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Chloroform is one of the most frequently found anthropogenic groundwater contaminants. Recent investigations, however, suggested that chloroform in groundwater may also originate from a natural production in soils. As societies response to the occurrence of chloroform in groundwater may depend upon its origin as anthropogenic or naturally produced, test methods are needed to measure the potential of natural soil chloroform production. Field measurements of ambient air and soil air, and field and laboratory incubation studies were evaluated for measurement of relative soil chloroform production at a site with four different vegetation types (spruce forest, beech forest, grassland, and grain field) on comparable geological soil. All test methods showed varying soil production of chloroform with spruce forest soil being most productive and grain field soil being least productive. Field measurements of the ratio of soil air to ambient air chloroform concentrations exhibited the smallest difference between high production and low production areas, whereas laboratory incubation studies showed the largest difference. Thus, laboratory incubation studies are suggested as most efficient for estimating relative chloroform production in soil. The study indicated that soil samples should be tested not more than 14 days after sampling. Furthermore, it was found that potentially limiting compounds, such as chloride or nitrate, are not needed to be added in spike experiments to obtain reliable production results. However, it should be recognized that the processes of soil chloroform production are not known yet in all details. Other factors than those studied here may affect the test methods for soil chloroform production too.

A test method for the determination of PAH relative bioaccessibility from contaminated soils was implemented and validated for use in risk assessment of soils from contaminated sites meeting performance requirement set for evaluation against regulatory limits. Relative bioaccessibilities of soil benzo(a)pyrene obtained with the test were linearly correlated to relative bioavailability data obtained previously in in vivo investigations with experimental animals, but the relative bioaccessibilities were lower than the relative bioavailabilities. Tests of soil samples from 4 Danish sites contaminated with benzo(a)pyrene and dibenz(a,h)anthracene from different sources and with different ages demonstrated that using the bioaccessible concentrations in risk assessment instead of total concentrations would have produced lower risk classifications of the sites. An urgent requirement is demonstrated for an accepted and valid method for investigating the bioavailability of organic soil contaminants such as PAH and also for soil samples with accepted relative bioavailability data.

A workshop on uncertainty in sampling was held in Hillerod, Denmark, on 12–13 April 2007 to launch a new handbook on sampling quality assurance and uncertainty estimation. The participants of the workshop were approximately 60 delegates from 15 European countries, representing institutions performing sampling, users of the data, research institutions, as well as accreditation bodies. Materials from the workshop, including examples, tools, and calculation aids for the work can be found at http://www.samplersguide.com. The Nordtest handbook Uncertainty from sampling will be made available on the Nordtest web site at http://www.nordicinnovation.net/nordtest.cfm under NT technical reports, report number NT tec 604. Until the final report is available on the Nordtest web site, an advance draft of the Nordtest handbook is available from http://www.samplersguide.com.

A set of test methods for estimating the risk for human health (oral bioaccessibility tests) and groundwater (leaching tests) was applied to contaminated soils from three sites with different sources of contamination. The bioaccessible soil concentrations of the contaminants cadmium, lead, nickel, benzo(a)pyrene and dibenz(a,h)anthracene were considerably lower than the total concentrations. The leached concentrations of the polycyclic aromatic hydrocarbons, cadmium and nickel were below the EU drinking water and Danish groundwater criteria, whereas the leached lead concentrations were below the drinking water criteria but above the groundwater criteria. Based upon the test results, a risk assessment of the soils with respect to human health (oral exposure) and groundwater was established that reflected a reduced availability and mobility of PAH and heavy metals in the soils.

Sewage sludge produced in wastewater treatment contains large amounts of organic matter and nutrients and could, therefore, be suitable as fertiliser. However, with the sludge, besides heavy metals and pathogenic bacteria, a variety of organic contaminants can be added to agricultural fields. Whether the organic contaminants from the sludge can have adverse effects on human health and wildlife if these compounds enter the food chain or groundwater still remains a point of controversial discussion.This paper presents an overview on the present situation in Europe and a summary of some recent results on the possible uptake of organic contaminants by crops after addition to agricultural fields by sewage sludge.Greenhouse experiments and field trials were performed to study the degradation and uptake of organic micro-contaminants in sludge-amended agricultural soil in crops, such as barley and carrots grown in agricultural soil amended with anaerobically-treated sewage sludge from a wastewater treatment plant, but studies hitherto have revealed no immediate risks. Common sludge contaminants such as linear alkylbenzene sulphonates (LAS), nonylphenol ethoxylates (NPE), polycyclic aromatic hydrocarbons (PAH), bis(diethylhexyl) phthalate (DEHP), showed neither accumulation in soil nor uptake in plants.It is assumed that the annual amount of sewage sludge produced in Europe will increase in the future, mainly due to larger amounts of high quality drinking water needed by an increasing population and due to increasing demands for cleaner sewage water. Application of sewage sludge to agricultural soils is sustainable and economical due to nutrient cycling and disposal of sewage sludge. However, this solution also involves risks with respect to the occurrence of organic contaminants and other potentially harmful contents such as pathogens and heavy metals present in the sludge. There have been concerns that organic contaminants may accumulate in the soil, be taken up by plants and thereby transferred to humans via the food chain. Results obtained so far revealed, however, no immediate risk of accumulation of common organic sludge contaminants in soil or uptake in plants when applying sewage sludge to agricultural soil. With very high dosages of sewage sludge, there may be a risk for accumulation of very apolar contaminants, such as DEHP, to the soil.Any conclusions on the safe use of sewage sludge in agriculture have to be drawn carefully, as the studies performed until now have been limited. Further studies are required, and before final statements can be drawn, it is imminent to study a larger variety of common crops and the effect sewage sludge application may have on a possible accumulation of organic contaminants in the crops. Furthermore, a larger variety of organic contaminants need to be studied and special focus should be given to contaminants newly introduced into the environment. Besides investigating possible plant uptake of organic contaminants, the fate of these compounds in soil after sludge application need to be monitored too. Here, special attention has to be given to studies on degradation and the formation of degradation products, to weathering and to leaching effects on groundwater, to the application of different crops on the same field (crop rotation), to the use of full-width tillage and strip tillage, and to long term application of sewage sludge on the soil.. There are environmental, political as well as economical incentives to increase the agricultural application of sludge. However, such usage should be performed with care as there are also ways in which sludge fertilisation could harm the environment and human health. Recently, a new European COST Action (859) has been established covering the field of food safety and improved food quality. Part of the Action is dealing with the application of sewage sludge in agriculture. Before any political and economical measures can be taken, the pros and cons have to be sufficiently investigated on a scientific level first.

The widespread use of volatile chlorinated compounds like chloroform, trichloroethene and tetrachloroethene in industrialized societies causes a large annual release of these compounds into the environment. Due to their role as a source for halogen radicals involved in various catalytic atmospheric reaction cycles, including the regulation of the stratospheric and tropospheric ozone layers, these compounds also constitute a risk for drinking water resources as they can be transported to the groundwater from contaminated field sites or even from atmospheric deposition. Therefore, identification and investigation of sources and sinks of volatile chlorinated compounds are of particular interest. Chloroform, a major contributor to natural gaseous chlorine, was found to be emitted by several anthropogenic and natural sources including the oceans and terrestrial areas. The origin of chloroform in the terrestrial environment can be anthropogenic point sources, atmospheric deposition, release by vegetation and production directly in the soil. The calculated annual biogenic global chloroform emission is 700 Gg, and marine and terrestrial environments are nearly equal contributors. The estimated emissions from anthropogenic sources account for less than 10% of the estimated total emissions from all sources. Among terrestrial sources, forests have recently been identified as contributing to the release of chloroform into the environment. With the data available, annual emissions of chloroform to the atmosphere from forest sites were calculated and compared to other natural sources. At present knowledge, forests are only a minor source in the total biogenic flux of chloroform, contributing less than 1% to the annual global atmospheric input. However, it should be noted that data are available for Northern temperate forests only. The large tropical forest areas may provide a yet unknown input of chloroform.

Soil air from top soil of a Danish spruce forest was investigatedmonthly from December 1997 to December 1998 for the occurrence ofchloroform, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene and tetrachloroethene. Within the monitoring period, three different patterns of soil air concentrations wereidentified. For chloroform, concentrations peaked in spring and autumn while 1,1,1-trichloroethane and tetrachloromethane peakedduring mid winter. Trichloroethene and tetrachloroethene, concentrations remained constant throughout the year. The relative ratios of soil air concentrations to ambient air concentrations indicated a natural production of chloroform, while the other chlorinated compounds investigated probably originated from non-point source pollution. The seasonal variation of the chloroform concentration suggested a productionby microorganisms, as high chloroform concentrations were found in the soil in warm and humid periods of the year (spring and autumn) with high microbial activity.

Two different humic acids (HA) and a fulvic acid (FA) were chemically immobilized to a high performance liquid chromatography (HPLC) silica column material. The immobilization was performed by binding amino groups in HA/FA to the free aldehyde group in glutardialdehyde attached to the silica gel. The HPLC column materials were compared with a blank column material made by applying the same procedure but without immobilizing HA or FA. Also, a column was made by binding carbonyl groups in HA to amino groups attached to the silica gel. The humic substances were selected to secure appropriate variation of their structural features. The retention factors of 45 polycyclic aromatic compounds (PAC) to the four columns were determined by HPLC. The advantage of the technique is a large number of compounds can easily be studied. The binding procedure does not appear to cause a drastic selection between the HA molecules. The k' values obtained for the two Aldrich HA columns agree in general reasonably. The retention or sorption of the compounds increased with the size of the PAC and the number of lipophilic substituents, but decreased when polar substituents were present. The PAC retention was much stronger to the two HA columns than to the FA and blank column, both for hydrophobic polycyclic aromatic hydrocarbons (PAH) and the polar PAC. Other factors impacting the PAC binding may be specific interactions with HA and the ionic strength of the aqueous phase. The technique has been applied to do direct determinations of Koc.

The release of chloroform, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene and tetrachloroethene from an organic rich spruce forest soil was studied in laboratory incubation experiments by dynamic headspace analysis, thermodesorption and gas chromatography. Performance parameters are presented for the dynamic headspace system. For spruce forest soil, the results showed a significant increase in chloroform concentration in the headspace under aerobic conditions over a period of seven days, whereas the concentration of the other compounds remained fairly constant. A biogenic formation of chloroform is suggested, whereas for the other compounds anthropogenic sources are assumed. The addition of trichloroacetic acid to the soil increased the release of chloroform from the soil. It is, therefore, suggested that trichloroacetic acid also contributed to the formation of chloroform. Under the experimental conditions, the spruce forest soil released chloroform concentrations corresponding to a rate of 12 microg m(-2) day(-1). Data on chloroform production rates are presented and compared with literature results, and possible formation mechanisms for chloroform are discussed.

Using a group parameter, totalorganic halogens (TOX), high TOX concentrationswere found in leachates and leachate contaminatedgroundwaters at two Danish mixed sanitary andhazardous waste sites. With commonly used screeningprocedures for organic contaminants, the individualhalogenated organic compounds behind the high TOXcould not be found. Conversely, part of the TOX couldbe attributed to halogenated humic substances that cannot be analysed with conventional organic contaminantanalyses. Even though TOX can still be considered anindicator of leachate contamination in the aquifers,attempts to identify the halogenated contaminantsbehind the TOX using screening methods such as GC-MSwill be unsuccessful in most cases.

Ambient air and soil air of spruce forest, beech forest and grassland from Zealand, Denmark, were investigated for volatile chlorinated compounds by adsorbent tube sampling, thermodesorption, cryo-trapping and analysis by high-resolution gas chromatography with electron capture detection. The mean concentration of chloroform in the top soil–air was in the range of 0.4–2.3 ng l−1. Compared to ambient air, the chloroform concentration in the topsoil was 6.7, 4.3 and 4.6 times higher for spruce forest, beech forest and grassland, respectively. For tetrachloromethane, 1,1,1-trichloroethane, trichloroethene and tetrachloroethene, the concentrations were in the same order of magnitude (0.04–1.2 ng l−1). However, the concentration ratios between soil air and ambient air were close to unity. Release studies in the topsoil of the spruce forest showed an increase of the chloroform concentration of approximately 4 times the initial soil air concentration after 38 h, while the concentrations of the other volatile chlorinated compounds investigated remained fairly constant. The observed chloroform concentration profiles and release rates may indicate a biogenic formation of chloroform in the upper soil layer of spruce forests, whereas an anthropogenic origin is suggested for the other chlorinated compounds investigated. From the release study and concentration gradient measurements in the spruce forest soil, chloroform release to the atmosphere was calculated for northern temperate regions. The release was in the range of the annual anthropogenic chloroform emissions, and, therefore, the terrestrial environment can be considered as an important contributor to the atmospheric chloroform input.

The efficiency of nano filtration (NF) in producing drinking water from two types of humic ground waters was studied on site at a pilot scale in Denmark. At one site, the natural organic matter (NOM) consisted almost entirely of humic acids with a concentration of 20–22 mg C/l, a broad molecular weight distribution and a large fraction of high molecular weight NOM. At the other site, the initial NOM concentration was 7–11 mg C/l with 60% of the NOM as fulvic acids and a narrow molecular weight distribution around 2000 D. A spiral wound NF membrane with a nominal molecular weight cut-off (MWCO) of 200–500 D and a feed spacer of 0.75 mm in diamond configuration demonstrated superior NOM removal for both waters. Membrane productivity decline was observed due to the accumulation of NOM on the membrane surface or the precipitation of inorganic salts such as calcite (CaCO 3 ), dependent upon NOM and inorganic water chemistry types. Accumulated NOM was removed with an alkaline detergent recovering the initial membrane productivity by 90%, whereas the inorganic precipitation was removed with an acidic detergent followed by the alkaline detergent, recovering the initial productivity completely. A spiral wound NF membrane with a nominal MWCO of 180 D and a feed spacer of 1.25 mm in parallel configuration exhibited the same product water quality, but a higher and more stable membrane productivity than the first membrane. High cross flow and low operating pressure reduced the membrane productivity decline. Nanofiltration of humic ground water resulted in efficient removal of NOM and a stable productivity, if differences in NOM and inorganic raw water composition were considered in designing the nanofiltration process.

The adsorption of benzoic acid on synthetic calcite dispersed in cyclohexane has been studied between 296 and 346 K. The results can be successfully explained by a two-step model involving a Langmuir adsorption of first a layer of molecules oriented parallel to the surface and next, as the concentration of the adsorbate in the liquid phase increases, a gradual replacement of this layer with a monolayer of molecules oriented perpendicular to the surface. The maximum adsorption of benzoic acid in the perpendicular oriented monolayer has been determined to be 7.345 µmol/m2, independent of the temperature, and close to the theoretical value of 7.4 µmol/m2. The Langmuir constant for the second step, in which parallel adsorbed molecules are replaced by perpendicular adsorbed ones, varies from 2 x 10(3) L/mol at 296 K to 16 x 10(3) L/mol at 346 K, and the enthalpy and entropy changes associated with this part of the adsorption process are 37.9 kJ/mol and 0.191 kJ/mol K, respectively. In the same temperature interval the Langmuir constant for the first step of the adsorption process involving parallely adsorbed benzoic acid molecules is estimated to be fairly constant, and within a factor of 2 from the best fit value of 33 x 10(3) L/mol. Copyright 1998 Academic Press.

We present a novel technique for analyzing volatile organic compounds in air samples using a solid adsorbent together with temperature-programmed desorption and subsequent detection by membrane inlet mass spectrometry (TPD-MIMS). The new system has the advantage of a fast separation of compounds prior to the detection by MIMS. The gaseous sample is simply adsorbed on the adsorbent, which is then rapidly heated from 30 °C to 250 °C at a rate of 50 °C/min. Trapped organic compounds are released from the adsorbent into a helium stream at different temperatures depending on the strength of the interaction between the individual compound and the adsorbent. The helium stream carries the desorbed compounds to a membrane inlet (90 °C) equipped with a thin (25 μm) silicone membrane. The thin membrane and the high temperature of the membrane inlet allows most volatile compounds to diffuse through the membrane into the mass spectrometer in a few seconds. In this fashion we could completely separate many similar volatile compounds, for example toluene from xylene and trichloroethene from tetrachloroethene. Typical detection limits were at low or sub-nanogram levels, the dynamic range was 3 orders of magnitude, and the analysis time for a mixture was about 3–4 minutes. © 1998 John Wiley & Sons, Ltd.

It is known that large amounts of organic halogens are present in soil, but the relative contribution from different sources is unclear. The aim of the present study was to determine the storage of organic halogens in a spruce forest soil and the deposition by needle litterfall and to elucidate the relative contribution from needle litterfall in relation to other sources and sinks. Sampling was conducted in a small spruce forest area in Denmark. Soil samples were collected at six locations to a depth of 60 cm. Litterfall was collected in 15 sample collectors every third month during 1 year. Soil leachate was collected below the Bh horizon over two periods of 5 days at five locations distributed over the study site. Throughfall data was compiled from a previous study conducted at the same site and during the same period as the present study, and data concerning net formation in soil was estimated from previous studies at similar sites. The pool was 630 kg of Clorg ha-1, contribution from litterfall was 0.3...

Deposition of dissolved organic halogens by throughfall was determined in a small spruce forest site in Denmark (56°28'N, 8°24'E). The mean annual deposition of dissolved organic halogens was 377 g ha−1yr−1, and larger than the general deposition by precipitation. No relationship between the position of the collectors and the forest edge or dominating wind-direction was found, suggesting that dry deposition was not a major source. The concentration of organic halogens was related to that of organic carbon and decreased from the tree-trunk and outwards. In addition, the concentrations were higher during the growing season than during the dormant season. This indicates that the major part of the organic carbon and organic halogens in spruce forest throughfall originates from canopy leachates or other internal sources.

Samples of dissolved organic carbon (DOC) were obtained from landfill leachate-polluted groundwater at Vejen Landfill, Denmark. The humic acids, fulvic acids and the hydrophilic fraction were isolated and purified. Based on DOC measurements, the fulvic acid fraction predominated, accounting for about 60% of the total amount of DOC with an apparent molecular weight of about 1800 Da. The hydrophilic fraction constituted about 30% of the total amount of DOC with an apparent molecular weight of about 2100 Da, and the humic acid fraction made up about 10% of the total amount of DOC with an apparent molecular weight of about 2600 Da. The elemental compositions of the humic acids, fulvic acids and the hydrophilic fraction were in the ranges typical for humic substances from other origins. The O/C ratios for humic acids, fulvic acids and the hydrophilic fraction were similar in the leachate-polluted groundwater. For humic acids the O/C ratios were slightly higher than reported in the literature, indicating a high content of carboxylic groups, phenolic groups or carbohydrates. Acid-base titration indicated that, in the fulvic acids and the hydrophilic fraction, carboxylic acids were the dominating functional group, representing about 6 meq g −1 . The weakly acidic groups in fulvic acids and the hydrophilic fraction represented about 1 and 3 meq g −1 , respectively. The total acidity in fulvic acids and the hydrophilic fraction accounted for 48–57% of the O/C ratio. In the humic acids, carboxylic groups made up about 3 meq g −1 and the weakly acidic groups made up about 1.5 meq g −1 . The total acidity accounted for 29–32% of the O/C ratio. The characterization of DOC in leachate-polluted groundwater in terms of humic acids, fulvic acids and hydrophilic fraction showed that the hydrophilic fraction resembles, in many ways, humic and fulvic acids; thus, a distinction between the fractions may be related to the methods only and be of little practical value. The three fractions constituting the DOC content in a sample should all be considered when evaluating processes such as metal complexation and transport of metals and hydrophobic, organic contaminants. © 1998 Elsevier Science Ltd. All rights reserved

The wettability of hydrocarbon reservoirs depends on how and to what extent the organic compounds are adsorbed onto the surfaces of calcite, quartz and clay. A model system of synthetic calcite, cyclohexane and the three probe molecules: benzoic acid, benzyl alcohol and benzylamine, have been studied by adsorption experiments. The results clearly demonstrate the differences in the adsorption behaviour between probes with different functional groups of varying polarity and acidity. The maximum adsorption decreases in the order: benzoic acid, benzyl alcohol and benzylamine. The order of magnitude of ΔG° for the adsorption process implies the formation of a strong bond between the calcite surface and the adsorbate molecules.

Determination of total organic halogens (TOX) has proven susceptible to bias from high concentrations of a non-halogenated organic compound, N-butylbenzenesulfonamide (NBSA). High apparent TOX values occurred with more than 5–10 mg of NBSA applied to the carbon columns of the TOX procedure. Other non-halogenated organic compounds and inorganic sulfide may bias the method as well. When the TOX method is used as a measure of total organic halogens in environmental regulation and control, the risk of positive bias from non-halogenated compounds should always be emphasized.

Humic substances were isolated from groundwater according to a revised method designed to avoid organohalogen artefacts. The prepared humic substances exhibited lower halogen contents than humic substances isolated according to the conventionally used method. Excessive oxidation or hydrolysis was not observed with the revised method.

Haloperoxidase-15:e activity was monitored in samples from a podzol soil in an uncontaminated spruce forest at Klosterhede, Denmark. Activity for the oxidation of chloride and bromide was found. The pH optima for chlorination and brontination ranged between pH 2.5 and 4. Very high activity, up to 4.4 ∗ 10 3 mU kg −1 soil and 6.8 ∗ 10 3 mU kg −1 soil, respectively, was found in the surface layer. In the deeper soil layers, lower activity, between 1.5 – 23 mU kg −1 soil, was detected.

Structural, chemical, and isotopic parameters were used to identify the origins of groundwater humic substances from three Danish aquifers. A variety of analytical techniques (visible light absorption, molecular weight distribution, 13C-NMR spectroscopy, elemental composition with major elements and halogens, hydrolyzable amino acids and carbohydrates, carbon isotopes) applied to aquatic humic and fulvic acids led to consistent structural interpretations for each of the three aquifers studied. For humic substances in two aquifers, the analyses suggested source rocks in agreement with geological and hydrogeochemical information. In a third aquifer, source rock identification was inconclusive, and multiple fossil and recent organic carbon sources are suggested.

The efficiency of ultrafiltration in drinking water treatment of Danish humic ground waters was investigated. Membranes with pore sizes corresponding to molecular weight cut-offs (MWCO) ranging from 300–2000 g/mol were tested. The removal of organic matter depended on molecular weight distribution of the organic matter and ultrafiltration process parameters (applied pressure, membrane material, and the pore size of the employed membrane). Also, the presence of other compounds in the water, such as iron, affected the process. With the ultrafiltration technique, drinking water could be even obtained from very humic ground waters.

International audience; The Bioaccessibility Research Group of Europe (BARGE) has carried out an inter-laboratory trial of a proposed harmonised in vitro physiologically based ingestion bioaccessibility procedure for soils, called the Unified BARGE Method (UBM). The UBM includes an initial saliva phase and simulated stomach and intestine compartments. The trial involved the participation of seven laboratories (five European and two North American) providing bioaccessibility data for As (11 samples), Cd (9 samples) and Pb (13 samples) using soils with in vivo relative bioavailability data measured using a swine model. The results of the study were compared with benchmark criteria for assessing the suitability of the UBM to provide data for human health risk assessments. Mine waste and slag soils containing high concentrations of As caused problems of poor repeatability and reproducibility which were alleviated when the samples were run at lower soil to solution ratios. The study showed that the UBM met the benchmark criteria for both the stomach and stomach & intestine phase for As. For Cd, three out of four criteria were met for the stomach phase but only one for the stomach & intestine phase. For Pb two, out of four criteria were met for the stomach phase and none for the stomach & intestine phase. However, the study recommends tighter control of pH in the stomach phase extraction to improve between-laboratory variability, more reproducible in vivo validation data and that a follow up inter-laboratory trial should be carried out.

A regional survey of Danish ground water demonstrated the presence of adsorbable organic halogens (AOX) in almost all of 142 wells (99 percent). Generally, the presence of AOX was not related to point or non-point source contamination with halogenated organics. However, the AOX concentrations varied with the geology of the aquifers. Extractable organic halogens (EOX) and volatile organic halogens (VOX) were far less prevalent (detected in 4 percent of sampled wells) and the detection could, in most cases, be explained by contamination or chlorination of the wells. The VOX concentrations corresponded to the concentrations of identified, volatile contaminants. The study demonstrates the presence of a natural background level of AOX in the investigated aquifers. This must be considered in the interpretation of AOX results as an indicator of ground water contamination with haloorganics. Similar background levels of EOX or VOX were not delected.

In a series of aerobic biodegradation studies it was demonstrated that up to 11% of dissolved organic carbon (DOC) of an unfractionated groundwater sample could be degraded microbiologically. After fractionation according to apparent molecular weight and polarity/p K a , the degradability accumulated for all fractions increased to 21–22%. DOC of apparent low molecular weight and hydrophilic organics was more readily degraded, 27% and 28%, respectively. The degradability of high molecular weight organics and hydrophobic acids was 8.5% and 14%, respectively. A considerable increase in viable bacterial counts (20–1300 times) was observed during degradation of the DOC. Bacterial activity, expressed by the ATP concentrations, was maintained even in periods of marginal turnover of groundwater DOC.

Humic acid from the B horizon of a podzol profile was extracted and purified by a revised procedure, which avoids organohalogen artefacts. The prepared humic acid contained 0.24% halogens. Analyses for adsorbable organic halogens (AOX), of aqueous solutions of the humic acid and molecular weight and polarity/pKa fractions showed, that 65% of the halogen content of the humic acid could be attributed to organic halogens and not to inorganic halogenides. A natural origin of the halogenated humic substances is suggested. Our general perception of organohalogens as antropogenics in the environment is discussed in view of the occurrence of a natural organohalogen pool in soil humic substances.

A set of analytical methods for the determination of the organic halogen group parameters AOX, EOX and VOX has been developed and tested for applicability in ground water studies. The methods can be applied in the range 1–100 μg ct/L with a relative standard deviation of 5–10%. The methods are unbiased by interference from many common constituents in ground waters, but high concentrations of iodide and sulphide may bias the AOX determination. Highly humic waters and waters heavily polluted with volatile, non-halogenated organics might exhibit reduced recoveries of EOX and VOX, respectively. Each method contributes with information on the nature of the organic halogens with respect to volatility and polarity, as demontrated by a recovery study for selected test compounds.

The occurrence and properties of halogenated organic compounds determined as adsorbable organic halogens (AOX) in Danish groundwaters were investigated. Preceded by a thorough evaluation of analytical procedures, a nation-wide survey of 145 wells was conducted. AOX was found in all wells but one, at levels from 1 µg Cl/l to 80 µg Cl/l. The occurrence of AOX was strongly correlated to the amount of organic carbon in the samples. Resampling of 6 wells and further characterization of these samples revealed, that the AOX consisted of organically bound chlorine, bromine and iodine of molecular weight distribution and polarity/pKa properties resembling those of the bulk mass of dissolved organic carbon. Except for a few locations, where inorganic iodide may have biased the AOX determinations, there was no indication of analytical artefacts. The ubiquitous occurrence of AOX in Danish groundwaters is not likely to be caused by man-made pollutants, but is attributed to naturally occurring halogenated, humic compounds.

Ambient air, soil air, and groundwater were monitored for volatile halogenated organic compounds in a pristine spruce forest at Klosterhede, Denmark. Although this location is remote from industrial areas and free of any point sources of either soil or groundwater contamination, several volatile chlorinated hydrocarbons were detected. The concentration profiles of chloroform indicated a formation of this compound in the soil. Low concentrations were found in ambient air (0.02 ng L−1), higher concentrations in the upper soil layers (9.6 ng L−1 at 0.75 m below the surface), and a decrease with increasing depth (down to 1.5 ng L−1 just above the groundwater table at 7.5 m below the surface). For the other identified chlorinated compounds the concentration profiles were different from those of chloroform and exhibited less systematic variation between ambient air and soil air and with increasing depth. In the phreatic groundwater, high concentrations (up to 1.6 μg L−1) of chloroform and low concentrations (