Necessity is the mother of invention, and the quest of one marine chemist to measure copper levels in Atlantic coastal waters has led her to some unusual working arrangements, including an impromptu lab in a van. Her experiments' results suggest trace copper levels can provide important information about local water mixing patterns and contamination.
"In seawater there are loads of different trace metals in very small concentrations," says Sarah Knight, a PhD candidate in the department of earth and ocean sciences at NUI Galway. She has spent several years analysing minute amounts of copper in seawater off the west coast of Ireland, the first survey of its kind here.
Copper is nutritionally important to many marine organisms and much of it is bound tightly to organic materials in the water, says Knight. The metal is present in the earth's crust so it tends to be more abundant in coastal regions. "Copper is higher in water that would have been in recent contact with the land, and also freshwater," she says.
Human activity can also play a part in determining copper levels in water masses - the metal is used in plumbing and also as an anti-fouling agent in paint on the hulls of boats, she adds. "You can use copper in surface waters to trace contaminated plumes of water, whether it is river plumes or waste-water run off."
Knight took samples of surface seawater on a number of sea-cruises, including a nine-day stint aboard the Marine Institute's research vessel Celtic Voyager, collecting data from waters between Galway Bay and the Shannon Estuary. The main issue was to avoid sample contamination. "The ship is metal and the dust floating around is full of all kinds of metals, so a sample could easily get contaminated," she says. "So we set up a system where we could do all of the sampling, sample pre-treatment and analysis there on the boat. We could do it all in real time."
The closed system sampled surface water several metres out from the boat's hull to avoid potential contamination, then pumped the water back to an onboard wet-lab system where the sample was filtered and then UV-treated to break down organic material and release any bound copper. Then using a technique called voltammetry, Knight measured a current as it passed through the sample to determine how much dissolved copper was present.
However, funding ran out for time at sea so Knight resourcefully made alternative arrangements. She modified the sample-collecting rig, attached it to a buoy and threw it off the ends of piers at different coastal locations to monitor copper levels over tidal cycles. The water samples pumped back to a van that she had converted into a roving wet-lab complete with plastic coating and air filters.
When Knight analysed copper levels from the collection points she found that at a local level they can add depth to the baseline characteristic information about water signatures. While the standard way to profile a water mass is to look at its salt content and temperature, adding in copper data to those measurements creates a different picture, says Knight. "It picks out some really interesting features," she says, adding that she found some unexpected results, including a high copper signature behind the Aran Islands. "What I concluded is that you could use copper concentrations to pick out individual signatures in dynamic coastal regions," she says.