Defining the Chemical Additives Driving In Vitro Toxicities of Plastics.

Increases in the global use of plastics have caused concerns regarding potential adverse effects on human health. Plastic products contain hundreds of potentially toxic chemical additives, yet the exact chemicals which drive toxicity currently remain unknown. In this study, we employed nontargeted analysis and in vitro bioassays to identify the toxicity drivers in plastics. A total of 56 chemical additives were tentatively identified in five commonly used plastic polymer pellets (i.e., PP, LDPE, HDPE, PET, and PVC) by employing suspect screening and nontargeted analysis. Phthalates and organophosphates were found to be dominant in PVC pellets. Triphenyl phosphate and 2-ethylhexyl diphenyl phosphate accounted for a high amount (53.6%) of the inhibition effect of PVC pellet extract on human carboxylesterase 1 (hCES1) activity. Inspired by the high abundances of chemical additives in PVC pellets, six different end-user PVC-based products including three widely used PVC water pipes were further examined. Among them, extracts of PVC pipe exerted the strongest PPARγ activity and cell viability suppression. Organotins were identified as the primary drivers to these in vitro toxicities induced by the PVC pipe extracts. This study clearly delineates specific chemical additives responsible for hCES1 inhibition, PPARγ activity, and cell viability suppression associated with plastic.

Assessment of Biofilm Growth on Microplastics in Freshwaters Using a Passive Flow-Through System.

Biofilms that colonize on the surface of microplastics (MPs) in freshwaters may pose a potential health risk. This study examined factors that influence MP-associated biofilm growth, including polymer type, degree of weathering, and source water quality. Weathered MPs produced in-lab were employed in biofilm trials conducted on site using a passive flow-through system with raw water at drinking water treatment facility intakes. Adenosine triphosphate (ATP) was used to quantify biofilm abundance; biofilm composition was assessed via metagenomic sequencing. Biofilm growth was observed on all polymer types examined and most prevalent on polyvinyl chloride (PVC), where ATP levels were 6 to 12 times higher when compared to other polymers. Pathogen-containing species including Salmonella enterica and Escherichia coli were present on all polymers with relative abundance up to 13.7%. S. enterica was selectively enriched on weathered MPs in specific water matrices. These findings support the need to research the potential accumulation of pathogenic organisms on microplastic surfaces.

Microplastic Removal from Drinking Water Using Point-of-Use Devices.

The occurrence of microplastics in drinking water has drawn increasing attention due to their ubiquity and unresolved implications regarding human health. Despite achieving high reduction efficiencies (70 to >90%) at conventional drinking water treatment plants (DWTPs), microplastics remain. Since human consumption represents a small portion of typical household water use, point-of-use (POU) water treatment devices may provide the additional removal of microplastics (MPs) prior to consumption. The primary objective of this study was to evaluate the performance of commonly used pour-through POU devices, including those that utilize combinations of granular activated carbon (GAC), ion exchange (IX), and microfiltration (MF), with respect to MP removal. Treated drinking water was spiked with polyethylene terephthalate (PET) and polyvinyl chloride (PVC) fragments, along with nylon fibers representing a range of particle sizes (30-1000 µm) at concentrations of 36-64 particles/L. Samples were collected from each POU device following 25, 50, 75, 100 and 125% increases in the manufacturer's rated treatment capacity, and subsequently analyzed via microscopy to determine their removal efficiency. Two POU devices that incorporate MF technologies exhibited 78-86% and 94-100% removal values for PVC and PET fragments, respectively, whereas one device that only incorporates GAC and IX resulted in a greater number of particles in its effluent when compared to the influent. When comparing the two devices that incorporate membranes, the device with the smaller nominal pore size (0.2 µm vs. ≥1 µm) exhibited the best performance. These findings suggest that POU devices that incorporate physical treatment barriers, including membrane filtration, may be optimal for MP removal (if desired) from drinking water.

Assessment of microplastic sampling and extraction methods for drinking waters.

To date, no standardized methods have been proposed for conducting microplastic analyses in treated drinking waters, resulting in challenges associated with direct comparisons among studies. This study compares known methods for collecting and extracting microplastics from drinking waters: an in-laboratory (in-lab) filtration method and an in-line filtration method (i.e., water filtered on-site without an intermediate storage and/or transportation step). In-lab methods have been the predominant method for sample collection in drinking water matrices, and in-line methods are emerging due to the potential to sample large volumes of water on site and minimize contamination from airborne particles, but the two methods have yet to be directly compared using real samples. In response, this study evaluates both methods in terms of recovering spiked reference microplastics, collecting microplastics from tap water samples using the same water volume, and quantifying the removal of microplastics through a full-scale ultrafiltration system. In-line filtration was shown to have higher recoveries for all the reference microplastics examined (+37 % for PVC fragments, +23 % for PET fragments, +22 % for nylon fibers and +7 % for PET fibers) and a greater potential to reduce microplastic contamination. It also resulted in lower standard deviations for total microplastic counts in the tap water and UF influent and effluent samples. The filtration capacity of the proposed in-line filtration method could exceed 350 L of treated water, but this is highly dependent on the water quality. This study therefore supports the use of in-line filtration methods towards the standardization of microplastic collection procedures in drinking water.

Adsorption of fluoranthene and phenanthrene by virgin and weathered polyethylene microplastics in freshwaters.

Concern exists regarding potential health impacts associated with contaminants of emerging concern (CECs) that adsorb to microplastics (MPs). Previous studies have examined MPs as potential contaminant vectors in marine environments as opposed to freshwaters that represent drinking water sources. This study examined adsorption of two polycyclic aromatic hydrocarbons (PAHs), phenanthrene and fluoranthene, by virgin and weathered polyethylene (PE) in both artificial and natural freshwater matrices. Adsorption kinetics and isotherms conducted in artificial freshwater (AFW) consistently showed higher adsorption onto smaller (200 µm) PE when compared to 1090 µm PE. Adsorption mechanisms were primarily associated with hydrophobic interactions and monolayer chemisorption. As well, environmental factors including dissolved organic matter (DOC), pH, and polymer weathering also impacted adsorption. This work provides new insights regarding the adsorption of organic pollutants to better understand the risk of MPs in drinking water sources.

Conventional and biological treatment for the removal of microplastics from drinking water.

This study examines the removal of microplastics and other anthropogenic particles (>10 µm) from surface water by a full-scale conventional drinking water treatment plant. The treatment process is composed of coagulation with aluminum hydroxide, flocculation, anthracite-sand filtration, and chlorination. Samples were also collected from pilot-scale biological filters consisting of anthracite-sand or granular activated carbon (GAC) media operated with or without pre-ozonation and at a range of different empty-bed contact times (EBCTs). Particles in 10 L water samples collected in duplicate using a fully enclosed sampling apparatus were separated using sieves with 500 µm, 300 µm, 125 µm, and 45 µm openings followed by filtration through 10 µm polycarbonate filters. Particles were counted using stereomicroscopy and characterized using µ-Raman spectroscopy. Full-scale conventional treatment removed 52 % of anthropogenic particles when comparing raw (42 ± 18 particles/L) and finished water (20 ± 8 particles/L). Coagulation, flocculation, and sedimentation accounted for the highest removal (70 %) of any individual unit process. Overall removal was reduced to 52 %, the difference being attributed to airborne particle deposition that occurred while water was detained in a clearwell (exposed to atmosphere via ventilation) that was used to achieve the required contact time for disinfection. The majority of the particles (>80 %) were identified as fibers 10-45 µm; microplastics were predominantly composed of polyester while the non-plastic anthropogenic particles were primarily cellulose. None of the pilot filter configurations examined resulted in significantly fewer microplastics when compared to full-scale conventional filtration. This study illustrates that the removal efficiency of conventional treatment may be limited when considering microfibers <45 µm in size.

Evaluation of enzyme activity for monitoring biofiltration performance in drinking water treatment.

Many water providers monitor adenosine triphosphate (ATP) as an indicator of biological acclimation of their biofilters; however, strong correlations between ATP concentration and filter performance (e.g., organic matter or disinfection by-product precursor removal) are not typically observed. As an alternative, this study evaluated the use of enzyme activity for monitoring biological processes within filters. Recent studies have proposed that enzyme activity may be used as an indicator of biofilter function as it provides a means to quantify biodegradation which may allow for a more accurate measure of degradation potential and to gain a better understanding of biofilter performance. Sampling was completed from full- and pilot-scale biofilters to assess impacts associated with pre-treatments, varying sources waters, as well as pre-treatment and operating conditions. Enzyme activity (carboxylic esterase, phosphatase, ß-glucosidase, α-glucosidase, ß-xylosidase, chitinase, and cellulase) and ATP were measured from the top 5 cm of biofilter media representative of typical full-scale sampling; water quality parameters included dissolved organic carbon (DOC) and disinfection by-products (DBPs): trihalomethane (THM) formation potential (FP), and haloacetic acid FP (HAA FP). Results confirmed that ATP was not a reliable monitoring tool for DOC and DBP FP reduction in biofilters. A strong relationship was observed between esterase activity and DOC reduction; chitinase activity significantly correlated to THM FP reduction for filters treating three different source waters and HAA FP reduction achieved by filters treating the same source water with a range of pre-treatment and backwash conditions. This study showed that enzyme activity may be appropriate for monitoring biological processes within drinking water filters and may act as a surrogate for the removal of organic compounds.

Effective enzyme activity: A proposed monitoring methodology for biofiltration systems with or without ozone.

"Effective Enzyme Activity", or simply "Effective Activity", is proposed as a biofiltration monitoring tool which combines enzyme activity with empty bed contact time (EBCT) to quantify biodegradation potential. The primary objective of this study was to evaluate the applicability of the Effective Activity concept for predicting water quality in biofiltration systems. This pilot-scale study evaluated eight different biofilter configurations in order to quantify impacts associated with filter media (anthracite/sand or granular activated carbon), pre-treatment (settled water with or without ozonation) and operating conditions (15- and 30-min EBCT, and backwash with or without chlorine). Microbial characterization included biomass concentration, as measured by adenosine triphosphate (ATP), in addition to esterase and phosphatase activity. Water quality parameters included dissolved organic carbon (DOC), trihalomethane (THM) formation potential (FP), haloacetic acid (HAA) FP, haloacetonitrile (HAN) FP, iodinated DBP FP (THMs and HAAs) and inorganic nutrients (phosphorus and nitrogen). Results confirmed the benefits to treated water quality associated with the application of an ozone residual of 0.5 mg/L, utilization of GAC filter media, eliminating chlorinated backwash, and extending EBCT. This study demonstrated a good relationship between effective esterase activity and reductions in DOC and THM FP, including those systems which incorporate pre-ozonation. As such, this study showed that Effective Activity may be appropriate for relating biomass characterization to treated water quality and highlights the importance of quantifying biomass activity in addition to quantity.

Pilot-scale comparison of cyclically and continuously operated drinking water biofilters: Evaluation of biomass, biological activity and treated water quality.

The objective of this pilot study was to evaluate the impact of cyclical (operated 8-12 h per day) and continuous biofilter operation with respect to biomass development, biological enzyme activity and treated water quality (in terms of organics, nutrients and disinfection by-product (DBP) formation potential). Continuously operated biofilters developed greater densities of biomass, as measured by ATP, when compared to cyclically operated filters; reducing the empty bed contact time (EBCT) increased biomass density under continuous flow conditions. However, once normalized to biomass, it was shown that cyclically operated filters exhibited higher enzyme activity, indicating that this method of operation may improve bacterial function. Reduction of organics was generally similar for both continuous and cyclical filters with the same EBCT, however, cyclical filters demonstrated higher variability during the first 4 h following start-up. Overall, HAA formation potential was better controlled by continuously operated filters, due to poor performance by the cyclical filters upon start-up while THM precursors were removed equally well by all filters. To understand the removal capacity for NDMA precursors through biological filters, both naturally occurring NDMA FP and NDMA FP resulting from spiked anthropogenic precursors was monitored through the filter depth. All the filters removed 90% of the naturally occurring NDMA FP within the first 45 cm; cyclical operation resulted in higher reduction of spiked anthropogenic NDMA precursors (50% higher than continuously operated) demonstrating the advantage of routine shut down on overall microbial activity. Tools to monitor and predict biofilter performance are in high demand. Here we present an "effective activity" term which combines enzyme activity with contact time (EBCT). Effective esterase activity was strongly correlated to DOC reduction as a function of filter operation (cyclical or continuous) and EBCT; effective phosphatase activity was indicative of phosphate removal. The results of this study indicate that routine shut down of the filters as this location improved enzyme activity without compromising control of chlorinated DBPs (THMs and HAAs) or NDMA derived from natural and anthropogenic precursors.

Biofilter scaling procedures for organics removal: A potential alternative to piloting.

To provide information for the design and improvement of full-scale biofilters, pilot-scale biofiltration studies are the current industry standard because they utilize the same filter media size and loading rate as the full-scale biofilters. In the current study, bench-scale biofilters were designed according to a biofilter scaling model from the literature, and the ability of the bench-scale biofilters to accurately represent the organics removal of pilot-scale biofilters was tested. To ensure similarity in effluent water quality between bench- and pilot- or full-scale biofilters at the same influent substrate concentration, the tested model requires that either mass transport resistance or biofilm shear loss takes primacy over the other. The potential primacy of mass transport resistance or biofilm shear loss was evaluated via water quality testing (dissolved organic carbon, specific ultraviolet absorbance, liquid chromatography - organic carbon detection, trihalomethane formation potential, and haloacetic acid formation potential). The biofilters also were characterized for adenosine triphosphate (ATP) content, enzyme activity, extracellular polymeric substances, and microbial community structure. The results of this study indicate that biofilm shear loss takes primacy over mass transport resistance for bench-scale biofilter design in this system; thus, bench-scale biofilters designed in this manner accurately represent organics removal in pilot-scale biofilters. Applying this scaling procedure can reduce filter media requirements from many kilograms to just a few grams and daily water requirements from thousands of liters to less than 10 L. This scaling procedure will allow future researchers to test alternative treatment designs and operating conditions without the need for expensive pilot-scale studies.

Conventional drinking water treatment and direct biofiltration for the removal of pharmaceuticals and artificial sweeteners: A pilot-scale approach.

The presence of endocrine disrupting compounds (EDCs), pharmaceutically active compounds (PhACs) and artificial sweeteners are of concern to water providers because they may be incompletely removed by wastewater treatment processes and they pose an unknown risk to consumers due to long-term consumption of low concentrations of these compounds. This study utilized pilot-scale conventional and biological drinking water treatment processes to assess the removal of nine PhACs and EDCs, and two artificial sweeteners. Conventional treatment (coagulation, flocculation, settling, non-biological dual-media filtration) was compared to biofilters with or without the addition of in-line coagulant (0.2-0.8 mg Al(3+)/L; alum or PACl). A combination of biofiltration, with or without in-line alum, and conventional filtration was able to reduce 7 of the 9 PhACs and EDCs by more than 50% from river water while artificial sweeteners were inconsistently removed by conventional treatment or biofiltration. Increasing doses of PACl from 0 to 0.8 mg/L resulted in average removals of PhACs, EDCs increasing from 39 to 70% and artificial sweeteners removal increasing from ~15% to ~35% in lake water. These results suggest that a combination of biological, chemical and physical treatment can be applied to effectively reduce the concentration of EDCs, PhACs, and artificial sweeteners.

Fluorescence spectroscopy for monitoring reduction of natural organic matter and halogenated furanone precursors by biofiltration.

The application of fluorescence spectroscopy to monitor natural organic matter (NOM) reduction as a function of biofiltration performance was investigated. This study was conducted at pilot-scale where a conventional media filter was compared to six biofilters employing varying enhancement strategies. Overall reductions of NOM were identified by measuring dissolved organic carbon (DOC), and UV absorbance at 254 nm, as well as characterization of organic sub-fractions by liquid chromatography-organic carbon detection (LC-OCD) and parallel factors analysis (PARAFAC) of fluorescence excitation-emission matrices (FEEM). The biofilter using granular activated carbon media, with exhausted absorptive capacity, was found to provide the highest removal of all identified PARAFAC components. A microbial or processed humic-like component was found to be most amenable to biodegradation by biofilters and removal by conventional treatment. One refractory humic-like component, detectable only by FEEM-PARAFAC, was not well removed by biofiltration or conventional treatment. All biofilters removed protein-like material to a high degree relative to conventional treatment. The formation potential of two halogenated furanones, 3-chloro-4(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA), as well as overall treated water genotoxicity are also reported. Using the organic characterization results possible halogenated furanone and genotoxicity precursors are identified. Comparison of FEEM-PARAFAC and LC-OCD results revealed polysaccharides as potential MX/MCA precursors.

Engineered biofiltration for the removal of disinfection by-product precursors and genotoxicity.

Disinfection by-products (DBPs) are formed when naturally occurring organic matter reacts with chlorine used in drinking water treatment, and DBPs formed in chlorinated drinking water samples have been shown to cause a genotoxic response. The objective of the current study was to further understand the principles of biofiltration and the resulting impacts on the formation of DBPs and genotoxicity. Pilot-scale systems were utilized to assess the performance of engineered biofilters enhanced with hydrogen peroxide, in-line coagulants, and nutrients when compared to passively operated biofilters and conventional treatment (coagulation, flocculation, sedimentation, non-biological filtration). Organic fractionation was completed using liquid chromatography-organic carbon detection (LC-OCD). Water samples were chlorinated after collection and examined for the removal of trihalomethane (THM), haloacetic acid (HAA), and adsorbable organic halide (AOX) precursors. Additionally, the formation potential of two halogenated furanones, 3-chloro-4(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA), and genotoxicity was determined. Biofiltration was shown to preferentially remove more DBP precursors than dissolved organic carbon (DOC). Formation potential of the unregulated DBPs, including MX and MCA, and genotoxic response was shown to be correlated to THM formation. These results infer that monitoring for THMs and HAAs provide insight to the formation of more mutagenic DBPs such as halogenated furanones, and that biofiltration may preferentially remove precursors to DBPs at a rate exceeding the removal of DOC.