SEGH Articles

Measuring the Bioaccessibility of Potentially Harmful Elements in Soil

01 May 2013
Mark Cave provides some background for bioaccessibility testing and insight into the contribution it has made to the risk assessment industry.
Dr Mark Cave is a leading scientist who has been a major driving force behind the development and adoption of bioaccessibility testing within the risk assessment and contaminated land community.  He is organising an upcoming International Conference in November 2013 at the British Geological Survey, bringing together many world players in bioavailability and bioaccessibility research  Here he provides background for bioaccessibility testing and insight into the contribution it has made to the risk assessment industry.
In terms of human health risk assessment there are three main exposure pathways for a given contaminant present in soil. The largest area of concern is the oral/ingestion pathway followed by the dermal and respiratory exposure routes (Paustenbach, 2000). Whether contaminated soils pose a human health risk depends on the potential of the contaminant to leave the soil and enter the human bloodstream. The use of total contaminant concentrations in soils provides a conservative approach as it assumes that all of the metal present in the soil can enter the bloodstream. Results from animal tests e.g. (Denys et al., 2012) suggest that contaminants in a soil matrix maybe absorbed to a lesser extent and show fewer toxic effects compared to the same concentration of soluble salts of the contaminants in a food or liquid matrix.
There is, therefore, a clear need for a practical methodology that measures the fraction of the contaminant in the soil that, through oral ingestion, can enter the systemic circulation of the human body and cause toxic effects. This is known as the oral bioavailability and can be formally defined as the fraction of an administered dose that reaches the central (blood) compartment from the gastrointestinal tract (Paustenbach, 2000). This term must not to be confused with the oral bioaccessibility of a substance, which is defined as the fraction that is soluble in the gastrointestinal environment and is available for absorption (Paustenbach, 2000).
Since bioavailability data is essentially related to the amount of contaminant in the animal/human bloodstream the data must be produced from the dosing of animals with contaminated soil and the subsequent measurement of the contaminant in the blood or organs of the animal; these are known as in-vivo animal models. Bioaccessibility data, however, is normally determined in a test tube environment (in-vitro) and represents the amount of contaminant dissolved in the gastrointestinal tract prior to crossing the mucosal walls. The amount of pollutant which is actually absorbed by an organism is generally less than or equal to the amount which is mobilised (Paustenbach, 2000). Bioaccessibility extraction tests are generally based around the gastrointestinal parameters of young children (0-3 yr). This age group is thought to be at most risk from accidental ingestion of soil. Also, since children can absorb a higher percentage of contaminant through the digestive system than adults, they are more susceptible to adverse health effects (Hamel et al., 1998).
Mammal dosing trials are time consuming and expensive. To supersede the use of animals in determining the bioavailability of potentially harmful elements for human health risk assessment, or to estimate bioavailability where animal studies are not available, a potential alternative is the use of in-vitro tests.
A number of in vitro bioaccessibility tests for mimicking human ingestion have been reported in the literature. As a result of research carried out by the Bioaccessibility Research Group of Europe (BARGE) and other research groups it was clear that the different bioaccessibility tests showed similar trends when used on the same soil samples, but the different operating conditions for each test produced widely ranging bioaccessibility values between the methods (Oomen et al., 2002). To overcome this problem, BARGE undertook a joint decision to progress the development of a harmonised in vitro bioaccessibility method (the Unified BARGE Method – UBM).
The chosen method was the RIVM method (Versantvoort et al., 2004). A schematic outline of the method is shown in Figure 1.

Figure 1 schematic outline of the BARGE unified method

The UBM has now undergone initial inter-laboratory trials (Wragg et al., 2011) and been validated against an in-vivo model (Denys et al., 2012)and has become widely accepted as the method of choice in European Countries.

In a study of the financial impact of research carried out for the Natural Environment Research Council by the British Geological Survey (Natural Environment Research Council (NERC), 2009) examples of the use of bioaccessibility testing were given that showed that:

i) In one case the assessment enabled the re-use of existing site materials as part of the land remediation process, which subsequently led to reduced costs of approximately £3.75 million. In addition, approximately 3,750 lorry trips to landfill were avoided and 105 tonnes of CO2 equivalent were saved. 

ii) In another example, BGS worked with Land Quality Management and University of Nottingham staff to save between £7-£30 million remediation expenses on one site. The more accurate bioaccessibility testing not only reassured local residents, but also allowed the stalled housing market in the area to restart.

Across England, there are an estimated 15,470 hectares of land in need of remediation. The cost of remediating this land is between £100,000-£325,000 per hectare, giving a potential market of £1.5-£5.0 billion. The research methods developed by BGS have the potential to save between £3.9 million and £12.6 million per year in remediating derelict land for development. Over a 20 year period, these cost savings are estimated to have a Net Present Value of between £55.0 million and £178.6 million.

The method is also being used on a national scale to provide bioaccessibility maps arsenic and Pb (Appleton et al., 2012a, b). Figure 2 shows an example of how a combination of the UBM test and data modelling has produced a map of the bioaccessible lead in soils in the Greater London area.


Figure 2 Estimated bioaccessible Pb in topsoils in the Greater London area (solid lines = motorways, major (A, B) and minor roads; Ordnance Survey Strategi data © Crown copyright 2012) (Appleton et al., 2012b)


Bioaccessibility testing cuts across a number of disciplines including chemistry, geochemistry, toxicology, human health and risk assessment but recent collaborative work untaken by research consortia such as the BARGE group have enabled the development of standardised testing protocols which have a direct impact on human health risk assessment and demonstrable economic benefits when used on a national and international scale.

Dr Mark Cave, British Geological Survey


Appleton, J D, Cave, M R, and Wragg, J. 2012a. Anthropogenic and geogenic impacts on arsenic bioaccessibility in UK topsoils. Science of the Total Environment, Vol. in Press.

Appleton, J D, Cave, M R, and Wragg, J. 2012b. Modelling lead bioaccessibility in urban topsoils based on data from Glasgow, London, Northampton and Swansea, UK. Environmental Pollution, Vol. in Press.

BARGE. Bioaccessibility Research Group of Europe. Cave, M. [cited November 27]. 

Denys, S, Caboche, J, Tack, K, Rychen, G, Wragg, J, Cave, M, Jondreville, C, and Feidt, C. 2012. In Vivo Validation of the Unified BARGE Method to Assess the Bioaccessibility of Arsenic, Antimony, Cadmium, and Lead in Soils. Environmental Science & Technology, Vol. 46, 6252-6260.

Hamel, S C, Buckley, B, and Lioy, P J. 1998. Bioaccessibility of metals in soils for different liquid to solid ratios in synthetic gastric fluid. Environmental Science & Technology, Vol. 32, 358-362.

Natural Environment Research Council (NERC). 2009. Bioaccessibility Testing of Contaminated Land for Threats to Human Health.

Oomen, A G, Hack, A, Minekus, M, Zeijdner, E, Cornelis, C, Schoeters, G, Verstraete, W, Van de Wiele, T, Wragg, J, Rompelberg, C J M, Sips, A, and Van Wijnen, J H. 2002. Comparison of five in vitro digestion models to study the bioaccessibility of soil contaminants. Environmental Science & Technology, Vol. 36, 3326-3334.

Paustenbach, D J. 2000. The practice of exposure assessment: A state-of-the-art review (Reprinted from Principles and Methods of Toxicology, 4th edition, 2001). Journal of Toxicology and Environmental Health-Part B-Critical Reviews, Vol. 3, 179-291. 

Versantvoort, C H M, Van de Kamp, E, and Rompelberg, C J M. 2004. Development and applicability of an in vitro digestion model in assessing the bioaccessibility of contaminants from food. RIVM, RIVM report 320102002/2004 (Bilthoven).

Wragg, J, Cave, M R, Basta, N, Brandon, E, Casteel, S, Denys, S e b, Gron, C, Oomen, A, Reimer, K, Tack, K, and Van de Wiele, T. 2011. An Inter-laboratory Trial of the Unified BARGE Bioaccessibility Method for Arsenic, Cadmium and Lead in Soil. Science of the Total Environment, Vol. 409, 4016-4030.




Keep up to date

SEGH Events

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Status, source identification, and health risks of potentially toxic element concentrations in road dust in a medium-sized city in a developing country 2017-09-19


    This study aims to determine the status of potentially toxic element concentrations of road dust in a medium-sized city (Rawang, Malaysia). This study adopts source identification via enrichment factor, Pearson correlation analysis, and Fourier spectral analysis to identify sources of potentially toxic element concentrations in road dust in Rawang City, Malaysia. Health risk assessment was conducted to determine potential health risks (carcinogenic and non-carcinogenic risks) among adults and children via multiple pathways (i.e., ingestion, dermal contact, and inhalation). Mean of potentially toxic element concentrations were found in the order of Pb > Zn > Cr(IV) > Cu > Ni > Cd > As > Co. Source identification revealed that Cu, Cd, Pb, Zn, Ni, and Cr(IV) are associated with anthropogenic sources in industrial and highly populated areas in northern and southern Rawang, cement factories in southern Rawang, as well as the rapid development and population growth in northwestern Rawang, which have resulted in high traffic congestion. Cobalt, Fe, and As are related to geological background and lithologies in Rawang. Pathway orders for both carcinogenic and non-carcinogenic risks are ingestion, dermal contact, and inhalation, involving adults and children. Non-carcinogenic health risks in adults were attributed to Cr(IV), Pb, and Cd, whereas Cu, Cd, Cr(IV), Pb, and Zn were found to have non-carcinogenic health risks for children. Cd, Cr(IV), Pb, and As may induce carcinogenic risks in adults and children, and the total lifetime cancer risk values exceeded incremental lifetime.

  • Erratum to: Preliminary assessment of surface soil lead concentrations in Melbourne, Australia 2017-09-11
  • In vivo uptake of iodine from a Fucus serratus Linnaeus seaweed bath: does volatile iodine contribute? 2017-09-02


    Seaweed baths containing Fucus serratus Linnaeus are a rich source of iodine which has the potential to increase the urinary iodide concentration (UIC) of the bather. In this study, the range of total iodine concentration in seawater (22–105 µg L−1) and seaweed baths (808–13,734 µg L−1) was measured over 1 year. The seasonal trend shows minimum levels in summer (May–July) and maximum in winter (November–January). The bathwater pH was found to be acidic, average pH 5.9 ± 0.3. An in vivo study with 30 volunteers was undertaken to measure the UIC of 15 bathers immersed in the bath and 15 non-bathers sitting adjacent to the bath. Their UIC was analysed pre- and post-seaweed bath and corrected for creatinine concentration. The corrected UIC of the population shows an increase following the seaweed bath from a pre-treatment median of 76 µg L−1 to a post-treatment median of 95 µg L−1. The pre-treatment UIC for both groups did not indicate significant difference (p = 0.479); however, the post-treatment UIC for both did (p = 0.015) where the median bather test UIC was 86 µg L−1 and the non-bather UIC test was 105 µg L−1. Results indicate the bath has the potential to increase the UIC by a significant amount and that inhalation of volatile iodine is a more significant contributor to UIC than previously documented.