Application of modeling and analytical methods for characterizing aquatic toxicity and toxicokinetics of petroleum substances
Date
2018
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Introduction: ☐ Petroleum substances such as crude oils, solvents, and fuels are complex
materials comprised of dozens to several thousand individual constituents, whose
physicochemical properties span several orders of magnitude. This translates into a
mixture of constituents with widely variable toxicity, all present at different
concentrations. Further, various exposure systems are used to perform toxicity tests
(e.g., oiled gravel, with dispersant, etc), which can alter the results. ☐ This results in conflicting conclusions and inconsistent interpretation of
toxicity studies on petroleum substances. There is a need for a conceptual and
quantitative framework for evaluating risks and hazards of petroleum substances.
These challenges were addressed with the development of the hydrocarbon block
method (HBM), which divided up a petroleum substance into narrowly defined blocks
of constituents with similar properties. ☐ Since this initial work advances in the analytical characterization have the
potential to refine risk assessments. Development of two dimensional GC methods
(GCxGC) provides more comprehensive characterization of the chemical class and
mass distribution within a substance. The initial HBM work was extended to
accommodate this improved analytical methods for hazard assessment and risk
assessment. ☐ The modeling provides a mechanistic connection between the composition and
the toxicity. However, the GCxGC data that is commonly used in the present work is
not widely available to the general research community. Therefore, an analytical tool
has been developed to measure bioavailable hydrocarbons. This is based on the
commonly available solid phase microextration (SPME) methods using siloxane
polymer-coated fibers. These methods have been modified for measurement of
bioavailable hydrocarbons, which can be related to toxicity. The fibers provide an
analytical analog to a toxic unit (TU), which characterize the sum of the fractional
toxicity of all the hydrocarbon constituents present in an exposure. ☐ The modeling and analytical tools typically are used to analyze results of
steady state exposures. In the environment, however, exposures can vary in time and
space such as during an oil spill, or downstream from an outfall, or a contaminated
site. Only recently have time variable tools been developed for these scenarios
with limited application to oil spill scenarios. This remains an open field of
research and will be addressed in the final third of this research proposal. ☐ There are three main research themes in this dissertation proposal. These all
address the various research areas discussed above. The major research theme is
refined hazard and risk assessment of petroleum substances. The components of this
research will provide stronger scientific basis and guidance to the research community
and will support setting scientifically sound environmental criteria. ☐ The first chapter is based on a paper published in Chemosphere
summarizes an analysis of a large library of internal SPME data to validate use of
this method to measure bioavailable hydrocarbons. The SPME method provides a
holistic measurement of the overall exposure and is compared to observed toxicity for
a wide variety of substances, and test species. The SPME method is an operationally
method (e.g., equilibration time, fiber-water volumes, etc) with a mechanistic basis
using the observed correlation between the SPME measurement and toxicity. This
was done by comparing SPME measurements to predicted toxic units using the
PETROTOX modeling framework. This analysis shows a consistent log-linear
relationship between accumulation in target lipid and SPME across all substance
classes and confirms the utility of the SPME method for risk assessment work for both
laboratory and field work. The fiber-based effect levels were compared to lipid-based
effect levels using empirical measurements and single- and polyparameter models. ☐ The second chapter is published in Environmental Toxicology and Chemistry
that characterizes the role of droplet oil in aquatic exposures. This is an issue that
is important during oil spill damage assessments. Chapter one presents results of
experimental work where exposures were prepared with a gradient of droplet
exposures. The results were analyzed using the state of the art analytical tools
discussed above (PETROTOX and SPME). The main conclusion is that
dissolved hydrocarbons are the primary toxicant and that the direct impact of droplet
oil is minimal. ☐ The third chapter addressed adaptation of existing time variable damage
models for prediction of toxicity of complex petroleum substances. This project
involved a modeling analysis of existing data as well as some experimental data to
support initial model development. Most applications of this modeling framework in
the literature are for single chemicals. This work calibrated this model to available
single chemical data and evaluated the variation in these parameters against logKOW,
organism weight, and test temperature. The existing data are generally from standard
toxicity tests with constant exposures. However, observations of toxicity are collected
at intermediate time steps. These data will help establish the damage-repair
relationships for individual chemicals across a range of physicochemical properties,
which supports modeling of the complex substance toxicity data.
Description
Keywords
Applied sciences, Petroeum substances, Risk assessment