Mercury concentrations in water resources potentially impacted by coal-fired power stations and artisanal gold mining in Mpumalanga, South Africa

Speciation and bioavailability of mercury in sediments from Mokolo River, Limpopo Province, South Africa

The presence of coal-based power plants and coal mine in the Waterberg area subjects the Mokolo River to potentially toxic elements (PTEs) such as mercury (Hg). Mercury is an extremely toxic element. Thus, monitoring and chemical speciation of Hg in water bodies; particularly in sediments is a vital tool for assessing water quality. The objective of this study was to investigate the levels of Hg(II) and methyl Hg (MeHg(I)) in sediment samples collected from Mokolo River in different seasons, as well as examining factors such as pH, temperature and organic matter content, which could affect Hg methylation rates. An ultrasonic based method was used for the extraction of Hg species in sediments. This was followed by the chromatographic separation and detection of Hg(II) and MeHg(I) by the on-line coupling of high-performance liquid chromatography (HPLC) to inductively coupled plasma-mass spectrometry (ICP-MS). A solution containing HCl and 2-mercaptoethanol was employed for the extraction of Hg species in sediments. Separation of the two species of Hg was achieved using isocratic elution mode with a mobile phase containing L-cysteine, 2-mercaptoethanol, ammonium acetate and methanol. The accuracy of the method was checked and yielded a percentage recovery of 86%. The Hg(II) concentrations ranged from 38.4 to 89.05 ng g^-1 and 34.8 to 57.3 ng g^-1 in low and high flow seasons, respectively. The concentrations of MeHg(I) ranged from 0.702 to 4.5 ng g^-1 and 0.5 to 2.5 ng g^-1 in the low and high flow seasons, respectively. Factors such as pH and temperature were found to influence the methylation rates, however correlation couldn't be established to organic matter content due to similar amount of organic matter in all the samples.

Mercury concentrations in eggshells of the Southern Ground-Hornbill (Bucorvus leadbeateri) and Wattled Crane (Bugeranus carunculatus) in South Africa

In this study, wild hatched eggshells were collected from the nests of threatened Wattled Crane and South Ground-Hornbill in an attempt to determine their total Hg concentrations. A total of fourteen eggshell samples from both bird species were collected from different study areas in the Mpumlanga and KwaZulu-Natal Provinces of South Africa. The eggshells were acid digested under reflux and their total Hg concentrations were determined using cold-vapour atomic absorption spectrophotometry (CV-AAS). The observed total Hg levels for the South Ground-Hornbill samples ranged from 1.31 to 8.88 µg g(-1) dry weight (dw), except for one outlier which had an elevated 75.0 µg g(-1) dw. The levels obtained for the Wattled Crane samples were relatively high and these ranged from 14.84 to 36.37 µg g(-1) dw. Generally, all the measured total Hg concentrations for the Wattled Crane samples exceeded the estimated total Hg levels derived for eggshell which were known to cause adverse reproductive effects in avian species from previous studies. Based on these findings, it is, therefore, possible that the exposure of these birds to elevated Hg may have contributed to their present population decline.

The effects of prenatal methylmercury exposure on trace element and antioxidant levels in rats following 6-hydroxydopamine-induced neuronal insult

Methylmercury (MeHg) is a metal toxin found commonly in the environment. Studies have shown severe neurotoxic effects of MeHg poisoning especially during pregnancy where it crosses the foetoplacental and the blood brain barrier of the foetus leading to neurodevelopmental deficits in the offspring. These deficits may predispose offspring to neurodegenerative diseases later in life. In this study we investigated the effects of prenatal methylmercury exposure (2.5 mg/L in drinking water from GND 1-GND 21) on the trace element status in the brain of adolescent offspring (PND 28). Total antioxidant capacity (TAC) was measured in their blood plasma. In a separate group of animals that was also exposed prenatally to MeHg, 6-hydroydopamine (6-OHDA) was administered at PND 60 as a model of neuronal insult. Trace element and TAC levels were compared before and after 6-OHDA exposure. Prenatal MeHg treatment alone resulted in significantly higher concentrations of zinc, copper, manganese and selenium in the brain of offspring at PND 28 (p < 0.05), when compared to controls. In contrast, brain iron levels in MeHg-exposed adolescent offspring were significantly lower than their controls (p < 0.05). Following 6-OHDA exposure, the levels of iron, zinc, copper and manganese were increased compared to sham-lesioned offspring (p < 0.05). Prenatal MeHg exposure further increased these trace element levels thereby promoting toxicity (p < 0.05). Total antioxidant capacity was not significantly different in MeHg and control groups prior to lesion. However, following 6-OHDA administration, MeHg-exposed animals had a significantly lower TAC than that of controls (p < 0.05). Brain TAC levels were higher in adult male rats than in female rats during adolescence however male rats that had been exposed to MeHg in utero failed to show this increase at PND 74. Prenatal MeHg exposure results in trace element dyshomeostasis in the brain of offspring and reduces total antioxidant capacity. This may reflect a mechanism by which methylmercury exerts its neurotoxicity and/or predispose offspring to further neurological insults during adulthood.

Differences in prenatal exposure to mercury in South African communities residing along the Indian Ocean

Mercury is a persistent environmental pollutant that has the potential to adversely affect human health, particularly, foetal neurodevelopment. The purpose of the study was to investigate prenatal mercury (Hg) exposure in the population in three sites along the South Africa coast. Study subjects included women (n=350) who were admitted for delivery at the local hospitals. Maternal and cord blood samples were collected to measure total mercury and each participant was required to answer a questionnaire. The 90th percentile of mercury levels in maternal and cord blood of the total population was 1.15 μg/l and 1.67 μg/l, respectively. Site 1 (Manguzi) participants had the highest maternal geometric mean (GM) values of 0.93 μg/l, which was significantly different from Site 2 (Port Shepstone) (0.49 μg/l) and Site 3 (Empangeni) (0.56 μg/l) (ANOVA test, p<0.001). Umbilical cord blood GM Hg level for Site 1 (1.45 μg/l) was more than double the GM Hg level in Site 2 (0.70 μg/l) and Site 3 (0.73 μg/l). Univariate analysis indicated that the following maternal characteristics were positive predictors for elevated umbilical cord Hg levels: maternal blood Hg levels, living with a partner, residing in Site 1, living in informal housing, using wood and gas for cooking, borehole water as a drinking source, and a member of the household being involved in fishing. Maternal dietary predictors of elevated Hg levels in umbilical cord blood included consuming fresh fish, tinned fish, fruit or dairy products, daily. This study provides baseline data and reveals that 2% of the study population were above the EPA's reference value (5.8 μg/l) suggesting low level exposure to mercury in pregnant women and the developing foetus in South Africa. Further research is required to explore the sources of elevated Hg levels in Site 1.

Mercury, arsenic and selenium concentrations in water and fish from sub-Saharan semi-arid freshwater reservoirs (Burkina Faso)

Despite intensive mining activities in Burkina Faso, little is known on the environmental impacts of metals and metalloids potentially released from these activities. Water samples and 334 fish from 10 reservoirs were taken in order to evaluate the extent of mercury (Hg), selenium (Se) and arsenic (As) contamination in aquatic systems and their potential health risk for humans and wildlife, taking into account their antagonistic interactions. Water and fish levels of these elements were relatively low and did not reveal an important impact of gold mining activities. Water temperature and conductivity were the key factors associated with higher levels of MeHg. Higher sulfate content was reported in sites with more particulate Hg, As and Se, suggesting anthropogenic origin of metal(loid) inputs in water reservoirs. Metal(loid) concentrations in fish were low and ranged from 0.002 to 0.607 μg/g wet weight (w.w.) for Hg, 0.023 to 0.672 for Se and 0.039 to 0.42 for As. These levels are similar or slightly higher than those reported in many other studies from Africa. Nevertheless, more than 70% of piscivore fish exceeded the threshold for wildlife protection for MeHg. Further, a traditional risk analysis performed ignoring Se antagonism indicated that these piscivores should be consumed by humans with caution. However, when taking into account the antagonistic effect of Se on Hg toxicity, up to 99% of all fish could be protected from Hg toxicity by their Se content. When considering both As/Se and Se/Hg antagonism, 83% instead the 99% of fish should be considered safe for consumption. Fish Se and As concentrations did not pose potential risk for both animals and humans. Overall, these reservoirs were relatively unaffected by As, Se and Hg contamination despite the rising gold mining activities. Further, considering antagonistic effects of As, Se and Hg may help refine consumption advisories.

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.