1,721,098 research outputs found
Adsorption, uptake and distribution of gold nanoparticles in Daphnia magna following long term exposure
No full textGold nanoparticles (nAu) have recently been studied and developed within the biological and photothermal therapeutic contexts. The major clinical interest is within the application of novel drug delivery systems. Environmental exposure to nanoparticles can occur in different stages of the lifecycle of the product; from their synthesis, applications, product weathering and their disposal. Freshwater Daphnids, specifically Daphnia magna, have been used since the 1960s as a standard species in acute and chronic aquatic toxicity testing. Visualization of the interactions and uptake of nAu by D. magna was related to reproduction and molting patterns. Exposure to nAu was done using a chronic reproduction test performed for 14 days at six concentrations (0.5 mg/L, 2 mg/L, 5 mg/L, 10 mg/L, 15 mg/L and 20 mg/L). Microscopy was used to determine whether there was any uptake or interaction of nAu with daphnia. However the concentration of nAu in the media and the charge of particles played a role in the uptake and surface adsorption. As exposure concentrations of nAu increased it appeared that the nAu aggregated onto the surface and in the gut of the organisms in higher concentrations. There was no evidence of nAu internalization into the body cavity of the daphnia. Aquatic exposure to nAu resulted in increased adhesion of the particles to the carapace of daphnia, ingestion and uptake into the gut of daphnia and had no significant effect on reproduction and molting pattern
South Africa
No full textSouth Africa has the second longest coastline on the African continent and spans two oceans. The confluence of the Benguela and Agulhas Currents off South Africa results in their dynamics being complex and often unpredictable, although it is these dynamic ocean systems that contribute to the high biodiversity and productivity of the South African coastal and marine ecosystems. There are 136 different habitat types ranging from subtropical coral reefs and mangroves on the north-east coast to temperate kelp forests and seamounts on the south and western coast. These habitats are under pressure from climate change as well as direct human impacts. Climate change is expected to influence the dynamic nature of the ocean systems through alterations of the currents, sea-level rise and increased water temperatures, ocean acidification, and storm events. Human activities such as fishing, overexploitation of marine resources, and coastal development have placed great pressures on marine and coastal habitats, biodiversity, and resources. Future threats include increased offshore mining activities in habitats that are not well studied or protected. Marine protection and management is achieved through the overarching National Environmental Management and Integrated Coastal Management Acts, which make provision for setting up marine protected areas (MPAs) and protection of individual species. Operation Phakisa is an exciting new initiative that has the potential to address the human resources capacity shortages, research requirements, and governance issues identified in this chapte
Perfluorinated compounds in the aquatic food chains of two subtropical estuaries
No full textPer- and polyfluoroalkyl substances (PFASs) are ubiquitous in the environment and remain in largely unknown concentrations and with unknown effects on the African continent. Here we aimed to assess the presence of 15 PFASs in different compartments of the aMatikulu and uMvoti estuaries and to examine potential risks for human health through the consumption of contaminated fish. This is the first known study to assess PFASs in South African estuaries. Thirteen out of the fifteen PFASs were detected in water, sediment and biota samples from both estuaries, with perfluorooctanoic acid (PFOA), detected in every sample. PFOA concentrations from uMvoti water samples were the highest recorded to date in South African waters. PFOA was found in high concentrations in all water samples with an average range between 171 and 258 ng/L in the aMatikulu and 711–788 ng/L in the uMvoti. Perfluorooctane sulfonate (PFOS) concentrations in fish tissue samples were significantly higher than other PFASs. PFOS concentrations in all fish species caught in the aMatikulu ranged between 0.09 and 2.25 ng/g wet weight (ww) in muscle tissue and 1.5–12.08 ng/g ww in liver tissue, while PFOA concentrations ranged between 0.08 and 0.67 ng/g ww in muscle tissue and 0.54–1.48 ng/g ww in liver tissue. Concentrations of PFASs were only measured in Oreochromis mossambicus from the uMvoti and contained PFOS concentrations ranging from 0.18 to 0.97 ng/g ww in muscle tissue and 7.29–27.96 ng/g ww in liver tissue. PFOA concentrations ranged between 0.12 and 0.58 ng/g ww in muscle tissue and 0.17–1.01 ng/g ww in liver tissue. PFAS concentrations in all fish sampled were below the calculated Minimum Risk Levels (MRLs) for safe human consumptio
Influence of mining pollution on metal bioaccumulation and biomarker responses in cave dwelling fish, Clarias gariepinus
No full textCave ecosystems remain largely unstudied and risk being severely degraded as a result of anthropogenic activities. The Wonderfontein Cave, situated in the extensive gold mining region of the Witwatersrand Basin, is one such system that hosts a population of Clarias gariepinus, which is exposed to the influx of polluted mine water from the Wonderfontein Spruit River. The aim of this study was to investigate the bioaccumulation of metals, as well as relevant biomarkers, in C. gariepinus specimens sampled from the Wonderfontein Cave during high (April 2013) and low (September 2013) flow surveys. Results were also compared to a surface population associated with the Wonderfontein Spruit River. There were temporal differences in metal bioaccumulation patterns and this was attributed to the lack of dilution during the low flow period. Metals associated with acid mine drainage, i.e. Co, Mn and Zn were significantly higher in the Wonderfontein Cave population and were reflected in an increase in oxidative stress biomarkers (catalase, protein carbonyls and superoxide dismutase) and the induction of metallothionein, a biomarker of metal exposure. The surface population was exposed to metals associated with geological weathering processes, i.e. Fe and A
Comparative aquatic toxicity of gold nanoparticles and ionic gold using a species sensitivity distribution approach
Get PDFGold nanoparticles (nAu) are used in drug delivery systems allowing for targeted cellular distribution. The effects of increased use and release of nanoparticles into the environment are not well known. A species sensitivity distribution (SSD) allows for the ecotoxicological hazard assessment of a chemical based on single species toxicity tests. Aquatic toxicity needs to be related to particle characterization in order to understand the effects. The behaviour of nAu in the medium changed as the concentration increased. The toxic potential of ionic gold and nAu was expressed as a hazardous concentration where 5% of species will be harmed (HC5). The HC5 for nAu was much higher (42.78 mg/L) compared to the ionic gold (2.44 mg/L). The differences between the hazard potentials of nAu and ionic gold were attributed to the nAu not releasing any Au ions into solution during the exposures and following an aggregation theory response. Exposures to ionic gold on the other hand followed a clear dose dependent response based on the concentration of the ionic metal. Although SSDs present an indication of the relative hazard potential of nanoparticles, the true worth can only be achieved once other nanoparticle characteristics and their behavior in the environment are also considere
Response of zooplankton communities to altered water quality and seasonal flow changes in selected river dominated estuaries in KwaZulu-Natal, South Africa
No full textGlobally, estuaries are among the most productive ecosystems with many threatened by anthropogenic activities. Zooplankton is a bioindicator of ecosystem integrity. The spatial and temporal composition of zooplankton communities were quantified and compared within and between three estuaries (uMvoti, Thukela and aMatikulu/Nyoni estuaries) with different levels of human pressure in KwaZulu-Natal, South Africa. Additional effects of some physico-chemical variables and seasonal flow patterns to zooplankton community structuring were analyzed. The aMatikulu/Nyoni Estuary was selected as a reference site due to its good ecological state. Sampling dates represented high flow (March and April) and low flow (August and September) from 2014 to 2016. Following aMatikulu/Nyoni, highest abundance was recorded in Thukela and then uMvoti Estuary with copepod Pseudodiaptomus hessei and Acartia natalensis dominating the three estuaries. Highest abundance was recorded during low flow in the uMvoti and Thukela estuaries. Redundancy analysis revealed higher salinity and oxygen as environmental determinants of zooplankton community structure in the aMatikulu/Nyoni while turbidity and pH were the determinants of zooplankton community structures in uMvoti and Thukela estuaries. Elevated concentrations of DIN in the Thukela Estuary during high flow identifies the Thukela River as an important source of nitrogen to this estuary. Our findings suggest that these estuaries be managed to ensure sufficient freshwater supply which controls primary production. Although the three estuaries were from the same biogeographical region with a similar river dominated function, high variability in their zooplankton communities could be explained by differing water quality due to differing human pressure in their catchment
Acute toxicity of double-walled carbon nanotubes to three aquatic organisms
Get PDFThis study investigated the toxicity of double walled carbon nanotubes (DWCNTs) to three aquatic organisms, namely, Pseudokirchneriella subcapitata, Daphnia pulex, and Poecilia reticulata under the influence of exposure media properties specifically the ionic strength and organic matter represented by humic acid. Results indicated that ionic strength enhanced DWCNTs agglomeration whilst humic acid stabilized the CNTs and in turn inhibited the formation of aggregates. LC50s for D. pulex were higher at 2.81 and 4.45 mg/L for pristine and oxidised DWCNTs, respectively; however, P. reticulata had lower values of 113.64 mg/L and 214.0 mg/L for the same CNTs correspondingly. P. subcapitata had EC50s of 17.95 mg/L and 10.93 mg/L for the pristine and oxidised DWCNTs, respectively. In the presence of humic acid high DWCNTs acute toxicity towards D. pulex and P. reticulata was observed but ionic strength led to opposite effect irrespective of DWCNTs form. Both humic acid and ionic strength shielded the P. subcapitata from toxic effects of DWCNTs. Overall, our findings suggest that the toxicity of DWCNTs in the aquatic systems (i) will be dependent on media properties and (ii) is likely to proceed at different rates to organisms at different trophic level
Persistent organic pollutants in the Olifants River Basin, South Africa: bioaccumulation and trophic transfer through a subtropical aquatic food web
No full textThis 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 ( 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 contaminatio
The contribution of physical and chemical sediment characteristics to environmental risk from an irrigation scheme in South Africa
No full textPurpose: The physical and chemical characteristics of sediment
from a South African irrigation scheme were used to
determine the sediment stressors within the system and to
determine whether or not stressors have the potential to contribute
to pollutant risk within the system. The information
generated also strengthens the database of sediment chemical
concentrations in South Africa.
Materials and methods: The sediment condition at various
sites along the Vaalharts Irrigation Scheme (VHIS) was
assessed based on physical and chemical characteristics. Sediment
samples were collected during three surveys from 2007
to 2009. Physical analysis included organic content and grain
size determination. The chemical characteristics were
analysed using sequential metal extractions and pesticide
analysis.
Results and discussion: Sediment samples from the Harts River
showed increasing organic content along the VHIS while
some sediment deposition was evident. Chemical analysis indicated
that no pesticide residueswere present in the sediment.
In general, the sediment metal concentrations indicated lower
concentrations than measured at other sites in South Africa.
The sequential extractions indicated that cadmium and manganese
were contained mostly in the soluble phase resulting in
a high to very high risk of metal pollution effects, as measured
with the Risk Assessment Code (RAC). A medium risk was
identified for cobalt and zinc concentrations. The high fractions
of cadmium present in the soluble fraction indicated
anthropogenic enrichment, potentially due to phosphate
fertiliser which is used in agriculture.
Conclusions" Sediment assessments are not routinely applied
in South Africa resulting in very little reference or background
data available for the area. The metal concentrations for the
study area were generally lower than those for other studies in
more polluted regions. A low risk for the majority of metals
was identified using the RAC methodologywith the exception
of manganese and cadmium. The study also contributes to the
available knowledge surrounding metal pollution in riverine
sediments in South Afric
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