Non-irradiated Soil Research Articles

Evaluation of in situ biosurfactant production by inoculum of P. putida and nutrient addition for the removal of polycyclic aromatic hydrocarbons from aged oil-polluted soil.

This work aimed to conduct a laboratory study to evaluate the use of Pseudomonas putida CB-100 and nutrient addition for the removal of PAHs from an aged oil-polluted soil of Veracruz, Mexico. Pseudomonas putida is a biosurfactant-producing bacterium capable of metabolizing polycyclic aromatic hydrocarbons (PAHs), which are toxic compounds with low water solubility, high melting, and boiling points, and low vapor pressure; characteristics that increase as their molecular weight increases and make them more recalcitrant. The methodology consisted in sampling the long-term oil-polluted soil and testing the use of Gamma irradiation (25kGy) for the sterilization of the soil for abiotic control. We evaluated serological bottles containing 20g of 35% moist soil (irradiated and non-irradiated) with the following treatments: the addition of nutrients (NH4Cl, NaNO3, KH2PO4, and K2HPO4), an inoculum of P. putida, and both P. putida and nutrients. The parameters assessed were pH, organic matter, humidity, available phosphorus, total nitrogen, cultivable heterotrophic microorganisms, CO2 production, rhamnolipids, surface tension, and the removal of eleven PAHs. The non-irradiated soil added with P. putida was the most efficient in the removal of PAHs; the pattern was: Benzo(a)anthracene > Phenanthrene > Fluoranthene > Benzo(k)fluoranthene > Chrysene > Pyrene > Anthracene > Acenaphthylene > Benzo(b)fluoranthene. In conclusion, P. putida in the non-irradiated soil produced in situ biosurfactants (1.55mg/kg of rhamnolipids and an 11.9 mN/m decrease in surface tension) and removed PAHs in 10days.

Nano zero-valent iron-induced changes in soil iron species and soil bacterial communities contribute to the fate of Cd

Nano zero-valent iron (nZVI) is used for soil remediation; however, the impact of nZVI on soil solid iron phases and its interactions with soil microorganisms in relation to the fate of Cd in soil remains unclear. In the current study, we investigated the mechanisms underlying the change in mobility of Cd in exogenous Cd-contaminated soil with nZVI and γ radiation treatments. The results showed that nZVI treatment decreased Cd availability but also increased the soil pH and dissolved Mn and poorly crystalline Fe contents. However, the increased poorly crystalline Fe(II) levels contributed to a reduction in Cd availability in soils treated with nZVI by immobilizing Cd associated with Fe oxides, rather than by increasing pH or Mn oxide levels. Moreover, Cd stabilization efficiency was higher in γ-irradiated soils than in non-irradiated soils regardless of the Cd level, with noticeable differences in bacterial community composition between the non-irradiated and irradiated soils. The genera Bacillus, Pullulanibacillus, and Alicyclobacillus are important in the redox of poorly crystalline Fe(II)-containing minerals in non-irradiated soil. This research provides a new method for further improving the Cd stabilization efficiency of nZVI in combination with microbial iron oxidization inhibitors.

Microbial and abiotic factors of flooded soil that affect redox biodegradation of lindane.

Pollution induces pressure to soil microorganism; and conversely, the degradation of pollutants is reported largely regulated by the soil microbiome assembly in situ. However, the specific-dependent core taxa of degraders were barely confirmed, which is not conducive to improving the soil remediation strategy. Taking pollution of a typical organochlorine pesticide (OCP), lindane, as an example, we explored the microbial community assembly in flooded soils and simultaneously quantified the corresponding dynamics of typical soil redox processes. Contrasting initial status of microbial diversity was set up by gamma irradiation or not, with additives (acetate, NaNO3, acetate + NaNO3) capable of modifying microbial growth employed simultaneously. Microorganism under lindane stress was reflected by microbial adaptability within complex co-occurrence networks, wherein some environment-dependent core taxa (e.g., Clostridia, Bacteroidia, Bacilli) were highly resilient to pollution and sterilization disturbances. Lindane had higher degradation rate in irradiated soil (0.96mgkg-1 d-1) than non-irradiated soil (0.83mgkg-1 d-1). In non-irradiated soil, addition of acetate promoted lindane degradation and methanogenesis, whereas nitrate inhibited lindane degradation but promoted denitrification. No significant differences in lindane degradation were observed in irradiated soils, which exhibited low-diversity microbiomes in parallel to stronger Fe reduction and methanogenesis. The varied corresponding trigger effects on soil redox processes are likely due to differences of soil microbiome, specifically, deterministic or stochastic assembly, in response to pollution stress under high or low initial microbial diversity conditions. Our results improve the knowledge of the adaptability of disturbed microbiomes and their feedback on microbial functional development in OCP-polluted soils, achieving for a more reliable understanding with respect to the ecological risk of soils resided with OCPs under the fact of global microbial diversity loss.

Response of soil native microbial community to Eschericia coli O157:H7 invasion

The presence of Eschericia coli O157:H7 in the natural environment is a serious threat to human health. The native microbial community in soil plays an important role in resisting E. coli O157:H7 invasion. This study examined the responses of soil microbial community to E. coli O157:H7 invasion during a 32-day incubation. The E. coli O157:H7 persisted longer in γ-irradiated soil than non-irradiated soil while glucose addition decreased its persistence in the irradiated soil which was associated with an increasing recovery of the native community. The invasion of E. coli O157:H7 increased soil organic carbon mineralization, an indicator of microbial activity, in both non-irradiated and irradiated soils, while glucose addition significantly promoted the carbon mineralization process. The 16S rRNA sequencing data showed the gradual recovery of the native bacterial population including specific taxa such as proteobacteria and actinobacteria following irradiation. It is concluded that soil microbial function and structure can affect persistence of E. coli O157:H7 and that lower biodiversity of the native community favors its persistence.

Robustness of the autochthonous microbial soil community after amendment of cattle manure or its digestate

In the last two decades, a change in land use has taken place in Europe. Manures that used to be applied to agricultural soils are now used in biogas reactors, and instead, digestate is applied. Here, we simulated soil amendment with either fresh or anaerobically digested cattle manure. The aim was to investigate the resilience of the resident microbiota and detect differences in the microbial biomass and activity after fertilizer amendment. Furthermore, the physiological community profile and the role of the indigenous microbial community was elucidated. In a microcosm experiment, two kinds of agricultural soil (γ-irradiated versus non-irradiated) were amended with either treatment. The effect of amendments on the community composition and physiological activity was tested immediately, after 1 and 3 months of incubation through 16S rRNA gene amplicon sequencing (initial soil community), genetic and physiological profiling (PCR-DGGE and MicroResp™), and measurement of basal respiration and microbial biomass. Either fertilizer did not affect the community composition of dominant fungi and bacteria in non-irradiated soils. This indicates the ability of the indigenous microbiota to outcompete allochthonous microorganisms. Soil microbial biomass was not changed, whereas basal respiration was significantly higher after amendment, especially when using fresh manure. MicroResp™ revealed slightly higher respiration for some substrates after 1 month; this finding was, however, not persistent and similar for manure and digestate. Generally, after 1 month, treatments returned to control levels for all parameters. In conclusion, amendment with anaerobically digested manure did not have a greater impact on soil microbial properties.

Native soil microorganisms hinder the soil enrichment with antibiotic resistance genes following manure applications

Bacterial genes responsible for resistance to antibiotic agents (ARG) are spread from livestock to soil through application of manure, threatening environmental and human health. We investigated the mechanisms of ARG dissemination and persistence to disentangle i) the influence of nutrients and microorganisms on the soil tetracycline (TET) resistome, and ii) the role of indigenous soil microbiota in preventing ARG spread. We analysed short-term (7 days) and persistent (84 days) effects of manure on the resistome of three antibiotic-free pasture soils. Four microcosm treatments were evaluated: control, mineral nutrient fertilization, and deposition of a layer of fresh manure onto soil or γ-irradiated soil. We quantified five TET-resistance genes, isolated 135 TET-resistant bacteria and sequenced both culturable TET-resistant and whole bacterial communities. Manure amendments, but not nutrient addition, increased the abundance of TET-r genes such as tet(Y). Such changes persisted with time, in contrast with the TET-resistant bacterial composition, which partially recovered after manure amendments. Manured γ-irradiated soils showed significantly lower nutrient content and higher TET-r gene abundance than non-irradiated soils, suggesting that native soil bacteria are essential for the fertilization effect of manure on soil as well as control the dissemination of potentially risky TET-r genes.

Effects of γ-irradiation of original and organic matter-amended soils on the sorption of triclosan and diuron from aqueous solutions

Soil γ-irradiation is a well-known method of inhibiting microbial activity in studies of the soil sorption of organic compounds. However, few studies have addressed the possible effect of γ-irradiation on the sorptive ability of soils enriched with different types of organic matter (OM). The objective of this study was to probe the effect of soil γ-irradiation on organic compound–soil interactions in two different situations representing adding OM to soils through land disposal of (a) OM-rich sewage sludge-originating biosolids and (b) olive mill wastewater (OMW). Both situations describe frequent environmental and agricultural scenarios. Comparisons of aqueous sorption on cobalt-60 γ-irradiated and non-irradiated soil sorbents were carried out for (a) triclosan (in a series of three soils and their lab-incubated mixtures with three different types of biosolids), and (b) the pesticide diuron (in two different untreated and OMW-affected soils). In each case, sodium azide was used as a biocide. Soil γ-irradiation affected the sorption of organic compounds by a factor generally not exceeding 2–3. Specifically, for triclosan, the sorbed concentration ratio between irradiated and non-irradiated soils when averaged over all the soil samples was 0.94. No significant effects of γ-irradiation on soil organic carbon or total nitrogen contents were observed. The effect of γ-irradiation on a soil sorbent may be less important when a rough estimate of a soil sorption coefficient of an organic compound is needed. However, it may need to be taken into account in mechanistic sorption studies, specifically, when the shape of sorption isotherms is of interest.

NanoSIMS investigation of glycine-derived C and N retention with soil organo-mineral associations

While microbial-mineral-organic matter interactions are key features controlling the fates of low molecular-weight compounds in soils, direct investigations of how they control their fine-scale spatial distribution are scant. Here, we addressed how microbial transformations affect the retention of 13C/15N-labeled glycine in a forest topsoil 8 h after application. We assessed the contribution of soil microorganisms to glycine-derived 13C and 15N retention using γ-irradiated and non-irradiated soils. We tracked down the glycine-derived 13C and 15N at the surface of particles randomly isolated from soil density fractions using nano-scale secondary ions mass spectrometry (NanoSIMS) imaging. Eight hours after addition, 7 % of the glycine-derived 13C and 15N initially applied was recovered among soil density fractions, mainly via the activity of soil microorganisms (>85 % of total retention). Glycine-derived 13C and 15N distribution among density fractions was correlated with that of soil organic matter (SOM) determined by NanoSIMS (R ≥ 0.85), suggesting that the spatial patterns of the mineral-attached SOM controls the spatial distribution of the glycine-derived 13C and 15N. NanoSIMS images showed largely decoupled glycine-derived 13C and 15N spots preferentially attached to aggregated particles. We speculate that the glycine-derived 13C was principally found within or in the vicinity of microbial cells, whereas the glycine-derived 15N was mostly found as NH4 + and/or exoenzymes spread across soil surfaces. The C:N ratios determined by NanoSIMS suggest that local chemical properties of mineral-attached SOM drive glycine-derived 15N attachment, with the preferential attachment to mineral-attached SOM rich in N (C:N ratios mostly 2.65 g cm−3).

In situ biosurfactant production and hydrocarbon removal by Pseudomonas putida CB-100 in bioaugmented and biostimulated oil-contaminated soil

In situ biosurfactant (rhamnolipid) production by Pseudomonas putida CB-100 was achieved during a bioaugmented and biostimulated treatment to remove hydrocarbons from aged contaminated soil from oil well drilling operations. Rhamnolipid production and contaminant removal were determined for several treatments of irradiated and non-irradiated soils: nutrient addition (nitrogen and phosphorus), P. putida addition, and addition of both (P. putida and nutrients). The results were compared against a control treatment that consisted of adding only sterilized water to the soils. In treatment with native microorganisms (non-irradiated soils) supplemented with P. putida, the removal of total petroleum hydrocarbons (TPH) was 40.6%, the rhamnolipid production was 1.54 mg/kg, and a surface tension of 64 mN/m was observed as well as a negative correlation (R = −0.54; p < 0.019) between TPH concentration (mg/kg) and surface tension (mN/m), When both bacteria and nutrients were involved, TPH levels were lowered to 33.7%, and biosurfactant production and surface tension were 2.03 mg/kg and 67.3 mN/m, respectively. In irradiated soil treated with P. putida, TPH removal was 24.5% with rhamnolipid generation of 1.79 mg/kg and 65.6 mN/m of surface tension, and a correlation between bacterial growth and biosurfactant production (R = −0.64; p < 0.009) was observed. When the nutrients and P. putida were added, TPH removal was 61.1%, 1.85 mg/kg of biosurfactants were produced, and the surface tension was 55.6 mN/m. In summary, in irradiated and non-irradiated soils, in situ rhamnolipid production by P. putida enhanced TPH decontamination of the soil.

Pathogenic bacteria and mineral N in soils following the land spreading of biogas digestates and fresh manure

The on-farm production of renewable energy from animal manures has rapidly expanded in central and northern Europe, with thousands of anaerobic reactors. This process has increased the land spreading of biogas digestates, replacing the use of fresh manure as a fertiliser. The environmental benefits and risks of such a change still need to be defined. We hypothesised that applying to the soil anaerobically digested instead of fresh manure might control the release of pathogens but increase that of inorganic N. Pots including γ- or non-irradiated soils, either control or amended with digestate or manure (80 kg N ha −1), were incubated for 0, 1 and 3 months. Escherichia coli, Salmonella and Listeria were cultivated and pathogenicity genes invA and hlyA PCR-amplified. Soil ammonium and nitrate concentrations, and their leaching through the upper soil layer was quantified in 20 cm-depth lysimeters for 100 d. Anaerobic digestion significantly sanitised the manure by completely eliminating cultivable E. coli and Salmonella but not Listeria (1.7 × 10 4 CFUs g −1). Thus, manure increased all microbes and invA gene numbers when applied to soils, while the digestate supplied only hlyA-negative Listeria. Potential pathogens were significantly more abundant in γ- than in non-irradiated treatments indicating suppression by indigenous soil microbiota. Control levels of all potential pathogens were recovered after 3 months, which could be thus considered a safe delay between land spreading amendments and harvesting. Concentration of nitrates in soil and their movement through the upper layer in soils amended with digestate were doubled compared to the other treatments. Hence, care should be taken that in the field nitrate liberation does not exceed plant demand.

Daily changes in bacterial-feeding nematode populations oscillate with similar periods as bacterial populations after a nutrient impulse in soil

Previously, we showed that bacterial populations oscillated in a regular manner in response to a nutrient impulse in soil. For this paper we investigated if the wave-like fluctuations in bacterial populations could be explained by their interactions with populations of bacterial-feeding nematodes (BFN). In two microcosm experiments, soil bacterial populations—colony forming units (CFUs) and microscopic counts of stained bacteria and nematode populations in 22 families were monitored daily for 25 or 30 days after incorporation of clover+grass (CG) plant material into soil. In another microcosm experiment, dynamics of bacteria and nematode populations were monitored in response to gamma-irradiated plant material added to gamma-irradiated soil mixed with filtered bacterial suspensions and in non-irradiated soil. In the first experiment, soil bacterial populations fluctuated significantly after incorporation of the plant material with two peaks within the first week and three or four smaller peaks thereafter. Populations of total nematodes and BFN started to increase in the second week after CG incorporation, but the proportion of BFN increased within 1 week. Inactive juvenile BFN (dauerlarvae) seemed to be activated after 2 days (as the percentage of Rhabditidae increased and dauerlarvae decreased), followed by stepwise increases in dauerlarvae every 4 days, indicating that there was a new generation every 4 days. There were significant wave-like fluctuations in daily population changes of BFN, but not for those of total nematode communities, over the duration of these experiments. These fluctuations had similar periods (5 days) as those of bacterial populations, but were shifted about 3 days relative to the bacterial fluctuations. Gamma-irradiation of soil significantly increased the periods and amplitudes of bacterial oscillations. Nematode populations were eliminated in gamma-irradiated soils, but small numbers of protozoa were accidentally introduced in the irradiated soil, and may have been partially responsible for the delayed regulation of bacterial growth. We conclude that fluctuations in bacterial populations were not directly related to similar fluctuations in populations of BFN, as expected from classical Lotka–Volterra equations for predator–prey relationships, but were related to changes in growth rates of BFN. An alternation in active and inactive stages in a synchronized predator community after a disturbance could allow periods of bacterial growth alternated with periods of death. Fluctuations in bacterial populations were dampened after a much longer period when the soil fauna was largely eliminated.

Basal organic phosphorus mineralization in soils under different farming systems

Soil organic P (P o) mineralization plays an important role in soil P cycling. Quantitative information on the release of available inorganic P (P i) by this process is difficult to obtain because any mineralized P i gets rapidly sorbed. We applied a new approach to quantify basal soil P o mineralization, based on 33PO 4 isotopic dilution during 10 days of incubation, in soils differing in microbiological activity. The soils originated from a 20 years old field experiment, including a conventional system receiving exclusively mineral fertilizers (MIN), a bio-organic (ORG) and bio-dynamic (DYN) system. Indicators of soil microbiological activity, such as size and activity of the soil microbial biomass and phosphatase activity, were highest in DYN and lowest in MIN. In order to assess P o hydrolysis driven by phosphatase in sterile soils, a set of soil samples was γ-irradiated. Basal P o mineralization rates in non-irradiated samples were between 1.4 and 2.5 mg P kg −1 day −1 and decreased in the order DYN>ORG≥MIN. This is an amount lower, approximately equivalent to, or higher than water soluble P i of MIN, ORG and DYN soils, respectively, but in every soil was less than 10% of the amount of P isotopically exchangeable during one day. This shows that physico-chemical processes are more important than basal mineralization in releasing plant available P i. Organic P mineralization rates were higher, and differences between soils were more pronounced in γ-irradiated than in non-irradiated soils, with mineralization rates ranging from 2.2 to 4.6 mg P kg −1 day −1. These rates of hydrolysis, however, cannot be compared to those in non-sterile soils as they are affected by the release of cellular compounds, e.g. easily mineralizable P o, derived from microbial cells killed by γ-irradiation.

Organic Phosphorus Mineralization Studies Using Isotopic Dilution Techniques

Soil organic P (Po) mineralization is an important process in P cycling. No accurate method for its quantification is available because any mineralized inorganic P (Pi) may be rapidly sorbed onto the soil solid phase where it cannot be separated from already present Pi A method for measuring soil Po mineralization is explored using isotopic dilution techniques under conditions of constant soil respiration rates. First, the specific activity (SA) as affected by physicochemical processes was extrapolated from an isotopic exchange kinetics batch experiment. Second, the SA was assessed during incubation after labeling soil with 33PO4 Lower SA measured during incubation than extrapolated from the batch experiment was attributed to the release of nonlabeled Pi due to mineralization of nonlabeled Po In order to separate biological from biochemical mineralization processes, one set of samples was γ‐irradiated to stop the microbial activity while maintaining phosphatase activity. The γ‐irradiated soil revealed higher mineralization rates than the corresponding nonirradiated soil. This was explained by an increase of the amount of easily mineralizable Po derived from killed microbial cells by γ‐irradiation. Consequently, a gross, but overestimated, biochemical P mineralization can be assessed. In the nonirradiated soil, mineralization not only of nonlabeled, but also of recently synthesized labeled Po resulting from microbial turnover, may occur. Thus, in the nonirradiated soil, after several days a gross, biologically and biochemically mediated mineralization is increasingly underestimated. During the first 7 d, the mineralization rate in the nonirradiated soil was 1.7 mg P kg−1 d−1, which is an amount approximately equivalent to soil solution P in this soil, indicating that soil P mineralization is a significant process in delivering available Pi

Soil solution dynamics of Cu and Zn in a Cu- and Zn-polluted soil as influenced by γ-irradiation and Cu–Zn interaction

A pot experiment was conducted to study soil solution dynamics of Cu and Zn in a Cu/Zn-polluted soil as influenced by γ-irradiation and Cu–Zn interaction. A slightly acid sandy loam was amended with Cu and Zn (as nitrates) either singly or in combination (100 mg Cu and 150 mg Zn kg −1 soil) and was then γ-irradiated (10 kGy). Unamended and unirradiated controls were included, and spring barley ( Hordeum vulgare L. cv. Forrester) was grown for 50 days. Soil solution samples obtained using soil moisture samplers immediately before transplantation and every ten days thereafter were used directly for determination of Cu, Zn, pH and absorbance at 360 nm (A 360). Cu and Zn concentrations in the solution of metal-polluted soil changed with time and were affected by γ-irradiation and metal interaction. γ-Irradiation raised soil solution Cu substantially but generally decreased soil solution Zn. These trends were consistent with increased dissolved organic matter (A 360) and solution pH after γ-irradiation. Combined addition of Cu and Zn usually gave higher soil solution concentrations of Cu or Zn compared with single addition of Cu or Zn in γ-irradiated and non-irradiated soils, indicating an interaction between Cu and Zn. Cu would have been organically complexed and consequently maintained a relatively high concentration in the soil solution under higher pH conditions. Zn tends to occur mainly as free ion forms in the soil solution and is therefore sensitive to changes in pH. The extent to which γ-irradiation and metal interaction affected solubility and bioavailability of Cu and Zn was a function of time during plant growth. Studies on soil solution metal dynamics provide very useful information for understanding metal mobility and bioavailability.

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was γ-irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.

HT Oxidation Activity of Soil Irradiated with Gamma Radiation.

The HT oxidation activity was examined for soils irradiated with 60Co γ-rays at various doses. The HT oxidation rate decreased with increase of initial H2 concentration, indicating a similar oxidation mechanism between HT and H2. Irradiated soils showed decrease of oxidation activity with dose suggests that HT and H2 oxidation activities were affected by sterilization with γ-rays. The decline of the oxidation activity with dose was analyzed by a composite of two components with different radiosensitivity and they were considered to be activities of soil microorganisms and abiotic soil enzymes. The oxidation activity due to soil microorganisms would be important at low dose range and more radioresistant abiotic soil enzymes would be responsible for the oxidation activity observed at more than several kGy. In non-irradiated soil about half of the oxidation activity was considered resulting from abiotic soil enzymes.

Degradation and bound residue formation of atrazine in a Western Tennessee soil

Biological and physical degradation, and metabolite and soil-bound residue formation, of [U-ring-14C]atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-1,3,5-triazine) were characterized in a western Tennessee soil using laboratory and field assays. Biological mineralization of [14C]atrazine was examined in the laboratory using intact surface soil cores in sealed microcosms. Physical mineralization was determined using gamma-radiation-sterilized soil microcosms. Metabolites measured were deethylatrazine (DEA), deisopropylatrazine (DIA), dealkylatrazine (DAA) and hydroxyatrazine (HYA). Atrazine was applied at a rate of 2.2 kg/ha (˜ 5.6 μg/g soil) to soil microcosms in two studies and 3.2 kg/ha to the field. Evolution of 14CO2 from [14C]atrazine in nonirradiated soil microcosms increased to 12 and 28% of the radiolabel added after 180 d incubation. Irradiated soil microcosms evolved less than 0.07% of the radiolabel as 14CO2 for both studies after the same period. The concentrations of metabolites throughout the laboratory and field studies were: HYA > DEA > DIA > DAA. The highest concentration of HYA detected during microcosm and field studies was approximately 0.5 μg/g soil. Atrazine dissipation rates and metabolite production in nonirradiated microcosms were comparable to field results. Atrazine concentrations after 180 d in nonirradiated microcosm and field samples were lower than HYA, and either equivalent to or greater than DEA. The DAA was not detected throughout microcosm or field studies. Rates of dissipation for atrazine followed first-order kinetics. Atrazine half-life, based on extractable residues, was approximately 21 d in the microcosm studies, compared to 14 d in surface field soil. Extractable 14C residues sampled from nonirradiated microcosms decreased in concentration during the incubation period. Soil-bound 14C residues increased and, at the termination of the two studies, accounted for 39 and 43% of the radioactivity added to nonirradiated microcosms. Bound 14C residues in irradiated microcosms accounted for 49 and 48% of the activity after 180 d. Similarity of results between microcosm and field studies suggests that those microcosms may be useful for predicting the fate of atrazine in surface soil.

Degradation and bound residue formation of four atrazine metabolites, deethylatrazine, deisopropylatrazine, dealkylatrazine and hydroxyatrazine, in a Western Tennessee soil

AbstractAtrazine (2‐chloro‐4‐[ethylamino]‐6‐[isopropylamino]‐1,3,5‐triazine) can be degraded to several metabolites in soil that include the dealkylated metabolites, deethylatrazine (DEA), deisopropylatrazine (DIA) and dealkylatrazine (DAA), and the dechlorinated metabolite, hydroxyatrazine (HYA). Biological and physical degradation and soil‐bound residue formation from uniformly 14C ring‐labeled DEA, DIA, DAA and HYA were characterized in a western Tennessee soil using intact surface soil core microcosms.Metabolites were applied to soil microcosms at a rate of 0.5 kg/ha (˜1.2 μg/g soil). Concentrations of the dealkylated metabolites in nonirradiated soil microcosms decreased to less than 2% of the applied compound or were not detected after 180 d incubation. Hydroxyatrazine residues decreased to 33% of the applied concentration. In nonirradiated microcosms after 180 d, evolution of 14CO2 from radiolabeled DEA, DIA, DAA and HYA increased to 25, 16, 59 and 21%, respectively, of the total radiolabel added. Irradiated soil microcosms evolved 0.6, 1.7, 0.1 and 0.9%, respectively, of the total radiolabel added. Rates of dissipation for the four metabolites followed first‐order kinetics. Half‐lives for the dealkylated metabolites, based on extractable residues, ranged from 17 to 26 d, whereas HYA was 121 d. Soil‐bound 14C residues increased in concentration in nonirradiated microcosms and ranged from 28% of the applied radiolabel for HYA to 60% for DEA after 180 d. In irradiated microcosms the range was from 24% for HYA to 72% for DAA on day 180. Extractable 14C residues in all microcosms decreased in concentration during this study and, after 180 d, ranged from 4% of the radioactivity added for DAA to 40% for HYA. Extractable 14C residues in irradiated microcosms ranged from 31% of the initial activity for DAA to 68% for HYA at the termination of the study.

Decomposition of Methyl Nitrite in Solutions and Soils

AbstractThe role of hydrolysis as a process affecting the concentration of CH3ONO in the soil atmosphere was investigated by measuring the sorption of CH3ONO and the formation of NO‐2 and NO‐3 in two soils (−33‐kPa soil water potential) and three solutions in the dark at 20°C for 10 h. Soil pH and the pH of distilled H2O decreased on absorption of CH3ONO. In acidic solutions (distilled H2O and 0.1 M H2SO4), &gt; 90% of CH3ONO was recovered as NO‐3, whereas to an alkaline soil and 0.2 M NaOH, &gt; 80% was recovered as NO‐2. Only 0 to 7% of CH3ONO remained in the atmosphere. In an acid soil only 50% of CH3ONO was recovered as [CH3ONO + NO‐2 + NO‐3]‐N. Recoveries of N in γ‐irradiated and nonirradiated soils did not differ significantly. The data indicate that CH3ONO was rapidly hydrolysed in solutions and in soils [CH3ONO + H2O ⇌ CH3OH + HNO2], and that NO‐3 formed via the self‐decomposition of HNO2. The low recovery of N in the acid soil may have been due to the participation of HNO2 in chemodenitrification reactions. The rapid hydrolysis of CH3ONO is likely to inhibit the emission of CH3ONO formed in soils, and to cause the sorption of CH3ONO evolved from soils in closed systems.

Structure and development of mycelial cord systems of Phanerochaete laevis in soil

The total length of a mycelial cord system of Phanerochaete laevis , present in the surface soil and litter of a deciduous woodland, increased from 1415 to 1479 cm over a period of 13 months. This increase was accompanied by loss of 270 cm from the central parts, and a corresponding proliferation at the periphery of the system. Mycelial growth from colonized beech blocks (approx. 8 cm 3 ) into 30 cm long glass tubes containing γ-irradiated soil showed little differentiation of cords and usually ceased well before reaching the ends of the tubes. By contrast, in similar tubes containing unsterilized soil, well-defined cord systems were formed which reached the ends of the tubes within about 15 weeks. These developed from an advancing front of more or less constant width containing numerous finely-branched cords. Following lysis at the rear of this front a relatively few large cords remained which were still connected to the blocks. Light inhibited mycelial development in the tubes in both γ-irradiated and unsterilized soil. After 15 weeks in the tubes wood blocks from γ-irradiated soil had undergone a greater loss in dry weight (22–27% compared with about 15%) and had a higher nitrogen content than those from non-irradiated soil.