Polyamide 6 microplastics as carriers led to changes in the fate of bisphenol A and dibutyl phthalate in drinking water distribution systems: The role of adsorption and interfacial partitioning.

Microplastics (MPs) co-exist with plastic additives and other emerging pollutants in the drinking water distribution systems (DWDSs). Due to their strong adsorption capacity, MPs may influence the occurrence of additives in DWDSs. The article investigated the occurrence of typical additives bisphenol A (BPA) and dibutyl phthalate (DBP) in DWDSs under the influence of polyamide 6 (PA6) MPs and further discussed the partitioning of BPA/DBP on PA6s, filling a research gap regarding the impact of adsorption between contaminants on their occurrence within DWDSs. In this study, adsorption experiments of BPA/DBP with PA6s and pipe scales were conducted and their interaction mechanisms were investigated. Competitive adsorption experiments of BPA/DBP were also carried out with site energy distribution theory (SEDT) calculations. The results demonstrated that PA6s might contribute to the accumulation of BPA/DBP on pipe scales. The adsorption efficiencies of BPA/DBP with both PA6s and pipe scales were 26.47 and 2.61 times higher than those with only pipe scales. It was noteworthy that BPA had a synergistic effect on the adsorption of DBP on PA6s, resulting in a 26.47 % increase in DBP adsorption. The article provides valuable insights for the compounding effect of different types of additives in water quality monitoring and evaluation.

Adsorption of Cr(VI) and Cr(III) on layered pipe scales and the effects of disinfectants in drinking water distribution systems.

Pipe scales in drinking water distribution systems (DWDS) potentially adsorb chromium (Cr). Meanwhile, the fate of Cr in pipe scales and water could be influenced by the disinfectants used in DWDS since they might influence the valence state of Cr. Therefore, the adsorption of Cr (Cr(VI) and Cr(III)) on pipe scales, the transformation between different valence states, and the effects of disinfectants present in DWDS are important research topics for improving tap water quality but have not yet been sufficiently investigated. This study investigated the properties of layered pipe scales and conducted adsorption kinetic experiments in single and binary Cr(VI) and Cr(III) systems, as well as experiments related to the oxidation and adsorption of Cr(III) under the influence of decaying disinfectants. According to the results, pipe scales exhibited distinct layered structures with varying mechanisms for the adsorption of Cr(VI) and Cr(III). Cr(VI) was adsorbed through surface complexation on the surface and porous core layers, while redox reactions predominantly occurred on the shell-like layer. Furthermore, Cr(III) was adsorbed via surface precipitation on the three-layer pipe scales. Importantly, disinfectants promoted the transformation of Cr(III) to the less readily released Cr(VI) in pipe scales, reducing the Cr exposure risk from the pipe scale phase. Pipe scales also decreased the Cr(VI) concentration in water (almost 0 mg/L), enhancing the safety of DWDS. This study provides theoretical guidance on the safe operation of DWDS.

[Research Progress on Colloid Pump Effect of Micro- and Nanoplastics in Drinking Water].

Currently, micro- and nanoplastics are the most concerning pollutants, which have been confirmed to exist in every stage of drinking water treatment process. Micro- and nanoplastics in drinking water have large specific surface areas, which could adsorb inorganic matter, organic matter, and microorganisms, thereby increasing their risk to human health. The adsorption and agglomeration behavior of micro- and nanoplastics on typical pollutants is called the "colloid pump effect." Focused on the micro- and nanoplastics in drinking water, the occurrence, colloid pump effect, and toxic effect on the human body and the effect of colloid pumps on the removal of micro- and nanoplastics were summarized and described. The results revealed that micro- and nanoplastics existed widely in source water, treated water, pipe network water, and tap water. The colloid pump effect of micro- and nanoplastics promoted their agglomeration with inorganic matter, organic matter, and microorganisms, which not only intensified the toxic effect of micro- and nanoplastics but also affected the removal effect. There were different viewpoints on the effect of coagulation and sedimentation on the removal of micro- and nanoplastics, and the removal effect of sand filters was limited. The advanced treatment was an efficient process to remove micro- and nanoplastics with a particle size smaller than 5 µm. The removal rate of micro- and nanoplastics could be effectively improved by exploring the mechanism of the colloid pump effect and its initiation conditions. Finally, from the perspective of the drinking water treatment process and colloid pump effect, the control of micro- and nanoplastics in drinking water was prospected in order to provide reference for reducing the occurrence and toxicity of micro- and nanoplastics in drinking water, ensuring drinking water quality safety and human health.

Co-transport behavior and Trojan-horse effect of colloidal microplastics with different functional groups and heavy metals in porous media.

The emerging global problems of microplastics pollution and their co-occurrence with other pollutants have presented major new challenges for environmental health and protection. This study used column experiments to investigate the co-transport behavior and Trojan-horse effect of colloidal microplastics (non-functional polystyrene microspheres (MS), carboxyl-modified polystyrene microspheres (CMS) and sulfonate-modified polystyrene microspheres (SMS)) and lead (Pb) in porous media. Results showed that a Trojan-horse effect occurred during the co-transport of colloidal microplastics and Pb. In the process of co-transport, colloidal microplastics and Pb mutually inhibited each other's transport at an ionic strength of 1 mM, which may be due to Pb absorption by microplastics, resulting in the destabilization of agglomerates and a reduction in the electronegativity of microplastics. At an ionic strength of 100 mM, colloidal microplastics and Pb promoted each other's transport, potentially due to their competition for adsorption in porous media. The functional groups present on colloidal microplastics inhibited the transport of Pb at low ionic strengths, while at high ionic strengths Pb transport was promoted. Furthermore, deposition experiments verified that quartz crystal microbalance with dissipation (QCM-D) monitoring could effectively account for and predict the transport and deposition behavior of microplastics in the presence or absence of Pb.

Stability of arsenic(â ¢, â ¤) in galvanized steel pipe scales coexisting with colloidal polystyrene microplastics under drinking water conditions.

The stability of metalloid arsenic (As(Ⅲ)) and As(V) in corrosion scales of drinking water distribution systems (DWDS) is closely related to drinking water safety. The effects of colloidal microplastics entering the DWDS on the stability of As(Ⅲ) and As(V) have not been understood. This study investigated the migration and transformation behaviors of As (Ⅲ) and As(V) in the galvanized steel pipe scales employing speciation simulation and sequential extraction methods. The stability of As(Ⅲ) and As(V) in the pipe scales coexisting with colloidal polystyrene microplastics (CPMPs) under drinking water conditions was studied for the first time from the release behaviors and form distributions. Finally, the optimum water quality conditions for As(Ⅲ) and As(V) fixation were summarized. The existing forms of As(Ⅲ) and As(V) under different pH conditions, the competitive action of anions, and the hydrolysis of cations all would significantly affect the stability of As(Ⅲ) and As(V). Sequential extraction method results revealed that the content of As fractions increased in different forms after the pipe scales adsorbed As(Ⅲ) and As(V). The contents of As and iron (Fe) in the form of residual fractions increased in the presence of CPMPs. The effect of three cations on the stability of As(Ⅲ) and As(V) was Fe3+ > Zn2+ > Ca2+. Neutral to weak alkalescence, proper Cl- and cation concentrations were conducive to the fixation of As in DWDS. Notably, the presence of CPMPs could increase the stability of As(Ⅲ) and As(V) in corrosion scales, thus reducing the risk of metalloid As release in DWDS.

[Research Progress on Trojan-horse Effect of Microplastics and Heavy Metals in Freshwater Environment].

As an emerging pollutant of global concern, microplastics (plastics with size<5 mm) and heavy metals are widely found in freshwater environments. Microplastics migrate easily, are difficult to degrade, and have large specific surface areas. They can enrich a variety of pollutants such as heavy metals and greatly increase their potential harm to the environment and ecology. Firstly, the special environmental behavior of microplastics carrying heavy metals and migrating together in freshwater environments was defined as the "Trojan-horse effect." Then, the Trojan-horse effect and its mechanism of microplastics and heavy metals in the freshwater environment were summarized and expounded from four aspects:the source and distribution of microplastics in the freshwater environment, the enrichment effect of microplastics on heavy metals, the impact of microplastics and the heavy metal Trojan-horse effect on its migration behavior, and the biological impact of microplastics and the heavy metal Trojan-horse effect. The results showed that, as a wide range of non-point source pollutants, microplastics widely existed in freshwater environments. In freshwater environments, the adsorption degree of single metals was different in different environments. It was mainly affected by microplastics, metals, and environmental factors. There was competitive adsorption in the presence of multiple metal ions. The Trojan-horse effect of microplastics and heavy metals could also affect their co-transport behavior. The Trojan-horse effect of microplastics and heavy metals in the freshwater environment frequently exacerbated their toxicity to aquatic organisms. This study provides references for comprehensively understanding the Trojan-horse effect and its mechanism in microplastics and heavy metals in the freshwater environment, which could effectively reduce the ecological risk and impact on human health of microplastics and heavy metals in the freshwater environment.

Study on release and occurrence of typical metals in corrosion products of drinking water distribution systems under stagnation conditions.

Metal contaminants in corrosion products of drinking water distribution systems (DWDS) can be released into potable water under specific conditions, thereby polluting drinking water and posing a health risk. Under stagnation conditions, the release characteristics, occurring forms, and environmental risks of ten metals were determined in loose and tubercle scale solids of an unlined cast iron pipe with a long service history, before and after immersion. Most Al, As, Cr, Fe, and V in corrosion scales existed in the residual fraction, with the released concentration and pollution risk being low. Since more than 59% of Ca in pipe scales existed in the exchangeable fraction, Ca release was high. Although the Pb and Cd content of corrosion solids was low, a high proportion of Pb and Cd was present in non-residual fractions with high mobility. Sudden severe Pb or Cd pollution events in DWDS could result in high pollution and environmental risk levels. The total content and released amount of Mn and Zn in corrosion scales were both high. Therefore, while special attention should be paid to Mn and Zn, Pb and Cd also present a high risk in pipe scales, despite their low concentrations. During stagnation immersion, metal release from powdered pipe scales occurred via the processes of mass release, re-adsorption into scales, and slow release until equilibrium was reached. The levels of metal re-adsorption into scales were much higher than the concentrations dissolved into bulk water. However, the amount of metal re-adsorption into tubercle scale blocks was less. Importantly, these findings highlight that during DWDS operation, the sudden release of metal pollutants caused by pipe scale breakage should be avoided.

Transport of E. coli colloids and surrogate microspheres in the filtration process: Effects of flow rate, media size, and media species.

Drinking water safety risks caused by bacterial contamination from Escherichia coli (E. coli) have aroused widespread concern. Filtration is crucial to drinking water treatment and can effectively capture and remove E. coli colloids without producing toxic by-products. This work systematically simulated the operating conditions of filtration by determining the transport behavior of E. coli colloids in lab-scale columns. Microspheres were used as surrogates of bio-colloids and breakthrough curves were drawn and analyzed at different flow rates, media sizes, and media species. The impact of media species on colloidal retention might be underestimated in the filtration process, and the removal efficiency of E. coli colloids varied by more than 59% between different media. From the point of interface interaction, excellent removal efficiency may be due to the strong attractive force caused by more positive zeta potential on the media surface. The results indicated that there were differences in transport behavior and environmental sensitivity between the E. coli colloids and surrogates. The DLVO theory cannot analyze the transport behavior between different colloids in media with opposite charges, and it is not easy to quantify the contribution of media species accurately. The study focuses on the adjustable parameters of the filtration process and provides new insights for ensuring the safety of drinking water.

The effect of adsorption on the fate of colloidal polystyrene microplastics in drinking water distribution system pipe scales.

With microplastics (MPs) being continuously found in various environments, the pollution of water supply systems by MPs is receiving increasing attention. As the sediment in drinking water distribution systems (DWDSs), pipe scales act as the interface for complex reactions between bulk water and pipe surfaces. Consequently, the fate of MPs in pipe scales requires exploration, especially colloidal MPs. In this study, MPs were detected in different pipe scale layers, with concentrations of 0.32-3.10 items g-1. Subsequently, the adsorption interaction mechanisms between pipe scales and colloidal polystyrene microplastics (PSMPs) were investigated through batch adsorption experiments. The findings indicated that pipe scales showed a potential adsorption capacity for PSMPs. The adsorption kinetics and isotherms results demonstrated that the PSMP adsorption process was physically dominant and complicated. van der Waals and electrostatic interactions, hydrogen bonding, and pore filling were the main adsorption mechanisms. These results verify that colloidal MPs can be adsorbed by pipe scales, demonstrating that pipe scales play an essential role in the fate of colloidal MPs in DWDSs and the quality and security of drinking water. The secondary release of MPs from pipe scales is also worthy of attention due to the environmental and health risks.

Effects of ionic strength and particle size on transport of microplastic and humic acid in porous media.

As an emerging pollutant, the transport behavior of colloidal microplastic particles (CMPs) in saturated porous media may be affected by the simultaneous presence of other substances in the natural environment. In this study, colloidal polystyrene microplastic particles (PSMPs) were selected as the representative of CMPs to investigate the cotransport behaviors of CMPs in the presence of humic acid (HA) under varied environmental conditions (ionic strength: 1, 100 mM KCl; HA concentration: 0, 5, 10, 20 mg⋅L-1) in porous media. The presence of HA with different concentrations was found to increase the mobility of 1.0-µm and 0.2-µm CMPs in porous media in a non-linear and non-monotonic manner. Furthermore, the HA-facilitated transport of CMPs occurred under both electrostatically unfavorable and favorable attachment conditions (limited to the conditions examined in this study, corresponding to 1 and 100 mM KCl, respectively). The transport behavior of the smaller-sized CMPs (0.2-µm CMPs) was more sensitive to the change of ionic strength and the presence of HA than that of the larger-sized CMPs (1.0-µm CMPs). The cotransport process of CMPs and HA was affected by many factors. Modeling results showed that a small amount of competitive blocking occurred during the cotransport process. Moreover, both the presence of HA and change in ionic strength could affect the surface properties of CMPs. Thus, the cotransport behavior of CMPs with HA was different from the transport of individual CMPs in porous media. Experimental results revealed that HA induced complexity in the transport behavior of CMPs in the aqueous environment. Therefore, undeniably, a lot more systematic explorations are further demanded to better comprehend the CMPs cotransport mechanism in the presence of other substances.

Characteristics of vanadium release from layered steel pipe scales to bulk, steady, and occluded water in drinking water distribution systems.

The release of vanadium (V) from drinking water distribution systems (DWDS) can endanger water quality and human health. Therefore, in this study, the physicochemical characteristics of old steel pipe scales were analyzed, and dynamic pipeline devices were constructed. Subsequently, static release experiments were conducted to find an optimum scale-water ratio and investigate the release behaviors of V in lumpy pipe scales. Besides, the release behaviors of V from layered pipe scales to bulk, steady, and occluded water under the combined effect of multiple water quality conditions were studied for the first time. Computational fluid dynamics (CFD) was adopted to explain the release behaviors of V in the dynamic pipeline. Results revealed that the adsorption performance of the layered scales decreased in the order of surface layer > porous core layer > hard shell-like layer. The release behaviors of V in the lumpy pipe scales were mainly divided into rapid desorption and colloidal agglomeration stages. The Double constant and Weber-Morris models can suitably describe release stage I (R2 > 0.919) and release stage II (R2 > 0.948), respectively. Notably, the release of V was aggravated by low pH, high temperature, and high SO42- concentration, and the release amount of V in the pipeline was more significant than the layered pipe scales. Steady water in the gaps of scales contained more V than bulk water, and the malignant occluded water encased in scales contained relatively low V concentrations. In short, the main mechanism of V release was competitive adsorption in the early stage, and pH was the main influencing factor in the later stage. The above results are of great significance for revealing the release behaviors of V and reducing its release in DWDS.

Cr release after Cr(III) and Cr(VI) enrichment from different layers of cast iron corrosion scales in drinking water distribution systems: the impact of pH, temperature, sulfate, and chloride.

Chromium accumulated from source water and pipeline lining materials in corrosion scales could potentially be released into bulk water in drinking water distribution systems (DWDS). This study examined the influence of pH (pH 4, pH 5.5, pH 7, pH 8.5, pH 10), temperature (5 °C, 15 °C, 25 °C), sulfate (50 mg/L, 150 mg/L, 250 mg/L), and chloride (50 mg/L, 150 mg/L, 250 mg/L) on chromium accumulation and release between iron corrosion scale phase and the surrounding water phase. For the first time, the accumulation and release behaviors of chromium were assessed and compared in two distinct layers of iron corrosion scales based on the speciation distributions of heavy metals. Results showed that in the outer and inner layers of corrosion scales, chromium exhibited an almost similar trend but significant differences in quantity, with the outer layer accumulating less and releasing more. In particular, the average difference of chromium released after Cr(VI) enrichment from the outer and inner layers was 50.53 µg/L under the same conditions. Further studies conclusively showed that in Cr(VI) accumulation process, a portion of Cr(VI) would be reduced to Cr(III) by Fe(II) in iron corrosion scales. The mechanisms of chromium retention based on different iron (oxyhydr)oxides were discussed.

Field study on the characteristics of scales in damaged multi-material water supply pipelines: Insights into heavy metal and biological stability.

Microbial corrosion and heavy metal accumulation in metal water supply pipelines aggravate scale formation and may result in pipeline leakage or bursting events. To better understand the corrosion and corrosion products in the damaged pipes, deposits excavated from three damaged pipes after 22-26 year service periods were analyzed. Using a combination of advanced micro-mineral techniques and 16S rRNA high-throughput sequencing, the micromorphology, chemical composition, and bacterial community were investigated systematically. Unlined pipe wall scales ruptured while lined pipes leaked due to joint scales. Dendrogram correlation results demonstrated that V/As, Al/Pb, and Cr/Mn clusters exhibited co-adsorption and co-precipitation characteristics. FTIR and XRD analysis detected the presence of γ-FeOOH, α-FeOOH in loose scales, and Fe3O4 in rigid scales. Scales were colonized by various corrosion bacteria, with sulfate reducing bacteria and ammonia producing bacteria being dominant in the scales of anticorrosive and non-corrosive pipe, respectively. Tl, Ca, Al, and Pb exhibited an extremely positive correlation with Rhodocyclaceae, Ferritrophicum, Thermodesulfovibrionia, and Clostridiaceae. Al and V presented a potential Hazard Quotient risk to consumers, while Cd was potentially bioavailable in all inner scales. Overall, this study provides valuable information for the effective management and avoidance of corrosion-induced pipeline damage and heavy metal release.

Study on the occurrence of typical heavy metals in drinking water and corrosion scales in a large community in northern China.

Excessive heavy metal content in drinking water could lead to red water and acute and chronic diseases. A field study in combination with batch experiments using pipe scales of drinking water distribution systems (DWDS) in the study area, was used to determine the content distribution and migration of As, Cd, Cr, Mn, Pb, and V in DWDS. In the field study, As, Cd, Cr, Pb, and V contents in pipe scales and drinking water were extremely low and did not exceed the Chinese drinking water standards. However, Mn concentrations at the end of the DWDS with aged and corrosive pipes were relatively high, which presented a risk of excessive release. The batch experiment showed that As in pipe scales would not be released into water under static immersion conditions; however, pipe scales would release excessive Cd, Cr, Mn, Pb, and V in the initial reaction stage, and the heavy metal contents released by tubercle scales in the initial release stage were at least twice as much as those released by loose scales. The mass percentage of four metals (excluding Cd and Pb) released from pipe scales was extremely low. The field study and batch experiment data both suggested a strong correlation between Cr and V released into the water, indicating a synergistic effect. There were differences in heavy metals released in the field research and the batch experiment. The amount of Cd, Cr, Pb, and V released were not consistent with its proportion in pipe scales. As release did not occur under static conditions, but may be promoted by the water flow in the actual network. The effect of water flow on heavy metal release in DWDS should be considered.

Transport and Retention of Free-Living Amoeba Spores in Porous Media: Effects of Operational Parameters and Extracellular Polymeric Substances.

Amoebas are protists that are widespread in water and soil environments. Some species are pathogenic, inducing potentially lethal effects on humans, making them a major threat to public health. Nonpathogenic amoebas are also of concern because they have the potential to carry a mini-microbiome of bacteria, either transiently or via more long-term stable transport. Due to their resistance to disinfection processes, the physical removal of amoeba by filtration is necessary to prevent their propagation throughout drinking water distribution networks and occurrence in tap water. In this study, a model amoeba species Dictyostelium discoideum was used to study the transport and retention behavior of amoeba spores in porous media. The key factors affecting the transport behavior of amoeba spores in fully saturated media were comprehensively evaluated, with experiments performed using a quartz crystal microbalance with dissipation monitoring (QCM-D) and parallel plate chamber system. The effects of ionic strength (IS) on the deposition of spores were found to be in contrast to the predicted Derjaguin-Landau-Verwey-Overbeek (DLVO) theory that more deposition is observed under lower-IS conditions. The presence of extracellular polymeric substances (EPS) was found to be the main contributor to deposition behavior. Overall, these results provide plausible evidence for the presence of amoeba in tap water. Furthermore, this is one of the first studies to examine the mechanisms affecting the fate of amoeba spores in porous media, providing a significant baseline for future research to minimize the safety risk presented by amoeba in drinking water systems.

Co-transport and retention of zwitterionic ciprofloxacin with nano-biochar in saturated porous media: Impact of oxidized aging.

While biochar (BC) is used for contaminant remediation (i.e. antibiotics) in the field, geochemical aging can alter its chemical structure, releasing nano-sized BC (NBC, sizes ranging from approximately 200 nm to 500 nm), and further influence the environmental behaviour of antibiotics affiliated with BC. In this study, we comprehensively examined the sorption behaviour of NBCs with and without aging toward ciprofloxacin (CIP), their aggregation performance, and transport behaviour in porous media. The results showed that aging improved the oxygen-containing groups within the NBCs and made their surfaces more negatively charged. The thermodynamic enhancements of specific interactions (i.e. π-π interaction or Coulombic force) with CIP resulted in the enhancement of slow sorption (from 60-64% to 40-58%) and a higher normalised sorption capacity (Qe). The aggregation of NBCs was affected by changes in individual specific interactions and interfacial forces between the NBCs before and after CIP sorption. Further, aging could enhance the transport of NBCs both in the absence and presence of CIP. In addition to the interaction with the quartz sand surface, the contributions of aggregation and chemical heterogeneity caused by rebalanced specific interactions with CIP, may explain the observed transport behaviours of the aged NBCs in porous media. Additionally, the presence of NBCs, regardless of aging, suppressed the transport of CIP. Thus, mechanisms such as increased sorption sites due to aggregation and competitive sorption between NBCs and CIP, rather than the contribution of co-transport from NBCs, might play an important role in determining the fate of CIP in the natural environment.

Multiple antibiotics distribution in drinking water and their co-adsorption behaviors by different size fractions of natural particles.

In recent years, natural particles in drinking water have attracted attention due to their carry of toxic organic matter. However, the adsorption behavior of multiple antibiotics at very low concentrations on different sized particles has not been revealed. Here, the content of 17 antibiotics in water samples collected from four process stages of the water supply plant was detected. Results showed the concentration of antibiotics in water plant was in the range of 0-69.24 ng L-1. Characterization of natural particles obtained directly from raw water of waterworks showed that the surface of large particles (>1 µm) was rougher and the composition was more complex than that of small particles (0.05-1 µm). Besides, the adsorption experiments of four antibiotics (nalidixic acid (NAL), trimethoprim (TMP), roxithromycin (ROX), and penicillin G potassium salt (PG)) on small (0.05-1 µm) and large (>1 µm) natural particles were studied. The results indicated that in the binary antibiotic system, the competition and synergy between antibiotics made a greater proportion of antibiotics soluble in water comparing with single systems, and the particle-water partition coefficient (kp-w) of the total antibiotics ranged from 1.13-1.78 was reduced to 0.57-0.84. The competitive adsorption of antibiotics appeared in the binary system showed that ROX and PG had a higher adsorption capacity than NAL and TMP. Furthermore, in the binary antibiotic systems, small particles played an important role in adsorption, suggesting the urgency of their removing. This work could help predict the possible risks of drinking water and provide some insights into future drinking water treatment.

Co-release potential and human health risk of heavy metals from galvanized steel pipe scales under stagnation conditions of drinking water.

The re-release of heavy metals accumulated in the drinking water distribution systems (DWDSs) may pose a significant threat to water quality and human health. In this work, the pipe scales in the actual DWDS were collected, and their physicochemical characteristics were investigated by SEM, XRF, XRD, XPS, and sequential extraction procedure. The co-release potential of heavy metals under different scale dosages, temperatures, and stagnation times was explored by stagnation release tests. Pearson correlation analysis on metal release and human health risk assessment was used to reveal the inter-metal correlation and potential risk of metal release. The results showed that the metal release potential under stagnation water conditions arose primarily from the acid-soluble fraction. The chronic non-carcinogenic risk of soluble metals followed the order: Mn > Fe > Zn > Pb. The risk caused by the soluble metal release could be ignored (HI < 1, HI: hazard index) under normal stagnation times (within 8 h). The major finding of this work was that Ca and Mn were more labile to release and had a significant linear co-release correlation (scale powder: R2 = 0.906, p < 0.01; pipe section: R2 = 0.982, p < 0.01), which indicated their co-existence and linear co-release. Ca was recognized as the "major metal" that affected the release of trace metals. The health risk probably increased with the release of Ca, which could also be used as an "indicator" of Mn release.

Accumulation of vanadium and arsenic by cast iron pipe scales under drinking water conditions: A batch study.

Metal pollutants accumulation in the scales of drinking water distribution systems presents a potential threat to water quality. Therefore, a study was carried out on the accumulation of V(V) and As(V) by cast iron pipe scales. The accumulation of V(V) and As(V) by scales and the effects of scale dosage, pH, temperature, and anion content on the accumulation process were assessed. Results showed that scales could rapidly accumulate V(V) and As(V), with maximum accumulation amounts of 3.94 mg/g and 3.90 mg/g, respectively. An increase in pH (from 3.0 to 9.0) and sulfate concentration (from 0 to 250 mg/L) decreased V(V) and As(V) accumulation by scales. Increased chloride ion concentrations (from 0 to 250 mg/L) reduced the amount of As(V) accumulated, while increasing the amount of V(V) accumulated. The V(V) and As(V) accumulation kinetics were well described by the Elovich model, with thermodynamic and accumulation isotherms showing that the accumulation process occurred via an entropic endothermic reaction. The mechanisms of accumulation of V(V) and As(V) by the scales include surface complexation, ligand exchange, electrostatic attraction and repulsion, and competitive adsorption.

Cotransport and deposition of colloidal polystyrene microplastic particles and tetracycline in porous media: The impact of ionic strength and cationic types.

The cotransport behaviors of colloidal polystyrene microplastic particles (PSMPs) and tetracycline (TC) (20 mg/L) were investigated in saturated porous media in KCl and CaCl2 solutions of various ionic strengths (1, 10, 50, 100 mM). Furthermore, the effects of TC concentration (0, 1, 5, 10, 20 mg/L) on the cotransport behaviors of PSMPs and TC in 100 mM KCl solution were assessed. The cotransport behaviors were analyzed by comparing the individual transport behaviors of PSMPs or TC. When cotransported, the presence of TC (20 mg/L) slightly inhibited PSMPs mobility in K+ solutions (the C/C0 decreased in the range of 0-5.9%), but facilitated it in Ca2+ solutions (the C/C0 increased in the range of 6.7-42.6%). In KCl solutions, although the presence of TC (PSMPs) did not significantly affect the transport behaviors of PSMPs (TC), the attachment efficiencies of both PSMPs and TC showed a non-linear and non-monotonic change with increase in ionic strength. However, in CaCl2 solutions, the effects of TC (PSMPs) on the transport behaviors of PSMPs (TC) were remarkable and a non-linear non-monotonic change was observed. The adsorption of TC on PSMPs might play a critical role during the cotransport. Thus, the balance between the transport-inhibiting (e.g., the reduction in electrostatic repulsive force) and transport-facilitating effects (e.g., the effects on hydrophilicity/hydrophobicity of PSMPs due to TC adsorption) may be responsible for the observed changes. Overall, the results demonstrated that the cotransport behaviors of PSMPs and TC were more complicated than their individual transport behaviors in porous media, which might vary considerably with environmental conditions. This work could greatly improve our understanding of complex cotransport behaviors and environmental risk of PSMPs.