Arsenic limits Trace Mineral Nutrition (Selenium, Zinc, and Nickel) in Bangladesh Rice Grain

A reconnaissance of 23 paddy fields, from three Bangladesh districts, encompassing a total of 230 soil and rice plant samples was conducted to identify the extent to which trace element characteristics in soils and irrigation waters are reflected by the harvested rice crop. Field sites were located on two soil physiographic units with distinctly different As soil baseline and groundwater concentrations. For arsenic (As), both straw and grain trends closely fitted patterns observed for the soils and water. Grain concentration characteristics for selenium (Se), zinc (Zn), and nickel (Ni), however, were markedly different. Regressions of shoot and grain As against grain Se, Zn, and Ni were highly significant (P <0.001), exhibiting a pronounced decline in grain trace-nutrient quality with increasing As content. To validate this further, a pot experiment cultivar screening trial, involving commonly cultivated high yielding variety (HYV) rice grown alongside two U.S. rice varieties characterized as being As tolerant and susceptible, was conducted on an As-amended uniform soil. Findings from the trial confirmed that As perturbed grain metal(loid) balances, resulting in severe yield reductions in addition to constraining the levels of Se, Zn, and Ni in the grain.

Identification of low inorganic and total grain arsenic rice cultivars from Bangladesh

For the world's population, rice consumption is a major source of inorganic arsenic (As), a nonthreshold class 1 carcinogen. Reducing the amount of total and inorganic As within the rice grain would reduce the exposure risk. In this study, grain As was measured in 76 cultivars consisting of Bangladeshi landraces, improved Bangladesh Rice Research Institute (BRRI) cultivars, and parents of permanent mapping populations grown in two field sites in Bangladesh, Faridpur and Sonargaon, irrigated with As-contaminated tubewell water. Grain As ranged from 0.16 to 0.74 mg kg(-1) at Faridpur and from 0.07 to 0.28 mg kg(-1) at Sonargaon. Highly significant cultivar differences were detected and a significant correlation (r = 0.802) in the grain As between the two field sites was observed, indicating stable genetic differences in As accumulation. The cultivars with the highest concentration of grain As were the Bangladeshi landraces. Landraces with red bran had significantly more grain As than the cultivars with brown bran. The percent of inorganic As decreased linearly with increasing total As, but genetic variation within this trend was identified. A number of local cultivars with low grain As were identified. Some tropical japonica cultivars with low grain As have the potential to be used in breeding programs and genetic studies aiming to identify genes which decrease grain As.

Baseline Soil Variation Is a Major Factor in Arsenic Accumulation in Bengal Delta Paddy Rice

Factors responsible for paddy soil arsenic accumulation in the tubewell irrigated systems of the Bengal Delta were investigated. Baseline (i.e., nonirrigated) and paddy soils were collected from 30 field systems across Bangladesh. For each field, soil sampled at dry season (Boro) harvest i.e., the crop cycle irrigated with tubewell water, was collected along a 90 m transect away from the tubewell irrigation source. Baseline soil arsenic levels ranged from 0.8 to 21. mg/kg, with lower values found on the Pliestocene Terrace around Gazipur (average, 1.6 +/- 0.2 mg/kg), and higher levels found in Holecene sediment tracts of Jessore and Faridpur (average, 6.6 +/- 1.0 mg/kg). Two independent approaches were used to assess the extent of arsenic build-up in irrigated paddy soils. First, arsenic build-up in paddy soil at the end of dry season production (irrigated - baseline soil arsenic) was regressed against number of years irrigated and tubewell arsenic concentration. Years of irrigation was not significant (P 0.711), indicating no year-on-year arsenic build-up, whereas tubewell As concentration was significant (P = 0.008). The second approach was analysis of irrigated soils for 20 fields over 2 successive years. For nine of the fields there was a significant (P <0.05) decrease in soil arsenic from year 1 to 2, one field had a significant increase, whereas there was no change for the remaining 10. Over the dry season irrigation cycle, soil arsenic built-up in soils at a rate dependent on irrigation tubewell water, 35* (tubewell water concentration in mg/kg, mg/L). Grain arsenic rises steeply at low soil/shoot arsenic levels, plateauing out at concentratations. Baseline soil arsenic at Faridpur sites corresponded to grain arsenic levels at the start of this saturation phase. Therefore, variation in baseline levels of soil arsenic leads to a large range in grain arsenic. Where sites have high baseline soil arsenic, further additional arsenic from irrigation water only leads to a gradual increase in grain arsenic concentration.

Occurrence and Partitioning of Cadmium, Arsenic and Lead in Mine Impacted Paddy Rice: Hunan, China

Paddy rice has been likened to nictiana sp in its ability to scavenge cadmium (Cd) from soil, whereas arsenic (As) accumulation is commonly an order of magnitude higher than in other cereal crops. In areas such as those found in parts of Hunan province in south central China, base-metal mining activities and rice farming coexist. Therefore there is a considerable likelihood that lead (Pb), in addition to Cd and As, will accumulate in rice grown in parts of this region above levels suitable for human consumption. To test this hypothesis, a widespread provincial survey of rice from mine spoilt paddies (n = 100), in addition to a follow-up market grain survey (n = 122) conducted in mine impacted areas was undertaken to determine the safety of local rice supply networks. Furthermore, a specific Cd, As, and Pb biogeochemical survey of paddy soil and rice was conducted within southern China, targeting sites impacted by mining of varying intensities to calibrate rice metal(loid) transfer models and transfer factors that can be used to predict tissue loading. Results revealed a number of highly significant correlations between shoot, husk, bran, and endosperm rice tissue fractions and that rice from mining areas was enriched in Cd, As, and Pb. Sixty-five, 50, and 34% of all the mine-impacted field rice was predicted to fail national food standards for Cd, As, and Pb, respectively. Although, not as elevated as the grains from the mine-impacted field survey, it was demonstrated that metal(loid) tainted rice was entering food supply chains intended for direct human consumption.

Enhanced transfer of arsenic to grain for Bangladesh grown rice compared to US and EU

A field survey was conducted in arsenic impacted and non-impacted paddies of Bangladesh to assess how arsenic levels in rice (Oryza sativa L) grain are related to soil and shoot concentrations. Ten field sites from an arsenic contaminated tubewell irrigation region (Faridpur) were compared to 10 field sites from a non-affected region (Gazipur). Analysis of the overall data set found that both grain and shoot total arsenic concentrations were highly correlated (P

High Percentage Inorganic Arsenic Content of Mining Impacted and Nonimpacted Chinese Rice

Two approaches were undertaken to characterize the arsenic (As) content of Chinese rice. First, a national market basket survey (n = 240) was conducted in provincial capitals, sourcing grain from China's premier rice production areas. Second, to reflect rural diets, paddy rice (n = 195) directly from farmers fields were collected from three regions in Hunan, a key rice producing province located in southern China. Two of the sites were within mining and smeltery districts, and the third was devoid of large-scale metal processing industries. Arsenic levels were determined in all the samples while a subset (n = 33) were characterized for As species, using a new simple and rapid extraction method suitable for use with Hamilton PRP-X100 anion exchange columns and HPLC-ICP-MS. The vast majority (85%) of the market rice grains possessed total As levels <150 ng g(-1). The rice collected from mine-impacted regions, however, were found to be highly enriched in As, reaching concentrations of up to 624 ng g(-1). Inorganic As (As(i)) was the predominant species detected in all of the speciated grain, with As(i) levels in some samples exceeding 300 ng g(-1). The As(i) concentration in polished and unpolished Chinese rice was successfully predicted from total As levels. The mean baseline concentrations for As(i) in Chinese market rice based on this survey were estimated to be 96 ng g(-1) while levels in mine-impacted areas were higher with ca. 50% of the rice in one region predicted to fail the national standard.

Diclofenac residues in carcasses of domestic ungulates available to vultures in India

Gyps vulture populations across the Indian subcontinent are declining rapidly and evidence indicates that veterinary use of the non-steroidal anti-inflammatory drug (NSAID) diclofenac is the major cause. Exposure of vultures to diclofenac is likely to arise from the consumption of livestock carcasses that have been treated shortly before death, however, detailed information regarding the prevalence and residual levels of diclofenac in carcasses available to vultures in India remains unreported. Here, we present data on diclofenac residues in 1848 liver samples taken from carcasses of dead livestock sampled at 67 sites in 12 states within India, between May 2004 and July 2005. Diclofenac residues were detected in carcasses in all states except Orisa, where only one site was sampled. The overall prevalence of detectable diclofenac (>10 microg kg(-1)) across all states was 10.1% and varied significantly among states, with up to 22.3% prevalence determined in Bihar. The geometric mean concentration of diclofenac found in samples in which the drug was detected was 352 microg kg(-1). The prevalence of carcasses containing diclofenac is similar to that previously proposed to be required to have caused the observed Gyps vulture declines in India. On the 11th of May 2006, the Drug Controller General (India) ordered the withdrawal of all licenses granted for the manufacture of diclofenac for veterinary use within India. However, if Gyps vultures are to be protected, potentially substantial existing stocks now need to be quickly and effectively removed from the Indian veterinary market.

Codeposition of organic carbon and arsenic in Bengal Delta aquifers

We present data showing that arsenic (As) was codeposited with organic carbon (OC) in Bengal Delta sediments as As and OC concentrations are highly (p <0.001) positively correlated in core profiles collected from widely dispersed geographical sites with different sedimentary depositional histories. Analysis of modern day depositional environments revealed that the As-OC correlations observed in cores are due to As retention and high OC inputs in vegetated zones of the deltaic environment. We hypothesize that elevated concentrations of As occur in vegetated wetland sediments due to concentration and retention of arsenate in aerated root zones and animal burrows where copious iron(III) oxides are deposited. On burial of the sediment, degradation of organic carbon from plant and animal biomass detritus provides the reducing conditions to dissolve iron(III) oxides and release arsenite into the porewater. As tubewell abstracted aquifer water is an invaluable resource on which much of Southeast Asia is now dependent, this increased understanding of the processes responsible for As buildup and release will identify, through knowledge of the palaeosedimentary environment, which sediments are at most risk of having high arsenic concentrations in porewater. Our data allow the development of a new unifying hypothesis of how As is mobilized into groundwaters in river flood plains and deltas of Southeast Asia, namely that in these highly biologically productive environments, As and OC are codeposited, and the codeposited OC drives As release from the sediments.

The legacy of past manuring practices on soil contamination in remote rural areas

This paper demonstrates that there can be a legacy of contamination on former arable land in remote rural areas as a result of past manuring practices. In the first part of the study four farms abandoned in the late 19th to mid-20th century were investigated with samples collected from residual material in domestic hearths, the midden heaps, kailyards (walled garden for vegetables), infields (intensively managed arable land) and outfields (less intensively managed land for cropping or grazing). Consistent sequences in concentration values were found for such elements as Pb, Zn, Cu and P in the order hearth>midden>kailyard>infield>outfield. Such patterns can in part be explained in terms of atmospheric deposition on peat and turf which were subsequently burnt in hearths to result in enhanced elemental concentrations. The ash then was deposited in midden heaps and subsequently on kailyards or infields. In the second part, microanalytical results from St. Kilda are discussed. Enhanced loadings of Pb and Zn were found in the old arable land. The highest levels of Zn were found in small fragments of carbonised and humified material and bone fragments; in contrast Pb tended to be more uniformly distributed. Seabird waste was extensively applied to the arable land and some of the Zn may have accumulated in the soil by this pathway. The retention of Zn in bone is likely to have been very minor given the rarity of bone fragments as evident in thin sections (0.3%); this compares with 6.8% for black carbonised particles which are likely to provide the main storage sites for Zn.

The distribution of arsenic in the body tissues of wood mice and bank voles

Arsenic is accumulated by free-living small mammals, but there is little information on the resultant concentrations in different tissues other than liver and kidney. Such information is important because the severity of toxicological effects may be related to the amount of arsenic accumulated in specific organs, and the availability of arsenic to predators is, in part, dependent on which tissues accumulate arsenic. The objective of this study was to quantify the arsenic concentrations and the percentage of the total body burden (%TBB) accumulated in different body tissues of free-living small mammals and to determine how these factors varied with severity of habitat contamination. Arsenic concentrations were measured in various tissues of wood mice (Apodemus sylvaticus) and bank voles (Clethrionomys glareolus) from a range of arsenic-contaminated sites in southwest Britain. Arsenic concentrations in the gastrointestinal (GI) tract (including contents), liver, kidneys, spleen, lung, femur, and fur of both species varied significantly between sites and were higher in mice and voles from heavily contaminated areas. Heart and brain arsenic concentrations did not vary with degree of environmental contamination. The GI tract and excised carcass contained roughly equal amounts of arsenic and, in sum, comprised 75-85% of the TBB on uncontaminated sites and 90-99% on contaminated sites. Although the excised carcass contains about half of the TBB, its importance in food-chain transfer of arsenic to predators may depend on the bioavailability of arsenic sequestered in fur. In contrast, the GI tract and its contents, provided that it is consumed, will always be a major transfer pathway for arsenic to predators, regardless of the severity of habitat contamination.

Polycyclic aromatic hydrocarbon (PAH) dispersion and deposition to vegetation and soil following a large scale chemical fire

Polycyclic aromatic hydrocarbons (PAHs) were determined in soil and vegetation following a large scale chemical fire involving 10,000 ton of polypropylene. In comparison with sites outside the plume from the fire, PAH concentrations were elevated in grass shoots (by up to 70-fold) and in soil (by up to 370-fold). The pattern of PAH dispersion under the plume was dependent on the physical-chemical properties of individual PAHs. The lighter, least hydrophobic PAHs were dispersed into the environment at greater distances than heavier, more hydrophobic PAHs. At the most distant sampling point (4.5 km) under the plume, the low molecular weight PAHs were still considerably elevated in vegetation samples compared to control sites. Dispersion appeared to be regulated by the compounds partitioning between the vapour and particulate phase, with dry particulate deposition occurring closer to the fire source than gaseous deposition. For all PAHs, the fire resulted in greater contamination of soils compared to grasses, with the relative ratio of plant/soil contamination decreasing as hydrophobicity increased.

The mechanistic basis of interactions between mycorrhizal associations and toxic metal cations

Mycorrhizal associations, including ericoid, arbuscular and ecto-mycorrhizas, are found colonising highly metal contaminated soils. How do mycorrhizal fungi achieve metal resistance, and does this metal resistance confer enhanced metal resistance to plant symbionts? These are the questions explored in this review by considering the mechanistic basis of mycorrhizal adaptation to metal cations. Recent molecular and physiological studies are discussed. The review reappraises what constitutes metal resistance in the context of mycorrhizal associations and sets out the constitutive and adaptive mechanisms available for mycorrhizas to adapt to contaminated sites. The only direct evidence of mycorrhizal adaptation to metal cation pollutants is the exudation of organic acids to alter pollutant availability in the rhizosphere. This is not to say that other mechanism of adaptation do not exist, but conclusive evidence of adaptive mechanisms of tolerance are lacking. For constitutive mechanisms of resistance, there is much more evidence, and mycorrhizas possess the same constitutive mechanisms for dealing with metal contaminants as other organisms. Rhizosphere chemistry is critical to understanding the interactions of mycorrhizas with polluted soils. Soil pH, mineral weathering, pollutant precipitation with plant excreted organic acids all may have a key role in constitutive and adaptive tolerance of mycorrhizal associations present on contaminated sites. The responses of mycorrhizal fungi to toxic metal cations are diverse. This, linked to the fact that mycorrhizal diversity is normally high, even on highly contaminated sites, suggests that this diversity may have a significant role in colonisation of contaminated sites by mycorrhizas. That is, the environment selects for the fungal community that can best cope with the environment, so having diverse physiological attributes will enable colonisation of a wide range of metal contaminated micro-habitats.

Inherited resistance to arsenate toxicity in two populations of Lumbricus rubellus

No unequivocal evidence exists of genetically inherited resistance to metals/metalloids in field populations of earthworms. We studied cocoon production in adult Lumbricus rubellus Hoffmeister collected from an abandoned arsenic and copper mine (Devon Great Consols, Devon, UK), and abandoned tungsten mine (Carrock Fell, Cumbria, UK) and an uncontaminated cultured population. The earthworms were kept in uncontaminated soil for nine weeks. From a total of 42 L. rubellus from each site, Devon Great Consols adults produced 301 cocoons, of which 42 were viable; Carrock Fell 60 cocoons, of which 11 were viable; and the reference population 101 cocoons, of which 62 were viable. The hatchlings were collected and stored at 4 degrees C at weekly intervals. After 12 weeks, all hatchlings were transferred to clean soil and maintained at 15 degrees C for 20 weeks until they showed evidence of a clitellum. In toxicity trials, F1 generation L. rubellus were exposed to 2,000 mg As/kg as sodium arsenate or 300 mg Cu/kg as copper chloride for 28 d. The F1 generation L. rubellus from Devon Great Consols mine demonstrated resistance to arsenate but not copper. All L. rubellus from Devon Great Consols kept in soil treated with sodium arsenate remained in good condition over the 28-d period but lost condition rapidly and suffered high mortality in soil treated with copper chloride. The control population suffered high mortality in soil treated with sodium arsenate and copper chloride. Previous work has shown that field-collected adults demonstrate resistance to both arsenate and Cu toxicity under these conditions. Thus, while arsenate resistance may be demonstrated in F1 generation L. rubellus from one of the contaminated sites, Cu resistance is not. The F1 adults and F2 cocoons did not have significantly higher levels of As than the control population, with no residual As tissue burden, suggesting that resistance to As in these populations may be inherited.

Arsenic speciation in the earthworms Lumbricus rubellus and Dendrodrilus rubidus

Two species of earthworm, Lumbricus rubellus Hoffmeister and Dendrodrilus rubidus (Savigny) collected from an arsenic-contaminated mine spoil site and an uncontaminated site were investigated for total tissue arsenic concentrations and for arsenic compounds by liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). For L. rubellus, whole-body total tissue arsenic concentrations were 7.0 to 17.0 mg arsenic/ kg dry weight in uncontaminated soil and 162 to 566 mg arsenic/kg dry weight in contaminated soil. For D. rubidus, whole-body tissue concentrations were 2.0 to 5.0 mg arsenic/kg dry weight and 97 to 321 mg arsenic/kg dry weight, respectively. Arsenobetaine was the only organic arsenic species detected in both species of earthworms, with the remainder of the extractable arsenic being arsenate and arsenite. There was an increase in the proportion of arsenic present as arsenobetaine in the total arsenic burden. Lumbricus rubellus and D. rubidus have similar life styles, both being surface living and litter feeding. Arsenic speciation was found to be similar in both species for both uncontaminated and contaminated sites, with dose-dependent formation of arsenobetaine. When L. rubellus and D. rabidus from contaminated sites were incubated in arsenic-free soils, the total tissue burden of arsenic diminished. Initially, L. rubellus from the tolerant populations (from the contaminated site) eliminated arsenic in the first 7 d of exposure before accumulating arsenic in tissues, whereas nontolerant populations (from the uncontaminated site) accumulated arsenic linearly. The tolerant and nontolerant L. rubellus eliminated tissue arsenic linearly over 21 d when incubated in uncontaminated soil.

Antimony bioavailability in mine soils

Five British former mining and smelting sites were investigated and found to have levels of total Sb of up to 700 mg kg(-1), indicating high levels of contamination which could be potentially harmful. However, this level of Sb was found to be biologically unavailable over a wide range of pH values, indicating that Sb is relatively unreactive and immobile in the surface layers of the soil, remaining where it is deposited rather than leaching into lower horizons and contaminating ground water. Sb, sparingly soluble in water, was unavailable to the bacterial biosensors tested. The bioluminescence responses were correlated to levels of co-contaminants such as arsenic and copper, rather than to Sb concentrations. This suggests that soil contamination by Sb due to mining and smelting operations is not a severe risk to the environment or human health provided that it is present as immobile species and contaminated sites are not used for purposes which increase the threat of exposure to identified receptors. Co-contaminants such as arsenic and copper are more bioavailable and may therefore be seen as a more significant risk.