Biodegradation of 2,4-dichlorophenol in the presence of volatile organic compounds in soils under different vegetation types

It has been suggested that monoterpenes emitted within the soil profile, either by roots or by decaying biomass, may enhance the biodegradation of organic pollutants. The aim of this study was to evaluate the effect of biogenic volatile organic compounds (VOCs) on the catabolism of 2,4-dichlorophenol in soils. Soils were collected from areas surrounding monoterpene (woodland) and nonmonoterpene (grassland)-emitting vegetation types. Soils were spiked with [UL-¹⁴C] 2,4-dichlorophenol at 10 mg kg⁻¹ and amended with α-pinene, p -cymene or a mix of monoterpenes (α-pinene, limonene and p -cymene in 1 : 1 : 1 ratio). The effects of monoterpene addition on the catabolism of [UL-¹⁴C] 2,4-dichlorophenol to ¹⁴CO₂ by indigenous soil microbial communities were assessed in freshly spiked and 4-week-aged soils. It was found that aged woodland soils exhibited a higher level of [UL-¹⁴C] 2,4-dichlorophenol degradation, which was subsequently enhanced by the addition of monoterpenes ( P <0.001), with the VOC mix and α-pinene amendments showing increased [UL-¹⁴C] 2,4-dichlorophenol catabolism. This study supports claims that the addition of biogenic VOCs to soils enhances the degradation of xenobiotic contaminants.     

Isolation and characterization of 2,4-dichlorophenoxyacetic acid-catabolizing bacteria and their biodegradation efficiency in soil

Bacterial isolates (NJ 10 and NJ 15) capable of degrading the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) were isolated from agricultural soil by enrichment culture technique. The isolates exhibited substantial growth in mineral salt medium supplemented with 0.1–0.5% of 2,4-D as a sole source of carbon and energy. Based on their morphological, cultural and biochemical characteristics, the isolates NJ 10 and NJ 15 have been identified as Pseudomonas species and Pseudomonas aeruginosa, respectively. Biodegradation studies in a soil microcosm enriched with pure cultures of the isolates demonstrated a time-dependent disappearance of 2,4-D from the 100 mg/kg herbicide-amended soil. The HPLC data analysis revealed 96.6 and 99.8% degradation in the soil inoculated with the pure cultures of isolates NJ 10 and NJ 15, respectively with in 20 days of incubation at 30 °C. Both the isolates showed significant solubilization of inorganic phosphate [Ca₃(PO₄)₂] on the specific Pikovskaya's medium.     

Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds

The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d^-1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions.     

南亚热带典型地区农业土壤中多环芳烃和有机氯农药研究

参考美国EPA标准方法对南亚热带潮汕地区农业土壤中持久性有机污染物多环芳烃（PAHs）和有机氯农药（OCPs）进行分析,并对其分布和来源进行研究,最后探讨了不同种植方式下污染物的污染特征。结果表明：该区农业土壤中PAHs含量范围从22．1ng／g到1256．9ng／g,与其它地区的污染程度和一些土壤环境质量标准相比,该区处于中等污染水平。高温裂解是土壤PAHs的主要来源。OCPs在被禁止20a后在土壤中仍有残留,残留水平从4．6ng／g到1021．5ng／g,其中HCHs和DDTs的残留未超过国家土壤环境质量标准。早期使用残留是其主要污染源,但新近仍有DDT和硫丹的输入。PAHs和OCPs的污染主要集中在土壤表层和亚表层,且随着深度的加深,污染逐渐减少,但40cm以下,污染变化很小。菜地土壤PAHs污染水平低于稻田土壤,而OCPs污染水平高于稻田土壤。     

Sulphate-reducing bacteria,palladium and the reductive dehalogenation of chlorinated aromatic compounds

The surfaces of cells of Desulfovibrio desulfuricans,Desulfovibrio vulgaris and a new strain, Desulfovibrio sp. `Oz-7' were used to manufacturea novel bioinorganic catalyst via the reduction of Pd(II) to Pd(0) at the cell surface usinghydrogen as the electron donor. The ability of the palladium coated (palladised) cells to reductivelydehalogenate chlorophenol and polychlorinated biphenyl species was demonstrated. Dried, palladisedcells of D. desulfuricans, D. vulgaris and Desulfovibrio sp. `Oz-7'were more effective bioinorganic catalysts than Pd(II) reduced chemically under H₂ orcommercially available finely divided Pd(0). Differences were observed in the catalyticactivity of the preparations when compared with each other. Negligible chloride release occurredfrom chlorophenol and polychlorinated biphenyls using biomass alone.     

Biodegradation and kinetics of organic compounds and heavy metals in an artificial wetland system (AWS) by using water hyacinths as a biological filter

The objective of the present study was to investigate the ability of water hyacinth (Eichhornia crassipes) to absorb organic compounds (potassium hydrogen phthalate, sodium tartrate, malathion, 2,4-dichlorophenoxy acetic acid (2,4-D), and piroxicam). For the aforementioned purpose, an artificial wetland system (AWS) was constructed and filled with water hyacinth collected from the Valsequillo Reservoir, Puebla, Mexico. Potassium hydrogen phthalate and sodium tartrate were measured in terms of chemical oxygen demand (COD) and biological oxygen demand (BOD). The present study indicated that the water hyacinths absorbed nearly 1.8–16.6 g of COD kg^?1 dm (dry mass of water hyacinth), while the absorbance efficiency of BOD was observed to be 45.8%. The results also indicated that the maximum absorbance efficiency of malathion, 2,4-D, and piroxicam was observed to be 67.6%, 58.3%, and 99.1%, respectively. The kinetics of organic compounds fitted different orders as malathion followed a zeroth-order reaction, while 2,4-D and piroxicam followed the first-order reactions. Preliminary assessment of absorption of heavy metals by the water hyacinth in the AWS was observed to be (all values in mg g^?1) 7 (Ni), 13.4 (Cd), 16.3 (Pb), and 17.5 (Zn) of dry biomass, thus proving its feasibility to depurate wastewater.     

Fate of the herbicides mecoprop, dichlorprop, and 2,4-D in aerobic and anaerobic sewage sludge as determined by laboratory batch studies and enantiomer-specific analysis

Aerobic degradation experiments with the racemic mixtures of mecoprop and dichlorprop revealed that activated sludge collected from the aeration tank of a municipal waste water treatment plant degraded both enantiomers of mecoprop and dichlorprop within 7 days, albeit in an enantioselective manner; the (S) enantiomers were preferentially degraded. Mecoprop, dichlorprop, and 2,4-D were completely metabolized under aerobic conditions, as shown by the 86–98% elimination of dissolved organic carbon. Under anaerobic conditions, the concentration of 2,4-D decreased exponentially with a first-order reaction rate constant of 0.24 per day and without a lag-phase. After an incubation time of 17 days, 2,4-D was completely removed. 2,4-Dichlorophenol was the main metabolite of anaerobic 2,4-D degradation; only traces of 4-chlorophenol were detected. In contrast, the chiral phenoxypropionic acid herbicides mecoprop and dichlorprop persisted under anaerobic conditions during 49 days of incubation.     

Factors affecting the growth of Eucalyptus delegatensis seedlings in inhibitory forest and grassland soils

In many highland forests of Eucalyptus delegatensis in Tasmania the establishment and healthy growth of eucalypts is promoted and maintained by fire. In the absence of fire, secondary succession from eucalypt forest to rainforest occurs, during which the eucalypts decline and die prematurely. On sites that are prone to radiation frost severe reduction or removal of a tree canopy allows a sward of tussock grasses to develop, in competition with which seedlings of eucalypts decline in growth and a high proportion dies.Factors of the soil that could contribute to these phenomena were investigated by means of pot experiments that used soils from:o     

Reaction of the soil microflora after contamination with chlorinated aromatic compounds and HCH

Abstract The effect of the pollution of an industrial land site with chlorinated benzenes, chlorinated phenols, hexachlorocyclohexane-isomers (HCH) on the soil microflora was investigated. Cell counts (microscopic and by plate count) as well as respiration rated did not correlate negatively with the concentration of the contaminants. Soil microorganisms grew in the presence of up to 750 μmol 1⁻¹ pf chlorinated compounds in liquid culture. Only 150 μmol l⁻¹ 2,4,5-trichlorophenol (2,4,5-TCP) inhibited growth totally. In enrichment cultures, bacteria used α- and γ-HCH, 3-chlorophenol (3-CP), 2,3-dichlorophenol (2,3-DCP), 2,6-DCP, 2,4,5-TCP, and 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB) as a sole source of carbon and energy under aerobic conditions. No growth was observed with β-HCH. Under anaerobic conditions no growth was observed with any of the substances tested     

Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes

Forest soils demonstrate in a microcosm the difficulties that are faced in quantifying methyl halide budgets. Carbon isotopic analyses have been proposed as a potential tool to address these concerns and in this study we have measured significant enrichment of the methyl chloride ¹³C/¹²C isotopic ratio (from ?40.2 ± 0.8‰ to ?33.4 ± 7.4‰) after 9 min chamber emplacement on local Irish forest soils. This enrichment occurred independent of direction of methyl chloride fluxes. Measurements from soil cores in a flow‐through system (FTS) are comparable with chamber‐based isotopic measurements and indicate that methyl chloride produced abiotically from organic soil horizons has an isotopic ¹³C signature of ?53 ± 49‰, significantly less depleted than previously reported. Average net methyl chloride, methyl bromide and methyl iodide fluxes from soils (77.8 ± 2.1, 1.25 ± 3.63 and 0.35 ± 2.00 μg MeX m^?2 day^?1, respectively) are in line with previously reported values; however, a better understanding of spatial and temporal variability is needed for budget quantification. Methyl halide fluxes from FTS soil cores demonstrate that, on a per gram basis, most consumption occurs through biologically driven processes in the O horizon, with progressively smaller contributions in deeper horizons. Sporadic biogenic production was observed in shallow soil horizons only. Abiotic production was at most one‐tenth the net biological reaction rate in the O horizon and did not appear to be significantly different from zero in lower horizons. Modelled emissions based upon observed and reported rates for production, consumption and diffusion within the soil atmosphere system are unable to replicate all observed isotopic signatures from chamber fluxes.     

2,4-D impact on bacterial communities, and the activity and genetic potential of 2,4-D degrading communities in soil

The key role of telluric microorganisms in pesticide degradation is well recognized but the possible relationships between the biodiversity of soil microbial communities and their functions still remain poorly documented. If microorganisms influence the fate of pesticides, pesticide application may reciprocally affect soil microorganisms. The objective of our work was to estimate the impact of 2,4-D application on the genetic structure of bacterial communities and the 2,4-D-degrading genetic potential in relation to 2,4-D mineralization. Experiments combined isotope measurements with molecular analyses. The impact of 2,4-D on soil bacterial populations was followed with ribosomal intergenic spacer analysis. The 2,4-D degrading genetic potential was estimated by real-time PCR targeted on tfdA sequences coding an enzyme specifically involved in 2,4-D mineralization. The genetic structure of bacterial communities was significantly modified in response to 2,4-D application, but only during the intense phase of 2,4-D biodegradation. This effect disappeared 7 days after the treatment. The 2,4-D degrading genetic potential increased rapidly following 2,4-D application. There was a concomitant increase between the tfdA copy number and the 14C microbial biomass. The maximum of tfdA sequences corresponded to the maximum rate of 2,4-D mineralization. In this soil, 2,4-D degrading microbial communities seem preferentially to use the tfd pathway to degrade 2,4-D.     

Contribution of amino compounds to dissolved organic nitrogen in forest soils

Dissolved organic nitrogen (DON) may play an important role in plantnutrition and nitrogen fluxes in forest ecosystems. In spite of the apparentimportance of DON, there is a paucity of information concerning its chemicalcomposition. However, it is exactly this chemical characterization that isrequired to understand the importance of DON in ecosystem processes. Theprimaryobjective of this study was to characterize the distribution of free aminoacidsand hydrolyzable peptides/proteins in the DON fraction of Oa horizon leachatesalong an extreme edaphic gradient in northern California. Insitu soil solutions were extracted by centrifugation from Oahorizonscollected beneath Pinus muricata (Bishop pine) andCupressus pygmaea (pygmy cypress) on slightlyacidic/fertile and highly acidic/infertile sites. DON accounted for 77 to99% of the total dissolved nitrogen in Oa horizon leachates. Nitrogen infree amino acids and alkyl amines ranged from 0.04–0.07 mgN/L on the low fertility site to 0.45–0.49 mg N/L onthe high fertility site, and accounted for 1.5 to 10.6% of the DON fraction.Serine, glutamic acid, leucine, ornithine, alanine, aspartic acid andmethylamine were generally the most abundant free amino compounds. Combinedamino acids released by acid hydrolysis accounted for 48 to 74% of theDON, suggesting that proteins and peptides were the main contributor to DON inOa horizon leachates. Together, nitrogen from free andcombined amino compounds accounted for 59 to 78% of the DON. Most of theDON was found in the hydrophobic fraction, which suggests the presence ofprotein/peptide-polyphenol complexes or amino compounds associated withhumic substances. Because free and combined amino acids can be an importantnitrogen source for some plants, soil DON may play an important role in plantnutrition and ecosystem function.     

农田和森林土壤中氧化亚氮的产生与还原

采用土壤淤浆方法对丹麦农田和山毛榉森林土壤反硝化过程中Ｎ２Ｏ的产生与还原进行了研究。同时考察了硝酸根和铵离子对反硝化作用的影响。结果表明,森林土壤反硝化活性大于农田土壤,但农田土壤中Ｎ２Ｏ还原活性大于森林土壤,表现在农田和森林土壤中Ｎ２Ｏ／Ｎ２的产生比率分别为０．１１和３．６５。硝酸根和铵离子能促进两种土壤中的Ｎ２Ｏ产生,但可降低农田土壤中的Ｎ２Ｏ还原速率,与农田土壤相比,硝酸根可降低森林土壤Ｎ２     

Human health risk assessment and source diagnosis of polycyclic aromatic hydrocarbons (PAHs) in the corn and agricultural soils along main roadside in Changchun,China

This work was to investigate distribution characteristics, human health risk assessment, and possible sources of 16 priority polycyclic aromatic hydrocarbons (PAHs) in corn and surface soils of farmlands along main roadside in Changchun City, Jilin Province, China. Total concentrations of 16 PAHs ranged from 1572.4 to 4390.2 µg/kg with a mean value of 2954.9 µg/kg in soils and from 219.9 to 627 µg/kg with a mean value of 362µg/kg in corn. Light-molecular-weight PAHs (2–3 rings) concentration was dominant in soils, accounting for 51%, whereas high-molecular-weight PAHs (5–6 rings) concentration was highest in corn, accounting for 48%. The results of plant concentration factor indicated that high-molecular-weight PAHs have greater mobility. To evaluate potential risk to human health, hazard index (HI) and risk index (RI) were employed. The values of HI for corn and soils were both smaller than 1, indicating that exposure of PAHs posed no or little potential risk to local residents. The fact that values of RI for corn and soils were smaller than 1 × 10^–4 suggested that exposure of PAHs posed no or little cancer risk to local residents. The possible sources of PAHs in corn and soils were both identified as mixture patterns of pyrogenic and petrogenic sources.     

The effect of agricultural utilization on the composition and yield of phenolic acids in low peat soils

Summary Levels of benzoic and cinnamic acids in low peat soils, maintained for 25 years under four different cropping systems, were studied in field experiments. The soil samples were obtained from four horizons of thirteen selected profiles. Seven phenolic acids were identified by high performance liquid chromatographic (HPLC) techniques and their amounts were determined quantitatively. The concentration of phenolic acids in the soils depended on the cropping system and the depth of the soil profiles. Permanent grassland had the highest yield of phenolic compounds in peat soils. Much smaller amounts were found in the order forest, alternate and field utilization. Thus, phenolic compounds may be useful markers with which to follow the decomposition in peat soils. The content of phenolic acids decreased with the depth of the profiles, but in some cases the 25–30 cm soil layers contained higher amounts of phenols than the 5–10 cm layers. Compared with the surface layers the deeper horizons (55–60 cm and 95–100 cm) were low in phenolic acids.     

A laser-T-jump study of the adsorption of dipolar molecules to planar lipid membranes

The adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as of other dipolar molecules to the interface of artificial lipid membranes gives rise to a change of the dipole potential between the membrane interior and water. As a consequence of the adsorption of the neutral species, the conductance of planar membranes, observed in the presence of the macrocyclic ion carriers nonactin or valinomycin, may change by many orders of magnitude. Using this effect in combination with a laser-T-jump technique, the kinetics of the adsorption process were measured and were interpreted on the basis of a Langmuir-isotherm. A partition coefficient (at small concentrations) of _HA =4.7·10^–4 cm, a rate constant of desorption k _HA100 s^-1 and a maximum surface density N _D=7.7·10¹³/cm² were found. The concentration at half saturation is K _HA=2.7·10^-4 M.Using these values the membrane conductance induced by the ion carrier nonactin and the shape of the current-voltage relationship as a function of the ligand concentration in water was analyzed. A maxiumum dipole potential of V _D ^max =-239 m V and a contribution of b=3.1·10^-15V cm² per single adsorbed 2,4-D molecule was found. 74% of the dipole potential acts on the inner membrane barrier separating the two interfacial adsorption planes of nonactin. The remainder (26%) favours interfacial complex formation between nonactin and K⁺ from the aqueous phase. The data hold for membranes formed from dioleoyllecithin in n-decane.     

A comparison of pinewood and moorland soils in the Abernethy Forest Reserve, Scotland

Despite considerable published literature on the above-ground ecology of the pinewoods of Scotland, little research has considered the way in which pinewood soils differ from those under other vegetation types. Soil properties were compared between ancient, semi-natural Scots pine forest and moorland on three soil types in the Abernethy Forest Reserve in the Cairngorm Mountains of Scotland. Soil morphology differed considerably between the vegetation types on each soil type, principally in the thickness of organic layers. Forest soils had thicker organic layers and this was particularly true of the F horizon. Forest soils were slightly less acid than equivalent moorland soils and had accumulated significantly more carbon. Forest soils in this environment therefore have the capacity to sequester larger amounts of carbon than moorland, and therefore represent a significant potential carbon sink. The quantity of nitrogen and phosphorus was also consistently larger in the organic layers under pine forest and since little difference existed in these properties in the mineral horizons, it was concluded that this accumulation was real and represented a net addition to the tree-soil system.