Simultaneous removal of neonicotinoid insecticides by a microbial degrading consortium: Detoxification at reactor scale.

Neonicotinoid insecticides show high persistence in the environment, and standard biological approaches such as biopurification systems have shown mostly inefficient removal of such compounds. In this work, soil pre-exposed to imidacloprid was used to obtain presumptive imidacloprid-degrading consortia. Cometabolic enrichment yielded a microbial consortium composed of eight bacterial and one yeast strains, capable of degrading not only this compound, but also thiamethoxam and acetamiprid, as demonstrated in cross-degradation assays. The biological removal process was scaled-up to batch stirred tank bioreactors (STBR); this configuration was able to simultaneously remove mixtures of imidacloprid + thiamethoxam or imidacloprid + thiamethoxam + acetamiprid, reaching elimination of 95.8% and 94.4% of total neonicotinoids, respectively. Removal rates in the bioreactors followed the pattern imidacloprid > acetamiprid > thiamethoxam, including >99% elimination of imidacloprid in 6 d and 17 d (binary and ternary mixtures, respectively). A comprehensive evaluation of the detoxification in the STBR was performed using different biomarkers: seed germination (Lactuca sativa), bioluminescence inhibition (Vibrio fischeri), and acute oral tests in honeybees. Overall, ecotoxicological tests revealed partial detoxification of the matrix, with clearer detoxification patterns in the binary mixture. This biological approach represents a promising option for the removal of neonicotinoids from agricultural wastewater; however, optimization of the process should be performed before application in farms.

Removal of Two Neonicotinoid Insecticides and Mineralization of 14C-Imidacloprid in Biomixtures.

Environmental contamination with neonicotinoid insecticides represents an issue of wide concern due to their negative effects on pollinators. The goal of this work was to evaluate the potential use of biomixtures employed in biopurification systems (BPS) to remove two neonicotinoid pesticides, imidacloprid and thiamethoxam, from wastewater of agricultural origin. The removal was assayed by quantification of the parent compounds and the detection of putative transformation products of imidacloprid by means of LC-MS/MS, and mineralization of radiolabeled imidacloprid. Two biomixtures (B1, B2) were prepared using coconut fiber, compost and two soils pre-exposed to imidacloprid (volumetric composition 50:25:25). After spiking of neonicotinoids and 228 days of treatment, the removal ranged from 22.3%-30.3% and 38.6%-43.7% for imidacloprid and thiamethoxam, respectively. Transformation products imidacloprid-urea, desnitro-imidacloprid and desnitro-olefin-imidacloprid were detected in both biomixtures. The mineralization of 14C-imidacloprid revealed DT50 (mineralization half-lives) values of 3466 and 7702 days in the biomixtures B1 and B2, respectively, markedly lower than those in the soil used in their preparation (8667 and 9902 days, respectively). As demonstrated by these findings, the high persistence of these compounds in the BPS suggests that additional biological (or physicochemical) approaches should be explored in order to decrease the impact of neonicotinoid-containing wastewater of agricultural origin.