Dry Wt Soil Research Articles

Exploring the Relationship Among Lipid Profile Changes, Growth, and Reproduction in Folsomia candida Exposed to Teflubenzuron Over Time.

The integration of untargeted lipidomics approaches in ecotoxicology has emerged as a strategy to enhance the comprehensiveness of environmental risk assessment. Although current toxicity tests with soil microarthropods focus on species performance, that is, growth, reproduction, and survival, understanding the mechanisms of toxicity across all levels of biological organization, from molecule to community is essential for informed decision-making. Our study focused on the impacts of sublethal concentrations of the insecticide teflubenzuron on the springtail Folsomia candida. Untargeted lipidomics was applied to link changes in growth, reproduction, and the overall stress response with lipid profile changes over various exposure durations. The accumulation of teflubenzuron in organisms exposed to the highest test concentration (0.035 mg a.s. kg-1 soil dry wt) significantly impacted reproductive output without compromising growth. The results suggested a resource allocation shift from reproduction to size maintenance. This hypothesis was supported by lipid shifts on day 7, at which point reductions in triacylglycerol and diacylglycerol content corresponded with decreased offspring production on day 21. The hypermetabolism of fatty acids and N-acylethanolamines on days 2 and 7 of exposure indicated oxidative stress and inflammation in the animals in response to teflubenzuron bioaccumulation, as measured using high-performance liquid chromatography-tandem mass spectrometry. Overall, the changes in lipid profiles in comparison with phenotypic adverse outcomes highlight the potential of lipid analysis as an early-warning tool for reproductive disturbances caused by pesticides in F. candida. Environ Toxicol Chem 2024;43:1149-1160. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

In situ electrokinetic (EK) remediation of the total and plant available cadmium (Cd) in paddy agricultural soil using low voltage gradients at pilot and full scales

Electrokinetic (EK) remediation has been widely studied at laboratory scales. However, field-scale research is far less. In this study, a 14-day EK remediation was carried out, in a field pilot (4 m2) test and a full-scale (200 m2) application for the first time, in a cadmium (Cd) contaminated paddy agricultural field near a mining area. A low voltage of 20 V was applied at both scales; voltage gradient was 20 V m−1 and 4 V m−1 at the pilot and full scales, respectively. Samples were taken from near the anode and cathode, and in the middle of the electric field, in the soil layers 0–10 cm, 10–20 cm, and 40–50 cm. After the EK remediation, a significant portion of the total Cd was removed in all the layers at the pilot scale, by 87%, 72%, and 54% from the top down, but only in the 0–10 cm layer at the full scale by 74%. As for the plant available (exchangeable and soluble) Cd, significant removal (64%) was only observed in the 0–10 cm layer at the pilot scale. The percentage reduction of the electrical conductivity and removal efficiency of the total Cd was higher near the anode than the cathode. The soil pH was elevated near the cathode but stayed below pH 6 due to the sufficient supply of lactic acid. After the EK remediation, the concentration of the total Cd dropped below the hazard threshold, i.e. 0.4 mg (kg dry wt soil)−1 for agricultural paddy fields in China. A total energy of 2 kW·h and 0.6 kW·h was consumed at the pilot and full scales, respectively. This study showed a successful in situ EK remediation of Cd contaminated paddy agricultural soil, especially in the surface layer, with low voltage and energy demand.

Phenolic acid-degrading Paraburkholderia prime decomposition in forest soil

Plant-derived phenolic acids are catabolized by soil microorganisms whose activity may enhance the decomposition of soil organic carbon (SOC). We characterized whether phenolic acid-degrading bacteria enhance SOC mineralization in forest soils when primed with 13C-labeled p-hydroxybenzoic acid (pHB). We further tested whether pHB-induced priming could explain differences in SOC content among mono-specific tree plantations in a 70-year-old common garden experiment. pHB addition primed significant losses of SOC (3–13 µmols C g−1 dry wt soil over 7 days) compared to glucose, which reduced mineralization (-3 to -8 µmols C g−1 dry wt soil over 7 days). The principal degraders of pHB were Paraburkholderia and Caballeronia in all plantations regardless of tree species or soil type, with one predominant phylotype (RP11ASV) enriched 23-fold following peak pHB respiration. We isolated and confirmed the phenolic degrading activity of a strain matching this phylotype (RP11T), which encoded numerous oxidative enzymes, including secretion signal-bearing laccase, Dyp-type peroxidase and aryl-alcohol oxidase. Increased relative abundance of RP11ASV corresponded with higher pHB respiration and expression of pHB monooxygenase (pobA), which was inversely proportional to SOC content among plantations. pobA expression proved a responsive measure of priming activity. We found that stimulating phenolic-acid degrading bacteria can prime decomposition and that this activity, corresponding with differences in tree species, is a potential mechanism in SOC cycling in forests. Overall, this study highlights the ecology and function of Paraburkholderia whose associations with plant roots and capacity to degrade phenolics suggest a role for specialized bacteria in the priming effect.

Effect of mineral enriched compost on soil microbiological properties

Two years field experiments were conducted at the Indian Institute of Rice Research Farm, Hyderabad, to compare the performance of field fortified poultry manure applications on some of the microbiological properties of soil. Continuous application of MEC treatments resulted in decline in the pH of the soil in all the treatments from the initial levels of 8.07. Analysis of post harvest soils of MEC for physical parameters revealed that plots treated with inorganic fertilizer alone had an adverse effect on soil dehydrogenase activities, soil phosphatase activites and soil microbial carbon. Soil microbial biomass C μg C/g soil dry wt was recorded in all the MEC plots compared to control and RDF. Soil enzyme observations such as Alkaline phosphatase μg p-nitrophenol/g soil/ha assayed in all the MEC plots were highly skewed. Lowest value of dehdrogenase μg TPF/g soil/24h activity was observed in the RDF plots. Higher values of soil dehdrogenase activities were recorded in all the MEC plots compared to control and fertilized plots.

Population Density and <I>In vitro</I> Characterization of Selected PGPRs from Tobacco Rhizosphere Soils

Present study revealed that PGPRs such as Bacillus, Pseudomonas, Trichoderma and Streptomyces spp. present predominantly in tobacco rhizosphere soils. Population density of PGPR was found to be higher in northern light soils (NLS) followed by Karnataka light soils (KLS) than in southern light soils (SLS) and traditional black soils (TBS) whereas lowest was recorded in chewing tobacco soils. Moreover, among the PGPRs, bacterial PGPRs such as B. subtilis and P. fluorescens were found to be higher than actinomycetes ( Streptomyces spp.) and fungi like T. viride . Similarly, of the bacterial PGPRs, P. fluorescens population was the highest (11.98 x10 5 ) in NLS while B. subtilis was the least (5.99 x10 5 cfu/gm soil dry wt.) in chewing tobacco. The population density of T. viride recorded least in chewing tobacco soils of West Bengal and Tamil Nadu (3.18 x 10 3 and 2.77 x 10 3 cfu/gm soil dry wt., respectively). The population density of PGPR strains positively coincided with soil nutrients like total organic matter, phosphorous and potassium contents. The results on biochemical characterization indicated that most of the strains were efficient in hydrolyzing starch, gelatin and casein. Among the different carbon and nitrogen sources tested, maltose and potassium nitrate, respectively were the good supplementary sources. Of the different amino acid and vitamin sources evaluated, alanine and riboflavin, respectively were found to be limiting substrates for maximum growth of PGPR strains. Antagonistic activity of Streptomyces sp. against Pythium aphanidermatum showed 37.52 per cent of inhibition over control.

Detection and enumeration of Pseudomonas aeruginosa in soil and manure assessed by an ecfX qPCR assay

To develop a qPCR approach for the detection of Pseudomonas aeruginosa in soil and manure and explore its efficacy and limitations compared with that of a classical culture-dependent approach. A Ps.aeruginosa ecfX qPCR assay was developed. This assay was optimized for soils of contrasting physico-chemical properties and evidenced a three-log dynamic range of detection [5×10(4) -5× 10(6) cells(gdrywtsoil)(-1) ] in inoculated microcosms. Sensitivity was determined to be around 5×10(4) cells(gdrywtsoil)(-1) . In parallel, the minimum detection limit was estimated in the range of 10-100CFU(gdrywtsoil)(-1) using a culture-dependent approach based on the use of a selective medium (cetrimide agar base medium supplemented with nalidixic acid), coupled to ecfX gene amplification to confirm isolate identity. These soil samples led to the growth of abundant non-Ps.aeruginosa colonies mainly belonging to other Pseudomonas species but also some beta-Proteobacteria. These bacteria strongly impacted the detection threshold of this approach. Efficacy of these approaches was compared for Ps.aeruginosa enumeration among manure and agricultural soil samples from various sites in France, Tunisia and Burkina Faso. The developed qPCR assay enabled a specific detection of Ps.aeruginosa in soil and manure samples. The culture-based approach was usually found more sensitive than the qPCR assay. However, abundance of non-Ps.aeruginosa species among the indigenous communities able to grow on the selective medium affected the sensitivity of this latter approach. This study describes the first specific and sensitive qPCR assay for the detection and enumeration of Ps.aeruginosa in soil and manure and shows its complementarity with a culture-based approach.

Dynamics of methanotrophic communities in tropical alkaline landfill upland soil

Landfill methanotrophs play an important role in greenhouse gas reduction. To understand the dynamics of methanotroph population, quantitative polymerase chain reaction methods (q-PCR) and terminal-restriction fragment length polymorphism (T-RFLP) analyses were used to explore the methanotrophic communities in tropical alkaline landfill soils at 20 and 40 cm depths with different vegetation during a year round study. The q-PCR revealed that the amount of methanotrophs were 1.25 × 10 3 to 1.93 × 10 6 pmoA-copy (g dry wt soil) −1 and were negatively correlated with accumulated precipitation before sampling. The pmoA-based T-RFLP analyses showed that Methylocaldum related populations were dominant for a long residence time, and Methylocystis related populations were dominant in the deeper sites of milk bush-covered region. Canonical correspondence analysis showed that vegetation, accumulated precipitation, temperature, sampling depth and soil pH could affect the methanotrophic community structures. The pmoA-based T-RFLP analysis used in this study provided good resolution within type I methanotrophs and could easily distinguish between type I and type II methanotrophs.

Development of a strain-specific genomic marker for monitoring a Bacillus subtilis biocontrol strain in the rhizosphere of tomato

A strain-specific molecular marker enabling the detection and tracking of the biological control agent Bacillus subtilis 101, when released into the environment, was developed. Random amplified polymorphic DNA (RAPD) technique was used to differentiate this from other B. subtilis strains. A differentially amplified fragment obtained from RAPD profiles was sequenced and characterized as sequence-characterized amplified region (SCAR) marker, and four primer pairs were designed and evaluated for their specificity towards this strain. The sensibility of the selected SCAR primer pair was evaluated by qualitative PCR and Southern blotting, and the detection limit was assessed around 10(2) CFU (g dry wt soil)(-1), thus providing a reliable tool for the traceability of this B. subtilis strain in greenhouse or field trials. A plating assay coupled to PCR with the SCAR primer pair was then used as a detection method in microcosm experiments for monitoring the population of B. subtilis 101 in the rhizosphere of tomato, grown under two different soil conditions, i.e. nonsterile peat-based substrate and sandy-loam agricultural soil, respectively. The data of rhizosphere colonization indicated that the soil conditions significantly affected the rhizosphere establishment of strain 101.

Changes in chromium distribution during the electrodialytic remediation of a Cr (VI)-contaminated soil

A laboratory study has been carried out to determine the feasibility of in situ remediation of chromium (VI)-contaminated soil using electrodialysis in relation to its speciation in soil. This technique is best suited for low-permeability soils or sediments, which may be difficult to remediate by other means and implies the application of a low-intensity direct current to the soil, which is separated from the electrode compartments by ion-exchange membranes. A clayey soil was prepared for use in the experiments and was characterized before being mixed with a solution of potassium dichromate for several days to produce a final Cr content of 4,056 mg/kg of soil dry wt. Remediation tests were carried out under constant-voltage conditions for periods of 7-14 days and the evolution of applied current to the cell, pH, and conductivity of the electrolytes were recorded periodically. Fractionation of chromium was determined for soil samples before and after remediation using a standardized four-step sequential extraction procedure (SEP) with acetic acid, hydroxylamine, hydrogen peroxide, and aqua regia solutions. Results show that chromium is mobilized from the most labile phases (soluble/exchangeable/carbonate). In a 15 V test, SEP results show that the amount of chromium extracted in the first step drops from 80% to 9%, but also that changes in the total chromium distribution occur during the treatment with some transferred to other soil phases that are more difficult to mobilize.

Impact of Black Carbon in the Extraction and Mineralization of Phenanthrene in Soil

During the past century, increased biomass burning and fossil fuel consumption have drastically increased the input of black carbon (BC) into the environment, and that has been shown to influence the behavior of organic contaminants in soil. A study was conducted to investigate the effects of BC on the relationship between aqueous hydroxypropyl-beta-cyclodextrin (HPCD) extraction and microbial mineralization (bioaccessibility) of 14C-phenanthrene (10 mg kg(-1)) in four soils amended with 0, 0.1, 0.5, 1, 2.5, and 5% (% dry wt soil) activated charcoal, a type of BC. Mineralisation was monitored over 20 d incubation, within respirometric assays, using an inoculum containing a phenanthrene-degrading pseudomonad and compared to HPCD extraction (24 h) using 50 mM aqueous solution; analyses were conducted after 1, 25, 50, and 100 d soil-phenanthrene contact time. Statistical analyses revealed that for each soil the addition of BC led to significant (P < 0.001) reductions in both HPCD extractability and microbial mineralization. Linear correlations for BC concentrations of 0% (r2 = 0.95; slope = 0.89) and 0.1% (r2 = 0.67; slope = 0.95) revealed a highly significant (P < 0.01) relationship between HPCD extractability and total mineralization (20 d), indicating a direct prediction of phenanthrene bioaccessibility by HPCD. However, in soils amended with 0.5, 1, 2.5, and 5% BC exhibited r2 values ranging 0.51-0.13 and slopes of 2.19-12.73. This study has shown that BC strongly sorbs phenanthrene causing reductions in extractability and, to a lesser extent, bioaccessibility to degrading microorganisms.

Metal uptake of two ecophysiologically different earthworms ( Eisenia fetida and Aporrectodea caliginosa) exposed to ultramafic soils

Ultramafic soils are characterized by a number of disadvantageous living conditions, especially extremely high concentrations of different metals. To evaluate the bioavailability of these metals, two ecophysiologically different earthworm species, Aporrectodea caliginosa and Eisenia fetida, were exposed for at least 14 weeks to ultramafic soils collected in the Barberton Region, Mpumalanga, South Africa (25°33′S, 30°47′E), containing extremely high concentrations of chromium, manganese and nickel with a maximum of 2894 mg Cr/kg, 1994 mg Mn/kg and 13,926 mg Ni/kg soil dry wt. In addition, a sequential fractionation evaluating the different metal phases in the soils was conducted to determine the environmental availability of selected metals. For the mobile metal fraction, easily exchangeable metals were substituted by a 0.01 mol/L CaCl 2 solution. The mobilisable fraction, resembling easily remobilisable complexed and carbonated metal ions, was addressed by a DTPA extraction. Especially in the bodies of A. caliginosa, a high individual variability, for example between 3 and 264 mg/kg for Cr, 19 and 454 mg/kg for Mn, and 0 and 86 mg/kg for Ni (24 weeks exposure, Agnes Mine) was measured even in the same replicate. For that reason, an analysis of three different body sections of both earthworm species was performed. In E. fetida a dynamic uptake behavior with an initial increase followed by a decrease of metal body burden and thereafter fluctuating concentrations was observed (e.g. 12 mg Ni/kg after 2 weeks of exposure and 3 mg Ni/kg after 4 weeks; Kaapsehoop 1). That makes it difficult to relate metal concentrations as measured by the different fractionations to the concentrations in the two earthworm species. The analysis of the different body sections showed that these ecophysiologically different species differed strongly in the distribution of chromium, manganese and nickel in their bodies. A. caliginosa seems to concentrate these metals preferentially in the posterior section, which is probably linked to the phenomenon of autotomization. In contrast to that, no differences in the longitudinal distribution of the metals were observed in E. fetida. Apart from different elimination and/or uptake mechanisms, A. caliginosa might also be able to avoid elevated metal concentrations by going into quiescence. Although no relation between extractable fractions and uptake of metals was found, the fractionation revealed that a lower proportion of metals was extractable from ultramafic soils than from non-ultramafic soils.

Decreased toxicity to terrestrial plants associated with a mixture of methyl tert‐butyl ether and its metabolite tert‐butyl alcohol

The influence of the main fuel oxygenate methyl tert-butyl ether (MTBE) and its key metabolite, tert-butyl alcohol (TBA), on the growth of a plant seedling was studied separately and in combination. The test plants were mung bean (Phaseolus radiatus), cucumber (Cucumis sativus), wheat (Triticum aestivum), sorghum (Sorghum bicolor), kale (Brassica alboglabra), Chinese cabbage (Brassica campestris), and sweet corn (Zea mays). The growth of all the plants was adversely affected by TBA and MTBE. The 5-d median effective concentration (EC50) for the plants exposed to MTBE and TBA were in the range of 680 to 1,000 mg MTBE/kg soil (dry wt) and 1,200 to 3,500 mg TBA/kg soil (dry wt), respectively. The relative order of the sensitivity rankings is almost the same for MTBE and TBA. Methyl tert-butyl ether is more toxic than TBA to most of the test species. Based on the EC50 values, MTBE is approximately 1.5 to 3 times more potent than TBA. The sum of the toxic unit (TU) at 50% inhibition of the mixture (EC50mix) was calculated from the dose (TU-based)-response relationships using the trimmed Spearman-Karber method. The combined effect of MTBE + TBA on the plant growth was less than additive because the EC50mix values were greater than I TU. This phenomenon may be due to the competition of MTBE and TBA in terms of their intake by plants. The combined effects of MTBE and TBA should be taken into account to assess their risk in gasoline-contaminated sites.

The influence of earthworms and organic additives on the biodegradation of oil contaminated soil

Oil pollution is a world-wide prevalent threat to the environment and the remediation of oil contaminated soils, sediments and water is a major challenge for environmental research. Bioremediation is a useful method for soil remediation, if pollutant concentrations are moderate and non-biological techniques are not economical. The scope of this study was to investigate if earthworms and/or additives (organic material) can enhance the microbial degradation of petroleum hydrocarbons in soil. Two experiments were conducted. The aim of the first was to investigate the influence of three different earthworm species ( Eisenia fetida, Allolobophora chlorotica, and Lumbricus terrestris) on the degradation of a crude oil contaminated soil (9500 mg total petroleum hydrocarbons (TPH)/kg soil dry wt.). A significant decrease in the TPH concentration was observed in treatments with earthworms, compared with the samples without worms. A decrease of the marker components phytane and pristane in the earthworm treatments indicated microbial degradation. Correspondingly, increased microbial activity (soil respiration) was observed in these samples, probably due to earthworm stimulation. Mixing of the soil (simulating burrowing activities of the earthworms), however, did not lead to a decrease in the TPH concentration. The aim of the second experiment was to investigate the influence of additives and/or earthworms ( Lumbricus terrestris) on TPH degradation in a crude oil polluted soil (5000 mg/kg TPH). Criteria for the choice of the additives were cost effectiveness and short transport distances. Industrial waste products were therefore chosen: (i) coffee grounds; (ii) horticultural waste (grass and wood chips); and (iii) brewery mash. Additives were either mixed into the soil or dispersed on the soil surface in mass concentrations 1:10 (additive:soil). After 28 days, significant TPH degradation (30–35%) was only observed in treatments with mash (mixed) and with earthworms without additives, although soil respiration measurements showed enhanced microbial activity in all treatments with worms or additives. It was assumed that micro-organisms prefer the more easily available additives as nutrient sources over the less easily degradable, nitrogen deficient, long-chain crude oil. Thus, the application of additives does not necessarily enhance bioremediation. Despite high mortality, earthworms may trigger the degradation process and might therefore, be applied in the remediation of oil contaminated soil with moderate TPH concentrations.

Lysosomal membrane stability in laboratory‐ and field‐exposed terrestrial isopods Porcellio scaber (Isopoda, Crustacea)

Two established methods for assessment of the cytotoxicity of contaminants, the lysosomal latency (LL) assay and the neutral red retention (NRR) assay, were successfully applied to in toto digestive gland tubes (hepatopancreas) of the terrestrial isopod Porcellio scaber (Isopoda, Crustacea). In vitro exposure of isolated gland tubes to copper was used as a positive control to determine the performance of the two methods. Lysosomal latency and the NRR assay were then used on in vivo (via food) laboratory-exposed animals and on field populations. Arbitrarily selected criteria for determination of the fitness of P. scaber were set on the basis of lysosomal membrane stability (LMS) as assessed with in toto digestive gland tubes. Decreased LMS was detected in animals from all polluted sites, but cytotoxicity data were not in agreement with concentrations of pollutants. Lysosomal membrane stability in the digestive gland tubes of animals from an environment in Idrija, Slovenia that was highly polluted with mercury (260 microg/g dry wt food and 1,600 microg/g dry wt soil) was less affected than LMS in laboratory animals fed with 5 and 50 microg Hg/g dry weight for 3 d. This probably indicates tolerance of P. scaber to mercury in the mercury-polluted environment and/or lower bioavailability of environmental mercury. In animals from the vicinity of a thermal power plant with environmental mercury concentrations three to four orders of magnitude lower than those in Idrija, LMS was severely affected. In general, the LL assay was more sensitive than the NRR assay. The LMS assay conducted on digestive gland tubes of terrestrial isopods is highly recommended for integrated biomarker studies.

Microbial Assemblages in Soil Microbial Succession After Glacial Retreat in Svalbard (High Arctic)

Microbial community composition (cyanobacteria and eukaryotic microalgae abundance and diversity, bacterial abundance, and soil respiration) was studied in subglacial and periglacial habitats on five glaciers near Ny-Alesund, Svalbard (79 degrees N). Soil microbial communities from nonvegetated sites (subglacial, recently deglaciated, and cryoconite sediments) and sites with plant cover (deglaciated some hundreds of years ago) were analyzed. Physicochemical analyses (pH, texture, water content, organic matter, total C and N content) were also performed on the samples. In total, 57 taxa of 23 genera of cyanobacteriaand algae were identified. Algae from the class Chlorophyceae (25 species) and cyanobacteria (23 species) were richest in biodiversity. The numbers of identified species in single habitat types were 23 in subglacial, 39 inbarren, 22 in cryoconite, and 24 in vegetated soils. The highest cyanobacterial and algal biovolume and cell numbers, respectively, were present in cryoconite (13x10(4) microm3 mg-1 soil and 508 cells per mg of soil), followed by barren (5.7x10(4) and 188), vegetated (2.6x10(4) and 120), and subglacial (0.1x10(4) and 5) soils. Cyanobacteria prevailed in all soil samples. Algae (mainly green algae) were present only as accessory organisms. The density of bacteria showed a slightly different trend to that of the cyanobacterial and algal assemblages. The highest number of bacteria was present in vegetated (mean: 13,722x10(8) cells per mg of soil dry wt.), followed by cryoconite (3802x10(8)), barren (654x10(8)), and subglacial (78x10(8)) soils. Response of cyanobacteria and algae to physical parameters showed that soil texture and water content are important for biomass development. In addition, it is shown that nitrogen and water content are the main factors affecting bacterial abundance and overall soil respiration. Redundancy analysis (RDA) with forward selection was used to create a model explaining variability in cyanobacterial, algal, and bacterial abundance. Cryoconites accounted for most of the variation in cyanobacteria and algae biovolume, followed by barren soils. Oscillatoriales, desmids, and green coccoid algae preferred cryoconites, whereas Nostocales and Chroococcales occurred mostly in barren soils. From the data obtained, it is evident that of the studied habitats cryoconite sediments are the most suitable ones for the development of microbial assemblages. Although subglacial sediments do not provide as good conditions as cryoconites, they support the survival of microbial communities. Both mentioned habitats are potential sources for the microbial recolonization of freshly deglaciated soil after the glacier retreat.

Dissipation of acetochlor and its distribution in surface and sub-surface soil fractions during laboratory incubations

Pesticides in soil are subject to a number of processes that result in transformation and biodegradation, sorption to and desorption from soil components, and diffusion and leaching. Pesticides leaching through a soil profile will be exposed to changing environmental conditions as different horizons with distinct physical, chemical and biological properties are encountered. The many ways in which soil properties influence pesticide retention and degradation need to be addressed to allow accurate predictions of environmental fate and the potential for groundwater pollution. Degradation and sorption processes were investigated in a long-term (100 days) study of the chloroacetanilide herbicide, acetochlor. Soil cores were collected from a clay soil profile and samples taken from 0-30 cm (surface), 1.0-1.3 m (mid) and 2.7-3.0 m (deep) and treated with acetochlor (2.5, 1.25, 0.67 microg acetochlor g(-1) dry wt soil, respectively). In sterile and non-sterile conditions, acetochlor concentration in the aqueous phase declined rapidly from the surface and subsoil layers, predominantly through nonextractable residue (NER) formation on soil surfaces, but also through biodegradation and biotic transformation. Abiotic transformation was also evident in the sterile soils. Several metabolites were produced, including acetochlor-ethane sulphonic acid and acetochlor-oxanilic acid. Transformation was principally microbial in origin, as shown by the differences between non-sterile and sterile soils. NER formation increased rapidly over the first 21 days in all soils and was mainly associated with the macroaggregate (>2000 microm diameter) size fractions. It is likely that acetochlor is incorporated into the macroaggregates through oxidative coupling, as humification of particulate organic matter progresses. The dissipation (ie total loss of acetochlor) half-life values were 9.3 (surface), 12.3 (mid) and 12.6 days (deep) in the non-sterile soils, compared with 20.9 [surface], 23.5 [mid], and 24 days [deep] in the sterile soils, demonstrating the importance of microbially driven processes in the rapid dissipation of acetochlor in soil.

Toxicologic and Histopathologic Response of the Terrestrial Salamander Plethodon cinereus to Soil Exposures of 1,3,5-Trinitrohexahydro-1,3,5-Triazine

Red-backed salamanders (Plethodon cinereus) were exposed to four different concentrations of 1,3,5-trinitrohexahydro-1,3,5-triazine (RDX) in soil under controlled laboratory conditions for 28 days. Wild-caught P. cinereus (N = 20/treatment) were exposed to target concentrations of 5,000, 1000, 100, 10, and 0 mg RDX/kg soil (dry wt) using a microcosm design. Animals were fed 5 to 10 uncontaminated mutant Drosophila flies every 3 days and monitored daily. Animals were weighed 1 day before being placed in treatment and weekly thereafter. RDX concentrations in soil were analytically determined after the compound was added and mixed at the beginning, the midpoint, and the end of exposure. RDX soil concentrations were relatively stable throughout the exposure period. Signs of overt toxicity were observed primarily in the highest exposure group. Salamanders exposed to 5,000 mg RDX/kg soil exhibited signs of neuromuscular effects (lethargy, gaping, hypersensitivity, tremors) and exhibited significant weight loss. A single moribund animal from this group lost >20% of its original body weight and was killed. Animals in this exposure group also lost weight relative to animals in other treatments. Histopathologic evaluations, including an evaluation of melanomacrophage parameters, indicated no strong treatment-related findings. This study provided information regarding the effects from subchronic dermal exposure of a terrestrial amphibian species to RDX in soil and provides a microcosm approach to the evaluation of toxicity of contaminants in soil to a terrestrial vertebrate.

The abundance of nahAc genes correlates with the 14C-naphthalene mineralization potential in petroleum hydrocarbon-contaminated oxic soil layers

In this study, we evaluated whether the abundance of the functional gene nahAc reflects aerobic naphthalene degradation potential in subsurface and surface samples taken from three petroleum hydrocarbon contaminated sites in southern Finland. The type of the contamination at the sites varied from lightweight diesel oil to high molecular weight residuals of crude oil. Samples were collected from both oxic and anoxic soil layers. The naphthalene dioxygenase gene nahAc was quantified using a replicate limiting dilution-polymerase chain reaction (RLD-PCR) method with a degenerate primer pair. In the non-contaminated samples nahAc genes were not detected. In the petroleum hydrocarbon-contaminated oxic soil samples nahAc gene abundance [range 3 × 10 1–9 × 10 4 copies (g dry wt soil) −1] was correlated (Kendall non-parametric correlation r 2 = 0.459, p < 0.01) with the aerobic 14C-naphthalene mineralization potential (range 1 × 10 −5–0.1 d −1) measured in microcosms at in situ temperatures (8 °C for subsurface and 20 °C for surface soil samples). In these samples nahAc gene abundance was also correlated with total microbial cell counts ( r 2 = 0.471, p < 0.01), respiration rate ( r 2 = 0.401, p < 0.01) and organic matter content ( r 2 = 0.341, p < 0.05). NahAc genes were amplified from anoxic soil layers indicating that, although involved in aerobic biodegradation of naphthalene, these genes or related sequences were also present in the anoxic subsurface. In the samples taken from the anoxic layers, the aerobic 14C-naphthalene mineralization rates were not correlated with nahAc gene abundance. In conclusion, current sequence information provides the basis for a robust tool to estimate the naphthalene degradation potential at oxic zones of different petroleum hydrocarbon-contaminated sites undergoing in situ bioremediation.

Sorption of linear alkylbenzene sulfonate to soil components and effects on microbial iron reduction

When sewage sludge is applied to arable land, linear alkylbenzene sulfonate (LAS) is released into the environment. In soils, LAS has been shown to impede microbial processes, such as bacterial iron reduction. The aim of the present study was to quantify LAS adsorption and desorption to agricultural soils and iron oxides and relate this to the inhibition of microbial iron reduction. Two agricultural soils were used, namely, Askov (coarse sandy loam soil) and Lundgaard (coarse sandy soil). In both soils, LAS inhibited microbial iron reduction even at low LAS concentrations with 10% effect concentrations of 6 to 7 and 26 to 32 mg LAS/kg dry-weight soil for Lundgaard and Askov soil, respectively. The sorption isotherms showed that sorption of LAS to iron oxides was 10 to 100 times stronger than sorption to the agricultural soils. Also, it appeared that at low LAS concentrations (< 10 mg/kg dry-wt soil), Lundgaard soil adsorbed approximately 10 times more LAS than Askov soil. Thus, the inhibitory effect of LAS on microbial iron reduction was highest in the Lundgaard soil, which exhibited both the strongest sorption and the lowest desorption of the two soils. A possible hypothesis to explain this correlation was that LAS toxicity toward bacterial iron reduction was, at least partly, caused by LAS adsorbed to iron oxides, which could interfere with transfer of electrons between the bacteria and their respiratory electron acceptor.

Effects of linear alkylbenzene sulfonates on functional diversity of microbial communities in soil

Linear alkylbenzene sulfonates (LAS) often occur in sewage sludge that is applied to agricultural soil. Here LAS may affect the microbial activity, which is an important basis for nutrient cycling. Previous studies have shown that single bacterial species and specific soil processes can be very sensitive to LAS. Here we report that two levels of LAS, 22 and 174 mg/kg dry weight soil, had little or no significant influence of the functional diversity of bacteria in a sandy soil, as tested by community-level physiological profiles. Briefly, these profiles are a characterization of the microbial communities based on the pattern of substrate utilization in 96-well microtiter plates (Biolog EcoPlates). Sandy agricultural soil was incubated in duplicate 1-L mesocosms with or without LAS, and bacteria were extracted after one, two, and four weeks. During incubation, more than 98 and 93% of LAS added to 22 and 174 mg/kg dry weight soil was degraded, respectively. The presence of LAS at 174 mg/kg dry weight caused a higher number of bacteria in the soil extracts, maximally corresponding to 2.5 times the numbers in LAS-free soil (1.8 x 10(7) cells/g dry wt soil) after four weeks of incubation. No inhibitory effect of LAS was observed when the substrate utilization data were analyzed for substrate richness and diversity (Shannon-Weaver indices). Principal component analysis, however, showed that the pattern of substrate utilization in soil with the highest LAS content (174 mg/kg dry wt) could be distinguished from control soil and soil with 22 mg LAS/kg dry weight. Yet the overall conclusion was that the functional diversity of the aerobic, heterotrophic bacterial community was rather insensitive to LAS.