Assessing the biodegradability of common pharmaceutical products (PPs) on the Zambian market

Biodegradation is the breakdown of complex organic compounds into simpler molecules like carbon dioxide and water by microorganisms like bacteria and fungi. Biodegradation studies of pharmaceuticals are initially done to assess which pharmaceuticals are persistent in the environment. Whole pharmaceuticals or their metabolites are excreted from the human body via urine or fecal matter after administration. These go into the Wastewater Treatment Plants (WWTP) and are later released into the environment with the treated wastewater. Recent studies have reported a number of pharmaceuticals in the ecosystem and the effects of these on non-target species has become an issue of environmental concern. The biodegradation studies of eight pharmaceuticals were carried out in this research. The choice of pharmaceuticals was based on the most commonly prescribed medications at the University of Zambia (UNZA) Clinic in seven therapeutic groups: anti-hypertensives, antibiotic, antimalarial drugs, anti-tuberculosis, antihelminthics, antifungals and antiretroviral drugs. The biodegradability tests were carried out using a modified carbon dioxide evolution method (modified Sturm test). The inoculum was derived from the secondary effluent of the UNZA WWTP plant and Dextrose monohydrate was used as a system control. Using this guideline, the system control, dextrose monohydrate biodegraded 77 ± 0.270% in seven days. All the pharmaceuticals except ciprofloxacin were found to be non-biodegradable: Atenolol degraded 6.8 ± 0.026%, ketoconazole degraded 1.0 ± 0.003%, isoniazid/rifampicin degraded 0.8 ± 0.003%, mebendazole degraded 13.0 ± 0.050%, nevirapine degraded 1.3 ± 0.005%, pen-v degraded 1.0 ± 0.004% and quinine sulfate degraded 1.8 ± 0.008%. Ciprofloxacin showed a negative carbon dioxide evolution and it was noted that bacteria were not viable as the drug proved to be very potent against bacterial strains in the inoculum used.