Risk quotients

The risks of NP have been evaluated in a recent risk assessment report from the EC states [10]. According to this document, currently there exists no limit value for NP in the EU. The document provides a PEC from model calculations at the regional scale of 0.6 pg L-1, as well as a PNEC of 0.33 pg L-1. Hence, for NP the risk quotient (PEC/PNEC) amounts to 1.8. 

The environmental risk assessment approach most commonly adopted consists of estimation of the risk quotient (RQ) (as suggested by Hernando et al. [103]), which is defined as the ratio between the environmental concentration (measured or predicted, respectively MEC and PEC) and the predicted no-effect concentration (PNEC), and can be used to collocate compounds in one of three risk bands RQ < 0.1, minimal risk to aquatic organisms 0.1 < RQ < 1, median risk and RQ > 1, high risk [103—105]. In their risk assessment calculations, [106], further to [107], estimated PNEC values at 1,000 times lower than the most sensitive species assayed, so as to take into account the effect on other, potentially more sensitive, aquatic species to those used in toxicity studies. 

Escher et al. [49] also proposed that PNEC calculations for mixtures could be based on a common species, assuming concentration addition for risk assessment. They suggested assessing the risk to algae, daphnia and fish individually for each of the n monitored compounds present in the water and then selecting the species with the highest resulting RQmix defined by (3). In this way, the risk quotients of the individual pharmaceuticals can be added up to yield a sum risk quotient (RQmix)-... 

Expanding the assessment parameters somewhat, however, the individual substance risk quotients reported in the literature show that the most critical compounds in hospital effluents are certain antibiotics, anti-neoplasties and disinfectants. Among these, antibiotics merit special attention due to their biological activity, which leads to their potential to generate multi-resistant bacteria, even in the presence of weak... 

Selection of the top-ten chemicals in the first step should be based on the level of exposure and level of toxicity of the individual chemicals. The higher the value of the risk quotient (RQ) the higher the probability of adverse health effect in humans (e.g., higher risk) and the higher the... 

Select a limited number of chemicals (e.g., ten) with the highest risk potential, using the risk quotient (RQ)... 

Safety or uncertainty factors are often applied at the end of an assessment, for example, as a level of concern to which a risk quotient or toxicity-exposure ratio is compared. 

Table 8.4 Predicted environmental concentrations (PECs), predicted no-effect concentrations (PNECs), and risk quotients (RQs) for nano-Ag, nano-Ti02, and CNTs in the environmental compartments air, water, and soil calculated in a realistic (RE) and a worst-case (HE) scenario.

Single-species test result to population Populations to community Risk quotient concentration addition Empirical... 

No addition Risk quotient concentration addition SSD concentration addition Do not evaluate mixture toxicity TU, TEQ, TEF, and CCU addition msPAF CA... 

The risk quotient (RQ) for each combination of contaminant and receptor (plant or animal) of concern is calculated by dividing the estimated environmental concentration (EEC) by the toxicity reference value (TRY) ... 

Risk Quotient Method of Risk Assessment and Its Limitations.34... 

RISK QUOTIENT METHOD OF RISK ASSESSMENT AND ITS LIMITATIONS... 

An important question is Can population modeling tell us anything different from the quotient method with individual endpoints of toxicity Before we try to answer this question, another question must be asked Does the risk quotient method work for the protection of populations It seems that if a population suffers only acute mortality, then the quotient method should work. However, exposure to toxicants can result not only in mortality but also in multiple sublethal effects. Additionally, effects on populations can different greatly from effects in individuals (Stark 2005). A comparison of risk quotients for several chemicals and species to population-level effects showed that the quotients using acute mortality and an EEC work well for some species-chemical combinations but not for others (Stark unpublished). Furthermore, the same level of mortality in 2 species may result in very different outcomes due to differences in life history strategies (Stark et al. 2004), and thus even a simple measure of mortality among species may not provide enough information to protect a population. 

USEPA] US Envirionmental Protection Agency. 2007b. Appendix F the risk quotient method and levels of concern. Available from http //www.epa.gOv/espp//litstatus/effects/ appendix f rq method and locs.pdf. 

Up to now it did not show possible to harmonise the risk quotient approach internationally ... 

In order to determine the mixture risk quotients for each of the study sites on each sampUng occasion, data were obtained from the literature on the ecotoxicity of the parent compounds to fish and daphnids. Experimental ecotoxicity data were also obtained for the transformation products where available. In instances where experimental data were not available for the transformation products, estimates of ecotoxicity were obtained using the predictive approach of Escher which is described in the previous section. Experimental and predicted ecotoxicity data were then used alongside the monitoring data to calculate mixture risk quotients for each of the sampHng sites on each sampling occasion for fish and daphnids. The mixture risk quotients were calculated a) using only the parent compound occurrence data and b) the parent compound and transformation product data. 

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