90-day Incubation Period Research Articles

Biodegradation of polypropylene plastics in vitro and natural condition by Streptomyces sp. isolated from plastic-contaminated sites

Most plastic degradation studies are conducted under controlled laboratory conditions. The current study investigated the ability to degrade Polypropylene (PP) plastic by Streptomyces ardesiacus strain NBI0111 under both laboratory and natural conditions. This strain exhibited the ability to degrade PP when cultured in BH medium and using PP plastics as carbon sources. After a 90-day incubation period, the weight loss of PP plastics reached 17.52 % (p < 0.05). The surface of the PP plastic showed significant changes compared to the control group. Chemical changes in the plastic were also detected on the 60th and 90th days, as confirmed by FTIR and GC-MS analyses. This strain was applied to degrade PP plastic in soils under natural conditions. Strain NBI0111 also resulted in a notable weight loss. The biodegradation test group exhibited a significant 12.5 % decrease compared to only a 3.88 % decrease in the control group (p < 0.05). Furthermore, a strong positive correlation between the weight loss of PP plastic cups and the density of microbial populations was observed. The capabilities demonstrated by Streptomyces ardesiacus strain NBI0111 in this study hold great promise for on-site plastic remediation, offering a sustainable solution to the problem of plastic pollution in the future.

A Study of the Composting Capacity of Different Kinds of Leathers, Leatherette and Alternative Materials

The leather industry is in the midst of a shift towards sustainability and circular economy principles, placing a strong emphasis on the biodegradability of its products. There has been a notable upswing in the traction gained by eco-friendly leather alternatives. Concurrently, a diverse spectrum of commercial substitutes for conventional leather has surfaced, encompassing a range from synthetic constructs like leatherette to plant-based options. The objective of this study was to evaluate the composting capabilities of genuine leather and three alternatives, namely leatherette, Piñatex®, and Desserto®, in conjunction with leather subjected to treatment with alginate derivatives. The composting evaluation was conducted in accordance with ISO standards, simulating an intensive aerobic composting process. Results revealed that bovine leather samples treated with alginate derivatives underwent complete degradation within 21 to 25 days, and conventional wet-blue production resulted in total degradation after 31 to 35 days. In contrast, vegetable-tanned bovine leather manifested initial signs of degradation after 60 days, but fell short of achieving complete disintegration even after a protracted 90-day incubation period. Alternative materials showed no degradation after the 90-day composting test, indicating a potentially lower degradation capacity compared to leather, likely attributed to the presence of non-biodegradable materials like PU and PVC, among others. The negligible degradation observed in alternative materials after 90 days of composting highlights their inferior composting performance compared to leather.

Nitrogen addition accelerates litter decomposition and arsenic release of Pteris vittata in arsenic-contaminated soil from mine

The arsenic (As) release from litter decomposition of As-hyperaccumulator (Pteris vittata L.) in mine areas poses an ecological risk for metal dispersion into the soil. However, the effect of atmospheric nitrogen (N) deposition on the litter decomposition of As-hyperaccumulator in the tailing mine area remains poorly understood. In this study, we conducted a microcosm experiment to investigate the As release during the decomposition of P. vittata litter under four gradients of N addition (0, 5, 10, and 20 mg N g−1). The N10 treatment (10 mg N g−1) enhanced As release from P. vittata litter by 1.2–2.6 folds compared to control. Furthermore, Streptomyces, Pantoea, and Curtobacterium were found to primarily affect the As release during the litter decomposition process. Additionally, N addition decreased the soil pH, subsequently increased the microbial biomass, as well as hydrolase activities (NAG) which regulated N release. Thereby, N addition increased the As release from P. vittata litter and then transferred to the soil. Moreover, this process caused a transformation of non-labile As fractions into labile forms, resulting in an increase of available As concentration by 13.02–20.16% within the soil after a 90-day incubation period. Our findings provide valuable insights into assessing the ecological risk associated with As release from the decomposition of P. vittata litter towards the soil, particularly under elevated atmospheric N deposition.

A field assessment to validate the assumptions of the Tea Bag Index (TBI) as a measure of soil health

This study evaluated key assumptions underlying the Tea Bag Index (TBI) as a soil health assessment tool through a time series conducted under field conditions. The TBI assesses soil health by measuring the decomposition rates of standardized green and red tea over a 90-day incubation period. Our research was conducted on a degraded 33.6-ha agricultural site in North Saanich, British Columbia, where we compared two plots: a reference site and a grazed site, each representing distinct land use conditions.The first assumption evaluated was that the TBI metrics of S (stabilization rate) and k (decomposition rate) follow exponential decay models. While S adhered to this assumption, k did not, suggesting additional as yet undetermined influences on decomposition rates. We introduced new biological metrics, Bg and Br, which followed polynomial models of decay, and may reflect the decomposition of different materials over time by different soil organisms.The second assumption tested was that a 90-day incubation period adequately captures the timeframe required for labile litter consumption. Our findings indicated that decomposition variance plateaued after 105 days, and that an increase in incubation time by 35 days increased the precision of mathematical decomposition models by a mean value of 18.1 %.The final assumption tested was that litter decomposition rate varies with land use. Our findings affirm that land use does affect litter decomposition rate, although the specific sources of that variance remain unclear.TBI accuracy can be improved by extending the litter incubation time to at least 105 days. Incorporating biological metrics (Bg and Br) increases the TBI's precision. Our results reaffirm the TBI's sensitivity to land use differences, highlighting its potential as a cost-effective tool for assessing soil health under varying conditions.

Metabolic profiling of petroleum-degrading microbial communities incubated under high-pressure conditions.

While pressure is a significant characteristic of petroleum reservoirs, it is often overlooked in laboratory studies. To clarify the composition and metabolic properties of microbial communities under high-pressure conditions, we established methanogenic and sulfate-reducing enrichment cultures under high-pressure conditions using production water from the Jilin Oilfield in China. We utilized a metagenomics approach to analyze the microbial community after a 90-day incubation period. Under methanogenic conditions, Firmicutes, Deferribacteres, Ignavibacteriae, Thermotogae, and Nitrospirae, in association with the hydrogenotrophic methanogen Archaeoglobaceae and acetoclastic Methanosaeta, were highly represented. Genomes for Ca. Odinarchaeota and the hydrogen-dependent methylotrophic Ca. Methanosuratus were also recovered from the methanogenic culture. The sulfate-reducing community was dominated by Firmicutes, Thermotogae, Nitrospirae, Archaeoglobus, and several candidate taxa including Ca. Bipolaricaulota, Ca. Aminicenantes, and Candidate division WOR-3. These candidate taxa were key pantothenate producers for other community members. The study expands present knowledge of the metabolic roles of petroleum-degrading microbial communities under high-pressure conditions. Our results also indicate that microbial community interactions were shaped by syntrophic metabolism and the exchange of amino acids and cofactors among members. Furthermore, incubation under in situ pressure conditions has the potential to reveal the roles of microbial dark matter.

Biochar amendment reassembles microbial community in a long-term phosphorus fertilization paddy soil.

This study investigates the effect of biochar amendment on microbial community structure and soil nutrient status in paddy soil that has been fertilized for an extended period of time, shedding light on sustainable agricultural practices. A 90-day incubation period revealed that biochar amendment, as opposed to long-term fertilization, significantly influenced the physicochemical properties and microbial composition of the soil. The microcosm experiment conducted using six treatments analyzed soil samples from a long-term rice ecosystem. We employed microbial biomarkers (phospholipid fatty acids, PLFAs; isoprenoid and branched glycerol dialkyl glycerol tetraethers, iGDGTs and brGDGTs; DNA) to assess microbial biomass and community structure. Biochar addition led to a decrease in PLFA biomass (15-32%) and archaeal iGDGT abundance (14-43%), while enhancing bacterial brGDGT abundance by 15-77%. Intact biochar increased archaeal and bacterial diversity, though fungal diversity remained unchanged. However, acid-washed biochar did not result in a uniform microbial diversity response. The abundance of various microbial taxa was changed by biochar amendment, including Crenarchaeota, Proteobacteria, Nitrospira, Basidiomycota, Halobacterota, Chloroflexi, Planctomycetota, and Ascomycota. Soil NH4+-N was found as the primary environmental factor impacting the composition of archaea, bacteria, and fungus in this study. These findings imply that the addition of biochar has a quick influence on the structure and activity of microbial communities, with fungi possibly having a critical role in acid paddy soil. This study contributes valuable knowledge for developing sustainable agricultural practices that promote healthy soil ecosystems. KEY POINTS: • Biochar type and phosphorus fertilization demonstrated an interactive effect on the diversity of archaea, but no such effect was observed for bacteria and fungi. • Soil fungi contribute to approximately 20% of the total phospholipid fatty acid (PLFA) content. • Biochar, especially acid-washed rice straw biochar, increases glucose metabolism in bacteria and archaea and decreases saprophytic fungi.

Gross nitrogen mineralization and nitrification at an optimal phosphorus input level in southern Chinese red soil with long-term fertilization

In China, phosphorus (P) is recognized as a “key limiting nutrient” for crop production, and its overuse results in underground leaching, ecosystem alterations and risks to humans, such as degraded surface water quality. The coupling of nitrogen (N) and P implies that soil N dynamics are largely affected by P availability. However, how the addition of P affects soil N transformations remains less understood. To determine the optimal P-input level, we performed an incubation experiment on an upland soil from Jinxian in China after long-term mineral fertilizer application and P addition. The two treatments without N addition T1 (no fertilizer) and T2 (inorganic potassium fertilizer) and the two treatments with N addition T3 (inorganic nitrogen fertilizer) and T4 (inorganic nitrogen and potassium fertilizer) were selected from the long-term experiment that involved scientific management at five P-input levels (0, 25, 50, 75, and 100 kg P2O5 ha−1) with three replications. The results showed that soil organic matter (SOM) increased in the T3 and T4 treatments compared with the T1 and T2 treatments. The T4 treatment resulted in the maximum N concentration of 1.28 g kg−1, followed by that in the T3 treatment (1.25 g kg−1), T2 (0.16 g kg−1) and that in the T1 treatment (0.10 g kg−1), in the soil. Among the different treatments, soil microbial biomass carbon (SMBC) and nitrogen (SMBN) were significantly higher (492.69 mg kg−1 and 73.36 mg kg−1, respectively) in the T3 treatment than in the other treatments, while soil microbial biomass phosphorus (SMBP) was higher in the T4 treatment (17.55 mg kg−1). With the addition of P, the gross N mineralization rate was substantially enhanced when N and K were applied. After the 90-day incubation period, with higher concentrations of NO3--N and NH4+-N in the T4 treatment than in the other treatments, the concentrations were significantly increased by P addition, specifically T4P4 by 11.27% and 37.37%, T4P3 by 12.64% and 30.29%, T4P2 by 22.94% and 64.53%, and T4P1 by 3.93% and 11.09%, compared with those of T4P0, respectively; these results indicated a maximum N mineralization potential (No) and mineralization rate constant, k (NMR). As a result of the increased gross nitrogen mineralization rates and associated NH4+ substrate availability, the gross nitrification rate was also increased by P addition. Based on the polynomial regression analysis, the inclusion of P at the rate of 60 kg P2O5 ha−1 can be used effectively to obtain maximum gross N mineralization rates in soil. Additionally, to fully understand why P addition is more effective under specific soil and environmental conditions, more research is necessary to determine the underlying mechanisms.

Soil microbial biomass and extracellular enzymes regulate nitrogen mineralization in a wheat-maize cropping system after three decades of fertilization in a Chinese Ferrosol

Soil net nitrogen (N) mineralization is a vital process that impacts the global N cycling and regulates the N availability for plant development. The objectives of this study were to evaluate the response of N mineralization to long-term organic versus inorganic fertilization and to quantify the relationships between N mineralization and soil microbial characteristics in the ferrosol (red soil) of South China after 30 years of mineral and manure application in a wheat-maize cropping system. Soil was sampled from a wheat-maize rotation system, consisting of five treatments. The treatments included (1) CK (no fertilizer), (2) PK (synthetic phosphorus and potassium fertilizer), (3) NK (synthetic nitrogen and K fertilizer), (4) N (synthetic N fertilizer), and (5) NPKM (synthetic NPK fertilizer and manure). The sampled soil was analyzed for physicochemical parameters and incubated for the determination of N mineralization, soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and associated soil enzymes related to C and N cycling. Results showed that NPKM increased soil organic carbon (SOC), available P (AP), total P (TP), and total nitrogen (TN) by 132%, 880%, 293%, and 76% respectively, over the control (CK). Among different treatments, soil microbial biomass nitrogen (SMBN) and carbon (SMBC) were highest under the NPKM treatment. N-cycling and P-cycling enzyme activities also showed significant differences among treatments. N-Acetyl-β-d-glucosaminidase (NAG), leucine-aminopeptidase (LAP), and acid phosphatase (AcP) activities were also highest under the NPKM treatment, at 650.36, 32.36, and 23.41 (mol g−1 h−1), respectively. A linear increase was observed in the NO3−-N and NH4+-N concentrations throughout the 90-day incubation period. NPKM showed a maximum N mineralization potential (No) and mineralization rate constant, k (NMR), at the end of the incubation period. A principal component analysis (PCA) interpreted the differences among fertilization and their effects on net N mineralization. A significant (p ≤ 0.05) positive correlation was observed between SMBC (R2 = 0.87), SMBN (R2 = 0.92), enzyme activities, and the No. Structural equation modeling (SEM) revealed that SOC, TN, and TP directly affected mineralization, while SMBC and SMBN indirectly affected the net mineralization. Manure input increased the extracellular enzymes in soil, which accelerated the net N mineralization due to enhanced soil microbial activities. Consequently, long-term manure addition appears to be an optimal approach to meet the nutrient demands and to enhance the N availability in a wheat-maize cropping system.

Rapid changes in the chemical composition of degrading ectomycorrhizal fungal necromass

Abstract Characterizing the chemical changes in fungal necromass as it degrades, particularly over short time intervals (days to weeks), is critical to clearly understanding how this organic matter source contributes to various belowground carbon and nutrient pools. Using a range of chemical analyses, we assessed the degradation of four types of ectomycorrhizal fungal necromass from three species differing in biochemical composition. Samples were buried in a forest in Minnesota, USA and harvested at eight time points over a 90-day incubation period (1, 2, 4, 7, 14, 28, 60, 90 days). Three of the necromass types lost greater than 50% of their initial mass in the first seven days, but mass loss plateaued for all four types at later harvests, and after 90 days, none of the samples were completely degraded. Relative to undegraded necromass, degraded necromass consistently contained a lower relative abundance of aliphatic compounds and a higher relative abundance of carbohydrates, sterols, and aromatic compounds. For three of the four necromass types, nitrogen content was lower after 90 days of degradation and FTIR spectra revealed distinct peaks broadening from day 0 to day 90. While melanin content significantly slowed degradation within species, differences in degradation rates across species were more closely aligned with initial nitrogen content. Collectively, our results indicate that the rapid mass loss of dead fungal mycelium is accompanied by a wide range of changes in necromass chemistry, likely contributing to both short-term soil nutrient and longer-term carbon pools.

Movement of boron from ulexite and colemanite minerals in sapwood and heartwood of Cryptomeria japonica

This study evaluated boron diffusion from raw boron minerals ulexite and colemanite with low water solubility in comparison to disodium octaborate tetrahydrate (DOT). Tests were conducted using sugi (Cryptomeria japonica (L.) f. D. Don) sapwood and heartwood blocks conditioned to 30, 60, and 90% target moisture content. The blocks were filled with the boron compounds through treatment holes and diffusion was observed at three assay zones across the blocks after 7, 30, 60 or 90-day incubation period at room temperatures. For comparison, ethylene glycol was also introduced into the holes to elevate boron diffusion. As expected, diffusion increased with increased moisture content and levels were higher at the 60% and 90% moisture levels compared to the 30% level. With some exceptions, boron levels did not follow consistent gradients with distance away from the treatment hole. Incorporation of ethylene glycol helped increase boron levels, even in heartwood blocks. Boron levels were higher from the ulexite source than from colemanite; however, DOT treatments resulted in the highest boron diffusion rates as a result of greater water solubility compared to both raw boron minerals. The results suggest that ulexite together with ethylene glycol may be useful in both sapwood and heartwood materials when kept at high moisture levels for extended periods.

Effect of long-term fertilization on decomposition of crop residues and their incorporation into microbial communities of 6-year stored soils

To investigate the effects of long-term fertilization on microbial decomposition of residues and priming effect (PE), 13C-labeled maize (Zea mays L.) residues were supplied to arable soils with a 20-year application of compost (COM), mineral NPK fertilizer (NPK), or without any treatments, the no-fertilizer control (NF). The soils that had been stored for 6 years were used in the present incubation experiment. The release of CO2–C and the microbial incorporation of residue-derived C determined by phospholipid fatty acids (PLFAs) analysis were monitored over a 90-day incubation period. Residue additions significantly increased cumulative CO2–C emission and induced positive PE. Cumulative residue-derived CO2-C emission and PE mainly occurred within the first 15 days. The COM soil had significantly higher cumulative residue-derived CO2–C emission but lower PE than the NF and NPK soils. Residue additions significantly increased microbial abundance and changed the composition of main microbial groups. The COM soil showed a significantly lower relative fungal abundance (mol%) but a higher relative actinomycetes abundance than the NF and NPK soils. The incorporation of residue-derived C within fungi was the highest among all the main microbial groups and decreased from 15 to 45 days, while the incorporation of residue-derived C within actinomycetes increased with time in three soils. The incorporation of residue-derived C within fungi was the highest in the COM soil over the course of incubation. The long-term compost input promoted fungal use of residue C and stimulated residue decomposition.

The role of organic/bio–fertilizer amendment on aggregate stability and organic carbon content in different aggregate scales

This study investigated the effects of different organic and bio–fertilizer (alone or in combination) applications on aggregate stability and organic carbon (OC) content in macro (2–1mm) and micro (0.25–0.050mm) aggregate sizes of clay loam (Typic Xerofluvent) textured soil. In addition, correlation between OC content and aggregate stability was determined. The study was conducted as a pot experiment under greenhouse conditions and was arranged in a completely randomized design with three replications. The treatments were: control (no fertilizer) (C), inorganic fertilizer (15:15:15 compound fertilizer+ammonium nitrate, 33% N) (F), mycorrhizal fungi (Glomus spp.) (M), microalgae (Chlorella spp.) (A), bacteria (Bacillus megaterium KBA–10+Pantoea agglomerans RK–134+Pseudomonas fluorescens FDG–37) (BMF), bacteria (Bacillus subtilis PA1+Paenibacillus azotofixans PA2) (BCP), vermicompost (V), vermicompost+mycorrhizal fungi (VM), vermicompost+microalgae (VA), vermicompost+bacteria (VBMF) and vermicompost+bacteria (VBCP) applied in 90days incubation period. At the end of the 90-day incubation period, organic and bio–fertilizer amendments had an increasing impact on aggregate stability and OC content in macro– and micro– aggregate scale. Especially, bio–fertilizers in combination with vermicompost mostly had stronger effects on stability and OC content of aggregates of both size classes in comparison with control and bio–fertilizer treatments alone. In addition, significant (p<0.05) and positive correlations were observed between stability and OC contents of macro (2–1mm) and micro (0.25–0.050mm) aggregates size classes in each treatment.

Determination of reactivity rates of silicate particle-size fractions

The efficiency of sources used for soil acidity correction depends on reactivity rate (RR) and neutralization power (NP), indicated by effective calcium carbonate (ECC). Few studies establish relative efficiency of reactivity (RER) for silicate particle-size fractions, therefore, the RER applied for lime are used. This study aimed to evaluate the reactivity of silicate materials affected by particle size throughout incubation periods in comparison to lime, and to calculate the RER for silicate particle-size fractions. Six correction sources were evaluated: three slags from distinct origins, dolomitic and calcitic lime separated into four particle-size fractions (2, 0.84, 0.30 and &lt;0.30-mm sieves), and wollastonite, as an additional treatment. The treatments were applied to three soils with different texture classes. The dose of neutralizing material (calcium and magnesium oxides) was applied at equal quantities, and the only variation was the particle-size material. After a 90-day incubation period, the RER was calculated for each particle-size fraction, as well as the RR and ECC of each source. The neutralization of soil acidity of the same particle-size fraction for different sources showed distinct solubility and a distinct reaction between silicates and lime. The RER for slag were higher than the limits established by Brazilian legislation, indicating that the method used for limes should not be used for the slags studied here.

Responses of soil microbial community to different concentration of fomesafen

Fomesafen degrades slowly in soils and has been linked to crop damage. However, the effect of its residues on soil microbial communities is unknown. The goal of this work was to assess the effect of applying three different doses of fomesafen on microbial community structure and functional diversity as measured by phospholipid fatty acid (PLFA) levels, community-level physiological profiles (CLPPs) and real-time PCR. Our results indicate that applying 100 times the recommended dose of fomesafen (T100) adversely affects soil microbial activity and stresses soil microbial communities as reflected by the reduced respiratory quotient (qCO2, QR). The PLFA analysis showed that high levels of fomesafen treatment (T100) decreased the total amount of PLFAs and both bacterial (both Gram-positive (GP) bacteria and Gram-negative (GN) bacteria) and fungal biomass but increased the microbial stress level. However, the BIOLOG results are not consistent with our other results. The addition of fomesafen significantly increased the average well color development, substrate utilization, and the functional diversity index (H′). Additionally, the abundance of the nifH (N2-fixing bacteria) gene was reduced in the presence of high concentrations of fomesafen (T100). Taken together, these results suggest that the addition of fomesafen can alter the microbial community structure and functional diversity of the soil, and these parameters do not recover even after a 90-day incubation period.

The importance of different forms of Pb on diminishing biological activities in a calcareous soil

In this experimental study, we evaluated the effect of different lead (Pb) fractions on biological properties in soil spiked with 0, 600, 1200 and 1800 mg kg−1 Pb, during a 90-day incubation period at 25−28°C. Different Pb fractions were measured by sequential extraction at days 1 and 90 after soil treatment. Diethylenetriaminepentaacetic acid (DTPA)-extractable Pb and soil biological properties at days 1, 5, 15, 45 and 90 were measured. The concentration of Pb in soluble and exchangeable fractions was very high at day 1, but it showed remarkable transfer into carbonate and residual fractions by day 90. Substrate-induced respiration, basal respiration, acid and alkaline phosphatases, microbial populations (bacterial, fungal and actinomycetes) and biomass carbon decreased significantly with soil contamination compared with the control. With Pb ageing, these biological properties increased. Metabolic quotient (qCO2) increased significantly compared with the control with increasing Pb concentration. The toxicity of various forms of Pb for the biological status of the soil was in the following order: KNO3 extractable>NaOH extractable>EDTA extractable>HNO 3 extractable>total content Pb. Thus, the bioavailable fractions are better indicators of Pb pollution in soils.

Deltamethrin degradation and effects on soil microbial activity

Deltamethrin [(S)-cyano-3-phenoxybenzyl-cis-(1R,3R)-2,2-dimethyl) cyclo–propane carboxylate),1] labelled at gem-dimethyl groups of the cyclopropane ring was applied on two Egyptian soils at a level of 10 mg/kg soil for a laboratory incubation experiment under aerobic and anaerobic conditions. A steady decrease of soil extractable14C-residues, accompanied by a corresponding increase of non- extractable bound 14C-residues was observed over a 90-day incubation period. The percentage of evolved 14CO2 increased with time under aerobic and anaerobic conditions in both soils. The effect of deltamethrin on soil microorganisms as well as the counter effect of microorganisms on the insecticide was also investigated. As the incubation period increased, the inhibitory effect of the insecticide on the microorganisms decreased and the evolution of carbon dioxide depended on the applied dose. The nature of soil methanol soluble residues was determined by chromatographic analysis which revealed the presence of the parent insecticide as the main product in addition to four metabolites: 3-(2′,2′-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (II); 3-phenoxybenzaldehyde (III); 3-phenoxybenzoic acid (IV); 3-phenoxybenzyl alcohol (V).

Fate and effect of naphthenic acids on oil refinery activated sludge wastewater treatment systems

Naphthenic acids (NAs) are a complex group of alkyl-substituted acyclic, monocyclic and polycyclic carboxylic acids present in oil sands process waters, crude oil, refinery wastewater and petroleum products. Crude oil, desalter brine, influent, activated sludge mixed liquor and effluent refinery samples were received from six United States refineries. The total acid number (TAN) of the six crudes tested ranged from 0.12 to 1.5 mg KOH/g crude oil and correlated to the total NA concentration in the crudes. The total NA concentration in the desalter brine, influent, activated sludge mixed liquor and effluent samples ranged from 4.2 to 40.4, 4.5 to 16.6, 9.6 to 140.3 and 2.8 to 11.6 mg NA/L, respectively. The NAs in all wastewater streams accounted for less than 16% of the total COD, indicating that many other organic compounds are present and that NAs are a minor component in refinery wastewaters. Susceptibility tests showed that none of the activated sludge heterotrophic microcosms was completely inhibited by NAs up to 400 mg/L. Growth inhibition ranging from 10 to 59% was observed in all microcosms at and above 100 mg NA/L. NAs chronically-sorbed to activated sludge mixed liquor biomass and powdered activated carbon (PAC) were recalcitrant and persistent. More than 80% of the total NAs remained in the solid phase at the end of the 10-day desorption period (five successive desorption steps). Throughout a 90-day incubation period, the total NA concentration decreased by 33 and 51% in PAC-free and PAC-containing mixed liquor microcosms, respectively. The lower molecular weight fraction of NAs was preferentially degraded in both mixed liquors. The persistence of the residual, higher molecular weight NAs is likely a combination of molecular recalcitrance and decreased bioavailability when chronically-sorbed to the biomass and/or PAC.

Can soil amendments (zeolite or lime) shift the balance between nitrous oxide and dinitrogen emissions from pasture and wetland soils receiving urine or urea-N?

To determine the effects of soil amendments (lime or ammonium-sorbed zeolite) on emissions of nitrous oxide (N2O) and dinitrogen (N2) gases from pasture and wetland soils, a 90-day incubation experiment was conducted under controlled moisture and temperature conditions. Soil samples (0–0.10 m soil depth) collected from pasture and adjacent wetland sites were treated with 2 nitrogen (N) sources (cow urine or urea) at 200 kg N/ha with and without added soil amendments using 10-L plastic containers and then incubated at 25°C. Subsoil samples were taken out at different intervals to measure gaseous emissions of N2O and N2 using the acetylene (C2H2) inhibition method, ammonium (NH4+), nitrate (NO3–), soluble organic C, and pH. The anaerobic conditions (81% water-filled pore space) in wetland soils precluded nitrification, and therefore no increase in NO3–, N2O, or N2 was observed during the 90-day incubation period. In the pasture soil, the application of urine, urea, and soil amendments significantly affected daily and total N2O and N2 emissions and their ratios over a 90-day incubation period. Total N2O emission from urea-treated soil (48 kg N2O-N/ha) was significantly higher than from urine-treated soil (39 kg N2O-N/ha) and the control soil (4.5 kg N2O-N/ha). The application of zeolite significantly reduced N2O emissions from urea and urine-treated soils by 45% and 33%, respectively, due to the sorption of NH4+ by zeolite. Liming had minor effect on N2O emission. However, when lime was applied with zeolite, a significant reduction in N2O emission was observed. Lime application alone was found to increase N2 emissions in urine and urea treated soils by 46% and 35%, respectively, and thereby lower N2O : N2 ratios. The results indicate that zeolite reduced N2O emission while lime increased N2 emissions and lowered N2O : N2 ratios, and warranting further attention for mitigation of N2O.

Effect of soil disturbance on N availability across a variable landscape in southern Ontario

Although the effect of soil disturbance on N mineralization has been studied under field conditions, the spatial variation of this effect at the landscape scale has not been investigated. The objective of this study was to determine the spatial variation of the effect of tillage on plant N availability across a variable landscape in southern Ontario and to identify the causal factors. A field experiment was conducted from 1998 to 2001 using two spring tillage operations (no-tillage (NT) and conventional tillage (CT)) prior to planting corn ( Zea mays L.) on a field, which was planted to barley ( Hordeum vulgare L.) in the preceding season. Tillage treatments were implemented at five positions in the landscape. The corn plants received either 0 or 140 kg N ha −1. Plant N availability was approximated by adding the amount of soil mineral N present in the 0–30 cm depth and N contained in the aerial phytomass in the zero N treatment. The plant available N (PAN) content was significantly higher in the CT treatment than that in the NT treatment during the first 2 months after the tillage operation, with differences ranging from 2.1 to 6.5 mg N kg −1. This effect did not vary with soil properties. In a supplementary laboratory incubation study, which simulated the field tillage operation under controlled conditions, the PAN did not increase in the disturbed soils at any point during the 90-day incubation period. It was hypothesized that the change in the soil physical environment (e.g., soil temperature) could have had a greater influence on the observed differences in the field experiment than the availability of physically protected organic matter in this long-term cultivated field.

Evaluation of TCDD biodegradability under different redox conditions

Polychlorinated dibenzo- p-dioxins have been generated as unwanted by-products in many industrial processes. Although their widespread distribution in different environmental compartments has been recognized, little is known about their fate in the ultimate environment sinks. The highly stable dioxin isomer 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) has been called the most toxic compound known to man. In this laboratory microcosm study, TCDD bioavailability was evaluated under five reduction/oxidation (redox) conditions including aerobic biodegradation, aerobic cometabolism, methanogenesis, iron reduction, and reductive dechlorination. Activated sludge and aquifer sediments from a TCDD and a pentachlorophenol (PCP) contaminated site were used as the inocula. Acetate, sludge cake, and cane molasses were used as the primary substrates (carbon sources) in cometabolism and reductive dechlorination microcosms. After a 90-day incubation period, microcosms constructed under reductive dechlorination conditions were the only treatment showing promising remediation results. The highest TCDD degradation rate [up to 86% of TCDD removal (with an initial concentration of 96 μg/kg of soil)] was observed in the microcosms with anaerobic activated sludge as the microbial inocula and sludge cakes as the primary substrates. Except for reductive dechlorination microcosms, no significant TCDD removal was observed in the microcosms prepared under other conditions. Thus, application of an effective primary substrate to enhance the reductive dechlorination process is a feasible method for TCDD bioremediation. Bioremediation expense can be significantly reduced by the supplement of some less expensive alternative substrates (e.g., sludge cakes, cane molasses). Results would be useful in designing a scale-up in situ or on-site bioremediation system such as bioslurry reactor for field application.