Risk assessment hazard quotient

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. 

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). 

In the case of noncarcinogenic substances, there exists a threshold this is an exposure with a dose below which there would not be adverse effect on the population that is exposed. This is the reference dose (RfD), and it is defined as the daily exposure of a human population without appreciable effects during a lifetime. The RfD value is calculated by dividing the no observed effect level (NOEL) by uncertainty factors. When NOEL is unknown, the lowest observed effect level (LOEL) is used. NOEL and LOEL are usually obtained in animal studies. The main uncertainty factor, usually tenfold, used to calculate the RfD are the following the variations in interspecies (from animal test to human), presence of sensitive individuals (child and old people), extrapolation from subchronic to chronic, and the use of LOEL instead of NOEL. Noncancer risk is assessed through the comparison of the dose exposed calculated in the exposure assessment and the RfD. The quotient between both, called in some studies as hazard quotient, is commonly calculated (Eq. 2). According to this equation, population with quotient >1 will be at risk to develop some specific effect related to the contaminant of concern. 

For the ecological assessment, risk analysis was based on the traditional PEC/ PNEC ratio (Hazard Quotient) where PEC is the predicted environmental concentration (resulting from chemical analysis) and PNEC the predicted no-effect concentration. Ecological assessment for aquatic species was based on rainbow trout or fathead minnow while terrestrial assessment was based on small rodents like mice rats and rabbits. Exposures associated with HQ<1 were considered negligible. 

Campbell PJ, Brown KC, Harrison EG et al (2000) A hazard quotient approach for assessing the risk to non-target arthropods from plant protection products under 91/414/EEC hazard quotient trigger value proposal and validation. J Pest Sci 73 117-124... 

In the final phase of risk analysis—risk characterization—one integrates outputs of effects and exposure assessments. Risk is expressed in qualitative or quantitative estimates by comparison with reference values (e.g., hazard quotient). The severity of potential or actual damage should be characterized with the degree of uncertainty of risk estimates. Assumptions, data uncertainties and limitations of analyses are to be described clearly and reflected in the conclusions. The final product is a report that communicates to the affected and interested parties the analysis findings (Byrd and Cothern, 2000). 

The risk evaluation involves comparing the predicted environmental concentrations (PECs) with the predicted no effect concentrations (PNECs) and is expressed as a hazard quotient for the aquatic environment (Table 3.1). This quotient will indicate the necessity for further refinement of the risk assessment or eventually for risk reduction. 

Volosin JS, Cardwell RD. 2002. Relationships between aquatic hazard quotients and probabilistic risk estimates what is the significance of a hazard quotient > 1 Human Ecol Risk Assess 8 355-368. 

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. 

Such threshold values are often estimated using no-observed-effect concentrations or levels (NOECs or NOELs). It might be tempting to substitute the individual ECx values in the CA equation (Equation 4.2) with NOELs in order to calculate a mixture NOEL. But this would imply that all NOELs provoke the same, statistically insignificant effect that is, all of them must have been determined in an identical experimental setup (in terms of number of replicates, spacing of test concentrations, variance structure), which is hardly ever the case. Nevertheless, a range of methods, such as TEFs or TEQs (see Chapters 1 and 5), makes use of a CA-like approach and sums up NOEL-based hazard quotients. This introduces an additional source of uncertainty in the risk assessment, which is fundamentally different from the question of whether CA is an appropriate concept for the mixture of interest. 

If the mixture of concern consists of a set of toxicologically well-characterized fractions, the mixture may be fractionated and its risk can be assessed based on the risks of the individual fractions for example, the hazard quotients for the individual fractions can be combined using a HI calculation that accounts for the combined action of the fractions. An example involves the fractionation of total petroleum hydrocarbons (TPHs) at contaminated sites for use in risk assessment. In this approach the TPH at a site is divided into analytically defined fractions, and then oral and inhalation toxicity values are assigned to these fractions for use in risk assessment (MADEP 2002,2003). A single surrogate chemical from each fraction is used to represent the risk for the entire fraction. The method does not totally account for all of the unidentified material, but does reflect differences in chemical composition across various sites and provides a reasonable method for calculating potential health risks. 

Hazard Index Approach A chemical mixtures risk assessment method where hazard quotients for component chemicals are only developed using the critical effect. Hazard quotient values are grouped by critical effect and summed. Multiple hazard indexes are developed, one for each affected target organ or system. 

Lemly AD. 1996. Evaluation of the hazard quotient method for risk assessment of selenium. 

An appropriate risk assessment is required where the hazard quotient is >50, further testing may be required (see above). 

The comparison of dosimetric quantities Sav and Eav with corresponding action values served for assessing risk acceptability. If the hazard quotient HQ is defined... 

The first method observed current standards. Risk assessment was based on comparing measured averaged values of power density designated as Sav with the effective action value of power density Sr = 50 W.m . The ratio of both values served for the assessment of the hazard quotient HQ which was overshot only once out of nine posts observed. The value for this post amoimted to HQ3 = 2.65. 

The ambient exposure concentration (AEC) of PAH in soil was compared with the published toxicolog-icaUy effective concentration (TEC). The value of the detected non-dimensional hazard quotient (HQ) is either lower or higher than 1 and represents the situation with either acceptable or non-acceptable risk requiring further assessment. 

When assessing the risks according to the Decree (Ministry of the Environment of the Czech Republic. 1994) for agriculmral soils the limits were exceeded for the total content of PAH only in samples T5 - T9. The Hazard Quotient (HQ) value did not exceed 2,8 and the quality of soil was very good with regard to the fact how the locations are utilized. 

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