Risk assessment hazard index

A similar application of ecotoxicological data is hazard assessment. Unlike risk assessment, hazard assessment is nonprobabilistic and relies upon indices rather than probabilities. One such index is the hazard quotient , which is the ratio of the expected environmental concentration (based upon field surveys or simulation models) divided by a benchmark concentration. The benchmark concentration is derived from some measure of toxicity such as the LC50 or no-observed-effect level. Hazard assessments are often conducted at different levels or tiers of increasing complexity and specificity if a chemical is identified as potentially hazardous by tier (the least complex and specific test), a decision is made to take action or, if more information is needed, to proceed to tier 2 tests. After tier 2 tests, a decision is made whether to take action or proceed to tier 3 tests, and so on. This process is repeated until it is decided that there is enough information to determine whether or not there is significant ecological hazard. If there is, then regulatory action is taken. 

Methods for performing hazard analysis and risk assessment include safety review, checkhsts, Dow Fire and Explosion Index, what-if analysis, hazard and operabihty analysis (HAZOP), failure modes and effects analysis (FMEA), fault tree analysis, and event tree analysis. Other methods are also available, but those given are used most often. 

To assess tlie overall potential for noncarcinogenic effects posed by more dian one chemical, a liazard index (HI) approach has been developed based on EPA s Guidelines for Healdi Risk Assessment of Chemical Mixtures. This approach assumes that simultaneous subtlu eshold exposures to several chemicals could result in an adverse healtli effect. It also assumes tliat tlie magnitude of the adverse effect will be proportional to tlie sum of the ratios of the subtlireshold exposures to acceptable exposures. The non cancer hazard index is equal to tlie sum of the hazard quotients, as described below, where E and tlie RfD represent the same exposure period (e.g., subclironic, clironic, or shorter-term). 

If there are specific data germane to the assumption of dose-additivity (e g., if two compounds arc present at the same site and it is known that the combination is five times more toxic than the sum of the toxicitics for the two compounds), then tire development of the hazard index should be modified accordingly. The reader can refer to the EPA (1986b) mi.xiure guidelines for discussion of a hazjird index equation that incorporates quantitative interaction data. If data on chemical interactions are available, but arc not adequate to support a quantitative assessment, note the information in the assumptions being documented for the risk assessment. 

In health risk assessments, non carcinogenic risks are estimated via Hazard Indices . A general equation for a liazard index (HI) is as follows ... 

The EPA makes decisions about clean-up of abandoned hazardous waste sites under the so-called Superfund law. Risk assessment outcomes are one guide to the decision process. The agency has declared that, for carcinogenic contaminants, clean-up must reach lifetime risks somewhere in the range of one in 10 000 to one-in-one million most decisions seem to aim at risks of one in 100 000 or lower. Hazard index values for non-carcinogens are not expected to exceed one. Costs and technical feasibility figure heavily in these decisions. 

Gros M, Petrovic M, Ginebreda A, Barcelo D (2010) Removal of pharmaceuticals during wastewater treatment and environmental risk assessment using hazard indexes. Environ Int 36 15-26... 

EU. 2007. DG Environment website, http //ec.europa.eu/environment/water/water-drink/index en.html OECD. 2003. Descriptions of Selected Key Generic Terms Used in Chemical Hazard/Risk Assessment. Joint Project with IPCS on the Harmonisation of Hazard/Risk Assessment Terminology. OECD Series on Testing and Assessment No. 44. Environment Directorate, Joint Meeting of the Chemicals Committee and the Working Party on Chemicals, Pesticides and Biotechnology. ENV/JM/MONO(2003)15. Paris OECD. 

A Guide to Health Risk Assessment. California Environmental Protection Agency, Office of Environmental Health Hazard Assessment. Available as a pdf file. Online. Available HTTP (accessed 10 April 2003). 

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. 

In many respects, the foundations and framework of the proposed risk-based hazardous waste classification system and the recommended approaches to implementation are intended to be neutral in regard to the degree of conservatism in protecting public health. With respect to calculations of risk or dose in the numerator of the risk index, important examples include (1) the recommendation that best estimates (MLEs) of probability coefficients for stochastic responses should be used for all substances that cause stochastic responses in classifying waste, rather than upper bounds (UCLs) as normally used in risk assessments for chemicals that induce stochastic effects, and (2) the recommended approach to estimating threshold doses of substances that induce deterministic effects in humans based on lower confidence limits of benchmark doses obtained from studies in humans or animals. Similarly, NCRP believes that the allowable (negligible or acceptable) risks or doses in the denominator of the risk index should be consistent with values used in health protection of the public in other routine exposure situations. NCRP does not believe that the allowable risks or doses assumed for purposes of waste classification should include margins of safety that are not applied in other situations. 

Recently, some models have been derived to analyze the occurrence of interactive joint action in binary single-species toxicity experiments (Jonker 2003). Such detailed analysis models are well equipped to serve as null models for a precision analysis of experimental data, next to the generalized use of concentration addition and response addition as alternative null models. However, in our opinion these models are not applicable to quantitatively predict the combined toxicity of mixtures with a complexity that is prevalent in a contaminated environment, because the parameters of such models are typically not known. Recently a hazard index (Hertzberg and Teus-chler 2002) was developed for human risk assessment for exposure to multiple chemicals. Based on a weight-of-evidence approach, this index can be equipped with an option to adjust the index value for possible interactions between toxicants. It seems plausible that a comparable kind of technique could be applied in ecotoxicological risk assessments of mixtures for single species. However, at present, the widespread application of this approach is prevented by lack of available information. 

NRC (1994) Science and judgment in risk assessment. Committee on Risk Assessment of Hazardous Air Pollutants, Board on Environmental Studies and Toxicology, Commission on Life Sciences, National Research Council. Washington, DC, National Academy Press (http //www.nap.edu/books/030904894X/html/index.html). 

The term toxic unit (TU) plays an important role in mixture concentration-response analysis. It is defined as the actual concentration of a chemical in the mixture divided by its effect concentration (e.g., c/EC50 Sprague 1970). The toxic unit is equivalent to the hazard quotient (HQ), which is used for calculating the hazard index (HI Hertzberg and Teuschler 2002). The term hazard quotient is generally used more in the context of risk assessment (see Chapter 5 on risk assessment), and the term toxic unit is used more in the context of concentration-response analysis, and therefore the latter term is used here. Toxic units are important for 2 reasons. First, toxic units are the core of the concept of concentration addition concentration addition occurs if the toxic units of the chemicals in a mixture that causes 50% effect sum up to 1. Second, toxic units can help to determine which concentrations of the chemicals to test when a mixture experiment needs to be designed. 

Figure 5.12 The principle of tiering in risk assessment simple questions can be answered by simple methods that yield conservative answers, and more complex questions require more sophisticated methods, more data, and more accurate risk predictions. PEC = Predicted Environmental Concentration, PNEC = Predicted No Effect Concentration, HI = Hazard Index, CA = Concentration Addition, RA = Response Addition, TEF = Toxicity Equivalency Factor, RPF = Relative Potency Factor, MOA = Mode of Action, PBPK = Physiologically Based Pharmacokinetic, BRN = Biochemical Reaction Network.

Eisler, R. Handbook of chemical risk assessment health hazards to humans, plants, and animals, metalloids, radiation, cumulative index to chemicals and species, vol. 3, chapter 28, CRC Press, Boca Raton (FL) 2000. 

This text is a comprehensive collection of concise and readable explanations of basic principles in toxicology and the potential hazards of chemicals. It contains more than 1000 entries, including entries related to research and clinical toxicology, risk assessment, ecotoxicology, epidemiology, radiation, noise, information resources, organizations, and education. As with the 1st edition, this volume is extensively cross-referenced, contains a detailed index, and provides numerous references to primary and secondary literature. 

EPA recommends three approaches (1) if the toxicity data on mixture of concern are available, the quantitative risk assessment is done directly form these preferred data (2) when toxicity data are not available for the mixture of concern, data of a sufficiently similar mixture can be used to derive quantitative risk assessment for mixture of concern and (3) if the data are not available for both mixture of concern and the similar mixture, mixture effects can be evaluated from the toxicity data of components. According to EPA, the dose-additive models reasonably predict the systemic toxicity of mixtures composed of similar (dose addition) and dissimilar (response addition) compounds. Therefore, the potential health risk of a mixture can be estimated using a hazard index (HI) derived by summation of the ratios of the actual human exposure level to estimated maximum acceptable level of each toxicant. A HI near to unity is suggestive of concern for public health. This approach will hold true for the mixtures that do not deviate from additivity and do not consider the mode of action of chemicals. Modifications of the standard HI approach are being developed to take account of the data on interactions. 

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