RECETOX Seminar Series: Foppe Smedes - Highlights of Foppe’s thesis "Passive Sampling: effective sensing of environmental quality"
23. března 2021
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A month ago I defended my thesis at the Vrije Universiteit Amsterdam titled: “Passive
Sampling: effective sensing of environmental quality” receiving a doctoral degree. The
presentation at the defense was a 9.5 minute talk for layman but this presentation is more
highlighting the science and result of my lifelong mission, or maybe passion, i.e. the attempt
to assure that measured monitoring data are meaningful and comparable in time and space.
Although this started with analytical quality assurance of the analysis of hydrophobic
contaminants (HOC) like PCB, PAH, etc. in water and sediment, I, however, rapidly learned
that knowing the exact HOC concentration in a matrix is of limited value when properties of
that matrix are undefined and vary in time and space. In water, the freely dissolved HOC
concentration relates to solubility, a well-defined property, but we were not able to find a way
to unambiguously isolate pure water from the whole water sample.
For sediments I worked for many years on improvement of data comparability by measuring
HOC concentrations in fine-grained fractions after wet sieving. Resulting fine-grained fractions
indeed had more similar physical composition, but the material’s nature remained ill-defined
and variable. HOC concentrations in organisms depend on so many factors that obtaining
comparable samples over time and space is virtually impossible.
Although partitioning passive sampling of HOC using polyethylene or silicone sheets is
generally known as a method to measure freely dissolved HOC concentrations, for me passive
sampling is inserting a “compartment” with defined and constant properties into the
environment consequently providing data on a comparable basis.
HOC concentrations in passive samplers, equilibrated with different environmental matrices,
represent HOC levels in equal units of ng/g sampler which can be simply converted to
concentrations freely dissolved in water, equivalent concentrations in lipid, or another relevant
matrix. For HOC concentrations I am strongly in favor of conversion to a lipid basis. HOC’s
lipid-based concentrations have comprehensible units and can be compared to those for
organism (e.g., fish). The Lipid-based levels derived from water essentially represents the
external HOC level organisms are exposed to. This external exposure level includes HOC that
are metabolized and therefore neglected if relying on analyses of organisms.
The outcome of my work is a scientific confirmation that aqueous monitoring and assessment
of HOC levels can conveniently be performed by passive sampling with an equal level of
protection. The method demonstrated a lower data variability compared to HOC monitoring in
fish sampled following currently applied technical guidance 32 in the Water Framework