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Substances with Dioxin-Like Activity in the Aquatic Environment Assessed by the CALUX Bioassay

Thursday, 17 September, 2009 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
Faculty: Science and Bio-engineering Sciences
Hermes Sanctorum
phd defence

Anthropogenic activity over the past century has generated an omnipresent level of chemical pollution.
Legislation, international conventions and new technologies have been developed during the past three
decades in order to lower or to avoid further pollution. However, emission of legislated ‘old’ and emerging
new chemicals continues to pollute the environment; moreover, some compounds are so persistent, that
they almost do not degrade.
Dioxins and related organic pollutants are environmentally and biologically stable hydrophobic chemicals
which tend to concentrate in the organic phase of soils, sediments and living organisms. In the aquatic
environment, sediments act as a reservoir for persistent organic pollutants, however, a small fraction remains
in solution and can be accumulated in aquatic organisms. These bioaccumulated compounds tend to be
biologically persistent, may induce carcinogenity and/or toxicity and leads to the increase of human
exposure and risk.
Monitoring of dioxins in the aquatic environment is rare, due to the fact that analysis is difficult, expensive
and time-consuming. Prior to this study, almost no dioxin data were available for aquatic systems in
Western Europe and Belgium in particular.
The first investigation in this study deals with dioxins and other compounds with dioxin-like activity in
marine sediments at the Belgian coast and river mouths (chapter 4). Sample extracts, both cleaned up and
crude, were analyzed using the Chemically Activated Luciferase Expression (CALUX) bioassay. The cells of
this bioassay are stably transfected with an AhR-responsive reporter plasmid, containing a firefly luciferase
gene. The transcriptional activity is a measure for the dioxin-like activity of the present compounds.
Without a clean-up step, a mixture of many compounds with dioxin-like activity was measured, resulting in
a complex CALUX signal. Therefore, interference effects between reference compounds 2,3,7,8-TCDD and
PCB 126 were investigated further in depth (chapter 5).
The fact that higher dioxin levels were found at the Scheldt and Yser mouth suggests that riverine input
represents an important contribution to dioxin pollution in marine sediments. Consequently, freshwater
samples were taken along the rivers and analyzed (after clean-up) to obtain longitudinal trends in these
rivers (chapter 6). The main objective of the work in this chapter was to estimate the potential risk these
sediments pose to the ecosystem. Also, high resolution gas chromatography analysis with mass spectrometry
was applied to all samples to determine a relationship between CALUX and chemical analysis, specific for
Scheldt and Yser risk assessment.
Sediments are important environmental sinks, however, the bioavailable dioxin fraction is present in water.
Therefore, current CALUX technology was evaluated to measure dioxin concentrations in samples of
interstitial water (chapter 7).
As dioxins may be present in low quantities, attempts were made to obtain a lower detection and
quantification limit for CALUX as the one currently available. Linear instead of non-linear regression
provides accurate and precise results as shown on a dioxin standard solution. In addition, quality control
aspects were investigated for CALUX (chapter 8).
CALUX is also able to detect PAHs in raw extracts, but a problem of quantification occurs. Therefore, a
relationship was determined between the CALUX signal of crude extracts and PAH concentrations and it
was verified if that relationship is useful for PAH risk assessment in the aquatic environment (chapter 9). It
was demonstrated that the model equations allow estimating the presence and toxicity of PAHs in an
unknown sample.