Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. 
Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. What was studied?
This original research article systematically quantified the concentrations of selected antibiotics, heavy metals, and biocides in an urban wastewater treatment plant (WWTP) and its receiving water body in KwaZulu-Natal, South Africa, with a special focus on their potential to exceed predicted no-effect concentrations (PNEC) known to drive antimicrobial resistance (AMR) in environmental bacteria. Using US EPA method 200.7 for heavy metals and validated ultra-high-performance liquid chromatography-tandem mass spectrometry for antibiotics and biocides, the study compared pollutant loads at the WWTP effluent discharge, upstream, and downstream sites. The research aimed to assess the WWTP’s role in environmental pollution and the implications of pollutant concentrations exceeding regulatory thresholds relevant for heavy metal certification and AMR risk management.
Who was studied?
The study focused on environmental water samples collected from three specific sites associated with a municipal WWTP: the effluent discharge point, an upstream location, and a downstream location in the uMsunduzi River system. No human or animal subjects were directly involved; instead, the analysis targeted the chemical and biological contamination burden in these aquatic environments. The study area represents a region with diverse demographics and varying land use, providing a representative environmental context for South African urban, periurban, and industrial settings. The investigation thus centers on the environmental exposure of aquatic microbial communities to heavy metals, antibiotics, and biocides, and the subsequent risk of AMR selection.
Most important findings
| Critical Point | Details |
|---|---|
| High pollutant concentrations in effluent | The WWTP effluent contained the highest summed concentrations of heavy metals (178,473 mg/L), antibiotics (1335.4 µg/L), and biocides (notably BAC 12 at 7.805 µg/L), compared to downstream and upstream sites. |
| Heavy metals above regulatory limits | Seven heavy metals, including Al (3.43 mg/L) and Zn (0.078 mg/L), exceeded World Health Organization (WHO) and South African National Standard (SANS) limits, particularly in effluent samples, implicating poor removal efficiency. |
| Antibiotics above PNEC | Several antibiotics (sulfamethoxazole, oxytetracycline, tetracycline, lincomycin, and amoxicillin) were found at concentrations above their PNEC, indicating potential to select for antibiotic-resistant bacteria. For example, sulfamethoxazole reached up to 144.41 µg/L in effluent, far exceeding the PNEC of 16 µg/L. |
| Biocide contamination | Benzalkonium chloride (BAC) 12 was the most prevalent biocide, with concentrations at effluent and downstream sites surpassing the recommended PNEC of 0.01 µg/L, raising concern about biocide-driven AMR selection. |
| Downstream impact | Pollutant concentrations were consistently higher downstream than upstream, confirming the WWTP as a significant source of environmental contamination and suggesting propagation of pollutants and AMR risk to communities relying on these water bodies. |
| Sub-inhibitory concentrations and co-selection | Even when some heavy metals were present below acute toxicity thresholds, their sub-inhibitory concentrations are sufficient to induce bacterial efflux pump gene expression and cross-resistance to antibiotics, amplifying the AMR risk. |
| Sampling limitations | The study acknowledges limitations in sampling frequency and environmental variables but provides compelling evidence for regulatory review and the need for robust monitoring as part of certification programs. |
Key implications
The findings strongly indicate that WWTPs can be major sources of heavy metal, antibiotic, and biocide pollution, contributing to AMR selection in aquatic environments. For heavy metal certification programs, setting and enforcing discharge limits based on PNECs is crucial, as even sub-lethal metal levels can drive AMR. Regular monitoring and improved treatment technologies are needed to protect environmental and public health.
Citation
Chukwu KB, Abafe OA, Amoako DG, Essack SY, Abia ALK. Antibiotic, Heavy Metal, and Biocide Concentrations in a Wastewater Treatment Plant and Its Receiving Water Body Exceed PNEC Limits: Potential for Antimicrobial Resistance Selective Pressure. Antibiotics. 2023;12(7):1166. doi:10.3390/antibiotics12071166
Heavy metals are high-density elements that accumulate in the body and environment, disrupting biological processes. Lead, cadmium, arsenic, mercury, nickel, tin, aluminum, and chromium are of greatest concern due to persistence, bioaccumulation, and health risks, making them central to the HMTC program’s safety standards.
Heavy metals are high-density elements that accumulate in the body and environment, disrupting biological processes. Lead, cadmium, arsenic, mercury, nickel, tin, aluminum, and chromium are of greatest concern due to persistence, bioaccumulation, and health risks, making them central to the HMTC program’s safety standards.
