A synthesis of mercury research in the Southern Hemisphere, part 2: Anthropogenic perturbations.

Environmental mercury (Hg) contamination is a global concern requiring action at national scales. Scientific understanding and regulatory policies are underpinned by global extrapolation of Northern Hemisphere Hg data, despite historical, political, and socioeconomic differences between the hemispheres that impact Hg sources and sinks. In this paper, we explore the primary anthropogenic perturbations to Hg emission and mobilization processes that differ between hemispheres and synthesize current understanding of the implications for Hg cycling. In the Southern Hemisphere (SH), lower historical production of Hg and other metals implies lower present-day legacy emissions, but the extent of the difference remains uncertain. More use of fire and higher deforestation rates drive re-mobilization of terrestrial Hg, while also removing vegetation that would otherwise provide a sink for atmospheric Hg. Prevalent Hg use in artisanal and small-scale gold mining is a dominant source of Hg inputs to the environment in tropical regions. Meanwhile, coal-fired power stations continue to be a significant Hg emission source and industrial production of non-ferrous metals is a large and growing contributor. Major uncertainties remain, hindering scientific understanding and effective policy formulation, and we argue for an urgent need to prioritize research activities in under-sampled regions of the SH.

The effects of silver nanoparticles on RAW 264.7. Macrophages and human whole blood cell cultures.

Silver nanoparticles (AgNPs) are commonly found in consumer products due to their antimicrobial properties. This study evaluated the effects of AgNPs on the murine macrophage cell line RAW 264.7 and human whole blood cell cultures (WBCs). Effects of AgNPs on RAW cells were assessed in the presence or absence of lipopolysaccharide (LPS). Effects of AgNPs on WBCs were monitored under basal conditions and in the presence of either LPS or phytohaemmagglutinin (PHA). AgNPs were cytotoxic to WBCs at 250 µg/ml. Under basal conditions, RAW cells ≥ 62.5. µg/ml and WBCs > 25 µg/ml AgNPs induced biomarkers associated with inflammation. Under LPS stimulated conditions, 250 µg/ml AgNP inhibited biomarkers associated with inflammation for both cultures. Under basal conditions, and in the presence of 250 µg/ml AgNP, WBCs produced acquired immune system cytokines IL-10 and IFNγ. IL-10 synthesis by WBCs was partially inhibited by 250 µg/ml AgNP in the presence of PHA. Proteome profiles of RAW cell supernatants show that AgNPs modulate biomarkers associated with inflammation. WBCs proteome analysis shows modulation of biomarkers associated with anti-inflammatory effects.

Effect of temperature on oxidative stress parameters and enzyme activity in tissues of Cape River crab (Potamanautes perlatus) following exposure to silver nanoparticles (AgNP).

Biomarkers of oxidative stress have been widely used in environmental assessments to evaluate the effects of exposure of aquatic organisms to contaminants from various anthropogenic sources. Silver nanoparticles (AgNP), the most produced NP worldwide and used in several consumer products, are known to produce oxidative stress in aquatic organisms. Similarly, temperature is also known to affect reactive oxygen species (ROS) by influencing the inputs of contaminants into the environment, as well as altering behavior, fate, and transport. Aquatic ecosystems are affected by both anthropogenic releases of contaminants and increased temperature. To test this hypothesis, the influence of AgNP and temperature in the response to multiple biomarkers of oxidative stress was studied in the gills and hepatopancreas of the Cape River crab Potamonautes perlatus. Responses were assessed through activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and the nonenzymatic antioxidant glutathione S-transferase (GST). The response of the oxidative stress biomarkers analyzed was always higher in hepatopancreas than in gills. Elevated temperatures (28°C) induced oxidative stress by increasing SOD, CAT, and GST activities, particularly at 100 µg/ml AgNP. These data indicate that AgNP-mediated toxicity to P. perlatus is modulated by elevated temperatures, but this relationship is not linear. Co-effects of AgNP and temperature are reported for the first time in P. perlatus.

Ecotoxicity of silver nanomaterials in the aquatic environment: a review of literature and gaps in nano-toxicological research.

There has been extensive growth in nanoscale technology in the last few decades to such a degree that nanomaterials (NMs) have become a constituent in a wide range of commercial and domestic products. With NMs already in use in several consumer products, concerns have emerged regarding their potential adverse environmental impacts. Although research has been undertaken in order to minimise the gaps in our understanding of NMs in the environment, little is known about their bioavailability and toxicity in the aquatic environment. Nano-toxicology is defined as the study of the toxicity of nanomaterials. Nano-toxicology studies remain poorly and unevenly distributed. To date most of the research undertaken has been restricted to a narrow range of test species such as daphnids. Crabs are bio-indicators that can be used for toxicological research on NMs since they occupy a significant position in the aquatic food chain. In addition, they are often used in conventional ecotoxicological studies due to their high sensitivity to environmental stressors and are abundantly available. Because they are benthic organisms they are prone to contaminant uptake and bioaccumulation. To our knowledge the crab has never been used in nano-toxicological studies. In this context, an extensive review on published scientific literature on the ecotoxicity of silver NPs (AgNPs) on aquatic organisms was conducted. Some of the most common biomarkers used in ecotoxicological studies are described. Emphasis is placed on the use of biomarker responses in crabs as monitoring tools, as well as on its limitations. Additionally, the gaps in nano-toxicological research and recommendations for future research initiatives are addressed.

A review of mercury pollution in South Africa: current status.

The present paper is a review on the status of mercury (Hg) as a pollutant in South African aquatic ecosystems. Spatial patterns of Hg distribution and bioaccumulation in water resources were investigated by collecting and analyzing multimedia samples for physiochemical and Hg-species determination from 62 sampling sites. The data presented showed a wide range in concentrations, which was expected given the array of environmental parameters, water chemistry and sources of Hg. Generally, higher Hg concentrations were measured in environmental compartments impacted by the major anthropogenic Hg sources which, in South Africa, are largely represented by emissions from coal-fired power stations (i.e. Olifants and Upper Vaal WMAs) and artisanal gold mining (i.e., Inkomati WMA). Ancillary water quality parameters (e.g. pH, temperature, DOC, EC and nutrients) were measured and regressed with the measured Hg concentrations to determine which environmental parameters most influenced regional Hg concentrations. The TotHg (sed) and DOC concentrations were identified as important factors controlling TotHg (aq), while TotHg(sed) were correlated to TotHg (aq). This result is indicative of the combined effects of sediment settling and resuspension in the aquatic environment. In contrast, MeHg (aq) was not correlated to DOC. MeHginvert were correlated to MeHg (sed), while MeHg (fish) were correlated to MeHg (aq) and water quality variables (chlorides--Cl(-) and electrical conductivity--EC). A steady progress has been made in Hg research in South Africa. However, despite the substantial knowledge about Hg toxicity, there are still considerable knowledge gaps on the fate and transport of Hg. Hence, further environmental and human health studies are proposed.