Abstract

Steel slag is a by-product of the steel production process. It resembles stone. In the Netherlands, large quantities of this material are used in construction. Among other things, it can serve as a substrate for roads or be used to fill in or raise the level of dykes, noise barriers and landfill sites. When steel slag comes into contact with rainwater or groundwater, hazardous substances found in the slag leach into that water. Virtually every kind of heavy metal imaginable then makes its way into the soil or surface water via this water, known as leachate. The leachate also has an extremely high pH value. Both effects are harmful to the environment.

The extremely high pH value disrupts chemical, biological and ecological processes in the soil and in surface water. Sandy soils are most vulnerable to changes in pH value, because they are less able to neutralise such changes. All these environmental effects may last for decades.

This is the outcome of a literature study commissioned by the Human Environment and Transport Inspectorate (ILT) and carried out by RIVM. The effects are especially evident when larger quantities of steel slag have been used. The study also makes it clear that the environmental risks for the impact remains unknown.

In addition, the concentrations of hazardous substances measured in leachate under laboratory conditions differed from those measured at sites where the steel slag was actually used. The laboratory tests were developed on the assumption that steel slag would be used in thinner layers and lesser quantities than is currently the case in practice. It is therefore vital to investigate whether the tests required by law for such use are still fit for purpose.