Mobility of arsenic in groundwater in the Obuasi gold-mining area of Ghana: some implications for human health

Abstract

Arsenic in drinking water from streams, shallow wells and boreholes in the Obuasi gold-mining area of Ghana range between < 2 and 175#gl -1. The main sources are mine pollution and natural oxidation of sulphide minerals, predominantly arsenopyrite (FeAsS). Streamwaters have been most affected by mining activity and contain some of the highest As concentrations observed. They are also of poor bacteriological quality. Some of the streams have a high As(III) content (As(III)/Astotaa > 0.5), probably as a result of methylation and reduction reactions mediated by bacteria and algae. Concentrations of As in groundwaters reach up to 64#gl -I, being highest in deeper (40-70m) and more reducing (220-250mV) waters. The As is thought to build up as a result of the longer residence times undergone by groundwaters in the deeper parts of the aquifer. The proportion of As present as As(III) is also higher in the deeper groundwaters. Deep mine exploration boreholes (70-100 m) have relatively low As contents of 5-17/zg 1-1, possibly due to As sorption onto precipitating ferric oxyhydroxides or to localized low As concentrations of sulphide minerals.Median concentrations of inorganic urinary As from sample populations in two villages, one a rural streamwater-drinking community, and the other a suburb of Obuasi using groundwater for potable supply, were 42 #g 1-" and 18 #g 1-1 respectively. The value for the community drinking groundwater is typical of background concentrations of urinary As. The slightly higher value for the streamwater-drinking community probably reflects different provenance of foodstuffs and higher As concentrations of water sources local to the village. The low value obtained for the inhabitants of the Obuasi suburb, living close to and abstracting groundwater from the area of major mining activity, suggests that groundwater can form a useful potable supply of good inorganic quality provided that deep, long residence time sources are avoided.

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“…After applying three indices, band ratio image (3/1), PC2 (1, 3), and PC4 (1,3,4,5), the different threshold values were used to find the most probable area of lateritic soil in the image. Thresholding, the simplest method of image segmentation, is an image processing technique for converting a greyscale or colour image into a binary image based upon a threshold value 25 .…”

“…If a pixel in the original image has an intensity value less than the threshold value, the corresponding pixel in the sub-layer image is set to black (value 0), otherwise, it was set to white (value 1) 26 . Thus where ƒ(i, j) is the pixel value in each layer of ratio image (3/1), PC2 (1,3) or PC4 (1,3,4,5), T is the threshold value, and g(i, j) is the corresponding pixel value in the sub-layer. The results of these three indices were overlaid on top of each other using GIS to define the preliminary lateritic soil image.…”

“…Lateritization produces infertile, poor draining. Goethite, formed during laterization, concentrates arsenic which can affect localized ground water 4 . Also, magnesium sulphate and sodium chloride in groundwater from lateritized basement causes diarrhoea.…”

Sustainable farming with native rocks: the transition without revolution

“…Leonardos et al 1987, van Straaten 2002, Theodoro 2005, Fonseca et al 2003. Results showed by Dissanayake and Chandrajith 1999, Smedley et al 1996and Smith et al 1996 point out the dependency between the availability or excess of determined nutrients in the soil and human and animal health. These authors mention that the study of the chemistry of the soil, rocks and sediments can indicate the preventive measures against a series of diseases with marked geographic distribution.…”

“…These authors mention that the study of the chemistry of the soil, rocks and sediments can indicate the preventive measures against a series of diseases with marked geographic distribution. Smedley et al 1996 andSmith et al 1996, suggest that in tropical regions, where the soils have high concentration of Al 2 O, SiO 2 and Fe 2 O 3 , the large reoccurrence of pneumonia cases, during the drought period, is related to the high percentages of aluminum in air dust due to population densifi cation and increment of agricultural areas.…”