Embedded Health Risk from Arsenic in Globally Traded Rice.

International food trade is fundamental to global food security but with often negative consequences in the producing country. We propose a method of quantifying flows of inorganic arsenic (iAs) and embedded increased lifetime cancer risks (EHR) at a global scale, where negative impacts are felt on the importing country. Computations were made for 153 countries. Vietnam exports the most iAs embedded in rice (796 kg/year) followed by India (788 kg/year), Thailand (485 kg/year), and the United States (323 kg/year). We show that continental China, Indonesia, and Malaysia have the highest imports of iAs (292, 174, and 123 kg/year, respectively). Bangladesh ranks highest in EHR followed by Vietnam and Cambodia (150, 141, and 111 per 100,000, respectively). Countries that depend exclusively on imported rice are importing a substantial amount of risk, as, e.g., Kiribati and Solomon Islands (57 and 53 per 100,000, respectively). We discuss the potential policy options for reducing population dietary health risks by well-balanced apportioning of rice sources. This study targets policy design solutions based on health gains, rather than on safe levels of the risk factor alone.

The Pedosphere as a Sink, Source, and Record of Anthropogenic and Natural Arsenic Atmospheric Deposition.

The Anthropocene has led to global-scale contamination of the biosphere through diffuse atmospheric dispersal of arsenic. This review considers the sources arsenic to soils and its subsequent fate, identifying key knowledge gaps. There is a particular focus on soil classification and stratigraphy, as this is central to the topic under consideration. For Europe and North America, peat core chrono-sequences record massive enhancement of arsenic depositional flux from the onset of the Industrial Revolution to the late 20th century, while modern mitigation efforts have led to a sharp decline in emissions. Recent arsenic wet and dry depositional flux measurements and modern ice core records suggest that it is South America and East Asia that are now primary global-scale polluters. Natural sources of arsenic to the atmosphere are primarily from volcanic emissions, aeolian soil dust entrainment, and microbial biomethylation. However, quantifying these natural inputs to the atmosphere, and subsequent redeposition to soils, is only starting to become better defined. The pedosphere acts as both a sink and source of deposited arsenic. Soil is highly heterogeneous in the natural arsenic already present, in the chemical and biological regulation of its mobility within soil horizons, and in interaction with climatic and geomorphological settings. Mineral soils tend to be an arsenic sink, while organic soils act as both a sink and a source. It is identified here that peatlands hold a considerable amount of Anthropocene released arsenic, and that this store can be potentially remobilized under climate change scenarios. Also, increased ambient temperature seems to cause enhanced arsine release from soils, and potentially also from the oceans, leading to enhanced rates of arsenic biogeochemical cycling through the atmosphere. With respect to agriculture, rice cultivation was identified as a particular concern in Southeast Asia due to the current high arsenic deposition rates to soil, the efficiency of arsenic assimilation by rice grain, and grain yield reduction through toxicity.

Iodine status of teenage girls on the island of Ireland.

PURPOSE: The trace element iodine is a vital constituent of thyroid hormones. Iodine requirements increase during pregnancy, when even mild deficiency may affect the neurocognitive development of the offspring. Urinary iodine concentration (UIC) is the means of assessing iodine status in population surveys; a median UIC of 100-199 µg/L is deemed sufficient in a non-pregnant population. Milk is the main dietary source of iodine in the UK and Ireland. METHODS: We surveyed the iodine status of 903 girls aged 14-15 years in seven sites across the island of Ireland. Urine iodine concentration was measured in spot-urine samples collected between March 2014 and October 2015. Food group intake was estimated from iodine-specific food-frequency questionnaire. Milk-iodine concentration was measured at each site in summer and winter. RESULTS: The median UIC overall was 111 µg/L. Galway was the only site in the deficient range (median UIC 98 µg/L). All five of the Republic of Ireland sites had UIC ≤ 105 µg/L. In the two sites surveyed twice, UIC was lower in summer vs winter months [117 µg/L (IQR 76-165) vs 130 µg/L (IQR 91-194) (p < 0.01)]. Milk samples collected from Galway and Roscommon had a lower mean iodine concentration than those from Derry/Londonderry (p < 0.05). Milk intake was positively associated with UIC (p < 0.001). CONCLUSIONS: This is the largest survey of its kind on the island of Ireland, which currently has no iodine-fortification programme. Overall, the results suggest that this young female population sits at the low end of sufficiency, which has implications if, in future, they enter pregnancy with borderline status.

Maritime Deposition of Organic and Inorganic Arsenic.

The speciation of arsenic in wet and dry deposition are ambiguously described in current literature. Presented here is a 2 year study quantifying arsenic species in atmospheric deposition collected daily from an E. Atlantic coastal, semirural site, with comparative urban locations. Inorganic arsenic (Asi) was the principal form of arsenic in wet deposition, with a mean concentration of 0.54 µmol/m3. Trimethylarsine oxide (TMAO) was found to be the dominant form of organic arsenic, determined as above the LoD in 33% of wet deposition samples with a mean concentration of 0.12 µmol/m3. Comparison with codeposited trace elements and prevailing weather trajectories indicated that both anthropogenic and marine sources contribute to atmospheric deposition. Analysis of dry deposition revealed it to be a less significant input to the land-surface for Asi, contributing 32% of that deposited by wet deposition. Dry deposition had a larger proportion of Asi than that found in wet deposition, with TMAO making up only 12% of the sum of species. In comparison, urban sites showed large spatial and temporal variations in organic arsenic deposition, indicating that local sources of methylated species may be likely and that further understanding of biogenic arsine evolution and degradation are required to adequately assess the atmospheric arsenic burden and subsequent contribution to terrestrial ecosystems.

Modifying the Parboiling of Rice to Remove Inorganic Arsenic, While Fortifying with Calcium.

Using village-based rice processing plants in rural Bangladesh, this study considered how parboiling rice could be altered to reduce the content of the carcinogen inorganic arsenic. Parboiling is normally conducted with rough rice (i.e., where the husk is intact) that is soaked overnight at ambient temperatures, and then either steamed or boiled for ∼10 min, followed by drying. Across 13 geographically dispersed facilities it was found that a simple alteration parboiling wholegrain, instead of rough rice, decreased the inorganic arsenic content by 25% ( P = 0.002) in the final polished grain. Also, parboiling wholegrain had little impact on milling quality of the final polished rice. The wholegrain parboiling approach caused statistically significant median enrichment of calcium, by 213%; and a reduction in potassium, by 40%; with all other nutrient elements tested being unaffected. Milled parboiled rough rice had an enriched inorganic arsenic compared to nonparboiled milled rice, but parboiling of wholegrain rice did not enrich inorganic arsenic in the final milled product. Polished rice produced from the parboiling of both rough and wholegrain rice significantly reduced cadmium compared to nonparboiled polished rice, by 25%. This study also identified that trimethylarsine oxide and tretramethylarsonium are widely elevated in the husk and bran of rice and, therefore, gives new insights into the biogeochemical cycling of arsenic in paddy ecosystems.

Inorganic arsenic exposure and neuropsychological development of children of 4-5 years of age living in Spain.

Early-life exposure to inorganic arsenic (iAs) may adversely impact health later in life. To date, evidence of iAs adverse effects on children's neurodevelopment comes mainly from populations highly exposed to contaminated water with conflicting results. Little is known about those effects among populations with low iAs exposure from food intake. We investigated the cross-sectional association between exposure to iAs and neurodevelopment scores among children living in Spain whose main route of exposure was diet. Arsenic species concentrations in urine from 400 children was determined, and the sum of urinary iAs, dimethylarsinic acid, and monomethylarsonic acid was used to estimate iAs exposure. The McCarthy Scales of Children's Abilities was used to assess children's neuropsychological development at about 4-5 years of age. The median (interquartile range) of children's sum of urinary iAs, MMA, and DMA was 4.85 (2.74-7.54) µg/L, and in adjusted linear regression analyses the natural logarithm transformed concentrations showed an inverse association with children's motor functions (ß, [95% confidence interval]; global scores (-2.29, [-3.95, -0.63])), gross scores (-1.92, [-3.52, -0.31]) and fine scores (-1.54, [-3.06, -0.03]). In stratified analyses by sex, negative associations were observed with the scores in the quantitative index (-2.59, [-5.36, 0.17]) and working memory function (-2.56, [-5.36, 0.24]) only in boys. Our study suggests that relatively low iAs exposure may impair children's neuropsychological development and that sex-related differences may be present in susceptibility to iAs related effects; however, our findings should be interpreted with caution given the possibility of residual confounding.

Soil attribute regulates assimilation of roxarsone metabolites by rice (Oryza sativa L.).

Roxarsone (ROX), an organoarsenic feed additive, and its metabolites, can be present in animal manure used to fertilize rice. Rice is prone to absorb arsenic, and is subject to straighthead disorder, which reduces rice yield and is linked with organic arsenic compounds. This study aims to elucidate how soil property affect arsenic accumulation in rice plants fertilized with chicken manure containing ROX metabolites. Manures of chickens fed without or with ROX, designated as control manure and ROX treated manure (ROXCM), respectively, were applied in eight paddy soils of different origins, to investigate the assimilation of arsenic species in rice plants. The results show that inorganic arsenic (arsenate and arsenite), monomethylarsonic acid and dimethylarsinic acid (DMA) were detected in all brown rice and husk, trace tetramethylarsonium and trimethylarsine oxide were occasionally found in these both parts, whereas all these arsenic species were determined in straw, irrespective of manure type. ROXCM application specifically and significantly increased brown rice DMA (P = 0.002), which remarkably enhanced the risk of straighthead disease in rice. Although soil total As impacted grain biomass, soil free-iron oxides and pH dominated arsenic accumulation by rice plants. The significantly increased grain DMA suggests manure bearing ROX metabolites is not suitable to be used in soils with abundant free-iron oxides and/or high pH, if straighthead disorder is to be avoided in rice.

Scopoletin 8-hydroxylase: a novel enzyme involved in coumarin biosynthesis and iron-deficiency responses in Arabidopsis.

Iron deficiency is a serious agricultural problem, particularly in alkaline soils. Secretion of coumarins by Arabidopsis thaliana roots is induced under iron deficiency. An essential enzyme for the biosynthesis of the major Arabidopsis coumarins, scopoletin and its derivatives, is Feruloyl-CoA 6'-Hydroxylase1 (F6'H1), which belongs to a large enzyme family of the 2-oxoglutarate and Fe2+-dependent dioxygenases. We have functionally characterized another enzyme of this family, which is a close homologue of F6'H1 and is encoded by a strongly iron-responsive gene, At3g12900. We purified At3g12900 protein heterologously expressed in Escherichia coli and demonstrated that it is involved in the conversion of scopoletin into fraxetin, via hydroxylation at the C8 position, and that it thus functions as a scopoletin 8-hydroxylase (S8H). Its function in plant cells was confirmed by the transient expression of S8H protein in Nicotiana benthamiana leaves, followed by metabolite profiling and biochemical and ionomic characterization of Arabidopsis s8h knockout lines grown under various iron regimes. Our results indicate that S8H is involved in coumarin biosynthesis, as part of mechanisms used by plants to assimilate iron.

Biovolatilization of Arsenic as Arsines from Seawater.

Marine sources of arsenic to the atmosphere are normally dismissed as minor. Here we show that arsenic can be biovolatilized from seawater, and that biovolatilzation is based on organic arsenic species present in the seawater. Even though inorganic arsenic is in great excess in seawaters, it is trimethylarsine (TMA) that is the primary biovolatilized product, with dimethylarsine (DMA) also observed if dimethylarsinic acid (DMAA) is spiked into seawaters. With respect to budgets, 0.04% of the total arsenic in the seawater was biovolatilized over a 2-week incubation period. To test the environmental significance of this finding, wet deposition was analyzed for arsenic species at coastal locations, one of which was the origin of the seawater. It was found that the oxidized product of TMA, trimethylarsine oxide (TMAO), and to a less extent DMAA were widely present. When outputs for arsines (0.9 nmol/m2/d) from seawater and inputs from wet deposition (0.3-0.5 nmol/m2/d) were compared, they were of the same order of magnitude. These findings provide impetus to reexamining the global arsenic cycle, as there is now a need to determine the flux of arsines from the ocean to the atmosphere.

Elemental distribution in developing rice grains and the effect of flag-leaf arsenate exposure.

We measured the bulk grain concentrations of arsenic (As), along with rubidium (Rb) and strontium (Sr) as indicators of phloem and xylem transport respectively, in rice (Oryza sativa cv. Italica Carolina) pulsed with arsenate at two exposure levels for 5 day periods at progressively later stages of grain fill, between anthesis and maturity, through the cut flag leaf. We compared these to unexposed (negative) controls and positive controls; pulsed with dimethylarsinic acid (DMA). We collected elemental maps of As and micronutrient elements (Fe, Zn, Mn, Cu and Ni) from developing grains of rice. Exposures were either 25 or 100 µg/ml arsenate (As(V)) at various stages of grain development, compared to 25 µg/ml dimethylarsinic acid (DMA); the most efficiently transported As species identified in rice. We used the spatial distribution of arsenic in the grain to infer the presence of As transporters. By exposing grains through the flag leaf rather than via the roots, we were able to measure arsenic transport into the grain during filling under controlled conditions. Exposure to 100 µg/ml As(V) resulted in widespread As localization in both embryo and endosperm, especially in grains exposed to As at later stages of panicle development. This suggests loss of selective transport, likely to be the result of As toxicity. At 25 µg/ml As(V), As colocalized with Mn in the ovular vascular trace (OVT). Exposure to either As(V) or DMA reduced grain Fe, an effect more pronounced when exposure occurred earlier in grain development. The abundance of Cu and Zn were also reduced by As. Arsenic exposure later in grain development caused higher grain As concentrations, indicating the existence of As transporters whose efficiency increases during grain fill. We conclude that localization of As in the grain is a product of both As species and exposure concentration, and that high As(V) translocation from the flag leaf can result in high As concentrations in the endosperm.

Linking Genes to Microbial Biogeochemical Cycling: Lessons from Arsenic.

The biotransformation of arsenic is highly relevant to the arsenic biogeochemical cycle. Identification of the molecular details of microbial pathways of arsenic biotransformation coupled with analyses of microbial communities by meta-omics can provide insights into detailed aspects of the complexities of this biocycle. Arsenic transformations couple to other biogeochemical cycles, and to the fate of both nutrients and other toxic environmental contaminants. Microbial redox metabolism of iron, carbon, sulfur, and nitrogen affects the redox and bioavailability of arsenic species. In this critical review we illustrate the biogeochemical processes and genes involved in arsenic biotransformations. We discuss how current and future metagenomic-, metatranscriptomic-, metaproteomic-, and metabolomic-based methods will help to decipher individual microbial arsenic transformation processes, and their connections to other biogeochemical cycle. These insights will allow future use of microbial metabolic capabilities for new biotechnological solutions to environmental problems. To understand the complex nature of inorganic and organic arsenic species and the fate of environmental arsenic will require integrating systematic approaches with biogeochemical modeling. Finally, from the lessons learned from these studies of arsenic biogeochemistry, we will be able to predict how the environment changes arsenic, and, in response, how arsenic biotransformations change the environment.

Elevated Trimethylarsine Oxide and Inorganic Arsenic in Northern Hemisphere Summer Monsoonal Wet Deposition.

For arsenic speciation, the inputs for wet deposition are not well understood. Here we demonstrate that trimethylarsine oxide (TMAO) and inorganic arsenic are the dominant species in monsoonal wet deposition in the summer Indian subcontinent, Bangladesh, with inorganic arsenic dominating, accounting for ∼80% of total arsenic in this medium. Lower concentrations of both species were found in monsoonal wet deposition in the winter Indian subcontinent, Sri Lanka. The only other species present was dimethylarsinic acid (DMAA), but this was usually below limits of detection (LoD). We hypothesize that TMAO and inorganic arsenic in monsoonal wet deposition are predominantly of marine origin. For TMAO, the potential source is the atmospheric oxidation of marine derived trimethylarsine. For inorganic arsenic, our evidence suggests entrainment of water column inorganic arsenic into atmospheric particulates. These conclusions are based on weather trajectory analysis and on the strong correlations with known wet deposition marine derived elements: boron, iodine, and selenium. The finding that TMAO and inorganic arsenic are widely present and elevated in monsoonal wet deposition identifies major knowledge gaps that need to be addressed regarding the understanding of arsenic's global cycle.

Concentrations of urinary arsenic species in relation to rice and seafood consumption among children living in Spain.

Inorganic arsenic (i-As) has been related to wide-ranging health effects in children, leading to lifelong concerns. Proportionally, dietary i-As exposure dominates in regions with low arsenic drinking water. This study aims to investigate the relation between rice and seafood consumption and urinary arsenic species during childhood and to assess the proportion of urinary i-As metabolites. Urinary arsenic species concentration in 400 4-year-old children living in four geographical areas of Spain, in addition to repeated measures from 100 children at 7 years of age are included in this study. Rice and seafood products intake was collected from children's parents using a validated food frequency questionnaire (FFQ). At 4 years of age, children's urine i-As and monomethylarsonic acid (MMA) concentrations increased with rice product consumption (p-value = 0.010 and 0.018, respectively), and urinary arsenobetaine (AsB) with seafood consumption (p = 0.002). Four-year-old children had a higher consumption of both rice and seafood per body weight and a higher urinary %MMA (p-value = 0.001) and lower % dimethylarsinic acid (DMA) (p-value = 0.017). This study suggests increased dietary i-As exposure related to rice product consumption among children living in Spain, and the younger ones may be especially vulnerable to the health impacts of this exposure also considering that they might have a lower i-As methylation capacity than older children. In contrast, seafood consumption did not appear to influence the presence of potentially toxic arsenic species in this population of children.

Cobalamin Concentrations in Fetal Liver Show Gender Differences: A Result from Using a High-Pressure Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry as an Ultratrace Cobalt Speciation Method.

Maternal diet and lifestyle choices may affect placental transfer of cobalamin (Cbl) to the fetus. Fetal liver concentration of Cbl reflects nutritional status with regards to vitamin B12, but at these low concentration current Cbl measurement methods lack robustness. An analytical method based on enzymatic extraction with subsequent reversed-phase-high-pressure liquid chromatography (RP-HPLC) separation and parallel ICPMS and electrospray ionization (ESI)-Orbitrap-MS to determine specifically Cbl species in liver samples of only 10-50 mg was developed using 14 pig livers. Subsequently 55 human fetal livers were analyzed. HPLC-ICPMS analysis for cobalt (Co) and Cbl gave detection limits of 0.18 ng/g and 0.88 ng/g d.m. in liver samples, respectively, with a recovery of >95%. Total Co (Cot) concentration did not reflect the amount of Cbl or vitamin B12 in the liver. Cbl bound Co contributes only 45 ± 15% to Cot. XRF mapping and µXANES analysis confirmed the occurrence of non-Cbl cobalt in pig liver hot spots indicating particular Co. No correlations of total cobalt nor Cbl with fetal weight or weeks of gestation were found for the human fetal livers. Although no gender difference could be identified for total Co concentration, female livers were significantly higher in Cbl concentration (24.1 ± 7.8 ng/g) than those from male fetuses (19.8 ± 7.1 ng/g) (p = 0.04). This HPLC-ICPMS method was able to quantify total Cot and Cbl in fetus liver, and it was sensitive and precise enough to identify this gender difference.

Assessing the Legacy of Red Mud Pollution in a Shallow Freshwater Lake: Arsenic Accumulation and Speciation in Macrophytes.

Little is known about long-term ecological responses in lakes following red mud pollution. Among red mud contaminants, arsenic (As) is of considerable concern. Determination of the species of As accumulated in aquatic organisms provides important information about the biogeochemical cycling of the element and transfer through the aquatic food-web to higher organisms. We used coupled ion chromatography and inductively coupled plasma mass spectrometry (ICP-MS) to assess As speciation in tissues of five macrophyte taxa in Kinghorn Loch, U.K., 30 years following the diversion of red mud pollution from the lake. Toxic inorganic As was the dominant species in the studied macrophytes, with As species concentrations varying with macrophyte taxon and tissue type. The highest As content measured in roots of Persicaria amphibia (L.) Gray (87.2 mg kg(-1)) greatly exceeded the 3-10 mg kg(-1) range suggested as a potential phytotoxic level. Accumulation of toxic As species by plants suggested toxicological risk to higher organisms known to utilize macrophytes as a food source.

In utero exposure to cigarette chemicals induces sex-specific disruption of one-carbon metabolism and DNA methylation in the human fetal liver.

BACKGROUND: Maternal smoking is one of the most important modifiable risk factors for low birthweight, which is strongly associated with increased cardiometabolic disease risk in adulthood. Maternal smoking reduces the levels of the methyl donor vitamin B12 and is associated with altered DNA methylation at birth. Altered DNA methylation may be an important mechanism underlying increased disease susceptibility; however, the extent to which this can be induced in the developing fetus is unknown. METHODS: In this retrospective study, we measured concentrations of cobalt, vitamin B12, and mRNA transcripts encoding key enzymes in the 1-carbon cycle in 55 fetal human livers obtained from 11 to 21 weeks of gestation elective terminations and matched for gestation and maternal smoking. DNA methylation was measured at critical regions known to be susceptible to the in utero environment. Homocysteine concentrations were analyzed in plasma from 60 fetuses. RESULTS: In addition to identifying baseline sex differences, we found that maternal smoking was associated with sex-specific alterations of fetal liver vitamin B12, plasma homocysteine and expression of enzymes in the 1-carbon cycle in fetal liver. In the majority of the measured parameters which showed a sex difference, maternal smoking reduced the magnitude of that difference. Maternal smoking also altered DNA methylation at the imprinted gene IGF2 and the glucocorticoid receptor (GR/NR3C1). CONCLUSIONS: Our unique data strengthen studies linking in utero exposures to altered DNA methylation by showing, for the first time, that such changes are present in fetal life and in a key metabolic target tissue, human fetal liver. Furthermore, these data propose a novel mechanism by which such changes are induced, namely through alterations in methyl donor availability and changes in 1-carbon metabolism.

Conserved histidine of metal transporter AtNRAMP1 is crucial for optimal plant growth under manganese deficiency at chilling temperatures.

Manganese (Mn) is an essential nutrient required for plant growth, in particular in the process of photosynthesis. Plant performance is influenced by various environmental stresses including contrasting temperatures, light or nutrient deficiencies. The molecular responses of plants exposed to such stress factors in combination are largely unknown. Screening of 108 Arabidopsis thaliana (Arabidopsis) accessions for reduced photosynthetic performance at chilling temperatures was performed and one accession (Hog) was isolated. Using genetic and molecular approaches, the molecular basis of this particular response to temperature (G × E interaction) was identified. Hog showed an induction of a severe leaf chlorosis and impaired growth after transfer to lower temperatures. We demonstrated that this response was dependent on the nutrient content of the soil. Genetic mapping and complementation identified NRAMP1 as the causal gene. Chlorotic phenotype was associated with a histidine to tyrosine (H239Y) substitution in the allele of Hog NRAMP1. This led to lethality when Hog seedlings were directly grown at 4°C. Chemical complementation and hydroponic culture experiments showed that Mn deficiency was the major cause of this G × E interaction. For the first time, the NRAMP-specific highly conserved histidine was shown to be crucial for plant performance.

Trait-directed de novo population transcriptome dissects genetic regulation of a balanced polymorphism in phosphorus nutrition/arsenate tolerance in a wild grass, Holcus lanatus.

The aim of this study was to characterize the transcriptome of a balanced polymorphism, under the regulation of a single gene, for phosphate fertilizer responsiveness/arsenate tolerance in wild grass Holcus lanatus genotypes screened from the same habitat. De novo transcriptome sequencing, RNAseq (RNA sequencing) and single nucleotide polymorphism (SNP) calling were conducted on RNA extracted from H. lanatus. Roche 454 sequencing data were assembled into c. 22,000 isotigs, and paired-end Illumina reads for phosphorus-starved (P-) and phosphorus-treated (P+) genovars of tolerant (T) and nontolerant (N) phenotypes were mapped to this reference transcriptome. Heatmaps of the gene expression data showed strong clustering of each P+/P- treated genovar, as well as clustering by N/T phenotype. Statistical analysis identified 87 isotigs to be significantly differentially expressed between N and T phenotypes and 258 between P+ and P- treated plants. SNPs and transcript expression that systematically differed between N and T phenotypes had regulatory function, namely proteases, kinases and ribonuclear RNA-binding protein and transposable elements. A single gene for arsenate tolerance led to distinct phenotype transcriptomes and SNP profiles, with large differences in upstream post-translational and post-transcriptional regulatory genes rather than in genes directly involved in P nutrition transport and metabolism per se.

A review on completing arsenic biogeochemical cycle: microbial volatilization of arsines in environment.

Arsenic (As) is ubiquitous in the environment in the carcinogenic inorganic forms, posing risks to human health in many parts of the world. Many microorganisms have evolved a series of mechanisms to cope with inorganic arsenic in their growth media such as transforming As compounds into volatile derivatives. Bio-volatilization of As has been suggested to play an important role in global As biogeochemical cycling, and can also be explored as a potential method for arsenic bioremediation. This review aims to provide an overview of the quality and quantity of As volatilization by fungi, bacteria, microalga and protozoans. Arsenic bio-volatilization is influenced by both biotic and abiotic factors that can be manipulated/elucidated for the purpose of As bioremediation. Since As bio-volatilization is a resurgent topic for both biogeochemistry and environmental health, our review serves as a concept paper for future research directions.