13. November 2026, Topic: Soil Ecotoxicology Risk Assessment

Guideline values for plant protection products in soils: A new tool for Swiss agriculture

How can we determine whether pesticide residues in agricultural soils pose a risk to soil fertility? The new risk-based soil reference values can provide an initial guide in this regard. The proposed values are based on ecotoxicological data and are intended to serve as screening values to identify sites of concern.

In 2017, the Federal Council adopted its action plan on risk reduction and the sustainable use of plant protection products. One of its objectives is to ensure that the use of plant protection products (PPPs) has no long-term impact on soil fertility. To verify this, PPP residues in agricultural soils are to be monitored in future and their impact on soil fertility assessed. This requires, on the one hand, risk-based reference values against which measured residues can be assessed, and, on the other hand, suitable bioindicators for recording effects in the field.

The Ecotox Centre is developing these two elements in collaboration with EnviBioSoil. The focus is on soil organisms and seedling emergence of crop plants, as these groups of organisms are crucial for soil fertility and are most likely to be directly affected by residues. As risk-based reference values, the project team has proposed so-called Soil Guideline Values (SGVs), which are determined on the basis of ecotoxicological data. SGVs are intended as screening values for PPP residues, above which negative effects on soil fertility cannot be ruled out.

Selection and assessment of substances

The researchers have determined SGVs for the majority of the approximately 80 PPPs detected in the Swiss Soil Monitoring Network (NABO). The SGV values range from 0.037 μg per kg of soil for atrazine to 8,500 μg/kg for metalaxyl. For most PPPs, so-called ad hoc SGVs were derived, based exclusively on the regulatory data. A number of prioritised PPPs were assessed with particular rigour, drawing not only on regulatory data but also on scientific literature data. The researchers assessed the data quality of the ecotoxicological data using a standardised procedure and only considered data classified as reliable and relevant. As numerous PPPs are detected in the soil at each site, the individual SGVs were subsequently integrated into an approach for assessing the risks posed by mixtures of PPPs.

Limitations of the data

Uncertainties in the SGVs due to data gaps were accounted for using safety factors, as screening values are intended to be precautionary in nature. The bioavailability of PPP residues was taken into account by normalising them to a standardised organic carbon content in the soil; however, questions remain as to the extent to which ageing in the soil further influences their bioavailability. For five substances – fenarimol, orbencarb, pencycuron, pyrifenox and zoxamide – no SGVs could be determined, as no regulatory data are publicly available.

Practical application

The SGVs are intended as screening values to assess the risk from PPP residues in winter, prior to the first PPP application. For sites where SGVs are exceeded, there is a potential risk for effects on soil fertility in the field; in this case, a more detailed assessment including bioindicators is recommended. Ideally, such investigations should be carried out over a longer period of around five years in order to identify long-term effects as well. The SGVs thus provide a methodologically sound initial filter to identify those sites where a more detailed investigation of the effects is warranted.

Publication

Junghans, M., Balk, F., Campiche, S., Lauber, E., Renaud, M., & Ferrari, B. J. D. (2026). Soil Guideline Values – proposed screening values for the integrated assessment of plant protection product residues in agricultural soils. doi.org/10.55408/eawag:37541 , Institutional Repository

Translations into German and French: see the project website.

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