Pharmaceutical occurrence, distribution and degradation in rural wastewaters and surface waters in Scotland
It is widely recognised that the inadequate removal of pharmaceuticals within wastewater treatment plants (WWTPs) may results in these compounds (and their transformation products (TPs) and metabolites) entering surface water. Knowledge gaps exist on pharmaceutical presence and potential effects in rural regions (e.g., Scotland’s Highlands and Islands), where historic monitoring has been limited. These areas may face challenges relating to wastewater management and environmental pollution, as wastewater is generally treated at small, less advanced WWTPs. These WWTPs may struggle to adequately eliminate pharmaceutical compounds as populations grow, wastewater volumes increase and pharmaceutical usage continues to rise. This thesis sought to fill knowledge gaps on pharmaceutical occurrence, distribution and degradation in rural wastewaters and surface waters in Scotland. The aim was carried out through: (i) comprehensive literature review; (ii) target compound selection; (iii) characterisation of hospital wastewater and its impact on pharmaceutical concentrations in a rural ‘source-to-sink’ water cycle; (iv) targeted monitoring and suspect screening of pharmaceuticals, TPs and metabolites within separate stages of a rural WWTP; and (v) assessment of temporal and spatial trends in pharmaceutical presence in the River Dee (Aberdeenshire) over 12 months using both passive and grab sampling. Eight common pharmaceutical compounds were selected for this work: paracetamol, diclofenac and ibuprofen (analgesics/nonsteroidal anti-inflammatory drugs); clarithromycin and trimethoprim (antibiotics); carbamazepine and fluoxetine (psychoactive drugs); and 17α-ethynylestradiol (synthetic hormone). Overall, results suggest that the studied rural community produced wastewater with significant concentrations of the target compounds. Paracetamol was generally detected in highest concentration within the hospital and municipal wastewaters. Values ranged: 3 ng/L (carbamazepine) to 105910 ng/L (paracetamol) in hospital discharge; 5 ng/L (ibuprofen) to 127437 ng/L (paracetamol) in WWTP influent; 95 ng/L (diclofenac) to 273859 ng/L (paracetamol) in WWTP primary wastewater; 6 ng/L (paracetamol) to 1047 ng/L (carbamazepine) in WWTP secondary wastewater; and 60 ng/L (clarithromycin) to 36201 ng/L (paracetamol) in WWTP effluent. The WWTP was unable to fully eliminate some compounds, with average removals ranging from >80% (for paracetamol, ibuprofen) to <0% (for diclofenac, carbamazepine and clarithromycin). Compound removal and behaviour (e.g., solid-phase sorption and biodegradability) within the WWTP may be related to the significant pharmaceutical–water quality relationships identified here, such as carbamazepine with dissolved inorganic carbon, dissolved organic carbon and wastewater flow. Suspect screening with high resolution mass spectrometry tentatively identified 12 TPs and metabolites. Several proposed compounds (e.g., 14-hydroxy-clarithromycin, n-acetyl-benzoquinonimine) were unmodified at the pharmacologically active site of the parent drug, and may possess similar (or higher) activity and potential ecotoxicity. Reference standard comparison is necessary for unambiguous confirmation of the TPs. Grab and passive sampling performed in the River Dee (Aberdeenshire) revealed that pharmaceutical concentration and distribution is generally linked to catchment urbanisation. Paracetamol, ibuprofen, diclofenac, carbamazepine and trimethoprim were the most abundant compounds throughout the river, and detected at the highest concentrations (maximum concentrations >100 ng/L). The concentrations were most pronounced near WWTP discharge sites, but passive sampling revealed persistent, low-level pollution of most compounds throughout the river. Combination of grab sampling (to characterise the magnitude of contamination peaks) and passive sampling (to capture trace concentrations and average overtime) may therefore provide the best assessment of contamination. Temporal trends and significant river flow relationships were identified for diclofenac and carbamazepine, indicating that dry weather may result in greater pharmaceutical pollution issues for the River Dee in future. This work highlights the need to reduce pharmaceuticals entering surface water in rural communities. Recommendations herein may guide site-specific research to assess sustainable and economically viable interventions (e.g., separate treatment of hospital wastewater), or preventative measures (e.g., source control). Focused research should continue filling knowledge gaps on the presence of pharmaceutical-based compounds in rural areas, and characterise degradation behaviour and fate in effluent-receiving surface water. Continued work is essential to provide evidence to policymakers, environment agencies and water regulators on pharmaceutical pollution to evaluate associated risks and mitigate environmental impacts.
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