Sampling for Pharmaceuticals and Personal Care Products (PPCPs) and Illicit Drugs in Wastewater Systems: Are Your Conclusions Valid? A Critical Review

Abstract

The analysis of 87 peer-reviewed journal articles reveals that sampling for pharmaceuticals and personal care products (PPCPs) and illicit drugs in sewers and sewage treatment plant influents is mostly carried out according to existing tradition or standard laboratory protocols. Less than 5% of all studies explicitly consider internationally acknowledged guidelines or methods for the experimental design of monitoring campaigns. In the absence of a proper analysis of the system under investigation, the importance of short-term pollutant variations was typically not addressed. Therefore, due to relatively long sampling intervals, potentially inadequate sampling modes, or insufficient documentation, it remains unclear for the majority of reviewed studies whether observed variations can be attributed to "real" variations or if they simply reflect sampling artifacts. Based on results from previous and current work, the present paper demonstrates that sampling errors can lead to overinterpretation of measured data and ultimately, wrong conclusions. Depending on catchment size, sewer type, sampling setup, substance of interest, and accuracy of analytical method, avoidable sampling artifacts can range from "not significant" to "100% or more" for different compounds even within the same study. However, in most situations sampling errors can be reduced greatly, and sampling biases can be eliminated completely, by choosing an appropriate sampling mode and frequency. This is crucial, because proper sampling will help to maximize the value of measured data for the experimental assessment of the fate of PPCPs as well as for the formulation and validation of mathematical models. The trend from reporting presence or absence of a compound in "clean" water samples toward the quantification of PPCPs in raw wastewater requires not only sophisticated analytical methods but also adapted sampling methods. With increasing accuracy of chemical analyses, inappropriate sampling increasingly represents the major source of inaccuracy. A condensed step-by-step Sampling Guide is proposed as a starting point for future studies.

Occurrence and behavior of illicit drugs and metabolites in sewage water from the Spanish Mediterranean coast (Valencia region)

“…In this study, the bias due to cocaine transformation is expected to be relatively low as the estimated mean residence time of wastewater in the sewers investigated is 3 h and the conditions for sampling and sample storage minimize degradation of the selected compounds. The highest uncertainty within this study seems to be related to the sampling (Ort et al 2010). In this work, sampling error was estimated to be relatively high (around 30%) (Castiglioni et al 2013) due to the time proportional sampling interval used (every hour).…”

Analysis of drugs of abuse in wastewater from two Canadian cities

“…These observations might also have been be due to mixing regime characteristics, as well as flow and concentration variability that may have led to negative elimination efficiencies, as demonstrated by Majewsky et al (2011). In any event, Ort et al (2010) pointed out the need for more sophisticated sampling strategies to accurately determine removals of drugs in wastewater treatment plants.…”

“…Another uncertainty is the Science of the Total Environment 487 (2014) [722][723][724][725][726][727][728][729][730] choice of sampling regime for wastewater, which may bias the estimates of drug consumption. Selecting water sampling techniques and a sampling regime that accounts for variations in wastewater flows and concentrations over time is of great importance for obtaining reliable estimates of drug consumption (Ort et al, 2010;Lai et al, 2011). Previous studies on drugs of abuse, opioid prescription pharmaceuticals in sewage were based on grab samples or 24-h composite samples of untreated wastewater (Bones et al, 2007;Postigo et al, 2008).…”

Assessment of Domestic Wastewater Disposal in Some Selected Wards of Maiduguri Metropolis, Borno State, Nigeria

“…The relatively low number of pharmaceutical users in the two WWTP catchments, and the Benson WWTP catchment in particular, leaves model estimates of antibiotic users highly susceptible to systematic errors, as previously described [50]. The heterogeneity in the content of wastewater associated with low flush events, typical of low flow periods in the middle of the night, are a major factor influencing variations in analyte recovery over much of the sampling period [51][52][53]. This higher variability can be witnessed by the higher standard deviation in hourly measures of OC in Benson (4336472 ng/L) as compared to Oxford (358660 ng/L).…”