## 3 Derivation of Water Quality Criteria and Relevant Fish Assay
### European Commission  
The European Commission has developed a strategy for the Water Framework Directive (WFD) [33]; the WFD requires the identification of priority substances with significant risks to aquatic environments. Since 2001, the European Commission has conducted chemical assessments of waterbodies alongside tests of the ecological status, and the priority substance lists have been selected. For deriving the environmental quality standard (EQS), a risk assessment paradigm has been developed based on worst-case scenarios, and the expert group on the EQS initiated a guideline for EQS derivation in water field policy in 2007. The EQS derivation requires ecological toxicity data for targeted substances for use in the species sensitivity distribution approach [34; 35; 36]. Fish are among the ecological receptors for which it is required to conduct acute or chronic toxicity tests. In terms of EQS data, both acute and chronic toxicity data are required; chronic toxicity is regarded by considering the toxicant exposure over at least a complete lifespan or in sensitive developmental stages. The EQS data can be secured by using the no observed effect concentration (NOEC) values from these chronic toxicity tests [37; 38; 39]. The technical guidance for deriving the EQS suggested the Organisation for Economic Co-operation and Development (OECD) test guidelines (TG) as reference methods for fish (Table 3) [3]; \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Acute/** & **Test Guideline** & **Test Species** & **Exposure Stage** & **Test Duration** & **Endpoints** \\ \hline \multirow{6}{*}{Acute} & Biological test & & & & \\ method; reference & & & & & \\ method for & & & & & \\ determining acute & & & & & \\ lethality using & & & & & \\ three-spine & & & & & \\ stickleback [28] & & & & & \\ \cline{2-6}  & Biological test & & & & \\ method; acute & & & & & \\ lethality test using & & & & & \\ rainbow trout [29] & & & & & \\ \hline \multirow{6}{*}{Chronic} & Biological test & & & & \\ method; Toxicity & & & & & \\ tests using early & & & & & \\ life stages of & & & & & \\ salmonid fish & & & & & \\ (rainbow trout) & & & & & \\ \cline{2-6}  & & & Embryo/larvae/juvenile & 30 days *** & (hatching delay, deformation), behavior \\ \cline{2-6}  & Biological test & & & & & \\ method; test of & & & & & \\ larval growth and & & & & & \\ survival using & & & & & \\ fathead minnow & & & & & \\ \cline{2-6}  & & & & & \\ \hline \hline \end{tabular}  
* A young, yolk-sac larval with feeding activity. *** 7 days after half of embryos in control group hatched. *** 30 days after half of survival fish in control group showed swimming behavior.  
\end{table} 
Table 2: Biological test method for fish in Canada (published by Environment Canada and Environment and Climate Change Canada). acute toxicity can be considered if the mortality is determined in the 96 h exposure test [40]. The acceptable chronic toxicity tests for fish are early-life-stage tests using embryo or larval organisms and observing hatching, growth inhibition, and abnormalities [13]; the reproduction test is also regarded as a chronic test [41]. There are three fish embryo assays, OECD TG 236, with a zebrafish embryo for 96 h, and OECD TG 210 and TG 212, with an early-life stage toxicity test, starting from embryonic stages, can be used as acute and chronic test methods [12; 13; 14]. The apical endpoints are observed in OECD TG 236, including coagulated embryos, deformation of the somite, and lack of development with low heartbeat; the LC\({}_{50}\) for 96 h is used as acute toxicity data for EQS derivation [12]. The OECD TG 212 [13; 14] is an alternative method for OECD TG 210, conducted for relatively long exposures, and covering the vulnerable life stages from the embryo, considered a chronic test [14]. Both OECD TG 210 and 212 start exposure to substances from the embryonic stage and use endpoints to derive the EQS by observing survival at all developmental stages, the hatching rate, and growth inhibition with malformations or behaviors [3; 13; 14].