pi. This is an important issue considering that very often the volume of sample obtained after the decontamination procedures amounts to just a few tens of milliliters in the best case and that this must be subdivided into different aliquots for a complete chemical characterisation. 

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