These dissimilarities observed in ratio, between the two catchment sites, could be attributed to the differences in sewage systems. Resident times for Bath vary between <0.5-9 hours, and for Keynsham between <0.5-2 hours. Bath also has a larger sewage system with an anoxic transport pipe that carries most of the community wastewater to the WWTP. This is likely an environment that can facilitate degradation, and potential transformation from SLZ to aSPY could be occurring in Bath's pipes, increasing the loads of aSPY. Further studies are needed to better understand potential biodegradation within the sewage system. SLZ had similar PNDLs (Bath: 50.0 ± 44.3 Keynsham: 38.8 ± 32.4 g/day). It is worth mentioning that SLZ is prescribed purely in tablet form and is not utilised topically in the UK (National Institute for Health and Care Excellence, n.d.). Complexities will arise for these compounds; as, whilst SPY is no longer prescribed for human use, it is still used in veterinary practices. The Southwest of England, where both catchments reside, has a strong agricultural presence. Hence, SPY and aSPY could be present in influent wastewater because of run-off, rather than from consumption of SLZ at the community level.