Microplastic water repellency impacts water flow and microplastic transport in soils

Soils are considered the largest sink of microplastic particles (MP) in terrestrial ecosystems. However, there is little knowledge on the implications of MP contaminating soils. In particular, we do not know the extent of and conditions under which MP are transported through porous media and, if they are deposited, how they affect soil hydraulic properties and soil moisture dynamics. We hypothesize that: 1) hydrophobic MP enhance soil water repellency; 2) isolated MP are displaced and transported by the air-water interface; 3) clusters of MP impede water flow and are retained in air-filled pores.We tested these hypotheses in mixtures of MP (&#181;m range) and sands (mm range) in a series of experiments. The Sessile Drop Method (SDM) was applied to measure the average contact angle (CA) of the mixtures for MP and model porous media in the same size range, ranging from 0 - 100 % MP content. Based on the specific surface and shape factor of MP and soil particles, the results are extrapolated to different MP and soil particle sizes. Capillary rise experiments were performed to measure the impact of MP on water infiltration. The applied MP contents of 0.35 % and 1.05 % reflect an average CA of 60&#176; and 90&#176; from the SDM extrapolation. Capillary rise of water and ethanol were carried out to estimate the apparent CA. Additionally and with the same MP content, we simultaneously imaged in three-dimensions the movement of deuterated water and MP during repeated drying / wetting cycles using X-Ray and Neutron tomography (at the beamline ICON, PSI). The different neutron attenuation coefficients of deuterated water and MP allows for estimating their distribution in the sand packing.Already at MP contents of 5 % the CA measured with the SDM exhibited a steep increase and reached 59&#176; to 81&#176;, depending on the grain size of MP. The capillary rise experiments showed that MP reduce capillary rise. The apparent CA (43&#176; and 53&#176;) were smaller compared to the average CA from the SDM (60&#176; and 90&#176;), but the added MP increased air entrapment during capillary rise leading to a reduced saturation of the pore space (18 % and 16.5 %). Accumulation of MP at the advancing air-water interface was visible. Neutron and X-ray imaging showed at high resolution that regions with major MP content are water repellent and, are bypassed by water flow, and remain in air-filled pores.Extrapolation of these results to soils suggests that in microregions with high MP contents, water infiltration is hindered. The low water content in these microregions might limit MP degradation due to reductions in: hydrolysis, coating of MP by e.g. dissolved organic substances, and colonization by microorganisms.

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Adhesion of Colloids and Bacteria to Porous Media: A Critical Review

Reviews of Adhesion and Adhesives ◽

10.7569/raa.2019.097314 ◽

2019 ◽

Vol 7 (4) ◽

pp. 417-460 ◽

Cited By ~ 1

Author(s):

Runwei Li ◽

Changfu Wei ◽

Hefa Cheng ◽

Gang Chen

Keyword(s):

Porous Medium ◽

Porous Media ◽

Bacterial Adhesion ◽

Fate And Transport ◽

Theoretical Models ◽

Water Interface ◽

Subsurface Soil ◽

Air Water Interface ◽

Surface Physicochemical Properties ◽

The Impact

Adhesion of colloids and bacteria to various surfaces is important for a variety of environmental phenomena including microbial biofouling and contamination prevention. Under saturated conditions, both colloids and bacteria have the opportunity to attach to porous medium surfaces. Under water unsaturated conditions or in the presence of the air-water interface, besides the porous medium surfaces, colloids and bacteria can also attach to the air-water interface, including the air-water-solid threephase interface. The magnitudes of adhesion of colloids and bacteria are correlated to the interactions of the colloids and bacteria with the surfaces, which are a function of their surface physicochemical properties. In this review, adhesion theories are revisited and adhesion of colloids and bacteria to porous media and the air-water interface is discussed. The interaction forces are quantified using various theoretical models including the DLVO models and used to interpret related adhesion. The impact of surfactants on colloid and bacterial adhesion is also discussed. The review also includes the implementation of the adhesion theory in interpreting colloid and bacterial fate and transport in the subsurface soil.

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Structural Changes in French VF Treatment Wetland Porous Media during the Rest Period: An Ex Situ Study Using X-ray Tomography

Water ◽

10.3390/w13030389 ◽

2021 ◽

Vol 13 (3) ◽

pp. 389

Author(s):

German Dario Martinez-Carvajal ◽

Laurent Oxarango ◽

Jérôme Adrien ◽

Pascal Molle ◽

Nicolas Forquet

Keyword(s):

Porous Media ◽

Structural Changes ◽

Rest Period ◽

Treatment Wetlands ◽

Ex Situ ◽

Initial Value ◽

Treatment Wetland ◽

X Ray ◽

The Impact ◽

Deposit Layer

Clogging constitutes a major operational issue for treatment wetlands. The rest period is a key feature of French Vertical Flow (VF) treatment wetlands and serves to mitigate clogging. An ex-situ drying experiment was performed to mimic the rest period and record structural changes in the porous media using X-ray Computed Tomography (CT). Samples containing the deposit and gravel layers of a first stage French VF treatment wetland were extracted and left to dry in a control environment. Based on CT scans, three phases were identified (voids, biosolids, and gravels). The impact of the rest period was assessed by means of different pore-scale variables. Ultimately, the volume of biosolids had reduced to 58% of its initial value, the deposit layer thickness dropped to 68% of its initial value, and the void/biosolid specific surface area ratio increased from a minimum value of 1.1 to a maximum of 4.2. Cracks greater than 3 mm developed at the uppermost part of the deposit layer, while, in the gravel layer, the rise in void volume corresponds to pores smaller than 2 mm in diameter. Lastly, the air-filled microporosity is estimated to have increased by 0.11 v/v.

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X-ray Scattering Studies of Mixed Monolayers of Tetrakis(3,5-di-tert-butylphenyl)porphinatocopper(II) with Cadmium Arachidate at the Air/Water Interface

Langmuir ◽

10.1021/la000209q ◽

2000 ◽

Vol 16 (17) ◽

pp. 7051-7055 ◽

Cited By ~ 4

Author(s):

Jian Bang Peng ◽

Gwen A. Lawrie ◽

Geoffrey T. Barnes ◽

Ian R. Gentle ◽

Garry J. Foran ◽

...

Keyword(s):

Water Interface ◽

Mixed Monolayers ◽

X Ray ◽

X Ray Scattering ◽

Air Water Interface ◽

Ray Scattering

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Chitosan-Behenic Acid Monolayer Interaction at the Air-Water Interface: Characterization of the Adsorbed Polymer Layers by X-Ray Reflectivity

International Journal of Polymer Analysis and Characterization ◽

10.1080/1023666x.2011.628780 ◽

2012 ◽

Vol 17 (1) ◽

pp. 11-20 ◽

Cited By ~ 8

Author(s):

Roberto Nervo ◽

Oleg Konovalov ◽

Marguerite Rinaudo

Keyword(s):

Behenic Acid ◽

Water Interface ◽

X Ray ◽

Polymer Layers ◽

Interface Characterization ◽

Adsorbed Polymer ◽

Air Water Interface

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Inorganic mixed phase templated by a fatty acid monolayer at the air–water interface: the Mn and Mg case

Physical Chemistry Chemical Physics ◽

10.1039/c8cp00308d ◽

2018 ◽

Vol 20 (9) ◽

pp. 6629-6637 ◽

Cited By ~ 1

Author(s):

Alae El Haitami ◽

Michel Goldmann ◽

Philippe Fontaine ◽

Marie-Claude Fauré ◽

Sophie Cantin

Keyword(s):

Grazing Incidence ◽

Water Interface ◽

X Ray Diffraction ◽

Inorganic Layer ◽

X Ray ◽

First Order ◽

First Order Phase Transition ◽

Air Water Interface ◽

First Order Phase

A first-order phase transition with a peculiar feature is evidenced by means of in situ grazing incidence X-ray diffraction in the 2D organic phase-mediated nucleation of an inorganic layer.

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Using X-ray radiography to image rapid water infiltration into soil

10.5194/egusphere-egu21-9479 ◽

2021 ◽

Author(s):

John Koestel ◽

Lorenzo Garbari ◽

Daniel Iseskog

Keyword(s):

Preferential Flow ◽

Sandy Loam ◽

Initial Moisture Content ◽

Image Data ◽

Water Repellency ◽

Water Infiltration ◽

Image Correction ◽

X Ray ◽

X Ray Scattering ◽

Ray Scattering

While the basic processes of water infiltration into soil are well understood, their details are difficult to quantify due to the opaque nature of soil. In this study, we investigated the potential and limitations of X-ray radiography to measure the water front progression in a narrow sample (15 &#215; 15 &#215; 1 cm) filled with dry soil under simulated rainfall of high intensity (53 mm/h). The temporal resolution of the acquired infiltration movies was 133 milliseconds. We evaluated three different kinds of soil samples. i) Bare samples filled with a 1:1 mixture of a sandy loam and peat. ii) The same soil-peat mixture, but cropped with Trifolium incarnatum, Trifolium repens, Lathyrus odoratus and Lupinus regalis, all of them plants that have been reported to induce water repellency; prior to the experiments, the plants were harvested and only the roots remained in place. iii) Sandy loam soil that had been incubated for four weeks in an outside garden plot. Due to time limitations of the project, the incubation period was in early spring, which meant that plant growth in the samples was negligible. All three sample types were replicated five times, resulting in 15 individual samples. We carried out the infiltration experiments in four-fold replications, from which it follows that we collected 60 individual infiltration movies. After each infiltration round, the samples were placed in a drying room to reset them to a similar initial moisture content. The experiments aimed at testing i) whether the infiltration patterns of the four consecutive infiltration runs conducted on each sample remained identical and ii) to document differences in infiltration patterns between bare, cropped and incubated samples. We found that increasing X-ray scattering with increasing soil water contents made it challenging to evaluate the image data quantitatively. Advantages of our setup are that X-ray captures the complete water content at a specific depth and that sample boxes with irregularly shaped walls can be used to prevent preferential flow along the walls. Preliminary analyses of the data showed that the infiltration fronts in the bare and the incubated samples were less uniform than the ones for the cropped samples. In contrast, the likelihood of observing the same infiltration pattern in all four consecutive infiltration runs was larger for the bare and the incubated samples. The latter fact may have been caused by the interaction with root exudates in the cropped samples that may have been redistributed or mineralized during the wetting-drying cycles. We conclude that the here presented setup has large potential to investigate unstable infiltration phenomena into soil after an image correction approach has been developed that removes X-ray scattering artifacts. Alternatively, scattering may be suppressed by using a collimator during image acquisition.

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