Fate and transport of monoterpenes through soils. Part I. Prediction of temperature dependent soil fate model input-parameters

Development, systematic optimisation and biofilm disruption activity of eugenol-based nanosized emulsions stabilised with Tween 80

The aims of this study were to systematically optimise a formula for eugenol emulsions via face-centered central composite design and to assess the activity against two-different bacterial strains (Staphylococcus aureus and Propionibacterium acnes) present at planktonic and biofilm forms. The molecular interaction of excipients, mean particle size (MPS) including zeta potential (ZP), drug entrapment efficiency (DEE) and in vitro drug release of optimised emulsions was done using FT-IR, Malvern Zetasizer, ultracentrifugation technique and membrane-free dissolution model, respectively. The emulsions consisted of 151.3 ± 1.45 nm MPS, -21.3 ± 1.25 mV ZP and 93.98 ± 1.41% DEE values. On storage of emulsions at 25 °C for 3 months, the value of DEE was found to be 72.12 ± 2.82%. The Tween 80 emulsifier film coverage onto the dispersed eugenol droplets of emulsions delayed significantly the drug release (12%-19%) compared to the drug release occurred from pure eugenol. The treatment of planktonic S. aureus and P. acnes with diluted eugenol emulsions showed the minimum inhibitory concentration and minimum bactericidal concentration values at 1.25-2.5 mg/ml whereas it occurred at 10 mg/ml for pure eugenol. Treating the biofilms with eugenol emulsions (1-2 mg/ml) yielded 59-70% minimum biofilm eradication concentration but 10 mg/ml pure eugenol showed 60%. Hence, the eugenol emulsions displayed antibacterial activity and could be projected as an antibiofilm or biofilm disruption agent.

Effect of waste-derived soil amendments on mitigating leaching impacts from municipal solid waste incineration (MSWI) ash

This study explores modifying a sandy soil with a low solid to liquid partitioning coefficient (Kd) by adding amendments including iron-rich industrial slag byproducts and biochars, which contain sorption sites for trace metals present in MSWI ash leachate (notably Sb, cited as a concern for reuse applications). Kd values for Sb were determined for the sandy soil to be as low as 1.6 ± 0.1 L/kg. With amendments, Kd values varied from 1.4 ± 0.2 L/kg for combined ash leachate exposed to a blend of sandy soil and 20% iron slag, to 990 L/kg for combined ash leachate exposed to a blend of sandy soil and 20% magnetic solids. A blend of 20% magnetic solids showed orders of magnitude increase beyond 100% sandy soil. The biochars showed limited capacity to reduce leached Sb in the ash-derived leachate, which is likely due to negative surface charges of the biochars and Sb at basic pH. A risk assessment (US EPA IWEM) performed using experimental Kd for each blend suggests that using soil amendments could reduce leached concentrations at points of concern, which could open additional avenues for ash reuse.

Biocontrol Activity of Aromatic and Medicinal Plants and Their Bioactive Components against Soil-Borne Pathogens

Soil-borne phytopathogens can have detrimental effects on both cereal and horticultural crops resulting in serious losses worldwide. Due to their high efficiency and easy applicability, synthetic pesticides are still the primary choice in modern plant disease control systems, but stringent regulations and increasing environmental concerns make the search for sustainable alternatives more pressing than ever. In addition to the incorporation of botanicals into agricultural practices, the diversification of cropping systems with aromatic and medicinal plants is also an effective tool to control plant diseases through providing nutrients and shaping soil microbial communities. However, these techniques are not universally accepted and may negatively affect soil fertility if their application is not thoroughly controlled. Because the biocontrol potential of aromatic and medicinal plants has been extensively examined over the past decades, the present study aims to overview the recent literature concerning the biopesticide effect of secondary metabolites derived from aromatic and medicinal plants on important soil-borne plant pathogens including bacteria, fungi, and nematodes. Most of the investigated herbs belong to the family of Lamiaceae (e.g., Origanum spp., Salvia spp., Thymus spp., Mentha spp., etc.) and have been associated with potent antimicrobial activity, primarily due to their chemical constituents. The most frequently tested organisms include fungi, such as Rhizoctonia spp., Fusarium spp., and Phytophthora spp., which may be highly persistent in soil. Despite the intense research efforts dedicated to the development of plant-based pesticides, only a few species of aromatic herbs are utilized for the production of commercial formulations due to inconsistent efficiency, lack of field verification, costs, and prolonged authorization requirements. However, recycling the wastes from aromatic and medicinal plant-utilizing industries may offer an economically feasible way to improve soil health and reduce environmental burdens at the same time. Overall, this review provides comprehensive knowledge on the efficiency of aromatic herb-based plant protection techniques, and it also highlights the importance of exploiting the residues generated by aromatic plant-utilizing sectors as part of agro-industrial processes.

Enantiomer-Selective Characterization of the Adsorption, Dissipation, and Phytotoxicity of the Plant Monoterpene Pulegone in Soils

Plant monoterpenes have received attention for their ecological functions and as potential surrogates for synthetic herbicides, but very little is known about the processes that govern their behavior in the soil environment, and even less about the possible enantioselectivity in the functions and environmental behavior of chiral monoterpenes. We characterized the adsorption and dissipation of the two enantiomers of the chiral monoterpene pulegone in different soils, and their phytotoxicity to different plant species through Petri dish and soil bioassays. R- and S-pulegone displayed a low-to-moderate non-enantioselective adsorption on the soils that involved weak interaction mechanisms. Soil incubation experiments indicated that, once in the soil, R- and S-pulegone are expected to suffer rapid volatilization and scarcely enantioselective, biodegradation losses. In Petri dishes, the phytotoxicity of pulegone and its enantioselectivity to Lactuca sativa, Hordeum vulgare, and Eruca sativa was species-dependent. Lactuca sativa was the most sensitive species and showed higher susceptibility to S- than to R-pulegone. Biodegradation and volatilization losses greatly reduced the phytotoxic activity of S-pulegone applied to soil, but the addition of a highly-adsorptive organoclay stabilized the monoterpene and increased its phytotoxic effect. Stabilization by adsorption may represent an important mechanism by which the bioactivity of plant monoterpenes in soils can be increased.

Deciphering the Supramolecular Organization of Multiple Guests Inside a Microporous MOF to Understand their Release Profile

Metal-organic frameworks (MOFs) give the opportunity of confining guest molecules into their pores even by a post-synthetic protocol. PUM168 is a Zn-based MOF characterized by microporous cavities that allows the encapsulation of a significant number of guest molecules. The pores engineered with different binding sites show a remarkable guest affinity towards a series of natural essential oils components, such as eugenol, thymol and carvacrol, relevant for environmental applications. Exploiting single crystal X-ray diffraction, it was possible to step-wisely monitor the rather complex three-components guest exchange process involving dimethylformamide (DMF, the pristine solvent) and binary mixtures of the flavoring agents. A picture of the structural evolution of the DMF-to-guest replacement occurring inside the MOF crystal was reached by a detailed single-crystal-to-single-crystal monitoring. The relation of the supramolecular arrangement in the pores with selective guests release was then investigated as a function of time and temperature by static headspace GC-MS analysis.

Ground Level Isoprenoid Exchanges Associated with Pinus pinea Trees in A Mediterranean Turf

The emissions of isoprenoids, a kind of biogenic volatile organic compounds (BVOCs), from soils is not well characterized. We quantified the exchange of isoprenoids between soil with litter and atmosphere along a horizontal gradient from the trunks of the trees, in a Mediterranean Pinus pinea plantation with dry and green needle litter to open herbaceous turf during mornings at mid-summer. Further, potential associated drivers were identified. Isoprenoid emissions were greatest and most diverse, and also can be roughly estimated by litter dry weight near the trunk, where the needle litter was denser. The composition of emitted isoprenoid by needle litter was different than the composition previously described for green needles. Low exchange rates of isoprenoids were recorded in open turf. Isoprenoid exchange rates were correlated positively with soil temperature and negatively with soil moisture. Given the variations in ground emissions with soil, vegetation, microorganisms, and associated interactions, we recommend widespread extensive spatio-temporal analysis of ground level BVOC exchanges in the different ecosystem types.

Sorption of the monoterpenes α-pinene and limonene to carbonaceous geosorbents including biochar

The sorption of two monoterpenes, α pinene and limonene to the carbonaceous geosorbents graphite, bituminous coal, lignite coke, biochar and Pahokee peat was quantified. Polyethylene (PE) passive samplers were calibrated for the first time for these compounds by determining the PE-water partitioning coefficients and used as a tool to determine sorption to the carbonaceous geosorbents. Log KPE-water values were 3.49±0.58 for α pinene and 4.08±0.27 for limonene. The sorption of limonene to all materials was stronger than that for α pinene (differences of 0.2-1.3 log units between distribution coefficients for the monoterpenes). Placing Kd values in increasing order for α pinene gave biochar≈Pahokee peat≈bituminous coal≈lignite coke<graphite. For limonene the order was: Pahokee peat≈biochar≈bituminous coal<graphite≈lignite coke. Micropore (defined as pores <1.5 nm) and nanopore surface area (defined as pores 1.5 nm to 50 nm) normalised carbonaceous geosorbent-water distribution coefficients were also calculated. There was no clear correlation of these distribution coefficients with SA. Elemental composition was used to assess the degree of condensation (or alteration) of the carbonaceous geosorbents. The degree of carbonisation increased in the order; Pahokee peat<lignite coke<bituminous coal<biochar<graphite, however this was not correlated with an increase in the experimental distribution coefficients.

Biogenic volatile emissions from the soil

Volatile compounds are usually associated with an appearance/presence in the atmosphere. Recent advances, however, indicated that the soil is a huge reservoir and source of biogenic volatile organic compounds (bVOCs), which are formed from decomposing litter and dead organic material or are synthesized by underground living organism or organs and tissues of plants. This review summarizes the scarce available data on the exchange of VOCs between soil and atmosphere and the features of the soil and particle structure allowing diffusion of volatiles in the soil, which is the prerequisite for biological VOC-based interactions. In fact, soil may function either as a sink or as a source of bVOCs. Soil VOC emissions to the atmosphere are often 1-2 (0-3) orders of magnitude lower than those from aboveground vegetation. Microorganisms and the plant root system are the major sources for bVOCs. The current methodology to detect belowground volatiles is described as well as the metabolic capabilities resulting in the wealth of microbial and root VOC emissions. Furthermore, VOC profiles are discussed as non-destructive fingerprints for the detection of organisms. In the last chapter, belowground volatile-based bi- and multi-trophic interactions between microorganisms, plants and invertebrates in the soil are discussed.

Effect of konjac glucomannan addition on aroma release in gels containing potato starch

The present study aimed to measure the retention of aroma compounds (ethyl acetate, ethyl hexanoate and carvacrol) in dispersions based on konjac glucomannan and/or potato starch, and to highlight the influence of konjac glucomannan on the mechanisms involved in aroma retention. Publications on the effect of konjac glucomannan on aroma release are scarce. Konjac glucomannan is a polysaccharide used as a food additive for its viscous and emulsifying properties. Retention of aroma compounds in dispersions was calculated from partition coefficients which were measured using the phase ratio variation method. This method, consisting of analyses of the headspace at equilibrium, enables the determination of the partition coefficient of volatile compounds in a gas/liquid system without external or internal calibration. The three aroma compounds chosen for this study behave differently toward amylose. Prior to the release study, the complexing behavior of carvacrol with starch, hitherto unknown, was investigated by X-ray diffraction: V_6III amylose complexes were formed with carvacrol. Our results showed no specific interaction between ethyl hexanoate and potato starch or konjac glucomannan. Ethyl acetate retention seemed to be due to trapping in the complex network of polysaccharides and to the density of this network. Retention of carvacrol was influenced by the nature of polysaccharides present in the dispersion, and was mainly governed by specific interaction with starch. Additionally, the addition of konjac glucomannan to potato starch dispersions decreased the retention of volatile compounds complexing starch, but had little effect on the retention of the other aroma compounds.

Persistency assessment and aerobic biodegradation of selected cyclic sesquiterpenes present in essential oils

Sesquiterpenes are ubiquitous in essential oils but an assessment of their environmental behavior is still required for their use as components of natural fragrance ingredients and oral care flavors. Persistency plays a key role in hazard and risk assessment, but the current knowledge on the biodegradation of sesquiterpenes in the aquatic environment is limited. This could have important consequences for the persistent, bioaccumulative and toxic (PBT) assessment of essential oils because most of the sesquiterpene components have a log K(OW) of >4.5 and are identified as potentially bioaccumulating according to REACH screening criteria. In the present study, a persistency screening assessment was conducted on 11 cyclic sesquiterpenes selected from 10 different families of sesquiterpenes characterized by their carbon skeleton. Current biodegradation prediction models (BioWin™, BioHCwin, and Catalogic) were found to be of limited use because most of the sesquiterpenes studied were outside the structural domain of the models. Aerobic biodegradation was measured in a standard or prolonged Organisation for Economic Co-operation and Development (OECD) 301F Manometric Respirometry test for ready biodegradability. α-Bisabolol, α-humulene, β-caryophyllene, α-cedrene, cedrol, longifolene, and δ-cadinene exceeded the pass level of 60% degradation and can be regarded as not persistent. Alpha-gurjunene, himachalenes (α, β, γ), and (-)-thujopsene almost achieved the pass level reaching between 51% and 56% ultimate biodegradation. Although germacrene D only achieved 24% ultimate biodegradation, specific analysis at the end of the test did indicate complete primary degradation. Given that the shape of the biodegradation curves indicates poor bioavailability and ready biodegradability tests are very stringent, it is expected that all the sesquiterpenes tested in the present study would be degraded under environmental conditions.