Toxicity agents

IDLH means immediately dangerous to life and health. This is a concentration at which immediate action is required. The exac4 effect on an individual depends on the individuals physical condition and susceptibility to the toxic agent involved. It is the maximum airborne contamination concentration from which one could escape within 30 min without any escape-impairing symptoms or irreversible health effects (developed by NIOSH). 

In experimental work, some accidental exposures, or in the administration of medicine, the dose may be a certain quantity of the chemical administered at one time, such as in a pill, an injection, or an accidentally swallowed poison. In industry, time is a factor in most exposures, and the dose is the result of both the concentration of the toxic agent and the duration of the exposure. 

Another difficulty comes from the consideration of the route of entry (sf the contaminant, as chemicals can enter the body by various routes and the human body responds to the action of a toxic agent primarily on the basis of the rate and route of exposure. Without any doubt, the most important route of exposure at the workplace is inhalation, and this should be the route used to set OELs. However, if there is a threat of significant exposure by other routes, such as cutaneously (including mucous membranes and the eyes), either by contact with vapors or by direct skin contact w ith the substance, additional recommendations may be necessary. 

Most human or environmental healtli hazards can be evaluated by dissecting tlie analysis into four parts liazard identification, dose-response assessment or hazard assessment, exposure assessment, and risk characterization. For some perceived healtli liazards, tlie risk assessment might stop with tlie first step, liazard identification, if no adverse effect is identified or if an agency elects to take regulatory action witliout furtlier analysis. Regarding liazard identification, a hazard is defined as a toxic agent or a set of conditions that luis the potential to cause adverse effects to hmnan health or tlie environment. Healtli hazard identification involves an evaluation of various forms of information in order to identify the different liaz.ards. Dose-response or toxicity assessment is required in an overall assessment responses/cffects can vary widely since all chemicals and contaminants vary in their capacity to cause adverse effects. This step frequently requires that assumptions be made to relate... 

Much of the attention focused on e.xposure assessment has come recently. This is because many of the risk assessments done in tlie past used too many conseix ative assumptions, wliich caused an ovcrcstimation of the actual exposure. Without exposures there are no risks. To experience adverse effects, one must first come into contact with the toxic agent(s). Exposures to chemicals can be via inlialation of air (brcatliing), ingestion of water and food (eating and drinking), or absorption Uu ough the skin. These arc all pathways to the human body. 

In hazard identification, a hazard is a toxic agent or a set of conditions that... 

Human bodies are constantly exposed to a plethora of bacteria, viruses, and other inflammatory substances. To combat these infections and toxic agents, the body has developed a carefully regulated inflammatory response system. Part of that response is the orderly migration of leukocytes to sites of inflammation. Leukocytes literally roll along the vascular wall and into the tissue site of inflammation. This rolling movement is mediated by reversible adhesive interactions between the leukocytes and the vascular surface. 

Although toxic agents have the potential to cause necrosis, some of them can interfere with intracellular signaling pathways and induce apoptosis instead of necrosis. It seems that organotin(IV) compounds exert their toxic effects involving all these processes. The precise balance of these actions and their outcomes may differ radically from one cell type to another and among different organisms. 

In experiments where relatively small volumes of sediment suspensions are employed, autoclaving may significantly alter the structure of the sediment as well as introducing possibly severe analytical difficulties. In such circumstances, there are few alternatives to incubation in the presence of toxic agents such as NaNj, which has been used at a concentration of 2g/L. There remains, of course, the possibility that azide-resistant strains could emerge during prolonged incubation, and the possible occurrence of reactions between the substrate and azide must also be taken into consideration. 

Tolerance in insects to increasing amounts of DDT, BHC, and several of the inorganic agents, such as arsenic, is known to occur. However, in animals, this phenomenon has not been demonstrated to the same degree. Ability of the cells of insects to function in the environment of a toxic agent, without alteration of cellular function, is one of the most striking of biologic phenomena. 

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