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Question 2
What is the hazard quotient, and at what stage of the risk assessment process is it used? Discuss the three possible levels of the hazard quotient and how the hazard is evaluated if a mixture of chemical exposures is being assessed. Your response should be at least 200 words in length. You are required to use at least your textbook as source material for your response. All sources used, including the textbook, must be referenced; paraphrased and quoted material must have accompanying citations.
Question 3
Differentiate between the roles of risk managers and risk assessors according to the EPA’s Guidance for Risk Characterization. Your response should be at least 200 words in length. You are required to use at least your required reading as source material for your response. All sources used, including the textbook, must be referenced; paraphrased and quoted material must have accompanying citations.
Question 4
Describe the elements of effective risk communication. Discuss one example of a risk that the general public tends to over- or underestimate. How might the elements of risk communication be used to give a clearer picture of the true risk in your example? Your response should be at least 200 words in length. You are required to use at least your textbook as source material for your response. All sources used, including the textbook, must be referenced; paraphrased and quoted material must have accompanying citations.
Learning Objectives
Upon completion of this unit, students should be able to:
1. Discuss the difference between risk managers and risk assessors.
2. Identify and discuss the four main steps of risk assessment.
3. Evaluate the role of uncertainty and variability in risk assessment.
4. Discuss the elements of risk communication to the general public.
5. Evaluate the differences between conducting risk assessments for carcinogenic and non-carcinogenic substances.
6. Define the hazard quotient and discuss how it is used to evaluate the overall risk associated with a substance.
7. Define common terms encountered in performing a risk assessment.
Written Lecture
After the toxicity and epidemiological data on a chemical has been collected, how do we decide what levels are safe for public health and the environment? Regulators use the process of risk assessment to set pollutant emission levels based on the benefits and consequences to society. In setting these limits, the exposure to the pollutant, as well as its toxicity, are considered. However, as Phalen & Phalen (2013) point out, there are gaps in the toxicity data due to the fact that most of the data is for large exposures. Our everyday exposure is more moderate, and there is uncertainty regarding the extrapolation of the high-exposure data to lower levels of exposure.
There are four main steps involved in risk assessment. Those steps are (1) hazard identification, (2) hazard assessment, (3) exposure assessment, and (4) risk characterization. During the hazard identification stage of a risk assessment, toxicolological, biological, epidemiological, and chemical data is examined to determine how toxic a substance is and what effects if will have on health. The hazard identification of carcinogens is difficult because the effects of certain carcinogens might not be seen for many years after the exposure (Phalen & Phalen, 2013). There are several different classification systems for carcinogens. One main system, used by the EPA, divides carcinogens into seven categories. Following is the general classification system:
•human carcinogen,
•probable human carcinogen,
•possible human carcinogen,
•not classifiable as to human carcinogenicity, and
•evidence of non-carcinogenicity in humans (Phalen & Phalen, 2013).
After analyzing the hazards associated with a pollutant, the hazard assessment stage begins. Phalen & Phalen (2013) identify two main goals of a hazard assessment: (1) to establish a dose-response relationship and (2) to define an acceptable exposure threshold or dose. There are both non-cancer and cancer processes. During a non-cancer assessment, a level is determined below which it is unlikely that health effects will occur. In a cancer assessment, however, it is generally assumed that there is no safe level of exposure. The EPA’s goal is to reduce cancer risk to less than one in a million per year (Phalen & Phalen, 2013).
The next step in the risk assessment is the exposure assessment. After the completion of the hazard identification and the hazard assessment, the relative toxicity and the acceptable exposure level has been established. Now, an estimate of the population exposure must be made. There are a variety of potential pollutant sources, some of which we have discussed in previous units (stationary sources, point sources, non-point sources, mobile sources, etc.). In addition to identifying the potential sources of community exposure, the routes of exposure must also be identified. Inhalation is the major route of exposure for air pollutants. However, particles may also deposit on soil or in waterways. The pollutant can then be ingested when we eat or drink. These exposures can be measured through environmental monitoring, personal monitoring, historical exposure records, or mathematical models (Phalen & Phalen, 2013). For example, Hart et al. (2009) studied the association between the incidence of rheumatoid arthritis and the exposure to traffic pollution. To assess the subject’s exposure, the distance to a road was analyzed. In this particular study, a correlation between traffic pollution exposure and rheumatoid arthritis was found.
Lastly, during the risk characterization, the information collected in the first three steps of the risk assessment (hazard identification, hazard assessment, and exposure assessment) can be analyzed to determine the overall risk of exposure to the pollutant. When the exposure concentration is divided by the acceptable threshold (if they are in the same unit of measurement), the hazard quotient is calculated. A quotient greater than one indicates that exposure exceeds the acceptable level, and a quotient less than one indicates that the exposure is below the acceptable level.
There are many uncertainties in the risk assessment process, but it provides a process by which regulators can analyze the available data about the toxicity of a pollutant and combine that information with exposure levels to determine whether or not the public health is being protected. However, communicating the meaning of the calculated risk to the public can be a difficult task. Humans often inaccurately over- or underestimate risks and make decisions about which risks to take based on emotion rather than data. Phalen & Phalen (2013) suggest several techniques for overcoming this communication barrier, including avoiding appeals to emotion, comparing alternative technologies, and making comparisons to other risks.
References
Hart, J. E., Laden, F., Puett, R. C., Costenbader, K. H., & Karlson, E. W. (2009). Exposure to traffic pollution and increased risk of rheumatoid arthritis. Environmental Health Perspectives, 117(7).
Phalen, R. F., & Phalen, R. N. (2013). Introduction to air pollution science: A public health perspective. Burlington, MA: Jones & Bartlett Learning.
Additional Required Reading
See attachment
UnitVIIReadingAssignment_GuidanceforRisk
