Measuring environmental concentrations MECs

As mentioned before, environmental exposure is the first key aspect to develop risk characterization from a defined scenario (see Fig. 1). Experimental analysis is the most obvious and classical procedure for determining the chemical occurrence in the environment. Measuring environmental concentrations (MECs) is more accurate and reflects the reality better than any other method, but the main drawback is the large amount of resources required for these laboratory measurements. Field environmental monitoring programs have become increasingly expensive as... 

MEC measured environmental concentrations ( ig L ), PNEC predicted no effect concentration, REEmec literature reference for the MEC value, REEnmc literature reference for the PNEC value... 

Risk characterization based on comparing either predicted or measured environmental concentrations with effects data for the most sensitive organisms (PEC/ PNEC or MEC/PNEC, respectively). An environmental risk is considered unacceptable if the ratio equals or exceeds 1. In general, this phase considers the worst-case scenario. 

Exposure assessment, quantification or prediction of environmental concentrations of the substance based on on-site measurements (MEC) or its projected fate and behaviour (PEC), respectively. 

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. 

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