Impact of different sterilisation techniques on sorption and NER formation of test chemicals in soil.

Standard OECD tests are used to generate data on biodegradation (OECD 307) and sorption (OECD 106) of test chemicals in soil. In such tests, data on abiotic degradation using sterile samples are utilised to investigate any losses due to abiotic processes. The data from sterile samples are also used to interpret results and findings of non-sterile samples, especially in the context of sorption and non-extractable residue (NER) formation. However, to ensure the comparability of the data obtained from sterile and non-sterile experiments, effects of sterilisation on the soil matrix should be minimal. The objective of this study was to investigate the efficiencies of different sterilisation techniques and the impact of the sterilisation on sorption and NER formation in soil. In this study, experiments in accordance with OECD 307 and OECD 106 guidelines were performed with two soils covering wide range of soil characteristics and treated with the three sterilisation techniques autoclaving, gamma(γ)-radiation and adding 1% (w/w) sodium azide. As a test item, 14C-labelled phenanthrene and bromoxynil was used for OECD 307 test, whereas non-labelled phenanthrene and atrazine was used for OECD 106. The sterilisation efficiencies were investigated using traditional viable plate count and molecular approaches (RNA extraction method). The results suggest that none of the tested techniques resulted in completely sterilised soil with autoclaving being the most efficient technique. Adding sodium azide led to most inefficient sterilisation and a significant increase (0.56 units) in soil pH. OECD 307 results showed differences in NER formation of the test chemicals, especially for soil poisoning and γ-radiation, which could be due to inefficient sterilisation and/or change in soil physico-chemical properties. OECD 106 results suggest that none of the sterilisation techniques considerably affected sorption behaviour of the test chemicals. Based on our results, we recommend autoclaving as most suitable sterilisation technique.

Improved closed test setup for biodegradation testing of slightly volatile substances in water-sediment systems (OECD 308).

Standardized biodegradation testing methods, like the OECD 308 Aerobic and Anaerobic Transformation in Aquatic Sediment Systems, generate data on biodegradation required during environmental risk and hazard assessment of chemicals under different European and international regulations. However, difficulties arise when applying the OECD 308 guideline for testing hydrophobic volatile chemicals. Especially the use of a co-solvent (like acetone) as a measure to facilitate the application of the test chemical in combination with a closed setup to reduce losses due to volatilization tend to deplete/restrict the amount of oxygen in the test system. The result is a low oxygen or even anoxic water column in the water-sediment system. Thus, the degradation half-lives of the chemical generated from such tests are not directly comparable to the regulatory half-life values for Persistence assessment of the test chemical. The aim of this work was to further develop the closed setup to improve and maintain aerobic conditions in the water phase of the water-sediment systems for testing slightly volatile hydrophobic test chemicals. This improvement was attained by optimizing the test system geometry and agitation technique to maintain aerobic conditions in the water phase in a closed test setup, investigating appropriate co-solvent application strategy, and trialing the resulting test setup. This study shows that when using a closed test setup for OECD 308 tests, agitation of the water phase overlaying the sediment and the test item application using low co-solvent volume is critical for maintaining an aerobic water layer.

Validation of a method to determine transformation of chemicals in anaerobic liquid pig and cattle manure for the OECD test guideline programme.

Manure is widely used as a fertilizer and applied to agricultural land. It may contain highly active chemicals like veterinary medicinal products or biocides, which enter into the environment by this pathway. This is recognized by several regulatory frameworks, however, a detailed method for examining the transformation of chemicals in manure was lacking. This article describes the validation of a method for studying the anaerobic transformation of chemicals in pig and cattle liquid manure. Different steps are covered with an emphasis on the validation ring test and the OECD (Organisation for Economic Cooperation and Development) process that led to the recent adoption of the method as OECD Test Guideline (TG) 320.

Leaching of Titanium Dioxide Nanomaterials from Agricultural Soil Amended with Sewage Sludge Incineration Ash: Comparison of a Pilot Scale Simulation with Standard Laboratory Column Elution Experiments.

Nanoscale titanium dioxide (nTiO2 (Hombikat UV 100 WP)) was applied to sewage sludge that was incinerated in a large-scale waste treatment plant. The incineration ash produced was applied to soil as fertilizer at a realistic rate of 5% and investigated in pilot plant simulations regarding its leaching behavior for nTiO2. In parallel, the applied soil material was subject to standard column leaching (DIN 19528) in order to test the suitability of the standard to predict the leaching of nanoscale contaminants from treated soil material. Relative to the reference material (similar composition but without nTiO2 application before incineration) the test material had a total TiO2 concentration, increased by a factor of two or 3.8 g/kg, respectively. In contrast, the TiO2 concentration in the respective leachates of the simulation experiment differed by a factor of around 25 (maximum 91.24 mg), indicating that the added nTiO2 might be significantly mobilisable. Nanoparticle specific analysis of the leachates (spICP-MS) confirmed this finding. In the standard column elution experiment the released amount of TiO2 in the percolates between test and reference material differed by a factor of 4 to 6. This was also confirmed for the nTiO2 concentrations in the percolates. Results demonstrate that the standard column leaching, developed and validated for leaching prediction of dissolved contaminants, might be also capable to indicate increased mobility of nTiO2 in soil materials. However, experiments with further soils are needed to verify those findings.

Biodegradation testing of volatile hydrophobic chemicals in water-sediment systems - Experimental developments and challenges.

Degradation data are crucial for the persistence assessment of chemicals and they are generated using standard OECD guidelines. The OECD 308 describes a simulation biodegradation test of chemicals in water-sediment systems. This guideline is not applicable for testing highly volatile chemicals and recommends a closed biometer test setup for testing slightly volatile chemicals. However, proper details on system geometries, construction and monitoring of aerobic conditions are not provided. The choice of system geometry and sediment:water ratio influences the partitioning of test chemicals between different compartments (water, sediment and headspace) and can therefore affect their degradation. The guideline recommends the addition of test chemical via aqueous solutions, which however is not possible for hydrophobic volatile chemicals due to their volatilization losses and low solubility. Thus, the use of a co-solvent is necessary for the application of such chemicals but its effects in a closed setup has not been studied. We recently developed an improved closed test setup for testing volatile chemicals in soil. The objective was to adapt this improved test setup to conduct OECD 308 tests using 14C labelled chemicals with different volatilities. Using the adapted test setup it was possible to obtain a complete mass balance even for n-decane and tetralin having the highest Henry's constants of the tested chemicals. However, the use of co-solvent affected the oxygen levels, which in turn affected microbial activity and likely also the degradation of test chemicals. Therefore, the adapted test setup needs further developments for the testing of volatile hydrophobic chemicals.

Biodegradation of Volatile Chemicals in Soil: Separating Volatilization and Degradation in an Improved Test Setup (OECD 307).

During environmental risk assessments of chemicals, higher-tier biodegradation tests in soil, sediment, and surface-water systems are required using OECD standards 307, 308, and 309 guidelines, respectively. These guidelines are not suitable for testing highly volatile chemicals, and a biometer closed-incubation setup is recommended for testing slightly volatile chemicals. In this setup, the degradation kinetics of highly volatile chemicals can largely be influenced by volatilization. Additionally, guidelines lack sufficient information on test-system geometry and guidance on how to measure and maintain aerobic conditions during the test. Our objectives were (1) to design a closed test setup for biodegradation tests in soil in which the maintaining and measuring of aerobic conditions was possible without the loss of volatile test chemicals and (2) to suggest data-treatment measures for evaluating the degradation kinetics of volatile test chemicals. With the new setup, full-scale OECD 307 tests were performed using the volatile 14C-labeled chemicals decane and tetralin. For both test chemicals, reproducible complete mass balances were observed, and the new setup ensured that the volatilization losses were kept below the mineralized fraction. Based on the obtained data, an extended model was developed that enabled consideration of the volatilization in the modeling of degradation kinetics.

Cationic polyacrylamide copolymers (PAMs): environmental half life determination in sludge-treated soil.

BACKGROUND: Cationic polyacrylamide copolymers (PAMs) are used for sludge dewatering in municipal waste water treatment and might enter the environment by spreading of the sludge on agricultural land. Concern has been expressed since little is known about the degradation of PAMs in soils. To obtain detailed information on the polymer's fate in the soil compartment, the degradation of 14C-radiolabelled PAM in an outdoor lysimeter was studied. RESULTS: No plant uptake and leaching of radioactivity was observed. There was practically no vertical movement of polymer and no transformation products found at the end of the study. For the top 10 cm soil layer, a mass balance was established throughout the study. About 10% of applied radioactivity was not extractable from soil even with a matrix destructive method, and this was concluded to be bound residue. Characterization of extractable radioactivity by means of GPC-analysis showed a significant decrease of the molecular weight of the PAM with time. The decrease in molecular weight indicates a breakdown of the polymer backbone (the C-C-chain), and is assumed to be primary degradation. The total radioactivity content in the 10 cm top soil layer was quantified every 6 months over a period of 3 years. The results show a significant decrease of the total radioactivity over time and this is defined as ultimate degradation following the definition of OECD and EPA. Based on the data, a half-life time of 2.0 × 103 days and a rate constant of 0.00035/day were calculated. With a χ2 of 12.0 the results of the calculation are thus valid and reliable. The rate constant indicates a mineralization of 22.5% within a period of 2 years based on the total recovered radioactivity. This half-life time is solely based on mineralization and does not take into account the degradation of the polymer backbone, hydrolysis of the side chains, incorporation into the soil matrix, and thus is a conservative approach. CONCLUSIONS: 14C-PAM degrades very slowly in soil after land-spreading as a component of sewage sludge. Even in a very conservative evaluation which only considered the loss of radioactivity, a half-life time of 5.4 years was determined.

Simulation Studies to Explore Biodegradation in Water-Sediment Systems: From OECD 308 to OECD 309.

Studies according to OECD 308 and OECD 309 are performed to simulate the biodegradation of chemicals in water-sediment systems in support of persistence assessment and exposure modeling. However, several shortcomings of OECD 308 have been identified that hamper data evaluation and interpretation, and its relation to OECD 309 is still unclear. The present study systematically compares OECD 308 and OECD 309 and two variants thereof to derive recommendations on how to experimentally address any shortcomings and improve data for persistence and risk assessment. To this end, four (14)C-labeled compounds with different biodegradation and sorption behavior were tested across standard OECD 308 and 309 test systems and two modified versions thereof. The well-degradable compounds showed slow equilibration and the least mineralization in OECD 308, whereas the modified systems provided the highest degree of mineralization. Different lines of evidence suggest that this was due to increased oxygenation of the sediment in the modified systems. Particularly for rapidly degrading compounds, non-extractable residue formation was in line with degradation and did not follow the sediment-water ratio. For the two more slowly degrading compounds, sorption in OECD 309 (standard and modified) increased with time beyond levels proposed by equilibrium partitioning, which could be attributed to the grinding of the sediment through the stirring of the sediment suspension. Overall, the large differences in degradation observed across the four test systems suggest that refined specifications in test guidelines are required to reduce variability in test outcomes. At the same time, the amount of sediment and its degree of oxygenation emerged as drivers across all test systems. This suggests that a unified description of the systems was possible and would pave the way toward a more consistent consideration of degradation in the water-sediment systems across different exposure situations and regulatory frameworks.

Bridging across OECD 308 and 309 Data in Search of a Robust Biotransformation Indicator.

The OECD guidelines 308 and 309 define simulation tests aimed at assessing biotransformation of chemicals in water-sediment systems. They should serve the estimation of persistence indicators for hazard assessment and half-lives for exposure modeling. Although dissipation half-lives of the parent compound are directly extractable from OECD 308 data, they are system-specific and mix up phase transfer with biotransformation. In contrast, aerobic biotransformation half-lives should be easier to extract from OECD 309 experiments with suspended sediments. Therefore, there is scope for OECD 309 tests with suspended sediment to serve as a proxy for degradation in the aerobic phase of the more complicated OECD 308 test, but that correspondence has remained untested so far. Our aim was to find a way to extract biotransformation rate constants that are universally valid across variants of water-sediment systems and, hence, provide a more general description of the compound's behavior in the environment. We developed a unified model that was able to simulate four experimental types (two variants of OECD 308 and two variants of OECD 309) for three compounds by using a biomass-corrected, generalized aerobic biotransformation parameter (k'bio). We used Bayesian calibration and uncertainty assessment to calibrate the models for individual experimental types separately and for combinations of experimental types. The results suggested that k'bio was a generally valid parameter for quantifying biotransformation across systems. However, its uncertainty remained significant when calibrated on individual systems alone. Using at least two different experimental types for the calibration of k'bio increased its robustness by clearly separating degradation from the phase-transfer processes taking place in the individual systems. Overall, k'bio has the potential to serve as a system-independent descriptor of aerobic biotransformation at the water-sediment interface that is equally and consistently applicable for both persistence and exposure assessment purposes.

Silver and gold nanoparticle separation using asymmetrical flow-field flow fractionation: Influence of run conditions and of particle and membrane charges.

Flow-Field Flow Fractionation (Flow-FFF), coupled with online detection systems is one of the most promising tools available for the separation and quantification of engineered nanoparticles (ENPs) in complex matrices. To correctly relate the retention of nanoparticles in the Flow-FFF-channel to the particle size, ideal separation conditions must be met. This requires optimization of the parameters that influence the separation behavior. The aim of this study was therefore to systematically investigate and evaluate the influence of parameters such as the carrier liquid, the cross flow, and the membrane material, on the separation behavior of two metallic ENPs. For this purpose the retention, recovery, and separation efficiency of sterically stabilized silver nanoparticles (AgNPs) and electrostatically stabilized gold nanoparticles (AuNPs), which represent two materials widely used in investigations on environmental fate and ecotoxicology, were investigated against a parameter matrix of three different cross-flow densities, four representative carrier solutions, and two membrane materials. The use of a complex mixture of buffers, ionic and non-ionic surfactants (FL-70 solution) together with a medium cross-flow density provided an acceptable compromise in peak quality and recovery for both types of ENPs. However, these separation conditions do not represent a perfect match for both particle types at the same time (maximized recovery at maximized retention). It could be shown that the behavior of particles within Flow-FFF channels cannot be predicted or explained purely in terms of electrostatic interactions. Particles were irreversibly lost under conditions where the measured zeta potentials suggested that there should have been sufficient electrostatic repulsion to ensure stabilization of the particles in the Flow-FFF channel resulting in good recoveries. The wide variations that we observed in ENP behavior under different conditions, together with the different behavior that has been reported in published literature for the same NPs under similar conditions, indicate a need for improvement in the membrane materials used for Flow-FFF analysis of NPs. This research has shown that careful adjustment of separation conditions can result in acceptable, but not ideal, separation conditions for two fundamentally different stabilized materials, and that it may not be possible to separate a set of different particles under ideal conditions for each particle type. This therefore needs to be taking into account in method development and when interpreting FFF results from complex samples.

Asymmetrical Flow-Field-Flow Fractionation coupled with inductively coupled plasma mass spectrometry for the analysis of gold nanoparticles in the presence of natural nanoparticles.

Flow-Field-Flow Fractionation (Flow-FFF), coupled with online detection systems, is one of the most promising tools available for the analysis and characterization of engineered nanoparticles (ENPs) in complex matrices. In order to demonstrate the applicability of Flow-FFF for the detection, quantification, and characterization of engineered gold nanoparticles (AuNPs), model dispersions were prepared containing AuNPs with diameters of 30 or 100nm, natural nanoparticles (NNPs) extracted from a soil sample, and different concentrations of natural organic matter (NOM), which were then used to investigate interactions between the AuNPs and the NNPs. It could be shown that light scattering detection can be used to evaluate the fractionation performance of the pure NNPs, but not the fractionation performance of the mixed samples that also contained AuNPs because of specific interactions between the AuNPs and the laser light. A combination of detectors (i.e. light absorbance and inductively coupled plasma mass spectrometry (ICP-MS)) was found to be useful for differentiating between heteroaggregation and homoaggregation of the nanoparticles (NPs). The addition of NOM to samples containing 30nm AuNPs stabilized the AuNPs without affecting the NP size distribution. However, fractograms for samples with no added NOM showed a change in the size distribution, suggesting interactions between the AuNPs and NNPs. This interpretation was supported by unchanged light absorption wavelengths for the AuNPs. In contrast, results for samples containing 100nm AuNPs were inconclusive with respect to recovery and size distributions because of problems with the separation system that probably related to the size and high density of these nanoparticles, highlighting the need for extensive method optimization strategies, even for nanoparticles of the same material but different sizes.

Effect of soil organic matter chemistry on sorption of trinitrotoluene and 2,4-dinitrotoluene.

The sorption of organic contaminants in soil is mainly attributed to the soil organic matter (SOM) content. However, recent studies have highlighted the fact that it is not the total carbon content of the organic matter, but its chemical structure which have a profound effect on the sorption of organic contaminants. In the present study sorption of two nitroaromatic contaminants viz. trinitrotoluene (TNT) and 2,4-dinitrotoluene (2,4-DNT) was studied in different SOM fractions viz. a commercial humic acid, commercial lignin and humic acid and humin extracted from a compost. (13)C-DP/MAS NMR studies indicated that the structural composition of the organic carbon in different SOM fractions was different. The order of sorption of the nitroaromatics in the different sorbents was: humic acid-commercial>humic acid-compost>humin approximately lignin. Among the aliphatic and aromatic carbon fractions (representing bulk of SOM matrix), adsorption parameter K(f)(1/n) for nitroaromatics sorption correlated well with the aliphatic carbon (r=0.791 for TNT and 0.829 for 2,4-DNT) than the aromatic carbon (r=0.634 for TNT and r=0.616 for 2,4-DNT). However, among carbon containing functional groups, carbonyl carbon showed strong positive correlation with sorption of TNT (r=0.991) and 2,4-DNT (r=0.967) while O-alkyl carbon showed negative correlation (r=0.832 for TNT and r=0.828 for 2,4-DNT). The study indicates that aliphatic domains in the SOM significantly affect the non-specific sorption of both the nitroaromatic contaminants.

Sorption-desorption of trinitrotoluene in soils: effect of saturating metal cations.

Clay minerals in soils control the sorption and mobility of nitroaromatics in munitions contaminated soils. Therefore, effect of exchangeable cations (NH4+ , K+, Ca2+, and Al3+) on sorption-desorption of trinitrotoluene (TNT) was studied in two reference soils viz sandy loam and silty clay. Compared to control soils, K+ ion saturation significantly increased TNT sorption in both the soils, while other cations decreased TNT sorption. Effect of K+ saturation on sorption of TNT was more pronounced in organic matter poor sandy loam soil (seven times) then silty clay (two times). Desorption followed the reverse trend and greater amounts of sorbed TNT were retained in the K+ saturated soils.

Mobility and degradation of trinitrotoluene/metabolites in soil columns: effect of soil organic carbon content.

There has been increasing interest in enhancing natural attenuation of munitions-contaminated soils. Present study reports the effect of increasing soil organic matter content on fate and mobility of trinitrotoluene (TNT) and metabolites in soil columns. This study was performed using 30-cm-long columns containing a top 5 cm of contaminated soil as a source layer and an uncontaminated soil (25 cm) adjusted to 0.5, 1.0, 1.5 and 3.0% organic carbon (OC) content using compost. Contaminated soil layer was fortified with uniformly ring-labeled (14)C-trinitrotoluene (TNT) or 2,4-dinitrotoluene (DNT); in total there were 8 treatments. Columns were leached with synthetic rain water under unsaturated flow conditions in downside up direction. There was significant increase in the retention of both (14)C-TNT and (14)C-DNT in soils with increasing soil OC content and in 3.0% soil OC content column < 1% TNT/DNT was recovered in the leachate. Further, degradation of TNT and metabolites from contaminated soil was significantly increased and resulted in greater soil-bound residues. Formation of monoamino-dinitrotoluene (ADNTs), diamino-mononitrotoluene (DANTs) and monoamino-mononitrotoluene (ANTs) metabolites was greatly enhanced with increase in OC content of soils. Study suggests that increasing OC content of contaminated soil to 3.0% significantly enhanced the reduction of nitroaromatics to more polar amine metabolites and the formation of soil-bound residues.

Degradation of trinitrotoluene in contaminated soils as affected by its initial concentrations and its binding to soil organic matter fractions.

Trinitrotoluene (TNT), a nitroaromatics, is a major pollutant in explosive contaminated soils. Present study reports the effect of initial concentration of TNT on its degradation kinetics in soils. Soils from two contaminated sites viz. Clausthal and Elsnig, Germany, were mixed with an uncontaminated reference soil to get different initial concentrations (mg/kg) viz Clausthal-1 (54.29), Clausthal-2 (30.86), Clausthal-3 (7.05) Elsnig-1 (879.67), Elsnig-2 (86.43); Elsnig-3 (8.16) and Elsnig-4 (0.99) and were spiked with ring UL-(14)C-TNT (100KBq/50g soil). Except Elsnig-1 and Elsnig-2 soils, TNT degraded at same rate in all the soils. Higher persistence of TNT in Elsnig-1 and Elsnig-2 soils appears to be due to higher initial concentrations of nitroaromatics which may be toxic to soil microorganisms. 2-Amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT) were recovered as major metabolites of TNT. Distribution of bound (14)C-activity in different soil organic matter (SOM) fractions (humic acid, fulvic acid and humin) was assayed by alkali extraction of solvent extracted Clausthal-1 and Elsnig-1 soils. Results indicate that humic acid accounted for maximum bound activity followed by fulvic acid and humin fractions. Expressing (14)C-activity bound/unit weight of organic carbon content of SOM fractions showed that 3 times more (14)C-activity was bound to Elsnig humic acid than Clausthal humic acid. Similarly, activity associated with Elsnig fulvic acid was 7 times higher than that of Clausthal fulvic acid suggesting that chemical nature of SOM fractions plays a significant role in binding of contaminants.