Widespread application of engineered nanoparticles for the purpose of crop protection – termed nanopesticides – are useful for agriculture, but little is known about the potential environmental impact on agro-ecosystems and downstream ecosystems, including wetlands. Here, we assessed the impact of a copper hydroxide nanopesticide on microbial communities in two large-scale mesocosm experiments. The first mesocosm experiment simulated the realistic application of the nanopesticide to an agro-ecosystem over a 6-month growing season. The second mesocosm study tested nanopesticide effects on wetlands with chronic weekly additions of low realistic concentrations over nine months. In these experiments, we employed full factorial experimental design of two factors: (1) nanopesticide treatment and (2) a nutrient enrichment treatment (ambient vs fertilized), as nanopesticide exposures will often co-occur with fertilizer enrichment. Our primary objective was to assess and compare the impacts of a nanopesticide on microbial communities in agro-ecosystems and wetland ecosystems of contrasting nutrient statuses. We hypothesized that resource availability may have a major effect in driving the resistance and resilience of microbial function to nanopesticides. Nutrient rich systems having a greater capacity for mitigating stress than nutrient poor ecosystems, given the elevated nutrient and energy demands of dealing with toxins.
In the agro-ecosystem mesocosms, the eight measured microbial extracellular enzyme activities (EEAs) on soils were suppressed (-41 to -71%, P<0.01) within 15 days of the first nanopesticide application under ambient nutrient conditions. Complete resilience of EEAs was observed after two months, and the subsequent nanopesticide applications did not impact microbial activities. In contrast, no negative effects were detected in fertilized mesocosms, but instead a stimulation of EEAs (+20 to +51%, P<0.01) was observed after the third application at five months. In the wetland mesocosms, the microbial EEAs were decreased in the sediment and periphyton samples in both nutrient conditions after 3 and 6 months of exposure, but recovered after 9 months. Our results show that the nanopesticide decreased microbial function only on short timescales, and only in the absence of fertilization in the agro-ecosystem experiment, as hypothesized. However, in the wetland study, microbial activities were altered during the first 6 months in both nutrient conditions. These findings suggest that nanopesticides could affect downstream wetland ecosystems in oligotrophic and eutrophic conditions, but that aquatic and terrestrial microbial communities can both be resilient to this stressor over the course of a growing season.