Persistent Organic Compounds Research Articles

The development of a novel, green, efficient, and eco-friendly GC-MS/MS analytical method for the reliable and rapid determination of dl-PCBs, and PCDD/Fs using hydrogen as a carrier gas and a modified ion source

The polychlorinated dibenzo–p–dioxins/furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) are worldwide contaminants, and they tend to accumulate in wide variety of matrices. Therefore, due to the highest accumulation rate and recalcitrancy, their precise quantification makes significant concern about their toxicological effects on both humans and organisms. The objective of the study is that using hydrogen carrier gas instead of helium in gas chromatography with triple quadrupole (GC-MS/MS) systems could contribute to improvements on the analysis of dl-PCBs and PCDD/Fs in environmental matrices. The study evaluates the performance of the analysis time under the desired chromatographic resolution criteria for PCDD/Fs analysis, monitoring the plausible mass spectrum/fragmentation ratio changes, and finally the quantification limits of the targeted most toxic persistent organic compound congeners. The main advantage of using H2 carrier gas is that the analysis time was drastically reduced (∼2.5 times) along with improved resolution due to an increase in peak widths in ∼0.6–0.7 factor. This study emphasized that the resolution was remarkably affected by the hexa congeners of PCDD/Fs; nearly baseline separation was observed. However, the sensitivity was slightly reduced (∼6–7 fold), which affected the calibration starting concentrations (0.8–3.2 pg/μl). The acquired mass spectra indicated that the lower fragment enhancement was noticeable, particularly on higher chlorinated ones (hexa, hepta, and octa congeners). The calculated ortho-effect values (1–58) in this study are consistent with the previous results in the literature (1–66 and 1–83) and supports the conclusion about the observations of lower fragment enhancement. Despite non-detection of hydrogenation, there is a significant difference in the quant/qual ion ratios in the studied compounds between helium and hydrogen carrier gas. The finalized methodology was examined, and the performance of the hydroinert® ion source was assessed over a three-month analysis period with a real sample analysis (RSD ≤17.8 %). The results indicate that hydrogen is a potential and reliable GC-MS/MS carrier gas in dl-PCBs and PCDD/Fs for environmental matrices.

Charge as a key physicochemical factor in adsorption of organic micropollutants from wastewater effluent by rice husk bio-silica

Wastewater treatment plants (WWTPs) often fail to fully remove organic micro-pollutants (OMPs), necessitating advanced treatment methods. This study examines the potential of an agricultural waste-derived adsorbent, rice husk (RH) – silica, for removing a complex mixture of 20 OMPs in MilliQ water and wastewater effluent. While RH-silica shows potential for OMP removal, its performance with multicomponent mixtures in real wastewater has yet to be investigated. Batch experiments demonstrated the efficacy of RH-silica in removing cationic, neutral, polar, and non-polar OMPs across various pH levels, with no adsorption of anionic OMPs. Column elution studies revealed that only positively charged compounds did not reach a breakthrough after 300 specific bed volumes (BVs), even when the filtration velocity was increased fivefold (3.8 m/h) and lower adsorbent-to-volume ratios (0.5 g/L) were employed. This indicates that electrostatic interactions via deprotonated silanol groups are the primary adsorption mechanism. RH-silica's ability to retain cationic pollutants regardless of their hydrophilicity degree highlights its potential as a novel adsorbent targeting positively charged persistent and mobile organic compounds (PMOCs). Moreover, the adsorption efficiency remained high in experiments with real wastewater effluent. Considering practical applications, a RH-silica column could be used to enhance removal of cationic polar compounds. This approach not only improves pollutant removal efficiency but also contributes to sustainability in WWTPs by using agricultural waste resources. Despite significant operational and end-of-life challenges for large-scale implementation, this study represents a crucial advancement in the investigation of RH-silica as an adsorbent.

Advanced Treatment Technologies for Pollutants Removal in Wastewater

Conventional wastewater treatment technologies have been extensively studied for degrading organic matter, suspended solids, nutrient removal, and lowering microbial loads. They produce acceptable-quality effluent, but researchers have reported several limitations. Recently, advanced wastewater treatment technologies have preceded as an alternative to the degradation of recalcitrant wastes such as persistent organic compounds (POPs), pharmaceutically active compounds (PhACs), contaminants of emerging concern (CECs), and heavy metals (H.M). They can be physical, chemical, biological, or integration between one or more technologies. This is to meet the requirements for reuse for different purposes, minimize or prevent the negative impacts on the environment, and create new untraditional water resources to solve the water shortage problem. This article is a collected review of advanced wastewater treatment technologies. Also, the applications of these technologies with special concern for partially/hardly degradable pollutants from wastewater are indicated. They are eco-friendly, cost-effective, low-energy systems with a small footprint. Their selection depends on the characterization of wastewater, biodegradability, available footprint, quality of treated effluent required, cost, availability of funds, and personal skills.

Techniques for quantification of organochlorine pesticides from a validated method by using gas chromatography-electron capture detector

Organochlorine pesticides (OCPs) are persistent organic compounds found in aquatic environments worldwide. A well-validated and well-established analytical method is crucial for detecting OCPs in the environment. In this study, an analytical method for quantifying OCPs in water was developed and evaluated. Here, the range of linearity, reproducibility, uncertainty, specificity, method detection limits (MDL), and special emphasis on detection and quantitation limits were assessed. Recovery studies were performed to measure the accuracy and precision of the method. This method exhibited excellent linearity in the range of 2.5–20 μg/L for all compounds. As none of the targeted compounds was detected in the chromatograms of the blank sample with no baseline noise, the limits of detection (LOD) and limits of quantification (LOQ) were determined using the linear regression method, external calibration curve slope, and laboratory fortified blank-based detection. All compounds showed different LOD and LOQ values, depending on the approach used. In particular, endosulfan sulfate, methoxychlor, endrin ketone, H. epoxide, heptachlor, and 4,4ʹ-DDT exhibited high detection limits. The recovery percentage of the 15 compounds at 5 μg/L spiked concentration was between 50 and 150 %, which is consistent with the accuracy of the APHA method. Except for endosulfan sulfate, the relative standard deviations of all other compounds were below 20 %, indicating good precision. This method has also been applied to real water samples. This validation technique is reliable, sensitive, simple, rapid, easy to comprehend, and reproducible. The application of this method in the real water samples was also conducted. Only α-BHC and γ-Chlordane were detected in the water sample.

Occurrence and fate of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in an urban aquifer located at the Besòs River Delta (Spain)

Urban aquifers are at risk of contamination from persistent and mobile organic compounds (PMOCs), especially per- and polyfluoroalkyl substances (PFAS), which are artificial organic substances widely used across various industrial sectors. PFAS are considered toxic, mobile and persistent, and have therefore gained significant attention in environmental chemistry. Moreover, precursors could transform into more recalcitrant products under natural conditions. However, there is limited information about the processes which affect their behaviour in groundwater at the field-scale. In this context, the aim of this study is to assess the presence of PFAS in an urban aquifer in Barcelona, and identify processes that control their evolution along the groundwater flow. 21 groundwater and 6 river samples were collected revealing the presence of 16 PFAS products and 3 novel PFAS. Short and ultra-short chain PFAS were found to be ubiquitous, with the highest concentrations detected for perfluorobutanesulfonic acid (PFBS), trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFSA). Long chain PFAS and novel PFAS were found to be present in very low concentrations (<50 ng/L). It was observed that redox conditions influence the behaviour of a number of PFAS controlling their attenuation or recalcitrant behaviour. Most substances showed accumulation, possibly explained by sorption/desorption processes or transformation processes, highlighting the challenges associated with PFAS remediation. In addition, the removal processes of different intensities for three PFAS were revealed. Our results help to establish the principles of the evolution of PFAS along the groundwater flow, which are important for the development of conceptual models used to plan and adopt site specific groundwater management activities (e.g., Managed Aquifer Recharge).

Bayesian analysis of physiologically based toxicokinetic (PBTK) modeling for pentachlorophenol exposure in pregnant women

Pentachlorophenol (PCP) is a persistent organic compound that is widely present in the environment. The estimation of internal exposure levels for a given external exposure using toxicokinetic models is key to the human health risk assessment of PCP. The present study developed a physiologically based multicompartmental pharmacokinetic (PBTK) model to describe and predict the behavior of pentachlorophenol (PCP) in an organism. The model consists of stomach, intestines, adipose tissue, kidneys and fast- and poorly perfused tissues that are interconnected via blood circulation. We constructed a PBTK model of PCP in rats and extrapolated it to human dietary PCP exposure. The toxicokinetic data of PCP in human tissues and excreta were obtained from the published literature. Based on the collected PCP dietary survey and internal exposure data of pregnant women in Shanghai, Bayesian statistical analysis was performed for the model using Markov chain Monte Carlo (MCMC) simulation. The posterior distributions of the sensitive parameters were estimated, and the model was parameter optimized and validated using the pregnant women's test dataset. The results showed that the root mean square error (RMSE) improved 37.3% compared to the original model, and a systematic literature search revealed that the optimized model achieved acceptable prediction results for other datasets in China. A PCP metabolism model based on the exposure characteristics of pregnant women in China was constructed in the present study. The model provides a theoretical basis for the study of PCP toxicity and risk assessment.

Photocatalytic degradation of metformin on a rectangular baffled reactor: CFD modeling and validation investigation

Solar-irradiated photocatalysis is an advanced oxidation process (AOP) commonly used for water purification due to its excellent potential to break down a diverse range of persistent organic compounds into non-toxic byproducts. Reactor design is crucial in the photocatalysis process's efficiency, effectiveness, and scalability. Computational fluid dynamics (CFD) is an effective tool to study and comprehend reactor designs, reduce system cost, design time, and optimise reactor performance. This investigation focuses on designing and developing a rectangular baffled photocatalytic reactor that can effectively degrade metformin (MTF). The experimental study optimized the value of pH and catalyst dosage for efficient removal. The photoreactor demonstrated an efficiency of 58.14 % and was validated. The CFD results, including velocity profile and mass fraction of metformin, strongly agreed with the experimental results with an R2 value of 0.9826. The combination of various baffle sizes and spacing configurations was modeled and analyzed to develop a rectangular baffled photocatalytic reactor with maximum removal efficiency. The inclusion of baffles increased the flow path, improved mixing and enhanced the degrading efficiency. The investigation findings indicated the highest degradation efficiency of 78.03 % with the seven number of baffles.

Heterostructural PbO2/Co3O4 composite for anodic oxidation of phenol: An energy-efficient hybrid process

The PbO2/Co3O4 composite electrodes were synthesized using the composite co-deposition method, which involved the incorporation of Co3O4 nanoparticles into a PbO2 coating. These composite electrodes were employed as anodes for phenol electrooxidation in wastewater treatment. The results demonstrate that the PbO2/Co3O4 composite electrode exhibits a three-dimensional porous structure, leading to a significant increase in the electrochemically active surface area. Electrochemical measurements indicate that the composite electrode achieves a minimum oxygen evolution potential of 526.5 mV. Moreover, the electrode facilitates the indirect degradation of phenol, even at low voltage (0.45 V). The unique structure, improved conductivity, and enhanced surface area of the electrode contribute to its exceptional performance in phenol degradation. Additionally, this approach offers the potential for synergistic integration with other treatment methods, providing a sustainable and energy-efficient solution for removing persistent organic compounds from wastewater.

Activated date carbon: a sustainable solution for Pentachlorophenol adsorption in reused wastewater

Industrial wastewaters contain persistent and toxic organic compounds that pose a significant risk to public health and the environment upon release. Phenol and its derivatives are examples of such pollutants. Activated carbon, often sourced from unconventional materials like plant biomass, provides a sustainable solution for treating wastewater. This research focuses on creating activated carbon from date nuts through chemical activation with phosphoric acid. The effectiveness of this carbon in removing pentachlorophenol (PCP) from secondary wastewater (SWW) is evaluated. The analysis of the date nut activated carbon (DAC) includes studying its adsorption capacities for iodine and Methylene Blue, surface functional groups, and the point of zero charge (pHpzc) compared to a commercial activated carbon (CAC). The DAC demonstrates promising adsorption capacities, with values of 368.03 mg/g for iodine and 619.9 mg/g for Methylene Blue, which are close to those of the CAC (444.17 mg/g and 620.25 mg/g, respectively). Both DAC and CAC exhibit acidic surface functionalities, with pHpzc values below 10. The efficiency of PCP removal from SWW contaminated with PCP (100 mg/L) reaches 78% within 72 hours. This study indicates that using DAC for PCP removal from SWW is a sustainable approach for wastewater treatment, potentially allowing for the reuse of non-traditional water sources.

Radon deficit technique applied to the study of the ageing of a spilled LNAPL in a shallow aquifer

A recent diesel spill (dated January 2019 ± 1 month) in a refilling station is investigated by the Radon deficit technique. The primary focus was on quantifying the LNAPL pore saturation as a function of duration of ageing, and on proposing a predictive model for on-site natural attenuation. A biennial monitoring of the local fluctuating shallow aquifer has involved the saturated zone nine times, and the vadose zone only once. Rn background generally measured in external and upstream wells is elaborated further due to the site characteristics, using drilling logs and phreatic oscillations. Notably, this study marks the first application of the Rn deficit method to produce a detailed Rn background mapping throughout the soil depth. Simultaneously, tests are performed on LNAPL surnatant samples to study diesel ageing. In particular, they are focused on temporal variations of LNAPL viscosity (from an initial 3.90 cP to 8.99 cP, measured at 25 °C, after 34 months), and Rn partition coefficient between the pollutant and water (from 47.7 to 80.2, measured at 25 °C, after 14 months). Rn diffusion is also measured in different fluids (0.092 cm2 s−1, 1.14 × 10−5 cm2 s−1, and 2.53 × 10−6 cm2 s−1 at 25 °C for air, water and LNAPL, respectively) directly. All parameters and equations utilized during this study are introduced, discussing their influence on Radon deficit technique from a theoretical point of view. Experimental findings are used to mitigate the effect of LNAPL ageing and of phreatic oscillations on determination of LNAPL saturation index (S.I.LNAPL). Finally, S.I.LNAPL dataset is discussed and elaborated to show the pollutant attenuation across subsurface over time, induced by natural processes primarily. The proposed predictive model for on-site natural attenuation suggests a half-removal time of one year and six months. The significance of such models lies in their capability to assess site-specific reactions to pollutants, thereby enhancing the effectiveness of remediation efforts over time. These experimental findings may offer a novel approach to application of Rn deficit technique and to environmental remediation of persistent organic compounds.

Implications of grouping per‐ and polyfluoroalkyl substances for contaminated site regulation

AbstractPer‐ and polyfluoroalkyl substances (PFAS) are a broad group of persistent organic compounds with vastly differing physicochemical and toxicological properties. Some jurisdictions have proposed to regulate PFAS as a single class to overcome the limitations of regulating such a diverse group on a chemical‐by‐chemical basis. Implications of regulating PFAS as a single class have been discussed for PFAS production and use, but equivalent discussion of implications for managing contaminated sites is largely lacking. This opinion piece summarizes the views of a group of environmental consultants, environmental regulators, land managers, and academics with significant experience in researching or managing PFAS. The group considered that neither a single PFAS class approach nor a chemical‐by‐chemical approach is well suited to managing risks from PFAS in a contaminated site setting, and defining PFAS subgroups would have value. Second, some but not all in the group, hypothesize that PFAS properties that drive fate and transport are those that influence toxicity and bioaccumulation in animals. This may be a valuable observation for future discussions on dividing PFAS into subclasses for contaminated site regulation based on physicochemical properties rather than purely structural definitions.

Platinum-modified bismuth molybdate flake balls as visible-light-responsive photocatalyst

Solar photocatalysis is considered as one of the best methods for “green” purification of environment. Accordingly, efficient, stable, and low-price materials must be developed for possible commercial application. Herein, flower-like bismuth molybdate (Bi2MoO6) photocatalysts were successfully synthesized by CTAB-assisted hydrothermal process, and then surface modified with platinum by photodeposition. The obtained materials were characterized by various methods, including XRD, DRS, XPS, SEM, TEM, ESR, photoluminescence spectroscopy and photoelectrochemical tests. Photocatalytic activity was tested mainly for tetracycline (TC) antibiotic degradation under visible-light irradiation (λ > 420 nm), including scavenger tests and experiments for different operation conditions (TC concentration, photocatalyst dose, pH value, in the presence of inorganic salts, water taken from different reservoirs). It has been found that the best photocatalyst containing 0.5 wt% of platinum exhibits 94.2 % TC removal during 60-min visible-light irradiation, reaching the reaction rate constant of 0.0392 min−1 (exceeding the data reported up to now). It is proposed that exceptional photocatalytic performance is caused by the synergy between the uniform flower structure (efficient light harvesting and large specific surface area) and double function of platinum deposits, i.e., as a sink for electrons (hindering charge carriers’ recombination) and a plasmonic sensitizer (allowing energy transfer from excited platinum to oxygen). Superoxide radicals (•O2−) are the main oxidation species, as proven by the quenching experiments and EPR analysis. However, in the case of platinum-modified samples, singlet oxygen plays also an important role, and thus an energy transfer from plasmonic platinum to oxygen could be expected. Additionally, TC degradation pathways, elucidated by the detection of intermediates, and the toxicity data (TC and its degradation products), assessed by a quantitative structure–activity relationship (QSAR) method, have confirmed that photocatalytic degradation of TC is indeed an environmental-friendly method, highly recommended for the decomposition of persistent organic compounds.

Characterization and health risk assessment of nine polychlorinated biphenyls in settled dust of residential buildings in a Middle Eastern area

Polychlorinated biphenyls (PCBs) are 209 persistent organic compounds with various applications in chemical, electrical and commercial industries. However, there is considerable evidence of environmental accumulation and potential adverse health effects of this compound. In this study, 40 indoor dust samples were randomly taken from Shiraz houses for the analysis of 9 PCB congeners (PCB-18, 28, 31, 44, 52, 138, 153, 189, 194). The dust samples were extracted with 100 ml dichloromethane/n-hexane/acetone in a Soxhlet appliance for 18 h and then analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The results showed that Σ9PCB were in the range of <dl – 9.31 ng/g and PCB-52, 31 and 28 were the predominant congeners. Moreover, houses with laminate floors had higher Σ9PCBs levels than the houses with ceramic floors. The hazard quotient (HQ) values for children and adults' exposure to 9 PCBs through ingestion route were lower than 1, indicating no adverse non-carcinogenic risk. Also, the incremental lifetime cancer risks (ILCRs) values were lower than 10−6 in low-risk and high-risk scenarios for the both age groups, which showed negligible carcinogenic risks arising from exposure to the analyzed PCBs. More studies focusing on biomonitoring and bioavailability approaches are recommended for future investigation to provide total intake of people to this pollutant from all routes of exposure.

Accumulation of polychlorinated biphenyls in the ovaries of deep-sea chemosynthetic clam Phreagena okutanii

Polychlorinated biphenyls (PCBs) persistently pollute marine ecosystems even though their production has been discontinued decades ago. Deep-sea organisms have been shown to accumulate PCBs and other persistent organic compounds; however, the extent of contamination and its effects remain poorly understood. Here, we measured PCB concentrations in separated organs of non-feeding bivalve clams belonging to Phreagena, a taxon representative of deep-sea chemosynthetic ecosystems. The highest concentrations of PCBs were detected in the ovaries. We also examined surface sediments of the clam habitat and observed concentrations comparable to those in the sediments of the seas around Japan, including shallow waters. The results showed that PCBs from the environment penetrate Phreagena clams through the body surface and accumulate in the female reproductive system. This raises concerns about a potentially severe direct impact on the survival of vulnerable and highly endemic deep-sea chemosynthetic bivalves.

Groundwater remediation by in-situ membrane ozonation: Removal of aliphatic 1,4-dioxane and monocyclic aromatic hydrocarbons

Groundwater contamination by widespread and persistent organic compounds requires extensive treatment efforts, for example by in-situ chemical oxidation (ISCO). In this study, we investigated ozone mass transfer and removal mechanisms of ozone-resistant monocyclic aromatic and non-aromatic compounds in a novel in-situ treatment method using ozone-permeable membranes as reactive barrier. Initial batch experiments confirmed fast depletion of ozone in presence of sub-stoichiometric benzoic acid (BA), in contrast to the non-aromatic 1,4-dioxane (DIOX), where ozone depleted much slower. Simulated in-situ membrane ozonation treatment of contaminated groundwater led to lower removal of 5 mg L−1 BA (52.7%) compared to DIOX (60.6%). Inhibited removal of BA compared to additional batch experiments could be explained by quick depletion of ozone by reactive intermediates on the membrane surface. Surprisingly, reactive porous media did not lead to substantial changes of in-situ DIOX oxidation, although a stronger impact of the media on DIOX oxidation was hypothesized. Furthermore, experimental ozone mass transfer coefficients were determined (3.94∙10−7 – 3.12∙10−6 m s−1) and compared to modeled values for different membrane types (polydimethylsiloxane and polytetrafluoroethylene). Finally, a mathematical model based on mass transfer data was developed to support upscaling efforts. We concluded that contaminant properties are crucial for the feasibility assessment of in-situ ozone membrane treatment technology.

Synthesis of selenium and fluorine co-doped graphitic carbon nitride for photodegradation of toxic organic pollutants and hydrogen peroxide photoproduction

Science is developing every day to race against the factual growth of industrial pollution in order to redeem the environment. In this study, modification of graphitic carbon nitride via selenium and fluoride doping was successfully conducted. Specifically, the process of co-calcination was conscripted using organic precursors, whilst the foreign elements were obtained from ammonium fluoride and selenium dioxide. The morphological assessment revealed the treated-graphitic carbon nitride possessed a flaky sheet form with high porosity and great crystalline uniformity. Photochemical investigation showed the co-doping of selenium and fluorine elevated the optical properties, including the decrement of bandgap and diminishing the recombination rate of electrons and holes. With interesting improvement in photocatalytic activity, the material was applied in persistent organic compound degradation and hydrogen peroxide production. The treatment improved the degradation percentage, in which the methylene blue removal achieved 99.96 % while the tetracycline removal reached 86.38 %. Moreover, high compatibility and great reusability over 4 cycles were also recorded. When applying the material for the generation of hydrogen peroxide, the co-doped material performance was observed to reach 3307 μM/g.h. The results concluded the advancement in material modification with great application in various aspects.

Ab initio kinetics of OH-initiated oxidation of naphthalene: A comprehensive revisited study

Naphthalene, the most prevalent and smallest member of the Polycyclic Aromatic Hydrocarbons (PAHs) family, has garnered significant scientific attention for its harmful environmental impacts and those of its degradation products. In this work, we comprehensively recharacterized the gas-phase reaction of naphthalene with OH radicals in a wide range of conditions (T = 200–2000 K &P = 0.76–7600 Torr), covering both atmospheric and combustion chemistry. Within the Rice–Ramsperger–Kassel–Marcus (RRKM)-based master equation framework, the detailed kinetic model was constructed on the potential energy surface explored at the ROCBS-QB3//M06–2X/aug-cc-pVTZ level of theory. Our model not only helps to resolve the existing large discrepancy (up to ∼1000 times) among the previously reported rate constants but also reveals mechanistic insights, including time-resolved species profiles and product distribution, for naphthalene transformation. It is shown that although naphthalene cannot be considered a persistent organic compound (POP) due to its rapid reaction with OH radicals, its chemical conversion can generate harmful substances such as O3 and carcinogenic derivatives. Also, the detailed conversion of naphthalene in water was investigated for the first time, revealing that naphthalene and its important degradation products pose a significant danger to aquatic life as hazardous pollutants.

Adsorption of Diclofenac and PFBS on a Hair Keratin Dimer.

Environmental pollution by man-made toxic and persistent organic compounds, found throughout the world in surface and groundwater, has various negative effects on aquatic life systems and even humans. Therefore, it is important to develop and improve water treatment technologies capable of removing such substances from wastewater and purifying drinking water. The two substances investigated are the widely used painkiller diclofenac and a member of the class of "forever chemicals", perfluorobutanesulfonate. Both are known to have serious negative effects on living organisms, especially under long-term exposure, and are detectable in human hair, suggesting adsorption to a part of the hair fiber complex. In this study, a human hair keratin dimer is investigated for its ability to absorb diclofenac and perfluorobutanesulfonate. Initial predictions for binding sites are obtained via molecular docking and subjected to molecular dynamics simulations for more than 1 μs. The binding affinities obtained by the linear interaction energy method are high enough to motivate further research on human hair keratins as a sustainable, low-cost, and easily allocatable filtration material.

Soil organic matter turnover: Global implications from δ13C and δ15N signatures

The turnover and residence time of carbon (C) and nitrogen (N) in soil is a fundamental parameter reflecting the rates of soil organic matter (SOM) transformation and the contribution of soils to greenhouse gases fluxes. Based on the global database of the stable isotope composition of C (δ13C) and N (δ15N) depending on soil depth (171 profiles), we assessed С and N turnover and related them to climate, biome types and soil properties. The 13C and 15N discrimination between the litter horizon and mineral soil was evaluated to explain the key processes of litter transformation. The 13C and 15N discrimination by microbial utilization of litter and SOM, as well as the continuous increase of δ13C and δ15N with depth, enabled to assess C and N turnover within SOM. N turnover was two times faster than that of C, which reflects i) repeated N recycling by microorganisms accelerating N turnover, ii) C loss as CO2 and input of new C atoms to cycling, which reduces the C turnover within soil, and iii) generally slower turnover of N free persistent organic compounds (e.g. lignin, suberin, cellulose) compared to the N containing compounds (e.g. amino acids, ribonucleic acids). An increase in temperature and precipitation accelerated C and N turnover because: i) higher microbial activity and SOM decomposition rate, ii) larger soil moisture and fast diffusion of dissolved organics towards exoenzymes, iii) downward transport of 13C-enriched organic matter (e.g. sugars, amino acids), and iii) leaching of 15N-depleted nitrates from the topsoil into subsoil and losses from the whole soil profile. Temperature accelerates SOM turnover stronger than precipitation. The temperature increase by 10 °C accelerates the C and N turnover for 40 %. SOM turnover is boosted by decreasing C/N ratio because: i) SOM with a high C/N ratio originated from litter is converted to microbially-derived SOM in mineral soil characterized by a low C/N ratio; ii) litter with a low C/N ratio is decomposed faster than litter with a high C/N; iii) microbial carbon-use efficiency increases with N availability. The biome type affects SOM decomposition by i) climate: slower turnover under wet and cold conditions, and ii) by litter quality: faster utilization of leaves than needles. Thus, the fastest C turnover is common under evergreen forests and the lowest under mixed and coniferous ones, whereas temperature and C/N ratio are the main factors controlling SOM turnover. Concluding, the assessment of SOM turnover by δ13C and δ15N approach showed two times faster N turnover compared to C, and specifics of SOM turnover depending on the biomes as well as climate conditions.

Comparative Analysis of Anisotropic Lipophilicity of a Series of 6-Chloro-1,3,5-Triazines Determined in Reversed Phase Ultra High Performance Liquid Chromatography System

Triazine derivatives are well-known commercially available compounds used for selective weed control in different crops, such as corn and sugarcane. Some of them are considered persistent organic compounds in the environment and it is important to improve the features of herbicide formulae, to estimate their physicochemical properties and to determine their retention behavior in modern analytical techniques that can be used in the determination of pesticides in environmental samples. The present study deals with a comprehensive analysis of the chromatographic behavior of a series of 6-chloro-1,3,5-triazines with alkyl and cycloalkyl substituents, among which some compounds possess herbicidal and fungicidal activity. The anisotropic lipophilicity of triazine derivatives was determined using reversed-phase ultra high performance liquid chromatography with octadecyl and phenyl columns and applying binary (methanol/water and acetonitrile/water) and ternary (methanol/acetonitrile/water) mobile phases under isocratic conditions. The retention data were analyzed using chemometric pattern recognition methods (hierarchical cluster analysis and principal component analysis) and sum of ranking differences method. The obtained results are excellent indicators of the retention behavior and the lipophilicity of the analyzed series of triazines and can serve as an outstanding basis for the development of new chromatographic methods for the determination of triazines in environmental samples.