Synthetic chemicals human exposure

Even Rachel Carson was made of chemicals natural vs. synthetic chemicals. Human exposure to naturally occurring rodent carcinogens is ubiquitous and dwarfs the exposure of the general public to synthetic rodent carcinogens. 

General considerations. Nitroaromatic compounds, such as nitro-furans and nitrobenzenes are commercially important chemicals used as drugs, food additives or synthetic intermediates. Since there is widespread human exposure to these chemicals, their metabolism has been studied extensively. Nitroaromatic compounds are reduced by both hepatic cytosol and microsomes. The microsomal activity... 

One human study of workers in a US synthetic chemical plant failed to find any specific association between exposure to vinyl acetate and excess lung cancer. ... 

Effects of Synthetic Chemical Exposures on Human Health... 

Hexamethylene diisocyanate is a highly reactive synthetic chemical that is widely used in the production of polyurethane materials. There is no natural somee of HDI. All of the potential exposures to this compound are associated with the production, handling, use, and disposal of HDI and HDI-containing products or materials. Exposures to HDI are often associated with exposures to its prepolymers, especially to a trimeric biinetic prepolymer of HDI (HDI-BT) (see Figure 5-Ia), whieh is widely used as a hardener in automobile and airplane paints, and whieh typieally contains 0.5-1% unreacted HDI (Alexandersson et al. 1987 Hulse 1984 Karol and Hauth 1982). There is evidence that diisocyanate prepolymers may induce asthma at the same or greater frequency as the monomers (Seguin et al. 1987) therefore, there is a need to assess the potential for human exposme to prepolymeric HDI as well as monomeric HDI. Except for limited data on occupational exposures, no information was foimd in the available literature related to the potential for human exposure to prepolymers of HDI. 

Substances produced in quantities of less than 10 tonnes per year include most of the chemicals used as textile dyestuffs and auxiliaries (CEC, 2003b). This illustrates the inadequacy of using tonnage thresholds as a measure of human exposure. Chemicals used to dye or treat cloth are present in our clothes and may leach from clothes through our skin into our bodies. We may also inhale the chemicals, after the skin has flaked off and become part of household dust (ENDS, 1994). Clothes are probably one of the major routes of human exposure to synthetic chemicals and the long-term effects of those chemicals should surely be investigated. 

Materials for ESR Dosimetry and Dating. Materials used for retrospective dosimetry of radiation exposure depend on the situation. In addition to human tooth enamel, materials worn by the person, such as shell buttons, or used nearby at the site, such as sugar,32 have been studied to evaluate the radiation dose. On the other hand, materials for ESR radiation dosimetry elements should be well-controlled synthetic chemicals, although natural materials like bovine bones and sugar were proposed in the past. 

The dose makes the poison. Half of all chemicals tested, whether natural or synthetic, cause cancer in high-dose rodent cancer tests. Evidence suggests that this high rate is due primarily to effects that are unique to high doses. The results of these high-dose tests have been used to regulate low-dose human exposures, but are not likely to be relevant. 

In one epidemiological study of 138 workers exposed to vinylidene chloride in the United States, no excess of cancer was found, but follow-up was incomplete, and nearly 40% of the workers had less than 15 years latency since first exposure (lARC, 1986). In a study in the Federal Republic of Germany of 629 workers exposed to vinylidene chloride, seven deaths from cancer (five bronchial carcinomas) were reported this number was not in excess of the expected value. Two cases of bronchial carcinoma were foimd in workers, both of whom were 37 years old, whereas 0.07 were expected for persons aged 35-39 years (Thiess et al., 1979). The limitations of these two studies preclude assessment of the carcinogenicity of the agent to humans. No specific association was found between exposure to vinylidene chloride and an excess of lung cancer observed in a synthetic chemicals plant in the United States. 

Toxicologists have only just begun to study the influence of individual synthetic chemicals at low levels on human health. Unfortunately, toxicologists know virtually nothing about the toxic effects of chemical mixtures. Given these unknowns, our exposure to complex mixtures of synthetic chemicals could be responsible for a portion of the background health effects measured in our society. 

Aryl halide derivatives of benzene and toluene have many uses in chemical synthesis as pesticides and raw materials for pesticides manufacture, solvents, and a diverse variety of other applications. These widespread uses over many decades have resulted in substantial human exposure and environmental contamination. Three example aryl halides are shown in Figure 1.17. Monochlorobenzene is a flammable liquid boiling at 132°C. It is used as a solvent, heat transfer fluid, and synthetic reagent. Used as a solvent, 1,2-dichlorobenzene is employed for degreasing hides and wool. It also serves as a synthetic reagent for dye manufacture. Bromobenzene is a liquid boiling at 156°C that is used as a solvent, motor oil additive, and intermediate for organic synthesis. 

Although the details are beyond the scope of this book, health problems can be caused by solids and liquids suspended in water (for example, in waste-tailings streams) or in air (for example, in stack-emission plumes). Specific potential hazards have been associated with a diverse spectrum of colloidal materials, including synthetic chemicals, coals, minerals, metals, pharmaceuticals, plastics, and wood pulp. Limits for human exposure for many particulate, hazardous materials are published [504,505],... 

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