Industrial exposure mixture toxicities

Exposures to chemical substances such as carbon tetrachloride, 1,1-dichloroeth-ylene, paradichlorobenzene, ethylbenzene, monochlorobenzene, tetrachloroethyl-ene, toluene, 1,1,2-trichloroethane, xylenes, cadmium, and lead are known to canse adverse effects on the kidney. The kidney is unusually susceptible because of its role in filtering harmful substances from the blood. Some of these toxicants canse acnte injury to the kidney, while others produce chronic changes that can lead to end-stage renal failure or cancer. Furthermore, evaluation of the nephrotoxicity of complex industrial waste mixtures with organic chemicals and metals reqnires more stndies. 

As can be expected, some chemicals are data-rich while others are data-poor. Often they are data-poor, especially for chemical mixtures where the data may be adequate, barely adequate or nonexistent for a specific mixture. Thus limited methods are available for the toxicity assessment of chemical mixtures [1,9]. Even though there are various uncertainties and assumptions embedded in these methods, the following three approaches have gained acceptance by the regulatory agencies and the regulated community for risk assessment of mixtures of industrial, occupational, and environmental chemicals. The method employed is on a case-by-case basis, it depends on the exposure scenario and the quality of available data on exposure and toxicity. 

Nickel may be a factor in asbestos carcinogenicity. The presence of chromium and manganese in asbestos fibers may enhance the carcinogenicity of nickel (USEPA 1980), but this relation needs to be verified. Barium-nickel mixtures inhibit calcium uptake in rats, resulting in reduced growth (WHO 1991). Pretreatment of animals with cadmium enhanced the toxicity of nickel to the kidneys and liver (USPHS 1993). Simultaneous exposure to nickel and cadmium — an industrial situation... 

Mahlman M. 1991. Dangerous and cancer-causing properties of products and chemicals in the oil refining and petrochemical industry, part Xll. Human health and environmental hazards. In MA Mehlman, ed.. Advances in Modern Environmental Toxicology, Vol XIX Health and Risks from Exposure to Complex Mixtures and Air Toxic Chemicals, Princeton Scientific Publishing CO, Inc., Princeton, New Jersey, 99-116. 

Which effect assessment method should be applied in a particular situation depends on the nature of the mixture problem at hand. Because the diversity in assessment methods is large, it is important to clearly describe the problem. For example, derivation of a safe level for a proposed industrial mixture emission requires a different approach than the prioritization of a number of sites contaminated with mixtures. The former problem requires the assessment of realistic risks, for example, by the application of a suite of fate, exposure, and effect models, whereas the application of a simple consistent method suffices to address the latter problem, for example, a toxic unit approach. A successful and efficient assessment procedure thus starts with an unambiguous definition of the mixture problem at hand. The problem definition consists of the assessment motive, the regulatory context, the aim of the assessment, and a structured or stepwise approach to realize the aim. Elaboration of the problem definition is an iterative process (Figure 5.1) that strongly depends on factors such as resources, methods, data availability, desired level of accuracy, and results of previous studies. 

Organic solvents, which induce CYP2E1, are comprised of a few broad chemical classes, including hydrocarbons such as benzene and toluene, halogenated aliphatic compounds such as carbon tetrachloride and dichloroethane, aliphatic alcohols such as ethanol, and hydroxyethers such as 2-methoxyethanol. Industrial solvents are frequently mixtures of several compounds. The most frequent solvent-associated toxicity occurs from occupational exposure. A number of organic solvents have been examined for their effects on the immune system, and the requirement for their bioactivation to produce immunotoxicity has been well established. 

Another study revealed effects, ranging from mild to severe, of benzene exposure in factory workers in China (Yin et al. 1987c). The primary activities in these factories were the manufacture of paints, shoes, rubber, leather, and/or adhesives (Yin et al. 1987c). Of the 528,729 workers, 95% were exposed to mixtures of benzene, toluene, and xylene, while 5% (26,319 workers) were exposed to benzene alone at 0.02-264 ppm in air in 95% of the work stations. Over half of the work stations had levels of benzene in the air of less than 13 ppm about 1% had levels of 13-264 ppm. Benzene toxicity, as indicated by leukopenia (leukocyte <4,000/mm3), aplastic anemia, and leukemia, was seen in 0.94% of the workers exposed to benzene and 0.44% of the workers exposed to the mixtures. Similar toxicity was found in employees of 28 of the 141 shoe factories studied (124 cases in 2,740 employees) (Yin et al. 1987c). A positive correlation was observed for prevalence of adverse benzene effects and benzene concentration in data from these 28 shoe factories. The authors determined that the affected people were exposed to benzene concentrations >29 ppm. In one workshop, there were 4 cases of aplastic anemia in 211 workers. These workers were exposed to benzene at a mean concentration of 324 ppm during an 8-month period of employment. The prevalence of aplastic anemia in the shoe-making industry was about 5.8 times that in the general population. The main limitation of this study is the lack of information on the duration of exposure. 

Use and exposure Diborane is a colorless gas at room temperature with a repulsive, sweet odor. It mixes well with air and easily forms explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature and can cause explosions. Diborane is used in rocket propellants and as a reducing agent, a rubber vulcanizer, a catalyst for hydrocarbon polymerization, a flame-speed accelerator, and a doping agent. Diborane is a very toxic and flammable gas used by chemists to make other compounds. It is also used in electronics to impart electrical properties in pure crystals. Industrial workers are exposed to diborane by breathing in its vapors in work areas. - ... 

At times, people react acutely or chronically to unknown stimulants. In such cases, it is hypothesized that unidentified mixtures are often the causative agents. Such toxic mixtures can arise from mixtures of two or more household products as well as from the mixture of household chemicals with chemicals from foods, outdoor air pollutants, water pollutants, or industrial chemicals that are carried into the home on the clothing of workers. In many of these mixture exposure instances, the health effects cannot be attributed to any of the individual chemicals present, but produce distinct clinically defined symptoms. 

Fly ash from municipal waste and industrial waste incinerators contains polychlorinated dibenzo-p-dioxins (PCDDs), including tetrachlorodibenzo-/j-dioxin (TCDD) and polychlorinated dibenzofurans (PCDFs), which are lipophiles, and heavy metals, including chromium, copper, manganese, vanadium, and lead, which are hydrophilesJ29-31 These chemicals have multiple toxicities and are known to impact the human liver, immune system, respiratory system, thyroid, male reproductive function, and CNS J32 34l Several are human carcinogensJ32 35 Enhanced toxic effects are observed in the mixtures of some of theseJ21,22 36 The mixtures of toxicants present in fly ash are complex and the mechanisms for their action on the human body are largely unknown. It is known that occupational exposure to fly... 

Human exposures to RF radiation arise from military use, industrial use, broadcasting, and cellular phone use. These exposures have been linked to increased numbers of spontaneous abortion, neurological effects, altered red and white blood cell counts, increased somatic mutation rates in lymphocytes, cardiovascular effects, increased cancer risk, and increased childhood cancers/28 311 Other studies.however, have refuted these findings) 27,32 As stated in the introduction, only a relatively few studies addressed the combined effects of toxic chemical and RF exposure. A thorough search of the literature shows that such studies have not been refuted. The following are illustrative examples of these mixture studies. 

Escalona E, Yanes L, Feo O, et al Neurobehavioral evaluation of Venezuelan workers exposed to organic solvent mixtures. AmJInd Med 27 15-27, 1995 Eskenazi B, Gaylord L, Bracken MB, et al In utero exposure to organic solvents and human neurodevelopment. Dev Med Child Neurol 30 492-501, 1988 Feldman RG, Ratner MH, Ptak T Chronic toxic encephalopathy in a painter exposed to mixed solvents. Environ Health Perspect 107 417 22,1999 Fidler AT, Baker EL, Letz RE Neurobehavioural effects of occupational exposure to organic solvents among construction painters. British Journal of Industrial Medicine 44 292-308, 1987... 

EXPLOSION and FIRE CONCERNS flammable liquid NFPA rating Health 2, Flammability 4, Reactivity 0 vapor is heavier than air, mixes well with air, and easily forms explosive mixtures flashback along vapor trail may occur very dangerous fire risk when exposed to heat or flame reacts vigorously with oxidants forms an explosive product when it reacts with methanol and sodium methoxide exposures to high concentrations have resulted in industrial fatalities combustion may produce irritants and toxic gases use water spray, alcohol-resistant foam, dry chemical, or carbon dioxide for firefighting purposes. 

In addition, workers may be exposed to a variety of different pollutants during the course of a shift some being more toxic than others, so that the degree of exposure to each might be required to be known. When a mixture of pollutants occurs, the presence of one may interfere with the measurement of another. Therefore, the measurement of the degree of exposure of a worker must be undertaken with care. Occupational (or industrial) hygienists are trained in the necessary skilled techniques and should be called in to carry out the measurements. 

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