Bioavailability and risk assessment of complex mixtures /
Risk assessments of soils contaminated by complex polycyclic aromatic hydrocarbon (PAH) mixtures are complicated by insufficient data for both exposure and toxicity calculations. The research described in this dissertation focuses on both of these areas by identifying parameters that determine avai...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=727853261&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Risk assessments of soils contaminated by complex polycyclic aromatic hydrocarbon (PAH) mixtures are complicated by insufficient data for both exposure and toxicity calculations. The research described in this dissertation focuses on both of these areas by identifying parameters that determine availability and by evaluating the applicability of several methods for predicting mixture toxicity. By comparing the availability of PAHs from simple and complex mixtures on soil through measurements of partitioning and desorption behavior, it was shown that PAHs from complex and simple mixtures behave differently when aged at ambient temperatures. The results also indicated that aging does not necessarily lead to greater sequestration as previously observed with single compounds. An in vivo study was conducted to investigate how accurately partitioning and desorption data approximate the bioavailability of soil-bound PAHs to Fischer 344 rats. The excretion of 1-OH-pyrene in urine was monitored as well as accumulation of unmetabolized PAHs in the liver. These results were compared to measurements of partitioning and desorption. Aging did not seem to produce many significant changes in availability either in vivo or in vitro. Field samples were studied to investigate the relationship between source and availability. Partitioning and desorption were measured for PAHs from sediments impacted by shipping activities or a creosote seep. Partitioning calculations show that organic carbon (OC):water distribution can vary depending on the type of OC present at a site. Data from this chapter emphasize the importance of using site-specific data. In order to examine the applicability of several methods for calculating the toxicity of PAH mixtures, a complex coal tar mixture was fractionated to separate PAHs by ring number. Fractions were analyzed with four bioassays that represent different endpoints associated with carcinogenesis. Toxic equivalency factors (TEFs) and other methods were evaluated for their abilities to predict the toxicity observed in each bioassay. No method of calculating toxicity was able to consistently predict responses. Numerous uncertainties underlie risk assessments of complex PAH mixtures. It is hoped that these studies will help to minimize those uncertainties and serve as the basis of future investigations into the factors that determine risk following exposure to complex mixtures. |
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| Item Description: | Vita. "Major Subject: Toxicology". |
| Physical Description: | xi, 194 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 175-193). |