Regarding MTZ/hMTZ, the ratios for Keynsham were slightly higher than for Bath, and whilst comparable, the difference was statistically significant (p≤0.05). The averaged ratio for MTZ/hMTZ in Bath was 1.70 ± 0.68, and for Keynsham it was 2.07 ± 1.27. Comparing these ratios to the urinary ratioexcretion (parent/metabolite), MTZ/hMTZ had the closest match, with a ratio of 1.03 (table ). Both parent and metabolite exhibited similar levels of degradation by ~40% in wastewater over 24 hours . Interestingly, on the 28/02/2019 in Keynsham, MTZ/hMTZ had a ratio of 9.37 ± 0.14. The parent MTZ levels observed were 82.6 ± 2.2 mg 1000inh -1 day -1 with hMTZ levels recorded only at 8.82 ± 0.36 mg 1000inh -1 day -1 . Whilst this was not the highest MTZ level recorded over the sampling period, it was still above average (average PNDL, MTZ: 28.4 ± 23.4 mg 1000inh -1 day -1 ). Several days measured ~100 mg 1000inh -1 day -1 for MTZ, but these days observed corresponding high levels of hMTZ (e.g. 09/02/2019, MTZ: 113.51 ± 0.21 mg 1000inh -1 day -1 , hMTZ: 74.5 ± 1.45 mg 1000inh -1 day -1 , ratio 1.52 ± 0.03). This, therefore, could be another potential disposal event. Of note, however, is that MTZ prescriptions can be prescribed as a gel rather than tablets, gels applied topically will result in significantly different metabolism in the body. Hence, the proportion of MTZ prescriptions in gel or tablet form could impact observed ratios in wastewater. However, MTZ in both Keynsham and Bath was predominantly prescribed in oral form in comparison to topical form during the sampling period (figure ). With Bath reporting on average 0.45 kg/month of tablets and capsules prescribed, versus 0.016 kg/month of creams and gels; and Keynsham reporting on average 0.39 kg/month of tablets capsules, versus 0.013 kg/month of creams and gel. Topical treatments of AAs tend to contain a lower dose than tablet or capsule form and are applied more frequently, so potential run off into the sewage system (e.g. from showering) may result in a low and consistent contribution to the overall AA level observed in wastewater. Ratios between SLZ/SPY were consistent in both Bath and Keynsham, at 0.15 ± 0.11 and 0.16 ± 0.11 respectively. SPY and aSPY are both active, major metabolites of SLZ consumption (a prescribed antiinflammatory). Ratios of SLZ/aSPY and SPY/aSPY did observe statistical differences between the two catchment sites, with Keynsham having higher ratios in both (figure ). This corresponds to lower levels of aSPY in Keynsham (PNDLs Bath:268 ± 109 mg -1 1000inh day -1 vs Keynsham: 65 ± 53 mg -1 1000inh day -1 ). This could be attributed to stability. Whilst SPY was reportedly stable in wastewater at room temperature (24 hour: 93.0 ± 7.6%), aSPY demonstrated a drop to 75.4 ± 6.0% after 24 hours . SLZ observed similar stability to aSPY, reporting a drop to 73.4 ± 5.4% after 24 hours.