Presence and origin of pesticide residues on twelve Dutch dairy farms and their ecological impacts

Abstract

Pesticide residues are omnipresent in the environment and may pose risks to pasture ecosystems by affecting soil biota and higher trophic levels. Previous studies detected pesticide residues in feed and dung, making dairy cows a possible vector in grassland systems. This study is the first to investigate the complete intake–excretion pathway of pesticide residues on dairy farms. Twelve dairy farms located on peat or sandy soils were selected, with a conventional or organic farming method. Complete rations as well as excreta were sampled and analysed for a wide spectrum of pesticide residues and their metabolites. Concentrates, and other grain and soy products (e.g., meal, brewers’ grain) contained the highest concentrations and diversity of pesticide residues. However, due to its substantial contribution to the total feed intake, fresh grass is an important source of pesticide residues. Farm location did not significantly impacted the amount of residues, whereas farming method did. No clear correlation was observed between dietary intake of pesticide residue and their concentration in excrements. It is suggested that type of residue, concentration, rumen biota, and cow’s metabolism could influence fate of ingested residues. Residue concentrations in dung were used to calculate a risk quotients for soil biota. In general, the risk was estimated to be low, with two samples containing a moderate risk. Nevertheless, pesticide residues excreted in dung contribute cumulatively to the overall environmental residue burden, alongside other sources such as atmospheric deposition and spray drift. These mixtures could have a larger impact than calculated with the risk quotient analysis. Compared with earlier studies, lower concentrations of pesticide residues were observed in both feed and dung. This reduction may be attributable to stricter regulatory frameworks and altered weather conditions leading to decreased pesticide application. Continued monitoring over time could provide more insides on pesticide residue exposure and associated risks.

Date of Award	Mar 2026
Original language	English
Supervisor	Frank Van Belleghem (Examiner), Lily Fredrix (Co-assessor), Prof. Dr. Ir. Nick J.M. van Eekeren (Co-assessor) & Dr. Ir. Ellen Geerlings (Co-assessor)