The water/sediment characteristics (Tables S2 and S3 in the Supporting Information) remained fairly consistent throughout study.
It seems that the sampling interval may be more frequent than what was needed to demonstrate stability and control of the sample conditions. Currently there are no “negative” abiotic controls, nor “positive” controls that represent pharmaceuticals of known “depletion” rates. As a long-term goal, it would be helpful to identify several pharmaceuticals representing a “rapid” depletion, and one representing something more typical. Such controls would be helpful in normalizing seasonal variations of the biological activity of the grab water/sediment samples used in the method. Based on the data from this study, and observations from other studies conducted, exemestane could be suggested as a
positive control of a relatively “rapid” depleting pharmaceutical showing extensive biotransformation and moderate mineralization. Negative abiotic controls could be added as well, by sterilizing sediment samples with ç radiation, treating with mercuric chloride, and/or autoclaving (24). Though negative controls could provide a means for assessing abiotic biodegradation, it is uncertain which sterilization treatment-(s) and what frequency of treatment(s) would be needed to maintain abiotic conditions for the duration of the study.