Hazard assessment exposure pathways

One should identify exposure pathways that have the potential to expose the same individual or sub-population at the key exposure areas evaluated in the exposure assessment, making sure to consider areas of highest exposure for each patliway for both current and future land-uses (c.g., nemest down-gradient well, nearest dowiuvind receptor). For each pathway, the risk estimates and hazard indices have been developed for a particular exposure area... 

Metal Emission Limits. Limits for metals, both carcinogenic and noncarcinogenic, are based on an adjusted stack height. Failure to meet these limits requires risk assessments using site specific factors and modeling to establish limits for each metal. The assessments are based on the probability of developing adverse health effects or cancer, based on an inhalation exposure pathway to maximum exposed individuals located near the incinerator (see Hazard ANALYSIS AND RISKASSESSL nt). 

In general, calculation of the risk or dose from waste disposal in the numerator of the risk index in Equation 6.2 or 6.3 involves the risk assessment process discussed in Section 3.1.5.1. As summarized in Section 6.1.3, NCRP recommends that generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites should be used in calculating risk or dose for purposes of waste classification. Implementation of models describing exposure scenarios for inadvertent intruders at waste disposal sites and their associated exposure pathways generally results in estimates of risk or dose per unit concentration of hazardous substances in waste. These results then are combined with the assumptions about allowable risk discussed in the previous section to obtain limits on concentrations of hazardous substances in exempt or low-hazard waste. 

For each generic exposure scenario to be used in classifying waste, and taking into account all relevant exposure pathways in each scenario, calculate the dose per unit concentration of each hazardous substance in the waste. These doses generally would be the highest values calculated over an assumed time frame for the risk assessment (see Section 6.4.5.3), taking into account the time-dependence of the concentrations of hazardous substances in the waste. For example, the quantity calculated for radionuclides would be the annual effective dose (sievert) per unit activity concentration (Bq nr3), and the quantity calculated for hazardous chemicals would be the dose (intake, mg kg 1 d-1) per unit concentration (kg m 3). 

In some complex risk assessments (e.g., for hazardous waste sites), risk characterization must consider multiple chemical exposures and multiple exposure pathways. Simultaneous exposure to several chemicals, each at a subthreshold level, can often cause adverse effects by the simple summation of injuries. 

Cumulative Assessment Group (CAG) A subset of chemicals selected from a common mechanism group for inclusion in a refined quantifative estimate of risk. The chemicals in the CAG, as well as their pathways/routes and pesticide uses, are judged to have a hazard and exposure potential that could result in the expression of a cumulative risk. Thus, negligible contributors are not included in quantifying the risk (USEPA, 2002). 

More specific data on levels in the environment around those particular sites where manganese is believed to have been dumped would be helpful in determining the extent of exposure levels around such waste sites. In particular, data on the concentration of manganese in the air around hazardous waste sites would be valuable in assessing the potential significance of this exposure pathway. 

Before any pesticide can be authorized for use, its human and environmental safety have to be considered through risk assessment i.e., a comparison of hazard and exposure. A key element in the risk assessment process is the determination of the residue definition, i.e., the components of the residue resulting from the use of the pesticide that are considered to be relevant. Residues remaining on items for food and feed are identified in metabolism studies, in which the pesticide is radiolabeled to enable its fate and behavior to be followed. The metabolic pathways can be extremely complex but can be grouped into four distinct categories or phases [1],... 

Assess how you might be exposed to these hazards. There are a limited number of exposure pathways and you need to focus on how to prevent these exposures. Keep in mind that if your assessment shows that there is a very good chance of being exposed to a hazard, then you need to rethink how you are doing this and find a better, safer way to do this experimental work. Incident 6.3.3.1 illustrates this point. If the researcher had not done this before, she should have used a much smaller scale reaction to gain valuable experience. Always consider doing experiments on a small scale initially. Always be more cautious with large scale reactions since their dynamics are often different than smaller scale reactions. 

Assess how you might be exposed to these hazards. There are a Umited number of exposure pathways and you need to focus on how to prevent these exposures. What is the risk of fire, explosions, spills, high pressure, skin exposure, gas release, eye exposure, and so on ... 

To summarize the noncancer health risk-assessment process, chemicals of concern, pathways of exposure, and exposed populations are identified in the first step of the risk assessment, hazard identification. In the second step, analysis of exposure, the doses are estimated for each population, each exposure pathway, and each chemical of concern in the form of chronic daily intakes, or CDIs. In the third step of the risk assessment, analysis of effect, noncancer health effects are estimated by comparing CDIs to reference doses, or RfDs, derived from animal toxicity studies (with input from human epidemiological studies, when available). If the CDI is greater... 

The chronic daily intake (CDI) estimated in the analysis of exposure, the second step of the risk assessment, is used to calculate the risks of both noncancer health effects and cancer. Risk calculations are also referred to as quantitative risk assessment, a term that is somewhat misleading because the word quantitative implies a high degree of accuracy, which is clearly not the case. In the first risk scenario described in Section 8.3, future residents drink arsenic-contaminated water from the aquifer beneath a former Superfund site. Their CDI by this pathway is estimated to be 0.0I6I mg/kg/day of arsenic. The oral reference dose (RfD) for arsenic is 3 x lO"" mg/kg/day, according to the EPA s Integrated Risk Information System (IRIS) (U.S. EPA 2009). The hazard index (HI) for noncancer health effects caused by this chemical of concern by this exposure pathway is calculated using Equation (8.3) ... 

Fate studies identify the type of compounds and their exposure concentration at different points in the ecosystem and the organism(s) at greatest risk of exposure. The toxicant released into the environment can reach humans through a number of pathways (Figure 11.10). Although greatest immediate attention should be paid to human health, ultimate human welfare may depend on the overall quality of the ecosystem. Future environmental hazard assessment should be based on comparative toxicology. 

Generally, the main pathways of exposure considered in tliis step are atmospheric surface and groundwater transport, ingestion of toxic materials that luu c passed tlu-ough the aquatic and tcncstrial food chain, and dermal absorption. Once an exposure assessment determines the quantity of a chemical with which human populations nniy come in contact, the information can be combined with toxicity data (from the hazard identification process) to estimate potential health risks." The primary purpose of an exposure assessment is to... 

Measurement of exposure can be made by determining levels of toxic chemicals in human serum or tissue if the chemicals of concern persist in tissue or if the exposure is recent. For most situations, neither of these conditions is met. As a result, most assessments of exposure depend primarily on chemical measurements in environmental media coupled with semi-quantitative assessments of environmental pathways. However, when measurements in human tissue are possible, valuable exposure information can be obtained, subject to the same limitations cited above for environmental measurement methodology. Interpretation of tissue concentration data is dependent on knowledge of the absorption, excretion, metabolism, and tissue specificity characteristics for the chemical under study. The toxic hazard posed by a particular chemical will depend critically upon the concentration achieved at particular target organ sites. This, in turn, depends upon rates of absorption, transport, and metabolic alteration. Metabolic alterations can involve either partial inactivation of toxic material or conversion to chemicals with increased or differing toxic properties. 

As discussed above, the risk of chemicals in the environment is dependent on both exposure and toxicity. Pathways through which organisms in the environment are exposed to chemicals are therefore key determinants of how safe (and therefore, how green ) a chemical is, and must be considered in moving towards a reduced risk or hazard approach to the production and use of chemicals. Fate in the environment is the principal determinant of exposure and designing chemicals for reduced hazard and risk to the environment involves consideration of processes that affect the chemical in the environment, in addition to toxicity. Assessment of environmental fate, including design of chemicals for nonpersistence, is discussed in detail in Chapter 16. 

Exposure Assessment. In exposure assessment, the population potentially exposed to hazardous substances and the pathways and routes through which exposure could occur are specified, and the magnitude, duration, and timing of the doses people might receive are quantified. The approach to exposure assessment for hazardous waste disposal can range from very sophisticated and complex e.g., Wilson et al., 1994) to a multiplication of simple factors (e.g., Dornsife, 1995 EG G, 1982 EPA, 1989 Smith et al., 1980). Exposure assessment for waste disposal is itself a multi-step process, and is discussed below. 

While the actinides Pu, Am, Np and Cm are critically important to assessments of the exposure of humans to environmental sources of radioactivity due to their highly hazardous a emissions, the role which the plant root absorption pathway plays in this exposure is relatively small. A conservative estimate of the degree to which plants will incorporate Pu from soil, for instance, is 10% (ie, a soil-to-plant transfer factor of... 

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