Triazole fungicides are widely detected in agricultural soils, yet their long-term persistence remains poorly understood. We evaluated how sorption, bioaccessibility, and degradation change with aging under field conditions. Topsoil was collected over 2 years from four Danish fields with detailed spray records. Tebuconazole, propiconazole, and epoxiconazole were detected 4-19 years after the last spray application, often at nearly constant concentrations. For these aged compounds, soil-water distribution coefficients could not be determined because sorption was too strong. Instead, bioaccessible fractions were quantified using hydroxypropyl-beta-cyclodextrin. Aged triazole fungicides consistently exhibited low bioaccessibility and very slow degradation. In contrast, freshly applied metconazole and prothioconazole-desthio declined rapidly and followed double first-order in parallel kinetics. Metconazole initially showed low sorption and high bioaccessibility but became increasingly inaccessible over the following year. As a result, total concentrations stabilized at a low plateau rather than approaching zero. These results demonstrate that aging reduces bioaccessibility and explains the persistence of triazole fungicides in topsoil. A fraction of applied triazole fungicides may therefore accumulate after repeated use, with implications for long-term soil quality and pesticide risk assessment.

The short-chain per- and polyfluoroalkyl substances trifluoroacetic acid (TFA) has been recognized as a degradation product of only three pesticides, but many other trifluoromethyl pesticides (C-CF3 pesticides) may potentially produce TFA based on their molecular structure. We determined TFA formation from seven C-CF3 pesticides with high sales rates (trifluralin, fluazifop-P-butyl, fluazinam, tau-fluvalinate, diflufenican, fluopyram, and mefentrifluconazole) over 52 weeks in a laboratory experiment with three agricultural soils. TFA was formed from all seven pesticides, but TFA formation varied both among compounds and among soils. Fluopyram had the highest TFA formation, at 10.7% of the pesticide amount added in one soil, but lower formation in the two other soils (3.3% and 7.9%). Fluazinam also had relatively high TFA formation (5.3%-6.5%), but unlike fluopyram, only minor differences were seen between soils. TFA formation was lower for the other pesticides with 2.4%-5.2% for diflufenican, 3.0%-5.3% for fluazifop-P-butyl, 1.1%-2.2% for trifluralin, 0.8%-3.3% for mefentrifluconazole, and 0.4%-1.0% for tau-fluvalinate. The measured TFA formation was used to estimate how spraying with C-CF3 pesticides may increase the annual average TFA concentrations in net precipitation infiltrating through arable topsoil (vadose zone water). The estimated TFA concentrations depended on crop type and growth stage and showed that the yearly TFA contribution from some C-CF3 pesticides may equal the atmospheric contribution in infiltrating soil water below sprayed fields.

Pesticides and degradation products are a major challenge for groundwater management in Europe, and in Denmark where drinking water relies entirely on groundwater. To protect drinking water resources, local Danish authorities must take groundwater-protective measures in areas designated as sensitive to pollution; however, official zonation for pesticides is lacking. Nitrate-sensitive groundwater abstraction areas have been used instead. The goal of our study was to test the appropriateness of this groundwater protection strategy. We used Køge municipality (Denmark) as a focus area and tested how our findings upscale to the national level. The data for Køge municipality included 1070 individual groundwater samples, analysed for at least one of 366 pesticide compounds during the period 2012–2022, which were aggregated at the well-screen level by the median. Four pesticide compounds (2,6-dichlorobenzamide (BAM), desphenylchloridazon (DPC), N,N-dimethylsulphamide (DMS), 1,2,4-triazole) and three pesticide groups (phenoxyalcanoic acids, triazines and dimethachlor and its metabolites) were found with the highest detection frequency in the study area. We found that groundwater pollution with pesticide compounds was not limited to nitrate-sensitive areas in Køge municipality or in Denmark as a whole. Therefore, nitrate-sensitive areas can only be used partially for identifying pesticide-sensitive groundwater abstraction areas. The management implication is that placing protective measures only within nitrate-sensitive areas would be insufficient to fully address the risk of future groundwater pesticide pollution. We identified knowledge gaps and discussed a potential way forward with a more integrated management of groundwater protection in Denmark.

Meltwater rivers in Greenland transport large quantities of freshwater from the Greenland ice sheet and local glaciers to the ocean, significantly influencing marine ecosystems and global biogeochemical cycles. With accelerating ice melt due to climate change, understanding the biogeochemistry of these rivers is critical. Here, we present a data set providing comprehensive biogeochemistry data from 28 meltwater rivers in south-western Greenland. Spanning a period from 2017 to 2021, it includes data on nutrients and other ions, trace metals, sediment, radio and water isotopes, microbiology and cyanotoxins, sampled during field campaigns in June and August–September. This data set offers valuable insights for research on glacial meltwater, biogeochemistry and microbiology, addressing key knowledge gaps in these fields.

Urban pollution from biocides used in building materials has raised emerging concern within recent years. The evidence that the use of biocides can pollute urban groundwaters is very limited, but in Denmark, the common degradation product from the two fungicides tolylfluanid and dichlofluanid, N,N-DMS, is particularly abundant in groundwater within urban areas, which suggests an urban source in addition to its well-known agricultural sources. In addition, another widespread groundwater pollutant, 1,2,4-triazole, may originate from the fungicides propiconazole and tebuconazole, that are also used in outdoor paint and wood protection products. To study the potential pollution of groundwater from fungicides used in outdoor paint and wood protection products, we surveyed concentrations in groundwater in two urban areas, we tested leaching from facades and soil concentrations close to facades and fences, and in lab-experiments, we determined the fate of N,N-DMS and 1,2,4-triazole under different redox conditions in soil sampled down to 7 m below surface.Shallow urban groundwater contained up to 1 mu g/L N,N-DMS with concentrations of 0.1-0.3 mu g/L below a typical Danish residential area. Despite a phase-out of tolylfluanid and dichlofluanid in paint in 2015, both compounds still wash-off wooden facades and fences and was detected in soil next to the treated wood. Much higher soil concentrations, however, were found for propiconazole and tebuconazole and their common degradation product 1,2,4-triazole, reflecting the fact that they are still in use in outdoor paint and wood protection products. 1,2,4-Triazole also leached to groundwater, but concentrations decreased sharply with depth, probably due to degradation that occurred at all tested soil depths and redox conditions. N,N-DMS, on the other hand, was not degraded in deeper soil layers or under anoxic conditions. Consequently, N,N-DMS may persist in groundwater below populated areas well into the future.

Seed dressing with fungicide or insecticide is a standard procedure for growing major crops, but very little is known about the leaching risk and the general fate of pesticides from coated seeds. Triazole fungicides are commonly used seed dressing fungicides and recently, there has been increasing concern that 1,2,4-triazole, a major degradation product of several triazole fungicides, may leach to groundwater in concentrations exceeding the 0.1 μg/L threshold limit of the European Union. We therefore carried out a laboratory column experiment with commercial barley seeds coated with the triazole fungicides tebuconazole and prothioconazole to study the fate of the fungicides and their degradation products, especially 1,2,4-triazole. Our experiment showed that the fungicides themselves were relatively immobile in the soil columns, but also that leaching of 1,2,4-triazole will occur no matter if tebuconazole or prothioconazole is used as seed dressing. Relatively high 1,2,4-triazole concentrations (up to 0.8 μg/L) were measured in the column leachates, but when the experiment was terminated after 63 days, a total of only 1 % of the fungicides was recovered as 1,2,4-triazole in the leachate. Our results suggest that seed dressing pesticides should be considered together with spray applications when estimating the total 1,2,4-triazole load from agriculture and that seed dressing pesticides and their degradation products should be included when evaluating leaching risks from pesticide applications in agriculture.

Quantitative assessments of long-term, national-scale responses of groundwater quality to pesticide applications are essential to evaluate the effectiveness of pesticide regulations. Retardation time in the unsaturated zone (Ru) was estimated for selected herbicides (atrazine, simazine, and bentazon) and degradation products (desethylatrazine (DEA), desisopropylatrazine (DIA), desethyldesisopropylatrazine (DEIA), and BAM) using a multidecadal time series of groundwater solute chemistry (∼30 years) and herbicide sales (∼60 years). The sampling year was converted to recharge year using groundwater age. Then, Ru was estimated using a cross-correlation analysis of the sales and the frequencies of detection and exceedance of the drinking water standard (0.1 μg/L) of each selected compound. The results showed no retardation of the highly polar, thus mobile, parent compounds (i.e., bentazon), while Ru of the moderately polar compounds (i.e., simazine) was about a decade, and their degradation products showed even longer Ru. The temporal trends of the degradation products did not mirror those of the sale data, which were attributed to the various sale periods of the parent compounds, sorption of the parent compounds, and complex degradation pathways. The longer Ru in clayey/organic sediments than in sandy sediments further confirmed the role of soil-specific retardation as an important factor to consider in groundwater protection.

A full-scale, experimental landfarm was tested for the capacity to biodegrade oil-polluted soil under high-Arctic tundra conditions in northeast Greenland at the military outpost 9117 Station Mestersvig. Soil contaminated with Arctic diesel was transferred to the landfarm in August 2012 followed by yearly addition of fertilizer and plowing and irrigation to optimize microbial diesel biodegradation. Biodegradation was determined from changes in total petroleum hydrocarbons (TPH), enumeration of specific subpopulations of oil-degrading microorganisms (MPN), and changes in selected classes of alkylated isomers and isomer ratios. Sixty-four percent of the diesel was removed in the landfarm within the first year, but a recalcitrant fraction (18%) remained after five years. n-alkanes and naphthalenes were biodegraded as demonstrated by changing isomer ratios. Dibenzothiophenes and phenanthrenes showed almost constant isomer ratios indicating that their removal was mostly abiotic. Oil-degrading microorganisms were present for the major components of diesel (n-alkanes, alkylbenzenes and alkylnaphthalenes). The degraders showed very large population increases in the landfarm with a peak population of 1.2 × 109 cells g-1 of total diesel degraders. Some diesel compounds such as cycloalkanes, hydroxy-PAHs and sulfur-heterocycles had very few or no specific degraders, these compounds may consequently be degraded only by slow co-metabolic processes or not at all.

When assessing oil spills in marine environments, focus has often been on describing degradation and removal of hydrocarbons. However, more and more attention is now given to the formation of mineral oil transformation products, and their potential toxicity and persistency in the environment. The aim of this study was to investigate the formation of dissolved acidic degradation products from crude oil in sea water from the Persian Gulf in a lab-experiment. A super-complex mixture of acidic degradation products was formed in the water phase and compound groups of aliphatic acids, monocyclic aromatic acids-, and polycyclic aromatic acids were identified. More specifically, alkylated PAHs were biodegraded to a high number of aromatic, carboxylic acids by hydroxylation of the alkyl side chains. These degradation products are more bioavailable than their parent compounds, and may therefore constitute a new group of contaminants that should be considered in oil spill assessments.

The aim of our study was to test whether surficial geochemical techniques are applicable under arctic conditions where pedogenesis is slow or absent, and where the vegetation is arctic dwarf shrub tundra. To this end, we sampled vegetation and topsoil at a known Zn-Pb-Ag anomaly at Kangerluarsuk, northwest Greenland. This Zn-Pb-Ag mineralization surfaces in part of the test area and is deeply buried in other parts. The surface mineralization could readily be identified by element analysis of the omnipresent plant Salix glauca. The strongest signal came from the pathfinder element Tl. The target elements Pb and Ag gave only weak signals and Zn gave no signal, probably because the cellular concentration of these elements is actively regulated by the plant. The use of regulated plant micronutrients as reference elements gave a small reduction of analytical noise in Tl/Cu and Tl/B concentration ratios at low Tl concentrations which improved identification of the deep mineralization. Pathfinder elements in plants may thus prove useful when combined with a detailed geophysical model. Tl, Zn, Pb and Ag concentrations in topsoil identified the surface mineralization but failed to identify the deep mineralization. This difference between samples of S. glauca and topsoil is probably because target elements from the deep mineralization must be mobile to reach the surface. Mobile elements may be more accessible for ion-exchange and uptake into the plants compared to the recalcitrant and crystalline fraction in the topsoil.

Pesticides frequently leach through clayey tills, even when they are expected to be strongly adsorbed. In this study, we observed that sorption of two strongly sorbing pesticides, tebuconazole and glyphosate, varied by more than an order of magnitude across soil domains in 5-m-deep clay till profiles with biopores and fractures. Eight soil domains were identified in each of the profiles: five matrix soils and three in the macropores. Tebuconazole sorption was controlled by soil organic matter content, except in the reduced matrix, which was low in organic matter, where there was surprisingly high sorption. Glyphosate showed high variation in sorption between fractures and matrix soil from the same depths. The domain-specific sorption of both tebuconazole and glyphosate was, however, overruled by dilute liquid manure. Sorption of tebuconazole was, as expected, decreased by liquid manure in several domains, but tebuconazole sorption increased in a few domains due to sorption of the manure-derived organic matter itself. Liquid manure unexpectedly had a greater effect on glyphosate sorption, which was strongly decreased by dissolved organic matter and phosphate in the manure. The variation in sorption across domains, as well as the effects of liquid manure, should be taken into account when assessing leaching risks.

The literature review aims to collect and analyse relevant existing knowledge about microbial degradation of oil in the seawater around Greenland. Thereby to identify and recommend to what future research on the topic should focus on and to add to the knowledge base for developing contingency plans and perform Net Environmental Benefit Analyses (NEBAs) for Greenland in relation to oil spill from oil exploration activities and shipping in Arctic waters. The knowledge presently available about natural degradation of oil under Arctic conditions shows a complex picture depending on oil type/components and environmental conditions as reflected in the marine environments of Greenland, which is also complex and consist of different water bodies characterised by different temperatures and nutrient levels.

This study aims to investigate the depth distribution of the Nitrate Reduction Potential (NRP) on a natural and a re-established wetland. The obtained NRP provides a valuable data of the driving factors affecting denitrification, the Dissimilatory Nitrate Reduction to Ammonium (DNRA) process and the performance of a re-established wetland. Intact soil cores were collected and divided in slices for the determination of Organic Matter (OM) through Loss of Ignition (LOI) as well as Dissolved Organic Carbon (DOC) and NRP spiking nitrate in batch tests. The Nitrate Reduction (NR) was fitted as a pseudo-first order rate constant (k) from where NRPs were obtained. NR took place in a narrow superficial zone showing a dropping natural logarithmic trend along depth. The main driving factor of denitrification, besides depth, was OM. Although, DOC and LOI could not express by themselves and absolute correlation with NRP, high amounts of DOC ensured enough quantity and quality of labile OM for NR. Besides, high concentration of LOI but a scarce abundance of DOC failed to drive NR. DNRA was only important in superficial samples with high contents of OM. Lastly, the high NRP of the re-established wetland confirms that wetlands can be restored satisfactorily.

A restored riparian zone was characterized to understand the effects of flooding on subsurface hydrological flow paths and nitrate removal in groundwater. Field and laboratory investigations were combined with numerical modeling of dynamic flow and reactive nitrate transport. Flooding enhances nitrate removal in groundwater primarily by two mechanisms. First, by creating a stagnant flow zone beneath the flooded area thereby increasing the residence time and leaving more time for nitrate removal. Secondly, nitrate removal is increased by enhancing upward flow into the highly reactive organic‐rich top layers. Flooding therefore contributes to nitrate removal in “hot spots”, where nitrate is transported to the peat and during “hot moments”, when flow is stagnant. The permeability of the capping peat layer relative to the aquifer is important as it controls both mechanisms. The model shows that the deep‐seated nitrate removal is greater than projected from the laboratory nitrate reduction experiments.

There has been increasing recognition of the occurrence of natural, halogenated organic compounds in marine and terrestrial environments. Chloroform is an example of a halogenated organic compound with natural formation as its primary source. Chloroform emission from soil has been reported from diverse Arctic, temperate, and (sub)tropical ecosystems. The terrestrial environment is a significant source to the atmosphere, but little is known about the formation pathway of chloroform in soil. Here, we present evidence that chloroform is formed through the hydrolysis of trichloroacetyl compounds in natural, organic-rich soils. In situ emissions of chloroform from soil in nine Arctic and subarctic ecosystems were linked to soil trichloroacetyl turnover. The residence time from formation of the trichloroacetyl compounds in soil to the release of chloroform to the atmosphere varied between 1 and 116 active months in unfrozen topsoil, depending on soil pH. Nonspecific halogenation that leads to trihaloacetyl formation does not discriminate between chloride and bromide, and brominated analogues were formed alongside chloroform. Soil may therefore be a previously unrecognized, natural source of brominated haloforms. The formation pathway of haloforms through trihaloacetyl compounds can most likely be extended to other ecosystems with organic topsoils.

Biological degradation is the main process for oil degradation in a subsurface oil plume. There is, however, little information on the biodegradation potential of Arctic, marine subsurface environments. We therefore investigated oil biodegradation in microcosms at 2 °C containing Arctic subsurface seawater from the Disko Bay (Greenland) and crude oil at three concentrations of 2.5-10 mg/L. Within 71 days, the total petroleum hydrocarbon concentration decreased only by 18 ± 18% for an initial concentration of 5 mg/L. The saturated alkanes nC13-nC30 and the isoprenoids iC18-iC21 were biodegraded at all concentrations indicating a substantial potential for biodegradation of these compound classes. Polycyclic aromatic compounds (PACs) disappeared from the oil phase, but dissolution was the main process of removal. Analysis of diagnostic ratios indicated almost no PAC biodegradation except for the C1-naphthalenes. To conclude, the marine subsurface microorganisms from the Disko Bay had the potential for biodegradation of n-alkanes and isoprenoids while the metabolically complex and toxic PACs and their alkylated homologs remained almost unchanged.

The aim of our study was to estimate emissions of natural chloroform from soil in arctic and subarctic ecosystems. We therefore determined the seasonal and spatial variation in soil-to-air fluxes of chloroform at 11 sites representing typical vegetation types in Greenland (Narsarsuaq, Kangerlussuaq and Disko Island) and northern Scandinavia (Abisko). Fluxes of chloroform showed a large variation, ranging from 4 to 2850 ng m−2 h−1. The local variation within a 12-m transect at each site was frequently five to tenfold, which emphasizes the need for multiple measurements even within field plots that seem homogenous. At one site, the transect was extended to 58 m and 40 measurements and a large number of environmental parameters were recorded as well. In this transect, collars separated by 60 cm distances were in most cases similar but at 3 m distance variation was as big as between collars with greater separation. CO2 flux was the parameter that showed the most correlation to the chloroform flux in the extended transect. Chloroform fluxes also varied over the year, but this variation was smaller than the variation between the five collars of each site and much smaller than the variation between sites. All arctic sites except a non-tussock sedge wetland showed low fluxes. A subarctic pine forest had by far the highest fluxes. Subarctic and boreal coniferous forests generally seem to be important global sources of biogenic chloroform to the troposphere. The future spatial extent of coniferous forest in the subarctic to arctic region, in response to climate change, may be the key driver of future chloroform emissions from these areas.

Nielsen, Niels Axel; Christensen, Thomas Højlund; Aagaard, Niels-Jørgen; Bach, Hanne; Larsen, Flemming; Britze, Peter; Molzen, Jan Eiersted; Hansen, Steffen Foss; Johnsen, Anders R.; Jensen, Poul Nordemann; Odgaard, Mads H; Bjerg, Poul Løgstrup; Fabricius, Ida Lykke; Jensen, Lotte Bjerregaard; Scheutz, Charlotte; Andersen, Henrik Rasmus; Kjeldsen, Peter; Hjorth, Rune; Baun, Anders; Kozin, Igor; Nikolajew, Maja Møller; Sørensen, Morten Kanne; Nielsen, Thomas Alexander Sick; Schovsbo, Niels; Kidmose, Jakob B.; Gravesen, Peter; Voss, Peter; Jakobsen, Rasmus; Pedersen, Stig Asbjørn Schack; Larsen, Tine B.; Dahl Jensen, Trine; Laier, Troels; Sanderson, Hans; Baattrup-Pedersen, Annette; Winding, Anne; Levin, Gregor; Jessen Rasmussen, Jes; Gustavson, Kim; Frederiksen, Pia