The potential effects of efavirenz on Oreochromis mossambicus after acute exposure

[Display omitted] •The ARV efavirenz is toxic and present in South African surface water.•Fish exposed to efavirenz showed liver damage and declined overall health.•Efavirenz exposure is a health risk to O. mossambicus.•ARVs in water could pose a threat to wildlife and ultimately human health. Antiretroviral drugs (ARVs) are hazardous therapeutic pharmaceuticals present in South African surface water. Efavirenz is an ARV commonly used in human immunodeficiency virus (HIV) treatment in South Africa. Although little is known about the toxic effects of efavirenz on fish health, threats of toxicity to the aquatic environment have been reported. Oreochromis mossambicus were exposed under controlled conditions to environmentally-relevant efavirenz concentrations (10.3ng/l) as measured in rivers that flow into the Nandoni Dam in the Vhembe District, South Africa. Acute (96h) exposures were conducted using efavirenz concentrations of 10.3ng/l and 20.6ng/l. The overall health of exposed fish was determined using a histology-based fish health assessment index. Necropsies and haematology were conducted and somatic indices calculated after which the liver, kidney, heart, gills and gonads were microscopically quantitatively assessed. Results indicated that fish exposed to 20.6ng/l efavirenz had significantly (p