Local authorities must scrap their own rules for the use of steel slag, the infrastructure ministry has told councils, provinces and environmental agencies.

The instruction was set out in a letter sent to councils in December, according to research by Investico and NU.nl in collaboration with the Groene Amsterdammer and several regional media outlets.

Steel slag, a waste product from the steel industry, has been found at at least 200 locations in the Netherlands and has come under increasing scrutiny because it can cause environmental pollution and health complaints.

Steel slag is often marketed as a building material rather than waste and is commonly used as a cheap base layer in roads, dykes and waterways. However, the public health institute RIVM said in a report in 2023 it can release harmful substances when it comes into contact with rain or groundwater.

The environment inspectorate has also warned twice that steel slag can damage the environment, even when used according to current regulations. The national audit office has also called for action.

Following the pressure from MPs, the previous government introduced a temporary national ban on the use of steel slag last year but the ban is due to expire in early 2027 and as yet no new national guidelines have been drawn up.

Several councils have therefore already introduced their own permanent restrictions, covering steel slag and other industrial waste used in construction, such as ash from waste incinerators.

Beverwijk, for example, imposed a full ban on the use of steel slag, while nine councils in South Holland introduced permit requirements for certain construction materials.

The ministry now says such local bans or permit systems “unnecessarily hinder the sale” of the slag and create an uneven playing field across the country, Nu.nl reported. The letter also states that the current regulations for use offer “sufficent” protection.”

Some councils say they will continue to pursue local measures and say they are prepared to defend their bans in court if necessary.