Health issues toxicity mechanisms

Critical research needs include definition of thresholds for adverse health effects and how these thresholds vary with exposure concentration and duration. Such data would be valuable for affirming AEGL values. Additionally, the mode of dimethylhydrazine toxicity is not fully understood and, therefore, research providing insight into the underlying mechanism(s) of dimethylhydrazine toxicity would reduce current uncertainties in quantitative health risk issues. 

CDDs and the structurally related CDFs and dioxin-like PCBs are of concern to ATSDR because of the potential of these chemicals to harm health at relatively low doses. As discussed in Section 2.5, many of the toxic effects of these compounds appear to be mediated by a common mechanism, and CDDs frequently occur with CDFs in the environment. Therefore, due to the common mechanism of toxicity, total toxicity of a CDD/CDF mixture probably results from the added contribution (not necessarily linear) of both classes of chemicals. Because of this, the complex issue of appropriate methodology for quantitatively assessing health risks of CDDs and CDFs is currently being evaluated by ATSDR. Additional information on toxic interactions between CDDs and CDFs, as well as PCBs, would facilitate health risk assessment of this class of chemicals. 

The objective of this section is to elucidate some of the current literature findings of environmental and health/safety issues with airborne nanoparticles. The Uterature review of the most recent articles in this area includes topics related to the multiple components of the risk assessment framework. This includes such important aspects as particle characteristics effecting toxicity, their fate and transport throughout the environment, the routes of exposure and the metrics by which exposure ought to be measured and the mechanisms of translocation to different parts of the body. In addition, recent studies are presented that involve the characterization of nanoparticles in the workplace during different operations and conditions. 

Attention to the basic science of health and safety issues not only provides an insight into the current understanding of a complex and broad-ranging subject, but also helps to eradicate misconceptions. For example, seeing is not believing where air pollution is concerned, nor is exhaust extraction a comprehensive solution to pollution control. Dust does not cease to be a problem when it settles on the floor and fully vulcanized rubber is not necessarily free of toxic hazard. The case where settled dust reduces pedestrian friction can be contrasted with that where mechanical handling creates air pollution. Without doubt the interactions of this science are complex and some procedures designed to solve one problem may merely serve to introduce another. 

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