Risk assessment minimal effect levels

Risk assessment is a scientific process whereby the level and nature of the risk is determined. If there is no exposure to a particular chemical then there will be no risk at all, for example potassium cyanide in a sealed container is a hazard but not a risk. Risk can therefore be minimized if exposure is minimized. If the chemical is effectively non-hazardous, that is the amount needed to cause harm is unrealistically high, such as with common salt or saccharin, then even if there is a level of exposure, the risk will be so small as to be virtually non-existent. Therefore both the level of exposure and the nature of the chemical (whether or not it is hazardous) must be known if the risk is to be assessed. 

The main focus of the ecological risk assessment is to minimize undesired events caused by chemicals. Species sensitivity distribution (SSD) is an example of an ecotoxicological method which is based on such events at above the no-effect level/concentration. We can assume that within a community species differ in... 

The initial process in the application of toxicity (dose-response) data in risk assessment is the extrapolation of findings to establish acceptable levels (AL) of human exposure. These levels may be reference values (inhalation reference concentrations, RfC or oral reference doses, RfD), minimal risk levels (MRL) values, occupational exposure limits, and so on. When the toxicity data are derived from animals, the lowest dose representing the NOAEL (preferably) or the LOAEL defines the point of departure (POD). In setting human RfD, RfC, or MRL values, the POD requires several extrapolations (see [13] and revisions). Extrapolations are often made for interspecies differences, intraspecies variability, duration of exposure, and effect level. Each area is generally addressed by applying a respective uncertainty factor having a default value of 10 their multiplicative value is called the composite uncertainty factor (UF). The UF is mathematically combined with the dose at the POD to determine the reference value ... 

Minimal Risk Levels, Critical Effects, and Cancer Assessments for Fractions of TPH... 

Tables (6-1 through 6-11) and Figures (6-1 through 6-16) summarize health effects and illustrate graphically levels of exposure associated with those effects. These levels cover health effects observed at increasing dose concentrations and durations, differences in response by species, minimal risk levels (MRLs) to humans for noncancer end points, and EPA s estimated range associated with an upper- bound individual lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. Use these tables and figures for a quick review of the health effects and to locate data for a specific exposure scenario. The Critical Effects tables and Exposure Assessment figures in Chapter 6 should always be used in conjunction with the text. All entries in these tables and figures represent studies that provide reliable, quantitative estimates of No-Observed-Adverse-Effect Levels (NOAELs), Lowest-Observed-Adverse-Effect Levels (LOAELs), or Cancer Effect Levels (CELs).

In some labs and in many industrial environments, however, there can be significant costs (in time and money) in reducing the risk level. Those who manage risk, which may be laboratory workers or their supervisors (who may or may not have technical training), have to make decisions about how to minimize risks and these are sometimes difficult judgment calls. Many incidents have been described throughout this book where the risk assessment and risk management processes simply did not work effectively. 

Estimates of exposure levels posing minimal risk to humans (MRLs) have been made, where data were believed reliable, for the most sensitive noncancer end point for each exposure duration. MRLs include adjustments to reflect human variability and, where appropriate, the uncertainty of extrapolating from laboratory animal data to humans. Although methods have been established to derive these levels (Barnes et al. 1987 EPA 1989a), uncertainties are associated with the techniques. Furthermore, ATSDR acknowledges additional uncertainties inherent in the application of these procedures to derive less than lifetime MRLs. As an example, acute inhalation MRLs may not be protective for health effects that are delayed in development or are acquired following repeated acute insults, such as hypersensitivity reactions, asthma, or chronic bronchitis. As these kinds of health effects data become available and methods to assess levels of significant human exposure improve, these MRLs will be revised. 

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