Environ. Sci. Technol. 2009 43, 9487–9494
Assessment of Four Commonly Employed in Vitro Arsenic Bioaccessibility Assays for Predicting in Vivo Relative Arsenic Bioavailability in Contaminated Soils A L B E R T L . J U H A S Z , * ,†,‡ J O H N W E B E R , †,‡ E U A N S M I T H , †,‡ R A V I N A I D U , †,‡ MATTHEW REES,§ ALLAN ROFE,§ TIM KUCHEL,§ AND LLOYD SANSOM| Centre for Environmental Risk Assessment and Remediation, Division of Information Technology, Engineering and the Environment, University of South Australia, Mawson Lakes Campus, Mawson Lakes, SA 5095 Australia, Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, Mawson Lakes, SA 5095 Australia, Institute of Medical and Veterinary Science, Frome Road, SA 5000 Australia, and Sansom Institute, School of Pharmacy and Medical Sciences, Division of Health Science, University of South Australia, City East Campus, SA 5001 Australia
Received August 9, 2009. Revised manuscript received October 18, 2009. Accepted October 27, 2009.
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 bioavailabilitydata(swineassay)toascertainwhichmethodologies 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).
* Corresponding author phone: +618 8302 5045; fax: +618 8302 3057; e-mail:
[email protected]. † University of South Australia. ‡ Cooperative Research Centre for Contamination Assessment and Remediation of the Environment. § Institute of Medical and Veterinary Science. | University of South Australia. 10.1021/es902427y CCC: $40.75
Published on Web 11/12/2009
2009 American Chemical Society
Introduction Incidental ingestion of contaminated soil is a major nondietary exposure pathway for arsenic (As). To more accurately quantify As exposure via soil ingestion, determination of As bioavailability is required. It has been established that As bioavailability could be less than 100% as a result of As mineralogy, the influence of soil properties (e.g., Fe content), and As soil residence time (aging) (1-6). As a result, exposure and therefore risk to human health can be overestimated if a conservative bioavailability approach is adopted (i.e., 100%). In vivo assays encompassing a variety of animal models (e.g., primate, swine, dog, rabbit, rodent) have been used to quantify relative As bioavailability in soil (2, 3, 6-12). Because of their similarities to man in As metabolism, nutritional requirements, bone development, and so on, immature swine are considered to be an appropriate surrogate model for assessing relative As bioavailability for human health risk assessment (13). However, given the time and cost requirements, in addition to ethical issues, there is great demand for an appropriate in vitro assay for estimating relative As bioavailability. In vitro assays are simple, rapid, and inexpensive, and numerous methods (e.g., SBRC, IVG, RIVM, PBET, DIN, SHIME, TIM) have been applied for the determination of As bioaccessibility (1, 3, 14-18). However, before these assays can act as a surrogate measurement for relative As bioavailability, a correlation between in vitro bioaccessibility and in vivo bioavailability is a mandatory prerequisite for both regulatory and scientific acceptance. A limited number of studies have established the relationship between in vivo relative As bioavailability and in vitro As bioaccessibility. Rodriguez et al. (3) and Basta et al. (19) determined that there was no statistical difference between the relative bioavailability of As in mining and smelting material when measured by an in vivo swine assay or by the gastric phase of the IVG bioaccessibility assay in the presence or absence of a dosing vehicle. Similarly, Juhasz et al. (6) determined that the gastric phase of the SBRC in vitro assay (termed SBET) could accurately predict in vivo relative As bioavailability (swine assay) in herbicide-/ pesticide-impacted soils, mine site soils, soils with naturally elevated As concentrations (gossans), and As-spiked soils. Although data from these studies demonstrate that relative As bioavailability can be predicted using simple, rapid, and inexpensive in vitro assays, it is unclear whether relative As bioavailability estimates vary depending on the in vitro assay utilized. In an attempt to evaluate the suitability of in vitro assays for assessing relative As bioavailability, a limited number of studies have compared the variability in bioaccessibility values derived using various in vitro assays. Oomen et al. (18) compared bioaccessibility values determined using five in vitro methods (SBET, DIN, RIVM, SHIME, TIM) for two historically contaminated soils (Flanders, Oker 11) and one NIST reference soil (Montana 2711). Arsenic bioaccessibility varied significantly between methods for all soils, with As bioaccessibility values in the ranges of 6-95%, 1-19%, and 10-59% for Flanders, Oker 11, and Montana 2711, respectively. Although the parameters for each in vitro method varied (e.g., chyme composition, soil/solution ratio, residence time), Oomen et al. (18) proposed that the disparity in As bioaccessibility values was due to the differences in the gastric pH of each method. However, a limitation of this study was that As bioaccessibility was unable to be compared to relative As bioavailability because of a lack of in vivo data for those soils. In the study of Rodriguez et al. (3), As bioaccessibility VOL. 43, NO. 24, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
9487
TABLE 1. Selected Properties of Soils Used in This Studya soil properties b
-1
-1
b
sample
total As (mg kg )
2 4 5 10 16 18
267 42 1114 257 751 91
24 27
713 228
94.7 22.4
33 34
807 577
10.9 17.6
44 45
190 88
8.3 9.6
total Feb,c (g kg-1)
total Al (g kg )
total Pb (mg kg-1)
pHb
234 385 874 242 422 130
8.8 8.4 7.8 6.4 8.3 7.5
98.6 (48.6) 17.9 (12.5)
3144 2941
5.7 5.2
23.5 (7.1) 24.6 (12.5)
546 468
7.6 6.6
21.0 (15.6) 21.0 (13.2)
200 370
8.6 8.1
Railway Corridors 22.2 17.6 (10.6) 18.3 13.7 (8.5) 16.3 68.3 (16.6) 27.8 25.8 (9.9) 10.8 14.5 (11.4) 5.1 10.0 (3.2) Dip Sites
Mine Sites
Gossans
a The
