The Little Akaki river wastewater (WW) exhibited seasonal variations in antibiotic concentrations. Ciprofloxacin concentrations ranged from 5.73 to 9.34 µg/L in the dry season and from 5.62 to 7.01 µg/L in the wet season. Cefotaxime concentrations ranged from 1.89 to 54.86 µg/L in the dry season and from 32.76 to 64.79 µg/L in the wet season. Sulfamethoxazole concentrations varied from 29.11 to 186.25 µg/L in the dry season and from 123.29 to 248.77 µg/L in the wet season. Erythromycin had the highest concentration at S4 (101.53 µg/L) in the dry season and ranged from 23.54 to 60.52 µg/L in the wet season. Risk quotients indicated a high risk of resistance promotion (RQ > 2) in both seasons, except for erythromycin.
Our study confirms the presence of elevated Ciprofloxacin in the Little Akaki River, aligning with reports from India (Balakrishna et al., 2017). Although not as high as hospital wastewater from Ghana, Germany, and Vietnam (Azanu et al., 2018; Lien et al., 2016; Schuster et al., 2022), our findings exceed those of WWTP effluents and surface water elsewhere, including Canada, Holland, Portugal, Italy, and various European countries (Balakrishna et al., 2017; Rodriguez-Mozaz et al., 2020). This suggests potential geographical variations in Ciprofloxacin usage patterns, wastewater treatment efficiency, and point-source pollution. Interestingly, our detected levels fall between higher concentrations reported in Indian WWTP sludge and influent (Bhagat et al., 2020; Giebułtowicz et al., 2020), and lower concentrations found in South Indian groundwater and European WWTP effluents (Arun et al., 2022; Rodriguez-Mozaz et al., 2020). This further highlights the diverse range of Ciprofloxacin contamination across regions and environmental compartments.
Our findings significantly exceed the predicted no-effect concentration (PNEC) for Ciprofloxacin-induced resistance (Murray et al., 2020). This raises concerns about potential resistance promotion in microbial communities within the Little Akaki River. Further investigation is needed to identify the specific sources of Ciprofloxacin in the river's catchment area, local antibiotic usage patterns, and the effectiveness of existing wastewater treatment practices in mitigating antibiotic pollution. Additionally, considering Ciprofloxacin's poor biodegradability (Girardi et al., 2011), its persistence in the environment and potential long-term impact on aquatic ecosystems necessities further research. Studies show ciprofloxacin as a key indicator of antibiotic pollution in wastewater (Rodriguez-Mozaz et al., 2020).
Our study identified significantly higher Sulfamethoxazole levels in the Little Akaki River wastewater compared to numerous other regions. While levels in Kenyan surface and wastewater ranged from 0.25 to 49.7 µg/L (Kairigo et al. 2020; Ngigi et al. 2020), our measurements reached up to 248.77 µg/L, exceeding the highest reported Kenyan value by five times. Similarly, our findings surpassed those reported in Brazil (27.8 µg/L), Bosnia (11.6 µg/L), and China (8 µg/L) (Brenner et al., 2011; Peng et al., 2006; Terzić et al., 2008). These comparisons highlight the notably elevated Sulfamethoxazole presence in the Little Akaki River. Furthermore, our detected Sulfamethoxazole concentrations significantly exceeded the predicted no-effect concentration (PNEC) for promoting bacterial resistance (0.5 µg/L) (Bengtsson-Palme & Larsson, 2016). This raises serious concerns about the potential for antibiotic resistance development within the Little Akaki River's microbial communities.
Several factors may contribute to these elevated Sulfamethoxazole levels. Variations in pollutant sources and distribution across wastewater systems are influenced by geographic location, treatment processes, and patterns of Sulfamethoxazole usage (Anh et al., 2021). Further investigation is crucial to identify the specific sources in the Little Akaki River's catchment area and assess potential contributions from hospitals, pharmaceutical waste, agricultural practices, and other sources for targeted mitigation strategies. Sulfamethoxazole exhibits significant persistence in riverine water ecosystems, with its biodegradation influenced by environmental factors like organic carbon content, pH, temperature, and the presence of other contaminants (Hassan et al., 2021; Larcher & Yargeau, 2012). This persistence increases the risk of prolonged exposure and potential harm to microbial diversity. The Little Akaki River faces a major threat from high Sulfamethoxazole levels, posing a risk of antibiotic resistance and environmental harm. Further research is urgently needed to pinpoint sources, assess resistance risks, and develop solutions. Stricter antibiotic regulations, improved wastewater treatment, and public awareness are crucial in tackling this growing challenge.
Our study is the first to report Cefotaxime concentrations in wastewater, revealing alarmingly high levels ranging from 1.89 to 64.79 µg/L in the Little Akaki River. This significantly exceeds the predicted no-effect concentration (PNEC) for promoting antibiotic resistance, set at 0.78 µg/L (Murray et al., 2020). These findings raise serious concerns about the potential for Cefotaxime-induced resistance development in the river's microbial communities. Further research is crucial to understand the sources of this antibiotic and its potential ecological impacts. On the contrary, Erythromycin concentrations in our study varied across sampling sites, with the highest reaching 101.53 µg/L at S4. While this surpasses the highest reported level in UK wastewater treatment plants (10.025 µg/L (Kasprzyk-Hordern et al. 2009), it remains well below the PNEC threshold for resistance promotion (1250 µg/L (Murray et al., 2020). Comparisons with other regions reveal substantial variations, with Erythromycin detected at much lower levels in Kuwait, South India, USA, and Poland (range: 0.058–0.22 µg/L) (Arun et al., 2022; Gevao et al., 2022; Giebułtowicz et al., 2020; Phonsiri et al., 2019). These differences highlight the influence of regional factors such as antibiotic usage patterns, wastewater treatment practices, and environmental conditions on Erythromycin presence. The detection of Cefotaxime at alarmingly high levels in the Little Akaki River presents a novel and concerning threat for antibiotic resistance development. In contrast, Erythromycin concentrations, while exceeding the highest reported level in one region, remain within acceptable limits for resistance promotion.
This study reveals a concerning scenario in the Little Akaki River, where the detected concentrations of Ciprofloxacin, Cefotaxime, and Sulfamethoxazole exceeded their respective PNEC (Predicted No-Effect Concentration) values established for minimizing antibiotic resistance development (Booth et al. 2020; Bengtsson-Palme and Larsson 2016). This finding highlights a significant threat to the river's ecosystem and potentially downstream environments.
Our results align with previous reports of Ciprofloxacin and Sulfamethoxazole exceeding PNECs in hospital and industrial wastewater (Azanu et al. 2018; Booth et al. 2020), though they remain within acceptable limits in drinking water (Booth et al. 2020). Additionally, ciprofloxacin levels has shown high resistance risk (RQ > 1) in Polish wastewater treatment plants (Giebułtowicz et al., 2020), aligning with our findings. This suggests a potential localized issue in the Little Akaki River catchment area. Interestingly, Erythromycin levels, while surpassing the reported peak in UK wastewater treatment plants, remained below its PNEC (Kasprzyk-Hordern et al. 2009; Murray et al. 2020). This emphasizes the regional variability in antibiotic presence, influenced by factors like usage patterns and treatment practices (Rodriguez-Mozaz et al., 2020).
Antimicrobial pollution in the Little Akaki River can have significant short- and long-term consequences. Aside from promoting resistance, it can disrupt microbial communities, alter nutrient cycling, and even accumulate resistant genes (Grenni et al. 2018; Munk et al. 2022). Studies suggest thresholds for organic matter degradation and resistance development, highlighting the importance of maintaining antibiotic concentrations below 0.1 µg/L (Jendrzejewska & Karwowska, 2018; Le Page et al., 2017). Implementing source wastewater treatment systems can significantly reduce antibiotic discharge and mitigate these ecological risks (Booth et al. 2020). Further research is crucial to identify the specific sources and pathways contributing to the elevated antibiotic levels in the Little Akaki River. Understanding these factors will inform targeted interventions and effective management strategies.