Plant protection products and persistence of different active substances in soil in the application of different agro technologies

The study is conducted as part of the evaluation activities of the Estonian 2014-2020 Rural Development Programme (RDP) in 2022, related to Priorities 4 and 5.

Adequate functioning of soil life is essential for maintaining soil health and its functions, and it requires soil conditions that meet the needs of microorganisms. Residues of active substances in agricultural plant protection products (PPPs) have an impact on soil life and the functioning of the soil ecosystem and therefore restrictions on their use have been imposed on producers who have participated in various support measures. The main objective of this study was to verify the residue levels of the various active substances in PPPs in agricultural soils and soils under horticultural crops in different regions. In addition to the data from the current study, residue data from previous studies were used for comparison to explain possible changes over time.

In 2022, a total of 52 soil samples were taken to determine residues of PPPs. Most of the 2022 soil samples were replicates from the 2018 and 2020 research areas, designed to describe the temporal dynamics of the residues of the active substances in the PPPs. Samples were taken with a shovel from the top 10-15 cm layer of soil, and each sample was formed from 8-10 incremental samples. All soil samples were stored at -18 °C to inhibit the degradation of the active substances in the plant protection product during the lifespan of the microorganisms. To determine the residue levels of the plant protection product, a multi-method approach (QuEChERS method) was employed in the organisation's laboratory for feed and residues. The content of glyphosate and its metabolite AMPA (aminomethylphosphonic acid) was determined at the Estonian environmental research centre. The data analysis collected the quantities of residues and traces of active substances in the plant protection product identified for each soil sample (substance below the limit of quantification) and calculated the total residue levels of the plant protection product. In addition to the data from the 2022 study, residue data of the plant protection product collected over the 2015-2021 period were also used as a comparison to explain possible changes over time.

The evaluation study reveals that residues of active substances of PPPs were found in all areas (52 study areas). 175 PPP active substances were found in the soil samples analysed, 93% of which were authorised active substances and 7% were prohibited substances.

Between 2018 and 2022, the concentrations of PPP active substances per sample have decreased, as well as the number of active substances, while the number of soil samples containing residues of PPP active substances has increased. This could be due to several factors, including the ongoing advancement in laboratory techniques, which allow for more precise detection of PPP active substances, and the increasingly widespread use of PPPs in agriculture. By 2022, there was a noticeable increase in the frequencies and concentrations of glyphosate and AMPA occurrences.

Comparing the trends between 2018 and 2022, it's observed that the findings of fungicide active substances have decreased over the years, while the concentrations of herbicide active substances in the soil have increased. In 2020, herbicides accounted for 39% of all PPP residue findings, which increased to 42% in 2021 and 63% in 2022. Over the years, there has also been a decrease in the number of insecticide findings, which accounted for only 1.6% of all PPP residue findings in 2022.