Spatial variability of arsenic concentration in soils and plants, and its relationship with iron, manganese and phosphorus

Spatial distribution of arsenic (As) concentrations of irrigation water, soil and plant (rice) in a shallow tube-well (STW) command area (8 ha), and their relationship with Fe, Mn and P were studied. Arsenic concentrations of water in the 110 m long irrigation channel clearly decreased with distance from the STW point, the range being 68-136 μg L⁻¹. Such decreasing trend was also noticed with Fe and P concentrations, but the trend for Mn concentrations was not remarkable. Concerning soil As, the concentration showed a decreasing tendency with distance from the pump. The NH₄-oxalate extractable As contributed 36% of total As and this amount of As was associated with poorly crystalline Fe-oxides. Furthermore only 22% of total As was phosphate extractable so that most of the As was tightly retained by soil constituents and was not readily exchangeable by phosphate. Soil As (both total and extractable As) was significantly and positively correlated with rice grain As (0.296 ± 0.063 μg g⁻¹, n = 56). Next to drinking water, rice could be a potential source of As exposure of the people living in the As affected areas of Bangladesh.     

Inorganic arsenic and trace elements in Ghanaian grain staples

A total of 549 samples of rice, maize, wheat, sorghum and millet were obtained from markets in Ghana, the EU, US and Asia. Analysis of the samples, originating from 21 countries in 5 continents, helped to establish global mean trace element concentrations in grains; thus placing the Ghanaian data within a global context. Ghanaian rice was generally low in potentially toxic elements, but high in essential nutrient elements. Arsenic concentrations in rice from US (0.22 mg/kg) and Thailand (0.15 mg/kg) were higher than in Ghanaian rice (0.11 mg/kg). Percentage inorganic arsenic content of the latter (83%) was, however, higher than for US (42%) and Thai rice (67%). Total arsenic concentration in Ghanaian maize, sorghum and millet samples (0.01 mg/kg) was an order of magnitude lower than in Ghanaian rice, indicating that a shift from rice-centric to multigrain diets could help reduce health risks posed by dietary exposure to inorganic As.     

Arsenic accumulation and phosphorus status in two rice (Oryza sativa L.) cultivars surveyed from fields in South China

The consumption of paddy rice (Oryza sativa L.) is a major inorganic arsenic exposure pathway in S.E. Asia. A multi-location survey was undertaken in Guangdong Province, South China to assess arsenic accumulation and speciation in 2 rice cultivars, one an Indica and the other a hybrid Indica. The results showed that arsenic concentrations in rice tissue increased in the order grain < husk < straw < root. Rice grain arsenic content of 2 rice cultivars was significant different and correlated with phosphorus concentration and molar ratio of P/As in shoot, being higher for the Indica cultivar than for the hybrid Indica, which suggests altering shoot phosphorus status as a promising route for breeding rice cultivars with reduced grain arsenic. Speciation of grain arsenic, performed using HPLC-ICP-MS, identified inorganic arsenic as the dominant arsenic species present in the rice grain.     

Arsenic Background Concentrations in Florida,U.S.A. Surface Soils: Determination and Interpretation

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO₃-HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n = 267) compared to 7.63 mg As/kg for disturbed soils (n = 181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were generally higher in south Florida than in north and central Florida, and associated with wet soils. Individual high arsenic sites were scattered throughout the state, but the most highly concentrated of these occurred in the Leon-Lee belt along the Ocala uplift district extending to the southwestern flatwoods district. Extrapolation of the data using a single arsenic value regardless of the taxonomic and geographical differences in soil arsenic distribution would underestimate potential arsenic contamination in upland soils.     

Relationship of urinary arsenic metabolites to intake estimates in residents of the Red River Delta, Vietnam

This study investigated the status of arsenic (As) exposure from groundwater and rice, and its methylation capacity in residents from the Red River Delta, Vietnam. Arsenic levels in groundwater ranged from <1.8 to 486 μg/L. Remarkably, 86% of groundwater samples exceeded WHO drinking water guideline of 10 μg/L. Also, estimated inorganic As intake from groundwater and rice were over Provisional Tolerable Weekly Intake (15 μg/week/kg body wt.) by FAO/WHO for 92% of the residents examined. Inorganic As and its metabolite (monomethylarsonic acid and dimethylarsinic acid) concentrations in human urine were positively correlated with estimated inorganic As intake. These results suggest that residents in these areas are exposed to As through consumption of groundwater and rice, and potential health risk of As is of great concern for these people. Urinary concentration ratios of dimethylarsinic acid to monomethylarsonic acid in children were higher than those in adults, especially among men, indicating greater As methylation capacity in children.     

Assessment of arsenic content in soil,rice grains and groundwater and associated health risks in human population from Ropar wetland,India, and its vicinity

In the present study, potential health risks posed to human population from Ropar wetland and its vicinity, by consumption of inorganic arsenic (i-As) via arsenic contaminated rice grains and groundwater, were assessed. Total arsenic (t-As) in soil and rice grains were found in the range of 0.06–0.11 mg/kg and 0.03–0.33 mg/kg, respectively, on dry weight basis. Total arsenic in groundwater was in the range of 2.31–15.91 μg/L. i-As was calculated from t-As using relevant conversion factors. Rice plants were found to be arsenic accumulators as bioconcentration factor (BCF) was observed to be >1 in 75% of rice grain samples. Further, correlation analysis revealed that arsenic accumulation in rice grains decreased with increase in the electrical conductivity of soil. One-way ANOVA, cluster analysis and principal component analysis indicated that both geogenic and anthropogenic sources affected t-As in soil and groundwater. Hazard index and total cancer risk estimated for individuals from the study area were above the USEPA limits of 1.00 and 1.00 × 10^?6, respectively. Kruskal-Wallis H test indicated that groundwater intake posed significantly higher health risk than rice grain consumption (χ ²(1) = 17.280, p = 0.00003).     

Effect of arsenic on photosynthesis, growth and yield of five widely cultivated rice (Oryza sativa L.) varieties in Bangladesh

A glass house experiment was conducted to investigate the effect of soil arsenic on photosynthetic pigments, chlorophyll-a and -b, and their correlations with rice yield and growth. The experiment was designed with three replications of six arsenic treatments viz. control, 10, 20, 30, 60, 90 mg of As kg(-1) soil. Arsenic concentration in initial soil, to which the above mentioned concentrations of arsenic were added, was 6.44+/-0.24 mg kg(-1). Both chlorophyll-a and -b contents in rice leaf decreased significantly (p<0.05) with the increase of soil arsenic concentrations. No rice plant survived up to maturity stage in soil treated with 60 and 90 mg of As kg(-1). The highest chlorophyll-a and -b contents were observed in control treatment (2.62+/-0.24 and 2.07+/-0.14 mg g(-1) were the average values of chlorophyll-a and -b, respectively of the five rice varieties) while 1.50+/-0.20 and 1.04+/-0.08 mg g(-1) (average of five rice varieties) of chlorophyll-a and -b, respectively were the lowest. The content of photosynthetic pigments in these five rice varieties did not differ significantly (p>0.05) from each other in control treatment though they differed significantly (p<0.05) from each other in 30 mg of As kg(-1) soil treatment. Among the five rice varieties, chlorophyll content in BRRI dhan 35 was found to be mostly affected with the increase of soil arsenic concentration while BRRI hybrid dhan 1 was least affected. Well correlations were observed between chlorophyll content and rice growth and yield suggesting that arsenic toxicity affects the photosynthesis which ultimately results in the reduction of rice growth and yield.     

Accumulation of arsenic in tissues of rice plant (Oryza sativa L.) and its distribution in fractions of rice grain

A study was conducted to investigate the accumulation and distribution of arsenic in different fractions of rice grain (Oryza sativa L.) collected from arsenic affected area of Bangladesh. The agricultural soil of study area has become highly contaminated with arsenic due to the excessive use of arsenic-rich underground water (0.070+/-0.006 mg l(-1), n=6) for irrigation. Arsenic content in tissues of rice plant and in fractions of rice grain of two widely cultivated rice varieties, namely BRRI dhan28 and BRRI hybrid dhan1, were determined. Regardless of rice varieties, arsenic content was about 28- and 75-folds higher in root than that of shoot and raw rice grain, respectively. In fractions of parboiled and non-parboiled rice grain of both varieties, the order of arsenic concentrations was; rice hull>bran-polish>brown rice>raw rice>polish rice. Arsenic content was higher in non-parboiled rice grain than that of parboiled rice. Arsenic concentrations in parboiled and non-parboiled brown rice of BRRI dhan28 were 0.8+/-0.1 and 0.5+/-0.0 mg kg(-1) dry weight, respectively while those of BRRI hybrid dhan1 were 0.8+/-0.2 and 0.6+/-0.2 mg kg(-1) dry weight, respectively. However, parboiled and non-parboiled polish rice grain of BRRI dhan28 contained 0.4+/-0.0 and 0.3+/-0.1 mg kg(-1) dry weight of arsenic, respectively while those of BRRI hybrid dhan1 contained 0.43+/-0.01 and 0.5+/-0.0 mg kg(-1) dry weight, respectively. Both polish and brown rice are readily cooked for human consumption. The concentration of arsenic found in the present study is much lower than the permissible limit in rice (1.0 mg kg(-1)) according to WHO recommendation. Thus, rice grown in soils of Bangladesh contaminated with arsenic of 14.5+/-0.1 mg kg(-1) could be considered safe for human consumption.     

Variation of As concentration between soil types and rice genotypes and the selection of cultivars for reducing As in the diet

Human exposure to toxic heavy metals via the food chain is of increasing concern. In the present study, the effects of soil type and genotype on variation in arsenic (As) concentrations of different organs were investigated by using nine rice cultivars grown in two soils, with two levels of As contamination. There were significant genotypic differences (P < 0.05) in As concentrations of all organs, and As concentrations of polished grain were significantly affected by genotype and soil type. The As concentration in polished grain was higher in red paddy soil under As treatment, with range from 0.24 to 1.03 mg kg⁻¹, and the As concentration of three cultivars exceeded the concentration of Chinese Food Hygiene Standard (0.7 mg kg⁻¹). The As concentrations in stems, leaves and polished grain were all significantly and positively correlated. The As concentrations in polished grain were positively and significantly (P < 0.01) correlated with As root-grain translocation factor. The results indicated that As concentration in grain was partially governed by As uptake and the transfer of As from root to grain. The grain As concentration of the nine cultivars was significantly correlated between the two soil types at different levels of As contamination. Some genotypes, such as japonica rice (e.g. Ning jing 1 and Nan jing 32) had consistently low grain As concentrations. The results suggest the possibility of breeding the As rice cultivars to produce grain for safe consumption from soils with slight and moderate levels of As.     

The dynamics of arsenic in four paddy fields in the Bengal delta

Irrigation with arsenic contaminated groundwater in the Bengal Delta may lead to As accumulation in the soil and rice grain. The dynamics of As concentration and speciation in paddy fields during dry season (boro) rice cultivation were investigated at 4 sites in Bangladesh and West Bengal, India. Three sites which were irrigated with high As groundwater had elevated As concentrations in the soils, showing a significant gradient from the irrigation inlet across the field. Arsenic concentration and speciation in soil pore water varied temporally and spatially; higher As concentrations were associated with an increasing percentage of arsenite, indicating a reductive mobilization. Concentrations of As in rice grain varied by 2-7 fold within individual fields and were poorly related with the soil As concentration. A field site employing alternating flooded-dry irrigation produced the lowest range of grain As concentration, suggesting a lower soil As availability caused by periodic aerobic conditions.     

Bioaccessibility of arsenic in various types of rice in an in vitro gastrointestinal fluid system

Rice can be a major contributor to dietary arsenic exposure because of the relatively high total arsenic concentration compared to other grains, especially for people whose main staple is rice. This study employed in vitro gastrointestinal fluid digestion to determine bioaccessible or gastrointestinal fluid extractable arsenic concentration in rice. Thirty-one rice samples, of which 60 % were grown in the United States, were purchased from food stores in New York City. Total arsenic concentrations in these samples ranged from 0.090 ± 0.004 to 0.85 ± 0.03 mg/kg with a mean value of 0.275 ± 0.161 mg/kg (n = 31). Rice samples with relatively high total arsenic (>0.20 mg/kg, n = 18) were treated by in vitro artificial gastrointestinal fluid digestion, and the extractable arsenic ranged from 53 % to 102 %. The bioaccessibility of arsenic in rice decreases in the general order of extra long grain, long grain, long grain parboiled, to brown rices.     

Can arbuscular mycorrhizal fungi improve grain yield, As uptake and tolerance of rice grown under aerobic conditions?

The effects of arbuscular mycorrhizal fungi (AMF) - Glomus intraradices and G. geosporum on arsenic (As) and phosphorus (P) uptake by lowland (Guangyinzhan) and upland rice (Handao 502) were investigated in soil, spiked with and without 60 mg As kg⁻¹. In As-contaminated soil, Guangyinzhan inoculated with G. intraradices or Handao 502 inoculated with G. geosporum enhanced As tolerance, grain P content, grain yield. However, Guangyinzhan inoculated with G. geosporum or Handao 502 inoculated with G. intraradices decreased grain P content, grain yield and the molar ratio of grain P/As content, and increased the As concentration and the ratio of grain/straw As concentration. These results show that rice/AMF combinations had significant (p < 0.05) effects on grain As concentration, grain yield and grain P uptake. The variation in the transfer and uptake of As and P reflected strong functional diversity in AM (arbuscular mycorrhizal) symbioses.     

Phytoremediation of arsenic contaminated paddy soils with Pteris vittata markedly reduces arsenic uptake by rice

Arsenic (As) accumulation in food crops such as rice is of major concern. To investigate whether phytoremediation can reduce As uptake by rice, the As hyperaccumulator Pteris vittata was grown in five contaminated paddy soils in a pot experiment. Over a 9-month period P. vittata removed 3.5-11.4% of the total soil As, and decreased phosphate-extractable As and soil pore water As by 11-38% and 18-77%, respectively. Rice grown following P. vittata had significantly lower As concentrations in straw and grain, being 17-82% and 22-58% of those in the control, respectively. Phytoremediation also resulted in significant changes in As speciation in rice grain by greatly decreasing the concentration of dimethylarsinic acid (DMA). In two soils the concentration of inorganic As in rice grain was decreased by 50-58%. The results demonstrate an effective stripping of bioavailable As from contaminated paddy soils thus reducing As uptake by rice.     

Inorganic arsenic levels in baby rice are of concern

Inorganic arsenic is a chronic exposure carcinogen. Analysis of UK baby rice revealed a median inorganic arsenic content (n = 17) of 0.11 mg/kg. By plotting inorganic arsenic against total arsenic, it was found that inorganic concentrations increased linearly up to 0.25 mg/kg total arsenic, then plateaued at 0.16 mg/kg at higher total arsenic concentrations. Inorganic arsenic intake by babies (4-12 months) was considered with respect to current dietary ingestion regulations. It was found that 35% of the baby rice samples analysed would be illegal for sale in China which has regulatory limit of 0.15 mg/kg inorganic arsenic. EU and US food regulations on arsenic are non-existent. When baby inorganic arsenic intake from rice was considered, median consumption (expressed as μg/kg/d) was higher than drinking water maximum exposures predicted for adults in these regions when water intake was expressed on a bodyweight basis.     

Bioaccessibility of arsenic in various types of rice in an in vitro gastrointestinal fluid system

Rice can be a major contributor to dietary arsenic exposure because of the relatively high total arsenic concentration compared to other grains, especially for people whose main staple is rice. This study employed in vitro gastrointestinal fluid digestion to determine bioaccessible or gastrointestinal fluid extractable arsenic concentration in rice. Thirty-one rice samples, of which 60 % were grown in the United States, were purchased from food stores in New York City. Total arsenic concentrations in these samples ranged from 0.090 ± 0.004 to 0.85 ± 0.03 mg/kg with a mean value of 0.275 ± 0.161 mg/kg (n = 31). Rice samples with relatively high total arsenic (>0.20 mg/kg, n = 18) were treated by in vitro artificial gastrointestinal fluid digestion, and the extractable arsenic ranged from 53 % to 102 %. The bioaccessibility of arsenic in rice decreases in the general order of extra long grain, long grain, long grain parboiled, to brown rices.     

Arsenic contamination and potential health risk implications at an abandoned tungsten mine, southern China

In an extensive environmental study, field samples, including soil, water, rice, vegetable, fish, human hair and urine, were collected at an abandoned tungsten mine in Shantou City, southern China. Results showed that arsenic (As) concentration in agricultural soils ranged from 3.5 to 935 mg kg⁻¹ with the mean value of 129 mg kg⁻¹. In addition, As concentration reached up to 325 μg L⁻¹ in the groundwater, and the maximum As concentration in local food were 1.09, 2.38 and 0.60 mg kg⁻¹ for brown rice, vegetable and fish samples, respectively, suggesting the local water resource and food have been severely contaminated with As. Health impact monitoring data revealed that As concentrations in hair and urine samples were up to 2.92 mg kg⁻¹ and 164 μg L⁻¹, respectively, indicating a potential health risk among the local residents. Effective measurements should be implemented to protect the local community from the As contamination in the environment.     

A simple inexpensive gas phase chemiluminescence analyzer for measuring trace levels of arsenic in drinking water

An inexpensive sensitive gas-phase chemiluminescence (GPCL) based analyzer for arsenic is described; this device utilizes manual fluid dispensing operations to reduce size, weight and cost. The analyzer in its present form has a limit of detection (LOD, S/N = 3) of 1.0 μg/L total inorganic As (peak heightbased, 3 mL sample). The system was used to measure low level arsenic in tap water samples from Texas and New Mexico and compared with results obtained by inductively coupled plasma-mass spectrometry (ICP-MS) as well as those from an automated GPCL analyzer. Good correlations were observed. Higher levels of As (50-500 μg/L, As(III), As(V) and mixtures thereof) were spiked into local tap water; the recoveries ranged from 95 ± 2% to 101 ± 1%. A single instrument weighs less than 3 kg, consumes <25 W in power, can be incorporated in a briefcase and constructed for <$US $1000. It is easily usable in the field.     

Effects of As levels on radial oxygen loss and As speciation in rice

Greenhouse experiment was conducted to examine effects of arsenic (As) on iron plaque formation, radial oxygen loss, As accumulation, and speciation in rice. Three genotypes were grown in soil with three different concentrations of As. The stress of As caused a slight increase of iron plaque formation (P?>?0.05) and a decrease in the rates of radial oxygen loss (ROL; P?<?0.01). The results of As speciation showed that the percentages of DMA increased from 19–28 % to 53–58 %, while the percentages of inorganic As decreased from 53–58 % to 36–42 % with the increasing soil As concentrations, indicating a strong environmental influence on As species in rice grain. The present study showed that elevated soil As may induce As toxicity towards rice plants, leading to the decrease of ROL; environmental factors could influence As methylation or As species transportation. Our study provided useful information on As tolerance and accumulation in rice which may contribute to reducing the health risk posed by As contamination in rice.     

Quaternary stratigraphy, sediment characteristics and geochemistry of arsenic-contaminated alluvial aquifers in the Ganges–Brahmaputra floodplain in central Bangladesh

This study focuses on the Quaternary stratigraphy, sediment composition, mineralogy, and geochemistry of arsenic (As)-contaminated alluvial aquifers in the Ganges–Brahmaputra floodplain in the central Bangladesh. Arsenic concentrations in 85 tubewells in Manikganj area, 70 km northwest of Dhaka City, range from 0.25 µg/L to 191 µg/L with a mean concentration of 33 µg/L. Groundwater is mainly Ca–HCO₃ type with high concentrations of dissolved As, Fe, and Mn, but low level of SO₄. The uppermost aquifer occurs between 10 m and 80 m below the surface that has a mean arsenic concentration of 35 µg/L. Deeper aquifer (> 100 m depth) has a mean arsenic concentration of 18 µg/L. Sediments in the upper aquifer are mostly gray to dark-gray, whereas sediments in the deep aquifer are mostly yellowing-gray to brown. Quartz, feldspar, mica, hornblende, garnet, kyanite, tourmaline, magnetite, ilmenite are the major minerals in sediments from both aquifers. Biotite and potassium feldspar are dominant in shallow aquifer, although plagioclase feldspar and garnet are abundant in deep aquifer sediments. Sediment composition suggests a mixed provenance with sediment supplies from both orogenic belts and cratons. High arsenic concentrations in sediments are found within the upper 50 m in drilled core samples. Statistical analysis shows that As, Fe, Mn, Ca, and P are strongly correlated in sediments. Concentrations of Cd, Cu, Ni, Zn, and Bi also show strong correlations with arsenic in the Manikganj sediment cores. Authigenic goethite concretions, possibly formed by bacteria, are found in the shallow sediments, which contain arsenic of a concentration as high as 8.8 mg/kg. High arsenic concentrations in aquifers are associated with fine-grained sediments that were derived mostly from the recycled orogens and relatively rapidly deposited mainly by meandering channels during the Early to Middle Holocene rising sea-level conditions.     

Comparative effects on arsenic uptake between iron (hydro)oxides on root surface and rhizosphere of rice in an alkaline paddy soil

The iron (Fe) (hydro)oxides deposited around rice roots play an important role in arsenic (As) sequestration in paddy soils, but there is no systematic study on the relative importance of Fe (hydro)oxides on root surface and in rhizosphere soil in limiting As bioavailability. Twenty-seven rice genotypes were selected to investigate effects of Fe (hydro)oxides on As uptake by rice in an alkaline paddy soil. Results indicated that the As content was positively correlated with the Fe content on root surface, and most of As (88–97%) was sequestered by poorly crystalline and crystalline Fe (hydro)oxides in the alkaline paddy soil. The As sequestration by Fe (hydro)oxides on root surface (IAS_root 16.8–25.0 mg As/(g Fe)) was much higher than that in rhizosphere (IAS_rhizo 1.4–2.0 mg As/(g Fe)); therefore, in terms of As immobilization, the Fe (hydro)oxides on root surface were more important than that in rhizosphere. However, the As content in brown rice did not have significant correlation with the As content on root surface but was significantly correlated (R²?=?0.43, P?<?0.05) with the partition ratio (PR_As?=?IAS_root/IAS_rhizo) of As sequestration on root surface and in rhizosphere, which suggested that Fe (hydro)oxides on root surface did not play the controlling role in lowering As uptake, and the partition ratio PR_As would be a better indicator to evaluate effects of Fe (hydro)oxides around roots on As uptake by rice.