Today, fluorine atoms occur in numerous compounds that are created in the laboratory. If they get into our drinking water, they can pose a danger to humans. BAM has developed a method for the detection of these critical substances.
Fluorine is a useful element: as fluoride it strengthens our tooth enamel and bones and is an essential trace element in the human body. But fluorine can also be very harmful: in a highly concentrated form it makes the bones brittle. Plants that have absorbed too much fluoride lose their leaves.
"As with all chemical substances, it is a question of dose," explains Björn Meermann, BAM elemental trace analyst. Together with his team, he has developed a method for detecting organically bound fluorine in rivers and lakes.
The problem is not so much the element’s natural occurrence, but that fluorine is also a kind of quick-change artist - in the appearance of so-called fluorine species. Fluorine atoms are nowadays incorporated into many compounds in laboratories around the world because they can favourably influence the properties of other molecules.
Everything is a cycle
Fluorine atoms have a repellent effect in the inner coating of fast food packaging: they prevent the fat from permeating through the cardboard to the outside. They let the rain roll off our outdoor jackets. Fluorine atoms can also be found in about a quarter of all pharmaceuticals such as antidepressants and antibiotics. They prolong the half-life period of molecules and thus ensure that the active medical ingredient is available to the body for a longer period of time.
"What is problematic about many of these man-made compounds is that they are persistent. This means that they are difficult to break down once they have been released into the environment," says Meermann. And there are many emission pathways to do this: coffee cups are ground up during recycling using a lot of water that flows to the wastewater treatment plants. Discarded outdoor jackets can end up in landfills. Decomposition products of medicines reach the wastewater via human excreta. Large wastewater treatment plants, where microorganisms break down harmful substances, are not, however, designed to intercept each of the numerous fluorine compounds. This means that many of them can be flushed into the groundwater. If fluorine compounds reach areas where drinking water is extracted, the issue becomes problematic.
Detection limits shifted downwards
Until recently, scientists have mainly utilised two methods to detect fluorine compounds: they either use a target method which aims to detect very specific fluorine compounds that are considered dangerous. "However, the list only covers part of what is now circulating in organically bound fluorine," explains Meermann. "In addition, the numerous compounds created in the laboratory can break apart and be transformed into new molecules with unknown properties."
In the second method, researchers determine a sum parameter which is the total amount of organically bound fluorine in a water sample. Here, too, they only find what they are looking for and unknown compounds can fall through the net. However, the process has shortcomings: "The common analytical method requires many steps and is therefore susceptible to errors and measurement inaccuracies," explains Meermann. "I was looking for a way to shorten the process."
A better tool for the job
The BAM chemist uses a method that previously served to detect metals in the environment. His measuring device has a special light source and a high-resolution spectrometer that can also detect fluorine in this combination. The method is significantly faster and finer than the previous method. "We have been able to lower the detection limits for organically bound fluorine by a factor of about 20 and thus can detect compounds that have so far slipped through the net," explains Meermann. He and his team can even detect a few billionths of a gram of a critical fluorine substance in a litre of water.
Meermann and his team colleagues plan to use the method to investigate organically bound fluorine in waste from the paper industry, galvanic factories and sewage sludge. They want to provide authorities responsible for supervising lakes and rivers with a better tool to prevent fluorine, the quick-change artist among the elements, from entering the human body in harmful concentrations.