RIVM has developed an approach which allows human health risks of vegetable consumption from contaminated sites to be assessed. A tiered approach was used to guarantee the scientific basis and efficient use in practice. The underlying principle is: simple when possible and complex when necessary. If the risk can be eliminated in an early step, the assessment can be stopped. If not, assessment continues in the next tier, becoming more site-specific with each tier. This results in a more realistic, but also more time-consuming, assessment. The approach consists of four tiers that are laid out as follows. Tier 0, which precedes the calculation and measurement tiers, investigates the possibilities for experiencing adverse human health effects due to vegetable consumption. Subsequently, the soil concentrations of pollutants are measured in Tier 1 and compared with so-called Critical soil concentrations (for which vegetable consumption from contaminated sites is safe). Tier 2 offers the possibility for a detailed assessment of the site-specific risks for human health on the basis of calculation. Finally, Tier 3 shows a standardized measurement protocol. This protocol offers guidance and advice on the type and amount of crops that can be sampled in the field, thereby providing an indication for human health risks.

The National Institute for Public Health and the Environment has derived Reference Values for maximum permissible soil pollution. The Netherlands Ministry of Housing, Spatial Planning and the Environment (VROM) used these values as a basis for the maximum values for soil pollution. The ministry set these values down according to a proposal for an update of soil policy and the Soil Protection Act in 2003. Reference values refer to allowed concentrations of pollutants in soil, depending on the land use. The soil concentrations of pollutants with values below these concentrations meet all the requirements. The risks for humans, the ecosystem and agriculture were analyzed as critical factors, with risk thresholds derived for different types of land use, such as playgrounds, gardens, and agricultural and nature areas. Furthermore, an accelerated procedure was used to compile a complete list of reference values in 2006. The RIVM used state-of-the-art knowledge to complete the 'old' knowledge for information on toxicity of substances; figures were used where knowledge gaps occurred. A recommendation for the coming years is to address resulting inconsistencies in the list of reference values.