Accumulation of microplastics in soil after long-term application of biosolids and atmospheric deposition

Land-applied biosolids can be a considerable source of microplastics in soils. Previous studies reported microplastics accumulation in soils from biosolid application, however, little is known about the contribution of atmospherically deposited microplastics to agricultural soils. In this study, we quantified and characterized microplastics in soils that have been amended with biosolids over the past 23 years. We also collected atmospheric deposition samples to determine the amount and type of plastics added to soils through atmospheric input over a period of about 2 years. Soil samples were taken from a replicated field trial where biosolids have been applied at rates of 0, 4.8, 6.9, and 9.0 t/ha every second crop. The biosolids were anaerobically digested and dewatered, and were applied by spreading onto the soil surface. Soil and atmospheric samples were extracted for microplastics by Fenton's reaction to remove organic matter followed by flotation in a zinc chloride solution to separate plastic from soil particles. Samples were analyzed for microplastics by optical microscopy and Laser Direct Infrared Imaging Analysis (LDIR). The mean number of microplastics identified from biosolids samples was 12,000 particles/kg dry biosolids. The long-term applications of biosolids to the soil led to mean plastics concentrations of 383, 500, and 361 particles/kg dry soil in the 0-10 cm depth for low, medium, and high biosolids application rates, respectively. These plastic concentrations were not significantly different from each other, but significantly higher than those found in non biosolids-amended soil (117 particles/kg dry soil). The dominant plastic types by number found in biosolids were polyurethane, followed by polyethylene, and polyamide. The most abundant plastics in soil samples were polyurethane, polyethylene terephthalate, polyamide, and polyethylene. Atmospheric deposition contributed to 15 particles/kg dry soil per year and was mainly composed of polyamide fibers. This study shows that long-term application of biosolids led to an accumulation of microplastics in soil, but that atmospheric deposition also contributes a considerable input of microplastics.

Stabilization of organic carbon in top- and subsoil by biochar application into calcareous farmland

Biochar is recognized for its role in carbon sequestration and emission mitigation in farmland topsoil. However, the mechanisms by which biochar affects soil organic carbon (SOC), its composition, and stability, in the topsoil (0-20 cm) and subsoil (140-160 cm) remain unclear. Applying biochar to the calcareous farmland topsoil significantly increased the topsoil SOC contents by 33 % after a decade, with a 5 % increase in dissolved organic carbon (DOC) contents (topsoil) and a substantial increase of 162 % in subsoil DOC contents. Additionally, humic substances showed an increase of 24 % (topsoil), while low-molecular-weight water-extracted DOC exhibited a remarkable increase of 142 % in the subsoil. The application of biochar significantly increases the contents of SOC, DOC, and microbial biomass carbon (MBC) in the topsoil, as well as SOC and DOC contents in the subsoil. However, a slight decrease is observed for MBC content in the subsoil. Biochar-amended soil significantly suppressed enzyme activity in the topsoil and decreased α diversity in topsoil and subsoil while increasing the content of mineral-associated soil organic matter (MAOM). These observed changes are conducive to stabilizing SOC, emphasizing MAOM formation as a primary mechanism for carbon sequestration in both topsoil and subsoils. This study provides evidence that biochar contributes to the long-term organic carbon sequestration in calcareous farmland, highlighting the importance of considering both topsoil and subsoil when evaluating the dynamic impacts of biochar on SOC.

Predawn leaf water potential of grapevines is not necessarily a good proxy for soil moisture

BACKGROUND

In plant water relations research, predawn leaf water potential (Ψ_pd) is often used as a proxy for soil water potential (Ψ_soil), without testing the underlying assumptions that nighttime transpiration is negligible and that enough time has passed for a hydrostatic equilibrium to be established. The goal of this research was to test the assumption Ψ_pd = Ψ_soil for field-grown grapevines.

RESULTS

A field trial was conducted with 30 different cultivars of wine grapes grown in a single vineyard in arid southeastern Washington, USA, for two years. The Ψ_pd and the volumetric soil water content (θ_v) under each sampled plant were measured multiple times during several dry-down cycles. The results show that in wet soil (Ψ_soil >  - 0.14 MPa or relative extractable water content, θ_e > 0.36), Ψ_pd was significantly lower than Ψ_soil for all 30 cultivars. Under dry soil conditions (Ψ_soil <  - 0.14 MPa or θ_e < 0.36) Ψ_pd lined up better with Ψ_soil. There were differences between cultivars, but these were not consistent over the years.

CONCLUSION

These results suggest that for wet soils Ψ_pd of grapevines cannot be used as a proxy for Ψ_soil, while the Ψ_pd = Ψ_soil assumption may hold for dry soils.

Formation, behavior, properties and impact of micro- and nanoplastics on agricultural soil ecosystems (A Review)

Micro and nanoplastics (MPs and NPs, respectively) in agricultural soil ecosystems represent a pervasive global environmental concern, posing risks to soil biota, hence soil health and food security. This review provides a comprehensive and current summary of the literature on sources and properties of MNPs in agricultural ecosystems, methodology for the isolation and characterization of MNPs recovered from soil, MNP surrogate materials that mimic the size and properties of soil-borne MNPs, and transport of MNPs through the soil matrix. Furthermore, this review elucidates the impacts and risks of agricultural MNPs on crops and soil microorganisms and fauna. A significant source of MPs in soil is plasticulture, involving the use of mulch films and other plastic-based implements to provide several agronomic benefits for specialty crop production, while other sources of MPs include irrigation water and fertilizer. Long-term studies are needed to address current knowledge gaps of formation, soil surface and subsurface transport, and environmental impacts of MNPs, including for MNPs derived from biodegradable mulch films, which, although ultimately undergoing complete mineralization, will reside in soil for several months. Because of the complexity and variability of agricultural soil ecosystems and the difficulty in recovering MNPs from soil, a deeper understanding is needed for the fundamental relationships between MPs, NPs, soil biota and microbiota, including ecotoxicological effects of MNPs on earthworms, soil-dwelling invertebrates, and beneficial soil microorganisms, and soil geochemical attributes. In addition, the geometry, size distribution, fundamental and chemical properties, and concentration of MNPs contained in soils are required to develop surrogate MNP reference materials that can be used across laboratories for conducting fundamental laboratory studies.

Dynamics of macroplastics and microplastics formed by biodegradable mulch film in an agricultural field

Conventional plastic mulch brings agronomic and economic benefits to crop production, but a large amount of plastic waste amasses when the mulch is removed from the fields after harvest. Soil-biodegradable plastic mulch (BDM) has emerged as a promising alternative to conventional plastic mulch as it can be tilled into the soil after harvest, thereby alleviating disposal problems. However, direct evidence on complete degradation of biodegradable mulch under natural conditions is still lacking. We quantified the dynamics of macro- (>5 mm) and microplastics (0.1-5 mm in size) four years after a one-time application of mulch in a field with monoculture maize. The BDM feedstock was polybutyleneadipate-co-terephthalate (PBAT) and polylactic acid (PLA)-based, and both a clear and black BDM were tested. The BDM plastic mulch films degraded into macro- and micoplastics. Macroplastics disappeared 2.5 years after mulch incorporation. We developed a new extraction method for biodegradable microplastics using a sequential density fractionation approach with a H₂O and a ZnCl₂ solution. Microplastic concentrations in the soil ranged from 350 to 525 particles/kg after 2.5 years, 175 to 250 particles/kg after 3 years, and 50 to 125 particles/kg after 3.5 year following mulch incorporation. This continuous decrease of visible plastic particle concentrations in soil suggests that BDMs fragment degrade into smaller and smaller particles, which eventually may biodegrade completely. While we cannot ascertain whether persistent and undetectable nanoplastics may form, macro- and microplastics formed from BDM seem to disappear with time.

Aggregation kinetics and stability of biodegradable nanoplastics in aquatic environments: Effects of UV-weathering and proteins

Plastic pollution caused by conventional plastics has promoted the development and use of biodegradable plastics. However, biodegradable plastics do not degrade readily in water; instead, they can generate micro- and nanoplastics. Compared to microplastics, nanoplastics are more likely to cause negative impacts to the aquatic environment due to their smaller size. The impacts of biodegradable nanoplastics highly depend on their aggregation behavior and colloidal stability, which still remain unknown. Here, we studied the aggregation kinetics of biodegradable nanoplastics made of polybutylene adipate co-terephthalate (PBAT) in NaCl and CaCl₂ solutions as well as in natural waters before and after weathering. We further studied the effect of proteins on aggregation kinetics with both negative-charged bovine serum albumin (BSA) and positive-charged lysozyme (LSZ). For pristine PBAT nanoplastics (before weathering), Ca^2＋ destabilized nanoplastic suspensions more aggressively than Na⁺, with the critical coagulation concentration being 20 mM in CaCl₂ vs 325 mM in NaCl. Both BSA and LSZ promoted the aggregation of pristine PBAT nanoplastics, and LSZ showed a more pronounced effect. However, no aggregation was observed for weathered PBAT nanoplastics under most experimental conditions. Further stability tests demonstrated that pristine PBAT nanoplastics aggregated substantially in seawater, but not in freshwater, and only slightly in soil pore water; while weathered PBAT nanoplastics remained stable in all natural waters. These results suggest that biodegradable nanoplastics, especially weathered biodegradable nanoplastics, are highly stable in the aquatic environment, even in the marine environment.

Minimal Impacts of Microplastics on Soil Physical Properties under Environmentally Relevant Concentrations

Agricultural soils are a major reservoir of microplastics, and concerns have arisen about the impacts of microplastics on soil properties and functioning. Here, we measured the physical properties of a silt loam in response to the incorporation of polyester fibers and polypropylene granules over a wide range of concentrations. We further elucidated the underlying mechanisms by determining the role of microplastic shape and the baseline effects from the amendment of soil particles. The incorporation of microplastics into soil tended to increase contact angle and saturated hydraulic conductivity and decrease bulk density and water holding capacity, but not affect aggregate stability. Polyester fibers affected soil physical properties more profoundly than polypropylene granules, due to the vastly different shape of fibers from that of soil particles. However, changes in soil properties were gradual, and significant changes did not occur until a high concentration of microplastics was reached (i.e., 0.5% w/w for polyester fibers and 2% w/w for polypropylene granules). Currently, microplastic concentrations in soils not heavily polluted with plastics are far below these concentrations, and results from this study suggest that microplastics at environmentally relevant concentrations have no significant effects on soil physical properties.

Inducing Inorganic Carbon Accrual in Subsoil through Biochar Application on Calcareous Topsoil

Biochar amendments add persistent organic carbon to soil and can stabilize rhizodeposits and existing soil organic carbon (SOC), but effects of biochar on subsoil carbon stocks have been overlooked. We quantified changes in soil inorganic carbon (SIC) and SOC to 2 m depth 10 years after biochar application to calcareous soil. The total soil carbon (i.e., existing SOC, SIC, and biochar-C) increased by 71, 182, and 210% for B30, B60, and B90, respectively. Biochar application at 30, 60, and 90 t ha^-1 rates significantly increased SIC by 10, 38, and 68 t ha^-1, respectively, with accumulation mainly occurring in the subsoil (below 1 m). This huge increase of SIC (mainly CaCO₃) is ∼100 times larger than the inorganic carbon present in the added biochar (0.3, 0.6, or 0.9 t ha^-1). The benzene polycarboxylic acid method showed that the biochar-amended soil contained more black carbon particles (6.8 times higher than control soil) in the depth of 1.4-1.6 m, which provided the direct quantitative evidence for biochar migration into subsoil after a decade. Spectral and energy spectrum analysis also showed an obvious biochar structure in the biochar-amended subsoil, accompanied by a Ca/Mg carbonate cluster, which provided further evidence for downward migration of biochar after a decade. To explain SIC accumulation in subsoil with biochar amendment, the interacting mechanisms are proposed: (1) biochar amendment significantly increases subsoil pH (0.3-0.5 units) 10 years after biochar application, thus forming a favorable pH environment in the subsoil to precipitate HCO₃^-; and (2) the transported biochar in subsoil can act as nuclei to precipitate SIC. Biochar amendment enhanced SIC by up to 80%; thus, the effects on carbon stocks in subsoil must be understood to inform strategies for carbon dioxide removal through biochar application. Our study provided critical knowledge on the impact of biochar application to topsoil on carbon stocks in subsoil in the long term.

Freeze-thaw cycles lead to enhanced colloid-facilitated Pb transport in a Chernozem soil

Freeze-thaw cycles in soils lead to break up of soil aggregates and the formation of dispersible soil colloids. Leaching events following freeze-thaw cycles can therefore mobilize and transport colloids through the soil profile. Here, we investigated the effect of freeze-thaw cycles on the subsequent mobilization of colloids in a Pb contaminated soil, and we quantified the amount of colloid-facilitated Pb transport. Soil contaminated with Pb (250 mg/kg or 1000 mg/kg) was packed into 15 cm tall columns, and the soil water content adjusted to field capacity (0.306 kg/kg). Columns were subjected to freeze-thaw cycles of 12 h freezing at -20 °C followed by 12 h of thawing at 25 °C. Then, the soil columns were leached with distilled water, and the effluent was analyzed for colloids, soluble Pb, and colloidal-bound Pb. Freeze-thaw cycles were found to generate dispersible soil colloids and lead to colloid-facilitated Pb transport. Colloid and Pb mobilization increased with increasing number of freeze-thaw cycles. The majority (83-97%) of the Pb that leached out of the columns was colloid-bound. Our findings suggest that freeze-thaw cycles in high latitude areas can mobilize heavy metals, which are otherwise immobile, through colloid-facilitated transport. More frequent freeze-thaw cycles in high-latitude regions, as predicted by climate change models, thus increases the risk of metal leaching from contaminated soils and can lead to subsequent ground water pollution.

End-of-Life Management Options for Agricultural Mulch Films in the United States—A Review

Polyethylene plastic mulches are widely used in specialty cropping systems in the United States due to the horticultural benefits they provide. However, polyethylene mulch is reapplied seasonally, generating large volumes of plastic waste that contribute to plastic pollution concerns. This review synthesizes scientific and industry findings to provide a state of current end-of-life options of polyethylene mulch in the United States and identifies opportunities that can improve plastic waste management with a special emphasis on soil-biodegradable plastic mulches. Major points discussed are: (1) polyethylene mulch use in specialty cropping systems, (2) economic, environmental and waste management impacts of polyethylene mulch use, (3) current common end-of-life pathways of used polyethylene mulch, (4) use of soil-biodegradable plastic mulch as an alternative to reduce the amount of plastic waste in the environment and offset the negative impacts associated with residual non-degradable plastics, (5) socioeconomic factors that reduce the adoption of soil-biodegradable plastic mulch, and (6) limitations of soil-biodegradable mulch. The results of this review conclude that recycling and upcycling of used polyethylene mulch can be a more sustainable disposal option, however cleaning and decontaminating used polyethylene mulch is costly and commercial technology is often not accessible nor economically viable in many regions in the current economic and political situation. To make recycling a viable pathway in the future, research and policy developments are necessary to refine and encourage recycling. Soil-biodegradable plastic mulches can offer an additional opportunity to help address these limitations, but they are not permitted in organic agriculture in the United States. Further studies are necessary to address the current knowledge gaps and gain a better understanding of the factors influencing the degradation of soil-biodegradable mulches under diverse field conditions. Improved end-of-life strategies should continue to be pursued that balance sustainable use of plastic mulch while minimizing environmental risks.

Macro- and microplastic accumulation in soil after 32 years of plastic film mulching

Plastic film mulch (PFM) is a double-edged-sword agricultural technology, which greatly improves global agricultural production but can also cause severe plastic pollution of the environment. Here, we characterized and quantified the amount of macro- and micro-plastics accumulated after 32 years of continuous plastic mulch film use in an agricultural field. An interactive field trial was established in 1987, where the effect of plastic mulching and N fertilization on maize yield was investigated. We assessed the abundance and type of macroplastics (>5 mm) at 0-20 cm soil depth and microplastic (<5 mm) at 0-100 cm depth. In the PFM plot, we found about 10 times more macroplastic particles in the fertilized plots than in the non-fertilized plots (6796 vs 653 pieces/m²), and the amount of film microplastics was about twice as abundant in the fertilized plots than in the non-fertilized plots (3.7 × 10⁶ vs 2.2 × 10⁶ particles/kg soil). These differences can be explained by entanglement of plastics with plant roots and stems, which made it more difficult to remove plastic film after harvest. Macroplastics consisted mainly of films, while microplastics consisted of films, fibers, and granules, with the films being identified as polyethylene originating from the plastic mulch films. Plastic mulch films contributed 33%-56% to the total microplastics in 0-100 cm depth. The total number of microplastics in the topsoil (0-10 cm) ranged as 7183-10,586 particles/kg, with an average of 8885 particles/kg. In the deep subsoil (80-100 cm) the plastic concentration ranged as 2268-3529 particles/kg, with an average of 2899 particles/kg. Long-term use of plastic mulch films caused considerable pollution of not only surface, but also subsurface soil. Migration of plastic to deeper soil layers makes removal and remediation more difficult, implying that the plastic pollution legacy will remain in soil for centuries.

Nano-enabled pesticides for sustainable agriculture and global food security

Achieving sustainable agricultural productivity and global food security are two of the biggest challenges of the new millennium. Addressing these challenges requires innovative technologies that can uplift global food production, while minimizing collateral environmental damage and preserving the resilience of agroecosystems against a rapidly changing climate. Nanomaterials with the ability to encapsulate and deliver pesticidal active ingredients (AIs) in a responsive (for example, controlled, targeted and synchronized) manner offer new opportunities to increase pesticidal efficacy and efficiency when compared with conventional pesticides. Here, we provide a comprehensive analysis of the key properties of nanopesticides in controlling agricultural pests for crop enhancement compared with their non-nanoscale analogues. Our analysis shows that when compared with non-nanoscale pesticides, the overall efficacy of nanopesticides against target organisms is 31.5% higher, including an 18.9% increased efficacy in field trials. Notably, the toxicity of nanopesticides toward non-target organisms is 43.1% lower, highlighting a decrease in collateral damage to the environment. The premature loss of AIs prior to reaching target organisms is reduced by 41.4%, paired with a 22.1% lower leaching potential of AIs in soils. Nanopesticides also render other benefits, including enhanced foliar adhesion, improved crop yield and quality, and a responsive nanoscale delivery platform of AIs to mitigate various pressing biotic and abiotic stresses (for example, heat, drought and salinity). Nonetheless, the uncertainties associated with the adverse effects of some nanopesticides are not well-understood, requiring further investigations. Overall, our findings show that nanopesticides are potentially more efficient, sustainable and resilient with lower adverse environmental impacts than their conventional analogues. These benefits, if harnessed appropriately, can promote higher crop yields and thus contribute towards sustainable agriculture and global food security.

Enhanced Transport of TiO2 in Unsaturated Sand and Soil after Release from Biodegradable Plastic during Composting

Biodegradable plastics can reach full degradation when disposed of appropriately and thus alleviate plastic pollution caused by conventional plastics. However, additives can be released into the environment during degradation and the fate of these additives can be affected by the degradation process. Here, we characterized TiO₂ particles released from a biodegradable plastic mulch during composting and studied the transport of the mulch-released TiO₂ particles in inert sand and agricultural soil columns under unsaturated flow conditions. TiO₂ particles (238 nm major axis and 154 nm minor axis) were released from the biodegradable plastic mulch in both single-particle and cluster forms. The mulch-released TiO₂ particles were fully retained in unsaturated soil columns due to attachment onto the solid-water interface and straining. However, in unsaturated sand columns, the mulch-released TiO₂ particles were highly mobile. A comparison with the pristine TiO₂ revealed that the mobility of the mulch-released TiO₂ particles was enhanced by humic acid present in the compost residues, which blocked attachment sites and imposed steric repulsion. This study demonstrates that TiO₂ particles can be released during composting of biodegradable plastics and the transport potential of the plastic-released TiO₂ particles in the terrestrial environment can be enhanced by compost residues.

In-field degradation of soil-biodegradable plastic mulch films in a Mediterranean climate

Soil-biodegradable plastic mulch films are a promising alternative to polyethylene mulches, but adoption has been slow, in part because of uncertainties about in-field degradation. The international biodegradability standard EN-17033 requires 90% degradation within 2 years in an aerobic incubation at constant temperature (20-28 °C). However, in-laboratory biodegradability does not guarantee in-field degradation will follow the same timeframe. Field test protocols are needed to assess biodegradable mulches under a range of environmental conditions and collate site-specific information to predict degradation. Our objectives were to (1) monitor in-field degradation of soil-biodegradable plastic mulches following successive applications and incorporations, (2) quantify mulch recovery 2 years after the final incorporation, and (3) compare in-field degradation with the laboratory standard in terms of calendar and thermal times based on a zeroth-order kinetics model. A field experiment was established in spring 2015 in Mount Vernon, WA testing five biodegradable mulches laid each spring and incorporated each fall until 2018. Mulch recovery was quantified every 6 months until fall 2020, 2 years after the final incorporation. While mulches were incorporated annually, recovery of visible fragments (>2.36 mm) was constant or decreasing over time, indicating mulch deterioration kept pace with new additions. In fall 2020, mulch recovery was 4-16% of total mulch mass incorporated. A zeroth-order kinetics model was used to analyze mulch degradation after the final application. Model extrapolations indicate it would take 21 to 58 months to reach 10% recovery (90% degradation), exceeding the laboratory standard's 24-month benchmark by up to a factor of 2.4. However, when the analysis is done with thermal time, better agreement between in-field and laboratory degradation rates is observed. While other factors, including soil type, soil moisture, and mulch fragment size are also at play, thermal time, rather than calendar time, will be more applicable for assessing site-specific, in-field mulch degradation.

Agronomic performance of polyethylene and biodegradable plastic film mulches in a maize cropping system in a humid continental climate

Plastic polyethylene mulch has been widely used in crop production, but also causes environmental pollution if plastic residues accumulate in soil. Biodegradable plastic mulches (BDM) are a potential solution to problems caused by polyethylene mulches, as BDMs are designed be tilled into the soil after the growing season and then biodegrade. However, the agronomic performance of BDMs still needs to be tested for comparison to polyethylene mulch. We carried out a two-year field experiment in 2018 and 2019 in a typical humid continental climate in Northeast China. Maize was planted in a ridge-furrow pattern, with mulching treatments consisting of no mulch (control), clear BDM, black BDM, clear polyethylene, and black polyethylene. Clear mulches increased soil temperature when compared to no mulch control treatments, while black mulches decreased or did not change soil temperature during the early growing season. Soil temperature and root morphology were similar between BDM and polyethylene mulches for a given type of plastic color. Maize yield did not differ across all the treatments. Maize protein, fat, N and P contents were generally higher for black BDM than other treatments, suggesting that maize quality benefited especially from black BDM. Overall, these results show that, in a humid continental climate, the agronomic performance of clear and black BDMs was equivalent to, or better than, that of polyethylene plastic mulches for maize production.

How to take representative samples to quantify microplastic particles in soil?

The amount of plastic particles in terrestrial ecosystems is not well known, not only because it is difficult to extract and identify plastic particles from terrestrial samples, but also because it is challenging to take representative samples from soils or sediments. Here, we numerically simulated how to take representative terrestrial samples to quantify plastic particles, and we evaluated the accuracy (error) of reported plastic concentrations in the literature. Fields with randomly distributed plastic particles (uniform and clustered) were numerically generated and sampled to determine the representative elementary volume (REV) and the required number of samples to quantify plastic concentrations (10 to 10⁶ particles/m²) with different relative errors (5%, 10%, 15%). The REV and the required number of samples decrease hyperbolically as the plastic concentration increases, indicating a strong non-linear relation. For instance, hundreds to thousands of soil cores (8-cm diameter) would be required to quantify plastics at low concentrations (10² particles/m²), while a few cores are sufficient at high plastic concentrations (10⁵ particles/m²). For an accurate measurement of plastic concentrations, the total surface area of samples taken should approach or exceed the REV. We recommend to take replicated samples with each sample as large as possible (e.g., 1 m × 1 m) rather than multiple small cores, and then reduce the soil volume by the quartering method.

Microbial Hotspots in Lithic Microhabitats Inferred from DNA Fractionation and Metagenomics in the Atacama Desert

The existence of microbial activity hotspots in temperate regions of Earth is driven by soil heterogeneities, especially the temporal and spatial availability of nutrients. Here we investigate whether microbial activity hotspots also exist in lithic microhabitats in one of the most arid regions of the world, the Atacama Desert in Chile. While previous studies evaluated the total DNA fraction to elucidate the microbial communities, we here for the first time use a DNA separation approach on lithic microhabitats, together with metagenomics and other analysis methods (i.e., ATP, PLFA, and metabolite analysis) to specifically gain insights on the living and potentially active microbial community. Our results show that hypolith colonized rocks are microbial hotspots in the desert environment. In contrast, our data do not support such a conclusion for gypsum crust and salt rock environments, because only limited microbial activity could be observed. The hypolith community is dominated by phototrophs, mostly Cyanobacteria and Chloroflexi, at both study sites. The gypsum crusts are dominated by methylotrophs and heterotrophic phototrophs, mostly Chloroflexi, and the salt rocks (halite nodules) by phototrophic and halotolerant endoliths, mostly Cyanobacteria and Archaea. The major environmental constraints in the organic-poor arid and hyperarid Atacama Desert are water availability and UV irradiation, allowing phototrophs and other extremophiles to play a key role in desert ecology.

Long-term accumulation, depth distribution, and speciation of silver nanoparticles in biosolids-amended soils

Biosolids can be a source of metals and metal nanoparticles. The objective of this study was to quantify and characterize the accumulation and transport of silver (Ag) in a natural soil that has received agronomically recommended rates of biosolids as fertilizer from 1994 to 2017. Total Ag concentrations were measured in biosolids and soil samples collected from 0 to 10 cm between 1996 and 2017. The depth distribution of Ag in soil to 60-cm depth was measured in 2017. Electron microscopy, in combination with X-ray spectroscopy, and X-ray absorption spectroscopy were used to characterize the Ag. The Ag concentrations in the biosolids-amended soil increased steadily from 1996 until 2007, after which the concentrations leveled off at about 1.25 mg Ag kg^-1 soil. This corresponded with a decrease of Ag concentrations in biosolids over time. The majority of the Ag (82%) was confined to the top 10 cm of the soil, small amounts (14%) were detected at 10-to-20-cm depth, and trace amounts (4%) were detected at 30-to-40-cm depth. The Ag in the biosolids was identified as S-containing nanoparticles (Ag₂ S) with a diameter of 10-12 nm; however, in soil, the Ag concentrations were too low to allow identification of Ag speciation. This study shows that in a real-world field scenario, biosolids applied at agronomic rates represent a long-term, economically viable source of crop nutrients without increasing the concentration of total Ag in soil above a maximum of 1.5 mg Ag kg^-1 . This concentration is below estimated ecotoxicity limits for Ag₂ S in soil.

In situ degradation of biodegradable plastic mulch films in compost and agricultural soils

The global use of agricultural plastic films, which provide multiple benefits for food production, is expected to grow by 59% from 2018 to 2026. Disposal options for agricultural plastics are limited and a major global concern, as plastic fragments from all sources ultimately accumulate in the sea. Biodegradable plastic mulches could potentially alleviate the disposal problem, but little is known about how well they degrade under different environmental conditions. We quantified the degradation of biodegradable plastic mulches in compost and in soil at warm and cool climates (Tennessee and Washington). Mulch degradation was assessed by Fourier-transformed infrared (FTIR) spectroscopy, molecular weight analysis, thermogravimetric analysis (TGA), nuclear-magnetic resonance (NMR), and mulch surface-area quantification. Biodegradable plastic mulches degraded faster in compost than in soil: degradation, as assessed by surface-area reduction, in compost ranged from 85 to 99% after 18 weeks, and in soil from 61 to 83% in Knoxville and 26 to 63% in Mount Vernon after 36 months. FTIR analyses indicate that hydrolytic degradation of ester bonds occurred, and a significant reduction of molecular weight was observed. TGA and NMR confirmed degradation of biodegradable polymers. Our results indicate that biodegradable plastic mulches degrade in soil, but at different rates in different climates and that degradation occurs over several years. Faster degradation occurred in compost, making composting a viable disposal method, especially in cool climates, where mulch fragments in soil may persist for many years.

Negatively Charged Lipids Exhibit Negligible Effects on the Water Repellency of Montmorillonite Films

Amphiphilic molecules can alter the wettability of soil minerals. To determine how the headgroup chemistry of amphiphiles determines these effects, we investigate a system of the clay montmorillonite with long-chain phospholipids. We use phosphatidylglycerol (PG) phospholipids to contrast with our previous work using phosphatidylethanolamine (PE) lipids. Zwitterionic PE lipids can sorb to the negatively charged montmorillonite surface, whereas negatively charged PG lipids cannot. Employing a suite of techniques from molecular dynamics, atomic force microscopy, fluorescence microscopy, and contact angle measurements, we define sample characteristics from molecular-scale structure to the macroscopic wettability. We find that PG lipids do not significantly alter montmorillonite wetting characteristics, such as the contact angle, flow viscosity, and the characteristic time scale for droplet imbibition. On comparing PE and PG lipid/clay films, we find that, among the phospholipids compared, they must have three characteristics to change clay/lipid film wettability: they must bind to the mineral surface, be solid at room temperature, and have a relatively continuous distribution throughout the film.

Effect of sulfamethazine on surface characteristics of biochar colloids and its implications for transport in porous media

Antibiotics are contaminants of emerging concern due to their potential effect on antibiotic resistance and human health. Antibiotics tend to sorb strongly to organic materials, and biochar, a high efficient agent for adsorbing and immobilizing pollutants, can thus be used for remediation of antibiotic-contaminated soil and water. The effect of ionizable antibiotics on surface characteristics and transport of biochar colloids (BC) in the environment is poorly studied. Column experiments of BC were conducted in 1 mM NaCl solution under three pH (5, 7, and 10) conditions in the presence of sulfamethazine (SMT). Additionally, the adsorption of SMT by BC and the zeta potential of BC were also studied. The experimental results showed that SMT sorption to BC was enhanced at pH 5 and 7, but reduced at pH 10. SMT sorption reduced the surface charge of BC at pH 5 and 7 due to charge shielding, but increased surface charge at pH 10 due to adsorption of the negatively charged SMT species. The mobility of BC was inhibited by SMT under acidic or neutral conditions, while enhanced by SMT under alkaline conditions, which can be well explained by the change of electrostatic repulsion between BC and sand grains. These findings imply that pH conditions played a crucial role in deciding whether the transport of BC would be promoted by SMT or not. Biochar for antibiotics remediation will be more effective under acidic and neutral soil conditions, and the mobility of BC will be less than in alkaline soils.

Release of micro- and nanoparticles from biodegradable plastic during in situ composting

Plastic is ubiquitous in modern life, but most conventional plastic is non-biodegradable and accumulates as waste after use. Biodegradable plastic is a promising alternative to conventional plastic. However, biodegradable plastics must be thoroughly evaluated to ensure that they undergo complete degradation and have no adverse impact on the environment. We evaluated the degradation of biodegradable plastics during 18-week full-scale composting, and determined whether additives from the plastics are released upon degradation. Two biodegradable plastic films-one containing polybutylene co-adipate co-terephthalate (PBAT) and the other containing polylactic acid/poly-hydroxy-alkanoate (PLA/PHA)-were placed into meshbags and buried in the compost. Degradation was assessed by image analysis, scanning electron microscopy, Fourier-transformed infrared spectroscopy, electrophoretic mobility, δ¹³C isotope analyses, and single particle mass spectrometry of mulch fragments. The results showed >99% macroscopic degradation of PLA/PHA and 97% for PBAT film. Polymers in the biodegradable films degraded; however, micro- and nanoparticles, most likely carbon black, were observed on the meshbags. Overall, biodegradable plastics hold promise, but the release of micro- and nanoparticles from biodegradable plastic upon degradation warrants additional investigation and calls for longer field testing to ensure that either complete biodegradation occurs or that no long-term harm to the environment is caused.

Effects of freezing-thawing and wetting-drying on heavy metal leaching from biosolids

The goal of this study was to evaluate the effects of freezing-thawing and wetting-drying on heavy metals leaching from biosolids. Biosolid samples were irrigated with water at two flow rates and three flow stop events in 24 hr intervals. During the period of flow stop, biosolids were subjected to different temperatures, water contents, or freezing-thawing. Leachates were analyzed for heavy metals. The concentrations of metals in biosolids ranged from lower than detection limits (for Pb) to 1,039 mg/kg (for Zn). The leaching percentage of metals ranged from 0% (Pb, Ag, Cs) to 25% (Ni). Lower flow rate with longer residence time induced more metal leaching compared with higher flow rate with shorter residence time. At each flow rate, flow stop caused enhanced metal leaching. Higher drying temperature enhanced metal leaching. Water content or freezing-thawing had no significant effects on metal leaching. We expect that intermittent irrigation or rainfall would enhance the risk of metals leaching from biosolids after land application. However, freezing of biosolids during winter will likely not cause an enhanced leaching of metals in spring when biosolids and soils thaw. Application of biosolids in fall should therefore not cause enhanced leaching of metals out of land-applied biosolids. PRACTITIONER POINTS: Lower flow rate with longer residence time induced more metal leaching compared with higher flow rate with shorter residence time. Flow stop or higher drying temperature enhanced metal leaching from biosolids. Water content or freezing-thawing had no significant effects on metal leaching.

Colloidal stability and aggregation kinetics of biochar colloids: Effects of pyrolysis temperature, cation type, and humic acid concentrations

An understanding of biochar colloid aggregation and stability in aqueous environments is critical for assessing biochar fate and mobility in the soil. The aggregation kinetics of wheat straw-derived biochar colloids pyrolyzed at two temperatures 300 and 600 °C (WB300 and WB600 colloids, respectively) were investigated in monovalent and divalent electrolyte solutions in absence/presence of humic acid (HA). Results show that the critical coagulation concentrations (CCCs) of WB300 colloids in NaCl and CaCl₂ solutions were 274 and 61.4 mM, which were higher than those (183 mM for NaCl and 38.1 mM for CaCl₂) of WB600 colloids. WB300 had more oxygen-containing functional groups than WB600, which induced more negative surface charge on WB300. HA of 5 mg L^-1 greatly increased the CCCs of WB300 and WB600 colloids to 1288 and 806 mM in NaCl solutions, but decreased the CCCs to 54.6 and 37.0 mM in CaCl₂ solutions because of strong bridging between HA and Ca²⁺. In CaCl₂ solutions with high salt concentrations (near to the CCCs), different HA concentrations caused distinct effects on the aggregation of biochar colloids. The aggregation of biochar colloids was accelerated by HA with the concentration higher than 5 mg L^-1 through cation-bridging while the aggregation was inhibited in the presence of <2.5 mg L^-1 HA. Our findings show that pyrolysis temperature used for biochar production had a large effect on the aggregation of biochar colloids in the aqueous environment and that cation type and dissolved natural organic matter are controlling variables.

Poor extraction efficiencies of polystyrene nano- and microplastics from biosolids and soil

Extraction and quantification of nano- and microplastics from sediments and soils is challenging. Although no standard method has been established so far, flotation is commonly used to separate plastic from mineral material. The objective of this study was to test the efficiency of flotation for the extraction of nano- and microplastics from biosolids and soil. We spiked biosolids and soil samples with polystyrene nano- and microbeads (0.05, 1.0, 2.6, 4.8, and 100 μm diameter). Different extraction methods (w/ and w/o H2O2 digestion) were tested, and plastic beads were separated from mineral particles by flotation in a ZnCl2 solution. Plastic particles were quantified by UV-Vis spectrometry and gravimetrically. While large beads (100 μm) could be quantitatively extracted (∼100%) from both biosolids and soils, smaller beads had low extraction efficiencies (ranging from 5 to 80%, with an average of 20%). Except for the 100 μm beads, oxidation with H2O2 negatively impacted the extraction efficiencies. For the soil, extraction with water only, followed by flotation in a ZnCl2 solution, resulted in relatively high extraction efficiencies (>75%) for beads larger than 1 μm, but low efficiencies (<30%) for the 0.05 and 1.0 μm beads. Our results indicate that while flotation generally works to separate plastic nano- and microbeads in a solution, the challenge is to quantitatively extract nano- and microbeads from a biosolids or soil matrix. Samples high in organic matter content require removal of the organic matter, but the common method of H2O2 oxidation leads to poor extraction efficiencies for nano- and microbeads.

DLVO Interaction Energies for Hollow Particles: The Filling Matters

A thorough knowledge of the interaction energy between a hollow particle (HP) and a surface or between two HPs is critical to the optimization of HP-based products and assessing the environmental risks of HPs and HP-associated pollutants. The van der Waals (vdW) energy between a HP and a surface is often calculated by subtracting the vdW energies of the inner and outer HP geometries. In this study, we show that this subtraction method is only valid when the interior and exterior fluids are the same, for example, for water-filled HPs (WHPs) dispersed in an aqueous solution. Expressions were developed to calculate the vdW energies for HPs whose interiors were filled with air (AHPs). The vdW energies were then calculated between a planar surface and a spherical or cylindrical WHP and AHP, and between WHPs or AHPs. The vdW attraction between a surface and a WHP was decreased at large separation distances compared to solid particles, and this reduced the depth of the secondary minimum. In contrast, the vdW attraction for AHPs and a surface was significantly reduced at all separation distances, and even became repulsive for thin shells, and this inhibited both primary and secondary minimum interactions. The vdW attraction between WHPs decreased with increasing shell thicknesses, and this reduced aggregation in both primary and secondary minima. In contrast, aggregation of AHPs was increased in both minima with decreasing shell thicknesses because of an increase in vdW attraction. Our theoretical calculations show the evolution of vdW and total interaction energies for HPs with different interior fluids and shell thicknesses. These results help explain various experimental observations such as inhibited attachment and favorable aggregation for AHPs (e.g., carbon nanotubes) and favorable bubble coalescence.

Interaction of Lumbricus terrestris with macroscopic polyethylene and biodegradable plastic mulch

Polyethylene mulch films used in agriculture are a major source of plastic pollution in soils. Biodegradable plastics have been introduced as alternative to commonly-used polyethylene. Here we studied the interaction of earthworms (Lumbricus terrestris) with polyethylene and biodegradable plastic mulches. The objective was to assess whether earthworms would select between different types of mulches when foraging for food, and whether they drag macroscopic plastic mulch into the soil. Laboratory experiments were carried out with earthworms in Petri dishes and mesocosms. The treatments were standard polyethylene mulch, four biodegradable plastic mulches (PLA/PHA [polylactic acid/polyhydroxy alkanoate], Organix, BioAgri, Naturecycle), a biodegradable paper mulch (WeedGuardPlus), and poplar litter, which served as control. Four and three replicates for the Petri dish and mesocosm experiments were used, respectively. Macroscopic plastic and paper mulch pieces (1.5 cm × 1.5 cm and 2 cm × 2 cm) were collected from an agricultural field after a growing season, after being buried in the soil for 6 and 12 months, and after being composted for 2 weeks. We found that earthworms did not ingest polyethylene. Field-weathered biodegradable plastic mulches were not ingested either, however, after soil burial and composting, some biodegradable plastics were eaten and could not be recovered from soil any longer. Earthworms, when foraging for food, dragged plastic mulch, including polyethylene and biodegradable plastic, and poplar leaves into their burrows. The burial of macroscopic plastic mulch underground led to a redistribution of plastics in the soil profile, and likely enhances the degradation of biodegradable mulches in soil, but also can lead to leaching of plastic fragments by macropore flow.

[Patch augmentation of the rotator cuff. A reasonable choice or a waste of money?]

BACKGROUND

Although reconstruction methods have improved, tendon retears remain a major complication associated with rotator cuff repair. With the application of patches, either by interposition or by augmentation, surgeons can attempt to close an irreparable cuff defect or improve the mechanical and biological properties of tendons respectively.

OBJECTIVES

Which factors need to be considered when using a patch and what outcome can be expected?

MATERIALS AND METHODS

Based on the current literature, an overview of the techniques and materials in use and biomechanical and clinical experience is provided.

RESULTS

The literature shows clear improvements in the biomechanical properties of a repair with patch augmentation; in particular, weakened tendons of the anterior supraspinatus and superior infraspinatus benefit most. It is important to keep in mind that each patch material has its own individual properties, which makes comparison of the various patch types difficult. The current scientific evidence is promising, although larger level 1 studies are still required.

CONCLUSIONS

The general use of patches cannot be recommended at this time. Nevertheless, the use of a patch should be considered in patients who are at a high risk of recurrent retears. In future, patches will probably be applied mainly as part of a combined effort, together with biological measures to further reduce retear rates.

Nutrient leaching and copper speciation in compost-amended bioretention systems

Bioretention systems are designed to remove contaminants from stormwater; however, studies have shown that bioretention systems can export excess nitrogen, phosphorus, and copper when amended with compost. The objectives of this study were (1) to quantify removal of nitrates, phosphorus, copper, and dissolved organic matter (DOM) from compost-amended bioretention systems, and (2) to investigate the role of DOM on the leaching of copper. Simulated bioretention systems were irrigated with stormwater for seven storms in two-weeks intervals. Leachates were analyzed for nutrients, copper, and DOM. Visual MINTEQ was used to determine the speciation of copper and to quantify interactions of copper with DOM. Results showed that compost-amended bioretention systems were a source of nitrates, phosphorus, and DOM. Nitrate and phosphorus amounts were elevated up to three orders of magnitude in the leachate compared to the stormwater itself. Bioretention systems were a source for copper during the first 3-5 storms, but during later storms, they were a sink for copper. Copper speciation modeling indicated that the majority of dissolved copper was complexed with DOM. Dissolved organic matter thus helps to mobilize copper from the compost, particularly in the first few storms after compost application. However, since copper-DOM complexes are usually much less toxic than free copper ions, we expect that compost amendments may reduce harmful effects of copper on aquatic organisms.

Intermittent rainstorms cause pulses of nitrogen, phosphorus, and copper in leachate from compost in bioretention systems

Bioretention systems rely on vegetation and mixtures of soil, sand, and compost to filter stormwater runoff. However, bioretention systems can also leach metals and nutrients, and compost may be a major contributor to this leaching. To safely implement bioretention systems, it is crucial to determine the composition of compost leachate. We characterized and quantified the leachate composition of compost following intermittent, simulated storm events. Columns of municipal compost were irrigated to simulate 6-month, 24-hour rain storms in the Seattle-Tacoma region. Outflow was analyzed for pH, electrical conductivity (EC), particulate concentration, surface tension, dissolved organic carbon (DOC), nitrogen, phosphorus, and copper. Results indicate a decrease of chemical concentrations over the course of individual storms and following repeated storms, but each new storm released another peak of constituents. The decrease in phosphorus, copper, and DOC concentrations with repeated storms was slower than for nitrate and EC. Nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) showed that the DOC consisted mainly of aliphatic and aromatic components typical of fulvic and humic acids. Less than 3% of the original copper content from the compost leached out even after nine storm events. Nonetheless, copper concentrations in the leachate exceeded regulatory discharge standards. Our results show that compost can serve as a sustained source of leaching of nutrients and metals.

Transport of barrel and spherical shaped colloids in unsaturated porous media

Model colloids are usually spherical, but natural colloids have irregular geometries. Transport experiments of spherical colloids may not reflect the transport characteristics of natural colloids in porous media. We investigated saturated and unsaturated transport of colloids with spherical and angular shapes under steady-state, flow conditions. A pulse of negatively-charged colloids was introduced into a silica sand column at three different effective water saturations (Se = 0.31, 0.45, and 1.0). Colloids were introduced under high ionic strength of [106]mM to cause attachment to the secondary energy minimum and later released by changing the pore water to low ionic strength. After the experiment, sand was sampled from different depths (0, -4, and -11 cm) for scanning electron microscopy (SEM) analysis and colloid extraction. Water saturation affected colloid transport with more retention under low than under high saturation. Colloids were retained and released from a secondary energy minimum with more angular-shaped colloids being retained and released. Colloids extracted from the sand revealed highest colloid deposition in the top layer and decreasing deposition with depth. Pore straining and grain-grain wedging dominated colloid retention.

Effect of biochar on leaching of organic carbon, nitrogen, and phosphorus from compost in bioretention systems

Compost is used in bioretention systems to improve soil quality, water infiltration, and retention of contaminants. However, compost contains dissolved organic matter, nitrate, and phosphorus, all of which can leach out and potentially contaminate ground and surface waters. To reduce the leaching of nutrients and dissolved organic matter from compost, biochar may be mixed into the bioretention systems. Our objective was to test whether biochar and co-composted biochar mixed into mature compost can reduce the leaching of organic carbon, nitrogen, and phosphorus. There was no significant difference between the effects of biochar and co-composted biochar amendments on nutrient leaching. Further, biochar amendments did not significantly reduce the leaching of dissolved organic carbon, nitrate, and phosphorus as compared to the compost only treatment. The compost-sand mix was the most effective in reducing nitrate and phosphorus leaching among the media.

Competitive incorporation of perrhenate and nitrate into sodalite

Nuclear waste storage tanks at the Hanford site in southeastern Washington have released highly alkaline solutions, containing radioactive and other contaminants, into subsurface sediments. When this waste reacts with subsurface sediments, feldspathoid minerals (sodalite, cancrinite) can form, sequestering pertechnetate (99TcO4-) and other ions. This study investigates the potential for incorporation of perrhenate (ReO4-), a chemical surrogate for 99TcO4-, into mixed perrhenate/nitrate (ReO4-/NO3-) sodalite. Mixed-anion sodalites were hydrothermally synthesized in the laboratory from zeolite A in sodium hydroxide, nitrate, and perrhenate solutions at 90 °C for 24 h. The resulting solids were characterized by bulk chemical analysis, X-ray diffraction, scanning electron microscopy, and X-ray absorption near edge structure spectroscopy (XANES) to determine the products' chemical composition, structure, morphology, and Re oxidation state. The XANES data indicated that nearly all rhenium (Re) was incorporated as Re(VII)O4-. The nonlinear increase of the unit cell parameter with ReO4-/NO3- ratios suggests formation of two separate sodalite phases in lieu of a mixed-anion sodalite. The results reveal that the sodalite cage is highly selective toward NO3- over ReO4-. Calculated enthalpy and Gibbs free energy of formation at 298 K for NO3- and ReO4-sodalite suggest that NO3- incorporation into the cage is favored over the incorporation of the larger ReO4-, due to the smaller ionic radius of NO3-. Based on these results, it is expected that NO3-, which is present at significantly higher concentrations in alkaline waste solutions than 99TcO4-, will be strongly preferred for incorporation into the sodalite cage.

Colloid mobilization and transport during capillary fringe fluctuations

Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead-filled column. We studied four specific conditions: (1) colloids suspended in the aqueous phase, (2) colloids attached to the glass beads in an initially wet porous medium, (3) colloids attached to the glass beads in an initially dry porous medium, and (4) colloids suspended in the aqueous phase with the presence of a static air bubble. Confocal images confirmed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively charged colloids did not attach to static air-bubbles, but hydrophobic negatively charged and hydrophilic positively charged colloids did. Our results demonstrate that capillary fringe fluctuations are an effective means for colloid mobilization.

Does water content or flow rate control colloid transport in unsaturated porous media?

Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations Se ranging from 0.1 to 1.0, with Se = (θ - θr)/(θs - θr)) and flow rates (pore water velocities v of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (Se < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transport in unsaturated porous media and highlight the dominant role of water content.

Effect of particle shape on capillary forces acting on particles at the air-water interface

The capillary forces exerted by moving air-water interfaces can dislodge particles from stationary surfaces. The magnitude of the capillary forces depends on particle shape, orientation, and surface properties, such as contact angle and roughness. The objective was to quantify, both experimentally and theoretically, capillary force variations as an air-water interface moves over the particles. We measured capillary forces as a function of position, i.e., force-position curves, on particles of different shape by using force tensiometry. The particles (5 mm nominal size) were made of polyacrylate and were fabricated using a 3D printer. Experimental measurements were compared with theoretical calculations. We found that force-position curves could be classified into in three categories according to particle shapes: (1) curves for particles with round cross sections, such as spheroidal particles, (2) curves for particles with fixed cross sections, such cylindrical or cubical particles, and (3) curves for particles with tapering cross sections, such as prismatic or tetrahedral particles. Spheroidal particles showed a continuously varying capillary force. Cylindrical or cubical particles showed pronounced pinning of the air-water interface line at edges. The pinning led to an increased capillary force, which was relaxed when the interface snapped off from the edges. Particles with tapering cross section did not show pinning and showed reduced capillary forces as the air-water interface line perimeter and displacement cross section continuously decrease when the air-water interface moved over the particles.

[Domestic violence against women of a crisis intervention population - forms of violence and risk factors]

BACKGROUND AND HYPOTHESES: Domestic violence is common and can lead to severe physical and psychological problems. Thus, we have investigated the frequency of occurrence, forms and risk factors of domestic violence against female patients on a crisis intervention ward.

METHODS

115 women were screened with the "screening spouse violence" (SPG) and the "index of spouse abuse" (ISA).

RESULTS

The life time prevalence concerning spouse violence was 70 %. Out of 74 women who were currently living in a relationship 28 (38 % )were victims of violence in the last 12 months prior to their admission. Women who experienced violence had a significantly lower level of education.

CONCLUSION

Screening for domestic violence in female patients in the field of crisis intervention and psychiatry should become a standard of "good clinical practice".