Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.@en

Nanoplastics are detected in surface water, yet accurately quantifying their particle number concentrations remains a significant challenge. In this study, we tested the applicability of a gold-labelling method to quantify nanoplastics in natural organic matter (NOM) containing water matrices. Gelatin-coated gold nanoparticles (Au-gel NPs) form conjugates with nanoplastics via electrostatic interaction which produces peak signals which can be translated into particle number concentration using single-particle inductively coupled plasma–mass spectrometry (SP-ICP-MS). We used water samples with various NOM concentrations, with and without the addition of 1 10 ⁷ particle ^–1 nanoplastics. Our results indicate that nanoplastics in low NOM samples (,1 mg·C L ¹) could be successfully quantified. However, in high NOM samples (.15 mg·C L ¹), only 13–19% of added nanoplastics were successfully quantified. Further digestion to remove NOM yielded only 10% of spiked nanoplastics. This discrepancy in high NOM samples could likely be attributed to the competition between nanoplastics and NOM existing in the water sample to bind with Au-gel NPs. Our study highlights the suitability of the Au-gel labelling method for quantifying nanoplastics in low NOM water samples. Nevertheless, further optimization, including pre-digestion steps, is essential to apply this method for high NOM water samples effectively.

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The transport of viruses in groundwater is a complex process controlled by both hydrodynamic and reaction parameters. Characterizing the transport of viruses in groundwater is of crucial importance for investigating health risks associated with groundwater consumption from private individual or residential pumping wells. Setback distances between septic systems, which are the source of viruses, and pumping wells must be designed to offer sufficient groundwater travel times to allow the viral load to degrade sufficiently to be acceptable for community health needs. This study consists of developing numerical simulations for the reactive transport of viruses in the subsurface. These simulations are validated using published results of laboratory and field experiments on virus transport in the subsurface and applying previously developed analytical solutions. The numerical model is then exploited to investigate the sensitivity of the fate of viruses in saturated porous media to hydraulic parameters and the coefficients of kinetic reactions. This sensitivity analysis provides valuable insights into the prevailing factors governing health risks caused by contaminated water in private wells in rural residential contexts. The simulations of virus transport are converted into health risk predictions through dose–response relationships. Risk predictions for a wide range of input parameters are compared with the international regulatory health risk target of a maximum of 10−4 infections/person/year and a 30 m setback distance to identify critical subsurface contexts that should be the focus of regulators.@en

Biological ion exchange (BIEX) refers to operating ion exchange (IX) filters with infrequent regeneration to favor the microbial growth on resin surface and thereby contribute to the removal of organic matter through biodegradation. However, the extent of biodegradation on BIEX resins is still debatable due to the difficulty in discriminating between biodegradation and IX. The objective of the present study was to evaluate the performance of BIEX resins for the removal of organic micropollutants and thereby validate the occurrence of biodegradation. The removals of biodegradable micropollutants (neutral: caffeine and estradiol; negative: ibuprofen and naproxen) and nonbiodegradable micropollutants with different charges (neutral: atrazine and thiamethoxam; negative: PFOA and PFOS) were respectively monitored during batch tests with biotic and abiotic BIEX resins. Results demonstrated that biodegradation contributed to the removal of caffeine, estradiol, and ibuprofen, confirming that biodegradation occurred on the BIEX resins. Furthermore, biodegradation contributed to a lower extent to the removal of naproxen probably due to the absence of an adapted bacterial community (Biotic: 49% vs Abiotic: 38% after 24 h batch test). The removal of naproxen, PFOS, and PFOA were attributable to ion exchange with previously retained natural organic matter on BIEX resins. Nonbiodegradable and neutral micropollutants (atrazine and thiamethoxam) were minimally (6%–10%) removed during the batch tests. Overall, the present study corroborates that biomass found on BIEX resins contribute to the removal of micropollutants through biodegradation and ion exchange resins can be used as biomass support for biofiltration.

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Recurring plans for building a large crude oil pipeline in the immediate neighborhood of the Saint Lawrence River and connected watercourses raise concerns about potential threats to this drinking water source serving over 3 million Canadians. Quebec has the lowest drinking water threshold for benzene in North America (0.5 μg L ⁻¹) - a toxic hydrocarbon present in crude oil. With powdered activated carbon (PAC) being an effective benzene adsorbent several municipalities around Montréal consider its application as an emergency barrier. Their current and primary PAC application is taste and odor removal caused by 2-methylisoborneol (MIB) and geosmin. Ideally, a single PAC would be selected as a suitable barrier against all three pollutants. The adsorption of MIB/geosmin was studied on 11 PAC in 3 source waters characterized by different concentrations of low molecular weight natural organic matter - the main competitor for adsorption sites on PAC. Results show that taste and odor removal was low in water with high fractions of small competitive natural organic matter. Benzene removal was studied separately in adsorption tests with 3 selected PAC. The highest (40 to 75%) and the lowest (10 to 15%) benzene removal was achieved by the same PAC types that also performed best and worst respectively for MIB/geosmin.

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Subsequent to an oil spill, conventional physico-chemical treatment processes such as ballasted flocculation would serve as the principal barrier in drinking water treatment plants (DWTP) against contamination from toxic soluble contaminants such as benzene. Benzene is a well-known carcinogenic compound and its maximum threshold concentrations in drinking water are regulated at 5 μg/L and 0.5 μg/L in the United States and in Quebec, Canada, respectively. Our study focused on ballasted flocculation in order to determine its removal efficiency for traces of dissolved petroleum hydrocarbons originating from diesel and gasoline contamination. Results show that ballasted flocculation alone, using alum or ferric sulphate as coagulant, is not efficient for benzene reduction below regulations. Addition of an adsorbent such as powdered activated carbon (PAC) is necessary. From PAC adsorption isotherms and kinetics, we found an optimal dose of 80 mg PAC/L and contact times of 15 and 30 min for diesel and gasoline-contaminated waters, respectively. The simultaneous addition of PAC and coagulant during ballasted flocculation showed that although benzene concentration declined substantially, alum treatment could not decrease concentrations below the Canadian threshold (0.5 μg/L) while the US regulation value was met. Analysis of PAC-ballasted flocculation tests demonstrated the likelihood of PAC pore blockage in the presence of coagulants. Although PAC doses as high as 80 mg PAC/L were introduced during ballasted flocculation, settled water quality was not negatively impacted. Findings from this study will help DWTP in their effort to prepare emergency response plans for the event of an oil spill.

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While researchers have been proposing magnetic powdered activated carbon (MPAC) for more than a decade, these materials are not yet commercially available in North America (though they are in Japan). MPAC combines two important characteristics: efficient separation from water using a magnetic field and good adsorption properties for organic micropollutants. The slightly higher costs of MPAC can be offset by its separability and reusability. Easy recirculation of PAC would allow working at high enough PAC age to colonize it with heterotrophic and nitrifying bacteria. Magnetic separation of MPAC requires the use of high-gradient magnetic separators, which might limit the adsorbent's application to low-flow systems.

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