Predicting logarithmic values of the subcooled liquid vapor pressure of halogenated persistent organic pollutants with QSPR: How different are chlorinated and brominated congeners?

Logarithmic values of the subcooled liquid vapor pressure (log P_L) were estimated for 1436 polychlorinated and polybrominated congeners of benzenes, biphenyls, dibenzo-p-dioxins, dibenzofurans, diphenyl ethers and naphthalenes by employing the Quantitative Structure–Property Relationships (QSPR) approach. The QSPR model developed with GA–PLS technique was characterized by satisfactory goodness-of-fit, robustness and the external predictive performance (R²Y = 0.970, Q_CV² = 0.970, Q_Ext² = 0.966, RMSE_C = 0.21, RMSE_CV = 0.22 and RMSE_P = 0.22). The externally validated model has been applied to predict subcooled liquid vapor pressure of uninvestigated halogenated persistent organic pollutants. Moreover, a simple arithmetic relationship between logarithmic values of subcooled liquid vapor pressures in pairs of chloro- and bromo-analogues has been found. This relationship can be used for estimating log P_L of a brominated compound, whenever log P_L of its chlorinated counterpart is known, without necessity of performing any time-consuming computations.     

Determination of vapor pressure-temperature relationships of current–use pesticides and transformation products

Sub-cooled liquid vapor pressures (P_L ⁰) of current–use organochlorine and organophosphate pesticides (chlorothalonil, chlorpyrifos methyl, diazinon, fipronil) and selected transformation products (chlorpyrifos oxon, heptachlor epoxide, oxychlordane, 3,5,6-trichloro-2-pyridinol) were determined at multiple temperatures using the gas chromatography retention time technique. Results were utilized to determine vapor pressure-temperature relationships and to calculate enthalpies of vaporization (ΔH_vap). While results for chlorothalonil and diazinon were comparable with published values, the measured value for fipronil (1.82 × 10^{? 6} Pa) is almost an order of magnitude higher than the reported literature value (3.7 × 10^{? 7} Pa). The availability of vapor pressure temperature relationships for these chemicals will aid in pesticide risk assessment development and improve the effectiveness of mitigation and remediation efforts.     

QSPR for prediction of subcooled vapor pressures (log PL) of polychlorinated trans-azobenzenes

In this study the values of subcooled vapor pressures (log P_L) were estimated for 209 trans chloroazobenzenes (Ct-ABs) that fill some gaps in analytical and experimental data on these compounds. There are 209 chloro derivatives of trans azobenzenes that are relatively stable and more environmentally relevant than 209 chloro cis congeners. The calculations models were based on the Quantitative Structure-Property Relationship (QSPR) scheme using the semi-empirical method (PM6) in molecular package (MOPAC) software and density functional theory (DFT) method using B3LYP functional and 6-311++G** basis set) in Gaussian 03 software method and the artificial neural networks (ANNs) prediction. The values of log P_L predicted by models used varied between ?3.94 to ?2.66 for Mono-; ?4.85 to ?2.97 for Di-; ?5.18 to ?3.17 for Tri-; ?6.02 to ?3.77 for Tetra-; ?6.64 to ?4.64 for Penta-; ?7.36 to ?4.76 for Hexa-; ?7.54 to ?5.79 for Hepta-; ?7.75 to ?6.64 for Octa-; ?7.89 to ?7.44 for Nona-Ct-Abs; and ?8.09 and ?8.13 for Deca-Ct-AB. Based on these values Ct-ABs can be grouped localized among relatively low (log P_L ?4 to ?2) and low (log P_L < ?4) mobile Persistent Organic Pollutants (POPs). Both the calculation methods employed were characterized by similar prediction ability of subcooled vapor pressure values of Ct-ABs, while those of PM6 are much more efficient due to a cheaper hardware used and around 300-fold less time spent on calculations.     

Gas/particle partitioning of polycyclic aromatic hydrocarbons in coastal atmosphere of the north Yellow Sea, China

Samples of gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs) were collected at three sampling stations (Xiaomai Island, Laohutan, and Zhangzi Island) in the north Yellow Sea, China during November 2008 and September 2009 to study their atmospheric transport potential and the gas/particle distributions. The composition of PAHs was dominated by gaseous compounds. The percentages of the particle-phase PAHs to the total concentrations were found to be higher during the heating period than the non-heating period. The ratios of naphthalene and acenaphthene to phenanthrene, chrysene and dibenzo(a,h)anthracene showed an increasing trend from Xiaomai Island to Zhangzi Island, which can be called as the local atmospheric distillation of PAHs. Gas/particle partitioning coefficients (K _p) and their relationship with the sub-cooled liquid vapor pressures (pº_L) of PAHs were investigated. The regressions of logK _p versus logpº_L gave significant correlations for all samples of the three sites with r ² values in the range 0.56–0.66 (p?<?0.01). Both Junge–Pankow adsorption model and octanol–air partition coefficient absorption model tended to underestimate the sorption for most PAHs, but the absorption model appeared to be more suitable for predicting the particle fraction of PAHs than the Junge–Pankow model.     

Determination of octanol-air partition coefficients and supercooled liquid vapor pressures of organochlorine pesticides

Octanol-air partition coefficients (K_OA) and supercooled liquid vapor pressures (P_L) of nine organochlorine pesticides (OCPs) including p,p′-DDE, p,p′-DDD, o,p′-DDT, o,p′-DDE, o,p′-DDD, α-HCH, β-HCH, γ-HCH, δ-HCH were determined as functions of temperature using a gas chromatographic retention time method. Among them, the K_OA of o,p′-DDE and o,p′-DDD and the P_L of o,p′-DDE, o,p′-DDD, β-HCH and δ-HCH were determined for the first time. The determined K_OA and P_L values of investigated compounds at 25°C ranged from 3.14 × 10⁷ (α-HCH) to 3.76×10⁹ (p,p′-DDD), and 8.95×10^{? 4} Pa (p,p′-DDD) to 1.08×10^{? 1} Pa (α-HCH), respectively. The K_OA and P_L data were compared with published data. The K_OA values of o,p′-DDT at 25°C were 3.23×10⁹, higher than o,p′-DDE (1.02×10⁹) and o,p′-DDD (2.01×10⁹), indicating o,p′-DDT were more preferred to partition in soil compared with the metabolites. The K_OA values were lower and P_L values were higher for o,p′-DDE and o,p′-DDD, compared with their p,p′-isomeric counterparts, leading to a potential difference in behavior and fate of these isomers. The discrepancies among chemicals are obvious, which reflected in the increasing K_OA and decreasing P_L values in order of α-HCH, γ-HCH, β-HCH, δ-HCH, o,p′-DDE, p,p′-DDE, o,p′-DDD, o,p′-DDT, p,p′-DDD. For each compound, the LogK_OA decreased linearly with reciprocal absolute temperature, while LogP_L had a significant positive correlation with the inverse absolute temperature. The present study suggested that the method of gas chromatographic retention time was appropriate to measure the K_OA and P_L of a number of OCPs.     

Perfluorinated compounds in Haihe River and Dagu Drainage Canal in Tianjin, China

In this study, nine perfluorinated compounds (PFCs) were investigated in water and sediment of Haihe River (HR) and Dagu Drainage Canal (DDC), Tianjin, China. The total PFCs in water samples from DDC (40-174 ng L⁻¹) was much greater than those from HR (12-74 ng L⁻¹). PFC contamination was severe at lower reaches of HR due to industry activities, while high PFCs were found in the middle of DDC due to the effluents from wastewater treatment plants. Perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) were the predominant PFCs in aqueous phase. The total PFCs in sediments from DDC (1.6-7.7 ng g⁻¹ dry weight) were lower as compared to HR (7.1-16 ng g⁻¹), maybe due to the dredging of sediment in DDC conducted recently. PFOS was the major PFC in HR sediments followed by PFOA; while PFHxA was the major PFC in DDC sediments. Organic carbon calibrated sediment-water distribution coefficients (K_OC) were calculated for HR. The Log K_OC ranged from 3.3 to 4.4 for C7-C11 perfluorinated carboxylic acids, increasing by 0.1-0.6 log units with each additional CF₂ moiety. The log K_OC for 8:2 fluorotelomer unsaturated acid was reported for the first time with a mean value of 4.0. The log Koc of PFOS was higher than perfluoronanoic acid by 0.8 log units.     

Estimating the vapor pressures of multi-functional oxygen-containing organic compounds using group contribution methods

A UNIFAC-based method for estimating the vapor pressure (p_L^o) values of oxygen-containing compounds of intermediate-to-low volatility has been developed as an aid in modeling the formation and behavior of organic aerosols. This UNIFAC-p_L^o method was constructed using a set of 76 compounds with experimentally determined p_L^o values. The compounds chosen are of intermediate-to-low volatility and contain multiple oxygen-containing functionalities. For test and development purposes, the 76 compounds were divided into a basis set of 43 compounds used to generate the coefficients required in the UNIFAC-p_L^o method and a second set of 33 compounds that was used to test the coefficients generated using the basis set. Both the basis and test sets contained compounds that possessed similar structures and functionalities. For the 33 compounds in the test set, on average UNIFAC-p_L^o predicted the p_L^o values to within a factor of 2 over the temperature range 290–320 K. Furthermore, the UNIFAC-p_L^o method did not show any correlation in prediction error with p_L^o so that it was equally likely to underpredict as overpredict p_L^o regardless of volatility. For comparison, three other vapor pressure estimation methods were applied to the test set of compounds. On average, these other methods all predicted the test set p_L^o values to within a factor of 3 over the temperature range 290–320 K. In contrast to the UNIFAC-p_L^o method, the prediction errors from the methods were found to be correlated with p_L^o so that the other methods overpredicted p_L^o as volatility decreased.     

Comparative sorption,desorption and leaching potential of aminocyclopyrachlor and picloram

Sorption and desorption of aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropylpyrimidine-4-carboxylic acid) were compared to that of the structurally similar herbicide picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) in three soils of differing origin and composition to determine if picloram data is representative of aminocyclopyrachlor behavior in soil. Aminocyclopyrachlor and picloram batch sorption data fit the Freundlich equation and was independent of concentration for aminocyclopyrachlor (1/n = 1), but not for picloram (1/n = 0.80–0.90). Freundlich sorption coefficients (K _f) for aminocyclopyrachlor were lowest in the eroded and depositional Minnesota soils (0.04 and 0.12 μmol ^(1–1/n) L^1/n kg^?1) and the highest in Molokai soil (0.31 μmol ^(1–1/n) L^1/n kg^?1). For picloram, K _f was lower in the eroded (0.28 μmol ^(1–1/n) L^1/n kg^?1) as compared to the depositional Minnesota soil (0.75 μmol ^(1–1/n) L^1/n kg^?1). Comparing soil to soil, K _f for picloram was consistently higher than those found for aminocyclopyrachlor. Desorption of aminocyclopyrachlor and picloram was hysteretic on all three soils. With regard to the theoretical leaching potential based on groundwater ubiquity score (GUS), leaching potential of both herbicides was considered to be similar. Aminocyclopyrachlor would be ranked as leacher in all three soils if t_1/2 was > 12.7 days. To be ranked as non-leacher in all three soils, aminocyclopyrachlor t_1/2 would have to be <3.3 days. Calculated half-life that would rank picloram as leacher was calculated to be ～15.6 d. Using the current information for aminocycloprachlor, or using picloram data as representative of aminocycloprachlor behavior, scientists can now more accurately predict the potential for offsite transport of aminocycloprachlor.     

Concentrations,atmospheric partitioning,and air–water/soil surface exchange of polychlorinated dibenzo-p-dioxin and dibenzofuran along the upper reaches of the Haihe River basin,North China

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/PCDF) were overall measured and compared in ambient air, water, soils, and sediments along the upper reaches of the Haihe River of North China, so as to evaluate their concentrations, profiles, and to understand the processes of gas–particle partitioning and air–water/soil exchange. The following results were obtained: (1) The average concentrations (toxic equivalents, TEQs) of 2,3,7,8-PCDD/PCDF in air, water, sediment, and soil samples were 4,855 fg/m³, 9.5 pg/L, 99.2 pg/g dry weight (dw), and 56.4 pg/g (203 fg TEQ/m³, 0.46 pg TEQ/L, 2.2 pg TEQ/g dw, and 1.3 pg TEQ/g, respectively), respectively. (2) Although OCDF, 1,2,3,4,6,7,8-HpCDF, OCDD, and 1,2,3,4,6,7,8-HpCDD were the dominant congeners among four environmental sinks, obvious discrepancies of these congener and homologue patterns of PCDD/PCDF were observed still. (3) Significant linear correlations for PCDD/PCDF were observed between the gas–particle partition coefficient (K _p) and the subcooled liquid vapor pressure (P _L ⁰) and octanol–air partition coefficient (K _oa). (4) Fugacity fraction values of air–water exchange indicated that most of PCDD/PCDF homologues were dominated by net volatilization from water into air. The low-chlorinated PCDD/PCDF (tetra- to hexa-) presented a strong net volatilization from the soil into air, while high-chlorinated PCDD/PCDF (hepta- to octa-) were mainly close to equilibrium for air–soil exchange.     

Measurement of vapour pressures of Fenitrothion and Matacil

Vapour pressures of Fenitrothion and Matacil were measured using a gas saturation method. Polyurethane foam was used to trap the volatilized materials from sand and glass surfaces, and Porapak Q for trapping materials volatilized from leaf surfaces. The vapour pressures (VP) were linearly related to the reciprocal temperature by the equation: $\text{Log (VP)}\text{= 6.3362 ? (}\text{3197.8}\text{T}\text{)}$ for a sand incorporated with Fenitrothion and $\text{Log (VP)}\text{= 8.8316 ? (}\text{4021.4}\text{T}\text{)}$ for a sand incorporated with Matacil. The greatest vapour loss rates were from sand incorporated with fenitrothion, followed by vapour loss rates from glass surfaces; the least vapour loss rate was from leaf surfaces.     

Copper bioaccumulation,photosystem II functioning,and oxidative stress in the seagrass <Emphasis Type="Italic">Cymodocea nodosa</Emphasis> exposed to copper oxide nanoparticles

Photosynthetic activity, oxidative stress, and Cu bioaccumulation in the seagrass Cymodocea nodosa were assessed 4, 12, 24, 48, and 72 h after exposure to two copper oxide nanoparticle (CuO NP) concentrations (5 and 10 mg L^?1). CuO NPs were characterized by scanning electron microscopy (SEM) and dynamic light scattering measurements (DLS). Chlorophyll fluorescence analysis was applied to detect photosystem II (PSII) functionality, while the Cu accumulation kinetics into the leaf blades was fitted to the Michaelis-Menten equation. The uptake kinetics was rapid during the first 4 h of exposure and reached an equilibrium state after 10 h exposure to 10 mg L^?1 and after 27 h to 5 mg L^?1 CuO NPs. As a result, 4-h treatment with 5 mg L^?1 CuO NPs, decreased the quantum yield of PS II photochemistry (Φ _PSΙΙ ) with a parallel increase in the regulated non-photochemical energy loss in PSII (Φ _NPQ ). However, the photoprotective dissipation of excess absorbed light energy as heat, through the process of non-photochemical quenching (NPQ), did not maintain the same fraction of open reaction centers (q _p ) as in control plants. This reduced number of open reaction centers resulted in a significant increase of H₂O₂ production in the leaf veins serving possibly as an antioxidant defense signal. Twenty-four-hour treatment had no significant effect on Φ _PSΙΙ and q _p compared to controls. However, 24 h exposure to 5 mg L^?1 CuO NPs increased the quantum yield of non-regulated energy loss in PSII (Φ _NO ), and thus the formation of singlet oxygen (¹O₂) via the triplet state of chlorophyll, possible because the uptake kinetics had not yet reached the equilibrium state as did 10 mg L^?1. Longer-duration treatment (48 and 72 h) had less effect on the allocation of absorbed light energy at PSII and the fraction of open reaction centers, compared to 4-h treatment, suggesting the function of a stress defense mechanism. The response of C. nodosa leaves to CuO NPs fits the “Threshold for Tolerance Model” with a threshold time (more than 4 h) required for induction of a stress defense mechanism, through H₂O₂ production.     

Degradation of ethylenethiourea pesticide metabolite from water by photocatalytic processes

In this study, photocatalytic (photo-Fenton and H₂O₂/UV) and dark Fenton processes were used to remove ethylenethiourea (ETU) from water. The experiments were conducted in a photo-reactor with an 80 W mercury vapor lamp. The mineralization of ETU was determined by total organic carbon analysis, and ETU degradation was qualitatively monitored by the reduction of UV absorbance at 232 nm. A higher mineralization efficiency was obtained by using the photo-peroxidation process (UV/H₂O₂). Approximately 77% of ETU was mineralized within 120 min of the reaction using [H₂O₂]₀ = 400 mg L^?1. The photo-Fenton process mineralized 70% of the ETU with [H₂O₂]₀ = 800 mg L^?1 and [Fe²⁺] = 400 mg L^?1, and there is evidence that hydrogen peroxide was the limiting reagent in the reaction because it was rapidly consumed. Moreover, increasing the concentration of H₂O₂ from 800 mg L^?1 to 1200 mg L^?1 did not enhance the degradation of ETU. Kinetics studies revealed that the pseudo-second-order model best fit the experimental conditions. The k values for the UV/H₂O₂ and photo-Fenton processes were determined to be 6.2 × 10^?4 mg L^?1 min^?1 and 7.7 × 10^?4 mg L^?1 min^?1, respectively. The mineralization of ETU in the absence of hydrogen peroxide has led to the conclusion that ETU transformation products are susceptible to photolysis by UV light. These are promising results for further research. The processes that were investigated can be used to remove pesticide metabolites from drinking water sources and wastewater in developing countries.     

Leaf age affects the responses of foliar injury and gas exchange to tropospheric ozone in Prunus serotina seedlings

We investigated the effect of leaf age on the response of net photosynthesis (A), stomatal conductance (g_wv), foliar injury, and leaf nitrogen concentration (N_L) to tropospheric ozone (O₃) on Prunus serotina seedlings grown in open-plots (AA) and open-top chambers, supplied with either carbon-filtered or non-filtered air. We found significant variation in A, g_wv, foliar injury, and N_L (P < 0.05) among O₃ treatments. Seedlings in AA showed the highest A and g_wv due to relatively low vapor pressure deficit (VPD). Older leaves showed significantly lower A, g_wv, N_L, and higher foliar injury (P < 0.001) than younger leaves. Leaf age affected the response of A, g_wv, and foliar injury to O₃. Both VPD and N_L had a strong influence on leaf gas exchange. Foliar O₃-induced injury appeared when cumulative O₃ uptake reached 8-12 mmol m⁻², depending on soil water availability. The mechanistic assessment of O₃-induced injury is a valuable approach for a biologically relevant O₃ risk assessment for forest trees.     

Single and combined effects of aluminum (Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) and zinc (ZnO) oxide nanoparticles in a freshwater fish, <Emphasis Type="Italic">Carassius auratus</Emphasis>

The increasing use of nanoparticles (NPs) worldwide has raised some concerns about their impact on the environment. The aim of the study was to assess the toxicity of metal oxide nanoparticles, singly or combined, in a freshwater fish (Carassius auratus). The fish were exposed for 7, 14, and 21 days to different concentrations of NPs (10 μg Al₂O₃.L^?1, 10 μg ZnO.L^?1, 10 μg Al₂O₃.L^?1 plus 10 μg ZnO.L^?1, 100 μg Al₂O₃.L^?1, 100 μg ZnO.L^?1, and 100 μg Al₂O₃.L^?1 plus 100 μg ZnO.L^?1). At the end of each exposure period, antioxidant enzyme activity (catalase, glutathione-S-transferase, and superoxide dismutase), lipid peroxidation, and histopathology were assessed in the gills and livers of C. auratus. The results show an increase in catalase (CAT) and superoxide dismutase (SOD) activity in the gills and livers of fish, especially after 14 days of exposure to single and combined NPs, followed by a reduction at 21 days. An increase in glutathione S-transferase (GST) was observed in gills after 7 days for all tested NP concentrations (single and combined); while in livers, a significant increase was determined after 14 days of exposure to 100 μg.L^?1 of both single ZnO and Al₂O₃ NPs. Lipid peroxidation (LPO) significantly increased in gills after 7 days of exposure to 100 μg.L^?1 Al₂O₃ NPs (single or combined). In livers, LPO increased significantly after 7 days of exposure to all tested concentrations of both single ZnO and Al₂O₃ (except for 10 μg Al₂O₃.L^?1), and after 14 days of exposure to ZnO (10 and 100 μg.L^?1) and Al₂O₃ (100 μg.L^?1)_. The results from histological observations suggest that exposure to metal oxide NPs affected both livers and gills, presenting alterations such as gill hyperplasia and liver degeneration. However, the most pronounced effects were found in gills. In general, this study shows that the tested NPs, single or combined, are capable of causing sub-lethal effects on C. auratus, but when combined, NPs seem to be slightly more toxic than when added alone.     

Influence of exogenous urea on photosynthetic pigments, 14CO2 uptake, and urease activity in Elodea densa—environmental implications

This paper analyzes the effect of exogenous urea in increased concentration gradient (0, 100, 500 and 1,000 mg L^?1) on photosynthetic pigments (measured spectrophotometrically), uptake of ¹⁴CO₂ (using radioisotope), and urease activity (by measuring ammonia with Nessler’s reagent) in leaves of Elodea densa Planch. We have observed that low concentration of urea (100 mg L^?1) stimulates the accumulation of photosynthetic pigments and intensifies photosynthesis in E. densa, whereas high concentration (1,000 mg L^?1) suppresses these processes. Urease activity increased by approximately 2.7 and 8 fold when exogenous urea concentrations were 100 and 500 mg L^?1, respectively. However, exogenous urea in high concentration (1,000 mg L^?1) decreased urease activity by 1.5 fold compared to the control. The necessity of mitigating urea and other nitrogen-containing compounds (NH₃ from urea) in water bodies has been discussed with emphasis on the potential for phytoremediation of urea using common water weed viz. E. densa.     

Toxicity of nanoparticulate and bulk ZnO, Al2O3 and TiO2 to the nematode Caenorhabditis elegans

Limited information is available on the environmental behavior and associated potential risk of manufactured oxide nanoparticles (NPs). In this research, toxicity of nanoparticulate and bulk ZnO, Al₂O₃ and TiO₂ were examined to the nematode Caenorhabditis elegans with Escherichia coli as a food source. Parallel experiments with dissolved metal ions from NPs were also conducted. The 24-h median lethal concentration (LC₅₀) and sublethal endpoints were assessed. Both NPs and their bulk counterparts were toxic, inhibiting growth and especially the reproductive capability of the nematode. The 24-h LC₅₀ for ZnO NPs (2.3 mg L⁻¹) and bulk ZnO was not significantly different, but significantly different between Al₂O₃ NPs (82 mg L⁻¹) and bulk Al₂O₃ (153 mg L⁻¹), and between TiO₂ NPs (80 mg L⁻¹) and bulk TiO₂ (136 mg L⁻¹). Oxide solubility influenced the toxicity of ZnO and Al₂O₃ NPs, but nanoparticle-dependent toxicity was indeed observed for the investigated NPs.     

Research and application of method of oxygen isotope of inorganic phosphate in Beijing agricultural soils

Phosphorus (P) in agricultural ecosystems is an essential and limited element for plants and microorganisms. However, environmental problems caused by P accumulation as well as by P loss have become more and more serious. Oxygen isotopes of phosphate can trace the sources, migration, and transformation of P in agricultural soils. In order to use the isotopes of phosphate oxygen, appropriate extraction and purification methods for inorganic phosphate from soils are necessary. Here, we combined two different methods to analyze the oxygen isotopic composition of inorganic phosphate (δ¹⁸O_P) from chemical fertilizers and different fractions (Milli-Q water, 0.5 mol L^?1 NaHCO₃ (pH = 8.5), 0.1 mol L^?1 NaOH and 1 mol L^?1 HCl) of agricultural soils from the Beijing area. The δ¹⁸O_P results of the water extracts and NaHCO₃ extracts in most samples were close to the calculated equilibrium value. These phenomena can be explained by rapid P cycling in soils and the influence of chemical fertilizers. The δ¹⁸O_P value of the water extracts and NaHCO₃ extracts in some soil samples below the equilibrium value may be caused by the hydrolysis of organic P fractions mediated by extracellular enzymes. The δ¹⁸O_P values of the NaOH extracts were above the calculated equilibrium value reflecting the balance state between microbial uptake of phosphate and the release of intracellular phosphate back to the soil. The HCl extracts with the lowest δ¹⁸O_P values and highest phosphate concentrations indicated that the HCl fraction was affected by microbial activity. Hence, these δ¹⁸O_p values likely reflected the oxygen isotopic values of the parent materials. The results suggested that phosphate oxygen isotope analyses could be an effective tool in order to trace phosphate sources, transformation processes, and its utilization by microorganisms in agricultural soils.     

The adsorption process during inorganic phosphorus removal by cultured periphyton

To explain the detailed process involved in phosphorus removal by periphyton, the periphyton dominated by photoautotrophic microorganisms was employed in this study to remove inorganic phosphorus (P _i ) from wastewater, and the removal kinetics and isotherms were then evaluated for the P _i removal process. Results showed that the periphyton was capable of effectively removing P _i that could completely remove the P _i in 24 h at an initial P _i concentration of 13 mg P L^?1. Furthermore, the P _i removal process by the periphyton was dominated by adsorption at initial stage (~24 h), which involved physical mechanistic process. However, this P _i adsorption process was significantly influenced by environmental conditions. This work provides an insight into the understanding of phosphorus adsorption by periphyton or similar microbial aggregates.