Experiment in Poland reveals persistence of DDT in soil

Since 1967, an experiment at the Bałcyny Agricultural Experiment Station, Poland, has compared continuous cultivation with crop rotation. The study provides information on the historical use of pesticides and their influence on soil and crop contamination. Winter rye fields were analyzed for the presence of pesticides in two cropping systems: continuous cropping (CCrye) and crop rotation (CRrye). Two levels of crop protection were also examined: herbicide and fungicide application (HF) and control treatment (CT).

Between 1967 and 2019, 58 different active substances were applied to fields. Soil and grain samples collected in 2019 were analyzed for the presence of hundreds of substances. Only DDT and its metabolites were detected in the soil. In rye grains, no pesticide residues were found.

About Bałcyny's experiment

Field experiments are essential tools for solving agricultural problems. Especially long-term ones, defined as having a minimum duration of 20 years. There are many long-term field experiments (LTEs) in the world, some existing for more than 100 years. 


Initially, LTEs were established to answer questions related to crop nutrition to maximize yields. They were later used to identify the effects of different agricultural practices on crop yields and soil characteristics.

One of the oldest field experiments in Poland was started in 1967 at the Bałcyny Agricultural Experimental Station. The original objective was to study the reaction of selected crops to continuous cultivation, compared to crop rotation. Over the years, different varieties have been compared, and fertilization and crop protection options have been investigated, providing a basis for interdisciplinary research.

The experiment in Bałcyny provides a long-term perspective on the use of chemicals in crop protection. For more than 50 years, pesticides have been applied annually or occasionally. The types of chemicals used, dosages and dates of application were recorded. In 2019, soil and grain samples were collected and analyzed for the presence of various substances.

The results showed the presence of DDT residues in the experimental soil. The use of DDT was banned in Poland in 1976, but its high persistence in soil has been confirmed by several studies. In Bałcyny, ΣDDT concentration in soil ranged from 38 to 130 µg/kg, exceeding the permissible limit of 120 µg/kg under CRrye-HF treatment. The presence of only one isomer of DDT, op,p'-DDT, and its metabolite p,p'-DDE, indicates ancient contamination, probably due to the intensive historical use of DDT.

The persistence of DDT in soil can be influenced by several factors, including sorption by soil organic matter and humic substances. The fractional composition of soil organic carbon may also explain the greater presence of DDT under crop rotation compared to continuous cultivation. The application of fungicides and herbicides over the years may also have contributed to the persistence of DDT in the soil.

Despite this, no residues of DDT or other pesticides were found in rye grains. The low absorption of DDT by plants is consistent with previous studies. The absence of residues on grains, even from those pesticides applied in the previous growing season, indicates that the pesticides were metabolized by the plant before harvest.

About DDT

Dichloro-Diphenyl-Trichloroethane (DDT - CAS 50-29-3, IRAC 3) was synthesized in the laboratory in 1874 by the German chemist Othmar Zeidler. It would have occurred during studies on the Friedel-Crafts reaction. However, it was only in 1939 (or 1940) that the use of the molecule as an insecticide was noticed. The discovery was made by Swiss chemist Paul Hermann Müller. Its efficiency and low cost made DDT quickly popular among farmers around the world.

The action of DDT as an insecticide can be summarized as:

(a) Penetration: the product can enter the body of insects through different routes, such as direct contact with the skin, ingestion through food or breathing contaminated dust.

(b) Binding to transport proteins: within the body, DDT binds to lipid transport proteins, which distribute it throughout the body, including the nervous system.

(c) Interaction with sodium channels: the pesticide binds to sodium channels in the membranes of nerve cells, interfering with their normal function.

(d) Ionic imbalance: interference causes imbalance in the entry and exit of sodium ions in nerve cells, leading to repetitive and uncontrolled depolarization of neurons.

(d) Erratic signals and convulsions: Ionic imbalance causes chaotic transmission of nerve signals, resulting in tremors, muscle spasms and convulsions in insects.

(e) Paralysis and death: Abnormal neuronal activity and intense convulsions can lead to paralysis and eventually death of the insect.

The use of DDT was banned in Poland in 1976. The high persistence of this pesticide in soils has been reported in different studies. For example, more than two decades after DDT was banned, studies in China, the European Union, and Australia have documented significant concentrations of ΣDDT in soils.

National soil monitoring in Poland, conducted in 2015, confirmed the presence of DDT or its metabolites in all soil samples examined. Considering the highest concentration of ΣDDT recorded in the country (485 µg/kg), the excess observed in Bałcyny (max. 130 µg/kg) is not large. But it is surprising when you think about the time passed between the last application and the soil analysis.

The agricultural use of DDT was banned in Brazil in 1985 (Ministry of Agriculture, Ordinance 329, of September 02, 1985).

Article by scientists who researched the subject can be read at doi.org/10.1016/j.eja.2024.127270