Environ. Sci. Technol. 2010, 44, 5240–5247
Determination of Cadmium Relative Bioavailability in Contaminated Soils and Its Prediction Using in Vitro Methodologies A L B E R T L . J U H A S Z , * ,†,‡ J O H N W E B E R , †,‡ R A V I N A I D U , †,‡ D O R O T A G A N C A R Z , § ALLAN ROFE,§ DAMIAN TODOR,† AND E U A N S M I T H †,‡ 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, and Institute of Medical and Veterinary Science, Frome Road, SA 5000, Australia
Received March 1, 2010. Revised manuscript received May 11, 2010. Accepted May 14, 2010.
In this study, cadmium (Cd) relative bioavailability in contaminated (n ) 5) and spiked (n ) 2) soils was assessed using an in vivo mouse model following administration of feed containing soil or Cd acetate (reference material) over a 15 day exposure period. Cadmium relative bioavailability varied depending on whether the accumulation of Cd in the kidneys, liver, or kidney plus liver was used for relative bioavailability calculations. When kidney plus liver Cd concentrations were used, Cd relative bioavailability ranged from 10.1 to 92.1%. Cadmium relative bioavailability was higher (14.4-115.2%) when kidney Cd concentrations were used, whereas lower values (7.2-76.5%) were derived when liver Cd concentrations were employed in calculations. Following in vivo studies, four in vitro methodologies (SBRC, IVG, PBET, and DIN), encompassing both gastric and intestinal phases, were assessed for their ability to predict Cd relative bioavailability. Pearson correlations demonstrated a strong linear relationship between Cd relative bioavailability and Cd bioaccessibility (0.62-0.91), however, stronger in vivo-in vitro relationships were observed when Cd relative bioavailability was calculated using kidney plus liver Cd concentrations. Whereas all in vitro assays could predict Cd relative bioavailability with varying degrees of confidence (r2 ) 0.348-0.835), large y intercepts were calculated for a number of in vitro assays which is undesirable for in vivo-in vitro predictive models. However, determination of Cd bioaccessibility using the intestinal phase of the PBET assay resulted in a small y intercept (5.14; slope )1.091) and the best estimate of in vivo Cd relative bioavailability (r2 ) 0.835).
* Corresponding author tel: +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. 5240
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 13, 2010
Introduction Cadmium (Cd) is an environmental pollutant arising from anthropogenic and geogenic origin. The concentration of Cd in soil has increased over the past decades as a result of mining and smelting activities, its increased industrial use in alloys, batteries, pigments, plastics, and ceramics, and due to its presence in agricultural fertilizers (1). Exposure to Cd via consumption of contaminated food or drinking water, inhalation of dust or vaporized Cd, or incidental ingestion of contaminated soil or dust may result in a variety of health effects including renal damage, proximal tubular reabsorptive dysfunction, and fractures and distortion of the long bones in the skeleton (i.e., itai itai disease) (2-5). In addition, Cd has been classified as a human carcinogen (group 1; via inhalation) by the International Agency for Research on Cancer (6) based on human and experimental animal carcinogenicity studies. While the diet is the main source of environmental exposure to Cd in nonsmokers (4), incidental ingestion of contaminated soil and dust is an important exposure pathway for young children. Soil and dust that adheres to the hands of children may be incidentally ingested due to the prevalence of hand-to-mouth contact (7). However, the amount of Cd that is absorbed into systemic circulation (the bioavailable fraction) may vary depending on a variety of parameters including its chemical form, environmental matrix, Cd-soil residence time, and soil constituents (e.g., Ca, Fe, Zn) in addition to receptor-related factors including intestinal content, diet composition, nutritional status, and interaction of Cd with other nutrients (8, 9). A number of studies have demonstrated that Cd absorption may be enhanced when dietary levels of Ca, Fe, and Zn are low (10, 11) or when protein intake is high (12, 13). Conversely, elevated dietary phytate may repress Cd absorption (14). The conservative assumption commonly used in human health risk assessment is that the relative bioavailability of soil-borne Cd is 100%. This assumption may overestimate the risk associated with the soil ingestion pathway, however, data are required to assess the aforementioned variables to adjust default relative bioavailability assumptions. In vivo assays utilizing animal models (e.g., rodents, swine, primates) have been developed to quantify the relative bioavailability of soil-borne contaminants for inclusion in human health risk assessment. For inorganic contaminants such as arsenic and lead, a growing in vivo relative bioavailability database is developing in the literature (7, 15-18), however, for Cd-contaminated soils, a paucity of published information is available. In vivo assays utilizing rodents and swine have been utilized for the assessment of Cd relative bioavailability in spiked (n ) 1) (19), smelter (n ) 1) (20), and hazardous waste (n ) 10) (21) soils. In these studies, Cd relative bioavailability was determined by comparing the accumulation of Cd in the kidney and/or liver after exposure to contaminated soil (incorporated into feed) to the accumulation of Cd in the kidney and/or liver following solution dosing studies (CdCl2). Studies by Schilderman et al. (19), Schoof and Freeman (20), and Schroder et al. (21) demonstrated that Cd relative bioavailability in spiked and contaminated soils was highly variable (10-116%), which was presumably due to differences in Cd mineralogy, soil properties, and Cd-soil residence time. Due to time and cost requirements to perform in vivo studies, relative bioavailability testing using animal assays is usually not practical. As a result, in vitro assays simulating gastrointestinal conditions have been developed as potential 10.1021/es1006516
2010 American Chemical Society
Published on Web 06/07/2010
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