General Toxicity Problems

Toxicity problems associated with isocyanates can be minimized by the use of good industrial hygiene, which is now obvious should constitute minimal exposure to vapour and skin contact. It has been established that exposure to low concentrations generally causes symptoms such as burning eyes, dry throat and coughing irritation, but normally work is not interrupted. It is known, however, that those frequently exposed to the inhalation of isocyanates at lower concentrations after several years are more often affected by diseases of the upper respiratory tract (e.g. chronic bronchitis or allergic asthma). The action of isocyanates over a period of several years at these levels of concentration, can lead to progressive impairment of pulmonary function with considerable shortness of breath which may produce cyanosis (Hunter, 1985). 

Long-term exposure studies at levels below the established TLV values of Table 14.1 have established for TDI, MDI and NDI that loss of pulmonary function does not occur compared with control groups. However, there is an important qualification to this generalization in that when respiratory sensitization to isocyanates has occurred, it is no longer safe to be exposed to even the TLV value and further contact with isocyanate must be avoided as a short instantaneous exposure will usually bring about an instantaneous asthmatic response. Individuals who suffer from constitutional respiratory problems or acquire hyperactivity of the bronchial system are always at greater risk from isocyanate exposure and should avoid its use. 

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Sulfur trioxide reactivity can also be moderated through the use of SO adducts. The reactivity of such complexes is inversely proportional to their stabihty, and consequentiy they can be selected for a wide variety of conditions. Whereas moderating SO reactivity by adducting agents is generally beneficial, the agents add cost and may contribute to odor and possible toxicity problems in derived products. CeUulosic material has been sulfated with SO.—trimethyl amine adduct in aqueous media at 0 to 5°C (16). Sulfur trioxide—triethyl phosphate has been used to sulfonate alkenes to the corresponding alkene sulfonate (17). Sulfur trioxide—pyridine adduct sulfates oleyl alcohol with no attack of the double bond (18). 

Much of the literature pertaining to putative inhibitors of HCV helicase has recently been discussed in the excellent review published by Frick (2007). As he points out, one of the main problems with a helicase as target for antiviral drugs is the potential for general toxicity related to the highly conserved nature of the... 

In addition, problems related to leaching of photocatalysts into the environment must be considered as metals are generally toxic, especially when present as reduced micro- or nanoparticles. 

Desferrioxamine and several related iron chelators have been demonstrated to inhibit the proliferation of a variety of malignant cell lines [148,149] as well proving inhibitory in acute neonatal leukaemia [150]. In addition desferrioxamine also exhibits in vivo anti-malarial activity in both humans and rats [151,152], Iron chelators have also been used to treat the inflammatory skin disorder, psoriasis, where there is hyperproliferation of keratinocytes and T-lymphocytes [153,154], A general problem still to be overcome with a number of powerful iron chelators is their lack of cell specificity and thus general toxicity for example to bone marrow function [144],... 

Shown in Table 3.8 are observed toxicity sequences for some plants. (Toxicity to plants is termed phytotoxicity). Soft-acid cations Hg(II), Ag(I), and Cd(II) are generally the most toxic of the metals. Close behind are the borderline hard-soft-acid cations. The only toxic hard cations listed are Cr(III) and Mn(II). Although not listed in Table 3.8, in soils affected by acid rain (see Chap. 7, Section 7.7), hard acid Al(III) presents a serious toxicity problem to plants (Bohn et al. 1985). 

Plant saponins are not normally considered to be promising anticancer lead compounds, partly because of problems with general toxicity. One exception to this rule is the acylated cholestane diglycoside OSW-1 (31), which was isolated from the bulbs of Omithogalum saundersiaehj Sashida and coworkers in 1992. In addition to OSW-1 three related compounds were also isolated and two were tested for inhibitory activity on cyclic AMP phosphodiesterase. OSW-1 and the related compound 32 were the most active, with IC50 values of 55 and 5 pmoir, respectively. ... 

Zinc salts may be used to inhibit corrosion of iron and steel due to the precipitation of Zn (OH) on the cathodic areas of the system. The barrier to oxygen transfer is not very durable and zinc is not generally used on its own. It is preferable to use zinc salts in conjunction with other additives, such as polyphosphates and phosphonate. Because of the toxicity problems the presence of Zri in plant effluents is generally not acceptable and if it is used, some form of effluent treatment is likely to be necessary before discharge. 

Municipal sewage sludges and fly-ash materials, both waste products, contain Mo that is available to crops. Because these two materials are applied to soils at relatively high rates (5-401 ha" ), their Mo contents should be considered when determining their application rates. Although toxicity problems generally do not result from application... 

Some of the most attractive solvents to dispose of in cement kilns are washings from paint mills. These contain substantial quantities of resins and pigments but, in general, have a high calorihc value (8500 kcal/kg) and are primarily composed of low-cost solvents, which makes them unattractive to recover. They tend to contain relatively high concentrations of iron and titanium, neither of which is harmful to the properties of cement. Because paint must not contain highly toxic metal compounds or solvents, it would be imhkely that paint mill washings would present toxicity problems. 

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