In 2012 the UK government issued revised statutory guidance on how local authorities should implement Part 2A of the Environmental Protection Act 1990: the ‘Contaminated Land Regulations’, or ‘Part 2A’. To help achieve a more targeted approach to identifying and managing contaminated land, the revised guidance presented a new four-category system for considering land under Part 2A, ranging from Category 4, where the risk is very low, to Category 1 where the risk is very high.
To support the new system, ‘Category 4 soil screening levels’ or ‘C4SLs’ were developed to define the boundary between categories 3 and 4.
C4SL project team
Ramboll provided toxicology and epidemiology expertise, and conducted a risk assessment for the C4SL project, along with global sustainability consultancy Ricardo-AEA as part of a team project managed by CL:AIRE, the UK’s respected independent body promoting sustainable remediation of contaminated land and groundwater. The output from the project was evaluated by a steering group made up of government departments and regulatory authorities.
A new toxicological framework
The project team drew on the Environment Agency’s existing CLEA model and supporting guidance. The overall objective was to identify changes that could be made to the existing methodology that would result in screening levels that represented a level of risk closer to the top of Category 4 for human health than the existing soil guideline values (SGVs). For four key substances (lead, arsenic, benzo[a]pyrene and hexavalent chromium), significant new and complex toxicological and epidemiological data that indicated lower toxicological parameters had been published since the development of the SGVs.
A fundamental requirement of the work to derive C4SLs was the need to combine a robust understanding of the toxicological response data with the context of the exposure model used. For the C4SL project, benchmark dose approaches were used within a new toxicological framework to deliver more quantitative toxicological information than has been used in previous contaminated land risk assessment.
The project team submitted the toxicological framework for review by the UK Committee on Toxicity, an independent scientific committee that provides advice to the government on matters concerning the toxicity of chemicals. The committee agreed that the broad approach is reasonable for use in the context of providing a toxicological basis to define C4SLs.
In order to ensure public safety, a priority throughout the project was to make sure that scientific principles, evidence and best practice always underpinned the work in order to assure public safety. This was achieved by using sound contemporary science with transparent risk management and policy decisions to help industry move forward with confidence. The project successfully derived six C4SLs for arsenic, cadmium, chromium VI, benzene, benzo(a)pyrene and lead.