1-A comparison of statistical methods for deriving freshwater quality criteria for the.pdf

ENVIRONMENTAL QUALITY BENCHMARKS FOR PROTECTING AQUATIC ECOSYSTEMS A comparison of statistical methods for deriving freshwater quality criteria for the protection of aquatic organisms Liqun Xing Hongling Liu Xiaowei Zhang Markus Hecker John P. Giesy Hongxia Yu Received: 6 August 2012 /Accepted: 2 January 2013 /Published online: 15 January 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract Species sensitivity distributions (SSDs) are in- creasingly used in both ecological risk assessment and deriva- tion of water quality criteria. However, there has been debate about the choice of an appropriate approach for derivation of water quality criteria based on SSDs because the various methods can generate different values. The objective of this study was to compare the differences among various methods. Data sets of acute toxicities of 12 substances to aquatic organ- isms, representing a range of classes with different modes of action, were studied. Nine typical statistical approaches, in- cluding parametric and nonparametric methods, were used to construct SSDs for 12 chemicals. Water quality criteria, expressed as hazardous concentration for 5 % of species (HC5), were derived by use of several approaches. All approaches produced comparable results, and the data gener- ated by the different approaches were significantly correlated. Variability among estimates of HC5 of all inclusive species decreased with increasing sample size, and variability was similar among the statistical methods applied. Of the statistical methods selected, the bootstrap method represented the best- fitting model for all chemicals, while log-triangle and Weibull were the best models among the parametric methods evaluated. The bootstrap method was the primary choice to derive water quality criteria when data points are sufficient (more than 20). If the available data are few, all other methods should be constructed, and that which best describes the distribution of the data was selected. Key