Levels of organochlorine pesticides in soils, mesofauna and streamwater from an agricultural watershed in Argentina

Pesticides are usually used in modern agriculture; however, their off-site migration and detrimental effects on terrestrial biota and nearby surface water environment are of great concern. Organochlorine pesticides (OCPs) can be found in different environmental matrices due to their persistence, representing a persistent pollution source. Soil (0–35 cm), terrestrial organisms (micro- and macro-invertebrates) and stream water samples were analysed to assess OCPs' uptake by terrestrial invertebrates and OCPs' levels in their surrounding environment. The study area involved agricultural plots from the Pampas area (Argentina) and the sampling was carried out during summer coincident with the pesticides application period. Although OCPs have been banned in Argentina, the concentration of OCPs in soils increased during the pesticide application period (2.8 ng g⁻¹) in comparison with the pre-application period (0.3 ng g⁻¹). It would be probably as a result of a flooding event, and a consequent transport of legacy pesticides adsorbed to soils particles from neighbor agricultural areas. The OCPs were highly bioaccumulated in soil mesofauna (acari and collembolans: 260 μg g⁻¹); therefore the high sensitivity to external impact combined with their importance for ecosystem functions make soil mesofauna extremely valuable for monitoring programmes. In the aquatic environment, high endosulfan concentrations (227 ng L⁻¹) were detected in stream water, being above the maximum limit for aquatic life protection. The different compositions of DDT, HCH, chlordane and endosulfan in all matrixes indicated that the residues of most compounds would be originated from historical application, and the implementation of long OCPs monitoring studies is highly recommended. As a whole, this study provides first results of OCPs levels in mesofauna of a typical intensive agricultural area from Argentina, and highlights the importance of soil mesofauna as a target group to understand the OCP migration process through the animal food chain.