## 3 Results and Discussion
### Evaluation of Chemical Stability during Shipment  
Simulated shipping events (\(n\) = 3) showed that the interior temperature of the polystyrene package remained below ambient temperature for 2.44 days (Figure 1). A negative relationship between chemical stability in water and both temperature and time was observed, and degradation was consistently higher with increasing temperature and time. Over 2 days, the degradation study determined a mean stability of 92% \(\pm\) 8.6% at 4 \({}^{\circ}\)C, 89% \(\pm\) 7.9% at 20 \({}^{\circ}\)C and 90% \(\pm\) 13% at 35 \({}^{\circ}\)C. After 7 days at respective temperatures, stability dropped to 83% \(\pm\) 11%, 80% \(\pm\) 13% and 77% \(\pm\) 19% at 4 \({}^{\circ}\)C, 20 \({}^{\circ}\)C and 35 \({}^{\circ}\)C respectively (Figure 2, Table S3). Fluoxetine and its metabolite nonfluoxetine were the least stable, exhibiting a mean degradation of 29.7-37.5% and 29.3-34.2% respectively over 2 days and 41.2-50.3% and 41.6-49.2% respectively over 7 days (Table S3). Interestingly, previous work has indicated that both fluoxetine and nonfluoxetine are relatively hydrolytically stable [21]. However, they are known to rapidly partition to solid matrices such as sediment [22]. Hence, the decreased stability of these chemicals observed here may partially be an artefact of sorption to test materials including the glass test vessel/PTFE cap or plastic pipette tips. The tetracycline antibiotics tetracycline and oxytetracycline were also relatively unstable exhibiting mean degradation of 20.9-24.2% and 21.1-29.3% respectively after 2 days and 34.8-43.1% and 32.3-39.3% respectively after 7 days (Table S3). Previous work has indicated that both tetracycline and oxytetracycline are quickly degradable via oxidation (e.g., [PERSON] et al. [23]). Despite the observed degradation, the dissipation of fluoxetine, nonfluoxetine and the tetracyclines were still of an acceptable level to draw conclusions over the relative fate and abundance of these contaminants in water. All remaining test chemicals generally demonstrated degradation of <20% over 2 days and <30% over 7 days (Table S3). As express shipping usually takes 1-2 days and samples are shipped frozen, it is unlikely that any API in this method would significantly degrade during shipment. Here, a mean degradation rate of \begin{table}
\begin{tabular}{c c c c} \hline
**Validation Parameter** & & **Mean \(\pm\) SD** & **Within Acceptable Range \({}^{\star}\)** \\ \hline Analyte Response in & 10 ng/L & 95 \(\pm\) 32 & 75\% \\ LCMS-grade water (\%) & 100 ng/L & 104 \(\pm\) 22 & 90\% \\  & 1000 ng/L & 94 \(\pm\) 15 & 97\% \\ \hline Analyte Response in tap & 10 ng/L & 110 \(\pm\) 27 & 59\% \\ water (\%) & 100 ng/L & 101 \(\pm\) 31 & 80\% \\  & 1000 ng/L & 106 \(\pm\) 28 & 90\% \\ \hline Analyte Response in surface & 10 ng/L & 101 \(\pm\) 88 & 56\% \\ water (\%) & 100 ng/L & 106 \(\pm\) 26 & 82\% \\  & 1000 ng/L & 106 \(\pm\) 18 & 92\% \\ \hline Analyte Response in WWTP & 10 ng/L & 195 \(\pm\) 212 & 39\% \\ effluent (\%) & 100 ng/L & 117 \(\pm\) 38 & 59\% \\  & 1000 ng/L & 108 \(\pm\) 18 & 92\% \\ \hline Analyte Response WWTP & 10 ng/L & 465 \(\pm\) 992 & 20\% \\  & 100 ng/L & 168 \(\pm\) 81 & 38\% \\  & 1000 ng/L & 145 \(\pm\) 48 & 54\% \\ \hline  & LCMS-grade water (ng/L) & 9.16 & \\  & Drinking water (ng/L) & 9.72 & \\ Limit of Detection (ng/L) & Surface water (ng/L) & 11.79 & \\  & WWTP effluent (ng/L) & 20.22 & \\  & WWTP influent (ng/L) & 54.45 & \\ \hline  & LCMS-grade water (ng/L) & 18.32 & \\ Limit of Quantification & Drinking water (ng/L) & 19.44 & \\ (ng/L) & Surface water (ng/L) & 23.57 & \\  & WWTP effluent (ng/L) & 40.43 & \\  & WWTP influent (ng/L) & 108.89 & \\ \hline \multicolumn{4}{l}{\({}^{\star}\) The acceptable range for analyte response was considered between 60–130\% and <20\% for intra-/inter-day repeatability and precision as established by USGS method No. 5-B10 [7].} \\ \end{tabular}
\end{table}