This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and

Transcription

1 This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier s archiving and manuscript policies are encouraged to visit:

2 Journal of African Earth Sciences 58 (2010) Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: Potential human health risks associated with historic ore processing at Berg Aukas, Grootfontein area, Namibia Benjamin Mapani a,, Rainer Ellmies b, Frederick Kamona a, Bohdan Kříbek c, Vladimír Majer c, Ilja Knésl c, Jan Pašava c, Maria Mufenda b, Filadelphia Mbingeneeko b a Department of Geology, University of Namibia, Private Bag 13301, Windhoek, Namibia b Geological Survey of Namibia, 1 Aviation Road, Windhoek, Namibia c Czech Geological Survey, Prague 5, Czech Republic article info abstract Article history: Available online 31 August 2010 Keywords: Health risks Metal contamination Lead Arsenic Pollution Health risks to people living at Berg Aukas have been identified through a geochemical study of mine dumps and soils at Berg Aukas. Berg Aukas once served as a mining town, where ores of Pb, V, and Zn were mined and roasted on site until Roasting of ores produced an unintended hazardous risk in the surrounding area. For this study, soil, crops, and water from the Berg Aukas area were analysed for various pollutants. The main pollutants are metals like Pb, Zn, Cu, Cd, As, Hg and Mo. They are bound to layered silicates, to easily soluble sulphide minerals, or occur in native form. The analytical results show severe heavy metal contamination of the surface soils south and east of Berg Aukas. Crops grown at the National Youth Service, like sweet potatoes, cabbage, and Irish potatoes, accumulate heavy elements that are deleterious to health. Prolonged exposure to As and heavy metals in concentrations as found in the soils and some crops in Berg Aukas can cause severe health problems like diabetes, skin lesions, bladder problems, neurological effects, as well as skin, kidney or lung cancer. Pb affects mental development of children and Pbs to brain retardation. The study aims to help the local community to delineate no-go areas for agricultural use and to either diversify the crops grown on contaminated soils or to grow crops that are less vulnerable to high heavy metal contents in soils or transfer the crops grown on contaminated soils to areas that are not contaminated. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Corresponding author. address: bmapani@unam.na (B. Mapani). In 2005, a comprehensive environmental geochemical survey was conducted at the abandoned Berg Aukas mining district. The aims of the survey were: to analyse the contamination of water, soils, stream sediments and agricultural plants by toxic metals; to determine the effect of ore mining and processing on the environment and; to formulate recommendations and concepts that should ensure protection of the environment both during and after mining operations. A specific consideration for this paper is the effect that heavy metals may have on humans still living in the area. Exposure to excessive amounts of heavy metals such as Pb, Cd, As, Cu, and Zn may have deleterious health effects especially to children. There exist over twenty (20) different heavy metal toxins that can impact human health and each metal will produce different behavioral, physiological, and cognitive changes in an exposed individual. The degree to which a system, organ, tissue, or cell is affected by a heavy metal depends on the metal itself, the individual s degree of exposure, the exposure pathway, element speciation, and individual sociability. Our research therefore is aimed at creating awareness, educating, and working out measures of remediation in areas where critical heavy metal contaminations have been identified. 2. Location of the Berg Aukas area Berg Aukas is located 15 km east of Grootfontein on the farm Berg Aukas 593, in the Otavi Mountain Land, Namibia (Fig. 1). The area is located on good loamy soils that are underlain by carbonates. Currently the National Youth Service camp is located on this former mine site, conducting training programs in agriculture. 3. Geology of Berg Aukas area The Berg Aukas mine is situated on the northern limb of the Berg Aukas Syncline. The syncline structure consists of dolostones, limestones and shales of the Berg Aukas Formation (at the base of Abenab Subgroup/Otavi Group). Berg Aukas Formation is part of the Neoproterzoic sedimentation on the Otavi Platform. The sedimentary rocks were folded during the Pan African Event X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi: /j.jafrearsci

3 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 1. Location map of the Berg Aukas and Grootfontein area, showing the regional geology. Two types of Pb Zn V mineralization occur at the Berg Aukas mine: (i) The Northern Ore Horizon consists of a series of lenses with oxidized ore of sulphide replacement bodies. The ore occurs along the contact between two texturally distinct varieties of grey dolomite. The zone of mineralization strikes roughly east west and dips about 50 to the south. In the topmost lens, the sulphides are confined to massive, fine-grained replacement bodies in which sphalerite, galena and subordinate pyrite are the only visible primary sulphides. Common secondary minerals are descloizite, willemite, cerussite, smithsonite and goethite. (ii) The complex Central Ore Body, Intermediate and Hanging Wall Ore body are located in recrystallised dolomite in which they follow solution cavities that are controlled by steeply dipping north south striking fractures. Ore bodies are arranged in an en echelon pattern, and dip almost vertically. In addition, the bodies are extremely irregular in outline and frequently contain blocks of barren dolomite. Galena and sphalerite, partly oxidized, are disseminated in layers of clay, mud and sand of varying dolomite content. The contacts between the ore bodies and country rocks are sporadically lined with solid willemite. 4. Mining and mining remnants The Pb Zn V deposit of Berg Aukas was discovered in 1913, when the apex of the Central Ore Body on top of a hill was located. Mining started in 1920 and was terminated at the groundwater level in In 1950 the mine was reopened and vanadinite and sulphide concentrate was produced and roasted on spot. The ore reserves at the time of mine closure in 1978 were estimated as 1.65 Mt grading 0.6% V 2 O 5, 5% Pb and 17% Zn (Misiewicz, 1988). Remnants of two waste rock heaps are located directly on the area of the former mining and metallurgical complex (Fig. 2). The waste dumps are not stable and in some places, slumping of large blocks and water erosion furrows can be observed. Access to some galleries of the old mine are not secured. The total amount of material deposited in waste rock heaps is estimated at 91,680 m 3. The slag deposit is also located within the mine area (Fig. 2). The slag was used for the construction of local roads and therefore this material is widely disseminated throughout the area. The surface of the slag deposit was covered by a mixture of concrete and slag. At present the sealing is eroded and the slag deposit represents an important source of dust. Two slimes (tailings) dams are located north of the mining area (Fig. 2). The total volume of slimes is estimated at 343,500 m 3. The tailings dams are not currently fenced and pose a hazard to

4 636 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 2. Location of tailings dam, slag dams and water reservoirs at Berg Aukas. children playing in the area. Tailings material has been spilled in larger quantities into adjacent ephemeral streams. The eastern part of tailings dam is partly covered by vegetation (grass, and acacia). 5. Hydrogeological aspects, water sampling and analyses Deeper parts of the Berg Aukas mine were spontaneously flooded after mine closure. Between 1981 and 1987, the Grootfontein Omatako canal was built in order to supply water from Berg Aukas, Kombat and other mines in the Otavi Mountainland to Windhoek. The mines in the Otavi Mountainland can supply a total of 15 Mm 3 water per year (Ploethner et al., 1998). The groundwater in the underground mine of Berg Aukas is currently used for the water supply of the town itself and for irrigation on surrounding farming projects. Water analyses of groundwater from the shaft were carried out at the laboratories of BGR, Hanover, Germany. Concentrations of Al, Ca, Fe, K, Mg, Mn, Na, Si and Ti were analysed from acidified solution with Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) based on standard DIN EN ISO (1998). For the determination of the anions F, Cl, Br, NO 3, NO 2, SO 2 4, an Ionic Chromatography method (IC) based on DIN EN ISO (1995) was used. Phosphate and ammonium were determined photometrically as a complex based on DIN EN 1189 (1996) and DIN (1983), respectively. Hydrogen carbonate is determined by titrimetric testing based on DIN EN (1993). Concentrations of trace elements As, B, Ba, Be, Cd, Co, Cr, Cu, Li, Ni, Pb, Sc, Sr, V and Zn were analysed from acidified solution with Inductively Coupled Plasma Atomic Emission Spectrometry (ICP- AES) based on standard DIN EN ISO (1998). For the determination of alkalinity (acid neutralizing capacity) a 10 ml aliquot of the unfiltrated sample was titrated with 0.02 N HCl to ph = 4.3. (DIN 38409, 1979). The final point is determined potentiometrically using a 2-cell ph-glass electrode. 6. Results of water analyses The water which is pumped from the Berg Aukas shaft shows a moderate electric conductivity of 850 ls/cm and neutral to slightly alkaline ph. A comparison with groundwater from farm Dornhügel, 18 km to the east of Berg Aukas, points to the fact that the hydrochemistry does not only reflect its carbonate host rock but the composition of the ore (Appendix A). Both groundwater samples are supersaturated with respect to calcite and dolomite. Additionally, the water from Berg Aukas mine is marked by very high Zn (2.34 mg/l) and elevated Cd (0.007 mg/l) as well as Pb (0.04 mg/l) concentrations. The concentration for Zn exceeds the Namibian guideline value for drinking water of excellent quality (Group A). All other metals of concern show concentrations below the detection limit of the ICP, e.g. <0.02 mg/l As and <0.005 mg/l V. Due to the high Zn-concentration and elevated hardness, the shaft water from Berg Aukas mine falls into Group B which refers to drinking water of acceptable quality. The water is widely used for irrigation purposes. The draft of the new Namibian regulation for irrigation water states that concentrations up to 5 mg Zn/l are tolerable for irrigation purposes on fine textured neutral to alkaline soils. The water is thus suitable for irrigation but has to be monitored regularly as Zn and Cd concentrations might become critical. The water also partly reflects the signature of the ore at Berg Aukas. 7. Soil sampling and analyses Mining and processing activities at Berg Aukas altered the soil composition of area. The northern and northeastern parts of the area are covered by soils that contain massive layers of slag and tailings (Fig. 3). Six tailings and slag samples as well as nineteen soil samples were collected around Berg Aukas using the methodology

5 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 3. Variety of soils in the Berg Aukas area: (A) Calcic regosol. Ah1-2 horizon: light brownish sandy clay, C horizon: weathered carbonate (caliche). (B) Calcic cambisol. Ah1-2: dark grey, granular loam with common roots and calcareous pseudomycelia. CBk horizon: whitish weathered limestone. (C) Pelitic vertisol. A1 horizon: dry, dark brownish-grey clay. A2 horizon: dark grey, moisture clay with slickenside surfaces. (D) Pelitic vertisol, covered by slag and slime. Fig. 4. Waste rock dump (a) and slimes dump (b) at Berg Aukas. recommended for the regional geochemical mapping by the FOREGS Geochemistry Working Group (Fig. 3). The sampled areas are shown with contours and sample points as dots for selected metals in Figs Reference to the sampled areas is done in two parts reflecting how the soil samples were obtained, i.e., a lower and an upper soil horizon was collected, and the data is reflected in two maps produced for the lower and upper soil horizons respectively. The lower soil horizons, collected 80 cm below the surface, reflect the bedrock chemistry, whereas the upper soil horizons, sampled at the surface (the first 3 cm of the topsoil) show eventual contaminations by dumping and air borne transport. Approximately 0.5 kg of each soil sample was sieved to <0.2 mm. The fraction of <0.2 mm was homogenized in an agate ball mill and the fraction <0.063 mm was used for chemical analyses. One gram of sample and 50 ml of a solution of HNO 3 and HCl in the ratio 1:9 were used to prepare a leachate. Trace elements were determined in the laboratory of the Czech Geological Survey (after the methodology of Dempírová and Vitková), and at Charles University, Prague. Fe, Cd, Cu, Mo, Pb and Zn were analysed using flame atomic absorption spectroscopy (FAAS) with a PE 4000 spectrometer. As was determined by a hydrite generation atomic absorption spectrometry (HGAAS) using a PE 503 equipment. Hg was analysed mercurometrically, using an AMA 254 analyser. The amount of total carbon was determined using ELTRA CS 500 equipment. Samples were combusted and the quantity of the resulting CO 2 was measured using an IR detector. The amount of carbonate carbon was determined using the Coulomat 7021 equipment. Samples were decomposed in the concentrated solution of H 3 PO 4 and the amount of liberated CO 2 was recalculated to that of carbonate carbon (C carb ). The amount of organic carbon (C org ) was determined by subtraction of carbonate carbon from total carbon content (C tot ): C org ¼ C tot C carb : Total sulphur (S tot ) was determined on the ELTRA CS 500 equipment. Samples were combusted at the temperature of 1450 C and the amount of released SO 2 was determined by an infrared detector. 8. Results of soils analyses The tailings contain very high amounts of Zn, V, Cd, As and Hg (Table 1). In contrast, the Pb concentrations are low. Approximately 18 wt.% of the tailings consists of particles of less than 8 lm in diameter (PM8s). These particles pose the most serious health effects, as they enter the lungs. The slag is rich in Zn, Pb, V, Cu and As (Table 1). The amount of PM8s particles in the slag dust is low (1.3 wt.%). The analytical results for the soil samples are presented in form of distribution maps of the pollutants, and were produced with SURFER of Golden Software Inc. (Figs. 4 11) Arsenic (Fig. 5) In the lower soil horizon, contents of As are generally low (median: 0.89 ppm, maximum: 9.62 ppm). Higher concentrations (>2.6 ppm) were detected in the area of the former mining and processing complex and eastward (downwind) of the slime dams. The elevated concentrations trace back to an infiltration of Asrich solution from the top soil. The median content of As in the topsoil is one order higher (4.99 ppm) when compared with lower soil horizon, and maximum values are two orders higher (363 ppm).

6 638 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 5. Arsenic in lower (a) and upper (b) soil horizons Cadmium (Fig. 6) Concentrations of Cd in lower soil horizons are very low (median: >0.8 ppm, maximum: 7.8 ppm). Two areas of slightly higher Cd values (from 2.3 to 5.3 ppm Cd) are located in the former mining and metallurgical complex. The Cd concentration in the upper soil horizon is much higher (median: 5.4 ppm, maximum value: 387 ppm). It is important to note that elevated concentrations of Cd in the upper soil horizon encircle the whole area of Berg Aukas and extend towards the east. The large-scale contamination cannot be explained by dust fall-out from mining operations and slime deposits. It is probably a result of emissions from roasting of ores in the past Copper (Fig. 7) Contents of Cu in the lower soil horizon are relatively low (median: 14 ppm), which correspond to the low values of Cu in ores. Concentrations of Cu in surface soils range from 6 to 327 ppm (median: 28 ppm) and they are only slightly higher compared with

7 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 6. Cadmium in lower (a) and upper (b) soil horizons. the lower soil horizon. The distribution of Cu values can reflect both, the position of ore bodies as well as an extent of contamination from surface Lead (Fig. 8) The contents of Pb in the lower soil horizon are relatively high (median: 54 ppm, maximum 1157 ppm). Increased Pb concentrations are located in heavily contaminated areas (area of mining and metallurgical complex and area downwind of tailing deposits) without a relation to the NW SE trending mineralized horizons. It can be therefore concluded that anomalous contents of Pb in the lower soil profile are predominantly constrained by a downward transport of the metal from contaminated topsoil. This can be supported by substantially higher and correlating values of Pb in the upper soil horizon (maximum value 34,400 ppm). The extent of contamination can be attributed to emissions from roasting.

8 640 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 7. Copper in lower (a) and upper (b) soil horizons Mercury (Fig. 9) Slightly elevated values of Hg occur in the lower soil horizon ( ppm). No relation is observed between the distribution of Hg and of the position of ore bodies. Hg concentration in the upper soil reaches a maximum value of 6.9 ppm. Hg is known to represent highly volatile products of ore roasting and smelting. Elevated concentrations of Hg in the upper soil horizon predominantly reflect in situ roasting. The coal used for ore roasting might be an additional source of Hg in the soils Vanadium (Fig. 10) Contents of V in the lower soil horizon are low (median: 24 ppm, maximum value: 163 ppm), although Berg Aukas ores were mined for V. No relationship was found between the

9 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 8. Lead in lower (a) and upper (b) soil horizons. distribution of V in the lower soil horizons and the position of ore bodies. The concentrations of V in topsoil (median: 61 ppm, maximum value: 2114 ppm) are much higher. The maximum value of V in surface soil (2114 ppm) is relatively lower compared with the maximum value for Zn (216,000 ppm) or Pb (34,400 ppm). It can be explained by the low volatility of V during ore roasting Zinc (Fig. 11) The values of Zn in lower soil horizon (median: 114 ppm) are relatively low. Higher concentrations ( ppm) were found in the area of the Berg Aukas mining and metallurgical complex. Zn-concentration in the upper soil horizon is much higher (median: 2047 ppm). The maximum value for Zn in the topsoil of

10 642 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 9. Mercury in lower (a) and upper (b) soil horizons. the ore roaster area is 216,000 ppm which is higher than in the original ores. Large-scale contamination of the whole Berg Aukas area can be attributed to the roasting of ores in the past and by dust fallout from slimes dams and slag deposit. In the absence of guideline values for soil contamination in Namibia, criteria from Canada, Germany and the Netherlands have been used in this publication. The guideline values refer to the allowable and acceptable concentration for the intended use of a particular site. The concentrations of trace metals in soils in the study area were compared with the Canadian guideline values. The guidelines vary for agricultural, commercial and industrial land uses. Concentrations of metals above these limits are expected to be associated with adverse health effects. Thirty-four percent of the 19 soil samples exceed the limits for agricultural use in case of Cu, 29% for Pb and 12% for As. A small part of the samples exceed the limits for Cd (3.4%), Mo (1.7%), and Zn (1.7%). The proportion of samples exceeding the limits for

11 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 10. Vanadium in lower (a) and upper (b) soil horizons. commercial and industrial land use is high in case of Cu (25.8%) and Pb (13.8% and 6.9% respectively). 9. Analyses of plant samples Agriculture in the Berg Aukas area is mostly based on livestock farming and crop farming. Therefore, different grass species were collected from pasturelands. Samples of maize (grains), cassava (leaves and bulbs) and sweet potatoes (leaves and bulbs) were collected form agricultural fields irrigated by shaft water. Additional, 30 rhizosphere samples were collected from a depth of 0 30 cm. The samples were combusted in a muffle oven at the temperature of 400 C. The amount of ash was scaled and the metals were analytically determined in HNO 3 and HCl leachate as described for the soil samples. Some results were recalculated on dry-weight basis to compare with the Czech limits for dry forage (As = 6 ppm, Mo = 3 ppm and Pb = 20 ppm (Knesl et al., 2005)). Concentrations

12 644 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Fig. 11. Zinc in lower (a) and upper (b) soil horizons. of As, Cu, Pb and Zn were compared to World Health Organization limits (As = 0.5 ppm, Cu = 20 ppm, Pb = 0.4 ppm and Zn = 50 ppm) after recalculation to wet fresh matter. The median value for Zn in the set of grass samples (202 ppm) and the maximum value of Zn (818 ppm) are in excess of the Czech limits for permanent grass cover (Zn = 35.2 ppm, Knesl et al., 2005). More than a third of the sampled grass species show Pb concentrations above the Czech limits for dry forage. The highly contaminated samples were collected mainly in the vicinity of the slime deposit and the former processing plant. The analysed cassava and sweet potato leaves as well as roots are characterized by As, Pb and Zn values in excess of WHO limits for food. The maximum concentrations in cassava leaves are for Pb 185 times higher, Zn almost nine times higher and As almost two times higher than the WHO limits. Maximum values in sweet potato leaves exceed the WHO limits for Pb (460 times), Zn (17 times) and As (almost five times). All cassava and sweet potato roots have Pb contents above the WHO limits and two thirds of cassava root samples are characterized by Cu values above the WHO limits. Furthermore, WHO limits for As and Zn are exceeded for two thirds and one third of the sweet potatoes respectively. Generally, higher concentrations of metals occur in leaves than in roots and the concentrations of heavy metals in potatoes are higher than in cassava roots.

13 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Table 1 Average chemical composition of tailings and slags at Berg Aukas. 10. Discussion Tailings Slags Ctot (wt.%) Stot (wt.%) CO2 (wt.%) Corg (wt.%) V (ppm) Fe (wt.%) Cu (ppm) Zn (ppm) 52,100 22,400 Mo (ppm) <5 13 Cd (ppm) 352 <0.8 Pb (ppm) <10 11,600 As (ppm) Hg (ppm) The analytical results demonstrate critical contaminations with respect to As, Cd, Cu, Pb, Hg, and Zn. Health effects of a permanent exposure to As are among others: Skin damages like keratosis and blackfoot disease. Skin, lung, bladder, kidney cancer. Increased infant mortality. Neurological problems. Cd occurs as minor constituents in sulphide ores, mainly sphalerite. Cd is an acute toxin and carcinogen whereby poisoning is experienced in lungs, kidneys and bones. As a result, it causes a disease which is known in Japan as Itai itai (pain). Patients suffer from pain in joints, also experience lumbago pains, pseudo fracturing of bones, skeletal deformation and renal dysfunction. Once absorbed, Cu is distributed primarily to the liver, kidneys, spleen, heart, lungs, stomach, intestines, nails, and hair. Individuals with Cu toxicity show an abnormally high level of Cu in the liver, kidneys, brain, eyes and bones (ATSDR, 1990a). Acute toxicity of ingested Cu is characterized by abdominal pain, diarrhoea, vomiting, tachycardia and a metallic taste in the mouth. Pb is absorbed into the body following inhalation or ingestion. Children absorb Pb much more efficiently than adults do after exposure, and ingested Pb is more readily absorbed in a fasting individual (US EPA, 1986). Adults distribute about 95% of their total body Pb to their bones, while children distribute about 73% of their total body Pb to their bones (US EPA, 1986a). Pb can cause irreversible brain damage (encephalopathy), seizure, coma and death if not treated immediately (US EPA, 1986). The Central Nervous System (CNS) becomes severely damaged at Pb concentrations starting at 40 mcg/dl in blood, causing a reduction in nerve conduction velocities and neuritis (ATSDR, 1993). Hg exposure can result in a wide variety of human health conditions. The degree of impairment and the clinical manifestations that accompany Hg exposure largely depend upon its chemical state and the route of exposure. While inorganic Hg compounds are considered less toxic than organic Hg compounds (primarily due to difficulties in absorption), inorganic Hg that is absorbed is readily converted to an organic form by physiological processes in the liver. Zn is a trace element essential in plants and animals, but high exposure may cause neuropathy, dehydration, growth retardation, anemia, and nausea. Fig. 12 shows a combined summary of the contaminated domains in the Berg Aukas area. The town centre, with the accommodation and classroom blocks for the National Youth League training camp, is heavily contaminated. It also portrays that the contamination extends to the northeast of the site complex. Areas to the southeast and northwest of the complex are relatively free of contamination. 11. Conclusions The study shows that parts of the soil and vegetation in the Berg Aukas area are severely contaminated by As, Cd, Cu, Pb, Hg, and Zn. The contamination traces back to historic ore roasting and wind blown dust from slag dumps and tailings (slikdam). Groundwater from the Berg Aukas shaft, used for drinking and irrigation, show high concentrations of Zn (2.23 mg/l) exceeding the Namibian guideline value for Group A (water of excellent quality). It meets the requirements for Group B (acceptable water) but Fig. 12. Coefficient of industrial pollution (CIP) for the Berg Aukas area.

14 646 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) regular monitoring of the water for Zn and Cd is recommended. The groundwater meets the requirements for waters intended for irrigation on alkaline soils according to the proposed Namibian standard. The people living and working in Berg Aukas face health risks from inhalation and ingestion of the dust as well as by ingestion of contaminated crops grown on the contaminated soils. If humans are exposed for longer periods to these heavy metals they may be amenable to various heavy metal triggered diseases and disorders. The coefficient of industrial pollution for Berg Aukas shows that metals have been added to the surface environment. This is determined by the equation: CIP ¼ As m As þ Pb þ Cu m pb m Cu þ Zn m Zn þ V m V 7 Hg m þ Cd m Cd where m is the mean value for the particular element and the numerator is the highest value in the analyses. There is an urgent need to react to the results of this study in the following ways: (1) Awareness about the hazards associated with living conditions in the area must be created. This needs to be communicated to the residents as well as the local politicians. (2) Heavily contaminated areas have to be delineated as no-go areas. (3) Contaminated urban areas have to be remediated e.g. by covering top soils with organic matter and grasses. (4) Cease crop production northeast of Berg Aukas. (5) Avoid growing of potatoes. (6) Change crops to less vulnerable types like maize. (7) Cattle pasturing is not recommended on an area 2 km around Berg Aukas due to Pb contamination. Contamination of soils northeast of the mining area poses a significant problem. Here, maize, cassava, potatoes, and other vegetables are grown by an agricultural co-operative on soils with severe contamination. Regular consumption of such plants will result in health problems. It is recommended to transfer most of the agricultural production of vegetables to the area southeast or northwest of the town. Here, the dust fall is very low due to the sheltering function of the mountain range. As the severe contamination is focused to the closer vicinity of the mining and smelter complex as well as the tailings dam, a distance of at least 2 km to those sites is recommended. Further, it is recommended to grow maize, whose grains show low metal contents even when grown in areas with elevated metal contents in the soil. The accommodation for the National Youth Service organization is located in the area of the former mining and smelter complex, where topsoil shows concentrations of 5 ppm As, 5.4 ppm Cd, 130 ppm Cu, 500 ppm Pb, 58,000 ppm Zn, and 1.5 ppm Hg. The area is characterized by a high dust fall due to wind erosion of the slag dump. Remediation should include coverage of the slag dump and the highly contaminated central part of the plant area using a layer of uncontaminated soil. It is further necessary to level the remnants of the tailings heaps and to secure the entrances into the subterranean adits and shafts of the former mine. Acknowledgements The authors would like to thank the commanding officer of the Berg Aukas National Service training camp. The officers at the vegetable garden were extremely helpful. We would also like to thank the farming community around Berg Aukas, who allowed us to sample in their private land. Appendix A Water analyses for shaft water from Berg Aukas and groundwater from farm Dornhügel, comparison with Namibian guideline values for drinking water. ID ph field ph EC field (ls/cm) EC (ls/cm) Total hardness (mg/l CaCO 3 ) Total dissolved solids (TDS) B1 Berg Aukas mine, shaftwater D1 Farm Dornhügel, western borehole Namibia guideline values mg/l CaCO 3 Group A: excellent quality Group B: acceptable quality Group C: low health risk Group D: high health risk, or unsuitable for human consumption Standard for effluent water (maximum levels) influent ID K Na Cl Mg Ca SO 4 HCO 3 Fe(II) Mn NO 3 Br NH 4 NO 2 F B <0.01 < D < Group A Group B Group C Group D Effluent 90 + in 1 PO 4 (continued on next page)

15 B. Mapani et al. / Journal of African Earth Sciences 58 (2010) Appendix A (continued) ID Al As BO 2 Ba Be Cd Co Cr Cu Li Ni B1 <0.003 < < <0.005 < <0.005 D1 <0.01 <0.01 < Group A Group B Group C Group D Effluent D Ni Pb Sc SiO 2 Sr Ti V Zn B1 < < <0.001 < D Group A Group B Group C Group D Effluent 1 5 References ATSDR (Agency for Toxic Substances and Disease Registry), Toxicological Profile for Aluminum. Agency for Toxic Substances and Disease Registry, US Public Health Service, Atlanta, GA, ATSDR/TP-88/01. ATSDR (Agency for Toxic Substances and disease Registry) Toxicological Profile for Lead. Update. Prepared by Clement International Corporation under Contract No for ATSDR, US Public Health Service, Atlanta, GA. Knesl, I., Kornapasek, J., Kribek, B., Majer, V., Pasava, J., Kamona, F., Mapani, B., Mwiya, S., Kawali, L., Kandjii, I., Keder, J., Ettler, V., Assessment of the Mining and Processing of Ores on the Environment in the Mining Districts of Namibia: B. Kombat, Berg Aukas and Kaokoland. Technical Report. 166 p. Misiewicz, J.E., The Geology and metallogeny of the Otavi Mountain Land, Damara Orogen, SWA/Namibia, with Particular Reference to the Berg Aukas Zn Pb V deposit A Model of Ore Genesis. Unpubl. M.Sc. Thesis, Rhodes University, 143 p. Ploethner, D., Teschner, M. and Schwartz, M.O., German Namibian Groundwater Exploration Project, Follow-up Report, vol 4. MS. Bundesanstalt ful Geowissenschaften und Rohstoffe, Hannover, Archives No , 70 p. US Environmental Protection Agency (EPA), Lead effects on cardiovascular function, early development, and stature: an addendum to EPA air quality criteria for lead (1986). In: Air Quality Criteria for Lead, vol. I. Environmental Criteria and Assessment Office, Research Triangle Park, NC. EPA-600/8-83/ 028aF. Available from NTIS, Springfield, VA, PB pp. A1 67.