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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 (

Volatile organic compounds (VOCs) is a group of highly reactive gaseous species in the atmosphere with significant environmental implications, such as influencing air quality and Earth’s radiation balance. Natural ecosystems constitutes a large part of VOCs inventory with vegetation as well-known sources and soils as potential unidirectional interface yet relatively less studied. Here, we collected soil samples from two representative temperate ecosystems: beech forest and heather heath, and incubated them under manipulated conditions, such as at different temperatures, and/or exposed to different ambient VOC levels, using a dynamic flow-through system coupled with a PTR-ToF-MS, from which production and/or uptake rates of some selected VOCs were measured and calculated. Results showed that these soils were natural sources of a variety of VOCs, and their emission strength and profile were influenced by soil biogeochemical properties (e.g., soil organic matter, moisture) and temperature. These soils were switched to natural sinks of most VOCs when supplying VOC substrates to the headspace of the enclosed soils at parts per billions level, and the sink size positively responded to the amount of VOCs available in the ambient air. Further analysis indicated that the observed VOC uptake by soils were likely driven by microbial metabolism plus a minor contribution from physical adsorption to soil particles. Overall, our study suggests that soil uptake of VOCs may conceal the simultaneous production and turn it into VOC sinks when ambient VOCs become readily available, such as significant VOC sources existing near surface, thereby regulating the net performance of ecosystem exchange of these environmentally important trace gases.

The large natural gas storage facility at Stenlille, Denmark, has been monitored to investigate the effect of pumping large amounts of gas into the subsurface. Here, we present a new dataset of microseismicity at Stenlille since 2018. We compare these data with methane in groundwater, which has been monitored since gas storage was established in 1989. Further, we conducted a controlled 172 day microcosm experiment of methane oxidation on an isolated microbial community under both aerobic and anaerobic conditions. For this experiment, water was filtered from a well at Stenlille with elevated levels of thermogenic methane and ethane. No microseismic activity was detected in the gas storage area above an estimated detection level of ML 0.0 for the established network. The long-term monitoring for methane in groundwater has still only detected one leak, in 1995, related to a technical problem during injection. The microcosm experiment revealed that oxidation of methane occurred only under aerobic conditions during the experiment, as compared to anaerobic conditions, even though the filtered water was anoxic

When groundwater-based drinking water supply becomes contaminated, the timing and source of contamination are obvious questions. However, contaminants often have diffuse sources and different contaminants may have different sources even in a single groundwater well, making these questions complicated to answer. Age dating of groundwater has been used to reconstruct contaminant travel times to wells; however, critics have highlighted that groundwater flow is often complex with mixing of groundwater of different ages. In drinking water wells, where water is typically abstracted from a large depth interval, such mixing is even more problematic. We present a way to overcome some of the obstacles in identifying the source and age of contaminants in drinking water wells by combining depth-specific sampling with age tracer modeling, particle tracking simulations, geological characterization, and contaminant properties. This multitool approach was applied to a drinking water well, where bentazon and dichlorprop contamination was found to have different pollutant sources and release histories, even though both pesticides can be associated with the same land use. Bentazon was derived from recent application to a golf course, while dichlorprop was derived from agricultural use more than 30 years ago. The advantages, limitations, and pitfalls of the proposed course of action are then further discussed.

Groundwater is an important drinking water resource. To ensure clean drinking water, managed aquifer recharge (MAR) could be an attractive solution when recharging with treated wastewater. The installation of reactive barriers, e.g. with compost or other organic materials at MAR facilities, may improve pollutant removal. To link pollutant transformation processes and microbiology in reactive barriers, we simulated infiltration through different sand-compost mixtures using laboratory columns with depth-specific sampling of water and barrier material. We also evaluated the effect of inoculation with activated sludge. Our focus was on the simultaneous removal of organic micropollutants and nitrogen species, with parallel monitoring of the development of microbial communities. During 17 weeks of operation, the columns were fed with synthetic wastewater containing five organic micropollutants (1–2 µg/L each) and ammonium (2 mg N/L). Unique communities developed in the columns in relation to barrier material, with high effects of compost addition and minor effect of inoculation. Removal of the micropollutant paracetamol (acetaminophen) occurred in all columns, while sulfamethoxazole was only removed in columns with 50% compost. By contrast, limited removal was observed for sulfadiazine, carbamazepine and diuron, with the latter two displaying transient removal, attributed sorption. Oxygen was depleted within the top few cm of the columns when compost was present, but this was sufficient to remove all ammonium through nitrification. The fate of accumulated nitrate at deeper layers depended on the fraction of compost, with more compost leading to removal of nitrate by denitrification, but also by dissimilatory nitrate reduction to ammonium, hampering the overall nitrogen removal efficiency. Introducing compost as reactive barrier in MAR facilities has a large effect on the microbial communities and processes, but whether it will provide overall cleaner water to the underlying aquifer is uncertain and will depend very much on the type of pollutant.

Diflufenican is used in both agricultural and urban areas to control weeds. However, in Europe pesticides are regulated using agricultural soil data only. Urban soils where the top layer is replaced by gravel (e.g. driveways, outdoor tiled areas) can evidently differ from agricultural soils in many biotic and physical properties. In the present study, we compared the degradation, mineralization, sorption and aging of diflufenican between an agricultural sandy soil to a gravel used in urban areas. Both diflufenican and its two main aerobic metabolites were investigated. Diflufenican and the metabolites degraded slower in gravel than in agricultural soil. One of the metabolites, 2-[3-(Trifluoromethyl)phenoxy]nicotinic acid (AE B107137 as identified by EFSA; further abbreviated as AE-B), was formed from the incubation of diflufenican in both soil and gravel, however, showing different formation patterns in the two materials: No accumulation of AE-B was determined in the soil, whereas in gravel, an accumulation of AE-B was determined over the full study period of 150 days. After 150 days, approximately 10% of the applied diflufenican was mineralised in the soil (cumulative), while it was not mineralised in the gravel. Diflufenican showed much stronger sorption to the soil than to the gravel, while the sorption of the metabolites was weaker than diflufenican in both soil and gravel. Within the experimental period, the influence of aging on the fate of diflufenican in soil and gravel is limited (

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.

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.

As groundwater-fed waterworks clean their raw inlet water with sand filters, a variety of pro- and eukaryotic microbial communities develop on these filters. While several studies have targeted the prokaryotic sand filter communities, little is known about the eukaryotic communities, despite the obvious need for knowledge of microorganisms that get in contact with human drinking water. With a new general eukaryotic primer set (18S, V1-V3 region), we performed FLX-454 sequencing of material from 21 waterworks' sand filters varying in age (3–40 years) and geographical location on a 250 km east–west axis in Denmark, and put the data in context of their previously published prokaryotic communities. We find that filters vary highly in trophic complexity depending on age, from simple systems with bacteria and protozoa (3–6 years) to complex, mature systems with nematodes, rotifers and turbellarians as apex predators (40 years). Unlike the bacterial communities, the eukaryotic communities display a clear distance–decay relationship that predominates over environmental variations, indicating that the underlying aquifers feeding the filters harbor distinct eukaryotic communities with limited dispersal in between. Our findings have implications for waterworks' filter management, and offer a window down to the largely unexplored eukaryotic microbiology of groundwater aquifers.

Managed Aquifer Recharge (MAR) is a key strategy to increase freshwater resources in many regions facing water scarcity. MAR issues are related to both quantity and quality of the infiltrating water. In most countries, very high quality of the infiltrating water is required, to limit the impact on the aquifer geochemistry. In this paper, the possibility of injecting water of lower quality in the aquifer and letting the biogeochemical reactions take place in order to enhance its quality is explored. Here, we present the fate of nutrients (C, N) in the biogeochemical system of a reactive barrier formed by mixture of different proportions of sand and compost, supplied with treated wastewater to mimic MAR. An integrated conceptual model involving the nutrient cycles and biomass dynamics (auto- and heterotrophic) was developed, and then tested with a number of solute transport experiments in columns with different compost fraction in the column filling. The model incorporated both saturation and inhibition processes (regarding the nutrients and their byproducts) to provide a comprehensive picture of the nutrient dynamics within the column. The model developed (three if considering the 3 column setups) allowed to discriminate the processes that govern the fate of nutrients in relation with the compost enhancing long-term nutrient degradation, yet hindering hydraulic parameters that affect infiltration rates.

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.

In this study, we investigated the establishment of natural bacterial degraders in a sand filter treating groundwater contaminated with the phenoxypropionate herbicides ( RS )-2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and ( RS )-2-(2,4-dichlorophenoxy)propanoic acid (DCPP) and the associated impurity/catabolite 4-chlorophenoxypropanoic acid (4-CPP). A pilot facility was set up in a contaminated landfill site. Anaerobic groundwater was pumped up and passed through an aeration basin and subsequently through a rapid sand filter, which is characterized by a short residence time of the water in the filter. For 3 months, the degradation of DCPP, MCPP, and 4-CPP in the sand filter increased to 15 to 30% of the inlet concentration. A significant selection for natural bacterial herbicide degraders also occurred in the sand filter. Using a most-probable-number (MPN) method, we found a steady increase in the number of culturable phenoxypropionate degraders, reaching approximately 5 × 10 5 degraders per g sand by the end of the study. Using a quantitative PCR targeting the two phenoxypropionate degradation genes, rdpA and sdpA , encoding stereospecific dioxygenases, a parallel increase was observed, but with the gene copy numbers being about 2 to 3 log units higher than the MPN. In general, the sdpA gene was more abundant than the rdpA gene, and the establishment of a significant population of bacteria harboring sdpA occurred faster than the establishment of an rdpA gene-carrying population. The identities of the specific herbicide degraders in the sand filter were assessed by Illumina MiSeq sequencing of 16S rRNA genes from sand filter samples and from selected MPN plate wells. We propose a list of potential degrader bacteria involved in herbicide degradation, including representatives belonging to the Comamonadaceae and Sphingomonadales .

Evidence from the past shows that pesticide use in populated areas may impact groundwater quality. The approval of herbicides such as diflufenican and glyphosate for use on paved and unpaved gravel surfaces in the European Union is based on their behaviour and fate in agricultural soils. However, this might be very different from their fate in gravel surfaces. We therefore conducted an outdoor study with 21 small lysimeters containing different gravel types and a sandy arable topsoil as control. The lysimeters were sprayed with a commercial product for gardening, containing diflufenican and glyphosate. The concentrations of the herbicides and their relevant degradation products in the outlet was followed for 19 months. Diflufenican, glyphosate and AMPA did not leach from any of the lysimeters. However, one diflufenican degradation product (AE-0) leached from two of the gravel types for more than a year and a second degradation product (AE-B) leached from all gravels for up to one year. Concentrations in the leachate peaked at 0.5–3 μg/L, with highest concentrations over the longest periods observed with rock chippings on top of the gravel. We conclude, that the different properties of gravel compared to those of agricultural soils may lead to very different herbicide leaching patterns but also that the leaching depends highly on the type of gravel and type of herbicide.

This report contains information on five selected locations that may be utilized for industrial collection of drinking water, and provides the technical background for the second licensing round of the Greenland Government in its Strategy for Export of Ice and Water. This report is not aimed at addressing any technical or engineering questions posed by the locations or water treatment, but only concerns the natural environment and the quality of the water as it was sampled. A prerequisite in the investigation has been that the water should be at least partly derived from meltwater originating either from the Greenland Ice Sheet or from local glaciers and ice caps. The identification and selection process for locations was de-scribed in detail in Ahlstrøm et al. (2018) and updated in Kjeldsen et al. (2019). Locations are defined as outlets of a significant meltwater river to accessible fjords in the southwestern part of Greenland, to minimize potential sea ice and iceberg interference. Catchments for each location or river outlet were derived employing advanced hydrological methods, using the most recent elevation models available.The five selected locations represent different catchment sizes with varying amounts of discharge, ranging from roughly 290,000 million litres per year, down to slightly over 10,000 million litres per year. The rivers at all locations are, on average, discharging water from May to November with the vast majority of water discharging in the period June-September. A comparison between modelled discharge for the catchments for the two periods 1980-1991 and 2006-2017, showed an increase in the discharge at all sites except one, which was stable. A similar method was also used to examine the change in discharge over the last few decades, showing a promising overall melt increase of more than 50 % for the region.The five selected locations were visited by boat to sample the water and collect additional data. The field visits were conducted in June and September in either 2018 or 2019, to capture the seasonal variability in the water quality. Two locations drain ice sheet catch-ments and three locations drain catchments with local mountain glaciers and ice caps.An extensive analysis of chemical, physical and microbiological parameters was performed on the water samples. Some types of analyses had to be performed on-site, some were performed at GEUS laboratories, and some at certified commercial laboratories.All of the locations provide large amounts of meltwater during the summer from June-September, with river outlets being relatively near deep fjord waters. The meltwater con-tains varying amounts of sediment derived from glacier erosion of the bedrock, requiring filtration of the meltwater before use. For all five locations, inorganic parameters are below drinking water requirements and guidelines in filtered water samples. Gentle UV-treatment of the water is recommended, as is commonly required for surface water, as microbiological parameters generally exceed the guideline limits at all locations.While the water quality can be expected to vary over the season, the results provide a strong indication of the potential for export of drinking water from meltwater rivers in Greenland.

Vast amounts of carbon are bound in both active layer and permafrost soils in the Arctic. As a consequence of climate warming, the depth of the active layer is increasing in size and permafrost soils are thawing. We hypothesize that pulses of biogenic volatile organic compounds are released from the near-surface active layer during spring, and during late summer season from thawing permafrost, while the subsequent biogeochemical processes occurring in thawed soils also lead to emissions. Biogenic volatile organic compounds are reactive gases that have both negative and positive climate forcing impacts when introduced to the Arctic atmosphere, and the knowledge of their emission magnitude and pattern is necessary to construct reliable climate models. However, it is unclear how different ecosystems and environmental factors such as drainage conditions upon permafrost thaw affect the emission and compound composition. Here we show that incubations of frozen B horizon of the active layer and permafrost soils collected from a High Arctic heath and fen release a range of biogenic volatile organic compounds upon thaw and during subsequent incubation experiments at temperatures of 10°C and 20°C. Meltwater drainage in the fen soils increased emission rates nine times, while having no effect in the drier heath soils. Emissions generally increased with temperature, and emission profiles for the fen soils were dominated by benzenoids and alkanes, while benzenoids, ketones, and alcohols dominated in heath soils. Our results emphasize that future changes affecting the drainage conditions of the Arctic tundra will have a large influence on volatile emissions from thawing permafrost soils – particularly in wetland/fen areas.

Warming in the Arctic accelerates thawing of permafrost-affected soils, which leads to a release of greenhouse gases to the atmosphere. We do not know whether permafrost thaw also releases non-methane volatile organic compounds that can contribute to both negative and positive radiative forcing on climate. Here we show using proton transfer reaction–time of flight–mass spectrometry that substantial amounts of ethanol and methanol and in total 316 organic ions were released from Greenlandic permafrost soils upon thaw in laboratory incubations. We demonstrate that the majority of this release is taken up in the active layer above. In an experiment using 14C-labeled ethanol and methanol, we demonstrate that these compounds are consumed by microorganisms. Our findings highlight that the thawing permafrost soils are not only a considerable source of volatile organic compounds but also that the active layer regulates their release into the atmosphere., Permafrost thaw allows biological activity in previously frozen ground, leading to a potential release of climate-relevant gases. Here the authors show that thawing permafrost emits volatile organic compounds but that their release to the atmosphere is limited by microbial consumption in the overlaying soil.

Ammonium oxidation to nitrite and then to nitrate (nitrification) is a key process in many waterworks treating groundwater to make it potable. In rapid sand filters, nitrifying microbial communities may evolve naturally from groundwater bacteria entering the filters. However, in new filters this may take several months, and in some cases the nitrification process is never sufficiently rapid to be efficient or is only performed partially, with nitrite as an undesired end product. The present study reports the first successful priming of nitrification in a rapid sand filter treating groundwater. It is shown that nitrifying communities could be enriched by microbiomes from well-functioning rapid sand filters in waterworks and that the enriched nitrifying consortium could be used to inoculate fresh filters, significantly shortening the time taken for the nitrification process to start. The key nitrifiers in the enrichment were different from those in the well-functioning filter, but similar to those that initiated the nitrification process in fresh filters without inoculation. Whether or not the nitrification was primed with the enriched nitrifying consortium, the bacteria performing the nitrification process during start-up appeared to be slowly outcompeted by Nitrospira, the dominant nitrifying bacterium in well-functioning rapid sand filters.

Meltwater from Greenland is an increasingly attractive resource of pure freshwater. To at-tract investments from the industry, an extensive effort has been launched to map possible extraction locations, determine the quality of the meltwater, and review the existing ice and water export legislation. This report presents results from mapping- and water quality anal-ysis of five selected locations, visited by boat in June 2017. Two locations drain ice sheet catchments and three locations drain catchments with local mountain glaciers.The mapping includes catchment delineation, ice- and land runoff modelling, ice-dynamic modelling of the age of the melting ice, collection of fjord depth data and an assessment of the risk from glacial lake outburst floods. An extensive analysis of chemical, physical and microbiological parameters were performed on the water samples collected during field-work. Some types of analysis had to be performed on-site, some were performed at GEUS laboratories, and some at certified commercial laboratories.Greenland has a diverse geology including areas with potential for mining of metals and radioactive isotopes. The existence of such areas could influence the water quality in melt-water rivers. The 2017 survey, however, showed excellent water quality at all locations with regards to inorganics like metal ions and radioisotopes. Toxic metals like arsenic, cadmium and nickel were well below the lowest criterion at all locations and so was fluoride, which may be an indicator for a number of toxic metals in Southern Greenland. Radioactivity was below the detection limit of the commercial laboratory at all locations. The seasonal varia-tion of metals and radioisotopes is not yet known, but so far the locations look promising with regards to these quality parameters.Biology is another factor that may influence water quality of meltwater rivers. Of most con-cern are cyanobacteria in lakes and rivers and bacteria from the gut of animals. Cyanobac-teria produce toxins like microcystins and Anatoxin-A. These compounds were not detected at any of the locations. Coliforms and enterococci were chosen as indicator bacteria. Coli-forms were not found at any location. Enterococcaceae were detected only at one location (2 per 5 mL). Total colony forming units (CFU) at 22 and 36°C were also analysed. While some CFU were found at 22°C (7-115 per mL) almost none were found at 36°C (0-2 per mL), which is a good safety indication. The bacterial parameters generally indicated good water quality, but some sort of simple disinfection should be considered, as is the case for all surface water for human consumption.In summary, the results indicate an excellent water quality at all five locations, with all pa-rameter values below the required drinking water standards for the European Union, the United States and The International Council of Bottled Water Associations (ICBWA) .

Rapid sand filtration is essential at most waterworks that treat anaerobic groundwater. Often the filtration depends on microbiological processes, but the microbial communities of the filters are largely unknown. We determined the prokaryotic community structures of 11 waterworks receiving groundwater from different geological settings by 16S rRNA gene-based 454 pyrosequencing and explored their relationships to filtration technology and raw water chemistry. Most of the variation in microbial diversity observed between different waterworks sand filters could be explained by the geochemistry of the inlet water. In addition, our findings suggested four features of particular interest: (1) Nitrospira dominated over Nitrobacter at all waterworks, suggesting that Nitrospira is a key nitrifying bacterium in groundwater-treating sand filters. (2) Hyphomicrobiaceae species were abundant at all waterworks, where they may be involved in manganese oxidation. (3) Six of 11 waterworks had significant concentrations of methane in their raw water and very high abundance of the methanotrophic Methylococcaceae. (4) The iron-oxidizing bacteria Gallionella was present at all waterworks suggesting that biological iron oxidation is occurring in addition to abiotic iron oxidation. Elucidation of key members of the microbial community in groundwater-treating sand filters has practical potential, for example, when methods are needed to improve filter function.

Real-time PCR for the quantitative assessment of microbial genes in DNA extracted from environmental samples is increasingly being used in microbial ecology studies. A significant problem with the quantitative aspect of the method is the possible inhibition of the PCR process by humic substances co-extracted with the DNA. A comparison of the inhibition exerted by five structurally different humic substances on six commercially available DNA polymerases revealed large differences in the resistance of the polymerases to inhibition. Depending on the DNA polymerases (or their formulation) the addition of Bovine Serum Albumin (BSA) to the mastermix reaction generally increased the resistance to the different humic substances and decreased differences between the polymerases. One of the tested polymerases was clearly hampered by the addition of BSA, indicating that BSA cannot be added to just any mastermix to improve enzyme performance. The structural differences in the tested humic acids suggest that the mecha...

A method for digestion of soils with high inorganic matter content (ranging from 50 to 92%) by microwave-induced combustion (MIC) is proposed for the first time for further halogens (F, Cl, Br, and I) determination by ion chromatography (IC) and also by inductively coupled plasma mass spectrometry (ICP-MS). Microcrystalline cellulose (100–500 mg), used as a combustion aid, was mixed with sample and water or NH4OH solutions (10–100 mmol L–1) were investigated for analytes absorption. The use of cellulose (400 mg) was mandatory to volatilize the halogens from soils with high inorganic matter. It was possible to use diluted absorbing solutions (up to 100 mmol L–1 NH4OH) for halogens retention, providing limits of quantification in the range of 0.06 (I) to 60 (Cl) μg g–1. Accuracy was evaluated using certified reference materials (CRMs), spiked samples, and pyrohydrolysis method. Recoveries for halogens after spiked samples were in the range of 94 to 103% and the results after digestion of CRMs by MIC were in...

Groundwater contamination by pesticide residues often leads to the closure of drinking water wells, making the development of new techniques to remediate drinking water resources of considerable interest. Pesticide-degrading bacteria were recently added to a waterworks sand filter in an attempt to remediate pesticide-polluted drinking water. The density of the introduced bacteria, however, decreased rapidly, which was partly attributed to predation by protozoa in the sand filter. This study investigated the effects of indigenous sand filter protozoa on the population density and degradation efficiency of degrader bacteria introduced into sand from a waterworks sand filter. The 2,6-dichlorobenzamide (BAM)-degrading bacterium Aminobacter sp. MSH1 was used as a model organism. The introduction of MSH1 at high cell densities was followed by a >1000-fold increase in the protozoan population size and at the same time a 29 % reduction in Aminobacter cell numbers. The protozoan population in the systems that had MSH1 added at a lower density only increased 50-fold, and a decrease in Aminobacter numbers was not detectable. Furthermore, a reduction in the number of Aminobacter and in BAM degradation efficiency was seen in flow-through sand filter columns inoculated with MSH1 and fed BAM-contaminated water, when comparing sand columns containing the indigenous microbial filter community, i.e. containing protozoa, to columns with sterilised sand. These results suggest that degrader bacteria introduced into waterworks sand filters are adversely affected by grazing from the indigenous protozoa, reducing the size of the degrader population and the sand filter degradation efficiency.

Degradation and mineralisation of the groundwater contaminant 2,6-dichloro-benzamide (BAM) was investigated in two Aminobacter strains focussing on the induction of BAM degradation and mineralisation and occurrence of intermediate metabolites. The BAM degradation rate was independent of whether the cells were pre-grown in the absence or presence of BAM, thus indicating that the first step in the degradation pathway was constitutively expressed. In contrast, (14)CO(2) production was stimulated when cells were pre-grown in the presence of BAM, suggesting that one or more of the subsequent steps in the degradation pathway were inducible. Accumulation of 2,6-dichlorobenzoate (DCBA) during degradation of BAM demonstrated that the first step involved amidase activity. Mass balance calculations and thin-layer chromatography coupled with autoradiographic detection indicated that degradation of DCBA and at least one unknown metabolite may comprise a bottleneck for BAM mineralisation by Aminobacter spp. The study thus provides novel information about the BAM degradation pathway and points to the involvement of unknown intermediate metabolites in degradation of this important groundwater contaminant.

Chemically chlorinated organic matter as well as natural background humic acids contain significant amounts of organically bound halogens that must be determined for assessment of environmental pollution. In this work the use of ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed for the determination of total organic Cl, Br and I concentration in humic acids extracted from various forest soil horizons after a single digestion by microwave-induced combustion (MIC). Samples were pressed as pellets and combusted using 20 bar of oxygen and ammonium nitrate solution as igniter. Analytes were absorbed in diluted alkaline solution (50mM (NH(4))(2)CO(3)) and a reflux step was applied after combustion to improve analyte recoveries (5 min, microwave power of 1400W). The accuracy was evaluated using certified reference materials (CRM) and spiked samples. Using MIC the agreement with CRM values and spike recoveries was higher than 97% for all analytes. As an advantage over conventional procedures, using MIC it was possible to digest up to eight samples in only 25 min, obtaining a single solution suitable for all halogens determination in humic acids samples by different techniques (IC and ICP-MS). The limit of detection (3σ) for Cl, Br and I obtained by IC was 1.2, 2.5 and 4.3μgg(-1) and by ICP-MS it was 1.4, 0.03 and 0.002μgg(-1), respectively.

Chloroform is a common groundwater pollutant but also a natural compound in forest ecosystems. Leaching of natural chloroform from forest soil to groundwater was followed by regular analysis of soil air and groundwater from multilevel wells at four different sites in Denmark for a period of up to 4 a. Significant seasonal variation in chloroform was observed in soil air 0.5 m below surface ranging at one site from 120 ppb by volume in summer to 20 ppb during winter. With depth, the seasonal variation diminished gradually, ranging from 30 ppb in summer to 20 ppb during winter, near the groundwater table. Chloroform in the shallowest groundwater ranged from 0.5–1.5 μg L−1 at one site to 2–5 μg L−1 at another site showing no clear correlation with season. Comparing changes in chloroform in soil air versus depth with on-site recorded meteorological data indicated that a clear relationship appears between rain events and leaching of chloroform. Chloroform in top soil air co-varied with CO2 given a delay of 3–4 weeks providing evidence for its biological origin. This was confirmed during laboratory incubation experiments which further located the fermentation layer as the most chloroform producing soil horizon. Sorption of chloroform to soils, examined using 14C–CHCl3, correlated with organic matter content, being high in the upper organic rich soils and low in the deeper more minerogenic soils. The marked decrease in chloroform in soil with depth may in part be due to microbial degradation which was shown to occur at all depths by laboratory tests using 14C–CHCl3.

Natural chloroform in soil gas below four coniferous forest sites was studied. High concentrations were found within narrow areas—Hot Spots—varying from ~25 to >400 m2 in size, with chloroform concentrations being typically 20–100 times those in corresponding Low Spots.Attempts to localize Hot Spots by visual inspection with regard to type and density of vegetation failed. Possible differences between Hot and Low Spots could be emission, leaching or degradation of chloroform. However, emissions of chloroform from Hot Spots were ~10 times higher than from Low Spots and similarly the chloroform concentration in groundwater below a Hot Spot was ~10 times higher than below the corresponding Low Spot. No differences in chloroform mineralization rates were observed between sites and incubation of soil cores confirmed a larger net formation of chloroform in the Hot Spots. Various soil parameters were measured in order to compare the soil sampled from Hot and Low Spots. The halogenation degree of organic soil samples was in the same range, although slightly higher in the H-horizon of the Hot Spot. The chloroform formation potential of the soil organic matter showed differences between soil horizons but not between sites. The high levels of chloroform in the Hot Spots are probably best explained by differences in chloroform forming activity caused by an uneven distribution of yet unidentified microorganisms, since differences in soil organic matter quality and in emission, leaching and degradation of chloroform as well as a number of additional soil parameters could be completely ruled out.

Soil organic matter (SOM) is generally believed not to influence the sorption of glyphosate in soil. To get a closer look on the dynamics between glyphosate and SOM, we used three approaches: I. Sorption studies with seven purified soil humic fractions showed that these could sorb glyphosate and that the aromatic content, possibly phenolic groups, seems to aid the sorption. II. Sorption studies with six whole soils and with SOM removed showed that several soil parameters including SOM are responsible for the strong sorption of glyphosate in soils. III. After an 80 day fate experiment, approximately 40% of the added glyphosate was associated with the humic and fulvic acid fractions in the sandy soils, while this was the case for only approximately 10% of the added glyphosate in the clayey soils. Glyphosate sorbed to humic substances in the natural soils seemed to be easier desorbed than glyphosate sorbed to amorphous Fe/Al-oxides.

Humic substances (HS) are the dominant constituents of soil organic matter (SOM). The interactions between the phenylurea herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) and several HS fractions, purified from various soil horizons, were studied. One commercial humic acid (HA) was included for comparison. Diuron was shown to adsorb significantly, but reversibly, to purified HA while sorption to fulvic acid (FA) was less pronounced. The sorption abilities of the purified HS fractions were correlated with their total aromatic content. In natural soils, SOM was the main adsorbent of diuron, but the organic matter partition coefficient was larger in sandy compared to clayey soils. Degradation of diuron in natural soils was slow and incomplete. Inoculation of a sandy C-horizon with a diuron-degrading bacterial strain led to substantial diuron degradation, but the addition of purified FA and HA to these inoculated soils decreased this degradation. The main metabolite produced during diuron degradation, 3,4-dichloroaniline, was bound irreversibly to HS within days after formation.

Summary Humic substances (HS) often are dominant constituents of soil organic matter. In this study 28 fractions of HS were purified and chemically characterized from horizons of three Danish soils differing in texture. A commercial humic acid (HA) was included for comparison. The HS fractions were chemically characterized by CHNS analysis, pH-titration and liquid state 13C-NMR experiments. Amino acids and carbohydrates could clearly be differentiated from other O- and N-aliphatic compounds. The data were analysed by principal component analysis. The analysis revealed greater difference between HS fractions than between locations. The characteristics of the HS fractions were compared with several models in the literature and an average structural model for one HA and one FA fraction is proposed.