Use of LD steel slag on land too risky for the environment

Signal report | 17-04-2025

The Human Environment and Transport Inspectorate (ILT) has observed that the risks of environmental damage associated with the use of Linz-Donawitz (LD) steel slag are not being properly managed in the Netherlands. In April 2023, the ILT reported that existing soil regulations weren’t effective in reducing the risk of environmental damage.

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This conclusion was based on research conducted on behalf of the ILT by the Rijksinstituut voor Volksgezondheid en Milieu, RIVM (National Institute for Public Health and the Environment). Follow-up research conducted by the ILT in the second half of 2024 into practical cases found that using LD steel slag in land-based infrastructure projects has caused environmental damage. There is also little information available about the trade flows and applications of steel slag in the Netherlands. This means that there are probably other places where the use of steel slag has or will have harmful consequences.

Steel slag is a residual material produced during steel production. These residues can be marketed as a certified building material. This signal report concerns an important type of steel slag used in the Netherlands: LD staalslakken (LD steel slag). This type is often used as a substitute for sand in land-based infrastructure projects. The use of steel slag in water is not included. The signal report focuses on the use of LD steel slag with a grain size of 0 to 90 millimetres in thick layers of more than half a metre on soil in the Netherlands. The thicker the layer, the greater the risk of environmental damage.

Steel slag in focus

The ILT conducted research to gain a clearer picture of how LD steel slag is used and traded, and what the practical consequences of this are. The ILT:

Looked at the environmental consequences at 10 locations where the use of LD steel slag was already known to the ILT at the start of the investigation.
Identified 14 locations that were not yet known to the ILT where LD steel slag is used on a large scale.
Looked at how steel slag is traded within the Netherlands and between the Netherlands and other countries.

The use of LD steel slag is permitted in the Netherlands. However, its use must comply with applicable laws and regulations, as described in the Besluit Bodemkwaliteit, BBK (Soil Quality Decree), the Regeling bodemkwaliteit 2022, RBK (Soil Quality Regulation 2022 (RBK) and the Besluit activiteiten leefomgeving, BAL (Environmental Activities Decree, BAL). Building materials in or on the soil may be used freely if they comply with the maximum composition and leaching values for building materials. LD steel slag complies with these maximum values. However, in practice, soil contamination has been found to occur as a result of the use of LD steel slag. Environmental damage occurs when LD steel slag comes into contact with soil or rainwater. This water then acquires a low acidity with an increased pH value, comparable to drain unblocker.

Environmental damage occurs at locations where the rules from BBK, RBK and BAL have been followed

The ILT has further investigated 10 locations where the use of LD steel slag is known and the rules from BBK, RBK and BAL have been followed. These 10 locations are: Spijk, Hellevoetsluis, Oude-Tonge, Strobosser Trekfeart, Falomster Faert, Feanwâlden motorway exit, Eerbeek, Aagtenpark/Aagtenbelt (Beverwijk), Haak om Leeuwarden Noord and Werpsterhoek (Leeuwarden).

The investigation shows that in 9 out of 10 cases, water with an elevated pH value is released. Previously, this caused plants to die, indicating damage to the environment. Out of the 10 locations, 2 have now been restored by completely removing or isolating, controlling and monitoring the LD steel slag. It is striking that no problems were identified at 1 out of the 10 locations. During the work, the LD steel slag was covered there due to rainfall. Based on additional research, it appears that the covering foil remained in place. This prevented rainwater from coming into contact with the LD steel slag. This means that more was done than was required by the conditions of use.

The ILT is currently conducting additional research into 14 locations where LD steel slag is suspected to have been used. Due to the ongoing investigation, these locations cannot yet be disclosed. At several of these locations, there are suspicions of environmental problems as a result of the use of LD steel slag. Finding unknown locations where LD steel slag has been used is like looking for a needle in a haystack. Organizations in the Netherlands are not obliged to report the use of LD steel slag to the government before placing it.

As a result, supervisory bodies have little information about the locations and methods of application of LD steel slag. This makes preventive monitoring and enforcement difficult. In the best-case scenario, supervisory bodies can only determine after the fact that something has gone wrong and then take measures.

Research by RIVM

Previous research by RIVM in February 2023 showed that:

Contrary to expectations, almost no waterproof layer is formed when LD steel slag is petrified. Petrification is a chemical process in which calcium carbonate is formed: carbonation.
After LD steel slag comes into contact with water, an extremely low acidity level develops, which has negative effects on the environment. Current legislation does not include any standards for acidity.
As a result of this acidity, heavy metals are released from the LD steel slag. For a number of these substances, no leaching standards are included in legislation and regulations.
The duration of leaching and the low pH value last for at least decades.
The results of the legally prescribed leaching tests appear to correspond poorly with leaching in practice.
There are no legal obligations to use LD steel slag in an isolated and controlled manner in order to mitigate risks.
There is no obligation to notify the competent authority prior to the application of LD steel slag. As a result, it is unclear at which locations in the Netherlands LD steel slag has been applied.

Legislation and regulations

In addition to the applicable laws and regulations, as described in BBK, RBK and BAL, users of the material must comply with the duty of care. However, the duty of care provision has not prevented problems from occurring.

In a recent study from 2024 (Evaluation of the regulatory framework for the (re)use of secondary building materials, in Dutch), commissioned by the ministerie van Infrastructuur en Waterstaat (Ministry of Infrastructure and Water Management), the RIVM concluded that: 'the current regulatory framework does not take sufficient account of the specific properties that different types of building materials can have. Building materials are also used in ways other than those taken into account in the standards'.

In addition, the RIVM's Bureau REACH (in Dutch) recently stated in an advisory report that LD steel slag is currently not correctly classified according to REACH. LD steel slag causes slight irritation of the respiratory tract and the material is harmful to the eyes. The impact of this is still being investigated.
REACH stands for: Registration, Evaluation, Authorisation and restriction of CHemicals. REACH is a European Union (EU) regulation on the production and trade of chemical substances. It describes what companies and governments must comply with.

Registration of trade in steel slag insufficient for risk-based supervision

It is likely that LD steel slag has been used at more locations in the Netherlands than are currently known to the ILT. LD steel slag is produced in, exported from and imported to the Netherlands. However, the import and export of steel slag is not well enough registered to provide a clear overview of the destination and quantities. For example, a shipment of exported LD steel slag known to the ILT cannot be found in international databases. In addition, the Netherlands imports large quantities of LD steel slag every year. The imports are probably similar in volume to the annual production of Tata Steel Netherlands. The question here is why the Netherlands imports LD steel slag.

Information available to the ILT on trade values shows that the value of LD steel slag varies depending on its origin and destination. Export tariffs are often more than twice as high as import tariffs.

Conclusion: the current regulatory framework is not good enough to prevent environmental damage

The ILT concludes from its investigation that the current regulatory framework for the use of LD steel slag in the Netherlands does not provide enough protection for the environment. In addition, there is no overview of locations where LD steel slag has been used in the Netherlands, as reporting is not mandatory. Amending the regulatory framework takes time. Until then, new environmental risks and problems must be prevented.