Statistical analysis techniques for the assessment of the toxicity of raw surface water intended for human consumption—a case study

Abstract

During a seven-year time period (2000–2006), the data obtained by the monthly toxicological analyses of raw (untreated) water from the main reservoirs supply sources of Athens, the Greek capital with more than 4 million inhabitants, had been registered using a bioluminescence test, which is based on the correlation between toxicity of the water sample and its effects on the light intensity of marine bacteria Vibrio fischeri, measured by the bioluminometer Microtox®. The statistical analysis of the water toxicity over a long time period can provide important and useful information for the management and quality control of the water resources. However, due to the inherent characteristics of the water quality data, sophisticated statistical techniques for their analysis may be required. In this study, the available data were subjected to exhaustive statistical analysis by the usage of specialized nonparametric statistical methods. A small amount of autocorrelation was observed for each time series implying that corrective actions should be made in the statistical analyses. The overall performance of the raw waters was apparently nontoxic. The study of seasonality for each reservoir resulted in no statistical significance. Trend analysis resulted in no statistically significant upward or downward trends. Moreover, no statistically significant differences of the central tendency measures between the reservoirs were observed.

Keywords:

• Nonparametric statistical methods
• Trend analysis
• Seasonality
• Autocorrelation
• Microtox® test.

Acknowledgments

The authors would like to thank the Quality Control Department of EYDAP and especially the biologist Mrs. Z. Melabianaki for her support in the toxicological analysis. Special thanks to Mr. G. Spithourakis for his support.

Notes

Third International Conference on Environmental Management, Engineering, Planning and Economics (CEMEPE 2011) & SECOTOX Conference, 19–24 June 2011, Skiathos Island, Greece