Evaluation of Bioassays and Wastewater Quality ... - Oekotoxzentrum

5. Evaluation of wastewater quality regarding micropollutants and
their effects
In environmental risk assessment, risk quotients are used to evaluate whether measured
concentrations of environmental chemicals pose a risk to the environment. Those quotients are
calculated by dividing the MEC (measured environmental concentration) by the respective quality
criterion (QC) (usually the annual average environmental quality standard, AA-EQS or the MAC-
EQS), which takes into account ecotoxicological effect data for the respective substance (see
below).
MEC
Risk quotient (RQ) � � ?
QC
1 intolerable risk
A risk quotient lower than 1 indicates a tolerable risk, whereas a risk quotient higher than 1
indicates an intolerable risk. The Annual Average-EQS (AA-EQS) is derived as a protection
against the effects of long-term exposure, and the Maximum Acceptable Concentration EQS
(MAC-EQS) against the effects of short-term exposure.
For an assessment of the wastewater quality, risk quotients were calculated for the three priority
substances diclofenac, carbamazepin and clarithromycin using the MECs (usually the 90 th
percentile) and the derived EQS (Götz et al., 2010). More detailed information on the derivation
of water quality criteria as well as on the classification of risk quotients for this purpose according
to Götz et al. (2010) can be found in the appendix.
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