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[en] The role of native soil microorganisms in the formation and release of non-extractable 14C-residues, previously treated with 14C-Dicamba, was investigated to examine their significance to the longer-term environmental effects on non-extractable pesticide residues. A 90 d study compared the fate of Dicamba under sterile and non-sterile regimes. In addition, soils were aged for 30 d and repeatedly extracted with a 0.01 M CaCl2 solution, to an extraction end point, to produce non-extractable residues. The extracted soil containing non-extractable residues was mixed with clean soil that had been freshly spiked with non-labeled Dicamba at 0.2 mg kg-1 to increase the bulk volume of the soil and stimulate microbial activity. Sub-samples were then introduced into microcosms to compare the extent of microbially facilitated release and mineralisation with release rates in sterile microcosms. The results show that microorganisms play a significant role in the formation and release of non-extractable Dicamba residues. The release of 14C-activity in sterile microcosms was linked to physical mixing of the extracted soil with field soil prior to the beginning of the incubations. The released 14C-activity may be further mineralized, reincorporated into humus, or taken up by plants or other soil inhabiting biota
[en] Laboratory based studies on the fate of organic contaminants in soil typically requires the test compound(s) to be spiked into the test medium. Consequently, such studies are inherently dependant on the homogeneity of the contaminant within the spiked soil. Three blending methods were compared for the addition of a phenanthrene-transformer oil mixture into field-wet soil. Spiking homogeneity, reproducibility and artefacts were assessed based on dichloromethane and hydroxypropyl-β-cyclodextrin chemical extractability, and bacterial mineralization. Spiking using a stainless-steel spoon, consistently produced good spike homogeneity as determined by sample oxidation, chemical extraction and mineralization, and was consistently more reliable than either the Waring blender or modified bench drill. Overall, neither transformer oil-concentration nor blending method influenced chemical extractability or mineralization of the PAH following 1 day equilibration. In general, spiking procedures require validation prior to use, as homogeneity cannot be assured. - Ensuring homogeneity in soil spiking studies is important and advice is given on how to achieve it
[en] This investigation considered the effects of Zn, Cu, Al and Fe (50 and 500 mg kg−1) on the loss, sequential extractability, using calcium chloride (CaCl2), hydroxypropyl-β-cyclodextrin (HPCD) and dichloromethane (DCM) and biodegradation of 14C-phenanthrene in soil over 63 d contact time. The key findings were that the presence of Cu and Al (500 mg kg−1) resulted in larger amounts of 14C-phenanthrene being extracted by CaCl2 and HPCD. Further, the CaCl2 + HPCD extractions directly predicted the biodegradation of the PAH in the presence of the metals, with the exception of 500 mg kg−1 Cu and Zn. The presence of high concentrations of some metals can impact on the mobility and accessibility of phenanthrene in soil, which may impact on the risk assessment of PAH contaminated soil. -- Highlights: •Phenanthrene partitioning and bioaccessibility is influenced by metals in soil. •Phenanthrene was more extractable at higher concentrations of Cu and Al. •Higher concentrations of Al inhibited phenanthrene mineralisation. -- Capsule: High concentrations of Cu and Al (500 mg kg−1) can retard the sequestration of phenanthrene in soil
[en] Six major use pesticides (Atrazine, Dicamba, Isoproturon, Lindane, Paraquat and Trifluralin) with differing physico-chemical properties were evaluated for the significance of 'bound' or non extractable residue formation. Investigations were carried out in purpose-built microcosms where mineralization, volatilisation, 'soil water' extractable and organic solvent extractable residues could be quantified. Extractable residues were defined as those accessible by sequential extraction where the solvent used became increasingly non-polar. Dichloromethane was the 'harshest' solvent used at the end of the sequential extraction procedure. 14C-labelled volatilised and 14CO2 fractions were trapped on exit from the microcosm. The pesticides were categorised into 3 classes based on their behaviour. (i) Type A (Atrazine, Lindane and Trifluralin) in which ring degradation was limited as was the formation of non-extractable residues; the remainder of the 14C-activity was found in the extractable fraction. (ii) Type B (Dicamba and Isoproturon) in which approximately 25% of the 14C-activity was mineralised and a large portion was found in the non-extractable fraction after 91 days. Finally, Type C (Paraquat) in which almost all of the 14C-activity was quickly incorporated into the non-extractable fraction. The implications of the data are discussed, with respect to the variability and significance of regulatory aspects of non-extractable residues
[en] The influence of PAH chemical structure and concentration, added in either single (75 or 300 mg kg-1) or multiple (2 x 75, 2 x 150 or 4 x 75 mg kg-1) applications as single- or multiple-contaminant systems, on the development of PAH biodegradation in a pristine soil was investigated. Development in microbial catabolic ability was assessed at 0, 28, 56 and 84 d by monitoring 14C-naphthalene, 14C-phenanthrene and 14C-pyrene mineralisation over 14 d in respirometric assays. The presence of other contaminants influenced the ability of the indigenous microflora to mineralise structurally different contaminants over time. 14C-Naphthalene mineralisation was inhibited by the presence of other contaminants; whereas the presence of naphthalene significantly enhanced rates of mineralisation in multiple-contaminant systems containing 14C-phenanthrene and 14C-pyrene. Generally, increasing the number of contaminant applications has implications for catabolic activity of soil microbes. It is suggested the toxic nature of PAHs retarded mineralisation at increased contaminant concentrations. - The simultaneous effects of PAH concentration, contaminant mixture and repeated application on the development of catabolic activity in soil.
[en] The desorption of polycyclic aromatic hydrocarbons (PAHs) often exhibits a biphasic profile similar to that observed for biodegradation whereby an initial rapid phase of degradation or desorption is followed by a phase of much slower transformation or release. Most investigations to-date have utilised a polymeric sorbent, such as Tenax, to characterise desorption, which is methodologically unsuitable for the analysis of soil. In this study, desorption kinetics of 14C-phenanthrene were measured by consecutive extraction using aqueous solutions of hydroxypropyl-β-cyclodextrin (HPCD). The data indicate that the fraction extracted after 24 h generally approximated the linearly sorbed, rapidly desorbing fraction (Frap), calculated using a three-compartment model. A good linear correlation between phenanthrene mineralised and Frap was observed (r2 = 0.89; gradient = 0.85; intercept = 8.20). Hence HPCD extraction (24 h) and first-order three-compartment modelling appear to provide an operationally straightforward tool for estimating mass-transfer limited biodegradation in soil. - Aqueous hydroxypropyl-β-cyclodextrin (HPCD) solutions can predict the rapidly desorbing and microbially degradable fractions of phenanthrene in soils.
[en] The behaviour of diazinon in the soil determines the likelihood of further pollution incidents, particularly leaching to water. The most significant processes in the control of the fate of diazinon in the soil are microbial degradation and the formation of bound residues. Soils from four sites in the UK were amended with diazinon and its 14C labelled analogue and incubated for 100 days. After 0, 10, 21, 50 and 100 days, the formation of bound residues was assessed by solvent extraction, and the microbial degradation of diazinon by mineralisation assay. In microbially active soils, diazinon is degraded rapidly, reducing the risk of future pollution incidents. However, where there was limited mineralisation there was also significantly lower formation of bound residues, which may lead to water pollution via leaching. The formation of bound residues was dependent on extraction type. Acetonitrile extraction identified bound residues in all soils, with the bound residue fraction increasing with increasing incubation time. - Research highlights: → Bound residues are defined by extraction method. → Microbial degradation is limited by the formation of bound residues. → Bioavailability of diazinon maybe estimated by chemical extraction. - The formation of bound residues and biodegradation of diazinon are dependent on soil type and the presence of degrading bacteria.
[en] The effect of cable oil concentration, nutrient amendment and bioaugmentation on cable oil component biodegradation in a pristine agricultural soil was investigated. Biodegradation potential was evaluated over 21 d by measuring cumulative CO2 respiration on a Micro-Oxymax respirometer and 14C-phenyldodecane mineralisation using a 14C-respirometric assay. Cable oil concentration had a significant effect upon oil biodegradation. Microbial respiratory activity increased with increasing cable oil concentration, whereas 14C-phenydodecane mineralisation decreased. Bioaugmentation achieved the best cable oil biodegradation performance, resulting in increases in cumulative CO2 respiration, and maximum rates and extents of 14C-phenyldodecane mineralisation. Generally, nutrient amendment also enhanced cable oil biodegradation, but not to the extent that degrader amendment did. Cable oil biodegradation was a function of (i) cable oil concentration and (ii) catabolic ability of microbial populations. Bioaugmentation may enhance cable oil biodegradation, and is dependent upon composition, cell number and application of catabolic inocula to soil. - Highlights: → Cable oil concentration had a significant effect upon oil biodegradation. → Microbial respiratory activity increased with increasing cable oil concentration. → Bioaugmentation achieved the best cable oil biodegradation performance. → Biodegradation was affected by cable oil concentration and microbial activity. - Cable oil concentration and bioaugmentation strongly influence cable oil biodegradation in soils.
[en] The effects of monoterpenes on the degradation of 14C-2,4-dichlorophenol (DCP) were investigated in soils collected from areas surrounding monoterpene and non-monoterpene-emitting vegetation. Indigenous microorganisms degraded 14C-2,4-DCP to 14CO2, after 1 d contact time. Degradation was enhanced by prior exposure of the soils to 2,4-DCP for 32 d, increasing extents of mineralisation up to 60%. Monoterpene amendments further enhanced 2,4-DCP degradation, but only following pre-exposure to both 2,4-DCP and monoterpene, with total 2,4-DCP mineralisation extents of up to 71%. Degradation was greatest at the higher monoterpene concentrations (≥1 μg kg-1). Total mineralisation extents were similar between concentrations, but higher than the control and the 0.1 μg kg-1 amendment, indicating that increases in monoterpene concentration has a diminishing enhancing effect. We suggest that monoterpenes can stimulate the biodegradation of 2,4-DCP by indigenous soil microorganisms and that monoterpene amendment in soils is an effective strategy for removing organic contaminants. - A amendment of soils with monoterpenes may induce organic contaminant degradation by indigenous soil microorganisms
[en] The work presented in this paper investigated the effects of plant species composition, species diversity and soil fertility on biodegradation of 14C-phenanthrene in soil. The two soils used were of contrasting fertility, taken from long term unfertilised and fertilised grassland, showing differences in total nitrogen content (%N). Plant communities consisted of six different plant species: two grasses, two forbs, and two legume species, and ranged in species richness from 1 to 6. The degradation of 14C-phenanthrene was evaluated by measuring indigenous catabolic activity following the addition of the contaminant to soil using respirometry. Soil fertility was a driving factor in all aspects of 14C-phenanthrene degradation; lag phase, maximum rates and total extents of 14C-phenanthrene mineralisation were higher in improved soils compared to unimproved soils. Plant identity had a significant effect on the lag phase and extents of mineralisation. Soil fertility was the major influence also on abundance of microbial communities. - Highlights: ► Two grassland soils of contrasting fertility showing differences in total nitrogen content (%N) were used in this study. ► The effects of individual plant species and plant diversity on mineralisation of 14C-phenanthrene in soil were investigated. ► Soil fertility was the major influence on mineralisation of 14C-phenanthrene, and abundance of microbial community. ► The presence of a specific plant plays a role in the extent of mineralisation of phenanthrene in soil. - Soil management was the main driver for the mineralisation of 14C-phenanthrene in soil.