Evidence for soil pesticide contamination of an agroecological farm from a neighboring chemical-based production system

Abstract

The global chemical-based agriculture (CBA) production system brought social and environmental consequences such as the contamination of soils, waters, bottom sediments and food, as well as negative effects on non-target species. As an alternative, a new paradigm emerged: agroecology-based agriculture (ABA), based on ecosystem services and the reduction of chemical inputs. More and more establishments have adopted this form of production; however, they are located next to crops to which pesticides are applied. The objective of this work was to study, through the spatio-temporal characterizations of pesticides in soils, how an ABA production system can be affected by the CBA fields around it. Two sampling campaigns were conducted and soil samples were obtained from "La Aurora", an agricultural establishment located in the Argentine pampa and recognized by the FAO for its agroecological practices, and from neighboring fields with CBA productions. The samples were tested for 19 herbicides (including 3 metabolites) and 3 fungicides by UPLC-MS/MS, of which we detected glyphosate and its metabolite AMPA, 2,4-D, atrazine, acetochlor, metsulfuron-methyl, desethyl-atrazine, epoxiconazole, and tebuconazole. Three or more pesticides co-occurred in 93% and 32% of the CBA and ABA samples, respectively. Glyphosate and AMPA, with the highest detection frequency, also accounted for 90% of the total pesticide load in both systems. The maximum concentrations (μg kg−1 dry weight) in the CBA/ABA fields, respectively, were glyphosate (1268.92/98.93), AMPA (2919.17/114.01), followed by 2,4-D (38.52/31.12), and epoxiconazole (13.35/18.41). No significant temporal differences were found in glyphosate concentration within each establishment, corroborating its pseudo-persistence in CBA establishments, and establishing it in ABA field. Moreover, glyphosate was found in the ABA field more than 300 m from the limit with the CBA fields. Glyphosate and AMPA concentrations are in the order of those reported to cause sublethal and lethal effects in soil organisms. These results highlight the mobility of pesticides, as the ABA establishment is affected by its surroundings where pesticides are used, even at sites far from the interface between them. Given their higher detection frequencies and environmental concentrations in comparison to the other pesticides, glyphosate and AMPA are proposed as environmental tracers of conventional agroproductive activities.