R. O. Jenkins

The impact of a rice based diet on urinary arsenic

Rice is elevated in arsenic (As) compared to other staple grains. The Bangladeshi community living in the United Kingdom (UK) has a ca. 30-fold higher consumption of rice than white Caucasians. In order to assess the impact of this difference in rice consumption, urinary arsenicals of 49 volunteers in the UK (Bangladeshi n = 37; white Caucasians n = 12) were monitored along with dietary habits. Total urinary arsenic (As(t)) and speciation analysis for dimethylarsinic acid (DMA), monomethylarsonic acid (MA) and inorganic arsenic (iAs) was conducted. Although no significant difference was found for As(t) (median: Bangladeshis 28.4 µg L(-1)) and white Caucasians (20.6 µg L(-1)), the sum of medians of DMA, MA and iAs for the Bangladeshi group was found to be over 3-fold higher (17.9 µg L(-1)) than for the Caucasians (3.50 µg L(-1)). Urinary DMA was significantly higher (p < 0.001) in the UK Bangladeshis (median: 16.9 µg DMA L(-1)) than in the white Caucasians (3.16 µg DMA L(-1)) as well as iAs (p < 0.001) with a median of 0.630 µg iAs L(-1) for Bangladeshi and 0.250 µg iAs L(-1) for Caucasians. Cationic compounds were significantly lower in the Bangladeshis (2.93 µg L(-1)) than in Caucasians (14.9 µg L(-1)). The higher DMA and iAs levels in the Bangladeshis are mainly the result of higher rice consumption: arsenic is speciated in rice as both iAs and DMA, and iAs can be metabolized, through MA, to DMA by humans. This study shows that a higher dietary intake of DMA alters the DMA/MA ratio in urine. Consequently, DMA/MA ratio as an indication of methylation capacity in populations consuming large quantities of rice should be applied with caution since variation in the quantity and type of rice eaten may alter this ratio.

Phosphine generation by mixed- and monoseptic-cultures of anaerobic bacteria.

A microbial basis for bioreductive generation of phosphine is proposed, which could account at least in part for the presence of this toxic gas in natural anaerobic environments and in sewage and landfill gases. Phosphine generation under anaerobic growth conditions was dependent upon both the culture inoculum source (animal faeces) and enrichment culture conditions. Phosphine was detected in headspace gases from mixed cultures under conditions promoting fermentative growth of mixed acid and butyric acid bacteria, either in the presence or absence of methane generation. Monoseptic cultures of certain mixed acid fermentors (Escherichia coli, Salmonella gallinarum, and Salmonella arizonae) and solvent fermentors (Clostridium sporogenes, Clostridium acetobutyricum and Clostridium cochliarium) also generated phosphine. Such fermentative bacteria participate in the multi-stage process of methanogenesis in nature. Generation of phosphine by these bacteria, rather than by methanoarchaea themselves, could explain the apparent correlation between methanogenesis and the formation of phosphine in nature.

Bacterial degradation of arsenobetaine via dimethylarsinoylacetate.

Microorganisms from Mytilus edulis (marine mussel) degraded arsenobetaine, with the formation of trimethylarsine oxide, dimethylarsinate and methylarsonate. Four bacterial isolates from these mixed-cultures were shown by HPLC/hydride generation-atomic fluorescence spectroscopy (HPLC/HG-AFS) analysis to degrade arsenobetaine to dimethylarsinate in pure culture; there was no evidence of trimethylarsine oxide formation. Two of the isolates ( Paenibacillus sp. strain 13943 and Pseudomonas sp. strain 13944) were shown by HPLC/inductively coupled plasma-mass spectrometry (HPLC/ICPMS) analysis to degrade arsenobetaine by initial cleavage of a methyl-arsenic bond to form dimethylarsinoylacetate, with subsequent cleavage of the carboxymethyl-arsenic bond to yield dimethylarsinate. Arsenobetaine biodegradation by pure cultures was biphasic, with dimethylarsinoylacetate accumulating in culture supernatants during the culture growth phase and its removal accompanying dimethylarsinate formation during a carbon-limited stationary phase. The Paenibacillus sp. also converted exogenously supplied dimethylarsinoylacetate to dimethylarsinate only under carbon-limited conditions. Lysed-cell extracts of the Paenibacillus sp. showed constitutive expression of enzyme(s) capable of arsenobetaine degradation through methyl-arsenic and carboxymethyl-arsenic bond cleavage. The work establishes the capability of particular bacteria to cleave both types of arsenic-carbon bonds of arsenobetaine and demonstrates that mixed-community functioning is not an obligate requirement for arsenobetaine biodegradation.

Increases in Oxidized Low-Density Lipoprotein and Other Inflammatory and Adhesion Molecules With a Concomitant Decrease in High-Density Lipoprotein in the Individuals Exposed to Arsenic in Bangladesh

Elevated exposure to arsenic has been suggested to be associated with atherosclerosis leading to cardiovascular disease (CVD). However, biochemical events underlying the arsenic-induced atherosclerosis have not yet been fully documented. The aim of this study was to investigate the associations of circulating molecules involved in atherosclerosis with arsenic exposure in the individuals exposed to arsenic in Bangladesh. A total of 324 study subjects, 218 from arsenic-endemic areas and 106 from nonendemic areas in Bangladesh, were recruited. Drinking water, hair, nail, and blood samples were collected from the study subjects for analysis. Total cholesterol (TC), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) levels were lower in arsenic-endemic subjects than those of nonendemic subjects. Oxidized LDL (Ox-LDL), C-reactive protein (CRP), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) levels were significantly higher in arsenic-endemic subjects than those in nonendemic subjects. All these circulating molecules showed significant correlations with arsenic exposure (water, hair, and nail arsenic concentrations), and all these relations were significant before and after adjusting for relevant covariates. Among the circulating molecules tested in this study, HDL, Ox-LDL, and CRP showed dose-response relationships with arsenic exposure. Ox-LDL/HDL ratios were increased with the increasing concentrations of arsenic in the water, hair, and nails. Furthermore, non-HDL cholesterol and TC/HDL ratios were significantly correlated with arsenic exposure before and after adjusting for relevant covariates. Thus, all the observed associations may be the major features of arsenic exposure-related atherosclerosis leading to CVD.

Antimony biomethylation by mixed cultures of micro-organisms under anaerobic conditions

The volatile antimony compound trimethylantimony (TMA) was detected in headspace gases over anaerobic soil enrichment cultures spiked with potassium antimony tartrate. The presence of TMA was variable (12 positives from 104 cultures) and dependent upon both the inoculum source (environmental sample) and enrichment culture conditions. Positives for TMA formation were obtained with variable frequency for four of the six soils tested and for three types of enrichment culture, designed to encourage growth of nitrate-reducing, methane-producing or fermentative bacteria. The identity of the volatile antimony compound produced in each of the three types of enrichment culture was confirmed by gas chromatography-mass spectrometry and gas chromatography-atomic absorption spectroscopy. There was no evidence of any other volatile antimony compound in the headspace gases. These data suggest that the capability to generate TMA is widely distributed in the terrestrial environment and is attributable to different metabolic types of micro-organisms.

Reactive oxygen species in pathogenesis of atherosclerosis.

The volume of publications on the role of reactive oxygen species (ROS) in biological processes has been increasing exponentially over the last decades. ROS in large amounts clearly have detrimental effects on cell physiology, whereas low concentrations of ROS are permanently produced in cells and play a role as signaling molecules. An imbalance in ROS production and defense mechanisms can lead to pathological vascular remodeling, atherosclerosis being among them. The aim of this review is to examine different sources of ROS from the point of view of their participation in pathogenesis of atherosclerosis and related cardiovascular risk. Among the possible sources of ROS discussed here are mitochondria, NADPH-oxidases, xanthine oxidase, peroxidases, NO-synthases, cytochrome P450, cyclooxygenases, lipoxygenases, and hemoglobin of red blood cells. A great challenge for future research is to establish interrelations, feedback and feed-forward regulation mechanisms of various sources of ROS in development of atherosclerosis and other vascular pathologies.

Arsenic speciation in Japanese rice drinks and condiments

Rice has been demonstrated to be one of the major contributors to inorganic arsenic (i-As) intake in humans. However, little is known about rice products as additional source of i-As exposure. In this study, misos, syrups and amazake (a fermented sweet rice drink) produced from rice, barley and millet were analysed for total arsenic (t-As) and a subset of samples were also analyzed for As speciation. Rice based products displayed a higher i-As content than those derived from barley and millet. Most of the t-As in the rice products studied was inorganic (63-83%), the remainder being dimethylarsinic acid. Those who regularly consume rice drinks and condiments, such as the Japanese population and those who follow health conscious diets based on the Japanese cuisine, could reach up to 23% of the World Health Organizations Provisional Tolerable Daily Intake of i-As, by only consuming these kinds of products. This study provides a wide appreciation of how i-As derived from rice based products enters the human diet and how this may be of concern to populations who are already exposed to high levels of i-As through consumption of foods such as rice and seaweed.

Trimethylantimony generation by Scopulariopsis brevicaulis during aerobic growth

Trimethylantimony was detected with high frequency in the headspace of Scopulariopsis brevicaulis cultures during aerobic growth. The compound was formed biologically from potassium antimony tartrate and no other volatile antimony species were detected. Complete biomethylation of antimony (III) species to trimethylantimony in the absence of an anoxic stage indicates that this gas could be formed in natural aerobic environments through the action of microorganisms. Biogenesis of trimethylantimony in aerobic environments, with subsequent abiotic oxidation of the compound, could account for the presence of involatile methylated antimony species in natural bodies of water and in the culture media of microbial cultures.

The analysis of inorganic and methyl mercury by derivatisation methods; opportunities and difficulties

Abstract We discuss three methods of analysis of methyl and inorganic mercury in sediments and water and present new results for one of these. The methods used are (1) solvent extraction and derivatization to CH 3 HgBr (with separate analysis of inorganic mercury) with determination by electron capture gas chromatography, (2) aqueous phase derivatization using NaB(C 2 H 5 ) 4 with detection by atomic absorption spectroscopy and (3) derivatization with NaBH 4 with detection of CH 3 Hg and inorganic mercury by atomic absorption and mass spectroscopes. We present new results on the analytical stability of CH 3 HgH and discuss errors arising in the methods.

Biovolatilization of antimony and sudden infant death syndrome (SIDS).

1 The aerobic filamentous fungus S. brevicaulis IMI 17297 methylated antimony from Sb2O3 substrate, with the formation of gaseous trimethylantimony (TMA). No evidence was found for the generation of other gaseous antimony compounds by this organism. 2 Biovolatilization of inorganic antimony was greatest during cultivation of the fungus on solid media at 258C, and occurred more readily from antimony (III) substrates than from antimony (V) substrates. 3 Under simulated cot environment conditions (CO2 enriched atmosphere, 338C) the fungus exhibited an altered morphology and a reduced capability to volatilize inorganic antimony from the pure compound. 4 No evidence of antimony biovolatilization from cot mattress PVC was found, unless antimony was released from PVC by heat treatment (at 80 or 1008C). 5 These data suggest that normal cot environment conditions are non-optimal for volatilization of antimony by S. brevicaulis, and that Sb2O3 in cot mattress PVC is not bioavailable. 6 Cot mattress isolates of S. brevicaulis also volatilized antimony (not encapsulated by PVC), whereas those of other filamentous fungi (Penicillium spp., Aspergillus niger, Aspergillus fumigatus, Alternaria sp.) and of bacteria (Bacillus spp.) did not. 7 The oxidation products of TMA may be the true determinants of toxicity for biogenic antimony gases produced in an aerobic environment.