Hydrophobic Organic Substances Research Articles

Salt tide affecting algae-laden micropolluted surface water treatment and membrane performance based on BDD electro-oxidation coupled with ceramic membrane process

Harmful algal blooms pose an emerging threat to freshwater ecological security and human health, necessitating further study in offshore areas. In this work, boron-doped diamond electro-oxidation (BDD/EO) coupled with a ceramic membrane filtration was employed aiming to assess the salt tide affecting algae-laden water treatment involving with various natural organic matters (e.g., HA, SA, and BSA). The results have demonstrated that BDD/EO remove chlorophyll from the algae-laden water effectively due to the inactivation of algal cells. Moreover, considering the influence of salt tide, NH3–N would be mainly oxidized through the in-situ generated active chlorine at the electrode-liquid interface. In addition, in three kinds of salt tide affecting algae-laden water, TOC content in BSA group was decreasing remarkably after BDD/EO with TOC removal efficiency above 80%; while those in HA and SA groups had no obvious reducing due to the more algae cells breakage synchronous with HA and SA removal. Based on the fluorescent characteristics and particle size distribution, the generated small molecular organics after electro-oxidation might raise the pore blockage probability and the hydrophobic organic and fluorescent substances were preferentially oxidized in BDD/EO process being beneficial to reducing membrane fouling. Besides, the membrane special flux in three groups were decreasing significantly and the irreversible fouling resistance in SA group accounted for a larger proportion of the total resistance than those of HA and BSA. At last, in BDD/EO-CM process, macromolecular substances degradation rate was greater than that of small molecules based on the molecular weight distribution in three groups of salt tide affected algae-laden water treatment. In a word, this work provides effective and innovative strategies for the harmful algal bloom control and contributes interesting insights of membrane fouling performance of electrochemical coupled ultrafiltration membrane process.

Bioaccumulation Screening of Neutral Hydrophobic Organic Chemicals in Air-Breathing Organisms Using In Vitro Rat Liver S9 Biotransformation Assays.

To advance methods for bioaccumulation assessment of organic substances in air-breathing organisms, the present study developed an in vitro approach for screening neutral hydrophobic organic substances for their bioaccumulation potential in air-breathing organisms consisting of (1) depletion assays for chemicals in rat liver S9 subcellular fractions, (2) in vitro-in vivo extrapolation, and (3) whole-organism bioaccumulation modeling to assess the biomagnification potential of neutral organic substances in the rat. Testing of the in vitro method on 14 test chemicals of potentially biomagnifying substances showed that the bioassays could be conducted with a high level of reproducibility and that in vitro-derived elimination rate constants were in good agreement with in vivo-determined elimination rate constants in the rat. Exploring the potential of the in vitro approach for screening organic chemicals for bioaccumulation in air-breathing organisms indicated that chemical substances that exhibit a depletion rate constant in the S9 in vitro bioassay ≥0.3 h-1 are not expected to biomagnify in rats independent of their octanol-water partitioning coefficient (KOW ) or octanol-air partitioning coefficient (KOA ). The high level of reproducibility achieved in the test, combined with the good agreement between in vitro-derived and in vivo-determined depuration rates, suggests that the in vitro approach in combination with a KOA - and KOW -based screening approach has good potential for screening chemicals in commerce for their bioaccumulation potential in air-breathing organisms in a cost-effective and expedient manner, especially if the bioassay can be automated. Environ Toxicol Chem 2022;41:2565-2579. © 2022 SETAC.

Effects of organic matter on polycyclic aromatic hydrocarbons in riverine sediments affected by human activities

Organic matter (OM) is an important component of riverine environments and a major factor in the migration and transformation of hydrophobic organic substances, such as polycyclic aromatic hydrocarbons (PAHs), to sediments. We studied the distributions, sources, and correlations between PAHs and OM in sediments from the Duliujian and the Beiyun rivers in North China. Sixteen PAHs were detected in the surface sediments at total concentrations ranging from 356 to 4652 ng·g−1 dry weight, which caused a moderate to high level of pollution. The PAH distributions were significantly and positively correlated with OM (p < 0.01) and higher concentrations were detected downstream of areas affected by human activity. Petroleum, coal, and wood combustion were the main sources of PAHs in riverine sediments, and the sources of OM in sediment included terrestrial and aquatic higher plants, soil, and sewage discharge. The OM accumulated and aged along the river, with increases in the degree of aromaticity and condensation, which led to stronger adsorption of PAHs. Our results will help to promote the management and restoration of contaminated riverine sediments.

Ultrafiltration pre-oxidation by boron-doped diamond anode for algae-laden water treatment: membrane fouling mitigation, interface characteristics and cake layer organic release

In this study, ultrafiltration (UF) pre-oxidation with a boron-doped diamond (BDD) electrode was employed aiming to mitigate membrane fouling during algae-laden water treatment. It was found that BDD anodizing can efficiently alleviate membrane fouling regardless of the filtration membrane material when the oxidation time was over 30 min. This was because that the cake layer fouling resistance was highly mitigated by the pre-oxidation process. The generated small molecular organics after anodic oxidation might increase the potential of pore blockage. The anodizing preferentially oxidized hydrophobic organic and fluorescent substances, which is conducive to reducing membrane fouling and improving production efficiency. Besides, disinfection byproduct precursors and harmful algae derived substances of UF filtrated solution were contained. The algae bodies tend to agglomeration and the zeta potential obviously declined after the pretreatment, which is instrumental in forming a loose cake layer structure. In addition, the interaction force between membrane and foulants also converted to a repulsion force after pre-oxidation, which implies that BDD pre-oxidation was an effective way to mitigate cake layer fouling by reducing foulant-membrane interactions. At last, the secondary organic release of a dynamic formed cake layer was proved to be limited especially for living algae cells.

Insight into the improvement of dewatering performance of waste activated sludge and the corresponding mechanism by biochar-activated persulfate oxidation

A novel activator, corn biochar, was produced to activate persulfate to dewater waste activated sludge (WAS). Results demonstrated that the biochar-activated persulfate oxidation can effectively improve the dewatering performance of WAS. After treating WAS by biochar-activated persulfate oxidation (biochar dosage: 2.1 g/L, persulfate concentration: 7.5 mM) at the original WAS pH, standardized-capillary suction time (SCST) increased to 4.21 times and moisture content (MC) decreased to 43.4%, indicating an excellent performance of WAS dewatering. The decrease of residual persulfate with the increasing biochar dosage during WAS dewatering process illustrated that the role of persulfate in improving WAS dewatering was because of the biochar activation. The behaviors of extracellular polymers (EPS) proved that the protein in tightly bound EPS (TB-EPS) linked to WAS dewatering, and its content significantly reduced to 10.5 mg/g-volatile solids (VS) after WAS treatment. Three-dimensional fluorescence spectroscopy for EPS once again proved that the disintegration of tryptophan protein and humic acid (hydrophobic organic substances in EPS) was responsible for the improvement of WAS dewatering. To sum up, the biochar-activated persulfate oxidation was a feasible application in improving WAS dewatering.

Hydrophilic Polysiloxane Microspheres and Ceramic SiOC Microspheres Derived from Them

In this overview article, the research on polysiloxane microspheres performed in the authors’ laboratory is briefly reviewed. These microspheres are prepared in water emulsion from polyhydromethylsiloxane (PHMS). This polymer is cross-linked in the emulsion process by hydrosilylation using various low molecular weight cross-linkers having at least two vinyl functions. The microspheres contain a large number of silanol groups which give them hydrophilicity and a broad possibility of functionalization by condensation with reactive silanes bearing a functional group in the organic radical. Further transformation of these functions leads to materials for practical use, such as catalysts and biocidal powders. The hydrophilic-hydrophobic properties of the microspheres may be fine-tuned by silylation or modification of the precursor PHMS polymer. Pristine microspheres are highly hydrophilic and well-dispersed in water. They do not adsorb proteins and hydrophobic organic substances. Macropores may be generated in these particles by a simple modification of the emulsion procedure. These microspheres are also very good precursors for ceramic silicon oxycarbide microsphers because they retain their shape in pyrolytic processes even at high temperatures; and they give a high yield of ceramic material. The polysiloxane microspheres heated at 600 °C give micro and mezo porous materials with specific surface above 500 m2/g. When pyrolysed at temperatures 1000–1400 °C, they form solid ceramic microspheres of high strength. They retain spherical shape at 1500 °C although cracks are formed at their surfaces. Etching them with HF(aq) solution gives porous microspheres with specific surface above 1000 m2/g that is almost devoid of SiO2.

The effect of humic substances on Cu migration in the soil profile

ABSTRACTHumic substances (HS) are widely used for diverse purposes. The effect of HS on the metal’s status in contaminated soils is contradictory. The aim of this work was to investigate the Cu migration in soils treated with HS. A model field experiment with the addition of Cu (1.243 mg Cu/kg) and HS Extra® (potassium humate) was performed. The Cu addition resulted in acidification (by 0.7 pH) after 3 months. The major part of the added Cu remained in the upper 7-cm-thick soil layer; 4% reached the lower soil layer, while only 0.1% were removed beyond the profile. The addition of HS mitigated soil acidification increased the content of Cu bound to solid-phase organic substances and abruptly reduced the Cu activity in the soil liquid phase. Simultaneously, the HS addition increased the water-soluble organic substances (WSOS) by four times, including those in the hydrophilic and hydrophobic fractions, resulting in a twofold increase in the content of soluble Cu. Copper complexes with hydrophilic WSOS mainly reached lysimeters, and hydrophobic organic substances were absorbed by the soil. The HS addition to a slightly acidic soil can accelerate the migration of Cu to adjacent environments.

Runoff and nutrient loss from a water-repellent soil

The effects of soil water repellency (SWR) on runoff and nutrient losses are difficult to isolate. Hydrophobic organic substances coating soil particles can severely delay water infiltration and enhance runoff. We used a portable run-on simulator to investigate the effect of SWR on runoff and nutrient loss. Intact soil slabs, 0.48 m long and 0.19 m wide, were collected from a severely water-repellent Andosol under pasture. One day before simulating 60-min long run-on events with an intensity of 60 mm h−1, superphosphate was applied at a rate of 45 kg P ha−1. The effects of SWR were quantified by comparing runoff volumes and nutrient losses from run-on events conducted with water and a fully wetting aqueous ethanol solution as run-on liquids. Further, through conducting multiple consecutive water run-on events with the same soil slab, the hypothesis, that SWR is lost through the washing off of hydrophobic materials, was tested. Finally, runoff dynamics were visualised by adding a dye to the run-on water. In the first run-on experiment, 88% of the water applied was captured as runoff, while no runoff was observed when aqueous ethanol was used as run-on liquid, providing strong evidence that SWR governed runoff generation from this Andosol. In consecutive water run-on experiments, approximately 23% of the applied P was recovered in the runoff from the first event, while the cumulative P loss over ten consecutive run-on events was around 30% of the applied P. This confirms that nutrient losses were associated with SWR and the occurrence of runoff. After ten consecutive run-on events, the persistence of both actual and potential SWR in areas of the slab that had been wetted were significantly (p < 0.5) reduced. But the persistence of potential SWR of the soil was still classified as severe, suggesting only minor losses of hydrophobic materials from the soil surface. The persistence of potential SWR and the degree of SWR of the dry areas remained more or less unchanged. In accordance with this, visualisation of the wetted areas showed that runoff occurred as rivulets guided by surface topography, rather than as sheet flow, with the wetted area increasing from approximately 20% of the slab in the first event to around one third of the total slab area in the final event. This pattern is reflected in the cumulative pattern of the P losses over the ten events. Consequently, we conclude that SWR should be considered as a factor in hydrological modelling and should be included in models to address appropriately the risk of surface water contamination by solutes exogenously applied to water-repellent soils.

The effectiveness of organic matter removal in unit processes of the technological groundwater treatment system

The study evaluated the content of hydrophobic and hydrophilic organic substances in water subjected to purification in the technological system: coagulation, filtration on anthracite-sand deposits and biofiltration on granular activated carbons. The estimation of the removal efficiency of individual NOM fractions was made on the basis of fractionation method using polymeric resins (DAX-8, XAD-4 and IRA-958). The obtained results allowed to state that the applied water treatment system is effective in removing organic matter and its effectiveness in relation to individual parameters was: 55% for total organic carbon (TOC), 49% for dissolved organic carbon (DOC), 80% for particulate organic carbon (POC), 68% for UV absorbance, 83% for permanganate value and 100% for colour. In the intaken groundwater, the value of the hydrophobic fraction was 84%. The dominant fraction was very hydrophobic acid (VHA), whose content was 4.87 mg C/L (65% DOC). On the grounds of the information on the content of the NOM fraction in the intaken waters, the effectiveness of their removal in the unit processes of the technological system cannot be unequivocally determined. The content of NOM fractions established on the basis of the fractionation procedure and the SUVA parameter does not give explicit results. Further research should be carried out in this respect.

Partitioning of hydrophobic organic contaminants between polymer and lipids for two silicones and low density polyethylene

Polymers are increasingly used for passive sampling of neutral hydrophobic organic substances (HOC) in environmental media including water, air, soil, sediment and even biological tissue. The equilibrium concentration of HOC in the polymer can be measured and then converted into equilibrium concentrations in other (defined) media, which however requires appropriate polymer to media partition coefficients. We determined thus polymer-lipid partition coefficients (KPL) of various PCB, PAH and organochlorine pesticides by equilibration of two silicones and low density polyethylene (LDPE) with fish oil and Triolein at 4 °C and 20 °C. We observed (i) that KPL was largely independent of lipid type and temperature, (ii) that lipid diffusion rates in the polymers were higher compared to predictions based on their molecular volume, (iii) that silicones showed higher lipid diffusion and lower lipid sorption compared to LDPE and (iv) that absorbed lipid behaved like a co-solute and did not affect the partitioning of HOC at least for the smaller molecular size HOC. The obtained KPL can convert measured equilibrium concentrations in passive sampling polymers into equilibrium concentrations in lipid, which then can be used (1) for environmental quality monitoring and assessment, (2) for thermodynamic exposure assessment and (3) for assessing the linkage between passive sampling and the traditionally measured lipid-normalized concentrations in biota. LDPE-lipid partition coefficients may also be of use for a thermodynamically sound risk assessment of HOC contained in microplastics.

In Vivo Biotransformation Rates of Organic Chemicals in Fish: Relationship with Bioconcentration and Biomagnification Factors.

In vivo dietary bioaccumulation experiments for 85 hydrophobic organic substances were conducted to derive the in vivo gastrointestinal biotransformation rates, somatic biotransformation rates, bioconcentration factors (BCF), and biomagnification factors (BMF) for improving methods for bioaccumulation assessment and to develop an in vivo biotransformation rate database for QSAR development and in vitro to in vivo biotransformation rate extrapolation. The capacity of chemicals to be biotransformed in fish was found to be highly dependent on the route of exposure. Somatic biotransformation was the dominant pathway for most chemicals absorbed via the respiratory route. Intestinal biotransformation was the dominant metabolic pathway for most chemicals absorbed via the diet. For substances not biotransformed or transformed exclusively in the body of the fish, the BCF and BMF appeared to be closely correlated. For substances subject to intestinal biotransformation, the same correlation did not apply. We conclude that intestinal biotransformation and bioavailability in water can modulate the relationship between the BCF and BMF. This study also supports a fairly simple rule of thumb that may be useful in the interpretation of dietary bioaccumulation tests; i.e., chemicals with a BMFL of <1 tend to exhibit BCFs based on either the freely dissolved (BCFWW,fd) or the total concentration (BCFWW,t) of the chemical in the water that is less than 5000.

The mechanism of protective effect of nanocomposite system «EKOSTIM» for seed pre-treatment

The method of low-temperature 1H NMR spectroscopy is applied to study the state of water in the hydrated KCl powder and composite system KCl/AM1/H2O in air and with addition of hydrophobic organic substances. It was discovered that in composite system, which consists of the hydrated powder of KCl salt and hydrophobic nanosilica AM1–300 (the analogue of the protective and stimulating nanocomposite system «Ekostim»), presence of hydrophobic nanoparticles significantly increases binding of water to the surface. The result is that the water content in a composite is much higher than in mineral fertilizer powder. Upon contact of composite system KCl/AM1/H2O with hydrophobic compound imitating hydrophobic fragments of seed surface, the additional growth of interfacial water binding, which apparently occurs due to the free energy gain caused by breaking of water clusters in nanodimensional systems with hydrophobic and hydrophilic components, is observed.

Peculiarities of water cluster formation on the surface of dispersed KCl: The influence of hydrophobic silica and organic media

Abstract The state of water in hydrated powders of KCl and KCl/AM1/H2O composite system before and after addition of hydrophobic organic substances was investigated using 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters. It is found that water retention in the nanocomposite consisting of hydrated powder of KCl and hydrophobic silica AM1-300 (model of stimulating protective composition “ECOSTIM”) is significantly higher than in the powders of mineral fertilizers. When KCl/AM1/H2O composite system is in contact with a hydrophobic substance, imitating the hydrophobic sites of the seed surface, the additional growth of interfacial water binding is observed. This takes place probably due to the gain of free energy as a result of water cluster defragmentation in nanoscale systems containing hydrophobic and hydrophilic constituents. The state of water in hydrated powders of KCl and KCl/AM1/H2O composite system was studied. It is found that water retention in the nanocomposite is significantly higher than in the powders of KCl. When a composite system is in contact with a CDCl3, the growth of water binding is observed. The growth of free energy as a result of water cluster defragmentation in nanoscale systems.

Assessing Soil Water Repellency of a Sandy Field with Visible near Infrared Spectroscopy

Soil water repellency (WR) is a widespread phenomenon caused by aggregated organic matter (OM) and layers of hydrophobic organic substances coating the surface of soil particles. These substances have a very low surface free energy, reducing a soil's water attraction. There is focus on WR due to its effects on germination, root growth, liquid–vapour dynamics, surface erosion and leaching of chemicals through fingered flow paths. However, common techniques for measuring WR are time-consuming and expensive. Meanwhile, it is well established that visible near infrared (vis-NIR) spectroscopy is a reliable method for determining soil OM. Potentially it could therefore provide fast measurements of WR through autocorrelation with OM. The aim of this study was to test the feasibility of vis-NIR spectroscopy for estimating the WR of soils with a small gradient in soil organic carbon (SOC) and texture, and to evaluate the effect of soil pretreatment on the predictive ability of WR models. A total of 87 soil samples from an agricultural coarse sandy field in Denmark were analysed for SOC, particle size fractions, water content and WR. Soil samples were scanned with a vis-NIR sensor (350–2500 nm) after air- and oven-drying at 60°C and 105°C. WR, expressed as liquid surface tension (mN m−1), was determined using the molarity of ethanol droplet test. Partial least squares regression models of SOC, texture and water content showed no predictive ability ( r2 values between 0.10 and 0.51). However, successful models ( r2 = 0.85) were generated for WR. The majority of bands important in the vis-NIR region of WR models were related to different components of OM indicating that, across the investigated field, WR was related to specific hydrophobic components of soil OM rather than to the total amount of carbon. A lower prediction error of the WR model for soils dried at 105°C (1.93 mN m−1) than at 60°C (2.52 mN m−1) can be explained by a lower range of WR values for the soils dried at 105°C. Moreover, a higher temperature reduced the number of absorption bands related to OM, indicating a degradation of hydrocarbon groups and a more hydrophobic character of the soil.

Somatic and gastrointestinal in vivo biotransformation rates of hydrophobic chemicals in fish.

To improve current bioaccumulation assessment methods, a methodology is developed, applied, and investigated for measuring in vivo biotransformation rates of hydrophobic organic substances in the body (soma) and gastrointestinal tract of the fish. The method resembles the Organisation for Economic Co-operation and Development (OECD) 305 dietary bioaccumulation test but includes reference chemicals to determine both somatic and gastrointestinal biotransformation rates of test chemicals. Somatic biotransformation rate constants for the test chemicals ranged between 0 d(-1) and 0.38 (standard error [SE] 0.03)/d(-1) . Gastrointestinal biotransformation rate constants varied from 0 d(-1) to 46 (SE 7) d(-1) . Gastrointestinal biotransformation contributed more to the overall biotransformation in fish than somatic biotransformation for all test substances but 1. Results suggest that biomagnification tests can reveal the full extent of biotransformation in fish. The common presumption that the liver is the main site of biotransformation may not apply to many substances exposed through the diet. The results suggest that the application of quantitative structure-activity relationships (QSARs) for somatic biotransformation rates and hepatic in vitro models to assess the effect of biotransformation on bioaccumulation can underestimate biotransformation rates and overestimate the biomagnification potential of chemicals that are biotransformed in the gastrointestinal tract. With some modifications, the OECD 305 test can generate somatic and gastrointestinal biotransformation data to develop biotransformation QSARs and test in vitro-in vivo biotransformation extrapolation methods.

Soil hydrophobicity: comparative study of usual determination methods

Hydrophobic or water repellent soils slowly absorb water because of the low wett ability of the soil particles which are coated with hydrophobic organic substances. These pose significant effects on plant growth, water infiltration and retention, surface runoff and erosion. The objective of this study was to compare the performance of tension micro-infiltrometer(TMI) and the water drop penetration time (WDPT) methods in the determination of the hydrophobicity index of eighteen soils from southern Brazil. Soil samples were collected from the 0-5cm soil layer to determine particle size distribution, organic matter content, hydrophobicity index of soil aggregates and droplet penetration time of disaggregated and sieved soil samples. For the TMI method the soil samples were subjected to minor changes due to the use of macroaggregates to preserve the distribution of solid constituents in the soil. Due to the homogeneity of the soil samples the WDPT method gave smaller coefficients of variation unlike the TMI method where the soil structure is preserved. However, both methods had low coefficients of variation, and are thus effective for determining the soil hydrophobicity, especially when the log hydrophobicity index or log WDPT is &gt;1.

Calibration of Chemcatcher® passive sampler for selected highly hydrophobic organic substances under fresh and sea water conditions

Sampling rates of the Chemcatcher® are measured for selected highly hydrophobic compounds in calibration experiments with fresh and salt water.

Initial water repellency affected organic matter depletion rates of manure amended soils in Sri Lanka

Abstract The wetting rate of soil is a measure of water repellency, which is a property of soils that prevents water from wetting or penetrating into dry soil. The objective of the present research was to examine the initial water repellency of organic manure amended soil, and its relation to the soil organic matter (SOM) depletion rates in the laboratory. Soil collected from the Wilpita natural forest, Sri Lanka, was mixed with organic manure to prepare soil samples with 0, 5, 10, 25, and 50% organic manure contents. Locally available cattle manure (CM), goat manure (GM), and Casuarina equisetifolia leaves (CE) were used as the organic manure amendments. Organic matter content of soils was measured in 1, 3, 7, 14, and 30 days intervals under the laboratory conditions with 74±5% relative humidity at 28±1°C. Initial water repellency of soil samples was measured as the wetting rates using the water drop penetration time (WDPT) test. Initial water repellency increased with increasing SOM content showing higher increasing rate for hydrophobic CE amended samples compared with those amended with CM and GM. The relation between water repellency and SOM content was considered to be governed by the original hydrophobicities of added manures. The SOM contents of all the soil samples decreased with the time to reach almost steady level at about 30 d. The initial SOM depletion rates were negatively related with the initial water repellency. However, all the CE amended samples initially showed prominent low SOM depletion rates, which were not significantly differed with the amended manure content or the difference in initial water repellency. It is explicable that the original hydrophobicity of the manure as well has a potentially important effect on initiation of SOM decomposition. In contrast, the overall SOM depletion rate can be attributed to the initial water repellency of the manure amended sample, however, not to the original hydrophobicity of the amended manure. Hydrophobic protection may prevent rapid microbial decomposition of SOM and it is conceivable that hydrophobic substances in appropriate composition may reduce organic matter mineralization in soil. These results suggest the contribution of hydrophobic organic substances in bioresistance of SOM and their long-term accumulation in soils

Temporal dynamics of soil water repellency and its impact on pasture productivity

New Zealand pastoral soils have the potential to develop water-repellent conditions irrespective of regional climate and soil orders. The aim of this study was to improve the understanding of the temporal dynamics of soil water repellency (SWR), the mechanisms leading to this transient soil condition and its effect on pasture productivity. Topsoil actual and potential SWR, water contents and pasture production were monitored at monthly to bi-monthly intervals on two hill country pastures located in Hawke's Bay and the Waikato, New Zealand, between December 2009 and March 2012. Clear seasonal dynamics of SWR were observed with peaks during dry and warm periods and breakdown of SWR after wet periods. While the actual persistence of SWR was negatively correlated with the soil water content, it was not directly related to rainfall. But it was significantly and negatively correlated to the soil moisture deficit. Low soil fertility promoted SWR. These results confirm that soil water content alone is not a reliable predictor for the appearance and disappearance of SWR. We also conclude that a large contact angle indicates not only a high degree of SWR, but also a high persistence. One potential explanation for the high variability of the potential of SWR might be that hydrophobic organic substances causing SWR are partly and periodically leached out of the soil profile. During the summer months, pasture productivity was reduced by 48% at the Hawke's Bay site, and 48% of the observed variability in dry matter production during the entire investigation period of 2 years could be explained by the degree and the potential persistence of SWR. Our results confirm that SWR is an issue for New Zealand pastoral production that requires development of mitigation strategies.

Microbiological characterization and sterilization-induced changes in the profile of the hydrophobic organic substances in Latvian balneological peat

The abundance and predominant groups of bacteria, filamentous fungi and yeasts have been studied by culture-dependent microbiological methods in peat probes obtained in two Latvian balneotherapy spa sites, Kemeri and Baldone. Unsterilized peat samples from both the sites contained 5.7–8.1 log bacterial colony-forming units (CFU) and 3.0–5.3 log fungal CFU per gram of dry peat. Isolated species belonged to Alpha-, Beta-, and Gamma-Proteobacteria, Actinobacteria, Clostridia, Bacilli and Flavobacteria as well as to filamentous fungi and yeasts. The composition of microbial population of the peat from both sites shared just four micro-organism groups (Bacillus mycoides, Burkholderia cepacia, Streptomyces spp. and Trichoderma spp.) within totally 36 groups identified. No pathogenic bacteria or fungi and no faecal pollution indicators were recovered. Decimal reduction doses for micro-organisms in peat samples and radiation sterilization doses of peat for the gamma and electron beam radiation were determined. The highest radiation resistance was observed for B. mycoides and Aureobasidium sp. Gamma-sitosterol was the most abundant hydrophobic organic compound in both peats according to GC–MS data. All the sterilization procedures increased concentration of alkanes, alcohols, and ketones and decreased the amount of fatty acids. Heat sterilization proved to be more preserving for the peat sterols than the radiation sterilization. It is concluded that the heat and radiation sterilization methods induce different changes of the profile of hydrophobic organic compounds of balneological peats, what may lead to different therapeutic effects at their application.