Dynamics of arsenic in agricultural soils irrigated with arsenic contaminated groundwater in Bangladesh

Arsenic (As) concentrations in the soil layers of 12 rice fields located in four As affected areas and two unaffected areas in Bangladesh were monitored during 2003. In the unaffected areas, where irrigation water contained little As (<1 microg/L), As concentrations of rice field soils ranged from 1.5 to 3.0 mg/kg and did not vary significantly with either depth or sampling time throughout the irrigation period. In the As affected areas where the irrigation water contained elevated As (79 to 436 microg/L), As concentrations of rice field soils were much higher compared to those in the unaffected areas and varied significantly with both depth and sampling time. For the top 0 to 150 mm of the soil, the As concentration increased significantly at the end of the irrigation season (May-June 2003). About 71% of the As that is applied to the rice field with irrigation water accumulates in the top 0 to 75 mm soil layer by the end of the irrigation season. After the wet season during which the rice fields were inundated with flood/rain water, the As concentrations in the soil layer decreased significantly and were reduced to levels comparable to those found in soil samples collected at the beginning of the irrigation period. The long-term As accumulation in agricultural soil appears to be counteracted by biogeochemical pathways leading to As removal from soil.     

Impacts of mercury contaminated mining waste on soil quality, crops, bivalves, and fish in the Naboc River area, Mindanao, Philippines

Rice paddy fields in the Naboc area, near Monkayo on the island of Mindanao, Philippines, have been irrigated four times a year over the last decade using Naboc River water contaminated with mercury (Hg) by artisanal gold mining in the Diwalwal area. Silt containing up to at least 90 mg Hg/kg (d.w.) has been deposited in rice paddy fields during the 1990s and this has been repeatedly mixed into the rice root zone through ploughing. Hg in the rice paddy field soils averages 24 mg Hg/kg and generally exceeds the UK and Canadian soil quality thresholds for agricultural soils as well as the proposed Dutch Intervention value and the USEPA soil ingestion Soil Screening Level (SSL) for inorganic Hg. Much lower Hg concentrations (0.05-0.99 mg/kg) within the range expected for uncontaminated soils, characterise soils on which corn and bananas are cultivated, largely because these are not irrigated with Hg-contaminated water from the Naboc River. The estimated total weekly MeHg intake for a person living in the Naboc area related to the weekly consumption of 2.1 kg of rice grown on Hg-contaminated soils (15 microg MeHg) in conjunction with 1 kg of fish (220 microg MeHg) and 100 g of mussels (50 microg MeHg) from the Naboc River, would total 285 microg MeHg (equivalent to 4.75 microg/kg bw for a 60 kg adult), which is nearly three times the JECFA PTWI of 1.6 microg/kg bw. This will significantly contribute to the population mercury exposure and might explain why 38% of the local inhabitants were classified as Hg intoxicated during a mercury toxicity assessment [Drasch GS, B?se, O'Reilly S, Beinhoff C, Roider G, Maydl S. The Mt. Diwata study on the Philippines 1999-assessing mercury intoxication of the population by small scale gold mining. Sci Total Environ 2001; 267(1-3): 151-168.].     

Oxidation and removal of arsenic (III) from aerated groundwater by filtration through sand and zero-valent iron

Removing arsenic from contaminated groundwater in Bangladesh is challenging due to high concentrations of As(III), phosphate and silicate. Application of zero-valent iron as a promising removal method was investigated in detail with synthetic groundwater containing 500 microg/L As(III), 2-3mg/L P, 20mg/L Si, 8.2mM HCO3-, 2.5mM Ca2+, 1.6mM Mg2+ and pH 7.0. In a series of experiments, 1L was repeatedly passed through a mixture of 1.5 g iron filings and 3-4 g quartz sand in a vertical glass column (10mm diameter), allowing the water to re-aerate between each filtration. At a flow rate of 1L/h, up to 8 mg/L dissolved Fe(II) was released. During the subsequent oxidation of Fe(II) by dissolved oxygen, As(III) was partially oxidized and As(V) sorbed on the forming hydrous ferric oxides (HFO). HFO was retained in the next filtration step and was removed by shaking of the sand-iron mixture with water. Rapid phosphate removal provided optimal conditions for the sorption of As(V). Four filtrations lead to almost complete As(III) oxidation and removal of As(tot) to below 50 microg/L. In a prototype treatment with a succession of four filters, each containing 1.5 g iron and 60 g sand, 36 L could be treated to below 50 microg/L in one continuous filtration, without an added oxidant.     

Arsenic intake via water and food by a population living in an arsenic-affected area of Bangladesh

More and more people in Bangladesh have recently become aware of the risk of drinking arsenic-contaminated groundwater, and have been trying to obtain drinking water from less arsenic-contaminated sources. In this study, arsenic intakes of 18 families living in one block of a rural village in an arsenic-affected district of Bangladesh were evaluated to investigate their actual arsenic intake via food, including from cooking water, and to estimate the contribution of each food category and of drinking water to the total arsenic intake. Water consumption rates were estimated by the self-reporting method. The mean drinking water intake was estimated as about 3 L/d without gender difference. Arsenic intakes from food were evaluated by the duplicate portion sampling method. The duplicated foods from each family were divided into four categories (cooked rice, solid food, cereals for breakfast, and liquid food), and the arsenic concentrations of each food category and of the drinking water were measured. The mean arsenic intake from water and food by all 18 respondents was 0.15 +/-0.11 mg/d (range, 0.043 - 0.49), that by male subjects was 0.18 +/- 0.13 mg/d (n = 12) and that by female subjects was 0.096 +/- 0.007 mg/d (n = 6). The average contributions to the total arsenic intake were, from drinking water, 13%; liquid food, 4.4%; cooked rice, 56%; solid food, 11%; and cereals, 16%. Arsenic intake via drinking water was not high despite the highly contaminated groundwater in the survey area because many families had changed their drinking water sources to less-contaminated ones. Instead, cooked rice contributed most to the daily arsenic intake. Use of contaminated water for cooking by several families was suspected based on comparisons of arsenic concentrations between drinking water and liquid food, and between rice before and after cooking. Detailed investigation suggested that six households used contaminated water for cooking but not drinking, leading to an increase of arsenic intake via arsenic-contaminated cooking water.     

Treatment of arsenic in Bangladesh well water using a household co-precipitation and filtration system

Laboratory and field tests were conducted to evaluate the effectiveness of a household filtration process and investigate the effects of phosphate and silicate on the removal of arsenic from Bangladesh groundwater by ferric hydroxides. Fe/As ratios of greater than 40 (mg/mg) were required to reduce arsenic to less than 50 microg/L in Bangladesh well water due to the presence of elevated phosphate and silicate concentrations. The household filtration process included co-precipitation of arsenic by adding a packet (approximately 2 g) of ferric and hypochlorite salts to 20 L of well water and subsequent filtration of the water through a bucket sand filter. A field demonstration study was performed to test the treatment system in seven households in Bangladesh in March and April 2000. Experimental results obtained from the participating families proved that the household treatment process removed arsenic from approximately 300 microg/L in the well water to less than 50 microg/L. The participating families liked this simple and affordable process and used it to prepare clean water for drinking and cooking. A larger scale field test is currently underway.     

Arsenic in hair and nails of individuals exposed to arsenic-rich groundwaters in Kandal province, Cambodia

The health implications of the consumption of high arsenic groundwater in Bangladesh and West Bengal are well-documented, however, little is known about the level of arsenic exposure elsewhere in Southeast Asia, where widespread exploitation of groundwater resources is less well established. We measured the arsenic concentrations of nail and hair samples collected from residents of Kandal province, Cambodia, an area recently identified to host arsenic-rich groundwaters, in order to evaluate the extent of arsenic exposure. Nail and hair arsenic concentrations ranged from 0.20 to 6.50 microg g(-1) (n=70) and 0.10 to 7.95 microg g(-1) (n=40), respectively, in many cases exceeding typical baseline levels. The arsenic content of the groundwater used for drinking water purposes (0.21-943 microg L(-1) (n=31)) was positively correlated with both nail (r=0.74, p<0.0001) and hair (r=0.86, p<0.0001) arsenic concentrations. In addition, the nail and hair samples collected from inhabitants using groundwater that exceeded the Cambodian drinking water legal limit of 50 microg L(-1) arsenic contained significantly more arsenic than those of individuals using groundwater containing <50 microg L(-1) arsenic. X-ray absorption near edge structure (XANES) spectroscopy suggested that sulfur-coordinated arsenic was the dominant species in the bulk of the samples analysed, with additional varying degrees of As(III)-O character. Tentative linear least squares fitting of the XANES data pointed towards differences in the pattern of arsenic speciation between the nail and hair samples analysed, however, mismatches in sample and standard absorption peak intensity prevented us from unambiguously determining the arsenic species distribution. The good correlation with the groundwater arsenic concentration, allied with the relative ease of sampling such tissues, indicate that the arsenic content of hair and nail samples may be used as an effective biomarker of arsenic intake in this relatively recently exposed population.     

Influence of cooking method on arsenic retention in cooked rice related to dietary exposure

Arsenic concentration in raw rice is not only the determinant in actual dietary exposure. Though there have been many reports on arsenic content in raw rice and different tissues of rice plant, little is known about arsenic content retained in cooked rice after being cooked following the traditional cooking methods employed by the people of arsenic epidemic areas. A field level experiment was conducted in Bangladesh to investigate the influence of cooking methods on arsenic retention in cooked rice. Rice samples were collected directly from a severely arsenic affected area and also from an unaffected area, to compare the results. Rice was cooked according to the traditional methods employed by the population of subjected areas. Arsenic concentrations were 0.40+/-0.03 and 0.58+/-0.12 mg/kg in parboiled rice of arsenic affected area, cooked with excess water and 1.35+/-0.04 and 1.59+/-0.07 mg/kg in gruel for BRRI dhan28 and BRRI hybrid dhan1, respectively. In non-parboiled rice, arsenic concentrations were 0.39+/-0.04 and 0.44+/-0.03 mg/kg in rice cooked with excess water and 1.62+/-0.07 and 1.74+/-0.05 mg/kg in gruel for BRRI dhan28 and BRRI hybrid dhan1, respectively. Total arsenic content in rice, cooked with limited water (therefore gruel was absorbed completely by rice) were 0.89+/-0.07 and 1.08+/-0.06 mg/kg (parboiled) and 0.75+/-0.04 and 1.09+/-0.06 mg/kg (non-parboiled) for BRRI dhan28 and BRRI hybrid dhan1, respectively. Water used for cooking rice contained 0.13 and 0.01 mg of As/l for contaminated and non-contaminated areas, respectively. Arsenic concentrations in cooked parboiled and non-parboiled rice and gruel of non-contaminated area were significantly lower (p<0.01) than that of contaminated area. The results imply that cooking of arsenic contaminated rice with arsenic contaminated water increases its concentration in cooked rice.     

Groundwater geochemistry and its implications for arsenic mobilization in shallow aquifers of the Hetao Basin, Inner Mongolia

Arsenic concentrations in shallow groundwaters from the Hetao Basin of Inner Mongolia range between 0.6 and 572 microg/L. High As groundwaters generally occur in the shallow alluvial-lacustrine aquifers, which are mainly composed of black (or dark grey) fine sands in a reducing environment. They are characterized by high concentrations of dissolved Fe, Mn, HCO(3)(-), P and S(2-), and low concentrations of NO(3)(-) and SO(4)(2-). Low SO(4)(2-) coupled with high S(2-) suggests that SO(4)(2-) reduction has been an active process. In the reducing groundwaters, inorganic As(III) accounts for around 75% of total dissolved As. Total As contents in the sediments from three representative boreholes are observed to be 7.3-73.3 mg/kg (average of 18.9 mg/kg). The total As is mildly-strongly correlated with total Fe and total Mn, while a quite weak correlation exists between total As and total S, suggesting that the As is associated with Fe-Mn oxides, rather than sulfides in the sediments. It is found in the sequential extraction that chemically active As is mainly bound to Fe-Mn oxides, up to 3500 microg/kg. The mobilization of As under reducing conditions is believed to include reductive dissolution of Fe-Mn oxides and reduction of adsorbed As. Although exchangeable As is labile and very vulnerable to hydrogeochemical condition, the contribution is relatively limited due to the low concentrations. The competition between As and other anions (such as HPO(4)(2-)) for binding sites on Fe-Mn oxides may also give rise to the release of As into groundwater. Slow groundwater movement helps accumulation of the released As in the groundwaters.     

Arsenic accumulation in irrigated agricultural soils in Northern Greece

The accumulation of arsenic in soils and food crops due to the use of arsenic contaminated groundwater for irrigation has created worldwide concern. In the Chalkidiki prefecture in Northern Greece, groundwater As reach levels above 1000 μg/L within the Nea Triglia geothermal area. While this groundwater is no longer used for drinking, it represents the sole source for irrigation.This paper provides a first assessment of the spatial extent of As accumulation and of As mobility during rainfall and irrigation periods. Arsenic content in sampled soils ranged from 20 to 513 mg/kg inside to 5-66 mg/kg outside the geothermal area. Around irrigation sprinklers, high As concentrations extended horizontally to distances of at least 1.5 m, and to 50 cm in depth. During simulated rain events in soil columns (pH = 5, 0 μg As/L), accumulated As was quite mobile, resulting in porewater As concentrations of 500-1500 μg/L and exposing plant roots to high As(V) concentrations. In experiments with irrigation water (pH = 7.5, 1500 μg As/L), As was strongly retained (50.5-99.5%) by the majority of the soils. Uncontaminated soils (< 30 mg As/kg) kept soil porewater As concentrations to below 50 μg/L. An estimated retardation factor R_f = 434 for weakly contaminated soil (< 100 mg/kg) indicates good ability to reduce As mobility. Highly contaminated soils (> 500 mg/kg) could not retain any of the added As. Invoked mechanisms affecting As mobility in those soils were adsorption on solid phases such as Fe/Mn-phases and As co-precipitation with Ca. Low As accumulation was found in collected olives (0.3-25 μg/kg in flesh and 0.3-5.6 μg/kg in pits). However, soil arsenic concentrations are frequently elevated to far above recommended levels and arsenic uptake in faster growing plants has to be assessed.     

Groundwater derived arsenic in high carbonate wetland soils: sources, sinks, and mobility

Wetlands and organic soils have been recognized as important sinks for arsenic in the environment, yet sources and immobilization mechanisms of As are often unclear. To begin rectifying this deficiency, we investigated As retention and binding mechanisms at a degraded, minerotrophic wetland site in contact with groundwater rich in As and Fe. Arsenic occurred in high dissolved concentrations of up to 467 microg L(-1) in the groundwater, but dropped to values below 10 microg L(-1) towards the surface. The solid phase As content instead was high in the topsoil with up to 3400 mg kg(-1) and decreased with depth to 15 mg kg(-1). A similar pattern was observed with respect to Fe. Amorphous and crystalline iron precipitates were the main sorbents for arsenic in the soil horizons according to results from wet chemical sequential extractions. Arsenic was apparently not associated with inorganic carbon phases, but a substantial portion of up to 31% of As(tot) could be mobilized by dispersion of soil organic matter. Ratios of dissolved As(III)/As(V) decreased from the deeper As(III) dominated groundwater to the As(V) dominated soil porewaters, where As was apparently immobilized in its oxidized form. Concentrations of the organic species DMA and MMA were negligible. According to the results of simple one-dimensional estimates the vertical arsenic transport from the source in the groundwater to the topsoil was slow given an extrapolation of current conditions. These results suggest that As accumulation started before the beginning of drainage in the now degraded peatland soils and the degradation and mass loss of organic matter under oxic conditions caused the very high As concentrations found in the topsoil horizon today.     

Magnitude of arsenic pollution in the Mekong and Red River Deltas--Cambodia and Vietnam

Large alluvial deltas of the Mekong River in southern Vietnam and Cambodia and the Red River in northern Vietnam have groundwaters that are exploited for drinking water by private tube-wells, which are of increasing demand since the mid-1990s. This paper presents an overview of groundwater arsenic pollution in the Mekong delta: arsenic concentrations ranged from 1-1610 microg/L in Cambodia (average 217 microg/L) and 1-845 microg/L in southern Vietnam (average 39 microg/L), respectively. It also evaluates the situation in Red River delta where groundwater arsenic concentrations vary from 1-3050 microg/L (average 159 microg/L). In addition to rural areas, the drinking water supply of the city of Hanoi has elevated arsenic concentrations. The sediments of 12-40 m deep cores from the Red River delta contain arsenic levels of 2-33 microg/g (average 7 microg/g, dry weight) and show a remarkable correlation with sediment-bound iron. In all three areas, the groundwater arsenic pollution seem to be of natural origin and caused by reductive dissolution of arsenic-bearing iron phases buried in aquifers. The population at risk of chronic arsenic poisoning is estimated to be 10 million in the Red River delta and 0.5-1 million in the Mekong delta. A subset of hair samples collected in Vietnam and Cambodia from residents drinking groundwater with arsenic levels >50 microg/L have a significantly higher arsenic content than control groups (<50 microg/L). Few cases of arsenic related health problems are recognized in the study areas compared to Bangladesh and West Bengal. This difference probably relates to arsenic contaminated tube-well water only being used substantially over the past 7 to 10 years in Vietnam and Cambodia. Because symptoms of chronic arsenic poisoning usually take more than 10 years to develop, the number of future arsenic related ailments in Cambodia and Vietnam is likely to increase. Early mitigation measures should be a high priority.     

Temporal variations in arsenic uptake by rice plants in Bangladesh: The role of iron plaque in paddy fields irrigated with groundwater

The transfer of arsenic to rice grains is a human health issue of growing relevance in regions of southern Asia where shallow groundwater used for irrigation of paddy fields is elevated in As. In the present study, As and Fe concentrations in soil water and in the roots of rice plants, primarily the Fe plaque surrounding the roots, were monitored during the 4-month growing season at two sites irrigated with groundwater containing ∼ 130 μg l^− 1 As and two control sites irrigated with water containing < 15 μg l^− 1 As. At both sites irrigated with contaminated water, As concentrations in soil water increased from < 10 μg l^− 1 to > 1000 μg l^− 1 during the first five weeks of the growth season and then gradually declined to < 10 μg l^− 1 during the last five weeks. At the two control sites, concentrations of As in soil water never exceeded 40 µg l^− 1. At both contaminated sites, the As content of roots and Fe plaque rose to 1000-1500 mg kg^− 1 towards the middle of the growth season. It then declined to ∼ 300 mg kg^− 1 towards the end, a level still well above As concentration of ∼ 100 mg kg^− 1 in roots and plaque measured throughout the growing season at the two control sites. These time series, combined with simple mass balance considerations, demonstrate that the formation of Fe plaque on the roots of rice plants by micro-aeration significantly limits the uptake of As by rice plants grown in paddy fields. Large variations in the As and Fe content of plant stems at two of the sites irrigated with contaminated water and one of the control sites were also recorded. The origin of these variations, particularly during the last month of the growth season, needs to be better understood because they are likely to influence the uptake of As in rice grains.     

A survey of arsenic in foodstuffs on sale in the United Kingdom and imported from Bangladesh

Arsenic is a highly toxic element and its presence in food composites is a matter of concern to the well being of both humans and animals. Arsenic-contaminated groundwater is often used in Bangladesh and West Bengal (India) to irrigate crops used for food and animal consumption, which could potentially lead to arsenic entering the human food chain. In this study, we used graphite furnace atomic absorption spectroscopy to determine the total arsenic concentrations in a range of foodstuffs, including vegetables, rice and fish, imported into the United Kingdom from Bangladesh. The mean and range of the total arsenic concentration in all the vegetables imported from Bangladesh were 54.5 and 5-540 microg/kg, respectively. The highest arsenic values found were for the skin of Arum tuber, 540 microg/kg, followed by Arum Stem, 168 microg/kg, and Amaranthus, 160 microg/kg. Among the other samples, freshwater fish contained total arsenic levels between 97 and 1318 microg/kg. The arsenic content of the vegetables from the UK was approximately 2- to 3-fold lower than those observed for the vegetables imported from Bangladesh. The levels of arsenic found in vegetables imported from Bangladesh in this study, in some cases, are similar to those previously recorded for vegetables grown in arsenic-affected areas of West Bengal, India, although lower than the levels reported in studies from Bangladesh. While the total arsenic content detected in our study in vegetables, imported from Bangladesh, is far less than the recommended maximum permitted level of arsenic, it does provide an additional source of arsenic in the diet. This raises the possibility that the level of arsenic intake by certain sectors of the UK population may be significantly higher then the general population and requires further investigations.     

Selenium level in the environment and the population of Zhoukoudian area, Beijing, China

The objective of this study was to detect the selenium level in the environment and the population of Zhoukoudian area, Beijing, and to discuss the influence of various factors on serum selenium level. The soil, drinking water, and foodstuff samples and venous blood samples of 401 individuals were obtained to determine the selenium level by gas chromatograph equipped with a (63)Ni electron capture detector (ECD). The selenium level was 0.210+/-0.013 microg/g in soil, 0.017 microg/L+/-0.002 in drinking water, 0.034+/-0.002 microg/g in rice, and 0.034+/-0.012 microg/g in wheat flour. This index showed that the Zhoukoudian area of Beijing was a moderate or marginal level selenium ecological landscape. The mean serum selenium level of the population was 75.01+/-28.35 microg/L, ranging between 35.2 and 160.4 microg/L. A total of 279 (69.6%) individuals exhibited serum selenium level below 80 microg/L, which is the lowest threshold for the activity of glutathione peroxidases (GPx) in vivo. A total of 35 (8.5%) individuals exhibited serum selenium level below 45 microg/L. It is widely recommended that below this value (45 microg/L) there is an increased risk of cardiovascular disease and cancer. Multiple linear regression analysis showed that serum selenium level was positively associated with body mass index (beta=0.137; P=0.011), serum total cholesterol TC (beta=0.785; P=0.000), however, negatively associated with systolic blood pressure (beta=-0.172; P=0.023), serum triglyceride (beta=-0.170; P=0.007), high density lipoprotein-cholesterol (beta=-0.121; P=0.027), and low high density lipoprotein-cholesterol (beta=-0.568; P=0.027).     

Fate and transport of copper-based crop protectants in plasticulture runoff and the impact of sedimentation as a best management practice

The fate and distribution of copper-based crop protectants, applied to plasticulture tomato fields to protect against disease, were investigated in a greenhouse-scale simulation of farming conditions in a coastal environment. Following rainfall, 99% of the applied copper was found to remain on the fields sorbed to the soil and plants; most of the soil-bound copper was found sorbed to the top 2.5 cm of soil between the plasticulture rows. Of the copper leaving the agricultural fields, 82% was found in the runoff with the majority, 74%. sorbed to the suspended solids. The remaining copper, 18%, leached through the soil and entered the groundwater with 10% in the dissolved phase and 8% sorbed to suspended solids. Although only 1% copper was found to leave the field, this was sufficient to cause high copper concentrations (average 2102+/-433 microg/L total copper and 189+/-139 microg/L dissolved copper) in the runoff. Copper concentrations in groundwater samples were also high (average 312+/-198 microg/L total copper and 216+/-99 microg/L dissolved copper). Sedimentation, a best management practice for reducing copper loadings. was found to reduce the total copper concentrations in runoff by 90% to a concentration of 245+/-127 microg/L; however, dissolved copper concentrations remained stable, averaging 139+/-55 microg/L. Total copper concentrations were significantly reduced by the effective removal of suspended solids with sorbed copper.     

Arsenic uptake and speciation in rice plants grown under greenhouse conditions with arsenic contaminated irrigation water

The accumulation of arsenic (As) by rice (Oryza sativa L.) is of great interest considering the dietary intake of rice is potentially a major As exposure pathway in countries where rice is irrigated with As contaminated groundwater. A small scale rice paddy experiment was conducted to evaluate the uptake of As by rice. Arsenic concentrations in rice tissue increased in the order grain相似文献   

Nonlinear association between soil lead and blood lead of children in metropolitan New Orleans, Louisiana: 2000-2005

Metropolitan New Orleans is unique because it has a universal blood lead (BL) screening dataset (n=55,551) from 2000-2005 spatially coupled with a soil lead (SL) dataset (n=5467) completed in 2000. We evaluated empirical associations between measurements of SL and BL exposure responses of children in New Orleans by stratifying the databases by Census Tracts and statistically analyzing them with permutation methods. A consistent curvilinear association occurred annually between SL and BL with robust significance (P-values<10(-23)). The mathematical model of the pooled BL datasets for 2000-2005 is: BL=2.038+0.172 x (SL)(0.5) (agreement (R) of 0.534, an r(2) of 0.528, and a P-value of 1.0 x 10(-211)) indicating that chance alone cannot explain the association. Below 100 mg/kg SL children's BL exposure response is steep (1.4 microg/dL per 100 mg/kg), while above 300 mg/kg SL the BL exposure response is gradual (0.32 microg/dL per 100 mg/kg). In 1995, the BL prevalence was 37%>or=10 microg/dL for the most vulnerable poor and predominantly African-American children. In the era of universal screening the prevalence of elevated BL is 11.8%>or=10 microg/dL for the general population of children. The SL map describes community variations of potential BL exposure. If health effects occur at BL>or=2 microg/dL, then 93.5% of the children in New Orleans are at risk. These results reinforce the proposal that prevention of childhood Pb exposure must include SL remediation as demonstrated by a New Orleans pilot project and a proactive Norwegian government program.     

Dynamics of arsenic in the mining sites of Pine Creek Geosyncline, Northern Australia

The transportation and fixation of arsenic (As) in soil and sediments from five mine sites within the Pine Creek Geosyncline, Northern Territory, were examined based on measurements of operationally-defined fractions of As in soils, sediment and evaporates. Arsenic was mainly retained in sediments in the form iron arsenate (Fe-As). In wetland systems, As was retained as Fe-As together with calcium arsenate (Ca-As) from alkaline groundwater and organic-bound As from detrital material. In retention ponds As was retained as Fe-As, Ca-As and residual As (Res-As) up to 1700 mg/kg. Sediment traps can retain As from alkaline and acidic source seepages. The retention of Res-As and other mineral particulates during erosional or controlled process water discharges was associated with high Fe-As and organic-bound As in sediment. Arsenic was retained as Fe-As, Ca-As and residual As in 100 year old tailings at Millar's Battery, Union Reefs mine nearby McKinlay River and the small copper mine lease MLN 95 adjacent Copperfield Creek nearby Pine Creek. Natural geo-mobilisation of As was observed in upstream sediments at Copperfield Creek (5-8 mg/kg), Mt. Bundey Creek (10-12 mg/kg), upstream Ryan's Creek (10-12 mg/kg) and downstream East branch Ryan's Creek (7 mg/kg). Erosion of As-containing mineralisation was observed in the McKinlay River upstream and downstream (23-26 mg/kg) and upstream Ryan's Creek boundary of the Goodall mine lease MLN 1049 (24-40 mg/kg). Overall, As was mainly retained in sediments in the form Fe-As. The concentration data for As were used to propose mechanisms of As dispersion and retention occurring at the various mine sites that can be utilised for future mine water management design to minimise As dispersion.     

Arsenic in tree rings at a highly contaminated site

Arsenic concentrations were measured in annual rings, pith, bark, and leaves of five tree species (four genera) from a site highly contaminated with As in Vineland, New Jersey, and two nearby uncontaminated areas. The highest As concentrations were found in bark (0.68+/-0.89 mg/kg, n=16) and leaves (1.9+/-1.8 mg/kg, n=4) from the contaminated area. Tree-ring As levels from the contaminated area (0.28+/-0.15 mg/kg, n=32) were low but still considerably higher than those from the control areas (0.06+/-0.06 mg/kg, n=30). There is a generally positive relationship between soil and tree-ring As levels. The overall low uptake of As by trees contrasts with that of P, a chemical analog for As(V) in aerated soils. Much higher P concentration in sapwood than in heartwood indicates that P is exported into more recently formed wood during the conversion from sapwood to heartwood; this again is drastically different than the behavior of As which is present in sapwood and heartwood at comparable levels. Variable sapwood As concentrations observed in detailed radial profiles of tree-ring chemistry of a pine and an oak from the contaminated site suggest that As is most likely transported among multiple rings within the sapwood. Therefore, tree species for which sapwood is thin (e.g., oak as in this study) should be preferred for reconstructing the history of contamination of a site. Due to the possibility of lateral translocation between growth rings, further studies are necessary to understand within-tree As transport and storage before dendrochemistry can be confidently accepted for such applications.     

Environmental assessment of mercury contamination from the Rwamagasa artisanal gold mining centre, Geita District, Tanzania

This study presents the results of an environmental assessment of mercury (Hg) contamination in the Rwamagasa artisanal gold mining area, northwest Tanzania, and the potential downstream dispersion along the River Malagarasi to Lake Tanganyika. At the time of sampling, generally low concentrations of Hg (<0.05 mg/kg) occurred in most cultivated soils although higher Hg (0.05-9.2 mg/kg) was recorded in urban soils and vegetable plot soils where these are impacted by Hg-contaminated water and sediment derived from mineral processing activities. Hg in vegetable and grain samples is mostly below the detection limit of 0.004 mg/kg Hg, apart from 0.007 and 0.092 mg/kg Hg in two yam samples and 0.011 to 0.013 mg/kg Hg in three rice samples. The standardized (i.e., standardized to 10 cm length) Hg concentrations in Clarias spp. increase from about 0.01 mg Hg/kg for the River Malagarasi delta to 0.07, 0.2, and 1.6 mg/kg, respectively, for the Rwamagasa 'background', moderately and most contaminated sites. For piscivorous (Lates, Brycinus, and Hydrocynus spp.), insectivorous (Barbus spp.), and planktivorous (Haplochromis spp.) fish species, the 10-cm standardized Hg concentrations increase from about 0.006 mg/kg for the River Malagarasi-Lake Tanganyika area to 0.5 and 3.5 mg/kg, respectively, for the Rwamagasa moderately and most contaminated sites. The low concentrations of Hg in fish from the Malagarasi River delta and Lake Tanganyika indicate that Hg contamination from the Rwamagasa area does not have a readily discernible impact on the biota of Lake Tanganyika. Many of the fish samples from Rwamagasa exceed guidelines for human consumption (0.5 mg/kg) as well as the WHO recommended limit for vulnerable groups (0.2 mg/kg). Tissue total Hg (THg) of all fish collected from the River Malagarasi-Lake Tanganyika subarea is well below these guidelines. Potential human exposure through consumption of 300 g/day of rice grown on Hg-contaminated soils is 5.5 microg/week. Consumption of 250 g Nile perch (Lates spp.), 500 g tilapia (Oreochromis spp.), and 250 g of catfish (Clarias spp.) each week would result in an intake of 65 microg Hg/week for people consuming only fish from the Mara and Mwanza regions of Lake Victoria and 116 microg Hg/week for people in the Rwamagasa area consuming tilapia and Nile perch from Lake Victoria and catfish from mining-impacted streams. This is lower than the Provisional Tolerable Weekly Intake (PTWI) of 300 microg for Hg in the diet set by the WHO and the FAO. Inadvertent ingestion of soil containing 9 mg Hg/kg at a rate of 80 mg/day would give an additional estimated weekly intake of 5 microg THg, whereas the persistent and purposeful consumption of soil (geophagia) at a rate of 26 g soil/day would produce an additional chemical exposure of 230 microg Hg/day.