Determination of organic pollution in Phongola and Vaal Rivers, and the possible effects to wildlife—a comparison

Abstract

The aquatic environment is impacted by a wide range of anthropogenic activities, these include application of agricultural products like herbicides, insecticides and pesticides, and fertilisers; sewage; and industrial waste. These activities introduce various pollutants into the environment including: Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), organochlorine pesticides (OCPs) including dichlorodiphenyltrichloroethane (DDT), and metals. These pollutants inevitably enter aquatic environments where aquatic organisms are exposed to these compounds and the various detrimental effects they induce. The main aims of this study were to determine presence of persistent organic pollution (POP) and the potential effects these have on biological life from three sites in the industrially impacted Vaal River (Vischgat, Barrage, and Thabela Thabeng), and the agriculturally impacted Phongola Floodplain, and to compare these two systems to each other. The objectives were to: (i) Determine the concentration of POPs from biotic matrices in each river system; (ii) evaluate the health of the sampled organisms by determining the biomarker responses; (iii) investigate whether the analysed compounds bioaccumulated in the organisms from each system. Concentrations of target POPs were determined in fish muscle tissues by instrumental analyses. The target compounds were extracted from the muscle tissue via accelerated solvent extraction, followed by solid phase extraction. The POPs were quantified with gas chromatography (GC) coupled to either a mass spectrometer (MS) or electron capture detector (ECD) depending on the compound class. The effects of environmental stressors on the organisms were assessed by using biomarker assays at the biochemical level. The biomarkers of exposure, oxidative stress, oxidative damage, and cellular energy allocation were performed. The trophic position of the organisms were determined by stable isotope analyses and possible bioaccumulation of the POPs were assessed using the trophic magnification factor. The organisms from the Vaal River were burdened predominantly with industrially associated pollutants. The Barrage site was the most impacted site the Σxenobiotics ranged from 3.0–35 ng/g, and the fish from Vischgat had the lowest concentrations with concentrations that ranged from 0.61–9.6 ng/g. PCBs and DDTs contributed the highest proportions to the Σxenobiotics. The biomarker assessment indicated that fish from Barrage were in the poorest state and the likely contributing factors to this was the presence of ΣPCBs, polybrominated diphenyl ethers (ΣPBDEs), and ΣDDTs. The biomarker responses at Thabela Thabeng responses were explained by the environmental factors, and the fish from Vischgat were in the best condition with the responses mostly attributed to the presence of hexachlorobenzene (HCB), chlordanes, and hexachlorocyclohexanes (ΣHCHs). The common organisms between the three sites often had very different trophic positions which is explained by the presence of allochthonous nitrogen inputs that differ between the sites. There was also an indication of biomagnification of most of the compounds, particularly at Barrage and Thabela Thabeng. The organisms sampled from the Phongola Floodplain had higher ΣOCPs during the April (high flow) sampling event. The red claw crayfish (Cherax quadricarinatus) followed by brown squeaker (Synodontis zambezensis) had the greatest ΣOCP burdens of <LOD–33 ng/g and 25–170 ng/g respectively. The predominant OCP class was the DDTs, these were mostly from aged sources. The biomarkers indicated that the organisms were in a poorer state during the April sampling event. The responses were explained more by the environmental parameters than the presence of OCPs. The only OCP class to biomagnify in the Phongola Floodplain were the total of the DDTs and metabolites (DDx). The Phongola system is less impacted than the Vaal River system based on the results from this study.