Hazard Quotient

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. 

The calculation of hazard quotients (HQs) was a useful tool to estimate the hazards that the occurrence of PhACs may pose to aquatic organisms. It was estimated that the overall relative order of susceptibility was algae>daphnia>fish. Results indicated that the reduction of pharmaceuticals concentration after wastewater treatment, as well as the dilution factor once they are discharged into the receiving river waters, efficiently mitigates possible environmental hazards. Nevertheless, risks are expected to be higher in areas with low river flow. 

Han, B.H., W.L. Jeng, R.Y. Chen, G.T. Fang, T.C. Hung, and R.J. Tseng. 1998. Estimation of target hazard quotients and potential health risks for metals by consumption of seafood in Taiwan. Arch. Environ. Contam. Toxicol. 35 711-720. 

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). 

Hazard quotient (HQ), 25 238 Hazards. See also Fire hazards Radiation hazards Safety entries assessments of, 27 839, 846 of ethylene-propylene polymers, 10 716 of hydrogen peroxide, 14 61-63 oxygen-related, 17 760-761 penalties for, 73 155-156 recognition in industrial hygiene, 74 205-213... 

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. 

Table 1 Estimation of hazard quotients (HQ) for different sulfonamides following the EMEA guidelines...

If a nonlinear dose-response function has been determined, it can be used with the expected exposure to estimate a risk. If an RfD or RfC is calculated, the hazard can be expressed as a Hazard Quotient (HQ), defined as the ratio of an exposure estimate over the RfD or RfC, i.e., HQ = Exposure/(RfD or RfC). 

Quantifying Risk for Noncarcinogenic Effects Hazard Quotient... 

The measure used to describe the potential for noncarcinogenic toxicity to occur is not expressed as the probability. Probabilistic approach is used in cancer RA. For noncancer RA, the potential for noncarcinogenic effects is evaluated by comparing an exposure level (E) over a specified time period with a reference dose (RfD). This ratio is called a hazard quotient ... 

Table 1.2 Hazard quotient (Q) values for some common chemical by-products.

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