First-order Exponential Decay Model Research Articles

Isotope Evidence for Rice Accumulation of Newly Deposited and Soil Legacy Cadmium: A Three-Year Field Study.

Biogeochemical processes of atmospherically deposited cadmium (Cd) in soils and accumulation in rice were investigated through a three-year fully factorial atmospheric exposure experiment using Cd stable isotopes and diffusive gradients in thin films (DGT). Our results showed that approximately 37-79% of Cd in rice grains was contributed by atmospheric deposition through root and foliar uptake during the rice growing season, while the deposited Cd accounted for a small proportion of the soil pools. The highly bioavailable metals in atmospheric deposition significantly increased the soil DGT-measured bioavailable fraction; yet, this fraction rapidly aged following a first-order exponential decay model, leading to similar percentages of the bioavailable fraction in soils exposed for 1-3 years. The enrichment of light Cd isotopes in the atmospheric deposition resulted in a significant shift toward lighter Cd isotopes in rice plants. Using a modified isotopic mass balance model, foliar and root uptake of deposited Cd accounted for 47-51% and 28-36% in leaves, 41-45% and 22-30% in stems, and 45-49% and 26-30% in grains, respectively. The implications of this study are that new atmospheric deposition disproportionately contributes to the uptake of Cd in rice, and managing emissions thus becomes very important versus remediation of impacted soils.

Dynamic Behaviors of Newly Deposited Atmospheric Heavy Metals in the Soil-Pak Choi System.

Dynamic behaviors of the newly deposited atmospheric heavy metals in the soil-pak choi (Brassica chinensis L.) system are investigated by a fully factorial atmospheric exposure experiment using soils exposed to 0.5-year and 1.5-year atmospheric depositions. The results showed approximately 17-87%, 19-64%, and 43-84% of the Cu, Cd, and Pb in pak choi edible parts were contributed from the new depositions, respectively. For the newly deposited metals, foliar uptake was the key pathway of shoot bioaccumulation rather than from root uptake of the deposited metals in soils, resulting in no significant soil contribution differences between pak chois growing in 0.5-year and 1.5-year exposed soils. Indeed, highly bioavailable metals in atmospheric deposition significantly increased the soil plant-bioavailable Cu, Cd, and Pb fractions; however, soil aging resulted in similar percentages of the plant-bioavailable fractions in 0.5-year and 1.5-year exposed soils, which indicated the bioavailability of metals deposited into soils rapidly decreased with aging. The soil aging process of the deposited metals was well fitted with the first-order exponential decay model, and soil organic matter and clay were the major driving factors. Our findings highlight high plant bioaccumulation rates and the rapid soil aging process of newly deposited metals during the plant growth period.

Microbial cultivation using mathematical representations accounting for the reaction kinetics in two-stage nitritation/ANAMMOX process

Mathematical representations accounting for the reaction kinetics were used to improve the cultivation rate of ANAMMOX microorganisms in the pilot-scale partial nitritation (PN)/anaerobic ammonium oxidation (ANAMMOX) reactor. In line with the fluctuations in the properties of raw reject water, control strategies of the hydraulic retention time (HRT) and the mixed liquid suspended solid (MLSS) concentration calculated by the mass balance-based model were proposed to improve PN performance. As a result, control of the MLSS concentration to cope with the fluctuation of C/N ratio resulted in a higher nitrite production rate (NPR) that was suitable for enhancing the cultivation rate of the ANAMMOX microorganisms. Based on the performance in the optimized PN, the observed yield of ANAMMOX microorganisms was calculated to be 0.091 gVSS/gNH4+−N. The biomass as volatile suspended solids (VSS) wasted was 309.8–554.3 gVSS/d. Based on the reaction kinetics of ANAMMOX, the quantity of stored microorganisms over time was simulated using a modified first-order exponential decay model; the calculated value was 6.3–11.2 kg/m3/year. These results can be used for the scale-up or design of the ANAMMOX process.

Urine treatment by solar disinfection for agriculture reuse purpose in a poor rural context: case of Burkina Faso

Abstract The study aimed to reduce the storage time of urine treatment and assess the quality of treated urine following the Solar DISinfection (SODIS) method. Microbiological analyses were performed on urine samples taken before each sunlight exposure, between 10am and 4pm at a frequency of 1 h, during which temperature was measured in PET bottles (1.5 L). The initial concentrations of Escherichia coli (E. coli) and Salmonella in unstored urine were 106 and 103 CFU/100 mL respectively. The combined effect of temperature and UV radiation increased inactivation efficiency of E. coli at 5 log units. On the other hand, 98% of Salmonella were inactivated in less than 3 h of continuous exposure between 12am and 3pm with temperature varying between 50 and 65 °C in PET bottles. The k values showed that the inactivation rate of Salmonella tested was accelerated when the temperature was above 50 °C. Then, the results indicated that the first-order exponential decay model was the best method to predict the inactivation of Salmonella in urine by SODIS. General results showed that after 3 days of exposure to sunlight, urine collected via eco-toilet becomes bacteriologically sanitized and therefore can be used in agriculture.

Biomimetic degradability of linear perfluorooctanesulfonate (L-PFOS): Degradation products and pathways

The reductive degradability and decomposition pathways of linear perfluorooctanesulfonate (L-PFOS) were investigated in a biomimetic system consisting of Ti(III)-citrate and Vitamin B12. Biomimetic degradation of L-PFOS could well be described by a first-order exponential decay model. Accompanied by the release of fluoride ion, technical PFOS could not only be transformed to perfluorocarboxylates (PFCAs) and perfluoroalkylsulfonates (PFSAs) with perfluoroalkyl carbon chain length < C8 (thereafter referred as carbon-chain-shortened degradation products), but also be transformed to PFCAs with perfluoroalkyl carbon chain length ≥ C8 (thereafter referred as carbon-chain-lengthened degradation products). Perfluorohexanesulfonate and perfluorotetradecanoate were the most abundant carbon-chain-shortened and -lengthened degradation products of technical PFOS, respectively. Based on the various degradation products detected during biomimetic reduction of linear [1,2,3,4–13C4]-PFOS, the degradation pathways of L-PFOS were proposed as follows: L-PFOS was first reduced to C8F17• radical by cleavage of C–S bond, and then transformed to PFOA through hydrolysis. However, the carbon-chain-shortened products were not generated through the sequential chain-shortening via C8F17• radicals and/or L-PFOS, while the carbon-chain-lengthened products were not formed via C8F17• radicals by stepwise addition of CF2 moiety. In fact, C8F17• radical and/or L-PFOS were further reduced to form CnF2n+1• (n = 1, 2, 3, 4) radicals, and these radicals were chain-lengthened by stepwise addition of C4F8 moiety and eventually transformed to various degradation products via hydrolysis (PFCAs) or combination reaction with sulfonyl hydroxide (PFSAs). All carbon-chain-lengthened chemicals were first reported as the degradation products during the decomposition of L-PFOS, while carbon-chain-shortened compounds were first identified as the biomimetic reduction products of L-PFOS.

Chemiresistive Detection of Silver Ions in Aqueous Media

Silver is a precious metal that is commonly used in water filters to reduce growth of biofilm within the filter itself. Ionic silver is used as an effective disinfectant for potable water, giving a log10 reduction for L. pneumophilia, P. aeruginosa, and E. coli of 2.4, 4, and 7, respectively.1 In terms of human exposure, silver is not an essential metal therefore any exposure to silver is unwanted. When silver is ingested orally, the most common adverse effect is argyria, which is an extreme blue pigmentation of the skin and abdominal viscera.2 Occupational exposure to silver nitrate has been correlated to respiratory tract irritation.3 Currently there are no guidelines for silver ions in drinking water, and the World Health Organization (WHO) has set a health advisory (not a guideline value) of 100 ppb. The only country with a Maximum Allowable Content (MAC) is Germany, whose drinking water regulations (Trinkwasserverordnung) have a MAC of 80 ppb.4 Here we demonstrate a chemiresistive sensor for the in situ detection of silver (I) in aqueous media. Chemiresistive sensors function through the changes that occur in the electronic structure of the sensor itself. A graphite film attached to two copper contacts at either end is exposed to the silver ions such that only the graphite and not the contacts interact with the ions. To functionalize the graphite, silver (I)-specific ligands, such as bathocuproine, can be deposited onto the film to adsorb onto it, protecting it from interfering ions.5 Chemiresistive sensors have been demonstrated before for the detection of free chlorine in aqueous media. Rather than using graphite, carbon nanotubes (CNT) were utilized as the conductive film, with phenyl-capped aniline tetramer (PCAT) as the chlorine-specific ligand. As the PCAT doped CNT was exposed to chlorine, the PCAT oxidized, and the electronic changes were probed using a bias voltage. The linear range for this sensor was from 60 ppb to 60 ppm, providing sufficient sensitivity for household use.6 When testing other common ions, there were no significant interference's that compete with the response of silver (I) in solution, making this sensor quite selective to silver (I). pH tests show that there is no change in current induced by pH between the range of 6-10 pH. Below 6, the sensor functions as a "proton sensor" due to the protonation of the adsorbed bathocuproine. Above pH 10, AgOH may be formed, which will precipitate out of solution. All tests were performed at an analyte conductance of 31 μS/cm, which is typical for freshwater samples.7 When the fabricated sensor was exposed to silver (I) in aqueous solution, detection of the ions was observed through a step up in the current going through the sensor. Each step up in current was proportional to the concentration of silver (I) in solution. Based on this, a calibration curve was made using the Langmuir Isotherm model and a first-order exponential decay model. For the range of 3 ppb to 1 ppm, both the Langmuir Isotherm and the first-order exponential decay model gave R2 values of 0.9982 and 0.9939, respectively. The sensor could also be reliably reset to the same 0 ppm baseline after use by exposing it to a pH 3 solution. When exposed to silver (I) post-reset, current changes were also quite reproducible, with the values having a relative standard deviation no greater than 1.24%, highlighting the re-usability of this sensor. The limit of detection, calculated using a signal:noise ratio of 3, for this sensor would be 3 ppb.We have therefore demonstrated that chemiresistors based on functionalized nanocarbon films can be used as selective ion sensors in addition to their previously demonstrated application as redox sensors. The toolbox of organometallic chemistry can now be applied to extend this sensing platform to other cations for water quality sensing.

Immobilized Cerrena sp. laccase: preparation, thermal inactivation, and operational stability in malachite green decolorization

Laccases are polyphenol oxidases with widespread applications in various industries. In the present study, the laccase from Cerrena sp. HYB07 was immobilized with four methods, namely entrapment in alginate, covalently binding to chitosan as well as formation of cross-linked enzyme aggregates (CLEAs) and magnetic CLEAs (M-CLEAs). The activity recovery rates of the immobilized laccases ranged from 29% to 68%. Immobilization elevated the reaction temperature optimum and reduced substrate specificity, but not necessarily the turnover rate. pH stability of immobilized laccases was improved compared with that of the free laccase, especially at acidic pH values. Thermal inactivation of all laccases followed a simple first-order exponential decay model, and immobilized laccases displayed higher thermostability, as manifested by lower thermal inactivation rate constants and longer enzyme half-life time. Operational stability of the immobilized laccase was demonstrated by decolorization of the triphenylmethane dye malachite green (MG) at 60 °C. MG decolorization with free laccase was accompanied by a shift of the absorption peak and accumulation of a stable, colored intermediate tetradesmethyl MG, probably due to lower thermostability of the free laccase and premature termination of the degradation pathway. In contrast, complete decolorization of MG was achieved with laccase CLEAs at 60 °C.

Biodegradation behavior and modelling of soil burial effect on degradation rate of PLA blended with starch and wood flour

The biodegradation behavior of Poly (lactic acid) (PLA) blended with starch and wood flour in outdoor soil was investigated comprehensively. As a result, starch provided a biological fuel for the growth of microorganisms in the soil which accelerated the degradation rate of PLA more obviously than wood flour. With the increase of starch content, the weight loss increased and the morphology exhibited more gullies and cavities. X-ray Photoelectron Spectroscopy (XPS) analysis indicated that the variation of O/C ratio was controlled by starch biodegradation and PLA hydrolysis and they were a concomitant process. The mechanical strengths of all the blends showed similar trend and fitted a first-order exponential decay model. The model is shown in good agreement with experimental results as the correlation coefficient is higher than 0.99, and the model can support an efficient method to estimate the durability of starch/wood flour/PLA blends.

Oyster's cells regulatory volume decrease: A new tool for evaluating the toxicity of low concentration hydrocarbons in marine waters

Human activities require fossil fuels for transport and energy, a substantial part of which can accidentally or voluntarily (oil spillage) flow to the marine environment and cause adverse effects in human and ecosystems' health. This experiment was designed to estimate the suitability of an original cellular biomarker to early quantify the biological risk associated to hydrocarbons pollutants in seawater. Oocytes and hepatopancreas cells, isolated from oyster (Crassostrea gigas), were tested for their capacity to regulate their volume following a hypo-osmotic challenge. Cell volumes were estimated from cell images recorded at regular time intervals during a 90min-period. When exposed to diluted seawater (osmolalities from 895 to 712mosmkg−1), both cell types first swell and then undergo a shrinkage known as Regulatory Volume Decrease (RVD). This process is inversely proportional to the magnitude of the osmotic shock and is best fitted using a first-order exponential decay model. The Recovered Volume Factor (RVF) calculated from this model appears to be an accurate tool to compare cells responses. As shown by an about 50% decrease in RVF, the RVD process was significantly inhibited in cells sampled from oysters previously exposed to a low concentration of diesel oil (8.4mgL−1 during 24h). This toxic effect was interpreted as a decreased permeability of the cell membranes resulting from an alteration of their lipidic structure by diesel oil compounds. In contrast, the previous contact of oysters with diesel did not induce any rise in the gills glutathione S-transferase specific activity. Therefore, this work demonstrates that the study of the RVD process of cells selected from sentinel animal species could be an alternative bioassay for the monitoring of hydrocarbons and probably, of various chemicals in the environment liable to alter the cellular regulations. Especially, given the high sensitivity of this biomarker compared with a proven one, it could become a relevant and accurate tool to estimate the biological hazards of micropollutants in the water.

Influence of preservation temperature on the characteristics of anaerobic ammonium oxidation (anammox) granular sludge.

Preserving active anaerobic ammonium oxidation (anammox) biomass is a potential method for securing sufficient seeding biomass for the rapid start-up of full-scale anammox processes. In this study, anammox granules were cultured in an upflow anaerobic sludge blanket (UASB) reactor (R0), and then the enriched anammox granules were preserved at 35, 20, 4, and -30°C. The subsequent reactivation characteristics of the granules were evaluated in four UASB reactors (denoted R1, R2, R3, and R4, respectively) to investigate the effect of preservation temperature on the characteristics of anammox granules and their reactivation performance. The results demonstrated that 4°C was the optimal preservation temperature for maintaining the biomass, activity, settleability, and integrity of the anammox granules and their cellular structures. During the preservation period, a first-order exponential decay model may be used to simulate the decay of anammox biomass and activity. The protein-to-polysaccharide ratio in the extracellular polymeric substances and the heme c content could not effectively indicate the changes in settleability and activity of the anammox granules, respectively, and a loss of bioactivity was positively associated with the degree of anaerobic ammonium-oxidizing bacteria cell lysis. After 42days of storage, the anammox granules preserved at 4°C (R3) exhibited a better recovery performance than those preserved at 20°C (R2), -30°C (R4), and 35°C (R1). The comprehensive comparison indicated that 4°C is the optimal storage temperature for anammox granular sludge because it promotes improved maintenance and recovery performance properties.

Short-term carbon dioxide emission under contrasting soil disturbance levels and organic amendments

Agriculture can be either a source or sink of atmospheric CO2 depending on soil management. The application of swine slurry in conventional tilled soils could enhance soil CO2 emission depleting soil organic C stocks. However, the use of recalcitrant C-rich organic fertilizers in no-till soils can offset soil CO2 emission promoting soil C sequestration. This hypothesis was tested by evaluating short-term CO2-C emissions from a Rhodic Nitisol under contrasting soil disturbance levels (disturbed (DS) and undisturbed soil (US)) top-dressed with mineral or organic fertilizers (urea (UR), raw swine slurry (RS), anaerobically digested swine slurry (ADS), and composted swine slurry (CS)). Soil CO2 emission was evaluated for 64 days using static chambers where gas samples were collected and analysed by photoacoustic infrared spectroscopy. Soil water-filled pore space (WFPS), temperature and meteorological data were concomitantly registered and a first-order exponential decay model was used to assess the decomposition of organic fertilizers and CO2 emissions induced by soil disturbance. Soil CO2-C emission was correlated with soil temperature, while limiting soil aeration impaired CO2-C efflux when WFPS >0.6cm3cm−3. Disturbance increased soil CO2-C efflux (36.3±2.2kg CO2-Cha−1 day−1) in relation to US (33.3±1.6kg CO2-Cha−1 day−1). Extra labile C input through RS amendment induced an increased soil CO2-C efflux for a longer period (t1/2=16.9 and 9.6 days in DS and US treatments, respectively), resulting in higher CO2-C emissions than soil amended with other fertilizers. The recalcitrant C input by ADS and CS had limited effect on soil CO2-C emissions. CS presented a genuine potential for substantial soil organic C accumulation while offsetting increased CO2-C emissions in comparison to RS amended soils.

Human mitochondrial DNA and endogenous bacterial surrogates for risk assessment of graywater reuse.

Previous graywater risk assessment studies have focused on fecal contamination, yet the low density of fecal indicators may not provide the most useful approach to assess pathogen removal during graywater treatment. In this study, we employed high throughput bacterial sequencing and qPCR to elucidate potential microbial surrogates in wastewater sourced from an industrial laundry. In addition, we explored human mitochondrial DNA (HmtDNA) as a new, potentially more reliable molecular marker, because it can be unambiguously sourced, has a high copy number per cell, and is persistent when released from cells with no self-replication in graywater. Pyrosequencing and qPCR revealed that laundry water microbiota was dominated by the skin-associated bacteria Staphylococcus, Corynebacterium, and Propionibacterium (6.5, 5.7, 5.4 log10 copies/100 mL, respectively). While HmtDNA was less abundant (2.8 log10 copies/100 mL), it showed a strong positive correlation with the opportunistic pathogen Staphylococcus aureus (r=0.54, P=3.2×10(-4)) and closely followed a first-order exponential decay model (R2=0.98), remaining detectable in stored laundry graywater for up to 6 days at 20 °C. Based on abundance and persistence, we propose HmtDNA and total Staphylococcus as future laundry graywater treatment surrogates to potentially assess a wide dynamic range of pathogen removal.

Can a first‐order exponential decay model fit heart rate recovery after resistance exercise?

The time-constant of postexercise heart rate recovery (HRRτ ) obtained by fitting heart rate decay curve by a first-order exponential fitting has being used to assess cardiac autonomic recovery after endurance exercise. The feasibility of this model was not tested after resistance exercise (RE). The aim of this study was to test the goodness of fit of the first-order exponential decay model to fit heart rate recovery (HRR) after RE. Ten healthy subjects participated in the study. The experimental sessions occurred in two separated days and consisted of performance of 1 set of 10 repetitions at 50% or 80% of the load achieved on the one-repetition maximum test [low-intensity (LI) and high-intensity (HI) sessions, respectively]. Heart rate (HR) was continuously registered before and during exercise and also for 10 min of recovery. A monoexponential equation was used to fit the HRR curve during the postexercise period using different time windows (i.e. 30, 60, 90, … 600 s). For each time window, (i) HRRτ was calculated and (ii) variation of HR explained by the model (R(2) goodness of fit index) was assessed. The HRRτ showed stabilization from 360 and 420 s on LI and HI, respectively. Acceptable R(2) values were observed from the 360 s on LI (R(2) > 0.65) and at all tested time windows on HI (R(2) > 0.75). In conclusion, this study showed that using a minimum length of monitoring (~420 s) HRR after RE can be adequately modelled by a first-order exponential fitting.

Sorption and degradation of pharmaceuticals and personal care products (PPCPs) in soils

Pharmaceuticals and personal care products (PPCPs) are one class of the most urgent emerging contaminants, which have drawn much public and scientific concern due to widespread contamination in aquatic environment. Most studies on the environmental fate and behavior of PPCPs have focused on nonsteroidal anti-inflammatory drugs. Some other compounds with high concentrations were less mentioned. In this study, sorption and degradation of five selected PPCPs, including bisphenol A (BPA), carbamazepine (CBZ), gemfibrozil (GFB), octylphenol (OP), and triclosan (TCS) have been investigated using three different soils. Sorption isotherms of all tested PPCPs in soils were well described by Freundlich equation. TCS and OP showed moderate to strong sorption, while the sorption of GFB and CBZ in soils was negligible. Degradation of PPCPs in three soils was generally fitted first-order exponential decay model, with half-lives (t 1/2) varying from 9.8 to 39.1days. Sterilization could prolong the t 1/2 of PPCPs in soil, indicating that microbial activity played an important role in the degradation of these chemicals in soils. Degradation of PPCPs in soils was also influenced by the soil organic carbon (f oc) contents. Results from our data show that sorption to the soils varied among the different PPCPs, and their sorption affinity on soil followed the order of TCS > OP > BPA > GFB > CBZ. The degradation of the selected PPCPs in soil was influenced by the microbial activity and soil type. The poor sorption and relative persistence of CBZ suggest that it may pose a high leaching risk for groundwater contamination when recycled for irrigation.

Synthesis of fly-ash cenospheres coated with polypyrrole using a layer-by-layer method

Uniform polypyrrole (PPy) films, of controlled thickness, were successfully synthesized and immobilized on polyelectrolyte (PE) multilayer-assembled fly-ash cenospheres (FACs) using a simple and versatile method. In this approach, FACs were assembled with multilayers of poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) using a layer-by-layer self-assembly procedure. The FACs were used as templates for the subsequent deposition of PPy. The deposition behaviours of PEs on the surfaces of the FACs were examined, and the results could be fitted to a first-order exponential decay model at pH 6. The surfaces of the PE-deposited FACs (FAC-(PDDA-PSS)n, n is the number of PE layers) became more homogeneous as n increased. Their properties were determined mainly by the PE, not by the FAC itself, after n = 4. PPy-coated FACs with PE precursor layers [(PPy/FAC-(PDDA-PSS)n] had different morphologies for different numbers of PE layers. The PPy loading amount on the FACs and the conductivities of the composites reached plateaus after the PE layer deposition number exceeded six.

Soil temperature and moisture effects on the persistence of synthetic androgen 17α-trenbolone, 17β-trenbolone and trendione

Trenbolone acetate (TBA) is a synthetic androgenic steroid hormone administered as a subcutaneous implant for growth promotion in beef cattle. The primary metabolite excreted in manure from implanted cattle is 17α-trenbolone with lesser amounts of 17β-trenbolone and trendione also present. At 22 °C and favorable moisture conditions in a controlled laboratory environment, trenbolone degrades to trendione in a few hours; however, these conditions are often not what exist in the field. Therefore, aerobic degradation rates of 17α-trenbolone, 17β-trenbolone and trendione were determined in a sandy soil and silty clay loam under a range of temperature and water availability combinations that may be expected in the field. A first-order exponential decay model was used to estimate rates and generally resulted in good model fits to the data. Degradation rates decreased with decreasing water availability ( i.e., more negative soil matric potential) and decreasing temperature. However, when water availability was substantially reduced (−1.0 MPa), hotter temperatures (35 °C) significantly reduced trenbolone degradation rates. Once temperature was low enough to limit microbial activity, no further changes were observed with decreasing matric potential. Trendione also exhibited similar moisture and temperature dependent degradation, but persisted longer than the parent trenbolone. The latter was discussed in light of extracellular versus intracellular enzymatic degradation and sorption. Half lives at colder temperatures (5 °C) even under favorable moisture conditions were 2–3 d for the trenbolone isomers and approached 10 d for trendione.

Degradation of Synthetic Androgens 17α- and 17β-Trenbolone and Trendione in Agricultural Soils

17Beta-trenbolone acetate (TBA) is a synthetic androgenic steroid hormone administered as a subcutaneous implant for growth promotion in beef cattle. TBA is converted metabolically to primarily 17alpha-trenbolone and trendione, and excreted in manure from implanted cattle. To predict the persistence of synthetic androgens once land-applied, aerobic degradation rates in two contrasting agricultural soil types (clay loam and a sandy soil) of both trenbolone isomers (17alpha and 17beta) and their primary metabolite trendione were measured and isomer interconversion was assessed. The impact of manure application was also evaluated in the clay loam soil. A pseudo first-order exponential decay model was derived assuming irreversible transformation and no impact of sorption on availability for degradation. The model generally resulted in good fits to the data. Both isomers degraded to trendione in a similar manner with half-lives (t1/2) on the order of a few hours to 0.5 days at applied concentrations of < or = 1 mg/kg. Similar degradation rates were observed in the presence and absence of manure applied at rates typical for land-application of cattle manure. Trenbolone degradation was concentration-dependent with degradation rates decreasing with increasing applied concentrations. Trendione, whether applied directly or produced from trenbolone, persisted longer than trenbolone with t1/2 values of 1 to 4 days. A small amount (1.5%) of conversion of trendione back to 17beta-trenbolone was observed during aerobic incubation regardless of the applied concentration. A small amount of 17alpha-isomer also converted back to 17beta-trenbolone, presumably through trendione. In autoclaved soils, no degradation of 17alpha- or 17beta-trenbolone was observed during the first 3 days, and trendione degradation was relatively small compared to a microbially active soil.

Comparison of models for describing measured VOC emissions from wood-based panels under dynamic chamber test condition

Measured emission factors are the experimental data used to represent emission characteristics of volatile organic compounds (VOCs) from testing materials under dynamic chamber test conditions. A simple empirical model that describes the measured emission factors will be very useful for practical purposes. In this study, a power law model was compared with a widely used first-order exponential decay model in their ability to describe measured emission factors of wood-based panel materials. It was demonstrated that the power law model is a better choice than the first-order model for describing emission characteristics for short-term (less than 100 h) experimental data. The power law model was also more superior in predicting long-term (up to 900 h) emission factors.

Gene expression and enzyme activities of the sodium pump during sea urchin development: implications for indices of physiological state.

The sodium pump consumes a large portion of the metabolic energy (40%) in sea urchin larvae. Understanding the developmental regulation of ion pumps is important for assessing the physiological state of embryos and larvae. We sequenced a partial cDNA clone (1769 bp) from the sea urchin Strongylocentrotus purpuratus and found it to contain the C-terminal portion of an open reading frame coding for 195 amino acids that exhibited high sequence similarity (89%) to invertebrate alpha-subunits of the Na+,K+-ATPase sodium pump. Northern blots using the 3' untranslated region of this cDNA specifically recognized a 4.6-kbp transcript under high stringency. During embryonic development, a rapid increase in levels of this mRNA transcript during gastrulation (25 h postfertilization) was paralleled by a concomitant increase in the total enzymatic activity of Na+,K+-ATPase. Expression of this subunit during gastrulation increased to a maximum at 36 h, followed by a rapid decline to trace levels by 60 h. The rate of removal of the transcript from the total RNA pool after 36 h closely followed a first-order exponential decay model (r2= 0.988), equivalent to a degradation rate of 7.8% h(-1). By 83 h, transcription of the alpha-subunit gene was low, yet sodium pump activity remained high. Molecular assays for the expression of this gene would underestimate sodium pump activities for assessing physiological state because of the temporal separation between maximal gene expression in a gastrula and maximal enzyme activities in the later larval stage. This finding illustrates the difficulty of using molecular probes for assessing the physiological state of invertebrate larvae.

Statistical Modeling of Litter Decomposition from Integrated Cellulase Activity

Efforts to model plant litter decomposition have centered around three approaches. On large spatiotemporal scales, decomposition rates have been estimated from climate parameters, typically temperature and potential evapotranspiration (e.g., Insam 1990). At the ecosystem scale, litter degradation models based on empirical fits to mass loss curves have been widely used (Webster and Benfield 1986, Boulton and Boon 1991). The simplest of these is the first-order exponential decay model. Rate constants for this model are routinely reported in litter decomposition papers, but at the same time, this approach is generally considered unrealistic. More precise twoand three-stage models have been developed that recognize different stages in decomposition, but their predictive value is limited. More general models have been produced by relating decomposition directly to litter chemistry. In this approach, both simple parameters, e.g., nitrogen and lignin, and compound parameters, e.g., C:N, fignin: N, and lignocellulose index, defined as lignin/(lignin + holocellulose), have been used as indices of biodegradability (Melillo et al. 1982, Taylor et al. 1989). While qualitatively predictive, these models do not consider the role of edaphic and climatic factors in the regulation of biotic activity, so cannot predict rates. In this report, we describe a new process-level modeling approach focused on microdecomposer activity. It offers three advantages: (1) ease of application, (2) realism, and (3) potential for linkage to larger scale models. The approach is an empirical one: the potential activities of key enzymes directly involved in the degradation of plant structural components are used as indices of microdecomposer activity. Previous studies have established correlations between cellulose activity and mass loss from decomposing leaf litter (Sinsabaugh et al. 1991, Sinsabaugh 1993). However, such correlations do not permit mass loss estimation because of the temporal difference between mass loss, a cumulative parameter, and enzyme