Case study: pesticide occurrence in a stream with a history of low anthropogenic impact.

LEDA ETCHEVERRY; SPACCESI F; FANELLI S.L.; CAPPELLETTI N; LAVARIAS S; MUGNI H

Buenos Aires

Congreso; X Congreso Latinoamericano de Residuos de Plaguicidas (LAPRW 2025); 2025

Universidad Nacional del Litoral

Monitoring pesticide occurrence in the aquatic environment is ecologicallyimportant. The aim of this work was to study the occurrence of pesticideresidues in bottom sediments in a freshwater stream located in theMagdalena district, Buenos Aires province. This site is located outsidethe horticultural belt of La Plata, one of the most important productiveregions in Buenos Aires. Based on previous reports, it was considered areference site. Sediment samples were collected on site from June 2023to January 2025. Samples (20 g) were treated with copper powder andanhydrous Na₂SO₄, then extracted via ultrasonication with dichloromethane/acetone (50:50). Extracts were cleaned with Florisil® columns, evaporated,resuspended in hexane, and analyzed by GC-ECD using a TR-5MS column.The concentration of the following pesticides in sediments was determined:chlorpyrifos, endosulfan (I, II, and sulfate), λ-cyhalothrin, permethrin,cypermethrin, and deltamethrin. Detection limits ranged from 0.1 to 0.2 ng/gdry weight for organophosphates-chlorinated and pyrethroids, respectively.The banned organochlorine endosulfan was frequently detected, indicatingits persistence. On the other hand, chlorpyrifos was not detected. Whencomparing the concentrations of total insecticides, pyrethroids in currentuse showed significantly higher mean values (4.3 ng/g dw) (p=0.021) thanorganochlorines (1.1 ng/g dw). Pyrethroids such as λ-cyhalothrin, permethrin,cypermethrin, and deltamethrin appeared intermittently and such a patterncould be linked to agricultural applications. The highest residue levels wereobserved for λ-cyhalothrin (22.4 ng/g dw) in September 2024. Even thoughthe sampling strategy was designed considering seasonality, no alterationsin the patterns of insecticide occurrence were detected across seasons.This finding may be attributable to the influence of the horticultural belt andthe consistent application of agrochemicals throughout the year as part ofthe continuous crop rotation. However, taking into account the progressiveincrease in production areas as well as climate change that could influencepesticide dynamics, it could be interesting to continue monitoring to assessenvironmental risks and biodiversity impacts in the area.