Page 130 - Statistics for Environmental Engineers

L1592_frame_C14 Page 126 Tuesday, December 18, 2001 1:49 PM

The MDL is based directly on an estimate of the variance of the measurement error at low concen-
trations. This quantity is not easy to estimate, which means that the MDL is not a well-known, fixed
value. Different chemists and different laboratories working from the same specimens will estimate
different MDLs. A result that is declared ≤MDL can come from a sample that has a concentration actually
greater than the MDL.
What are the implications of the MDL on judging violations? Suppose that a standard is considered
to be met as long as all samples analyzed are “non-detect.” By the EPA’s definition, if truly blank
specimens were analyzed, the odds of a hit above the MDL on one particular specimen is 1%. As more
specimens are analyzed, the collective odds of getting a hit increase. If, for example, a blank is analyzed
every day for one month, the probability of having at least one blank declared above the MDL is about
25% and there is a 3% chance of having two above the MDL. Analyze blanks for 90 days and the odds
of having at least one hit are 60% and the odds of having two hits is 16%. Koorse (1989, 1990) discusses
some legal implications of the MDL.

References
American Chemical Society, Committee on Environmental Improvement (1983). “Principles of Environmental
Analysis,” Anal. Chem., 55(14), 2210–2218.
APHA, AWWA, WEF (1998). Standard Methods for the Examination of Water and Wastewater, 20th ed.,
Clesceri, L. S., A. E. Greenberg, and A. D. Eaton, Eds.
ASTM (1988). Standard Practice for Determination of Precision and Bias of Applicable Methods of Committee
D-19 on Water, D2777–86, ASTM Standards of Precision and Bias for Various Applications, 3rd ed.
Berthouex, P. M. (1993). “A Study of the Precision of Lead Measurements at Concentrations Near the Limit
of Detection,” Water Envir. Res., 65(5), 620–629.
Currie, L. A. (1984). “Chemometrics and Analytical Chemistry,” in Chemometrics: Mathematics and Statistics
in Chemistry, NATO ASI Series C, 138, 115–146, Dordrecht, Germany, D. Reidel Publ. Co.
Gibbons, R. D. (1994). Statistical Methods for Groundwater Monitoring, New York, John Wiley.
Gilbert, R. O. (1987). Statistical Methods for Environmental Pollution Monitoring, New York, Van Nostrand
Reinhold.
Glaser, J. A., D. L. Foerst, G. D. McKee, S. A. Quave, and W. L Budde (1981). “Trace Analyses for
Wastewaters,” Environ. Sci. & Tech., 15(12), 1426–1435.
Holland, D. M. and F. F. McElroy (1986). “Analytical Method Comparison by Estimates of Precision and
Lower Detection Limit,” Environ. Sci. & Tech., 20, 1157–1161.
Hunt, D. T. E. and A. L. Wilson (1986). The Chemical Analysis of Water, 2nd ed., London, The Royal Society
of Chemistry.
Kaiser, H. H. and A. C. Menzes (1968). Two Papers on the Limit of Detection of a Complete Analytical
Procedure, London, Adam Hilger Ltd.
Kaiser, H. H. (1970). “Quantitation in Elemental Analysis: Part II,” Anal. Chem., 42(4), 26A–59A.
Koorse, S. J. (1989). “False Positives, Detection Limits, and Other Laboratory Imperfections: The Regulatory
Implications,” Environmental Law Reporter, 19, 10211–10222.
Koorse, S. J. (1990). “MCL Noncompliance: Is the Laboratory at Fault,” J. AWWA, Feb., pp. 53–58.
Maddelone, R. F., J. W. Scott, and J. Frank (1988). Round-Robin Study of Methods for Trace Metal Analysis:
Vols. 1 and 2: Atomic Absorption Spectroscopy — Parts 1 and 2, EPRI CS-5910.
Maddelone, R. F., J. W. Scott, and N. T. Whiddon (1991). Round-Robin Study of Methods for Trace Metal
Analysis: Vol. 3: Inductively Coupled Plasma-Atomic Emission Spectroscopy, EPRI CS-5910.
Maddelone, R. F., J. K. Rice, B. C. Edmondson, B. R. Nott, and J. W. Scott (1993). “Defining Detection and
Quantitation Levels,” Water Env. & Tech., January, pp. 41–44.
Pallesen, L. (1985). “The Interpretation of Analytical Measurements Made Near the Limit of Detection,”
Technical Report, IMSOR, Technical University of Denmark.
Porter, P. S., R. C. Ward, and H. F. Bell (1988). “The Detection Limit,” Environ. Sci. & Tech., 22(8), 856–861.
Rhodes, R. C. (1981). “Much Ado About Next to Nothing, Or What to Do with Measurements Below the
Detection Limit,” Environmetrics 81: Selected Papers, pp. 174–175, SIAM–SIMS Conference Series
No. 8, Philadelphia, Society for Industrial and Applied Mathematics, pp. 157–162.
© 2002 By CRC Press LLC