However, given the recent spate of media coverage focused on occurrence of pharmaceuticals in drinking water and public sensitivity,
we felt it was important to use the MDL as the criteria for defining
detections in this study so that our results would conform to the
meaning of detection as defined for regulatory purposes.
TheMDL is the concentration above which there is more than 99 percent probability
that the measured concentration in the sample is greater than concentrations measured in blanks, i.e., that the result represents a detection of the compound present in the environmental sample (U.S.Environmental Protection Agency, 1997).
Results with concentrations less than the MDL have increased probability of being “false-positive” detections of the compound in the environmental sample. Of the 550
individual detections of pharmaceutical compounds in groundwater samples, 484 had concentrations below MDLs.