Arctic and Subarctic Natural Soils Emit Chloroform and Brominated Analogues by Alkaline Hydrolysis of Trihaloacetyl Compounds.

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.

Degradation of the potato glycoalkaloids--alpha-solanine and alpha-chaconine in groundwater.

The potato glycoalkaloids alpha-chaconine and alpha-solanine are produced in high amounts in potato plants from where release to soil takes place. Degradation of the compounds in groundwater was investigated, as their fate in the terrestrial environment is unknown. Abiotic and microbial degradation were followed in groundwater sampled from below a potato field and spiked with the glycoalkaloids (115 nmol/l). Degradation was primarily microbial and the glycoalkaloids were degraded within 21-42 days. The metabolites beta(1)-solanine, gamma-solanine, and solanidine were formed from alpha-solanine, while beta-chaconine, gamma-chaconine and solanidine were detected from alpha-chaconine. Thus, indigenous groundwater microorganisms are capable of degrading the glycoalkaloids.

Potato glycoalkaloids in soil-optimising liquid chromatography-time-of-flight mass spectrometry for quantitative studies.

Potato glycoalkaloids are produced in high amounts in potato fields during the growth season and losses to soil potentially impact shallow groundwater and via tiles to fresh water ecosystems. A quantitative liquid chromatography-electrospray ionization time-of-flight mass spectrometry (LC-ESI-TOF-MS) method for determination and quantification of potato glycoalkaloids and their metabolites in aqueous soil extracts was developed. The LC-ESI-TOF-MS method had linearities up to 2000microg/L for alpha-solanine and alpha-chaconine and up to 760microg/L for solanidine. No matrix effect was observed, and the detection limits found were in the range 2.2-4.7microg/L. The method enabled quantification of the potato glycoalkaloids in environmental samples.

Sorption, desorption and mineralisation of the herbicides glyphosate and MCPA in samples from two Danish soil and subsurface profiles.

The vertical distribution of the sorption, desorption and mineralisation of glyphosate and MCPA was examined in samples from two contrasting soil and subsurface profiles, obtained from a sandy agricultural site and a non-agricultural clay rich site. The highest mineralisation of [14C-methylen]glyphosate, with 9.3-14.7% degraded to 14CO2 within 3 months was found in the deepest sample from the clay site. In the deeper parts of the sandy profile high sorption and low desorption of glyphosate coincided with no or minor mineralisation indicating a limited glyphosate bioavailability. MCPA was readily mineralised except in the deepest samples from both sites. The highest MCPA mineralisation was detected just below the surface layers with 72% or 44% degraded to 14CO2 at the sandy or the clay sites, respectively. MCPA sorped to a minor extent in all samples and no indications of sorption-controlled mineralisation was revealed. None of the herbicides were mineralised under anoxic conditions.

Aging of triazine amine in soils demonstrated through sorption, desorption, and bioavailability measurements.

The aging of triazine amine in soil was studied during a time course of 119 d by measuring bioavailability in terms of mineralization after inoculation of the triazine amine-degrading bacterium Rhodococcus erythropolis TA57. The bioavailability was measured in four soil samples: A-, B-, and C-horizons from an agricultural soil profile and in a peat soil. The sorption of triazine amine in the soil samples was quantified during the period of aging in terms of sorption distribution coefficients (Kd) and desorption distribution coefficients (Kd,des). Measures of bioavailability and triazine amine concentration in the nonavailable fraction showed effects of aging in the soils that were rich in organic matter. The triazine amine bioavailability declined significantly during the aging period in soils containing greater than 2% organic carbon, whereas the B- and C-horizons showed no signs of aging, in agreement with their low content of organic material. Corresponding to this, desorption decreased significantly in the A-horizon but, surprisingly, not in the peat soil. Analyses by thin-layer chromatography indicated an association of aqueous triazine amine and dissolved organic matter in the peat soil. This gives an explanation for both the significant decrease in bioavailability and the noncorresponding stability of the nonavailable (i.e., nondesorbed) fraction.

Spatial variability in the mineralisation of the phenylurea herbicide linuron within a Danish agricultural field: multivariate correlation to simple soil parameters.

The spatial variability in the mineralisation rate of linuron [N-(3,4-dichlorophenyl)-N'-methoxy-N'-methylurea] was studied within a previously treated Danish agricultural field by sampling soils from eleven different plots randomly distributed across an area of 20 x 20 m. The soils were characterised with respect to different abiotic and biotic properties including moisture content, organic matter content, pH, nutrient content, bacterial biomass, potential for mineralisation of MCPA [(4-chloro-2-methylphenoxy)acetic acid] and linuron. Five soils had a potential for mineralisation of linuron, with 5-15% of the added [ring-U-14C]linuron metabolised to 14CO2 within 60 days at 10 degrees C, while no extensive mineralisation of linuron was observed in the six remaining soils within this period. A TLC analysis of the methanol-extractable residues showed no development of 14C-labelled metabolites from linuron in any of the samples. Multivariate analysis was conducted to elucidate relationships between the intrinsic properties of single soil samples and initial rate of linuron mineralisation. The analysis indicated that important soil parameters in determining the spatial heterogeneity included the C(total)/N(total) ratio, pH and the water-extractable potassium contents, with the first of these highly negatively correlated and the last two highly positively correlated to the initial linuron mineralisation rate. This study shows that enhanced biodegradation of linuron may develop with successive field treatments, but that considerable in-field spatial heterogeneity in the degradation rate still exists. Combined with a parallel enrichment study focused on the underlying microbial processes, the present results suggest that intrinsic soil properties affect the linuron-metabolising bacterial population and thereby determine the spatial variability in the linuron mineralisation activity.

Sorption, mineralization and mobility of N-(phosphonomethyl)glycine (glyphosate) in five different types of gravel.

Sorption, mineralization and mobility of glyphosate were studied in six substrates: the five types of gravel most frequently used as surfacing in Denmark and a sandy agricultural soil from Simmelkaer that served as a reference soil. Cumulative mineralization of [methyl-14C]glyphosate in batch studies was highest in coarse gravel, amounting to 14% after 4 days at 30 degrees C and 32% after 31 days. Mineralization was slowest in the sandy reference soil, amounting to only 2% after 31 days. The adsorption coefficient (Kd) of glyphosate in gravel ranged from 62 to 164 litre kg(-1), while that in the sandy reference soil was 410 litre kg(-1). The results indicate that the relatively low Kd in gravel allows a relatively high rate of glyphosate mineralization by the biomass. When Kd is high, in contrast, mineralization is slow. Lowering the temperature to 10 degrees C decreased mineralization by 50% in one of two gravels. The leaching of glyphosate was screened in simple columns of gravel or soil in which precipitation events (20 mm over a 2-h period) were simulated on three occasions, starting either immediately after or 2 days after application of glyphosate. [14C]Glyphosate was applied as a tracer mixed with the commercial product Roundup Garden at the recommended rate of 2.4 kg glyphosate ha(-1), equivalent to 1 microg g(-1) soil. The highest concentration of [14C] compounds (expressed in terms of glyphosate concentration) in leachate from the columns exceeded 1300 microg litre(-1), and was detected in rounded gravel after the first rain event. No glyphosate was detected in leachate from the sandy reference soil.

The naturally occurring carcinogen ptaquiloside is present in groundwater below bracken vegetation.

The present study demonstrates unequivocally the presence of the natural carcinogen ptaquiloside and its transformation product pterosin B in groundwater and surface water. Groundwater concentrations up to 0.23 nmol/L (92 ng/L) ptaquiloside and up to 2.2 nmol/L (0.47 µg/L) pterosin B were found. Of 21 groundwater samples, 5 contained ptaquiloside, exceeding the estimated threshold for drinking water (1.3-40 pmol/L). The results are critical for water abstraction in bracken-infested areas.

Determination of total organic halogen (TOX) in humic acids after microwave-induced combustion.

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.

The influence of organic matter on sorption and fate of glyphosate in soil--comparing different soils and humic substances.

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.

A radiorespirometric method for measuring mineralization of [14C]-compounds in a 96-well microplate format.

A radiorespirometric method was developed for quantifying mineralization of [14C]-labeled substrates in deep-well microplates. Ninety-six 14CO2-traps were placed on an adhesive microplate sealing tape which made it possible to trap 14CO2 simultaneously from all wells. Trapped radioactivity was quantified by digital autoradiography.

Effect of different humic substances on the fate of diuron and its main metabolite 3,4-dichloroaniline in soil.

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.

Quantification of ptaquiloside and pterosin B in soil and groundwater using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

The carcinogenic compound ptaquiloside is produced by bracken fern (Pteridium aquilinum L.). Ptaquiloside can enter the soil matrix and potentially leach to the aquatic environment, and methods for characterizing ptaquiloside content and fate in soil and groundwater are needed. A sensitive detection method has been developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for analyzing ptaquiloside and its transformation product pterosin B. Detection limits are 0.19 microg/L (ptaquiloside) and 0.15 microg/L (pterosin B), which are 300-650 times better than previously published LC-UV methods. Sequential soil extractions are made using 5 mM ammonium acetate for extraction of ptaquiloside, followed by 80% methanol extraction for pterosin B. Groundwater samples are cleaned-up and preconcentrated by a factor of 20 using solid-phase extraction. The LC-MS/MS method enables quantification of ptaquiloside and pterosin B in soil and groundwater samples at environmentally relevant concentrations and delivers a reliable identification because of the structure-specific detection method.

Elucidating the key member of a linuron-mineralizing bacterial community by PCR and reverse transcription-PCR denaturing gradient gel electrophoresis 16S rRNA gene fingerprinting and cultivation.

A bacterial community from Danish agricultural soil was enriched with linuron [N-(3,4-dichlorophenyl)-N'-methoxy-N'-methylurea] as the sole carbon and nitrogen source. The community mineralized [ring-U-14C]linuron completely to 14CO2 and 14C-biomass. Denaturing gradient gel electrophoresis analysis and cultivation revealed that a Variovorax sp. was responsible for the mineralization activity.

Sorption-controlled degradation kinetics of MCPA in soil.

The relationship between sorption strength and degradation kinetics has been studied for the pesticide MCPA in a sandy top- and subsoil. After adding two types of sorbents (crushed peat and activated carbon) in various amounts to the sandy soils, sorption, desorption, and mineralization of 14C-MCPA were measured. The obtained Freundlich constants (KF) varied between 0.7 and 27.2 mg(1-nF) x L(nF)/kg, and the first-order mineralization rate constants varied between 0.001 and 0.128 d(-1). The results showed an inverse relationship between sorption strength and mineralization. A higher KF value corresponded to a smaller mineralization rate and less mineralization. A correlation coefficient of r2 = 0.934 between the log-transformed Freundlich desorption coefficient (K(F,des)) and the log-transformed mineralization rate constant (k) was obtained. After 7, 14, 22, and 35 days of incubation, soil samples were consecutively extracted by water, methanol, and 5 M NaOH to separate the remaining 14C into 3 different pools. The extractions showed that the mineralization only proceeded from the water extractable pool of MCPA. Thin-layer chromatography revealed a formation of small amounts of metabolites; <7% of initially added 14C was present as other compounds than 14C-MCPA in the water and methanol extractable pools. The study showed mineralization to be strongly correlated with sorption, represented by the desorption coefficient, and hence stresses the significance of bonding strength for estimating pesticide degradation in soil.