The Ecotox Centre, EnviBioSoil and the Swiss Soil Monitoring Network (NABO) were commis-
sioned to develop a long-term monitoring of PPP residues in soil as a task of the measure 6.3.3.7
of the Action Plan for the reduction and sustainable use of Plant Protection Products in Switzer-
land. The NABO is in charge of the exposure monitoring of Plant Protection Product (PPP) resi-
dues in the soils and the Ecotox Centre and EnviBioSoil on the development of bioindicators and
risk-based reference values for PPP residues.
This report is the first part of a two-part report on the methodology for the derivation of Soil Guide-
line Values for Plant Protection Product residues and intends to review the current state of the
methodologies used to derive risk-based reference values for PPPs. The first part will support the
second part, which is a proposed methodology to derive reference values for PPP residues in
agricultural soils from the Ecotox Centre and EnviBioSoil.
The current report can be divided in four parts. The first part of the report (section 1) intends to
give an overview of what are soil reference values, their application and use. The second part
(section 2) describes the general steps used for the derivation of soil reference values. The third
part (section 3) focuses on the description of some of the most important methodologies used in
prospective and retrospective soil risk assessment. Finally, the fourth part (section 4), intends to
compare the derivation process of some of the main methodologies by using two case studies.
This extensive review has the focus on methodologies that have been used to derive values for
PPPs and, when possible, under agricultural land use. Among all the methodologies reviewed
and presented in this report, there are two for prospective and four for retrospective risk assess-
ment that have been selected and described in more detail due to their relevance in the regulatory
context. The two prospective methodologies are the one used by the European Food Safety Au-
thority (EFSA) for the PPP authorization and the one used by the European Chemical Agency
(ECHA) for the authorization of biocidal products. The four retrospective methodologies have
been developed and applied in the following countries: The Netherlands, Canada, the US and
Australia; and have been used as reference methodologies by many other countries.
Two active ingredients used as PPPs were selected for the case studies: the herbicide diuron and
the fungicide fluazinam. The two substances contrast in terms of datasets (quality and availability
of data), mode of action and physico-chemical properties. The two prospective and the four ret-
rospective methodologies previously mentioned were applied to both datasets (diuron and fluazi-
nam). The results showed large differences between the soil protection values, mostly driven by
the inclusion or exclusion of the most sensitive group of organisms from the dataset, the approach
used for the derivation, the food chain model used (for highly bioaccumulative substances like
Fluazinam) and the assessment factors applied to account for uncertainties.
The review and better understanding of the methodologies and their feasibility after being applied
to the case studies will be used as the foundation for a proposal of a methodology to derive risk-
based reference values for PPP residues in agricultural soils in Switzerland.