Passive sampling as non-invasive monitoring of water quality
Foppe Smedes, a recognized member of the research group of Dr. Branislav Vrana at RECETOX, summarised 25 years of his research and experiences on passive sampling in the form of a dissertation thesis, which was recently defended at Vrije Universiteit Amsterdam. Dr. Smedes applied, developed and advocated a new, gentle, accurate and sustainable way how to monitor the quality of water and especially the contamination caused by hydrophobic organic chemicals.
“The work basically started with analytical quality assurance of the analysis of hydrophobic contaminants (HOC) like PCB, PAH, etc. in water and sediment. However, I 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.” explains dr. Smedes his long-term motivation.
The environment is contaminated with poorly water-soluble (hydrophobic) chemicals, such as (polychlorinated biphenyls (PCBs), hexachlorobenzene, DDT and brominated flame retardants, which tend to accumulate in aquatic organisms and eventually in humans. Long-term exposure of human to these toxic chemicals may cause various health effect, including the disruption of hormonal, immune or nervous system. The accumulation in aquatic environment differs greatly for various compartments such as water, sediment, fish or plants, which have different binding properties that also vary in time and space. To examine the level of toxic chemicals organisms are exposed to, fish is commonly considered the most relevant compartment within the aquatic environment. But the concentrations in fish depend strongly on the species of fish, sex, age and trophic level. Furthermore, variable biological factors such as lipid content, growth rate, reproduction, food supply or food chain position, affect the concentrations, reducing comparability.
In contrast, passive sampling – placing a sheet of silicone (or other polymer) in the monitored environment – adds a compartment to the environment with constant uptake properties that are not affected by biological processes. The silicone the samplers are made from, absorbs hydrophobic chemicals because of their million times or greater solubility therein compared to water. The chemical’s solubility in silicone does not differ much from that in fish lipid, and results from passive sampling can accurately be converted to an equivalent lipid-based concentration.
“Concentrations of hydrophobic contaminants (HOC) 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 document no. 32 for chemical monitoring in fish, used by Member states in implementation of European the Water Framework Directive.” says Foppe Smedes about his work.
In other words, these lipid-based concentrations of hydrophobic chemicals obtained by passive sampling varies less than in fish. Passive sampling is therefore a stable method providing data on a comparable basis enabling to investigate whether levels of poorly water-soluble chemicals in surface waters meet EU quality criteria, without the need to sacrifice the lives of a significant number of fish.
Foppe has inspired half of Europe to apply passive sampling for monitoring hydrophobic chemicals. Already in 2001 he started monitoring by passive sampling in the Netherland’s coastal waters what is still ongoing. Presently, passive sampling is worldwide applied in the Aqua-MONET program, coordinated by RECETOX center of Masaryk University in Brno, Czech Republic, where samplers are deployed all over the globe studying the spread of these hydrophobic chemicals, following methodologies developed in 2006 within the ICES-OSPAR trial survey. Passive sampling is also applied in sediment to assess remediation studies where the presence of black carbon makes it impossible to define the sediment properties necessary for risk assessment. In many rivers, lakes and coastal water in France, Germany, the Netherlands, as well as in countries of the Danube river basin passive samplers are deployed parallel to chemical monitoring in biota to build a case for replacing chemical monitoring in biota by passive sampling. In Czech Republic, passive samplers have been providing authorities with valuable information on occurrence and levels of emerging contaminants, such as brominated flame retardants, in surface- and waste-waters.
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