29 research outputs found
Recommended from our members
Comparison of the bioavailability of elemental waste laden soils using in vivo and in vitro analytical methodology and refinement of exposure/dose model. 1997 annual progress report
'The bioavailability study has made significant progress in developing in vitro methodology, and the authors have completed the time course in vivo studies. The in vitro studies have been conducted to establish the major digestive variables of concern and the values to be used in application of both the saliva/gastric juice and intestinal fluid components of a synthetic digestive extraction. In vitro and in vivo experiments have been conducted on the 575 urn particle fraction of a soil sample collected in a Jersey City State Park. Five Jersey City soil samples were first characterized for physical and chemical characteristics. Based upon the composition of the five soils, one was selected for use in the first series of experiments. The second set of in vivo studies are to be conducted on a standard NIST Montana soil. It has already been examined for bioaccessibility and availability with the in vitro methodology. A sample has been collected in Bayonne to obtain an urban background soil. Surficial soil samples have been acquired from the Savannah River Site of the DOE. These are not radioactive but are contaminated with heavy metals, e.g. arsenic, and are being analyzed by both the in vivo and in vitro methodology. During this past summer a second set of soil samples were collected at Savannah River Site. These contain levels of both heavy metals and radionuclides. Recently, a special extraction laboratory has been constructed at EOHSI, with resources made available from the organization. It will handle the extraction and measurement of the radio activity of the soil, and extracts obtained by the in vivo techniques. It is anticipated that the SRS samples collected this summer will be available for analysis in both the in vivo and in vitro systems this fall. The initial characterization will be for soil, physical and chemical content, and microbial characteristics. The samples will be analyzed for the 5 75 urn particle size fraction, and the total mass 5 250 urn in particle size. Previous experience has suggested a preferential distribution of toxic materials in the small size fraction of soils, and that these particles will define the majority of the potential bioavailabiity of the soil. Initial mass balance experiments have been completed on the in vitro methodology, and they are attempting to optimize the recovery of total mass of each metal or radionuclide present in a soil. The mass balance studies have proceeded with the use of test soils from a home in Califon that has known arsenic contamination, and a lead contaminated soil from Columbia Univ. which has been used in human feeding studies. The plans for next year intend to focus on the analysis of the SRS samples, radioactive and non-radioactive and soils from other DOE sites and pharmacokinetic modeling. The technique development has moved to the point where the applications can be made using a reproducible protocol.
Recommended from our members
Comparison of the bioavailability of elemental waste laden soils using in vivo and in vitro analytical methodology and refinement of exposure/dose models. 1998 annual progress report
'The authors hypotheses are: (1) the more closely the synthetic, in vitro, extractant mimics the extraction properties of the human digestive bio-fluids, the more accurate will be the estimate of an internal dose; (2) performance can be evaluated by in vivo studies with a rat model and quantitative examination of a mass balance, calculation and dose estimates from model simulations for the in vitro and in vivo system; and (3) the concentration of the elements Pb, Cd, Cr and selected Radionuclides present in the bioavailable fraction obtained with a synthetic extraction system will be a better indicator of contaminant ingestion from a contaminated soil because it represents the portion of the mass which can yield exposure, uptake and then the internal dose to an individual. As of April 15, 1998, they have made significant progress in the development of a unified approach to the examination of bioavailability and bioaccessibility of elemental contamination of soils for the ingestion route of exposure. This includes the initial characterization of the soil, in vitro measurements of bioaccessibility, and in vivo measurements of bioavailability. They have identified the basic chemical and microbiological characteristics of waste laden soils. These have been used to prioritize the soils for potential mobility of the trace elements present in the soil. Subsequently they have employed a mass balance technique, which for the first time tracked the movement and distribution of elements through an in vitro or in vivo experimental protocol to define the bioaccessible and the bioavailable fractions of digested soil. The basic mass balance equation for the in vitro system is: MT = MSGJ + MIJ + MR. where MT is the total mass extractable by a specific method, MSGJ, is the mass extracted by the saliva and the gastric juices, MIJ is the mass extracted by the intestinal fluid, and MR is the unextractable portion of the initial mass. The above is based upon the use of a synthetic digestive bio-fluids model that includes the saliva, gastric juices, and intestinal fluids. The system has been devised to sequentially extract elements from soil by starting with an extraction by the saliva and carrying the entire mixture to the subsequent bio-fluids for further extraction. The residence time of the soil in each extractant and the liquid to mass ratio in the gastric juices are based upon typical values known for the human digestive system. Experiments were conducted to examine the sensitivity of the extractions to changes in these major variables. The results indicated the lack of significant extraction after 2 h of residence in gastric fluid. The range of variation of the liquid to mass ratio was element dependent over the interval 100:1 and 5,000:1. The final values used for the extraction protocol were: 2 h residence time , and a ratio of 1,000:1. Details of the chemical composition of the extraction protocol are found in Hamel, 1998.