PFOS has been found in ditches in the residential area of Leidschenveen in The Hague. The Delfland Water Board measured between 98.5 and 13 nanograms of PFOS per liter of ditch water. According to the European standard, ditch water may contain no more than 0.65 nanograms of PFOS per liter. The consequences for public health will be made known next week. The RIVM still advises locals not to use the water for vegetable gardens, not to swim in it, and not to eat fish caught in the ditches.

In recent weeks, the board has taken 14 measurements in the ditches in the residential area and on the adjacent Forepark business park. In July, the board measured 85 nanograms of PFOS per liter of ditch water there. At the last measurement, it was no less than 260 nanograms. “Of course, we are shocked; it is just too much. We can only guess at the cause,” said a spokesperson of the water board. “Dilution and evaporation may be an explanation. It had been dry for a long time when we took the first measurement.” The ditch on the industrial estate was closed last month as a precaution to prevent the polluted water from spreading. It will remain closed.

Delfland and the Environment Agency Haaglanden are now investigating the possible sources of the pollution. “The question is whether it is an active source and there are discharges or whether it is a historical source,” said the spokesperson. It may be some time before more is known about this. Additional measurements may need to be made.

PFOS is a type of PFAS, which stands for per- and poly-fluoroalkyl substances – substances that don’t or hardly degrade. The chemicals are used, among other things, for non-stick coatings in pans, water-repellent clothing, fire-fighting foam, and cosmetics. They are associated with cancer, elevated cholesterol, and reproductive problems. In addition to PFOS, the waterboard also found other PFAS during the measurements in the ditches.

The research program Pointer recently brought the issue to light. It found that the water at Forepark contained 180 nanograms of PFOS per liter in 2021. Due to an error, the water board had not sounded the alarm at the time and took new measurements in the ditch in July. Then it found 85 nanograms, but now it found 260.

“We understand very well that locals are concerned when high concentrations of PFOS are found in a nearby ditch,” said Stijn van Boxmeer of water board Delfland. “Of course, they want to know what’s going on. And what this means for the health of themselves and their pets.”

At the request of the water board, the RIVM is mapping out the significance of the new measurement results for public health. The institute will likely publish its advice in the course of next week.

Reporting by ANP