A Multivariate Analysis of Metal Concentrations in Two Fish Species of the Nyl River System, Limpopo Province, South Africa

Element contamination of the Orange-Vaal River basin, South Africa: a One Health approach

Numerous low-income groups and rural communities depend on fish as an inexpensive protein source worldwide, especially in developing countries. These communities are constantly exposed to various pollutants when they frequently consume polluted fish. The largest river basin in South Africa is the Orange-Vaal River basin, and several anthropogenic impacts, especially gold mining activities and industrial and urban effluents, affect this basin. The Department of Environment, Forestry and Fisheries in South Africa has approved the much-anticipated National Freshwater (Inland) Wild Capture Fisheries Policy in 2021. The aims of this study were (1) to analyze element concentrations in the widely distributed Clarias gariepinus from six sites from the Orange-Vaal River basin and (2) to determine the carcinogenic and non-carcinogenic human health risks associated with fish consumption. The bioaccumulation of eight potentially toxic elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) was assessed in C. gariepinus from sites with different anthropogenic sources. The human health risks were determined to assess the potential risks posed by consuming contaminated C. gariepinus from these sites. Carcinogenic health risks were associated with fish consumption, where it ranged between 21 and 75 out of 10,000 people having the probability to develop cancer from As exposure. The cancer risk between the sites ranged between 1 and 7 out of 10,000 people to developing cancer from Cr exposure. A high probability of adverse non-carcinogenic health risks is expected if the hazard quotient (HQ) is higher than one. The HQ in C. gariepinus from the six sites ranged between 1.5 and 5.6 for As, while for Hg, it was between 1.8 and 5.1. These results highlight the need for monitoring programs of toxic pollutants in major river systems and impoundments in South Africa, especially with the new fisheries policy, as there are possible human health risks associated with the consumption of contaminated fish.

Human health risks associated with consumption of fish contaminated with trace elements from intensive mining activities in a peri-urban region

Worldwide, numerous rural communities and low-income groups depend on fish harvested by subsistence fishers from local rivers and its impoundments as a source of protein. The aim of the present study was to determine the trace element bioaccumulation (As, Cd, Cr, Cu, Ni, Pb, Pt, Zn) in three edible fish species (Cyprinus carpio, Clarias gariepinus, Oreochromis mossambicus) from two impoundments in the Hex River system, South Africa, as well as the chronic health risk these trace elements pose to regular fish consumers. Trace element concentrations in the Hex River are naturally high (geogenic source), however, increased anthropogenic activities, such as intensive platinum mining activities, elevate the already high background concentrations. Concentrations of As, Cr, and Pt in C. carpio and C. gariepinus, as well as Ni and Zn in O. mossambicus were significantly higher in the impacted impoundment as compared to the reference impoundment. Concentrations of Cr and Cu were at both sampling sites the highest in O. mossambicus. From the human health risk assessment, As poses non-carcinogenic (HQ = 2-7) and carcinogenic risks (33-93 out of 10,000 people), while Cr (3-10 out of 10,000 people) and Ni (2-6 out of 10,000 people) pose only carcinogenic risks for the regular consumption of all three fish species from both impoundments, indicating a high probability of adverse human health effects. For As, Cr and Ni, also the sediment concentrations exceeded the levels of concern within the consensus based sediment quality guideline (CBSQG), while Cd, Cu, Ni and Zn exceeded the water quality guideline values. Thus, the CBSQG approach could be a promising tool for predicting human health risk associated with fish consumption. Since the present study only focused on the individual trace element risks, mixed toxicity of these trace elements and possible other pollutants within these fish species may pose an even greater risk to people who consume these fish regularly.

Drivers of aquatic macroinvertebrate communities in a Ramsar declared wetland system

Wetlands in the Global South are under increasing pressure due to multiple stressors associated with global change. Water and sediment quality assessments, as well as biomonitoring using macroinvertebrate communities, are fundamental tools for informing wetland condition and management strategies. Here, we examine water and sediment parameters affecting aquatic macroinvertebrates in Nlyslvey Wetland, Limpopo Province, South Africa. Water quality, sediments, fish and macroinvertebrate community data were collected across three seasons (hot-dry, hot-wet, cool-dry) from five sites. Baetidae, Corixidae, Coenogrionidae, Dytiscidae and Physidae were the most abundant and dominant families, with functional feeding group (FFG) ratios indicating that all sites were strongly autotrophic, had high predator-prey ratios, few shredders and had a stable substrate across seasons. Fish abundances increased significantly towards the cool-dry season. Based on redundancy analysis, P, Ca, pH, Cu and Na were strongly positively associated with macroinvertebrates, including Physidae, Corixidae, Planorbidae, Ostracoda, Potamonautidae and Hydropyschidae; turbidity and sulphur were associated with Dytiscidae, Oligochaetae, Libellulidae, Gerridae and Dixidae; and fish abundance, Fe, oxygen reduction potential and total dissolved solids were negatively associated with Baetidae, Belostomatidae, Hydrophilidae and Leptoceridae. Therefore, these variables accounted for high levels of variation in macroinvertebrate families, with the cool-dry season clearly distinguished from the hot-wet and hot-dry seasons according to functional feeding groups. Being a protected area, this information could provide a useful baseline for further studies into wetlands in the region subject to greater anthropogenic stresses, as well as future studies in this Ramsar site. Further studies are required to assess the importance of environmental factors influencing the richness and distribution of macroinvertebrate communities in wetlands under growing anthropogenic pressures.

Evaluation of Trace Element and Metal Accumulation and Edibility Risk Associated with Consumption of Labeo umbratus from the Vaal Dam, South Africa

With the occurrence of recreational and small scale subsistence fishing activities at the Vaal Dam, South Africa, consumption of fish from this dam may result in health risks associated with trace elements and metals. The Vaal Dam is one of the largest dams in South Africa, located between the Gauteng Province and Orange Free State, and supplies water to approximately 11.6 million people. A total of 38 specimens of the benthic cyprinid fish Labeo umbratus were collected from the Vaal Dam during two surveys, in 2011 and 2016. Samples of muscle, liver, kidney, gill and spinal cord were analysed, along with sediment samples collected during the same surveys. Thirteen trace elements were analysed in the samples by Inductively Coupled Plasma–Optical Emission Spectrometry, Inductively Coupled Plasma–Mass Spectrometry, Atomic Absorption Spectroscopy and Total Reflection X-ray Fluorescence spectroscopy. This is the first survey on trace element and Hg accumulation in this fish species from the Vaal Dam and target hazard quotients (THQ) indicated that there is a risk for consumers of fish for As and Hg (THQ = 1.43 and 1.14 respectively). Although levels of trace elements in this impoundment have shown little change for a number of years and are lower than global background levels, studies detailing the accumulation of metals by fish inhabiting the Vaal Dam have indicated that trace elements in muscle tissue are above food safety guidelines. Trace element levels in L. umbratus are lower compared to other species inhabiting the Vaal Dam and further indicate that risks for consumers can be decreased if humans relying on fish from the Vaal Dam preferentially consume this species over others.