Hazard-exposure relationship

This simple statement has profound implications in the management of risk, i.e., that even toxic substances can be effectively managed through control of exposure, at least in industrial environments, and even substances typically thought to be safe can become toxic if exposure is excessive. Although the hazard-exposure relationship suggests that risk is eliminated if exposure is zero, in practice achievement of zero risk is not possible. Under the Toxic Substances Control Act (TSCA), the Environmental Protection Agency (EPA) carries out three risk assessments one each for acute and chronic... 

Based in this information difference between the NOEL and human exposure or the risk at a given exposure is determined. Humans may be exposed to chemicals in the air, water, food, or on the skin. From the concentrations of a chemical in these different compartments the external daily exposure is estimated. The response to the chemical depends upon duration and route of exposure, the toxicokinetics of the chemical, the dose-response relationship and the susceptibility of the individual. Thus, the precise definition of the terms hazard, exposure, and risk is essential to understand toxicological evaluations (details on data requirements and procedures for risk assessment are given subsequently). 

If possible, there should be measurement of the toxic effect in order quantitatively to relate the observations made to the degree of exposure (exposure dose). Ideally, there is a need to determine quantitatively the toxic response to several differing exposure doses, in order to determine the relationship, if any, between exposure dose and the nature and magnitude of any effect. Such dose—response relationship studies are of considerable value in determining whether an effect is causally related to the exposure material, in assessing the possible practical (in-use) relevance of the exposure conditions, and to allow the most reasonable estimates of hazard. 

Hazard characterization and delineation of dose-effect or dose-response relationships. 3. Assessment of exposure 4. Risk characterization... 

Thus, there is a clear need to establish the relationship between the health effects of hazardous chemical agents in the environment and the level of occupational exposure to the body by means of an occupational exposure limit, in which a reference figure for the concentration of a chemical agent is set. In fact, occupational exposure limits (OELs) have been a feature of the industrialized world since the early 1950s. They were introduced, primarily in the United States, at a time when measures to prevent occupational diseases were considered more beneficial than compensating victims, and in this sense OELs have played an important part in the control of occupational illnesses. 

Stages in hazard characterization according to the European Commission s Scientific Steering Committee are (1) establishment of the dose-response relationship for each critical effect (2) identification of the most sensitive species and strain (3) characterization of the mode of action and mechanisms of critical effects (including the possible roles of active metabolites) (4) high to low dose (exposure) extrapolation and interspecies extrapolation and (5) evaluation of factors that can influence severity and duration of adverse health effects. 

Dose-response assessment is the process of obtaining quantitative information about the probability of human illness following exposure to a hazard it is the translation of exposure into harm. Dose-response curves have been determined for some hazards. The curves show the relationship of dose exposure and the probabihty of a response. Since vahdated dose-response relationships are scarce, various other inputs are used to underpin the hazard characterization phase of risk assessment. 

This relationship clearly shows that risk is a function of both the intrinsic hazard of a chemical and the exposure to that chemical which includes the frequency, duration and... 

Probit Equation The probit equation has been used in an attempt to quantitatively correlate hazardous material concentration, duration of exposure, and probability of effect/injury, for several types of exposures. The objective of such use is to transform the typical sigmoidal (S-shaped) relationship between cause and effect to a straight-line relationship (Mannan, Lees Loss Prevention in the Process Industries, 3d ed., p. 9/68, 2005). 

We have seen that many different factors can contribute to chemical hazard in the workplace. The degree of hazard, however, is fundamentally determined by two factors the basic toxicity of the agent concerned, that is, its intrinsic capacity to damage or affect biological tissue and the severity of the exposure, or what is sometimes called the dose-response relationship. The duration of the exposure, of course, must also be considered. 

Models for determining the dose-response relationship vary based upon the type of toxicological hazard. In the dose-response for chemical carcinogens, it is frequently assumed that no threshold level of exposure (an exposure below which no effects would occur) exists, and, therefore, any level of exposure leads to some finite level of risk. As a practical matter, cancer risks of below one excess cancer per million members of the population exposed (1 x 10 ), when calculated using conservative (risk exaggerating) methods, are considered to represent a reasonable certainty of no harm (Winter and Francis, 1997). 

Effect. There are no specific disease states in humans or animals that have been associated with exposure to 3,3 -dichlorobenzidine. Hemoglobin adducts have been isolated from the blood of 3,3 -dichlorobenzidine-treated animals (Bimer et al. 1990 Joppich-Kuhn et al. 1997). It is not known what relationship exists between adduct levels in the blood and 3,3 -dichlorobenzidine toxicity. Further research in animal models is needed to determine if these adducts could be correlated with effects of 3,3 -dichlorobenzidine exposure. Further studies to identify more sensitive toxic effects (noncancer) that are specific for 3,3 -dichlorobenzidine would be useful in monitoring effects in people living near hazardous waste sites containing 3,3 -dichlorobenzidine. 

Fiber has been given a legal, if not operational definition, at least as it applies to asbestos. Unfortunately tlie definition bears little relationship to the present use of the term. It was essential to set standards to reduce occupational exposure but the detection, identification, and suppression of asbestos materials opened several areas of problems that remain unsolved. For example, six minerals are included in the definition of asbestos. Are they all equally hazardous If not, why not There are many other inorganic particles with diameters of less than 3 micrometers and a diameter-to-length ratio of 1 3. Should we be concerned that they too might be hazardous to our health ... 

Health hazards associated with exposure to fibrous materials have been studied since the turn of the century. Fibers less than 5 microns in diameter are likely to become airborne and, as part of the enviromnent, may be inhaled or ingested. The relationship of fiber size to cell size and function, especially clearance once the fiber is inside the human body, sets off a cascade of events that can, and often does, lead to disease. The dimensions, dose, and durability of inorganic fibers are the salient determinants of disease (Lei-neweber, 1981). 

In spite of the publication of thousands of articles on asbestos, and its role as a hazard, the ability to assess the risks to low-level exposure is limited. Many basie scientific and medical questions remain unanswered. For example, we are still a long way from understanding the material known as asbestos, much less the relationship between it and disease. 

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