CONICET | Buscador de Institutos y Recursos Humanos

Pesticides represent an important stressor for freshwater ecosystems and can impact all groups of organisms. Agriculture represents the second most important economic activity in the North Patagonian Region of Argentina and nonselective insecticides are still being used with significant implications to the quality of the environment. The aim of this study was to evaluate the risk to aquatic macroinvertebrate inhabiting in pesticide-contaminated waters channels by a tiered approach, beginning with conservative assumptions and moving towards more realistic estimates of exposure and effects. The system under study involved a 110-ha section of an agricultural area near the Neuquén River, where 82% of this area is committed to apple and pear growing. Pesticides were monitored over the pesticide application period (October to April) from 2008 to 2011 at five sites along the drainage channels and one site from an upstream irrigation channel (control site) in the studied area. Organophosphate and carbamate pesticides were analyzed in the water channels. Samples were filtered and analyzed by solid phase extraction using C18 columns. Concentrated extract quantitation was performed with a gas chromatograph (Agilent 6890), splitless mode, provided with capillary column and nitrogen-phosphorus detector for organophosphates and carbamates (slightly modified from the method 3535A by USEPA 2015). The positive detections were confirmed with gas chromatography-mass spectrometry (GC-MS), provided with a PTV injector. Physicochemical conditions (water temperature, pH, electric conductivity and dissolved oxygen) were measured before each sampling period with a multiparametric equipment. Macroinvertebrate were collected with a Surber net sampler. Samples were fixed in a 4 % formaldehyde solution and were sorted under 5x magnification before being stored in 70 % ethyl alcohol. The risk of pesticides to aquatic organisms inhabiting drainage channels was assessed using a tiered approach according to the ECOFRAM Aquatic Report. The range of concentrations (μg/L) determined for azinphosmethyl, chlorpyrifos, and carbaryl in drainage channels were from non-detected to 1.02, 1.45, and 11.21, respectively. Macroinvertebrate abundance and taxon richness in drainage channels were significantly lower in November compared to the other sampling months (October, February). The decrease in taxon richness observed in November was associated with chlorpyrifos and azinphosmethyl peak concentrations. The most remarkable changes were the decrease in sensitive taxa such as Baetidae and the increase in some tolerant taxa such as Chironomidae and Gastropoda. For all three pesticides, the acute hazard quotient exceeded the risk criteria for invertebrates. The effects of the three pesticides on aquatic organisms, characterized by joint probability curves, showed that the LC50 of 10% of the species were exceeded five and three times by the concentrations of azinphosmethyl and chlorpyrifos during the study period, respectively. However, the correlation between the pesticides concentrations and both taxon richness and abundance of macroinvertebrates at each site (irrigation and drainage channels) was indicative that only chlorpyrifos was negatively correlated with both parameters. We conclude that macroinvertebrate assemblages in drainage channels were highly affected by chlorpyrifos levels.