Water-Soluble Synthetic Polymers: Their Environmental Emission Relevant Usage, Transport and Transformation, Persistence, and Toxicity

Acute toxicity of petroleum asphalt seal coat leachates to Ceriodaphnia dubia is linked to polymer preservatives

Low-VOC waterborne asphalt-emulsion (AE) seal coat is considered more sustainable than solvent-based coal-tar emulsion seal coat because asphalt emulsions contain negligible amounts of carcinogenic PAHs and release fewer harmful volatile organic compounds. Yet, many low-VOC coatings leach water-soluble substances under outdoor conditions. To investigate the chemical composition of seal coat leachates, three AE formulations were cured under natural weathering conditions and exposed to simulated runoff over a 10-day field trial. Runoff was collected and concentrated using ion-exchange solid-phase extraction (SPE) and analyzed using gas chromatography/mass spectrometry (GC-MS). Leached compounds included hydrocarbons, esters, amines, siloxanes, plasticizers, biocides, polyethylene glycol (PEG) ethers, urethanes, and toluene diisocyanate (TDI). Glycol ethers comprised 29-97 % of the measured leachate mass. Two seal coat formulations contained isothiazolinone biocides, methylchloro- and methylisothiazolinone (CMIT/MIT; 0.5 mg/L in runoff), while a third seal coat formulation continuously leached TDI, a reactive polyurethane (PU) precursor (0.7 mg/L in runoff). Biocide-containing leachates showed acute toxicity to the freshwater water flea, Ceriodaphnia dubia after 48 h, while TDI-containing leachate showed no acute toxicity, suggesting that leachate toxicity was due to in-can polymer preservatives. As biocides are implicated in impaired reproductive signaling, these results support the use of alkaline pH to avoid biofouling and reinforce the goal of reducing and/or avoiding the use of biocides altogether, especially for environmentally friendly products.

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.

Exposure of polyethylene microplastics affects sulfur migration and transformation in anaerobic system

Polyethylene (PE) microplastic, which is detected in various environmental media worldwide, also inevitably enters wastewater treatment plants, which may have an impact on anaerobic processes in wastewater treatment. In this work, the effect of PE microplastics on anaerobic sulfur transformation was explored. Experimental results showed that PE microplastics addition at 0.1%- 0.5% w/w promoted H2S production by 14.8%-27.4%. PE microplastics enhanced the release of soluble organic sulfur and inorganic sulfate, and promoted the bioprocesses of organosulfur compounds hydrolysis and sulfate reduction. Mechanism analysis showed that PE microplastics increased the content of electroactive components (e.g., protein and humic acids) contained in extracellular polymeric substances (EPS). In particular, PE microplastics increased the proportion and the dipole moment of α-helix, an important component involved in electron transfer contained in extracelluar protein, which provided more electron transfer sites and promoted the α-helix mediated electron transfer. These enhanced the direct electron transfer ability of EPSs, which might explain why PE microplastics facilitated the bioprocesses of organosulfur compounds hydrolysis and sulfate reduction. Correspondingly, metagenomic analysis revealed that PE microplastics increased the relative abundance of S2- producers (e.g., Desulfobacula and Desulfonema) and the relative abundance of functional genes involved in anaerobic sulfur transformation (e.g., PepD and cysD), which were beneficial to H2S production in anaerobic system.

Unveiling the multilevel impact of four water-soluble polymers on Daphnia magna: From proteome to behaviour (a case study)

The ubiquitous presence of water-soluble polymers (WSPs) in freshwater environments raises concerns regarding potential threats to aquatic organisms. This study investigated, for the first time, the effects of widely used WSPs -polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyethylene glycol (PEG)- using a multi-level approach in the freshwater biological model Daphnia magna. This integrated assessment employed a suite of biomarkers, evaluation of swimming behaviour, and proteomic analysis to investigate the effects of three environmentally relevant concentrations (0.001, 0.5, and 1 mg/L) of the tested WSPs from molecular to organismal levels, assessing both acute and chronic effects. Our findings reveal that exposure to different WSPs induces specific responses at each biological level, with PEG being the only WSP inducing lethal effects at 0.5 mg/L. At the physiological level, although all WSPs impacted both swimming performance and heart rate of D. magna specimens, PAA exhibited the greatest effects on the measured behavioural parameters. Furthermore, proteomic analyses demonstrated altered protein profiles following exposure to all WSPs, with PVA emerging as the most effective.

Adsorption characteristics and mechanisms of water-soluble polymers (PVP and PEG) on kaolin and montmorillonite minerals

The excessive use and accumulation of water-soluble polymers (WSPs, known as "liquid plastics") in the environment can pose potential risks to both ecosystems and human health, but the environmental fate of WSPs remains unclear. Here, the adsorption behavior of WSPs with different molecular weight on kaolinite (Kaol) and montmorillonite (Mt) were examined. The results showed that the adsorption of PEG and PVP on minerals were controlled by hydrogen bond and van der Waals force. The Fourier transform infrared (FTIR) spectra and two-dimensional correlation spectroscopy (2D-COS) analysis revealed that there were interactions between the Al-O and Si-O groups of the minerals and the polar O- or N-containing functional groups as well as the alkyl groups of PEG and PVP. The adsorption characteristics of WSPs were closely related to their molecular weight and the pore size of minerals. Due to the relatively large mesopore size of Kaol, both PEG and PVP were absorbed into inner spaces, for which the adsorption capacity increased with molecular weight of the polymers. For Mt, all types of PEG could enter its micropores, while PVP with larger molecular weights appeared to be confined externally, leading to a decrease in the adsorption capacity of PVP with increasing molecular weight. The findings of this study provide a theoretical basis for scientific evaluation of environmental processes of WSPs.

To be or not to be plastics? Protein modulation and biochemical effects in zebrafish embryos exposed to three water-soluble polymers

Water-soluble polymers (WSPs) are a particular category of polymers that, due to their capability to be soluble in water, come out of the classic definition of plastic and therefore also from its regulation and control, representing a possible new environmental problem considering the number of consumer products in which they are contained. For this reason, the aim of this study was to evaluate the possible adverse effects of three of the most used WSPs (polyacrylic acid - PAA, polyethylene glycol - PEG, polyvinylpyrrolidone - PVP), administered at relevant environmental concentrations (0.001, 0.5 and 1 mg/L) to Danio rerio (zebrafish) embryos up to 120 h post fertilization. To assess the WSP toxicity at the molecular, cellular and organism level we used an integrated ecotoxicological approach of both biomarkers and high-throughput technology based on gel-free proteomics. The main results showed how all the three WSPs up-regulated many proteins (up to 74 in specimens exposed to 1 mg/L PVP) with a wide range of molecular functions and involved in numerous cellular pathways of exposed specimens. On the other hand, the measurement of biomarkers showed how PAA and PVP were able to activate the antioxidant machinery following an over-production of reactive oxygen species, while PEG produced no significant changes in the biomarkers measured. Based on the obtained results, the use and application of WSPs should be revised and regulated.

Water-soluble polymers: Emerging contaminants detected, separated and quantified by a novel GPC/MALDI-TOF method

Water-soluble polymers (WSPs) are additives used as thickeners, stabilisers and flocculants in industry and in household products, including personal care products. Given their widespread use, it is likely WSPs enter the environment, particularly through wastewaters. This is of concern as there is little ecotoxicological research on their fate and behaviour once in the environment, which means their risk to aquatic life is not understood. The lack of suitable analytical techniques to detect, characterise and quantify WSPs hinders research on the potential impact of these polymers. A novel method has been developed that identifies polymers within a sample and separates them using gel-permeation chromatography (GPC). This is coupled with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS), to quantify the polymer fractions using molecular weight information. This process has been carried out on a range of aqueous media. Polyethylene glycol (PEG) ingredients were successfully separated from non-polymeric material in a commercial shaving gel personal care product (PCP), before being quantified at 1.62 wt%. This method was applied to a spiked wastewater influent sample to demonstrate the extraction and separation of PEG from organic constituents such as dissolved organic matter (DOM). This highlighted the additional challenges of analysing WSPs in the environment, as factors such as sorption and biodegradation affected the total recovery of PEG, with an extraction efficiency of 53%. Overall, this method was applied for the extraction of PEG from a PCP with accurate quantification, before a proof-of-concept extraction from wastewater demonstrated the difficulties associated with WSP analysis in environmental samples. This method provides opportunities to use tandem GPC/MALDI-TOF MS to quantify WSPs in a broad array of environmental samples. Additional studies could include its application to wastewater or freshwater monitoring.

The Application of an Eco-Friendly Synthetic Polymer as a Sandy Soil Stabilizer

The conducted investigation encompassed the comprehensive integration of mechanical, environmental, chemical, and microstructural evaluations of a composite amalgamating sandy soil and a synthetic polymer at two distinct concentrations (2.5% and 5%) across multiple curing intervals (0, 1, 2, 4, 7, 15, 30, and 45 days). The studied soil originates from an environmentally significant protected area in Brazil. The implementation of mechanisms for soil improvement in the region must adhere to technical criteria without causing environmental harm. Direct shear testing was conducted, permeability was assessed, and microstructure analysis and XRD and XRF/EDX studies of both the soil and composites were conducted. It was observed that longer curing times yielded improved results in shear stress, friction angle, and cohesive intercept, with SP_5% exhibiting the highest values compared with the soil and SP_2.5%. Adding the polymeric solution to the soil contributed to cementation and cohesion gains in the substrate. Through microstructural characterization, the polymer's role as a cementing agent for the grains is evident, forming a film on the grains and binding them together. Based on the analyses and studies conducted in the research, it can be concluded that there is technical feasibility for applying the polymeric solution at both dosages in geotechnical projects.

Evaluation of nuclear magnetic resonance spectroscopy for characterisation and quantitation of water-soluble polymers in river water

Water-soluble polymers (WSPs) are commonly used in industrial, commercial, agricultural and pharmaceutical products and their molecular weights and concentrations vary considerably. Methods commonly used in the analysis of WSPs are often for pure products or formulations with only a few other high MW constituents. These methods, like size exclusion chromatography (SEC) or Gel Permeation Chromatography coupled with Mass Spectrometry (MS) can be frustrated by the impact of the necessary separation steps prior to identification and the limitations of MS when identifying and quantifying polymers. To that end, the employment of a Nuclear Magnetic Resonance (NMR) method to identify, characterize and quantify WSPs in the real-world is reported for the first time. Samples were taken from fourteen UK inland river sites, concentrated via air-drying, freeze-drying or vacuum-drying and analyzed using 1D 1H NMR and 2D 1H Diffusion Ordered Spectroscopy (DOSY) NMR analysis. Seven of the river sites showed the presence of polyethylene glycol (PEG) with a range of molecular weights, evidencing the application of these techniques in analysis of WSPs. Soil percolation models evidenced the proof of principle that these techniques can also be used for the detection of polyacrylamide (PAM) and polyacrylic acid (PAA). This work should better enable the evaluation of the biological impact of WSPs on aquatic organisms in future studies.