Overcoming biochar limitations to remediate pentachlorophenol in soil by modifying its electrochemical properties.

In this study, we produced modified biochars with enhanced electrochemical properties to increase PCP remediation in soil. Although all biochars enhanced PCP remediation in aerobic conditions, only a few did in anaerobic soil. The most successful modifications were (i) the preloading of biomass with 10% w/w FeCl3, to obtain a biochar rich in redox-active metals (B-Fe); (ii) the oxidation of a conductive biochar pyrolyzed at 1000 ºC with 0.025 M KMnO4, to produce a biochar with both moderate conductivity and redox capacity (B-1000-KMnO4); and (iii) KMnO4 oxidation of an amorphous biochar pyrolyzed at 400 ºC to obtain a biochar with very high redox capacity (B-KMnO4). B-Fe reduced extractable PCP to almost zero after 50 days in both incubations, but showed slow kinetics of remediation in aerobic soil. B-1000-KMnO4 had the highest rate of remediation under aerobic conditions, but no significant effect under anaerobic conditions. B-KMnO4, however, presented high rates of remediation and high removal of extractable PCP under both conditions, which made it the recommended modification strategy for increased PCP remediation. We found that the degree of remediation primarily depends on the redox capacity, while the rate of remediation was determined by both the conductivity and redox capacity of biochar.

Environmental fate of glyphosate used on Swedish railways - Results from environmental monitoring conducted between 2007-2010 and 2015-2019.

Glyphosate herbicides are widely relied upon by European railway operators for controlling vegetation growing on railway tracks. In Sweden, concentrations of glyphosate and its main degradation product AMPA have been monitored in the groundwater close to railways during two monitoring periods: between 2007-2010 and 2015-2019. In total, 603 groundwater samples from 12 different monitoring sites and 645 soil samples from 5 of these sites were analyzed. Glyphosate and AMPA were detected in 16% and 14%, respectively, of groundwater samples taken from directly beneath the track, with concentrations exceeding the EU groundwater quality standard of 0.1 µg/L in 6 and 4% of the cases, respectively. The highest concentrations detected in single samples were 7 µg glyphosate/L and 1.1 µg AMPA/L. However, further horizontal spread in the groundwater zone appeared to be limited as glyphosate and AMPA were only detected in 1-3% of the groundwater samples taken from outside the track area itself, and since no difference was seen between water from reference and down-gradient wells. In the autumn of 2018, higher concentrations were detected in the groundwater from beneath 3 out of the 5 then active monitoring sites and a possible explanation is that the unusually hot and dry summer of 2018 limited degradation, thus leading to an increased susceptibility of leaching. The contents of glyphosate and AMPA in soil samples from three of the sites were very low (average < 0.05 mg/kg in soil from 0 to 30 cm), indicating that they were only sprayed to a limited degree, whereas the contents from two of the test sites were in line with what would be expected based on the used dose and a predicted half-life of about 4 ± 2 months (average 0.22-0.84 mg/kg). No signs of accumulation of glyphosate in the railway ballast over time were observed.

Decyl glucoside surfactant Triton CG-110 does not significantly affect the environmental fate of glyphosate in the soil at environmentally relevant concentrations.

Glyphosate is the most common herbicide worldwide, and its impact on the environment has increasingly been scrutinized. Glyphosate-based formulations can contain co-formulants, among which are surfactants. This study aimed to investigate whether the presence of an alkyl polyglucoside-based surfactant, Triton CG-110, affects the adsorption, leaching, and mineralisation of glyphosate in the soil. The experiments were conducted in two soils with different textures (sandy and clay) and in washed sand. Glyphosate and surfactant mixtures were applied at realistic field rates. Because of ponding and scarce leaching from the field soil, the leaching experiments were conducted only with washed sand. The results indicate a reduction of glyphosate adsorption in washed sand (from Kf = 13.5 to 3.99 µg1-1/n (ml)1/n g-1) and in sandy soil (from Kf = 165 to 90.8 µg1-1/ n (ml)1/n g-1) when using a Triton CG-110 concentration of 0.5 %, which corresponds to that of a spraying solution applied in the field, whereas adsorption in clay soil was unaffected. Triton CG-110 did not significantly affect glyphosate leaching in washed sand or mineralisation in any of the tested soils. The results indicate that Triton CG-110 is unlikely to significantly affect the environmental fate of glyphosate in the soil at environmentally relevant concentrations.

Effects of spray drift of glyphosate on nontarget terrestrial plants-A critical review.

Glyphosate is a widely used broad-spectrum postemergent herbicide used for weed control in both agricultural and nonagricultural settings. Spray drift of glyphosate can pose a risk to nontarget terrestrial plants and plant communities outside the intended area of application, but the lack of a well-established predicted-no-effect drift rate makes properly assessing such risk difficult. For this reason, a literature review and meta-analysis was carried out with the aim to determine the level of drift that is likely to cause harm to plants and to explore what spray-reducing targets would be sufficiently protective. No-observed-adverse effect rates, lowest-observed-adverse effect rates, and effect rates giving 10, 25, and 50% effects were extracted from a total of 39 different publications. The data were combined per species, and species sensitivity distributions were constructed and fitted with a log-logistic model to assess protectiveness. No systematic differences were detected between the responses of monocotyledons or dicotyledons, but wild plants were found to be generally less sensitive to glyphosate drift than domesticated plants. The results indicate that restricting spray drift to a level below 5 g a.e./ha would protect approximately 95% of all higher plant species against minor adverse effects of glyphosate drift and that rates below 1 to 2 g a.e./ha would be almost completely protective. No studies were encountered that evaluated effects of spray drift against nonvascular plants, and therefore, the conclusions are only valid for vascular plants. Environ Toxicol Chem 2017;36:2879-2886. © 2017 SETAC.

Effect of Biochar Amendment and Ageing on Adsorption and Degradation of Two Herbicides.

Biochar amendment can alter soil properties, for instance, the ability to adsorb and degrade different chemicals. However, ageing of the biochar, due to processes occurring in the soil over time, can influence such biochar-mediated effects. This study examined how biochar affected adsorption and degradation of two herbicides, glyphosate (N-(phosphonomethyl)-glycine) and diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in soil and how these effects were modulated by ageing of the biochar. One sandy and one clayey soil that had been freshly amended with a wood-based biochar (0, 1, 10, 20 and 30% w/w) were studied. An ageing experiment, in which the soil-biochar mixtures were aged for 3.5 months in the laboratory, was also performed. Adsorption and degradation were studied in these soil and soil-biochar mixtures, and compared to results from a soil historically enriched with charcoal. Biochar amendment increased the pH in both soils and increased the water-holding capacity of the sandy soil. Adsorption of diuron was enhanced by biochar amendment in both soils, while glyphosate adsorption was decreased in the sandy soil. Ageing of soil-biochar mixtures decreased adsorption of both herbicides in comparison with freshly biochar-amended soil. Herbicide degradation rates were not consistently affected by biochar amendment or ageing in any of the soils. However, glyphosate half-lives correlated with the Freundlich Kf values in the clayey soil, indicating that degradation was limited by availability there.

Effects of a wood-based biochar on the leaching of pesticides chlorpyrifos, diuron, glyphosate and MCPA.

We studied the ability of a wood-based biochar to reduce the leaching of the pesticides chlorpyrifos, diuron, glyphosate and MCPA in a sand column test system. In addition, time-dependent adsorption of the pesticides to the biochar and to the sand used in the columns was determined. The sorption kinetics was shown to be controlled by the log Kow-values of the pesticides and sorption rates varied in the order: chlorpyrifos (log Kow = 4.7) > diuron (log Kow = 2.87) > MCPA (log Kow = -0.8) > glyphosate (log Kow = -3.2). Glyphosate sorbed very weakly to the biochar but strongly to the sand. Biochar was most effective at retaining the pesticides if applied as a distinct layer rather than mixed with the sand. Leaching of diuron and MCPA was reduced by biochar application, and the retention was linearly related to the thickness of the biochar layers. However, leaching of chlorpyrifos and glyphosate was not affected by biochar addition. Leaching was low for all pesticides when the pesticides were added directly to biochar that was then added to the column. Together, our results suggest that a viable strategy for using biochar as a means to mitigate leaching of pesticides may be to use it as an adsorptive layer directly on or close to the soil surface. This would be especially useful in areas where pesticides are routinely handled and potentially spilled.

Comparative characterization of digestate versus pig slurry and cow manure - Chemical composition and effects on soil microbial activity.

The growing number of biogas plants in Europe has resulted in increased production of nutrient-rich digestate with great potential as fertilizer for arable land. The nutrient composition of digestate varies with the substrate treated in the biogas plant and may contain compounds that stimulate or inhibit soil microbial activity. This study compared 20 digestates (D) with 10 pig slurries (PS) and 10 cow manures (CM) regarding their chemical content and their effect on soil microbial activities, i.e. potential ammonia oxidation rate (PAO) and soil respiration. The results showed no significant differences within the D group when divided based on substrate type. i.e. manure dominated vs. other organic waste materials in any of the tests. In general D contained significantly higher concentrations of ammonium while the concentrations of total carbon and volatile fatty acids were higher in PS and CM than in D. The D showed both stimulating and inhibiting effects on PAO, while all CM and all PS except one showed inhibiting effects on PAO. However, PAO activity was negatively correlated with the content of volatile fatty acids in the residues indicating that these compounds may be the cause of the inhibition. The maximum respiration activity (hpeakmax) was lower and the time point for the maximum respiration activity (tpeakmax) occurred earlier for D compared with CM and PS. This earlier peak time could be indicative of a high proportion of easily degradable carbon in D compared with PS and CM. However, the utilization rate of carbon, i.e. the proportion of added organic C converted to CO2-C during 12days, did not differ significantly between D, PS and CM, indicating that overall carbon quality in the different fertilizers was still roughly comparable. In short, our results suggest that digestates were different compared with PS and CM but without posing a higher risk with respect to their impact on soil microbial activity.

Functional microbial diversity of the railway track bed.

Railways constitute relatively unexplored microbial habitats. Little is known about the amounts, activities or distributions of microorganisms and their associated heterotrophic capabilities on railway embankments. The aim of this study was to investigate the microbiology of two Swedish railway tracks in order to fill some of the gaps in the available information. We estimated microbial biomass by means of substrate-induced respiration, microbial activity as basal respiration (BR) and as a kinetically derived parameter (r) hypothesised to correspond to the active fraction of the microbial biomass. It was confirmed that the microbial biomass and activity were low as compared with agricultural soils and that their distributions were distinctly positively skewed. Spatial Kriging revealed that covariance structures were sustained on a scale smaller than the employed sampling grid (<1 m). Substrate richness (SR), as measured with Biolog ECO plates, was used as a quantitative measure of functional diversity. SR correlated to microbial activity and SIR, indicating that functional traits were lacking where the microbial biomass was low or less active. The dependence of microbial activities on basic soil characteristics were inferred by separately designed general linear models. Water content was found to be the most important factor moderating basal respiration and functional diversity, whereas the organic matter content was identified as the most important covariate for SIR. Multivariate analysis of the carbon source utilisation patterns of the Biolog plates with equivalent average well-colour development revealed homogenous substrate utilisation among samples. This indicates that the microbial functional potential is randomly distributed in the railway track bed. In combination, our findings imply that the ecosystem functionality of railway embankments may be seriously hampered as compared with agricultural soils. This has consequences for the risk assessment of herbicides applied to railways.

Microbial biomass and activity on railway track and embankments.

The spatial distribution of microbial biomass and microbial activity was studied in two Swedish railway embankments (located close to Mora and Nässjö). Basal respiration and substrate-induced respiration (SIR) as well as the active (r) and dormant (K) fractions of the microbial biomass were determined in samples taken from the surface layer of the ballast. The SIR, r, K and basal respiration values were all of an overall low magnitude, but were highly variable over short distances on the track. Both the biomass and basal respiration were higher on the sides of the embankment than in the middle of the tracks. SIR, K and basal respiration were correlated to the organic matter content as measured by loss on ignition, whereas r was not. None of the parameters correlated with pH. It is proposed that organic matter content could be used as a predictor for microbial biomass in railway embankments.