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Risk Assessment Techniques and Methods of Approach
Published in D. Kofi Asante-Duah, Hazardous Waste Risk Assessment, 2021
Traditionally, risk decisions on systemic toxicity have been made using the concept of “acceptable daily intake” (ADI) derived from an experimentally determined NOAEL. The ADI is the amount of chemical (in mg/kg body weight/day) to which a receptor can be exposed to on a daily basis over an extended period of time — usually a lifetime — without suffering a deleterious effect. A NOAEL is an experimentally determined dose at which there has been no statistically or biologically significant indication of the toxic effect of concern. In cases where a NOAEL has not been demonstrated experimentally, the term “lowest observed adverse effect level” (LOAEL) is used. For chemicals possessing carcinogenic potentials, the LADD is compared with the NOEL identified in the long-term bioassay experimental tests; for chemicals with acute effects, the MDD is compared with the NOEL observed in short-term animal studies. In assessing the chronic and subchronic effects of noncarcinogens and also noncarcinogenic effects associated with carcinogens, the experimental dose value (e.g., NOEL values) is typically divided by a safety (or uncertainty) factor to yield an RfD (or ADI).
Risk Assessment of Metals in Groundwater
Published in Herbert E. Allen, E. Michael Perdue, David S. Brown, Metals in Groundwater, 2020
Reva Rubenstein, Sharon A. Segal
As part of the evaluation of a dose-response relationship, a NOAEL (No Observed Adverse Effect Level), if possible, or a LOAEL (Lowest Observed Adverse Effect Level) may be determined. The NOAEL is defined as the highest experimental dose of a chemical at which there is no statistically or biologically significant increase in frequency or severity of a toxicological effect between an exposed group and its appropriate control. Adverse effects are defined as any effects that result in functional impairment and/or pathological lesions that may affect the performance of the whole organism or that reduce an organism’s ability to respond to an additional challenge. In general, NOAELs for several different toxicological endpoints will differ. Everything else being equal, the critical end point is the one with the lowest NOAEL. In some instances, the NOAEL for the critical toxic effect is simply referred to as the NOEL (No Observed Effect Level). This latter term, however, is ambiguous because there may be observable effects that are statistically significant but are not considered to be of biological or toxicological significance and thus are not “adverse”. This is often a matter of professional judgment.
Human Health Risk Assessment
Published in Lorris G. Cockerham, Barbara S. Shane, Basic Environmental Toxicology, 2019
The critical study used in the calculation of an RfD is one having the lowest exposure level at which a statistical or biological increase in an adverse effect has been demonstrated. The EPA default position is that humans are as equally sensitive as the most sensitive animal species unless scientific evidence is available to decide otherwise. In determining the RfD, the highest dose level which did not produce an effect or the dose which did produce an effect is divided by uncertainty factors to provide a margin of safety for allowable human exposure. The no observed adverse effect level (NOAEL) is the highest dose tested that did not produce an effect. Effects may vary from lethality to minor functional decrements. When a NOAEL is not available, a lowest observed adverse effect level (LOAEL) can be used to calculate the RfD. A dose response for noncarcinogenic effects is illustrated in Figure 21.2 which also identifies the threshold, NOAEL, and LOAEL. Any toxic effect might be used for the NOAEL or LOAEL so long as it is the most sensitive toxic effect and considered likely to occur in humans.
Exposure to lead, mercury, styrene, and toluene and hearing impairment: evaluation of dose-response relationships, regulations, and controls
Published in Journal of Occupational and Environmental Hygiene, 2020
Research was reviewed to find if there were any relationships between exposure to substances of interest and hearing impairment. When significant associations were identified, exposure levels were evaluated to determine whether concentrations associated with increased risk of hearing loss could be identified including the No Observed Adverse Effect Level (NOAEL) and/or the Lowest Observed Adverse Effect Level (LOAEL). NOAEL is the highest exposure level at which there are no statistically significant increases in the frequency or severity of adverse effects between the exposed group and its appropriate control. LOAEL is the lowest exposure level at which there are statistically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control (Lewis et al. 2002).
Hazard characterization of silver nanoparticles for human exposure routes
Published in Journal of Environmental Science and Health, Part A, 2020
A number of studies have been conducted on AgNP toxicity in animal models. In the last decade, a number of these nanoparticle toxicity studies have gained attention due to increased public concern regarding the seemingly unlimited applications in the market. Acute toxicity studies determine metric values such as LD50 (lethal dose 50) (single dose or 14 days). A deeper analysis in subacute toxicity studies (28 days) further identified specific effects. The NOAEL (no observable adverse effect level) can be determined by subchronic toxicity studies (90 days). In Europe, the OECD (the organization for economic co-operation and development) guidelines provided protocols for studying chemical toxicity. OECD Guidelines (No. 401—413) have been used in identifying health effects of AgNPs through oral, dermal and inhalation pathways over different exposure periods. However, the evaluation of nanoparticle in the category of chemicals causes difficulty. Therefore, OECD has provided guidelines for characterizing physical and chemical properties for studying nanoparticles,[22] and updated related protocols to enable testing and characterization of the effects of nanomaterials.[23] In vivo toxicity studies have provided a means of hazard characterization by exploring dose-response relationships of pharmacokinetics and toxic performances on targeting tissues, which are shown in Figure 1.
Application of the Draft NIOSH Occupational Exposure Banding Process to Bisphenol A: A case study
Published in Journal of Occupational and Environmental Hygiene, 2019
Cynthia J. Hines, Thomas J. Lentz, Lauralynn McKernan, Pranav Rane, Christine Whittaker
In conducting this case study of BPA, we also informally assessed the effort and knowledge needed to conduct a Tier 1 and Tier 2 assessment by an experienced, certified industrial hygienist (author CJH). Assigning an OEB for BPA under Tier 1 was straightforward and most OS&H professionals should be able to conduct a Tier 1 assessment easily. The effort and knowledge needed to complete Tier 2 varied by endpoint for BPA. The reproductive toxicity endpoint had the most data to review under the Draft NIOSH Occupational Exposure Banding guidelines and was the most time consuming of the endpoints to assess. Studies with no observable adverse effects levels (NOAELs) for the reproductive toxicity endpoint were numerous and the effects diverse (Table 3). The Draft NIOSH Occupational Exposure Banding process weights NOAELs for all effects equally (i.e., a particular effect is not considered more or less important than another effect). For some studies, including some GLP studies, the reported NOAELs could not be used because the NOAEL was expressed as “greater than” a certain value. Such values are not used in the Draft NIOSH banding process.