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Frequent Questions
Responses to frequent questions were compiled from inquiries made either by telephone to the Bioavailability Committee hotline (toll-free 1-866-282-8622) or via mailto:BAhelp@epa.gov (please refer to the Technical Assistance Page for further information).
- What is the purpose of the bioavailability guidance?
- Where can I find the Standard Operating Procedures for the in vitro lead bioaccessibility (IVBA) assay?
- Now that I have a relative bioavailability (RBA) value for lead in soil/dust, what do I do?
- Is guidance available concerning sampling (number and location) to ensure adequate site coverage?
- Can the IVBA method be used to assess RBA of lead in any soil?
- Can the IVBA method for lead be used to assess bioavailability of phosphate amended soils?
- What is the validation status of other assays of bioaccessibility?
- What is the validation status of the bioavailability and bioaccessibility methods for other metals, including arsenic?
- What are the standard reference materials for IVBA?
- Are the values shown in the IEUBK (e.g., 30% for soil) absolute bioavailability values or relative bioavailability values?
- Are all the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) criteria presented in the guidance equally important in the evaluation of new methods?
- In terms of bioavailability research, how is the STOP after Step 2 (“Has EPA identified a validated method available for estimating site-specific BA?”) to be interpreted if it is determined no acceptable approach is available for obtaining reliable data?
What is the purpose of the bioavailability guidance?
The guidance addresses three issues:- a recommended process for deciding when to collect site-specific information on the oral bioavailability of metals in soils for use in human health risk assessments
- a recommended process for documenting the data collection, analysis, and implementation of a validated method that would support site-specific estimates of oral bioavailability
- general criteria that EPA will use to evaluate whether a specific bioavailability method has been validated for regulatory risk assessment purposes.
Where can I find the Standard Operating Procedures for the in vitro lead bioaccessibility (IVBA) assay?
The Standard Operating Procedures for the in vitro lead bioaccessibility assay may be found in Section 3 of the Estimation of Relative Bioavailability of Lead in Soil and Soil-Like Materials Using In Vivo and In Vitro Methods (PDF)(206 pp., 2.38 MB). A separate SOP is being developed and will be posted when finalized.Now that I have a relative bioavailability (RBA) value for lead in soil/dust, what do I do?
The RBA value for lead in soil/dust that is reported by IVBA assays typically needs to be converted to a predicted relative bioavailability (the TSD for lead provides the necessary equation). The IEUBK model accepts absolute bioavailability (ABA) inputs. To convert RBA to ABA, multiply the RBA by 0.5 (ABA for lead acetate in diet and water) and use that value. For example if IVBA results reported that lead RBA in the soil/dust sample was 52%, the ABA of the sample would be 26%. The value 26 would be entered into the IEUBK model in the soil and dust fields of the GI/Bio Data entry window.Is guidance available concerning sampling (number and location) to ensure adequate site coverage?
The requirements for sampling will depend on the intended objectives of the RBA assessment and site characteristics (i.e., geography, geology, and history of lead contamination of soil). Guidance documents specifically directed at sampling for RBA assessments have not been developed by US EPA; however, the existing Agency guidance on soil sampling can be found at the Soil Sampling Quality Assurance User's Guide (PDF)(267 pp., 3.61 MB). In addition, the Bioavailability Committee can be consulted for advice on sampling objectives and strategies to address factors that can impact bioavailability (e.g., minderal composition, particle size, etc.). Inquires can be directed to the Bioavailability Committee Co-Chairs BAhelp@epa.gov.Can the IVBA method be used to assess RBA of lead in any soil?
The IVBA method has been found to reliably predict RBA of lead mineral types in a variety of soil types, in samples collected from lead mining and milling sites. Detailed descriptions of the composition of these samples can be found in Appendix F of the Lead TSD: Estimation of Relative Bioavailability of Lead in Soil and Soil-Like Materials Using In Vivo and In Vitro Methods (PDF)(206 pp., 2.38 MB). Hence, the IVBA method may be used without in vivo analyses for these lead mineral types and soil compositions. Soil speciation of a representative portion of the samples is generally recommended to characterize the lead mineral types and soil compositions at a site.Although, these evaluations described in the TSD suggest that the IVBA method would be applicable to a wide range of lead mineral types and soil compositions, the reliability of the method for predicting RBA of other lead mineral types contained in other soil composition, not described in the Lead TSD, is unknown. This uncertainty should be considered (and documented) if the method is applied to soils dissimilar from those described in the Lead TSD (including mixtures with other mineral or soil types), or for which there is no in vivo verification of the IVBA test results. In the future, as additional samples with a variety of new and different lead forms and soil types are tested by both in vivo and in vitro methods, the verified applicability range of the IVBA method may be expanded.
Can the IVBA method for lead be used to assess bioavailability of phosphate amended soils?
The IVBA method for lead has not been validated for phosphate-amended soils. Thus, EPA does not recommend that the IVBA method in the Lead TSD be used for assessing the RBA of lead in phosphate-amended soils.What is the validation status of other assays of bioaccessibility?
A variety of in vitro lead bioaaccessibility assays have been reported; however, at this time only the assay described in the Lead TSD: Estimation of Relative Bioavailability of Lead in Soil and Soil-Like Materials Using In Vivo and In Vitro Methods (PDF)(206 pp., 2.38 MB) has been validated for applications in US EPA risk assessments. As described in the bioavailability guidance, other methods and associated validation data may be submitted to the Bioavailability Committee for consideration as valid test methods.What is the validation status of the bioavailability and bioaccessibility methods for other metals, including arsenic?
At this time, bioavailability and bioaccessibility assays have only been validated for lead. EPA is currently in the process of evaluating the in vitro bioaccessibility assay for predicting RBA of arsenic in soil.EPA encourages further development of new methods for lead and other metals; however, as discussed in the guidance only the information provided by validated models is recommended to be used for quantitative human health risk assessments in the Superfund program.