Exposure and toxicity of mixtures of plant protection products in the environment under Norwegian conditions (HerbRisk).

The impact of complex mixtures of plant protection products (PPPs) in the environment is often unknown and approaches to determine the combined effects are poorly developed. The NIVA project HerbRisk contributes to the development of predictive modeling approaches for risk assessment of complex mixtures and to implementing the use of these in risk assessment of PPPs in ecologically relevant exposure scenarios in Norway.


A vast number of different PPPs are used in Norwegian agriculture to protect the crop against diseases, fungi, pests and invasion of other plant species. The Norwegian Food Safety Authority is responsible for approval of PPPs, and in 2010, 113 active compounds were approved for use. The environmental concentrations of several of the most used PPPs in water recipients in the agricultural areas are monitored through the Norwegian Agricultural Environmental Monitoring Programme, JOVA, and it has been shown that several PPPs temporally and spatially co-occur in rivers within the catchment area from different types of agricultural activities.

There is little knowledge of how PPPs act together in mixtures in the Norwegian environment, and environmental risk assessment are mainly performed on individual compounds. Even though the environmental concentrations of pollutants may be below the reported no observed effect concentrations (NOECs) and 50% effect concentrations (EC50s), the presence of several similarly acting compounds is expected to cause effects through combined toxicity at concentrations below their individual effect threshold (Kortenkamp, 2008). It is now generally accepted that compounds causing the same type of effect or having a similar mode of action (MoA) can be additive when occurring together in a mixture. The combined effects of chemicals can be studied by application of the two widely used prediction models for additive effects, the concentration addition (CA) and independent action (IA) prediction models. These concepts were first introduced by Loewe and Muischnek (1926, CA) and Bliss (1939, IA), and are based on the assumption that the compounds in a mixture affect the same endpoint in the same direction, and that the compounds act by similar (CA) or dissimilar (IA) MoA.

Due to increased focus and knowledge on combined effects over the last years, several approaches for how to include assessment of combined effects in the environmental risk assessment have been proposed. One of the most recent publications is by Backhaus and Faust (2012) who proposes a two tired approach that incorporates the concept of concentration addition (CA) and independent action (IA) for environmental risk assessment of combined effects using available baseline data (EC50s), predicted or measured environmental concentrations (MEC and PEC respectively) and predicted no effect concentration (PNEC) values.

NIVA is addressing the complex issue of hazard and risk assessment of mixtures in the Norwegian Food Safety Authority funded project “Exposure and toxicity of mixtures of plant protection products in the environment under Norwegian conditions (HerbRisk)”. The project, which is financed by the “action plan for reduced risk for use of plant protection products”, has been conducted in collaboration with Bioforsk.


The objective of the HerbRisk project was to quantify the risk for effects of environmentally relevant mixtures of plant protection products (PPPs) under ecologically relevant aquatic exposure scenarios in Norway.

A combination of data compilation, predictive mixture risk assessment and expert judgment aim to assess the risk of complex PPP mixtures, identify relevant risk scenarios and potentially contribute to better management of PPP use in Norway. In the current approach, concentrations of PPPs in the environment were collected from the Norwegian Agricultural Environmental Monitoring Programme JOVA, whereas effect data for algae, crustaceans, fish and water plants were collected from the pesticide properties database (PPDB).

The collected data was used to calculate risk quotients for the PPP mixtures at different locations (Backhaus and Faust, 2012). The resulting risk quotient (RQ) based on the most conservative approach (RQMEC/PNEC) was determined and species-specific RQs using the sum of toxic units (RQSTU) were calculated in cases where initial assessment identified a risk (i.e. RQMEC/PNEC> 1).

>> Further reading: Pesticide cocktails cause environmental risk


Backhaus, T., Faust, M., 2012. Predictive environmental risk assessment of chemical mixtures: A conceptual framework. Environmental science and technology 46, 2564-2573.

Bliss, C.I., 1939. The toxicity of poisons applied jointly. Ann. J. Appl. Biol. 26, 585-615.

Kortenkamp, A., 2008. Low dose mixture effects of endocrine disrupters: implications for risk assessment and epidemiology. Int. J. Androl. 31(2), 233-237.

Loewe, S., Muischnek, H., 1926. Über Kombinationswirkungen I. Mitteilung: Hilfsmittel der Fragestellung. Naunyn-Schmiedebergs Arch. Exp. Pathol. U. Pharmakol. 114, 313-326.

Last updated 27.01.2021