Tim Kuchel

In Vivo Assessment of Arsenic Bioavailability in Rice and Its Significance for Human Health Risk Assessment

Background Millions of people worldwide consume arsenic-contaminated rice; however, little is known about the uptake and bioavailability of arsenic species after arsenic-contaminated rice ingestion. Objectives In this study, we assessed arsenic speciation in greenhouse-grown and supermarket-bought rice, and determined arsenic bioavailability in cooked rice using an in vivo swine model. Results In supermarket-bought rice, arsenic was present entirely in the inorganic form compared to greenhouse-grown rice (using irrigation water contaminated with sodium arsenate), where most (~ 86%) arsenic was present as dimethylarsinic acid (organic arsenic). Because of the low absolute bioavailability of dimethylarsinic acid and the high proportion of dimethylarsinic acid in greenhouse-grown rice, only 33 ± 3% (mean ± SD) of the total rice-bound arsenic was bioavailable. Conversely, in supermarket-bought rice cooked in water contaminated with sodium arsenate, arsenic was present entirely in the inorganic form, and bioavailability was high (89 ± 9%). Conclusions These results indicate that arsenic bioavailability in rice is highly dependent on arsenic speciation, which in turn can vary depending on rice cultivar, arsenic in irrigation water, and the presence and nature of arsenic speciation in cooking water. Arsenic speciation and bioavailability are therefore critical parameters for reducing uncertainties when estimating exposure from the consumption of rice grown and cooked using arsenic-contaminated water.

Assessment of Four Commonly Employed in Vitro Arsenic Bioaccessibility Assays for Predicting in Vivo Relative Arsenic Bioavailability in Contaminated Soils

Currently, a number of in vitro methods are in use worldwide to assess arsenic (As) bioaccessibility in soils. However, a dearth of research has been undertaken to compare the efficacy of the in vitro methods for estimating in vivo relative As bioavailability. In this study, As bioaccessibility in contaminated soils (n = 12) was assessed using four in vitro assays (SBRC, IVG, PBET, DIN). In vitro results were compared to in vivo relative As bioavailability data (swine assay) to ascertain which methodologies best correlate with in vivo data. Arsenic bioaccessibility in contaminated soils varied depending on the in vitro method employed. For the SBRC and IVG methods, As bioaccessibility generally decreased when gastric-phase values were compared to the intestinal phase. In contrast, extending the PBET and DIN assays from the gastric to the intestinal phase resulted in an increase in As bioaccessibility for some soils tested. Comparison of in vitro and in vivo results demonstrated that the in vitro assay encompassing the SBRC gastric phase provided the best prediction of in vivo relative As bioavailability (R(2) = 0.75, Pearson correlation = 0.87). However, relative As bioavailability could also be predicted using gastric or intestinal phases of IVG, PBET, and DIN assays but with varying degrees of confidence (R(2) = 0.53-0.67, Pearson correlation = 0.73-0.82).

Effect of soil ageing on in vivo arsenic bioavailability in two dissimilar soils

Arsenic (As) bioavailability in spiked soils aged for up to 12 months was assessed using in vitro and in vivo methodologies. Ageing (natural attenuation) of spiked soils resulted in a decline in in vivo As bioavailability (swine assay) of over 75% in soil A (Red Ferrosol) but had no significant effect on in vivo As bioavailability even after 12 months of ageing in soil B (Brown Chromosol). Sequential fractionation, however, indicated that there was repartitioning of As within the soil fractions extracted during the time course investigated. In soil A, the As fraction associated with the more weakly bound soil fractions decreased while the residual fraction increased from 12% to 35%. In contrast, little repartitioning of As was observed in soil B indicating that natural attenuation may be only applicable for As in soils containing specific mineralogical properties.

Principles and application of an in vivo swine assay for the determination of arsenic bioavailability in contaminated matrices

The assessment of arsenic (As) bioavailability from contaminated matrices is a crucial parameter for reducing the uncertainty when estimating exposure for human health risk assessment. In vivo assessment of As utilising swine is considered an appropriate model for human health risk assessment applications as swine are remarkably similar to humans in terms of physiology and As metabolism. While limited in vivo As bioavailability data is available in the literature, few details have been provided regarding technical considerations for performing in vivo assays. This paper describes, with examples, surgical, experimental design and analytical issues associated with performing chronic and acute in vivo swine assays to determine As bioavailability in contaminated soil and food.

Effects of ageing and soil properties on the oral bioavailability of benzo[a]pyrene using a swine model

Oral bioavailability of benzo[a]pyrene (B[a]P) was studied in a swine model using eight spiked soil samples after incubation for 50 and/or 90 days. Silica sand was used as a reference material and the relative bioavailability (RB) of B[a]P in soils was calculated as the quotient of the area under the plasma B[a]P curve (AUC) for soil and AUC for the silica sand. Significantly reduced RB was observed in all study soils after 90 days ageing, ranging from 22.1±0.4% to 62.7±10.1%, except for one very sandy soil (sand content 87.6%) where RB was unchanged (108.1±8.0%). Apart from this, bioavailability decreased during ageing with the decrease (from day 50 to day 90) being only significant for a clayey soil containing expandable clay minerals. Statistical analyses of B[a]P RB at day 90 (eight soils) and soil properties showed no direct correlation between RB and specific soil properties such as total organic carbon (TOC) and clay content which were commonly linked to organic contaminant sequestration. However, strongly significant relationships (p<0.001) were found between RB and the fine particle associated carbon (FPAC) defined as (Silt+Clay)/TOC, and between RB and the soil mesopore (<6nm; p<0.001) fraction, after two samples with high pH and high EC being excluded from the analyses. The bioaccessibility estimated by four in vitro extraction methods: dichloromethane/acetone sonication (DCM/Ace), butanol vortex (BuOH), hydroxypropyl-β-cyclodextrin extraction (HPCD) and Milli Q water leaching methods at different sampling time (1 day, 50 days and 90 days after spiking) also showed a decreasing trend. Significant correlations were found between B[a]P RB and DCM/Ace (R(2)=0.67, p<0.05) extractable fraction and BuOH (R(2)=0.75, p<0.01) extractable fraction.

Application of an in vivo swine model for the determination of arsenic bioavailability in contaminated vegetables

Considerable information is available in the literature regarding the uptake of arsenic (As) from contaminated soil and irrigation water by vegetables. However, few studies have investigated As speciation in these crops while a dearth of information is available on As bioavailability following their consumption. In this study, the concentration and speciation of As in chard, radish, lettuce and mung beans was determined following hydroponic growth of the vegetables using As-contaminated water. In addition, As bioavailability was assessed using an in vivo swine feeding assay. While As concentrations ranged from 3.0 to 84.2mg As kg(-1) (dry weight), only inorganic As (arsenite and arsenate) was detected in the edible portions of the vegetables. When As bioavailability was assessed through monitoring blood plasma As concentrations following swine consumption of As-contaminated vegetables, between 50% and 100% of the administered As dose was absorbed and entered systemic circulation. Arsenic bioavailability decreased in the order mung beans>radish>lettuce=chard.

Predicting lead relative bioavailability in peri-urban contaminated soils using in vitro bioaccessibility assays

In this study, lead (Pb) bioaccessibility was assessed in peri-urban contaminated soils using a variety of established in vitro assays. Bioaccessibility data was then used to predict Pb relative bioavailability (RBA) using published in vivo-in vitro regression models in order to compare calculated estimates and measured values. Lead bioaccessibility varied depending on the in vitro methodology employed with the relative bioavailability leaching procedure (RBALP) and in vitro gastrointestinal (IVG) assays providing more conservative Pb bioaccessibility values compared to those determined using PBET, UBM and Rel-SBRC-I assays. When Pb RBA was calculated, predicted values using PBET-G and UBM-G data were similar to measured Pb RBA values. However, Pb RBA was over-estimated by 1.6–5.5- and 2.6–6.6-fold when data and regression models from RBALP and IVG-G assays were employed.

ANTIVENOM DEVELOPMENT IN AUSTRALIA

Brown snakes, Pseudonaja genus, cause more bites and deaths to animals and humans in Australia than any other terrestrial snake genus. Some aspects of treatment of brown snakebites with antivenom remain poorly managed due to the apparent inability of the antivenom to counter the prothrombin activator in the venom. We present evidence of a new novel antivenom (Antiven Pty Ltd Brown snake antivenom (ABSAV)), which shows high efficacy in reversing the hemostatic abnormality caused by brown snake envenomation. It is also more efficient at reversing overall toxicity. In clotting tests, it is substantially more potent than Commonwealth Serum Laboratories Ltd (CSL) Brown snake antivenom and is twice as effective in reversing overall toxicity than CSL Brown snake antivenom. Antiven Pty. Ltd. Brown snake antivenom is currently being assessed by the National Registration Authority (veterinary regulative body in Australia).

Comparison of oral bioavailability of benzo[a]pyrene in soils using rat and swine and the implications for human health risk assessment.

BACKGROUND There are many uncertainties concerning variations in benzo[a]pyrene (B[a]P) soil guidelines protecting human health based on carcinogenic data obtained in animal studies. Although swine is recognised as being much more representative of the human child in terms of body size, gut physiology and genetic profile the rat/mice model is commonly used in practice. OBJECTIVES We compare B[a]P bioavailability using a rat model to that estimated in a swine model, to investigate the correlation between these two animal models. This may help reduce uncertainty in applying bioavailability to human health risk assessment. METHODS Twelve spiked soil samples and a spiked silica sand (reference material) were dosed to rats in parallel with a swine study. B[a]P bioavailability was estimated by the area under the plasma B[a]P concentration-time curve (AUC) and faecal excretion as well in the rats. Direct comparison between the two animal models was made for: firstly, relative bioavailability (RB) using AUC assay; and secondly, the two assays in the rat model. RESULTS Both AUC and faecal excretion assays showed linear dose-response for the reference material. However, absolute bioavailability was significantly higher when using faecal excretion assay (p<0.001). In aged soils faecal excretion estimated based on solvent extraction was not accurate due to the form of non-extractable fraction through ageing. A significant correlation existed between the two models using RB for soil samples (RBrat=0.26RBswine+17.3, R(2)=0.70, p<0.001), despite the regression slope coefficient revealing that the rat model would underestimate RB by about one quarter compared to using swine. CONCLUSIONS In the comparison employed in this study, an interspecies difference of four in RB using AUC assay was identified between the rat and swine models regarding pharmacokinetic differences, which supported the body weight scaling method recommended by US EPA. Future research should focus on the carcinogenic competency (pharmacodynamics) used in experiment animals and humans.

Variation in arsenic bioavailability in rice genotypes using swine model: An animal study

An in vivo assay using swine was used to measure the absolute bioavailability (AB) of As from cooked rice of twelve genotypes commonly grown in Bangladesh. An assessment of both total As in rice and its bioavailability is crucial for estimating human exposure following dietary intake by the local community. Average As concentrations in each rice genotype ranged from 108±4μg/kg to 580±6μg/kg. Arsenic speciation shows that most of the rice genotype contains 73 to 100% inorganic As. Swine were administered with As orally and via intravenous method, i.e. injection and fed certain common Bangladeshi rice genotypes (cooked). Swine blood As levels were measured to calculate As bioavailability from rice. Pilot studies shows that for As(III) and As(V), 90.8±12.4% and 85.0±19.2% of the administered oral dose was absorbed from the gastrointestinal tract whereas organic As was poorly absorbed resulting in low bioavailability values 20.2±2.6% (MMA) to 31.2±3.4% (DMA), respectively. These studies demonstrates that rice genotypic characters influenced As bioavailability in rice grown in As-contaminated areas and the bioavailability varied between 25% and 94%. Arsenic in salt tolerant rice genotypes Binadhan-10 and BRRI dhan47 as well as brown rice genotypes Kheali Boro and Local Boro has lower bioavailability (<50%) compared to other rice genotypes. The most commonly cultivated and consumed variety (BRRI dhan28) has As bioavailability of 70%, which poses a significant risk to consumers. Calculation of maximum tolerable daily intake (MTDI) for humans due to consumption of rice based on bioavailability data was higher than those calculated based on inorganic and organic As concentration in rice genotypes.