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To understand the resilience of African savannas to global change, quantitative information on the long-term dynamics of vegetation is required. Past dynamics can be reconstructed with the REVEALS model, which requires pollen productivity estimates (PPE) that are calibrated using surface pollen and vegetation data. Here we calculated PPE values for five savanna taxa using the extended R-value (ERV) model and two pollen dispersal options: the Gaussian plume model (GPM) and the Lagrangian stochastic model (LSM). The ERV calculations failed to produce a reliable PPE for Poaceae. We therefore used Combretaceae as the reference taxon – although values obtained with Poaceae as the reference taxon are presented in the supplement. Our results indicate that Combretaceae is the taxon with the highest pollen productivity and Grewia the taxon with the lowest productivity. Acacia and Dichrostachys are intermediate pollen producers. We find no clear indication of whether the GPM PPEs or the LSM PPEs are more realistic, but the differences between these values confirmed that the pollen fall speed has a greater effect in the modelling of GPM than in the LSM. We also applied REVEALS to the pollen record of Lake Otjikoto (northern Namibia) and obtained the first quantitative reconstruction of the last 130 years of vegetation history in the region. Cover estimates for Poaceae indicate the predominance of a semi-open landscape throughout the 20th century, while cover values below 50% since the 21st century correspond to a thick savanna. This change in grass cover is associated with the spread of Vachellia, Senegalia and Grewia reflecting an encroached state.

Volcanic and sedimentary rocks of the Sinclair Supergroup occur in the Konkiep Terrane of Southern Namibia. Three volcanic and sedimentary cycles are recognised. In this work we describe and date volcanic rocks of the Barby Formation, a key unit in the Sinclair area. The coeval Spes Bona Syenite and the Tiras Granite Gneiss are also described and dated. The rock types in the Barby Formation are rhyolites, basaltic trachyandesites, trachybasalts and trachydacites as well as volcanoclastic rocks. The rocks are largely undeformed and partly altered by deuteric and contact metamorphic processes but not regionally metamorphosed. Our samples represent both the calc-alkaline and alkaline trends documented in previous work. U-Pb ion probe and laser ablation inductively coupled plasma (LA-ICP) multicollector mass spectrometer Lu-Hf microbeam analyses were made of zircon and baddeleyite grains from four samples. A felsic tuff sample from the base of the Barby Formation has a 207Pb/206Pb zircon age of 1214 ± 5 Ma (2σ). A rhomb porphyry sample from the top of an 8.5 km-thick stratigraphic section gives a 207Pb/206Pb baddeleyite age of 1217 ± 2 Ma. The Spes Bona Syenite which intrudes the top of the Barby Formation has a 207Pb/206Pb baddeleyite age of 1217 ± 3 Ma and an indistinguishable LA-ICP collision cell mass spectrometer Rb-Sr biotite isochron age of 1238 ± 20 Ma, showing that there was no >350°C regional metamorphic event. Multi-element diagrams for the calc-alkaline samples show a dominant signature of reworked crust which is superimposed on a possible subduction signature. However the alkaline samples contain clear subduction signatures which are not seen in the underlying 1.37 Ga Kumbis rhyolite. The Barby Formation samples and coeval Spes Bona Syenite have Lu-Hf crustal residence ages between 1682 and 1873 Ma, suggesting that both of these units formed from a mixture of juvenile mantle-derived and older crustal material. The Barby Formation is considered to have originated due to a subduction event which took place during the assembly of the Rodinia supercontinent. The duration of the Barby magmatic episode is constrained to a maximum 9 m.y. period between 1219 and 1210 Ma, and during this period the Konkiep Terrane was an active continental margin. The 1204 ± 9 Ma Tiras Granite Gneiss is slightly younger than the Barby Formation and intruded across the Lord Hills Shear Zone, which is the suture between the hardly metamorphosed Konkiep Terrane and the highly metamorphosed Grunau Terrane of the Namaqua-Natal Province. Its intrusion reflects the end of subduction-related volcanism, due to the collision of Namaqua terranes with the Konkiep Terrane.

The scarcity of freshwater is a growing concern around the world, especially in the developing world and is increasingly threatening human survival in less affluent parts of the world. In arid and semiarid regions, freshwater resources are imperative for the survival of populations as well as development activities in urban centres. Preceding assessments for potential solutions have underestimated the scarcity of water by failing to capture main trends of precipitation and the extent of drought periods. This paper aims to investigate rainfall trends for the City of Windhoek, Namibia. A century scale is examined by reconstructing historical precipitation records, and future trends are subsequently estimated and interpolated using Ordinary Kriging in ArcGIS 10.3. Kriging responds and handles spatial correlation much better for observed data points. The results show locations that receive high rainfall and potential periods for harvesting rainwater. The findings further show that the periods of high rainfall are shorter, and after each high rainfall stretch, a long period of lower rainfall follows immediately. Each low rainfall period is anticipated to last longer than the previous one. These scenarios are highly significant for urban managers in dryland cities such as Windhoek, as they demonstrate when water would need to be extra sparingly managed. This study highlights the need for better water management strategies, if cities in dry climates are to survive the anticipated future water crises.

The dynamics of Cu and Pb were studied in eight soil profiles (Luvisols, Chernozems), located at various distances from the tailing dams near a closed Cu-Pb-(Zn)-Ag mine at Kombat (Namibia) by a combination of isotope and elemental studies, leaching techniques and speciation modelling. Tailings, soils and bedrocks were analyzed for the bulk Cu and Pb concentrations, for their chemical forms using the sequential extraction procedure and for the isotope compositions of Cu (δ65Cu) and Pb (206Pb/207Pb, 208Pb/206Pb). In spite of the differences in the contamination of the studied profiles by tailing dust, both soil types exhibit characteristic trends in the behaviour of metals and distribution of their isotopes. While most Luvisols exhibit an increase in the metal content towards depth in the profile, Chernozems exhibit the opposite trend (decrease in metal content with depth) or similar contents in the whole profile. Luvisols were mostly characterized by changing δ65Cu values as a function of depth. The value of δ65Cu decreases with depth to the Bt horizon and then the δ65Cu value increases with increasing depth. Chernozems mostly yielded uniform Cu concentrations and isotope compositions in all the soil horizons, clearly contrasting with the isotopically lighter compositions of the carbonate bedrocks. Positive δ65Cu values in the tailing material affect the surface of the soil, especially soil sampled in its vicinity. In most Luvisols and Chernozems, the isotope composition of Pb exhibits similar patterns with a low 206Pb/207Pb ratio on the surface of the profile and with a slight increase to depth. The low 206Pb/207Pb values at the surface of the profiles are caused by dust from the tailings. The elemental and isotopic patterns of both contaminated and uncontaminated soil types reflect not only the distance from the tailing dam but also pedogenetic processes in the profiles and geochemical behaviour of both contaminants. The copper elemental and isotope patterns reflect the formation of more mobile species in the surface environment and movement of solutions and colloids and precipitation onto secondary minerals in Luvisols. Plant uptake of lighter isotopes in Chernozems can influence the Cu isotope patterns in these soil types. The limited movement of colloids and higher sorption capacity of Chernozems is manifested in the isotope compositions of Cu and Pb in their profiles.

Global Circulation Models (GCMs) are used to forecast climate change in Southern Africa, and the evidence shows that the region is going to warm up by up to 2° by the year 2050. Namibia is one of the driest countries in Southern Africa and is at a high risk of becoming much drier than current situation by 57%. Very few studies have been carried out in Southern Africa to show actual impacts of climate change. Practical applicability of GCMs at a local spatial scale remains limited due to the coarse nature of the models. Hence, improvement of the GCMs must begin with better understanding of the local microclimates and how they respond to regional circulation patterns. In many regions of Southern Africa, the lack of potential tools to access old climatic records precludes the estimation of climate trends beyond 100 years. In spite of these impediments, there are areas with excellent tree species such as Dichrostachys cinerea that are able to be used as climatic archives for specific time periods. In this chapter, the study shows that the combination of tree ring chronologies and precipitation records is a powerful methodology in climate modeling in the southern hemisphere and reveals nuances that show climate change. The evaluation of data from tree rings coupled with precipitation trends reveals signals that show that climate has indeed been changing over the past ten decades and will have a negative impact on livelihoods. These data can now be used in predictive models that can be used to project future scenarios and assist policy makers and planners to see how climate will evolve in the next 50–60 years.

Woody plants provide natural archives of climatic variation which can be investigated by applying dendroclimatological methods. Such studies are limited in Southern Africa but have great potential of improving our understanding of past climates and plant functional adaptations in the region. This study therefore investigated the responsiveness of Dichrostachys cinerea to seasonal variations in temperature and rainfall at two sites in central Namibia, Waterberg and Kuzikus. Dichrostachys cinerea is one of the encroacher species thriving well in Namibia. A moving correlation and response function analysis were used to test its responsiveness to seasonal climatic variations over time. Dichrostachys cinerea growth rings showed relationships to late summer warming, lasting up to half of the rainy season. The results also revealed that past temperatures had been fluctuating and their influence on growth rings had been intensifying over the years, but to varying extents between the two sites. Temperature was a more important determinant of ring growth at the drier site (Kuzikus), while rainfall was more important at the wetter site (Waterberg). Growth ring responsiveness to rainfall was not immediate but showed a rather lagged pattern. We conclude that D. cinerea differentially responds to variations in rainfall and temperature across short climatic gradients. This study shows that the species, due to its somewhat wide ecological amplitude, has great potential for dendroclimatological studies in many tropical regions.

We studied arid desert soils from Namibia (Rosh Pinah) that were contaminated with up to 7 mg kg−1 of thallium (Tl) via dust emitted from a local flotation tailing dam. Chemical extractions of waste and soil materials indicated that most of the Tl is strongly bound, in accordance with X-ray diffraction and X-ray absorption spectroscopy data that point to the predominant association of Tl with metal sulfides and phyllosilicates. The isotope fractionation factor e205Tl of the soil samples (from −0.4 to +3.8) shows a positive linear relationship (R2 = 0.62) with 1/Tl, indicative for the mixing of two major Tl pools, presumably anthropogenic Tl and geogenic Tl. The e205Tl value for the topmost soil samples (∼+3) closely matches the e205Tl value for post-flotation waste particles with a diameter of

The Tsumeb mining District (Namibia) is affected by prolonged exposure to multisource contamination related to the mining and smelting of copper ores. This study was performed to assess the extent of contamination of topsoil and grass shoots on the basis of the copper isotopic composition. Compared to an uncontaminated area (δ65Cusoil = −0.01 to +0.14‰; δ65Cugrass = −0.17 to +0.03‰), the soil and grass in the contaminated area are enriched in the heavy isotope (δ65Cusoil = +0.13 to +0.76‰ and δ65Cugrass = +0.15 to +0.64‰). The Δ65Cugrass-soil value exhibits small variations (+0.06 to −0.17) due to the variable degree of grass surface contamination, depending on the grass washing procedure used. The enrichment of soil and grass in the contaminated area in 65Cu reflects the Cu isotopic composition of old flotation tailings (δ65Cu = +0.95 to +1.1‰), slag (+0.11 to +0.55‰) and particles which originate from the smelting and flue gas cleaning processes (+0.15 to +0.49‰). The long history of mining and processing of copper ores in the Tsumeb area and the different isotopic composition of ore concentrates smelted in the local metallurgical plant do not allow assessment of whether the smelting process leads to isotope fractionation of copper. However, the isotopic composition of Cu in the sulfidic feed, slag and dust particles sampled over several hours showed that the dust collected from the dusthouse of the local smelter is isotopically lighter (δ65Cu = +0.15‰) relative to the isotopic composition of the charge (δ65Cu = +0.28 and +0.44‰). The results of this investigation demonstrate that the isotopic composition of Cu in soils and grasses can be used to assess the intensity of contamination in areas where Cu ores are mined and processed provided that the isotopic compositions of the ore processing products are different from the isotopic compositions of the uncontaminated soils and vegetation.

Understanding vegetation-modern pollen relationships is essential to provide confidence in fossil pollen reconstructions of long-term vegetation changes in savanna ecosystems. In this paper we compare the taxonomical composition and the diversity (Hill NO, N1, N2) of vegetation and modern pollen along precipitation and local grazing-intensity gradients in Namibian savannas. Modern pollen was extracted from surface soil samples collected from 5 x 5 m plots distributed along four 500 m gradients. Vegetation was surveyed in each plot. The results show a high correspondence between vegetation and pollen data in terms of composition. Precipitation and grazing explain a significant although low proportion of compositional change in the vegetation and pollen spectra. We identified pollen taxa as indicators of grazing pressure such as Limeum, Alternanthera, and particularly Tribulus. Correspondence between vegetation and pollen data in terms of taxa richness (NO) is limited, probably because of the influence of landscape heterogeneity and openness, as well as low pollen concentrations. In contrast, the effective numbers of common and dominant taxa (N1, N2) are consistent among the different datasets. We conclude that in spite of limitations, modern pollen assemblages can reflect changes in vegetation composition, richness and diversity patterns along precipitation and grazing gradients in savanna environments. (C) 2018 Elsevier B.V. All rights reserved.

The Naukluft Mountains in the Namib Desert are a high rainfall-high discharge area. It sees increased stream-, spring-flow as well as waterfalls during the rainy season. The mountains are a major resource for additional recharge to the Namib and Nama aquifers that are adjacent to the mountains. This paper aimed to highlight the potential vulnerability of the aquifers that surround the Naukluft Mountain area; if the strategic importance of the Naukluft Karst Aquifer (NKA) for bulk water supply becomes necessary. Chloride Mass Balance Method (CMBM) was applied to estimate rainfall available for recharge as well as actual recharge thereof. This was applied using chloride concentration in precipitation, borehole and spring samples collected from the study area. Groundwater flow patterns were mapped from hydraulic head values. A 2D digital elevation model was developed using Arc-GIS. Results highlighted the influence of the NKA on regional groundwater flow. This paper found that groundwater flow was controlled by structural dip and elevation. Groundwater was observed to flow predominantly from the NKA to the south west towards the Namib Aquifer in two distinct flow patterns that separate at the center of the NKA. A distinct groundwater divide was defined between the two flow patterns. A minor flow pattern from the northern parts of the NKA to the north east towards the Nama Aquifer was validated. Due to the substantial water losses, the NKA is not a typical karst aquifer. While the project area receives an average rainfall of 170.36 mm/a, it was estimated that 1–14.24% (maximum 24.43 mm/a) rainfall was available for recharge to the NKA. Actual recharge to the NKA was estimated to be less than 1–18.21% (maximum 4.45 mm/a) reflecting the vast losses incurred by the NKA via discharge. This paper concluded that groundwater resources of the NKA were potentially finite. The possibility of developing the aquifer for bulk water supply would therefore drastically lower recharge to surrounding aquifers that sustain local populations because all received rainfall will be utilized to maximise recharge to the NKA instead of surrounding aquifers.

This work investigates Mesoproterozoic volcanic rocks of the Haiber Flats, Barby, Welverdiend and Kairab Formations, and associated intrusive rocks in the Konkiep Terrane . Various correlations have been made in the past and recent dating work yields contrasting ages. U–Pb dating of zircons is applied in combination with Sm–Nd and Lu–Hf isotopes to determine the age, assess correlation and ascertain the much-debated tectonic setting . Ion probe U–Pb zircon dating yields ages of 1218 ± 5 Ma, 1212 ± 4 Ma and 1212 ± 5 Ma (all errors 2σ) for three samples of the Haiber Flats Formation and 1219 ± 13 Ma, 1215 ± 19 Ma for the Barby Formation. The ages obtained for the Barby Formation agree with the 1217 ± 2 Ma and 1214 ± 5 Ma ages reported from previous investigations. Rocks mapped as the supposedly older Kairab rhyolite and felsic tuff gave younger ages of 1220 ± 4 Ma and 1222 ± 10 Ma, respectively, which are coeval with the Barby and Haiber Flats Formations. Two Gorab Gabbro samples, previously mapped as Kairab Formation, yield ages of 1341 ± 8 Ma and 1336 ± 8 Ma. These older ages are within error of two Welverdiend Formation samples which gave ages of 1344 ± 6 Ma and 1337 ± 9 Ma, and the formation was previously dated in the type area at 1327 ± 10 Ma. These ages confirm the reassignment of rocks originally mapped as tholeiitic Barby Formation into the Welverdiend Formation, north of a newly identified stratigraphic hiatus corresponding to the geophysically defined Wereldend Lineament . Sm–Nd and Lu–Hf isotopic signatures for the Barby, Haiber Flats and coeval Kairab samples indicate that they are co-magmatic and derived from partly depleted mantle contaminated by older crust. TDM model ages of these samples range from 2.5 to 1.5 Ga with a major 2.2 to 1.8 Ga group. This suggests that the older crustal component was Paleoproterozoic but included some Archean material. The Welverdiend Formation and Gorab Gabbros show similarity in age, Sm–Nd and Lu–Hf characteristics and were probably derived from partially depleted mantle, or from a well-homogenised mixture of depleted mantle and older crust. REE diagrams indicate enrichment in LREE (La–Gd) and a flat HREE pattern (Tb to Lu). On spidergrams, most samples are characterised by negative Nb–Ta anomalies and positive K and Pb anomalies which indicate a subduction-related setting (with positive Sr anomaly) or a reworked crustal origin. The similarity in ages, isotopic signatures and geochemistry confirms the correlation of the Barby and Haiber Flats Formation.

Tree ring studies, have been an important tool for studying climate variations since the beginning of 1900s due to their ability to preserve of information about abiotic and biotic factors. This study is aimed at understanding the growth rings of two aggressive encroachers in Namibia, Dichrostachys cinerea and Senegalia mellifera. We used three sites across a rainfall gradient from 250 to 600 mm/yr, where the stem discs were collected and processed from all species. Stem discs of different sizes of the two species were sampled from each site, air dried, polished and characteristics of growth rings were analysed using WinDENDRO, COFECHA and SPSS software. Growth rings were present for both species across all three sites, however the characteristics of the rings varied by site. Both species show a positive relationship between stem diameter and heartwood diameter and also between numbers of growth rings and stem diameter. Stem diameter did not necessarily relate to the age of the tree. It is concluded see that growth ring characteristics of the two species vary by geographical location and are influenced by complex environmental interactions, mostly rainfall.

The area of the city of Tsumeb in northern Namibia is strongly affected by gaseous emissions and by dust fallout from the local smelter. This is also reflected in increased concentrations of lead and arsenic in blood and urine of the residents. Consequently, modeling of the dispersion of dust and SO2 emissions from the smelter was used in this study to delineate the contaminated area and to assess the health risks. The modeling results were verified by ground-based geochemical survey of soil and grass in the area. The results of modeling revealed that the concentrations of SO2 in the Tsumeb town were relatively low, whereas the highest dust fallout concentrations were found around the Tsumeb smelter. The Tsumeb town residential area was less affected due to favorable landscape morphology between the smelter and the city (the Tsumeb Hills). The results of modeling of dust fallout and geochemical survey coincided very well. Since the anthropogenic contamination was bound only to the surface layer of soil, the local soils were sampled at two depth horizons: topsoil and the deeper soil horizon. This enabled us to distinguish between the anthropogenic contamination of soil surface from natural (geogenic) concentrations of studied metals in the deeper part of the soil profile. Concentrations of metals in grass correlated with the concentration of metals in topsoil. In contrast to a good conformity with the modeling of dust fallout from the smelter and geochemical survey, the results of modeling of SO2 contents in the air, and total sulfur content in soils were different. Differences can be explained by additional sources of contamination, as for example a sulfate-rich dust fallout from local tailings ponds and slag dumps that were not considered in the SO2 dispersion model. The results of the present investigation can be used by the mining companies in the management of air quality, assessment of the efficacy of applied remediation measures, and in reducing the impact of dust fallout on the local ecosystem. The Municipal Administration may use these results to plan further development of the city of Tsumeb, especially in terms of further expansion of housing construction.

The southern Central Zone (sCZ) of the Neoproterozoic to early Palaeozoic Damara orogenic belt hosts significant uranium deposits in Namibia. Rossing South-West, a leucogranite-hosted uranium deposit in the sCZ is partitioned into two sections; north-easterly and south-westerly sections with the latter (termed mining licence 120, i.e. ML120) forming the locus of this investigation. The deposit lies within the vicinity and to the west of the Welwitschia lineament which served as a conduit for mineralized fluids along with the Rossing and Husab deposits. Mineralogy and major and trace element geochemistry of the uraniferous leucogranites in ML120 suggest they are S-type granites derived from a sedimentary source as evidenced by the presence of igneous phases of garnet and cordierite together. Microscope and electron microprobe results from 133 powdered, drill core and hand samples prove that the deposits host similar primary uranium mineralization (chiefly uraninite which mainly exist as independent uranium minerals) and similar secondary U mineralization. At Rossing-SW U minerals include uraninite, coffinite, pitchblende, betafite, uranophane, betauranophane, carnotite, gummite and might partially exist as Th isomorphs. Mineralization at all locales is associated with post-tectonic D and E-type sheeted leucogranites containing quartz, alkali-feldspar and variable amounts of plagioclase producing rocks of variable compositions from tonalite to alkali-feldspar granite. Total reserves calculated at a cut-off grade of 100 ppm were reported as 171 Mt of ore at 376 ppm for Rossing and 205 Mt of ore at 497 ppm for Husab (probable). The Rossing-SW orebody is open-ended however total inferred resources stand at 304.4 Mt of ore at 235 ppm while measured resources stand at 8830t ore at circa 231 ppm. A comparison of the geological parameters (uranium mineralogy, leucogranite petrology and geochemistry) suggests similar ore composition. Consequently, ore from Rossing-SW's ML120 area could be processed at existing metallurgical plants (such as at Rossing or Husab) with a probable increase in U3O8 yield.

Dichrostachys cinerea and Senegalia mellifera trees are the most widespread invasive encroacher species in Namibia. Understanding their growth performance under arid conditions is key to understanding and managing the arid ecosystems of Namibia. To determine their utility in dendrochronology, we analyzed the formation of growth rings for two species from three sites in Namibia. We applied cross-dating techniques to 69 tree discs, the analysis of which confirmed the formation of annual growth rings. The rings are characterised by alternating layers of low and high vessel density and are separated by bands of marginal parenchyma. D. cinerea shows a well-defined pattern of growth rings, whereas the ring patterns of S. mellifera are more complex. Because aging trees tend to display narrower rings toward the outside of the stem, we applied both ring-width index and basal area increment methods in developing ring-width chronologies for the two species. Descriptive statistics for the chronologies indicate that the average ring chronologies are of good quality and that the trees are responding to common environmental signals. The basal area increment methodology produced better statistics than the ring-width index for these two species. Furthermore, statistical characteristics of the chronologies indicate that D. cinerea has a higher mean sensitivity (MS), expressed population signal (EPS), and signal-to-noise ratio (SNR) than S. mellifera. Thus, we find that both species are suitable for dendrochronological study, with D. cinerea being better than S. mellifera.

The Hohewarte Metamorphic Complex has been variously correlated with the Abbabis Complex, Kamanjab Inlier and the Rehoboth inlier, which is better studied. The Hohewarte Metamorphic Complex is wholly surrounded by the Damara Sequence that experienced peak orogenesis at circa 550 Ma. The Damaran cover has been thrusted over the Hohewarte gneisses, producing subhorizontal fabrics. The Hohewarte Metamorphic Complex was already accreted onto the Kalahari craton during Damaran peak orogenesis. The Hohewarte Metamorphic Complex is composed of a variety of gneisses, ranging from amphibolites, quartz-feldspathic gneiss, plagioclase-rich striped gneisses that enclose two varieties of augen gneiss; a felsic K-feldspar-augen gneiss and an augen gneiss with plagioclase and K-feldspar augens in a matrix of biotite and hornblende rich matrix, occurring mainly to the east of the complex. To the northeast in the Seeis inlier, occurs a medium-grained granitic gneiss with a weak foliation. To the west occurs the ubiquitous banded quartz-feldspar-biotite gneisses, that were intruded by megacrystic granites that are now gneisses. The whole complex has been deformed with two deformations prior to the Damaran orogeny. The fabrics in the gneisses are vertical to subhorizontal, whereas the Damaran cover rocks show a distinct ENE trending fabrics with a consistent dip of 30–45° to the NW. Four samples were selected for single zircon U–Pb dating to establish the age relations; the amphibolite unit within the quartzo-feldspathic gneiss records an age of 1758 ± 10 Ma; the felsic augen gneiss yielded an age of 1290 ± 10 Ma. The megacrystic K-feldspar gneiss yielded an age of 1168 ± 38 Ma, whereas the granitic gneiss gave the youngest age of 1061 ± 10 Ma. eHf model ages show that all the Hohewarte Metamorphic Complex gneisses plot close to the CHUR and posses very primitive crustal signatures and have not been recycled much in the crust. A depleted mantle source is suggested for their origin.

Kinetic batch leaching of the flotation wastes from Berg Aukas and Kombat mining districts (northern Namibia) in 500 μM solutions of citric, oxalic and acetic acids was performed to simulate the release of trace metals and As in the rhizosphere-like environment. The obtained data demonstrate that citric acid may significantly contribute to mineral waste alteration accompanied by contaminant mobilization; the maximum dissolution rates corresponded to 7% (Cu), 3% (As), 2% (Cd), 0.8% (Pb) and 0.3% (Zn) of their total amounts. In contrast, the role of oxalic and acetic acids in the complex process of contaminant leaching was usually negligible and/or comparable with water. The precipitation of newly formed Fe (hydr)oxides followed by the adsorption of Pb, Cd and eventually Zn from the model solutions seems to be the key mechanism which led to the metals' stabilization, as predicted by speciation modeling. Considering the neutral and slightly alkaline (and lowly organic) character of soils around the investigated flotation waste dams, Cu and As, present as neutral or anionic species, are suggested to be contaminants with the highest potential for rhizospheric mobilization and subsequent vertical mobility in local soils and/or transfer to plants.

The dust blown out from the tailings dam – and to a lesser extent from the ore treatment plant – appears to be the major environmental threat in the Rosh Pinah town. The amount of suspended dust particles in the air (TSP) monitored on the surface of the tailings dam ranges between 8 and 84 mg m− 3. The air contains (in μg m− 3) high amounts of Zn (median: 792), Pb (median: 412), Mn (median: 163), and Cu (median: 42), and lesser amounts of As (median: 5) and Cd (median: 2). Sampling of topsoil together with reference sampling of subsurface soil at a depth of 80–90 cm revealed that the shape of the dust contamination halo is elongated northwestward according to the prevailing direction of winds during summer. The eastern and northeastern parts of the Rosh Pinah town are affected by dust fallout. The factor analysis of data acquired from topsoil revealed two factors governing the source and the nature of individual components: (a) “tailings specific factor” grouping predominantly CO2 (carbonate), Stot, Fe, Mn and As, and (b) “ore processing plant specific ones”, grouping Stot, As, Cd, Cu, Hg, Pb and Zn. Dispersion modeling of suspended dust particles (TSP) in the air at Rosh Pinah revealed that while the whole surface of the tailings dam was dry in the past due to infiltration and evaporation of water, the average yearly concentrations of TPS in the Rosh Pinah town amounted to 100–300 μg m− 3, but when two thirds of tailings dam surface has currently been covered with water, the concentrations of TPS markedly decreased to 30–100 μg m− 3. The results of dispersion modeling fit well with the results of ground geochemical survey. The topsoil metal and arsenic contents are in good agreement with their contents in subaerial part of grass (Stipagrostis geminofolia L). The contents of Pb in 52% of collected samples of grass exceed permissible values for dry fodder. The bioaccessibility of metals and arsenic in topsoils was tested by a US EPA-adopted in vitro method using a simulating gastric fluid formed of a 0.4 M solution of glycine adjusted to pH 1.5 by HCl addition. Gastric accessible contents of chemical elements in topsoil increase (in % of their total contents in topsoil) in the ascending sequence: Fe (6.2%) → As (8.6%) → Cu (23.6%) → Zn (39.3%) → Mn (66.7%) → Pb (85.9%). The evaluation of obtained data on gastric bioaccessibility indicates that a health risk related to soil or dust ingestion should be taken into account only in the case of lead.

A fingerprinting method for identifying sources of uranium in shallow groundwater alluvial aquifers of the Khan and Swakop Rivers was established using 234 U/ 238 U ratios and 235 U/ 238 U ratios in the areas that drain the Rossing Uranium mine and the Langer Heinrich Uranium mine, in Namibia. In most groundwater aquifers that drain basement granitoids enriched in uranium the contribution of the total uranium in the shallow alluvial aquifers may be significant. Another source of uranium in shallow alluvial aquifers maybe from anthropogenic sources associated with mining activities as is the case in our study area. The distribution of radionuclides in water depend on various factors that influence their solubility and mobility and control their concentration in water such as pH, Eh, O 2 and availability of ligands. The study identified a methodology that can fingerprint the two sources i.e., a natural source where 234 U/ 238 U ratios are above unity and a second one where this ratio is below unity implying that the source is anthropogenic. In the study area, 234 U/ 238 U activity ratio is above unity (1.3–1.7) and 235 U/ 238 U is 0.045 ± 0.015 that both identify a natural source for all elevated uranium and other radionuclides in groundwater of the study area. The uranium values in groundwater exceed the WHO guideline value of 15 μg/l and it increases in the lowest part of Swakop River; but there is no gradual or systematic change in uranium concentration thus indicating that concentration is related to local factors such as the geology and lithology of the aquifer material, Eh and pH for each borehole. The 238 U decay series exhibits disequilibrium due to different fractionation processes that include decaying of radioactive elements and alpha recoiling.

Effects of mine dump pollution on semiarid savanna vegetation were investigated in Kombat, Namibia. Vegetation structure, species richness, composition and diversity were compared between polluted and control sites. Concentrations of arsenic, chromium, copper, lead and zinc in soils were significantly higher closer to a 99-year-old mine dump than in a control site and exceeded internationally recommended guidelines by as high as 11 times. Mine dump pollution has significantly reduced woody plant densities, species richness and diversity in the affected area due to disappearance of pollution-sensitive species and preponderance of tolerant ones. Species composition and structure of vegetation close to the mine dump significantly changed, possibly due to negative impacts of heavy metals on recruitment as pollution-sensitive species died off, whereas tolerant species invaded the vacated ecological niches. Ordination analyses confirmed a strong pollution gradient, with measured heavy metals accounting for 57.3...

The stratigraphic position of the Otjosondu ferromanganese deposit in the Neoproterozoic Damara Supergroup in the Central Zone of the Pan-African Damara orogenic belt is uncertain. Comparison of the enclosing host rocks with regional profiles in the southern Central Zone would indicate that it is hosted by the Etusis Formation (Fe-rich feldspar-quartz rocks) of the Nosib Group, in a condensed stratigraphic section of the supergroup, and not the Chuos Formation (diamictite, turbidite and thin iron-formation layers) of the Swakop Group, as previously proposed. The Otjosondu ore comprises ferromanganese silicate-oxide assemblages that occur in a feldspathic-quartzite sequence lacking the mixtite facies typical of the Chuos Formation. Hematitic iron formation containing minor hyalophane, spessartine and barite, and hyalophane-bearing spessartine-quartz rock are present in close spatial association with the Mn silicate-oxide rocks. Barite is a widespread and locally abundant mineral in the Mn silicate-oxide ore. Bulk-rock chemical analyses indicate trace-element associations of Ag-As-Cu-Co-Bi-B-P with Mn and Sr-Mo-W with Ba in the Mn silicate-oxide and spessartine-quartz rocks. These element associations are explained by adsorption/substitution processes in an oxygenated alkaline marine setting. Sulfur-isotope compositions of barite from the Mn silicate-oxide ore vary from +10.1 to +16.7 ‰, a range of δ34S values that shows negative correlation with bulk-rock Fe content and is interpreted as mixing of isotopically light hydrothermal S with heavier sea-water S. The protoliths of the ferromanganese rocks were precipitates deposited in a basin-margin setting as a result of mixing of an exhalative hydrothermal fluid with oxygenated, sulfate-bearing sea water, and varying degrees of detrital addition. These conclusions are in contradiction to the deep-water, anoxic, sulfate-depleted oceanic settings required for formation of glacially associated Rapitan-type iron and manganese formations. The formation of the Otjosondu ferromanganese deposit is therefore unrelated to any Chuos/Sturtian global glacial event. Origins as hydrogenetic deposits are mostly excluded due to the base-metal- and P-poor, but Ba-rich nature of the Otjosondu ores. The baritic ferromanganese, hematite-quartz and spessartine-quartz rocks at Otjosondu may be compared to oxidised baritic portions of the Gamsberg (Broken Hill-type) base-metal deposit in South Africa and may represent the distal or shallow-water oxidised equivalents of sediment-hosted exhalative base-metal mineralisation such as the penecontemporaneous Tsongoari and Rosh Pinah deposits.

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 1979. 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.

Ion microprobe U-Th-Pb analyses of zircon from 40 granitoid rocks collected from the late Mesoproterozoic Irumide Belt in Central Southern Africa, along the southern margin of the Archean to Paleoproterozoic Bangweulu Block, provide a comprehensive set of age data for this complex orogen. The data indicate that the Irumide Belt is constructed on a basement of principally Paleoproterozoic (ca. 2.05-1.93 Ga) age with a subordinate Neoarchean (ca. 2.73 Ga) component, which is overlain by a platformal quartzite-pelite succession known as the Muva Supergroup. Previously published U-Pb detrital zircon data for the Paleoproterozoic Muva Super- group, which show age populations that match all of the pre-1.9 Ga basement components identified within the Irumide Belt, suggest that the pre-Muva basement was assembled as a coherent block by 1.8 Ga, which we refer to as the Bangweulu Craton. The southern margin of the Bangweulu Craton was then intruded by a previously unrecognized suite of biotite-bearing granitoid rocks between 1.66 and 1.55 Ga, not recorded elsewhere in the region, and was later the site of emplacement of voluminous granitoid magmatism during the Irumide Orogeny at between 1.05 and 1.00 Ga. Hf isotopic data from zircon in these suites indicate variable influence from cryptic Archean rocks in the lower crustal melting zone of the Bangweulu Block. U-Pb analyses of inherited zircon cores in magmatic zircon in these granitoid rocks, directly confirm the presence of this reworked cryptic Archean basement of the Bangweulu Craton. The age data confirm previously proposed tectonic models for the Mesoprot- erozoic evolution of central Africa, refuting the presence of a continent-spanning Grenvillian-aged Orogen, including the Kibaran Belt, Irumide Belt and Choma- Kalomo Block of central Africa and connecting with Mesoproterozoic terranes further south along the margins of the Kalahari Craton. The data clearly show that the Proterozoic tectonic evolution of the Bangweulu Craton, which became attached to the southern margin of the larger Congo Craton during the Mesoproterozoic, involved a series of distinct convergent orogenic episodes affecting and reworking its southern (passive) margin. The mismatch in timing of Mesoproterozoic orogenic activity along the Bangweulu Craton, compared to that on the margins of the Kalahari, is compatible with the notion that these continental fragments were not juxtaposed along these Mesoproterozoic belts and in their present-day relative positions at the time. Whether either of these central and southern African cratons did form part of Rodinia, however, remains a matter for debate.

As the city of Windhoek is growing rapidly, it has become increasingly obvious that dangers to the underlying groundwater aquifer have become imminent, and need addressing immediately. Water infiltration and the transportation of contaminants from anthropogenic activities through soils into the bedrock and hence the aquifer involve soil maturity, chemical and microbial processes and the climate of a particular area. The thin immature soil horizon (circa 5–20 cm) over the Windhoek schist implies that most areas of the city are built directly on bedrock, making the aquifer vulnerable. Anthropogenic activities from the use of pesticides for weed control, oil spills, toxic chemical spills, dumping of undesired substances by residents and high fertilizer application rates for lawns can lead to the contamination of groundwater. The result of our study show that the soil composition in Windhoek lacks mature clay minerals and is enriched in micas, quartz and albite. Some areas in the northern and southern industrial areas show contamination in heavy metals Pb, Zn, Cu and Ni. To the west of the city, close to the textile factory, soils are contaminated with ammonium compounds. The hydrochemistry of these pesticides and fertilizers can cause severe pollution to the groundwater if the practice is not carefully monitored. In addition, the rapid expansion of uncontrolled settlements without proper sanitation and reticulation has made the problems much more difficult. The geology of the city of Windhoek consists of the Kuiseb Schist, locally known as the “Windhoek Schist” and amphibolites. The Kuiseb schist possesses pervasive cleavage that renders the underlying lithology to be permeable to percolating water and fluids from the surface into the aquifer. The fissility and fracture density of the schist imply that leakage of surface waters, phenols, septic tank spills and industrial contaminants may reach the aquifer in unusually high rainfall years. Organic fuels and oils are much more adverse, as they are able to reside in soils for long periods of time. The weathering of soils in humid climes produces silicic acid, which has an effect in sealing the conduits due to soil generation from rocks; an element lacking in Windhoek due to the arid climate. Thus the close monitoring of all sewage pipes, filling stations, dump sites including cemeteries preferably on a GIS based model is the best possible way to save the aquifer from future pollution.

The contents of As, Cu, Cd, Pb, Mn, along with the Pb isotopic ratios 206Pb/207Pb and 208Pb/206Pb were studied in both soils and tree rings of the marula tree (Sclerocarya birrea) in the vicinity of the Tsumeb deposit (Namibia). Amounts of all the studied metals and As are higher in the immediate vicinity of the Tsumeb Cu-Pb smelter in the soil. The tree rings also have their maximum content of all the studied substances in the vicinity of the smelter (with the exception of Pb). At a more distant site, the maximum concentration of Pb in the soils was 29.8 mg/kg, while the content in the soil in the vicinity of the smelter was as much as 8,174 mg/kg. In the vicinity of the smelter, the maximum Pb content in the tree rings reaches a value of 5.7 mg/kg, compared to a more distant site, where the contents are as high as 9.2 mg/kg. The lower Pb content in the trees on contaminated soil indicates that the composition of the xylem determines the above-ground uptake, rather than the root uptake. Similarly, the above-ground uptake is documented by the isotopic composition of Pb at the distant location, where the tree rings have different contents of Pb isotopes compared to in the soil. The As, Cd, Cu, Pb, and Zn contents are highest in the tree rings from the 1950s (and older), along with those from the 1990s, while the Mn contents were highest in those from the 1960s and 1990s. The contaminant peaks in the 1950s and 1960s could be associated with the roasting of sulfidic ores, while the peak values in the 1990s could have been caused by the start of Cu slag reprocessing in the late 1980s, and culmination of works at the smelter prior to the closing of the mine. The tree rings of the marula tree were found to be a suitable archive for above-ground pollution close to Cu and Pb smelters.

Zimbabwe has a substantial number of mines and 67 minerals have been mined in the country since 1900 but at present only 30 different minerals are being mined. Exploitation of a variety of ores, in rocks of diverse composition, provides the potential for a range of pollution problems. The severity and extent of contamination differs with the type of minerals mined. This paper presents part of the results of a broad study, carried out across Zimbabwe, which assessed the potential of different mine tailings dumps to cause environmental problems. The dumps considered in the study were divided into six dump types, namely: gold-mine dumps, base-metal mine dumps (dumps associated with the mining of nickel, zinc, copper and lead), minor-metals mine dumps (dumps associated with mining of antimony, arsenic, and selenium), platinum-group metal mine dumps, chromite and asbestos mine dumps, and sulphur (pyrite) mine dumps. The elemental chemistry of the dumps and physical characteristics (pH, total dissolved solids) of the dumps, tailings’ leachates, and stream waters around the dumps were used to assess the potential of the dumps to pollute water bodies. Samples were collected in both the dry and wet seasons. The dispersion and pollution patterns were derived from Eh-pH conditions around the dumps after considering the mobility of the elements present in these dumps under different Eh-pH conditions. In this paper potential to pollute is considered as the likelihood of the elements to disperse under the prevailing conditions at the dump. The concentrations of elements, type of elements and the potential dispersion and pollution patterns from each dump were used to characterise potential risk of water pollution associated with the different dump types. The results showed a slight increase in concentrations of most elements studied in downstream waters compared to upstream waters. The dump conditions varied from acidic to alkaline, and so the elements studied have different mobilities in different dumps. The elements that pose environmental risks differed from one dump type to another thus different dumps have different potentials to pollute the water bodies. From the study it emerged that the minor metals dumps show the worst pollution risk, followed by base metal dumps, gold-mine dumps, platinum group metals mine dumps, chromite asbestos mine dumps and sulphur mine dumps. The pH values of 79% of the waters sampled in streams both before and after the dumps were neutral, though the pH values of the leachates themselves was frequently very acidic (pH

The City of Windhoek is underlain by the Kuiseb Schist, locally known as the “Windhoek Schist” and amphibolites. In the low-lying parts of the Windhoek valley, gravels and sands are present. The Windhoek schist has several lithologies, dominated by garnet–muscovite–chlorite–biotite schist, with distinctive cleavage. This pervasive cleavage renders the underlying lithology permeable to fluids percolating from the surface into the aquifer. Other minor lithologies are trachytes, metarhyolites and quartzites found to the east of the city. The amphibolite is part of the Matchless belt, and traverses the city in a NE–SW fashion. When weathered, it forms a perfect aquiclude. North–south and northeast–southwest trending faults with a few splays cut across the Kuiseb Schist. The faults play a significant role in increasing the fracture density of the fissile schist. The faults are the major links that form channels between the surface and the aquifer below. The city of Windhoek uses the aquifer both as a source of fresh water and as a storage facility. The recharge areas of the aquifer lie to the east and south- to southeast of the city in the vicinity of the suburb of Kleine Kuppe. The soil horizon over the Windhoek schist is very shallow and most buildings are built directly on bedrock. The thin soil horizon makes the aquifer prone to pollution, caused either by accidents such as spills or by carelessness due to unsupervised dumping. The fissility and fracture density of the schist imply that leakage of surface waters, phenols, septic-tank spills, sewer-bursts, chemical and industrial contaminants and other such materials can reach the aquifer in unusually high rainfall years. The effects of fuels and oils are much more adverse, as they may remain in soils for long periods. The rapid urbanization and building of informal settlements without sewage reticulation has increased the risk of pollution to the Windhoek aquifer. The close monitoring of sewage pipes, filling stations and dump sites (including cemeteries), preferably using a GIS-based model, is the best way to prevent future pollution.

The Mazowe Valley contains several of Zimbabwes largest current mining operations, is densely populated and is also a major agricultural area. The urban areas of Bindura, Goromonzi, Shamva, Marondera, Murehwa and Mutoko all draw water from within the Mazowe Valley. Irrigation of commercial crops is also a major water user. Accordingly, managing the impact of mining oper- ations on water quality in the Mazowe Valley must be a major priority for sustainable development in this area. Madziwa Mine, 150 km north-east of Harare, is a case in point. Mining took place between 1966 and 2001. The main sulphides were chalcopyrite, pyrrhotite, pentlandite and pyrite. Waste from the mines plant has been disposed of via a tailings dam, the focus of this study. Surface water samples were collected at 12 sites around the slimes dam and groundwater samples were collected from six bore- holes. The samples were analysed for dissolved metals using atomic absorption spectrometry and for anions using gravimetry and titration. The surface water chemical analyses showed that acidic effluent with high concentrations of iron, nickel and sulphate emanates from the tailings dam. Concentrations of metals are lower after the water has passed through natural wetlands. Chemical analysis of groundwater showed similarly high levels of acidity, sulphate and metal. These findings show that acid mine drainage is seeping from the tailings dam. Efforts are being made to reduce the effects of the acid mine drainage. For surface seepage from the dumps these efforts include diverting acidic effluent from the dump into natural wetlands that neutralise the acidity. To reduce drainage into the groundwater efforts are being made to plant trees with high evaporation rates to minimise the amount of water that can cause acid mine drainage. 2004 Elsevier Ltd. All rights reserved.

The Irumide Fold belt of Zambia consists of a Palaeo to Mesoproterozoic complex of gneisses and granite gneisses and a supracrustal sequence of quartzites and pelites. Although no direct correlation is possible, the metasedimentary sequence is tentatively equated with the Manshya River Group described in the NE. The basement to the Irumide belt consists of the Bangweulu Granites to the North, and the Mkushi gneiss basement (MGB) to the Southwest. Age constraints on the Bangweulu Block are limited, but the Mkushi Gneiss has been dated at ∼2050 Ma. A detrital provenance study on a quartzite of the Manshya River Group near Mkushi indicates derivation from terranes of up to 3180 Ma, with a maximum age for the Manshya River Group set by the youngest detrital grain at 1941 Ma. Detrital cores from paragneisses and migmatites in the Serenje area indicate a more uniform detrital source for the sedimentary protolith of 2050–2000 Ma. A more direct age constraint on the Manshya River Group has been provided through an age of 1880 Ma on a concordant rhyolite in the metasedimentary sequence near Chinsali. The Manshya River Group consists of a succession of four pelite and four quartzite Formations. The granitoids, which make up a large portion of the Irumide belt, can be subdivided into an older suite of leucocratic gneisses and biotite-granites, and a younger suite of alkaline, often porphyritic K-feldspar granites. Oversimplified lithostratigraphic division of the “crystalline basement” in the southwest of the Irumide belt has lead to an overestimation of the Palaeoproterozoic basement (MGB). The extent of the Palaeoproterozoic basement awaits re-evaluation through fieldwork. The main structural trend of the Irumide belt is northeast and is related to extensive crustal shortening during the main stage of the Irumide orogeny. Tectonic transport is directed towards the northwest, with southwest directed backthrusting locally developed to define a double verging overall structure. The compressional stage is characterised by amphibolite grade metamorphism and accompanied by widespread granite magmatism and anatexis.

Mineralogical and microfabric studies of the Magdala gold deposit together with isotopic and fluid inclusion studies have shown that the mineralising fluid is externally derived. The host rocks to the quartz veins do not possess any significant amounts of gold, whereas the quartz veins can contain >7 g/t gold. The walls to the quartz veins possess alteration haloes in the form of stilpnomelane porphyroblasts, attesting to the fact that the fluid in the veins was out of equilibrium with the host rocks. The distribution of alteration haloes that occur parallel to the quartz vein margins necessitates that a subvertical fluid gradient, be more or less constant during the deposition process in order to produce the observed architecture of the alteration haloes. Quartz lodes possess δ 18 O values that range from 15.8 to 17.3 per mil while associated host rocks range between 9.7 to 12 per mil in the metabasalts and 10.2 to 14.1 per mil in the volcanogenic and metasedimentary rocks. The dissimilarity of δ 18 O values between host rocks and quartz veins suggests that there has been a high fluid influx in the veins, implying external buffering. Four types of fluid inclusions were distinguished on the basis of spatial arrangement and composition using the Laser Raman Spectroscopy method. The salinity of the fluid inclusions range from 0.7 to 8.4 wt% NaCl equivalent, suggesting that gold was deposited due to the influx of different external fluids. The association of pyrite–arsenopyrite–pyrrhotite with gold and with PGEs suggests that these fluids have a lower crustal origin and may have originated from the upper mantle and mixed with fluids derived from deep seated metasediments.

In the modern world there are several sources of pesticides and other phenyl type organic compounds. Why do we use pesticides? Simply that the world’s agricultural practices have commercialized to feed an overgrowing world population. Agriculture has also become a very lucrative business, where various players try to find niches to market their products. At the same time, societies have continued to become more aware about their natural environment and how to sustain it. As far back as 500 A.D., the city of Athens passed a law requiring all refuse to be disposed in a designated landfill outside the city walls (Zakrzewski, 1997); this was followed by many such laws in Europe. However direct linking of disease and health to environmental occupation was done by Dr. Percival Pott, in 1775 (quoted in Zakrzewski, 1997), who correctly linked the “chimney workers” with the unusual high rate of scrotal cancer, which he associated with exposure to soot in their work environment (Zakrzewski, 1997). In a city like Windhoek, pesticides may arise from the control of grasses on road pavements (Mapani, 2005); or from small scale urban agricultural gardens behind homes. However the major source of pesticides is by far from the farming industry. It is estimated that in the United States alone, close to 98% of the sprayed insecticides and 95% of the herbicides finally reach an unintended sink (destination) (Miller, 2004). The effect of this is obvious when it comes to infiltration of water into the ground that has been used in the irrigation of crops. Pesticides are one type of compounds that undergo “biomagnification” in the food chain (US EPA, 2003). This aspect is especially dangerous as it ensures that the threat from the pesticide is not decreased with time, but rather increased. The United States Environmental Protection Agency (US EPA, 2003) has classified pesticides into four categories; namely; (i) organophospates; (ii) N-methyl carbomates; (iii) triazines and (iv) chloroacetanilides. Some specific pesticide compounds have common mechanisms of toxicity, and require cumulative risk assessment over a relative long period, in order to define the potential risks. However the danger to aquatic life as described below in section 2 is well known, but the danger to human health is ill defined in comparison; with only a few

Tsumeb, in northern Namibia, is a famous copper mining town with over a century of mining and smelting operations. The subject of this study was soil in Nomtsoub township, a poor and under developed quarter where children spend most of their time outside their homes and are exposed to a dusty environment. The aim of the study was to determine the degree of residential soil pollution, environmental risk and bioaccessibility of potentially toxic elements in order to estimate the impact of mining and especially smelting activities on the children’s health. Laboratory analysis of samples included x-ray diffraction, aqua regia extraction, sequential extraction and body fluids (gastric and intestinal) extraction. Potentially toxic elements (PTE) in extracts were analyzed using atomic absorption spectrometry. Indicators of soil contamination, environmental risk and daily intake of contaminants were calculated. Although there is high level of pollution (especially from arsenic and cadmium) and there is an environmental risk from As, Cd, Zn, Pb and Cu, bioaccessibility tests showed that the estimated daily intake of PTE through the soil is low and does not exceed the allowable daily intake for children weighing over 5 kg. Pb and As represent potential risk, for children weighing less than 5 kg.