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Clarias gariepinus is increasing in importance as a global aquaculture species with a 100 fold increase in production over the past decade but this species still remains one of the most important wild harvested freshwater food fish throughout rural Africa. However, this species has been shown to accumulate metals from contaminated inland waters. In this paper, the metal concentrations in muscle tissue of C . gariepinus from two main-stem impoundments in the Olifants River, Limpopo Basin, were measured and a desktop risk assessment based on the US-EPA methodology completed to evaluate whether long-term consumption of C . gariepinus from these impoundments may pose a health risk to rural communities. Our results show that metals are accumulating in the muscle tissue of C . gariepinus and have appeared to have increased in the last two decades. Risk assessment generated Hazard quotients (HQ) greater than 1 indicate that long term consumption of fish from these impoundments may cause adverse health impacts. We found that lead (HQ=9), antimony (HQ=14), cobalt (HQ=2) and chromium (HQ=1) at one impoundment and lead (HQ=2) at the other impoundment were above acceptable levels for weekly consumption of 150 g C . gariepinus muscle tissue. [ABSTRACT FROM AUTHOR]

Macrophytes are important in the biogeochemistry of flowing rivers, although most information so far has relied on measurements of nutrients in plant tissues. This yields only indirect information on the nutrient uptake fluxes by roots and shoots and about nutrient translocation between roots and shoots. Here, we studied nitrogen uptake through experiments with enriched 15 N stable isotopes., Two macrophytes ( Potamogeton natans and Ranunculus fluitans) were grown in a closed race track-shaped flume, allowing us to control the hydraulic conditions in and around the plants. Overall ammonium uptake rates (μmol g−1 dry mass h−1) were higher for R. fluitans than P. natans., In addition to differences between the species, the spatial position of individuals within the plant patch and water flow were also important in explaining ammonium uptake. Thus, ammonium uptake was high at the leading edge of the patch and increased with velocity., Plant characteristic, such as the angle at which the plants bent in the flow, was also correlated with ammonium uptake. Differences in nutrient uptake associated with hydrodynamic parameters raised the question of how the two are related. For both species, uptake was not correlated with Reynolds stress, indicating the poor effect of turbulent mixing in determining ammonium uptake. [ABSTRACT FROM AUTHOR]

The authors investigate the discovery of pentastomid parasites in fish in the Olifants and Incomati River systems in South Africa. According to the authors, sebekiid and subtriquetrid pentastome larvae were recovered from the body cavity or swim bladder of several fish species from various localities in Limpopo and Mpumalanga Provinces in South Africa during parasitological field surveys of freshwater fish in the areas. They note that pentastomid infections in the Mormyridae and Clariidae represent new host records.

Many elements become toxic when they exceed certain concentrations in the environment. In the aquatic ecosystems, they can be accumulated in the biota such as fish and may be toxic to humans upon consumption. This study assessed bioaccumulation of the following elements; arsenic, cadmium, chromium, copper, lead and Zinc in the muscle tissue of ten common consumable fish species from Groot Letaba River in South Africa and assessed the potential human health risks. In the water, only zinc exceeded the recommended safe limit. However, most of the elements were found to be significantly accumulated in the sediments and the muscle tissue of the fish species. The elements were more accumulated in the omnivorous and some predatory fish species than the herbivores. Concentrations of As, Cd, Cr and Zn in the fish muscle tissue were above the recommended food safety guideline values, indicating a potential health risk to consumers, especially As at Site 1 and Zn at Site 4. There is a need therefore for continuous monitoring of trace metals and metalloids in the river in order to ensure the safety of aquatic organisms and humans who rely on the river. [ABSTRACT FROM AUTHOR]

Abstract The present study describes total mercury (THg) levels in surface water, sediment and biota from the Olifants River Basin (ORB) (South Africa) and investigates the trophic transfer of THg by means of trophic magnification factors (TMFs) in the subtropical ORB food web. Although levels in surface water, sediment and invertebrates were low, elevated levels of THg were measured in fish species of higher trophic levels (0.10–6.1 μg/g dw). This finding supports the biomagnificative character of mercury. THg concentrations in fish from the present study were find to be higher than most values reported in fish from other African aquatic ecosystems and comparable or lower compared to more industrialized regions. Fish length, trophic level, sediment THg levels and TOC in sediment were determining factors for THg levels in fish tissue. Concentrations were found to be higher in larger (and older) fish. Mercury has a high affinity for organic matter and will bind with the TOC in sediment, thus reducing the bioavailability of THg for aquatic biota which is reflected in the significant negative correlation between THg and TOC in sediment. A significant positive relationship between relative trophic level and THg concentrations was observed and also TMFs indicate biomagnification in the ORB food web. However, the trend of lower TMFs in tropical areas compared to temperate and arctic regions was not supported by the results. The consumption of fish from higher trophic levels at the average South African consumption rate is expected to pose a significant health risk. Graphical abstract Image 1 Highlights • Large data gap on THg levels and trophic transfer in (sub)tropical ecosystems. • Pollution status and biomagnification of THg in the subtropical ORB is studied. • This study confirms the previously reported biomagnificative character of Hg. • Higher levels of THg in fish species of higher trophic levels and TMFs > 1. • The consumption of fish from ORB is expected to pose a significant health risk. This paper contributes to the knowledge gap on the fate and transport of THg in (sub)tropical aquatic ecosystems, specifically in Africa. [ABSTRACT FROM AUTHOR]

Abstract Biomagnification of Hg and persistent organic pollutants (POPs: polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs)) in aquatic food chains can lead to high pollutant concentrations in top predators, including humans. Despite this threat to human health, research concerning bioaccumulation is still underrepresented in the southern hemisphere and in (sub)arctic and (sub)tropical areas, emphasizing the need for research in these locations. In this study, samples of water, sediment and aquatic biota were analyzed to determine concentrations of POPs and total mercury (THg) in the Ga-Selati river (South Africa) and two rivers Rena and Gudbrandsdalslågen in Norway. Trophic magnification factors (TMFs) were determined to evaluate and compare the biomagnification and the threat to human health due to consumption of the fish was assessed. Concentrations of POPs in sediment and biota samples were generally low except for relatively high concentrations of ∑DDX (dichlorodiphenyltrichloroethane and metabolites) in aquatic biota from the Ga-Selati river (ranging from 1.9 to 133 ng/g ww in invertebrates and 1.9 to 5643 ng/g ww in fish). Dissolved THg concentrations were high in the Ga-Selati river (ranging from 0.009 to 0.036 μg/l) but THg concentrations in sediment and biota were low in studied rivers compared to other studies. Biomagnification occurred for THg, several DDT-metabolites and PCB compounds, TN and CN. Biomagnification of p,p′ -DDT and THg differed significantly between the two countries, supporting existing patterns found in literature, although more data is needed to attribute these differences to climatic or other factors. Concentrations in fish from the rivers Ga-Selati and Rena were under the threshold levels reported for THg and POPs, but caution should be taken when consuming Northern pike (Esox Lucius) from the subarctic river Gudbrandsdalslågen, to avoid harmful effects due to both elevated THg and PBDE exposure. Graphical abstract Unlabelled Image Highlights • POPs and Hg biomagnify ls in the river ecosystems of the Ga-Selati (South Africa), Rena and Laagen (Norway). • Overall low concentrations in water, sediment and aquatic biota • Biomagnification of Hg and pp ′-DDT differs significantly between the two climates. • Levels of Hg and PBDE in Northern pike (river Laagen) is of concern to human health. [ABSTRACT FROM AUTHOR]

This study investigates the trophic transfer of persistent organic pollutants (POPs: PCBs, PBDEs, OCPs and PFASs) in the subtropical aquatic ecosystem of the Olifants River Basin (South Africa) by means of trophic magnification factors (TMFs). Relative trophic levels were determined by stable isotope analysis. POP levels in surface water, sediment and biota were low. Only ∑ DDTs levels in fish muscle (< LOQ-61 ng/g ww) were comparable or higher than values from other temperate and tropical regions. Significant positive relationships between relative trophic level and PCB, DDT and HCH concentrations were observed so trophic levels play an important role in the movement of contaminants through the food web. TMFs were > 1, indicating biomagnification of all detected POPs. Calculated TMFs for PCBs were comparable to TMF values reported from the tropical Congo River basin and lower than TMFs from temperate and arctic regions. For p , p ′-DDT, a higher TMF value was observed for the subtropical Olifants River during the winter low flow season than for the tropical Congo river. TMFs of DDTs from the present study were unexpectedly higher than TMFs from temperate and arctic aquatic food webs. The fish species in the aquatic ecosystem of the Olifants River can be consumed with a low risk for POP contamination. [ABSTRACT FROM AUTHOR]