An article from NIVA - Norwegian Institute for Water Research
Ferryboats as mobile lab assistants
By attaching sampling devices to ferries and ships on regular routes around the globe, researchers can detect the smallest amounts of environmental contaminants.
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Environmental contaminants are often difficult to measure in seawater because they are extremely diluted. Norwegian researchers have developed a new method to detect pollution.
“We place small extraction devices, so-called passive samplers, in water and these absorb and store substances from freshwater and seawater,” says Ian Allan, researcher at the Norwegian Institute for Water Research (NIVA).
When samplers are in contact with water for a sufficient amount of time, they trap these substances effectively enough to enable measurement of extremely low levels.
But the researchers had an even brighter idea. Instead of stationing these devices at one sampling site for weeks or months, they could be pulled through the water.
“By towing the samplers through the water at high velocity, we can achieve even lower detection limits,” says Allan.
Unconventional research vessels
The method will also reduce time spent on colleciting samples. In turn, this makes it possible to use ferries and ships which run on fixed routes when collecting the samples.
“We are already carrying out experiments on ferries where we have equipment installed for monitoring water quality,” says Allan.
Seawater is pumped in persistently while the ship is underway, and the water is analysed continuously.
“Now we need to find a way to place the passive samplers outside of ships to measure the specific environmental pollutants that we're interested in,” he says. “This way we can measure concentrations of different environmental contaminants, even in parts of the ocean that are not very polluted.”
In principle this technology can be installed onto ships on fixed routes, along the coast or across the vast oceans, and then obtain information on background levels that has been inaccessible so far.
Tiny amounts are vital
“Most of the substances we deem as environmental contaminants are man-made and they pervade nature in very low concentrations,” Christopher Harman point out. He is a research scientist at Norwegian Institute for Water Research and a colleague of Allan.
Many of these substances are persistent, since they do not degrade easily and can spread over long distances and to areas where they are not necessarily expected.
“Now we want to determine the quantities of a number of these substances in the environment − even if they are only found in small concentrations. We need to know these so-called background values to evalute pollution in other areas,” explains Harman.
Passive samplers
Several kinds of passive samplers have been developed over the last two decades. They are often constructed with a thin polymeric membrane, such as polyethylene or silicone, or gels that only admits certain types of chemical compounds.
The samplers are commonly placed in a cage onto a rig or hung from a rope for period of weeks to months to collect a sufficient amount of substances for analysis.
Many man-made contaminants can potentially damage organisms in the environment, even in small doses. For instance minor concentrations of tributyltin (TBT), which was formerly used in paint on the hulls of boats, were found to interfere with the reproduction of beach snails.
It is therefor necessary to be able to measure very low concentrations of such substances. The analytical equipment used in quantification of these chemicals is under constant development, making it possible to reduse our limitations when it comes to analysing.
Speed does the trick
A certain velocity is required to enable the absorption of these chemical substances at a high rate into a polymeric passive sampling device.
The results were encouraging when the researchers tried towing experimental samplers through the water to see if they could measure lower concentrations.
In collaboration with researchers from the Water Research Institute in Slovakia and RECETOX in the Czech Republic), the Norwegian researchers will now focus on deploying these samplers during a research cruise on the Danube River.
“We can for instance measure chlorinated biphenyls and brominated diphenyl ethers down to concentrations of a single picogram per litre of seawater. This is the equivalent of adding 0.0025 mg of the substance to an Olympic-sized swimming pool,” Harman explains.
Scientific links
- Allan and Harman: Global Aquatic Passive Sampling: Maximizing Available Resources Using a Novel Exposure Procedure, Environmental Science and Technology, 2011, 45 (15), doi: 10.1021/es2021022.
- Allan et.al.: Mobile passive samplers: Concept for a novel mode of exposure, Environmental Pollution, Volume 159, Issue 10, October 2011, doi:10.1016/j.envpol.2011.06.039.
