Use of biomarkers in monitoring pollution status of urban rivers, Limpopo, South Africa

This study investigated the use of enzymes and histology as potential biomarkers in Sand and Blood Rivers in Limpopo Province, South Africa. Physico-chemical parameters were analyzed at sites S1, S2, S3, S4, and S5 of the Sand River and sites B1 and B2 of the Blood River. Sites S1 and B1 were selected as the reference sites and located upstream of the Polokwane and Seshego wastewater treatment plants (WWTPs) effluent discharge points, respectively. Water quality parameters assessed were water temperature, dissolved oxygen (DO), biological oxygen demand (BOD), total dissolved solids (TDS), turbidity, ammonia, nitrogen, phosphorus, and pH. Sites downstream the WWTPs recorded elevated levels of nitrogen, phosphorus, and ammonia. DO, ammonia, nitrogen, and phosphorus were above the targeted water quality range (TWQR) for aquatic ecosystems. The Canadian council of ministers of the environment water quality index (CCME WQI) showed that the reference sites had good water condition while sites downstream (S2, B2, S3, and S4) had poor water condition. Acetylcholinesterase (AChE) enzyme activity in the brain of Clarias gariepinus from sites downstream was lower than those from sites upstream of the effluent discharge points. The liver of Clarias gariepinus from sites downstream showed higher lactate dehydrogenase (LDH) enzyme activity compared to fish caught at the reference sites. Furthermore, Clarias gariepinus from sites downstream showed a number of histological alterations in gills and liver than fish from upstream. Histological alterations observed in gills included fusion of the secondary lamellae, hyperplasia of the interlamellar, epithelial lifting of secondary lamellae, and hyperplasia of the secondary lamellae. In the liver, histological alterations observed included melanomacrophage centers (MMCs), macrovesicular steatosis, sinusoid congested with kupffer cells, nuclei pleomorphism, and vacuolation. The gill and liver indices were significantly lower at the reference sites compared to sites downstream. Evidently, AChE, LDH, and gill and liver histology can be used as early warning signs of aquatic degradation in rivers that are recipients of poorly treated sewage effluent.

Automated summary

The study found that enzyme activity and histological changes in fish can be used as potential biomarkers for assessing aquatic pollution in rivers. Elevated levels of nitrogen, phosphorus, and ammonia downstream of wastewater treatment plants negatively impacted enzyme activity and histology in fish.