Important Considerations for Estimating Odor Threshold Concentrations of Contaminants Found in Water Supplies

Natural and man-made chemicals affect the odor characteristics of drinking water, creating the need to set guidelines for treatment, consumer communication, monitoring, and other considerations. Limits can be based on estimates of odor detection or recognition threshold concentrations by humans. Informed guidance, however, is needed to use threshold testing to identify the levels of odor-causing chemicals humans can detect. In this article, we touch on this issue, discuss challenges associated with human threshold measurement, and provide examples of how procedures can be made more reliable and less dependent on large numbers of subjects and trials. For example, the single ascending method of limits, a once-through procedure recommended by ASTM International, can be extended to become a staircase procedure that repeatedly samples the perithreshold region with relatively few trials. Multiple data analyses can be used to determine individual and group thresholds, thereby increasing confidence in the selection of odor threshold concentrations for setting guidelines and standards. Clearly, further research and additional guidance are needed to address how to best measure the sensitivity of humans to odor-causing chemicals in water.