Hospital Wastewater as a Reservoir of Contaminants of Emerging Concern: A Study Report from South America, Chile

Background/Objectives: Hospital wastewater is a complex effluent containing a wide range of biological and chemical contaminants, including pharmaceuticals, pathogens, and antimicrobial resistance determinants. These discharges pose a growing threat to aquatic ecosystems and public health, particularly in regions where wastewater treatment is insufficient. This study aimed to characterize the chemical and microbiological composition of untreated effluent from a tertiary care hospital in southern Chile, focusing on contaminants of emerging concern. Methods: Wastewater samples were collected at the hospital outlet before any treatment. The presence of two commonly used pharmaceutical compounds, paracetamol and amoxicillin, was quantified using high-performance liquid chromatography (HPLC). Bacterial isolation was performed using selective media, and antibiotic susceptibility testing was conducted via the disk diffusion method following CLSI guidelines. In addition, metagenomic DNA was extracted and sequenced to assess microbial community composition and functional gene content, focusing on the identification of resistance genes and potential pathogens. Results: A total of 42 bacterial isolates were recovered, including genera with known pathogenic potential such as Aeromonas, Klebsiella, and Enterococcus. Antibiotic susceptibility tests revealed a high prevalence of multidrug-resistant strains. Metagenomic analysis identified the dominance of Bacillota and Bacteroidota, together with 56 antimicrobial-resistance gene (ARG) families and 38 virulence-factor families. Functional gene analysis indicated the presence of efflux-pump systems, β-lactamases, and mobile genetic elements, suggesting that untreated hospital effluents serve as potential sources of resistance and virulence determinants entering the environment. Paracetamol was detected in all samples, with an average concentration of 277.4 ± 10.7 µg/L; amoxicillin was not detected, likely due to its instability and rapid degradation in the wastewater matrix. Conclusions: These findings highlight the complex microbiological and chemical burden of untreated hospital wastewater and reinforce the need for continuous monitoring and improved treatment strategies to mitigate environmental dissemination of antibiotic resistance.