Barge Special Session

Consoil 2008 Proceedings from Barge Special Session Milan 3-6 June 2008

C. Gron: Bioaccessibility and leaching tests in site risk assessment

As it is not possible to estimate the real risk to human health or water from the total concentration of contaminants in soil, the author described the use of bioaccessibility testing and leaching experiments to provide a better understanding of the associated risk.

To achieve this, a battery of tests is applied: Inorganic contaminant bioaccessibility: fasted state of a child, simulating mouth, stomach, intestinal compartments and analysis by ICP-OES. PAH bioaccessibility: fed state of a child, simulating mouth, stomach, intestinal compartments and analysis by GC-MS after SPE Metal leaching: by batch extraction at a L/S ration of 2 using 1mM CaCl2 and analysis by ICP-OES PAH leaching: column extractions at a L/S ration of 1.0-1.02 using 5mM CaCl2 and analysis by GC-MS after LLE.

Consideration was given to the adaptation of different test methods for application to different contaminants.

The author asked what other information was needed in order that bioaccessibility and leaching tests become a routine part of the accepted practice of contaminated land assessment:  Reliable and robust bioaccessibility and leaching methods for inorganic and organic contaminants  Technical performance guidance which includes Standardised methods, proficiency tests and certified reference materials  Agreement in some points of compliance and accepted standard scenarios in the assessment of risk from contaminated soil  Regulatory implementation of bioaccessibility methods through acceptance of data and guidance documents etc.,

C. Collins : Bioaccessibility of organic pollutants in the human gut

The objectives of the presented work were to assess both the degradation and release of PAH in the compartments of the gut and the impact of PAH on the gut microfolora community composition and also to develop robust model to assess the fate of such compounds in the gut.

The presented gut model system included stomach and small intestinal phases but additional colon phases simulating the proximal, transverse and distal colon. For the colonic stage of the gut model, the system was inoculated with human faecal bacteria. The processes occurring throughout the system were described; breaking down of large molecules and adsorption of lipid soluble compounds in the stomach, the adsorption of food in the small intestine and the break-down of recalcitrant compounds in the colonic phase.

One problem encountered in the presented study was the loss of PAH when the system was operated in its ‘open vessel’ mode. This problem was shown to be a result of gas flow rate in the system, volatilisation and microbial degradation. Initial results from testing the ‘closed vessel’ system showed a reduction in PAKH loss.

P. Nathanail: Uses and abuses of bioaccessibility in risk assessment

The author reminded the audience that bioaccessibility testing is currently routinely used in UK for As, Ni, Pb. However, huge uncertainties remain in the area of bioaccessibility. A review of the uses and abuses of bioaccessibility data was presented and summarised in Table 1, which forms an integral part of a practice note for the application of bioaccessibility data in UK risk assessment.

Table 1 A Baker’s Dozen Misuses of bioaccessibility-based estimates (after Nathanail 2008) Misuses Commentary 1. Insufficient samples A minimum of 10 samples per averaging zone is typical in order to gain an adequate appreciation of the variation in bioaccessibility. 2. Use of peer review literature rather There is not necessarily a relationship between literature than site specific values values and site specific bioaccessibility. 3. Application to non ingestion The PBET seeks only to simulate the direct oral ingestion pathways pathway. 4. Application to other substances Inappropriate appreciation of substance specific bioaccessibility. 5. Lack of line of evidence Bioaccessibility test results may not be compatible with geological history, geochemistry. 6. Mixing samples from different soil/ Bioaccessibility varies with medium. ground types 7. Poorly documented test procedure Bioaccessibility tests are empirical and interpretation should be based on the specific method applied. 8. Analysis of samples not Bioaccessibility varies with total concentration but the representative of concentrations of relationship is not necessarily either linear or positive. concern 9. Inappropriate use of statistics Statistical summaries of bioaccessibility tests may result in discordant matching of bioavailability estimate and total concentration 10. Application of summary (average) The relationship between total and bioaccessible or single values to a dataset concentrations is not necessarily linear. 11. Use of wrong test Results are not relevant to the risk estimation. 12. Lack of details in reports Reviewer cannot evaluate the robustness of the risk estimate and the compliance of the risk evaluation with the specific legal context. 13. NOT using bioavailability at all Over conservative risk assessments and unnecessary remediation

Nathanail, C.P. 2008. Professional Practice Note: Reviewing human health risk assessment reports invoking contaminant oral bioavailability measurements or estimates. CIEH, London (in prep)

H. Roussel: Assessment of the Cd, Pb and Zn oral bioaccessibility in urban topsoils near two smelters in Northern France.

The author presents a case study involving two smelter impacted soils located in North of France (Metaleurop – Lead smelter and Umicore – Zinc smelter). Twenty-seven urban soils, from lawns and kitchen gardens were sampled, 20 soils around Metaleurop, 7 around Umicore, because it was found that urban soils used for recreational purposes and vegetable production were potentially contaminated. The primary aim of the work was to evaluate the bioaccessibility of Cd, Pb and Zn in urban soils for human health risk assessment. The bioaccessibility testing was carried out using the Unified Barge Method (UBM), in addition to total analysis of the soils, CEC and organic carbon data collection and other soil physico- chemical properties. The results showed that:  There was no clear differences in the bioaccessibility between the two smelters  Bioaccessibility appears to be positively correlated to total concentrations, cationic exchange capacity, clay content and pH, but not correlated to carbonates.

The presentation highlighted the importance of understanding the source and the solid phase distribution of the contaminants at a given location.

A. Oomen: The bioavailability of lead from soils taken from Dutch urban cities: can a generic bioavailability factor be derived for these specific soils ?

The overall topic of the presentation was to provide insights into a testing regime used to derive an ‘average physiological state’ correction factor for lead bioaccessibility in the Netherlands. The study compared lead bioaccessibility measurements for 45 Dutch city soils using the RIVM in vitro method, under both fasted and fed conditions, as in the Netherlands the use of average physiological conditions in human health risk assessment is encouraged. It was reported that currently in the Netherlands, the ratio between bioaccessibility for fasted over bioaccessibility for fed, for deducing a correction factor is advised for taking into account bioaccessibility in human health risk study assessment.

The results of the research showed that: A smaller difference between the bioaccessibility of lead from soils under fasted and fed conditions.  An increase in the ‘average physiological state’ correction factor for lead, from 0.855 (based on previous research, 11 soils) to 0.922 (based on current research, 70 samples)  The new dataset provides a better foundation of the average physiological state correction factor, leading to the potential reduction in conservancy used by Dutch policy makers.

V. Paquin: Bioaccessibility of Cr at a former Tannery Site

Bioaccessibility measurements in site specific assessment over Canadian sites was described including the exposure dose calculations to derive Hazard Quotients (HQ) and Incremental Lifetime Cancer Risk (ICR) in Canada. Guidelines are available for both human health and environmental receptors in Canada, with respect to human health, the maximum exposure is calculated and used in the resulting risk assessment, whereas for the environmental guidelines, the most sensitive receptor to exposure is used.

The regulatory acceptance of bioaccessibility in Canada was described, whereby Health Canada considers the use of this form of evidence on a site-by-site basis for the relevant environmental media. To be accepted the data package should include: testing on a range of particle sizes should be tested e.g., <250 um, <125 um, <45 um and liquid to solid ratio’s; that the solubility of the contaminant is not confounding the bioaccessibility and that the measured bioaccessibility must be adjusted to relative to the (likely) bioavailability of the contaminant in the key toxicological or epidemiological study upon which the TRV (e.g. tolerable daily intake or cancer slope factor) was derived.

The presentation described the application of different test types to the same soils (some of which had been previously assessed by other workers) in order to evaluate the reproducibility and repeatability of the different available methods.

A case study was presented for a brownfield site, a former tannery and lead smelter. The total Cr concentrations were assessed to be up to 50,000 mg kg-1 with lead concentrations of up to 20,000 mg kg-1. Using a physiologically based extraction test to determine the bioaccessibility, it was found that the average Cr bioaccessibility was 6 % and the average Pb bioaccessibility was 77 %. The results indicated that the risk from the site to posed to two different receptor groups (toddlers and adults) was reduced when bioaccessibility data was incorporated into the risk assessment.

Mark Cave: Mapping and Modelling of Arsenic Bioaccessibility in the Tamar valley in Southwest England.

The UK soil guideline value for As is 20 mg kg-1, when considering residential land uses and allotments. In the Tamar Catchment in the south-west of the UK, areas of strong mineralization exist and a large proportion of these areas which are influenced by the underlying geology exceed the SGV value. Selected site bioaccessibility testing was coupled with geostatistical analysis of total element data for the area, to provide probability maps for the Tamar Catchment in order to predict where the bioaccessibility would exceed the SGV. Using a ‘lines of evidence’ approach, the author described the use of a self modelling mixture resolution approach, applied to the analysis of 467 soils analysed for the total concentration of 44 elements, to determine the distinct physical-chemical instrinsic soil geochemical components that were the sources of the bioaccessible As present (determined on c. 100 soil samples collected from the area).

 The results showed that 56% of the As bioaccessibility was explained by the presence of a mineralised soil component, and organic component and an Fe oxide coated sand.  The As associated to crystalline Fe oxides was not bioaccessible

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