Nanoscale Abrasive Wear of Polyethylene: A Novel Approach To Probe Nanoplastic Release at the Single Asperity Level.

There is a growing concern that nanoplastic pollution may pose planetary threats to human and ecosystem health. However, a quantitative and mechanistic understanding of nanoplastic release via nanoscale mechanical degradation of bulk plastics and its interplay with photoweathering remains elusive. We developed a lateral force microscope (LFM)-based nanoscratch method to investigate mechanisms of nanoscale abrasive wear of low-density polyethylene (LDPE) surfaces by a single sand particle (simulated by a 300 nm tip) under environmentally relevant load, sliding motion, and sand size. For virgin LDPE, we found plowing as the dominant wear mechanism (i.e., deformed material pushed around the perimeter of scratch). After UVA-weathering, the wear mechanism of LDPE distinctively shifted to cutting wear (i.e., deformed material detached and pushed to the end of scratch). The shift in the mechanism was quantitatively described by a new parameter, which can be incorporated into calculating the NP release rate. We determined a 10-fold higher wear rate due to UV weathering. We also observed an unexpected resistance to initiate wear for UV-aged LDPE, likely due to nanohardness increase induced by UV. For the first time, we report 0.4-4 × 10-3 µm3/µm sliding distance/µN applied load as an initial approximate nanoplastic release rate for LDPE. Our novel findings reveal nanoplastic release mechanisms in the environment, enabling physics-based prediction of the global environmental inventory of nanoplastics.

Deciphering polymer degradation chemistry via integrating new database construction into suspect screening analysis.

Water-soluble synthetic polymers and their environmental degradation products are overlooked but important industrial pollutants in wastewater. However, the detection of degradation products is limited to bulk solution chemistry and molecular-level analysis remains unreachable. In this work, we assessed the feasibility of current suspect screening and nontarget workflow using liquid chromatography-high resolution mass spectrometry (LC-HRMS) to elucidate molecular level information about polyacrylamide (PAM) and its degraded products by free radicals. Radical chain scission of PAM (10 kDa) using heat-activated persulfate was conducted to simulate hydraulic fracturing conditions in the deep subsurface. We found that the current workflows in the commercial software generated predicted formulae with low accuracy, due to limited capability of peak picking and formula prediction for high mass and charge features. By modeling literature-reported degradation pathways, we constructed a degradation product database of over 463 000 unique formulae, which improved the accuracy of the predicted formula. For the matched features, the ratio of aldehyde/ketone terminating molecule abundance was found to increase over 24 h degradation time, suggesting increasing content of aldehydes by radical-induced oxidative chain scission of PAM. This is contradictory to previously proposed ratios of carbon-centered radical position on polymer backbone initiated by hydroxyl radicals. Using in silico fragmentation of MS1 features, we identified 11 structures with confidence levels 2b and 3 using their MS2 information. This is the first attempt to resolve complex polymer degradation chemistry using HRMS that can advance our ability to detect water-soluble polymer pollutants and their transformation products in environmental samples.

Exploring additives beyond phthalates: Release from plastic mulching films, biodegradation and occurrence in agricultural soils.

It is widely recognized that applications of plastic films result in plastic pollution in agroecosystems. However, there is limited knowledge on the release and occurrence of additives beyond phthalates in agricultural soil. In this study, the rates of release and biodegradation of various additives, including phthalates, bisphenols, organophosphate esters, phenolic antioxidants, and ultraviolet absorbents from mulching films in soil were quantified by laboratory incubation. The rates of release and biodegradation ranged from 0.069 d-1 to 5.893 d-1 and from 1.43 × 10-3 d-1 to 0.600 d-1, respectively. Both of these rates were affected by temperature, flooding, and the properties of additives, films, and soils. An estimated 4000 metric tons of these additives were released into soil annually in China exclusively. The total concentrations of these additives in 80 agricultural soils varied between 228 and 3455 µg kg-1, with phenolic antioxidants, phthalates, and bisphenols accounting for 54.1%, 25.2%, and 17.9% of the total concentrations, respectively. A preliminary risk assessment suggested that the current levels of these additives could potentially present moderate hazards to the soil ecosystem.

Groundwaters in Northeastern Pennsylvania near intense hydraulic fracturing activities exhibit few organic chemical impacts.

Horizontal drilling with hydraulic fracturing (HDHF) relies on the use of anthropogenic organic chemicals in proximity to residential areas, raising concern for groundwater contamination. Here, we extensively characterized organic contaminants in 94 domestic groundwater sites in Northeastern Pennsylvania after ten years of activity in the region. All analyzed volatile and semi-volatile compounds were below recommended United States Environmental Protection Agency maximum contaminant levels, and integrated concentrations across two volatility ranges, gasoline range organic compounds (GRO) and diesel range organic compounds (DRO), were low (0.13 ± 0.06 to 2.2 ± 0.7 ppb and 5.2-101.6 ppb, respectively). Following dozens of correlation analyses with distance-to-well metrics and inter-chemical indicator correlations, no statistically significant correlations were found except: (1) GRO levels were higher within 2 km of violations and (2) correlation between DRO and a few inorganic species (e.g., Ba and Sr) and methane. The correlation of DRO with inorganic species suggests a potential high salinity source, whereas elevated GRO may result from nearby safety violations. Highest-concentration DRO samples contained bis-2-ethylhexyl phthalate and N,N-dimethyltetradecylamine. Nevertheless, the overall low rate of contamination for the analytes could be explained by a spatially-resolved hydrogeologic model, where estimated transport distances from gas wells over the relevant timeframes were short relative to the distance to the nearest groundwater wells. Together, the observations and modeled results suggest a low probability of systematic groundwater organic contamination in the region.

Assessing Unconventional Oil and Gas Exposure in the Appalachian Basin: Comparison of Exposure Surrogates and Residential Drinking Water Measurements.

Health studies report associations between metrics of residential proximity to unconventional oil and gas (UOG) development and adverse health endpoints. We investigated whether exposure through household groundwater is captured by existing metrics and a newly developed metric incorporating groundwater flow paths. We compared metrics with detection frequencies/concentrations of 64 organic and inorganic UOG-related chemicals/groups in residential groundwater from 255 homes (Pennsylvania n = 94 and Ohio n = 161). Twenty-seven chemicals were detected in ≥20% of water samples at concentrations generally below U.S. Environmental Protection Agency standards. In Pennsylvania, two organic chemicals/groups had reduced odds of detection with increasing distance to the nearest well: 1,2-dichloroethene and benzene (Odds Ratio [OR]: 0.46, 95% confidence interval [CI]: 0.23-0.93) and m- and p-xylene (OR: 0.28, 95% CI: 0.10-0.80); results were consistent across metrics. In Ohio, the odds of detecting toluene increased with increasing distance to the nearest well (OR: 1.48, 95% CI: 1.12-1.95), also consistent across metrics. Correlations between inorganic chemicals and metrics were limited (all |ρ| ≤ 0.28). Limited associations between metrics and chemicals may indicate that UOG-related water contamination occurs rarely/episodically, more complex metrics may be needed to capture drinking water exposure, and/or spatial metrics in health studies may better reflect exposure to other stressors.

Groundwater Methane in Northeastern Pennsylvania Attributable to Thermogenic Sources and Hydrogeomorphologic Migration Pathways.

Conflicting evidence exists as to whether or not unconventional oil and gas (UOG) development has enhanced methane transport into groundwater aquifers over the past 15 years. In this study, recent groundwater samples were collected from 90 domestic wells and 4 springs in Northeastern Pennsylvania located above the Marcellus Shale after more than a decade of UOG development. No statistically significant correlations were observed between the groundwater methane level and various UOG geospatial metrics, including proximity to UOG wells and well violations, as well as the number of UOG wells and violations within particular radii. The δ13C and methane-to-higher chain hydrocarbon signatures suggested that the elevated methane levels were not attributable to UOG development nor could they be explained by using simple biogenic-thermogenic end-member mixing models. Instead, groundwater methane levels were significantly correlated with geochemical water type and topographical location. Comparing a subset of contemporary methane measurements to their co-located pre-drilling records (n = 64 at 49 distinct locations) did not indicate systematic increases in methane concentration but did reveal several cases of elevated concentration (n = 12) across a spectrum of topographies. Multiple lines of evidence suggested that the high-concentration groundwater methane could have originated from shallow thermogenic methane that migrated upward into groundwater aquifers with Appalachian Basin brine.

Publisher Correction: Cleavable comonomers enable degradable, recyclable thermoset plastics.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Cleavable comonomers enable degradable, recyclable thermoset plastics.

Thermosets-polymeric materials that adopt a permanent shape upon curing-have a key role in the modern plastics and rubber industries, comprising about 20 per cent of polymeric materials manufactured today, with a worldwide annual production of about 65 million tons1,2. The high density of crosslinks that gives thermosets their useful properties (for example, chemical and thermal resistance and tensile strength) comes at the expense of degradability and recyclability. Here, using the industrial thermoset polydicyclopentadiene as a model system, we show that when a small number of cleavable bonds are selectively installed within the strands of thermosets using a comonomer additive in otherwise traditional curing workflows, the resulting materials can display the same mechanical properties as the native material, but they can undergo triggered, mild degradation to yield soluble, recyclable products of controlled size and functionality. By contrast, installation of cleavable crosslinks, even at much higher loadings, does not produce degradable materials. These findings reveal that optimization of the cleavable bond location can be used as a design principle to achieve controlled thermoset degradation. Moreover, we introduce a class of recyclable thermosets poised for rapid deployment.

Detection and removal of biologically active organic micropollutants from hospital wastewater.

The presence of contaminants of emerging concern (CECs), such as antibiotics, antimicrobial disinfectants, nonprescription drugs, personal care products, pharmaceuticals, and steroids, in water resources can impact aquatic and human health. A large portion of the CECs entering regional wastewater treatment plants originate from hospitals. The purposes of this study were to conduct exploratory analytical work to characterize two hospital wastewaters and to evaluate treatment of CECs at hospitals before dilution with domestic wastewater. A 24-h batch reaction with biogenic manganese oxides coated onto coir fiber was used to treat the wastewaters. Organic contaminants in the wastewaters were concentrated by both liquid-liquid extraction (LLE) and solid-phase extraction (SPE). LLE extracts were analyzed by Comprehensive Two-Dimensional Gas Chromatography/Time-of-Flight Mass Spectrometry (GC × GC-TOFMS) while SPE extracts were analyzedby UltraHigh Performance Liquid Chromatography/Time-of-Flight Mass Spectrometry (UHPLC-TOFMS). Fifty-two organic micropollutants were detected (26 by GC × GC-TOFMS, 25 by UHPLC-TOFMS, 1 by both) in the wastewaters, while 29 were removed by >90% and six were degraded by <50% after treatment. Control experiments revealed that sorption to coir fiber and oxidation by manganese oxides were the primary contaminant removal mechanisms. Both the LLE and SPE extracts were used to evaluate potential human toxicity of the hospital wastewaters before and after treatment. Twenty-eight human cell-based bioreceptor assays were used to screen the wastewaters, and secondary tests were run to quantify toxicity equivalents to activated receptors. The wastewaters initially contained organic micropollutants that strongly activated the Androgen Receptor, Estrogen Receptor ß, and the Mineralocorticoid Receptor but no bioactive compounds were detected after treatment. Point-of-entry treatment of hospital wastewater should reduce bioactive compounds from entering the environment.

7 Log Virus Removal in a Simple Functionalized Sand Filter.

Viral contamination of drinking water due to fecal contamination is difficult to detect and treat effectively, leading to frequent outbreaks worldwide. The purpose of this paper is to report on the molecular mechanism for unprecedented high virus removal from a practical sand filter. Sand filters functionalized using a water extract of Moringa oleifera (MO) seeds, functionalized sand (f-sand) filters, achieved a ∼7 log10 virus removal. These tests were conducted with MS2 bacteriophage, a recognized surrogate for pathogenic norovirus and rotavirus. We studied the molecular mechanism of this high removal since it can have important implications for sand filtration, the most common water treatment technology worldwide. Our data reveal that the virus removal activity of f-sand is due to the presence of a chitin-binding protein, M. oleifera chitin-binding protein (MoCBP) on f-sand. Standard column experiments were supported by proteomic analysis and molecular docking simulations. Our simulations show that MoCBP binds preferentially to MS2 capsid proteins demonstrating that specific molecular interactions are responsible for enhanced virus removal. In addition, we simplified the process of making f-sand and evinced how it could be regenerated using saline water. At present, no definitive solution exists for the challenge of treating fecally contaminated drinking and irrigation water for viruses without using technologies that demand high energy or chemical consumption. We propose functionalized sand (f-sand) filters as a highly effective, energy-efficient, and practical technology for virus removal applicable to both developing and developed countries.

Chemical Degradation of Polyacrylamide during Hydraulic Fracturing.

Polyacrylamide (PAM) based friction reducers are a primary ingredient of slickwater hydraulic fracturing fluids. Little is known regarding the fate of these polymers under downhole conditions, which could have important environmental impacts including decisions on strategies for reuse or treatment of flowback water. The objective of this study was to evaluate the chemical degradation of high molecular weight PAM, including the effects of shale, oxygen, temperature, pressure, and salinity. Data were obtained with a slickwater fracturing fluid exposed to both a shale sample collected from a Marcellus outcrop and to Marcellus core samples at high pressures/temperatures (HPT) simulating downhole conditions. Based on size exclusion chromatography analyses, the peak molecular weight of the PAM was reduced by 2 orders of magnitude, from roughly 10 MDa to 200 kDa under typical HPT fracturing conditions. The rate of degradation was independent of pressure and salinity but increased significantly at high temperatures and in the presence of oxygen dissolved in fracturing fluids. Results were consistent with a free radical chain scission mechanism, supported by measurements of sub-µM hydroxyl radical concentrations. The shale sample adsorbed some PAM (∼30%), but importantly it catalyzed the chemical degradation of PAM, likely due to dissolution of Fe2+ at low pH. These results provide the first evidence of radical-induced degradation of PAM under HPT hydraulic fracturing conditions without additional oxidative breaker.

Fouling of microfiltration membranes by flowback and produced waters from the Marcellus shale gas play.

There is growing interest in possible options for treatment or reuse of flowback and produced waters from natural gas processing. Here we investigated the fouling characteristics during microfiltration of different flowback and produced waters from hydraulic fracturing sites in the Marcellus shale. All samples caused severe and highly variable fouling, although there was no direct correlation between the fouling rate and total suspended solids, turbidity, or total organic carbon. Furthermore, the fouling of water after prefiltration through a 0.2 µm membrane was also highly variable. Low fouling seen with prefiltered water was mainly due to removal of submicron particles 0.4-0.8 µm during prefiltration. High fouling seen with prefiltered water was mainly caused by a combination of hydrophobic organics and colloidal particles <100 nm in size (quantified by transmission electron microscopy) that passed through the prefiltration membranes. The small colloidal particles were highly stable, likely due to the surfactants and other organics present in the fracking fluids. The colloid concentration was as high as 10(11) colloids/ml, which is more than 100 times greater than that in typical seawater. Furthermore, these colloids were only partially removed by MF, causing substantial fouling during a subsequent ultrafiltration. These results clearly show the importance of organics and colloidal material in membrane fouling caused by flowback and produced waters, which is of critical importance in the development of more sustainable treatment strategies in natural gas processing.