Seasonal Dynamics of Glyphosate and AMPA in Lake Greifensee: Rapid Microbial Degradation in the Epilimnion During Summer

Occurrence and fate of glyphosate, a widely used herbicide, and its main metabolite AMPA was investigated in Lake Greifensee, Switzerland. Monthly vertical concentration profiles in the lake showed an increase of glyphosate concentrations in the epilimnion from 15 ng/L in March to 145 ng/L in July, followed by a sharp decline to <5 ng/L in August. A similar pattern was observed for AMPA. Concentrations of glyphosate and AMPA in the two main tributaries generally were much higher than in the lake. Simulations using a numerical lake model indicated that a substantial amount of glyphosate and AMPA dissipated in the epilimnion, mainly in July and August, with half-lives of only ≈2-4 days which is ≫100 times faster than in the preceding months. Fast dissipation coincided with high water temperatures and phytoplankton densities, and low phosphate concentrations. This indicates that glyphosate might have been used as an alternative phosphorus source by bacterio- and phytoplankton. Metagenomic analysis of lake water revealed the presence of organisms known to be capable of degrading glyphosate and AMPA.

Leaching of the Neonicotinoids Thiamethoxam and Imidacloprid from Sugar Beet Seed Dressings to Subsurface Tile Drains

Pesticide transport from seed dressings toward subsurface tile drains is still poorly understood. We monitored the neonicotinoid insecticides imidacloprid and thiamethoxam from sugar beet seed dressings in flow-proportional drainage water samples, together with spray applications of bromide and the herbicide S-metolachlor in spring and the fungicides epoxiconazole and kresoxim-methyl in summer. Event-driven, high first concentration maxima up to 2830 and 1290 ng/L for thiamethoxam and imidacloprid, respectively, were followed by an extended period of tailing and suggested preferential flow. Nevertheless, mass recoveries declined in agreement with the degradation and sorption properties collated in the groundwater ubiquity score, following the order bromide (4.9%), thiamethoxam (1.2%), imidacloprid (0.48%), kresoxim-methyl acid (0.17%), S-metolachlor (0.032%), epoxiconazole (0.013%), and kresoxim-methyl (0.003%), and indicated increased leaching from seed dressings compared to spray applications. Measured concentrations and mass recoveries indicate that subsurface tile drains contribute to surface water contamination with neonicotinoids from seed dressings.

Biotransformation of benzotriazoles: insights from transformation product identification and compound-specific isotope analysis

Benzotriazoles are widely used domestic and industrial corrosion inhibitors and have become omnipresent organic micropollutants in the aquatic environment. Here, the range of aerobic biological degradation mechanisms of benzotriazoles in activated sludge was investigated. Degradation pathways were elucidated by identifying transient and persistent transformation products in batch experiments using liquid chromatography-high-resolution tandem mass spectrometry (LC-HR-MS/MS). In addition, initial reactions were studied using compound-specific isotope analysis (CSIA). Biodegradation half-lives of 1.0 days for 1H-benzotriazole, 8.5 days for 4-methyl-1H-benzotriazole, and 0.9 days for 5-methyl-1H-benzotriazole with activated sludge confirmed their known partial persistence in conventional wastewater treatment. Major transformation products were identified as 4- and 5-hydroxy-1H-benzotriazole for the degradation of 1H-benzotriazole, and 1H-benzotriazole-5-carboxylic acid for the degradation of 5-methyl-1H-benzotriazole. These transformation products were found in wastewater effluents, showing their environmental relevance. Many other candidate transformation products, tentatively identified by interpretation of HR-MS/MS spectra, showed the broad range of possible reaction pathways including oxidation, alkylation, hydroxylation and indicate the significance of cometabolic processes for micropollutant degradation in biological wastewater treatment in general. The combination of evidence from product analysis with the significant carbon and nitrogen isotope fractionation suggests that aromatic monohydroxylation is the predominant step during the biotransformation of 1H-benzotriazole.

Degradation of polar organic micropollutants during riverbank filtration: complementary results from spatiotemporal sampling and push-pull tests

The fate of polar organic micropollutants (logDOW (pH 7) between -4.2 and +3.5) during riverbank filtration (RBF) at the river Thur was studied using both spatiotemporally resolved sampling and single-well push-pull tests (PPT), followed by LC-MS/MS analysis. The Thur is a dynamic prealpine river with an alluvial sandy-gravel aquifer, which is characterized by short groundwater travel times (a few days) from surface water infiltration to groundwater extraction. The spatiotemporal sampling allowed tracing concentration dynamics in the river and the groundwater and revealed persistence for the drug carbamazepine, while the herbicide MCPA (2-methyl-4-chloro-phenoxyacetic acid) and the drug 4-acetamidoantipyrine were very quickly degraded under the prevalent aerobic conditions. The corrosion inhibitor 1H-benzotriazole was degraded slightly, particularly in a transect influenced by river restoration measures. For the first time in situ first-order degradation rate constants for three pesticides and two pharmaceuticals were determined by PPTs, which confirmed the results of the spatiotemporal sampling. Atenolol was transformed almost completely to atenolol acid. Rate constants of 0.1-1.3 h(-1) for MCPA, 2,4-D, mecoprop, atenolol, and diclofenac, corresponding to half-lives of 0.6-6.3 h, demonstrated the great potential of RBF systems to degrade organic micropollutants and simultaneously the applicability of PPTs for micropollutants in such dynamic systems.

Multiresidue analysis of 88 polar organic micropollutants in ground, surface and wastewater using online mixed-bed multilayer solid-phase extraction coupled to high performance liquid chromatography-tandem mass spectrometry

An automated multiresidue method consisting of an online solid-phase extraction step coupled to a high performance liquid chromatography-tandem mass spectrometer (online-SPE-HPLC-MS/MS method) was developed for the determination of 88 polar organic micropollutants with a broad range of physicochemical properties (logD(OW) (pH 7): -4.2 to 4.2). Based on theoretical considerations, a single mixed-bed multilayer cartridge containing four different extraction materials was composed for the automated enrichment of water samples. This allowed the simultaneous analysis of pesticides, biocides, pharmaceuticals, corrosion inhibitors, many of their transformation products, and the artificial sweetener sucralose in three matrices groundwater, surface water, and wastewater. Limits of quantification (LOQs) were in the environmentally relevant concentration range of 0.1-87 ng/L for groundwater and surface water, and 1.5-206 ng/L for wastewater. The majority of the compounds could be quantified below 10 ng/L in groundwater (82%) and surface water (80%) and below 100 ng/L in wastewater (80%). Relative recoveries were largely between 80 and 120%. Intraday and inter-day precision, expressed as relative standard deviation, were generally better than 10% and 20%, respectively. 50 isotope labeled internal standards were used for quantification and accordingly, relative recoveries as well as intraday and inter-day precision were better for compounds with corresponding internal standard. The applicability of this method was shown during a sampling campaign at a riverbank filtration site for drinking water production with travel times of up to 5 days. 36 substances of all compound classes investigated could be found in concentrations between 0.1 and 600 ng/L. The results revealed the persistence of carbamazepine and sucralose in the groundwater aquifer as well as degradation of the metamizole metabolite 4-acetamidoantipyrine.

Input dynamics and fate in surface water of the herbicide metolachlor and of its highly mobile transformation product metolachlor

A large number of herbicide transformation products has been detected in surface waters and groundwaters of agricultural areas, often even in higher concentrations and more frequently than their parent compounds. However, their input dynamics and fate in surface waters are still rather poorly understood. This study compares the aquatic fate, concentration levels, and dynamics of the transformation product metolachlor ethanesulfonic acid (metolachlor ESA) and its parent compound metolachlor, an often-used corn herbicide. To this end, laboratory photolysis studies were combined with highly temporally resolved concentration measurements and lake mass balance modeling in the study area of Lake Greifensee (Switzerland). It is found that the two compounds show distinctly different concentration dynamics in the lake tributaries. Concentration-discharge relationships for metolachlor ESA in the main tributary showed a high baseflow concentration and increasing discharge dependence during harvest season, whereas baseflow concentrations of metolachlor were negligible and the discharge dependence was restricted to the period immediately following application. From this it was estimated that 70% of the yearly load of metolachlor ESA to the lake was due to groundwater recharge, whereas, for metolachlor, the bigger part of the load, 50-80%, stemmed from event-driven runoff. Lake mass balance modeling showed that the input dynamics of metolachlor and metolachlor ESA are reflected in their concentration dynamics in the lake's epilimnion and that both compounds show a similar fate in the epilimnion of Lake Greifensee during the summer months with half-lives on the order of 100-200 days, attributable to photolysis and another loss process of similar magnitude, potentially biodegradation. The behavior of metolachlor ESA can likely be generalized to other persistent and highly mobile transformation products. In the future, this distinctly different behavior of mobile pesticide transformation products should find a more appropriate reflection in exposure models used in chemical risk assessment and in pesticide risk management.