Abstract
Pharmaceutical compounds, including antiretroviral (ARV) drugs, are not wholly metabolised by the human body, nor are they completely removed from wastewater treatment plants’ effluents. Thus, a variety of pharmaceutical compounds are introduced into aquatic environments every day. Recent studies showed that ARV drug concentrations in South African aquatic ecosystems are increasing; this may negatively affect the integrity of the ecological systems. Fish can serve as bio-indicator organisms as they are directly exposed to the water throughout their life. The effects of increasing ARV drug concentrations in aquatic environments need to be investigated to determine the possible negative impact on aquatic life. This study aimed to determine the toxic effects of the ARV efavirenz (EFV) on Oreochromis mossambicus early life stages following acute exposure under controlled laboratory conditions and to determine the median lethal concentration (96h LC50) of EFV for O. mossambicus fry.
Adult O. mossambicus were bred under laboratory conditions in an aquarium at the University of Johannesburg and embryos (24 h post-fertilization) were collected. The collected embryos were exposed to increasing EFV concentrations in a static system to assess hatching success. Separately, embryos (24 h post-fertilization) were reared to 2-week old fry, before they were exposed to increasing EFV concentrations in a static system for 96 h. The starting exposure concentration of EFV (2.45 μg/L) was increased (with 5x increments) up to 1531.25 μg/L. There were eight exposure groups (including a control and solvent control) with four replicates each. Each replicate had 160 individuals and the total sample size for the embryos and the 2-week old fry exposure experiment was 1280 individuals each. The endpoints of the study included determining the hatching success, identifying any macroscopic abnormalities or abnormal behaviour, monitoring survival of the fry throughout the exposure period, determining the LC50 value for O. mossambicus fry after a 96 h exposure, and assessing selected target organs (kidney and liver) for any histological alterations.
The results showed a reduction in hatching success, delayed hatching, and a decrease in survival as the EFV concentration increased. There was no statistically significant difference (p > 0.05) across all the exposure groups for the condition factor. Morphological and behavioural alterations were seen in fish exposed to the higher concentrations (850 μg/L and 1531.25 μg/L). The AAT Bioquest LC50
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calculator, which is a symmetric regression model, was used to calculate the LC50 value of 4339.21 μg/L. The LC50 value was higher than the highest concentration of EFV used in the study. Histological alterations were identified in the liver and kidney tissue of the 2-week old fry. These alterations included vacuolation (steatosis), nuclear alterations that included binucleation, binucleoli and chromatin clearing. There were significant differences between the exposure groups for the liver indices (p < 0.05) and the liver indices increased with increasing concentrations of EFV. There was also a significant difference between the control and the exposure groups for the kidney indices (p < 0.05) and similarly to the liver, the kidney indices increased with increasing concentrations of EFV. The number of the different types of identified alterations in both the kidney and the liver increased with increasing concentrations of EFV.
These findings show that increasing concentrations of EFV in South African waters may have adverse effects, such as neurotoxicity (resulting in behavioural changes), hepatotoxicity, and nephrotoxicity on the early life stages of O. mossambicus after acute exposure. It is important to monitor the increasing levels of EFV and assess its effects on aquatic biota as it could have adverse effects on overall fish population health, sustainability and growth.