A national ban on pesticide spraying cannot stand alone. It takes more to ensure clean groundwater
The debate on groundwater contamination gives the impression that a national pesticide ban will solve all problems. But that is far from the case writes DTU-professor Hans-Jørgen Albrechtsen in an opinion piece in Politiken in which he highlights the key items on the Minister of Environment’s to-do list.
The government’s plans to introduce a national ban on spraying and further restrictions on nitrate in vulnerable groundwater recharge areas in Denmark are far from sufficient, Professor Hans-Jørgen Albrechtsen at DTU Sustain argues in an opinion piece in Danish newspaper Politiken. Photo: Thomas Steen Sørensen
The Danish Environment Minister, Maria Reumert Gjerding, and a wide range of parties in the Danish Parliament are back at the negotiating table to discuss a national ban on pesticide spraying.
In short, the national pesticide ban—which was the subject of a heated political debate during the spring election campaign—is intended to prevent the spread of contaminating pesticides. This applies to areas that are vulnerable to the leaching of pesticides into groundwater that is used as drinking water—the so-called SGRAs (significant groundwater recharge areas). The plan is to introduce a bill already this year. That is an important first step.
It is also important that the government plans to lower the limit for nitrate in drinking water and, at the same time, introduce further restrictions on fertilizer use in the nitrate-sensitive drinking water areas of the SGRAs.
The question now is: To what extent will the planned measures actually solve the contamination problem?
My guess is that very few Danes know the answer. Maybe the politicians don't know it either. Because the overall threat of groundwater contamination is much more far-reaching and complex than the simple public discussion we have had.
Or, put differently: If the groundwater is to be protected for the future, the Environment Minister’s to-do list is still long. Here are the most important items on the list.
The ban on pesticide spraying should apply to all
If we start where the debate has divided opinion—with the national spraying ban—then the SGRAs where the ban is to apply have so far only been fully mapped on Funen.
Once the work is completed nationwide, it is estimated that the SGRAs will account for 3.7-6 per cent of Denmark’ total land area, and they will extend across fields and agricultural land, among other places, but also private gardens, urban areas, and planted forests.
So not only farmers can be a source of contamination, even though the political debate has given that impression. The use of pesticides in private gardens and by landscape gardeners can also contribute to contamination.
That is why a pesticide ban should apply to everyone—not just the agricultural sector.
All pesticide contamination must be stopped
If we take a closer look at pesticide contamination, it does not come solely from the pesticides themselves.
One of the most commonly found pesticide degradation products in water supply wells is called DMS, and there is strong evidence that it originates from places such as cities, where wood preservatives, paint, building materials, and sealants contain so-called biocides designed to combat bacteria, algae, and fungi.
These biocides serve the same purpose as pesticides, and they seep down into the groundwater in the same way when they are washed off surfaces such as painted fences. Nevertheless, they are governed by entirely different regulations.
If we are to protect the groundwater, we must stop contamination from wood preservatives and other building materials. Specifically, so-called biocides should be banned in the same way as pesticides used in spraying.
New challenges—stay ahead of the curve
Another significant challenge in the vulnerable groundwater recharge areas is the more complex types of contamination, such as soil contamination, sewage sludge, manure, and the disposal of contaminated soil. Of course, they should also be regulated here—and, ideally, be banned entirely.
At the same time, pharmaceutical residues have recently been detected in the groundwater; therefore, measures to prevent leaks from sewers near vulnerable groundwater recharge areas are essential.
The pharmaceutical residues do not pose a threat to the groundwater—yet. But if we do nothing, the situation may change.
Finally, there is a need for ongoing updates regarding new chemical substances, such as nitrification inhibitors. These substances are used in agriculture to slow the release of nitrogen fertilizer into the soil in order to reduce leaching. These substances are not covered by current legislation, and we do not yet know enough about whether there is a risk that they will seep into the groundwater, or how they affect the groundwater over time.
That is why there needs to be ongoing political attention to this area so that problems can be addressed before they become major issues.
PFAS substances everywhere
Finally, it is worth mentioning one of the most complex and far-reaching problems we are facing: The so-called ‘forever chemicals’—known collectively as PFAS, which are almost impossible to break down in nature and in the body.
In 2024, elevated levels of PFAS substances forced Skagen Vandværk water treatment plant to shut down its drinking water wells in Skagen Klitplantage, which actually happens to be a nature preserve.
Since 2023, Fanø Vandværk water treatment plant has also been required to treat its drinking water to remove PFAS.
The most likely cause of the problems at the two coastal water treatment plants is that PFAS substances accumulate on the ocean surface, are blown ashore with ocean foam, and are washed into the soil.
This is a complex issue, as the term ‘PFAS’ encompasses more than 12,000 substances that are used, among other things, in industrial manufacturing. Some of the substances found in the groundwater come from pesticides and will be eliminated by the pesticide ban.
However, as the examples from the water treatment plants in Skagen and on Fanø show, there are other sources of PFAS contamination that have not received the attention of policymakers and therefore continue to pose a threat.
It is necessary to identify and take into account the sources of PFAS contamination, so that vulnerable groundwater recharge areas can be fully protected.
Don’t leave anything out
A national ban on pesticide spraying and nitrate restrictions are a good place to start—but these solutions cannot stand alone.
Right now, there is momentum and a willingness to protect our groundwater, and we should take advantage of this to clean up—not just when it comes to pesticides and nitrates, but across the board.
The impact of, for example, the pesticide ban will not be measurable in the groundwater for another 30-50 years, because that is how long it takes for pesticides and other harmful substances to travel down through the soil layers to our groundwater.
The longer it takes to reach a political decision, the more decades will pass before any effects are felt. So action is needed now.
My call for action to the Minister and the negotiating parties is therefore clear: Get at it. Clean it. And don’t leave anything out!
This is the path to lasting, future protection of our groundwater—and thus our drinking water. For the benefit of society and future generations.
