where EECmax is the maximum environmental concentration of selected metal in estuary water or river water if estuary metal concentration was not available, P5EC50 is the 5th percentile of selected metal derived from the included EC/LC50-values from the EPA ECOTOX database and Cb is the estimated background concentration. The 5th percentile was derived with the weighted average method of SPSS statistical software (IBM, 2013) (Al: n =2; Cd: n =30; Zn: n=13).