Effect of pH, sulphate concentration and total organic carbon on mercury accumulation in sediments in the Volta Lake at Yeji, Ghana

In this study, pH, total organic carbon, sulphate concentration and mercury concentrations of sediment samples from the Volta Lake at Yeji in the northern part of Ghana were determined. The results indicate that pH ranged from 6.32 to 8.21, total organic carbon ranged from 0.17 to 3.02 g/kg and sulphate concentration from 10.00 to 57.51 mg/kg. Total mercury concentrations ranged from 32.61 to 700 ng/g which is below the International Atomic Energy Agency recommended value of 810 ng/g. Humic substance-bound mercury ranged from 81.15 to 481.31 mg/kg in sediments and its two fractions existed as humic acid-bound mercury > fulvic acid-bound mercury with the ratio of humic substance-bound mercury to fulvic acid-bound mercury as 1.62 on the average. Humic substance-bound mercury and the two fractions fulvic acid-bound mercury and humic substance-bound mercury in sediments were favorably determined and found to correlate significantly positive with total organic carbon (r = 0.538) and total mercury (r = 0.574). However, there were poor correlations between SO(4) (2-) concentrations and humic substance-bound mercury (r = -0.391) as well as the two fractions; fulvic acid (r = -0.406) and humic acid (r = -0.381). By assuming that methyl mercury is mostly formed in sediments, these significant relations suggest that the efficiency of mercury being methylated from a given inorganic form depends on the amount, and most likely biochemical composition of total organic carbon in the lake sediment but not the SO(4) (2-) concentration.

Levels of total mercury in different fish species and sediments from the Upper Volta Basin at Yeji in Ghana

In this study, total mercury concentrations were determined in sediments and seven different fish species from the Upper Volta Basin area of Yeji in Ghana. Mercury concentrations found ranged from 44.17 to 85.88 ng/g wet weight for Synodontis gambiesis, from 11.25 to 79.73 ng/g wet weight for Synodontis membranaceus, from 13.11 to 38.64 ng/g wet weight for Synodontis ocellifer, from 16.39 to 25.82 ng/g wet weight for Distishodus rotratus, from 40.80 to 90.30 ng/g wet weight for Bagrus docmac, from 10.48 to 61.90 ng/g wet weight for Chrysichthys nigrodigitatus and from 12.33 to 24.18 ng/g wet weight for Gnathoneus senegalensis. These values are below the 500 ng/g guideline recommended by the WHO/FAO, implying that fish from the Upper Volta Basin area of Yeji are safe for human consumption. Good correlation was observed between mercury concentration and fresh weight (R(2) = 0.6067) and total length (R(2) = 0.8754) for Gnathonemus senegalensis. However, poor correlations were observed between mercury concentration and fresh weight and total length for the other six species. Mercury in sediments ranged from 11.87 to 70.25 ng/g dry weights with a mean of 41.60 ng/g dry weight being below the IAEA threshold of 810 ng/g.. These values show that sections of the Upper Volta River remain relatively clean in spite of substantial loadings of mercury into the river's basin from gold mining activities.

Environmental and occupational exposures to mercury among indigenous people in Dunkwa-On-Offin, a small scale gold mining area in the South-West of Ghana

Total mercury concentrations in human hair and urine samples were determined to ascertain the extent of environmental and occupational mercury exposure in Dunkwa-On-Offin, a small scale gold mining area of the central-west region of Ghana. In all ninety-four (94) hair and urine samples comprising of forty (40) small scale miners and fifty-four (54) farmers were collected and analyzed for their total mercury levels using the cold vapour atomic absorption spectrometry. The hair total mercury concentrations ranged from 0.63 to 7.19 ug/g with a mean of 2.35 ± 1.58 ug/g for the farmers and 0.57-6.07 ug/g with a mean of 2.14 ± 1.53 ug/g for the small scale gold miners. There was no significant correlation between the total mercury concentration and the average weekly fish diet. The total mercury concentrations in urine of the miners were higher than those of the farmers and ranged from 0.32 to 3.62 ug/L with a mean of 1.23 ± 0.86 ug/L. The urine concentrations of farmers ranged from 0.075 to 2.31 ug/L with a mean of 0.69 ± 0.39 ug/L. Although the results indicate elevated internal dose of mercury the current levels of exposures do not appear to pose a significant health threat to the people.

Emissions of lead and zinc from candles with metal-core wicks

We measured the amount of lead released from 14 different brands of candles with metal-core wicks sold in Michigan. The emissions of lead were found to range from 0.5 to 66 microg/h, and the rates for zinc were from 1.2 to 124 microg/h. It is estimated that burning four of the candles bought in Michigan for 2 h can result in airborne lead concentrations that can pose a threat to human health. In addition to inhalation of lead in the air, children get exposed to lead in candle fumes deposited on the floor, furniture and walls through their hand-to-mouth activity. Burning candles with leaded-core wick may be an important exposure route for lead that has generally been ignored.

Saturation of ecosystems with toxic metals in Sudbury basin, Ontario, Canada

Mining and resource recovery activities have not been kind to ecosystems in the Sudbury basin, Ontario. The combination of logging, smelting, fires and erosion resulted in an unusual anthropogenic ecosystem of denuded barren land with lifeless lakes, or a micro-desert. Since the 1970s, however, the concerted efforts made to reduce the emissions and rehabilitate parts of the degraded ecosystem have resulted in improvements in water quality, and recoveries in phytoplankton, zooplankton, zoobenthos and fish communities but have had little impact on toxic metal concentrations in many lakes. We show that most of the catchments in the Sudbury basin have become saturated with Cu and Ni, and some with Zn and Pb. It is estimated that mobilization of metals stored in soils and glacial overburden by surface runoff, groundwater drainage and wind re-working of tailings can sustain the high concentrations of Cu and Ni in many lakes for well over 1000 years. Strategies to immobilize the pollutant metals in the watershed rather than further emission controls may be required for dealing with high levels of toxic metals in surface waters of the saturated ecosystems.

Lead poisoning of children in Africa, IV: Exposure to dust lead in primary schools in south-central Durban, South Africa

Twenty primary schools in three areas (Merebank, Austerville and Bluff) of south-central Durban, South Africa were studied to determine if dust lead loading (microgram/m2) is high enough to constitute a risk to children. Atmospheric lead fallout rates in the schools varied from 9 to 264 micrograms/m2 per day and were higher than the values now being reported in the developed countries. Mean outside dust lead loadings were 425 micrograms/m2 in Merebank, 771 micrograms/m2 in Austerville and 1174 micrograms/m2 in Bluff areas, and 25% of the primary schools were found to have mean outside dust lead loading above 1000 micrograms/m2. Mean dust lead loadings inside classrooms were 2-4 times lower than the outside rates, and showed no significant difference among schools in the three areas. Dust lead loadings were correlated with lead concentrations in dust but not with distance from the highway or with atmospheric lead deposition rates. Exposure to dust lead in classrooms and in the school yard is considered to be an important contributor to blood lead levels in, and hence a potential health hazard to, children in many urban areas of the city.

Clair Patterson and Robert Kehoe's paradigm of "show me the data" on environmental lead poisoning

In 1925, Robert A. Kehoe enunciated a paradigm predicated upon categorical distinction between expectations and conjecture ("show me the data" mentality) from hard scientific facts on exposure outcomes. It led to a precedent-setting system of voluntary self-regulation by lead industry as a model for environmental control and implicitly signaled the level of industrial responsibility for lead pollution. It combined a cascading uncertainty rule (there is always uncertainty to be found in a world of imperfect information) with a highly skewed cost-benefit concept (immediate benefits of tetraethyl lead additives must be weighed against possible future health hazards). Many studies were funded by the lead industry to develop a theoretical framework for the paradigm which served as a strong defensive strategy against lead critics. It resulted in an unfettered growth in automotive lead pollution to over 270,000 tons per year in the United States and 350,000 tons per year worldwide during the early 1970s. Clair Patterson is credited with being the first person to mount an effective challenge against the Kehoe paradigm, and with his success came an upsurge of activity and attention to the risks of environmental lead pollution on public health.

Childhood lead poisoning in Africa: a growing public health problem

Gasoline sold in most African countries contain 0.5-0.8 g/l lead. In urban and rural areas and near mining centers, average lead concentrations reach 0.5-3.0 mu g/m3 in the atmosphere and > 1000 mu g/g in dust and soils. In addition to automotive and industrial sources, cottage industries and the burning of paper products, discarded rubber, battery casings and painted woods for cooking and heating represent additional hazards to individual households. Lead paint, lead solder and lead cosmetics are unregulated in some countries. Although African children are particularly predisposed to environmental lead exposure, because of their lifestyle and socioecological factors, a true picture of childhood lead poisoning in the continent remains undefined. Recent prevalence studies show that over 90% of the children in urban and rural communities of the Cape Province, South Africa have blood lead levels > or = 10 mu g/dl. Studies in other countries likewise suggest that childhood lead poisoning is a widespread urban health problem throughout the continent.

Quantitative assessment of worldwide contamination of air, water and soils by trace metals

Calculated loading rates of trace metals into the three environmental compartments demonstrate that human activities now have major impacts on the global and regional cycles of most of the trace elements. There is significant contamination of freshwater resources and an accelerating accumulation of toxic metals in the human food chain.

A silent epidemic of environmental metal poisoning?

The main objective of this paper is to provoke and stimulate debate on the health effects of long-term, low-level exposure of human populations to toxic metals. Over one billion (10(9)) human guinea pigs are now being exposed to elevated levels of toxic metals and metalloids in the environment. The number of persons suffering from subclinical metal poisoning is believed to be several million. A large portion of the cases are in developed countries but the urban areas of developing countries have become 'hot-spots' of metal pollution, and the populations of such countries are particularly susceptible to environmental toxins. As a global problem, the potential health effects of metallic hazards should be a matter of public health concern, especially if the emissions of toxic metals into the environment continue at the current rate.

Biogenic Sulfur and the Acidity of Rainfall in Remote Areas of Canada

Sulfur released from any given natural or anthropogenic source carries an isotopic signature that can be used to trace its flow through the environment. Measurements of the concentration and isotopic composition of sulfur in weekly bulk precipitation samples collected over a 4-year period at a remote location in northern Ontario were recorded. The long-term isotopic data and the measurement on the production and release of dimethyl sulfide from boreal wetlands show that biogenic sources can account for up to 30 percent of the acidifying sulfur burden in the atmosphere in remote areas of Canada. The data suggest that significant biological reemission of anthropogenic sulfur is occurring. The role of this process in the continuing acidification of the environment for years to come must be a matter of concern.

Response of lake sediments to changes in trace metal emission from the smelters at Sudbury, Ontario

Historical records preserved in sediments show that the lakes are extremely sensitive to metal emissions from the smelters in the Sudbury basin. From the observed quick response, a strong capacity for rapid recovery (deacidification) of acid-stressed lakes in the area is deduced. The study thus emphasises the need for curtailing the emissions of acidic and acidifying substances as a critical step in reducing lake acidification as well as in rehabilitating many of the afflicted lakes.

Occupational exposure to lead in ancient times

The uses and regional production of lead in ancient times are summarized. Since there is no evidence to suggest that any deliberate attempts were made to curtail personal exposure to the mine dusts or the emissions from the forges and crucibles, it is surmised that many of the ancient artisans who worked with lead probably contracted plumbism. The number of workers so exposed is estimated to be over 140,000 per year during the Roman Empire. The ancient literary records of work-related plumbism, however, are surprisingly sparse.

Global inventory of natural and anthropogenic emissions of trace metals to the atmosphere

FEW (if any) recent studies on the atmospheric cycle of trace metals have considered the flux of the metals into the atmosphere on a global scale. Information on worldwide emissions is needed to assess the transboundary movement of pollutant metals and to validate models of the global atmospheric circulation patterns. The worldwide inventories of the natural and anthropogenic sources and emissions of airborne cadmium, copper, lead, nickel and zinc are presented here. The data summarised here are taken from very detailed studies published elsehwere(1-5).

Isotopic Composition of Dissolved Inorganic Carbon in the Great Lakes

Values for the δ13C of the dissolved total inorganic carbon in the Great Lakes are presented. The surface values are about two parts per thousand more negative than the values to be expected assuming equilibrium with the atmospheric CO2 reservoir. In the hypolimnion of Lake Erie, the values become more negative as the summer progresses due to the increasing amounts of CO2 from decaying organic matter. Although Lakes Erie and Ontario receive considerably larger amounts of organic carbon as domestic and industrial sewage effluents than the upper Great Lakes, their higher inorganic carbon concentrations evidently mask any isotopic effects from the decay of the organic pollutants. Models to explain the variation in the δ13C in the hypolimnion and epilimnion of a lake are presented. The agreement between predicted and observed δ13C trends for the hypolimnion model is reasonable, suggesting that the flux rates assumed in the model are reasonable for the processes occurring in the lakes. Key words: carbon isotopes, Great Lakes, inorganic carbon, models

Forms of Iron and Manganese in Lake Erie Waters

About 95% of the iron observed in the lake water is bound to inorganic particles and is present in the water because of sediment resuspension. Contrary to popular belief, the upwelling of interstitial waters charged with ferrous iron does not appear to play an important part in the regeneration of iron from Lake Erie sediments except when anoxic conditions exist at the sediment–water interface. By contrast, manganese is usually found in the overlying water as a result of the release of interstitial water containing dissolved manganese. This precipitates in oxygenated water so that most of the manganese present in the water is found in the particulate form. However, the released manganese will remain soluble if the oxygen saturation is less than 50%. In general, it was found that both the iron and manganese were in the particulate or soluble form in accordance with the geochemical solubility rules.