The U.S. EPA recently announced the revision of the Lead and Copper Rule to establish a new lead action level at 10 mu g L-1; however, the formation and release of lead phosphate nanoparticles in drinking water are ubiquitous in lead-containing drinking water distribution systems, and these particles are poorly removed by conventional filters, thus making it challenging for lead control in light of the new regulation. To address this urgent issue, this study developed a treatment train combining hydrogen peroxide photolysis (UV/H2O2) pre-oxidation with point-of-use (POU) filtration to efficiently remove lead phosphate nanoparticles (nano-Pb3(PO4)2(s)) from drinking water. The results showed that hydroxyl radicals produced via UV/H2O2 oxidized divalent nano-Pb3(PO4)2(s) to tetravalent lead dioxide solid PbO2(s) and aggregated them into larger cluster particles, facilitating efficient removal by subsequent POU filtration. Without the UV/H2O2 pre-oxidation, stand-alone POU filtration was ineffective at reducing the nano-Pb3(PO4)2(s) concentration below 10 mu g L-1. Furthermore, UV/H2O2 pre-oxidation was effective in diverse drinking water chemical conditions at varying levels of pH (6-8), chloride (0-50 mg L-1), and alkalinity (0-200 mg L-1 as CaCO3). Overall, this study provides an urgently needed and promising lead removal technology that is robust to guarantee drinking water safety to consumers.

In drinking water distribution systems, the oxidation of zerovalent chromium, Cr(0), in iron corrosion scales by chlorine residual disinfectant is the dominant reaction to form carcinogenic hexavalent chromium, Cr(VI). This study investigates inhibitive corrosion control strategies through adjustments of chemical water parameters (i.e., pH, silicate, phosphate, calcium, and alkalinity) on Cr(VI) formation through oxidation of Cr(0)(s) by free chlorine under drinking water conditions. The results show that an increase in pH, silicate, alkalinity, and calcium suppressed Cr(VI) formation that was mainly attributed to in situ surface precipitation of new Cr(III) solids on the surface of Cr(0)(s), including Cr(OH)3(s), Cr2(SiO3)3(s), CrPO4(s), Cr2(CO3)3(s), and Cr10Ca(CO3)16(s). The Cr(III) surface precipitates were much less reactive with chlorine than Cr(0)(s) and suppressed the Cr redox reactivity. The concentration of surface Cr(III) solids was inversely correlated with the rate constant of Cr(VI) formation. Adding phosphate either promoted or inhibited the Cr(VI) formation, depending on the phosphate concentration. This study provides fundamental insight into the Cr(VI) formation mechanisms via Cr(0) oxidation by chlorine and the importance of surface precipitation of Cr(III) solids with different corrosion control strategies and suggests that increasing the pH/alkalinity and addition of phosphate or silicate can be effective control strategies to minimize Cr(VI) formation.

Adding CrIII or AlIII salts into the water suspension of platinum group metal (PGM) catalysts accelerated oxyanion pollutant reduction by up to 600%. Our initial attempts of adding K2CrVIO4, K2CrVI2O7, or KCrIII(SO4)2 into Pd/C enhanced BrO3– reduction with 1 atm H2 by 6-fold. Instrument characterizations and kinetic explorations collectively confirmed the immobilization of reduced CrVI as CrIII(OH)3 on the catalyst surface. This process altered the ζ-potentials from negative to positive, thus substantially enhancing the Langmuir–Hinshelwood adsorption equilibrium constant for BrO3– onto Pd/C by 37-fold. Adding AlIII(OH)3 from alum at pH 7 achieved similar enhancements. The Cr–Pd/C and Al–Pd/C showed top-tier efficiency of catalytic performance (normalized with Pd dosage) among all the reported Pd catalysts on conventional and nanostructured support materials. The strategy of adding inert metal hydroxides works for diverse PGMs (palladium and rhodium), substrates (BrO3– and ClO3–), and support materials (carbon, alumina, and silica). This work shows a simple, inexpensive, and effective example of enhancing catalyst activity and saving PGMs for environmental applications.

Chlorate (ClO3-) is a toxic oxyanion pollutant from industrial wastes, agricultural applications, drinking water disinfection, and wastewater treatment. Catalytic reduction of ClO3- using palladium (Pd) nanoparticle catalysts exhibited sluggish kinetics. This work demonstrates an 18-fold activity enhancement by integrating earth-abundant vanadium (V) into the common Pd/C catalyst. X-ray photoelectron spectroscopy and electrochemical studies indicated that V-V and V-IV precursors are reduced to V-III in the aqueous phase (rather than immobilized on the carbon support) by Pd-activated H-2. The V-III/IV redox cycle is the predominant mechanism for the ClO3- reduction. Further reduction of chlorine intermediates to Cl- could proceed via V-III/IV and V-IV/V redox cycles or direct reduction by Pd/C. To capture the potentially toxic V metal from the treated solution, we adjusted the pH from 3 to 8 after the reaction, which completely immobilized V-III onto Pd/C for catalyst recycling. The enhanced performance of reductive catalysis using a Group 5 metal adds to the diversity of transition metals (e.g., Cr, Mo, Re, Fe, and Ru in Groups 6-8) for water pollutant treatment via various unique mechanisms.

Upon cast iron corrosion in contact with residual disinfectants, drinking water distribution systems have become potential geogenic sources for hexavalent chromium Cr(VI) release. This study investigated mechanisms of Cr(VI) release from cast iron corrosion scales. The oxidation of the corrosion scales by residual disinfectant chlorine released Cr(VI) and exhibited a three-phase kinetics behavior: an initial 2 h fast reaction phase, a subsequent 2-to-12 h transitional phase, and a final 7-day slow reaction phase approximately 2 orders of magnitude slower than the initial phase. X-ray absorption spectroscopy analysis discovered that zerovalent Cr(0) coexisted with trivalent Cr(III) solids in the corrosion scales. Electrochemical corrosion analyses strongly suggested that Cr(0) in the corrosion scales originated from Cr(0) in the cast iron alloy. Cr(0) exhibited a much higher reactivity than Cr(III) in the formation of Cr(VI) by chlorine. The presence of bromide in drinking water significantly accelerated Cr(VI) release because of its catalytic effect. Meanwhile, chlorine consumption was mainly attributed to the oxidation of organic matter and ferrous iron. Findings from this study point to a previously unknown but important pathway of Cr(VI) formation in drinking water, that is, direct oxidation of Cr(0) by chlorine, and suggest new strategies to control Cr(VI) in drinking water by inhibiting Cr(0) reactivity.

The bioaccumulation and the main source of total Hg (THg) and methylmercury (MMHg) in the deposit-feeding polychaete Neanthes japonica collected in Jinzhou Bay, China, were investigated. Compared with the historical data, THg bioaccumulation in polychaetes collected in sediment of Jinzhou Bay was distinctly higher due to higher sediment THg concentration, but MMHg bioaccumulation was significantly lower. THg accumulation in polychaetes mainly derived from its accumulation in sediment. However, MMHg bioaccumulation in polychaetes did not correlate with Hg concentration in sediment. Besides sediment ingestion, MMHg accumulation in polychaetes may partially source from the process of in vivo transformation. The in vivo Hg methylation may take place in polychaetes, according to the excellent correlation between MMHg concentration and THg and inorganic Hg concentration in polychaetes. The biochemical characters in polychaete body, the oxidation-reduction environment and the microbial activity in polychaete gut may be beneficial to in vivo Hg methylation.

Nicotinamide (NAM) is the main precursor of NAD+, a co-enzyme essential to glycolysis and OXPHOS. NAM is known for its anti-aging activity on human skin, however the underlying mechanisms remain unclear. The purpose of this study was to define the cellular pathways involved. Human primary keratinocytes (HPKs) isolated from skin of healthy donors were used to assess proliferation, differentiation and stemness in vitro, as well as senescence and metabolism. Our data showed that NAM increased the proliferative capacity of HPKs. This was characterized by a better clonogenicity when HPKs were grown on irradiated 3T3-J2 feeders, with an increase in the proportion of holoclone (stem)-like cells. Concomitantly, NAM lowered the expression of epidermal differentiation markers. By contrast, inhibiting the conversion of NAM to NAD+ by targeting NAMPT (the rate-limiting enzyme in NAD+ biosynthesis) using FK866 led to barely detectable NAD+ levels, accelerated differentiation and senescence. These phenotypes correlated with a drop in glycolysis (but also in OXPHOS to a lesser extend) and a dramatic drop in ATP levels. Interestingly, NAM rescued both glycolysis and OXPHOS in FK866-treated cells, as well as both the differentiation and senescence phenotypes. The effects of NAM on HPKs were further confirmed in 3D organotypic models, where NAM maintained proliferation in the basal layer while inhibiting differentiation in the upper layers. In conclusion, our data provide new insights into the control of differentiation, proliferation and senescence by NAD+. They will be valuable to improve treatments of a number of skin conditions where a loss/dysregulation of the epidermal homeostasis occurs (e.g. eczema, psoriasis), as well as to better control premature skin aging.

In the present study, we tested whether bioaccumulation in specific tissues of Daphnia magna could explain silver nanoparticle (AgNP) toxicity. Daphnids were exposed to different concentrations of well-suspended AgNPs and AgNO3 . The accumulations of Ag in the whole body, gut, and nongut tissues, as well as the mortality of daphnids, were recorded over a period of 7 d. Regression analysis showed a higher degree of positive correlation between the concentration of Ag in the nongut tissues than gut tissues and the mortality of daphnids. The results strongly suggested that the toxicity of AgNPs could be better explained in terms of bioaccumulation of AgNPs in the nongut tissues. We further tested the maternal transfer of AgNPs in daphnids into the next generation using radioactive tracers, which were able to detect as low as 1.0 to 3.2% of total accumulated Ag transferred to the neonates. The AgNPs significantly affected the reproduction process during the first 2 broods after exposure, whereas AgNO3 only had significant effects on the first brood. It is possible that AgNPs have longer adverse effects than AgNO3 on the reproduction of Daphnia. The present study identified the sensitive site of AgNP toxic action in daphnids and documented the extent of maternal transfer and the significant influence of AgNPs on the reproduction of daphnids. Environ Toxicol Chem 2017;36:3359-3366. © 2017 SETAC.

Increasing applications of titanium dioxide nanoparticles (nano-TiO2) have intensified the risk of environmental contamination. Since nano-TiO2 can absorb metals and be consumed as 'food' by zooplankton but also can interact with phytoplankton, they could significantly disturb the existing metal assimilation patterns. In the present study, we quantified the dietary assimilation of Cd and Zn from nano-TiO2 and algae (Chlamydomonas reinhardtii) at comparable particle concentrations as well as in complex food environment (variable food quality and quantity) in a freshwater zooplankton Daphnia magna using the radiotracer technique. For both nano-TiO2 and algae as food, the feeding food quality and depuration food quantity significantly affected the assimilation efficiencies (AEs) of Cd and Zn. At feeding food quantity of 1 mg/L to 10 mg/L without food in depuration, the AEs of Cd and Zn from nano-TiO2 were lower than those from algae. When food was added during depuration, the influences of nano-TiO2 on metal AEs were variable due to the differential effects of food quantity on the gut passage of nano-TiO2 and algae. Furthermore, mixed nano-TiO2 and algae had the lowest metal AEs compared to sole nano-TiO2 or algae as a result of interaction between nano-TiO2 and algae during feeding. Overall, this study showed the distinguishing metal AEs between nano-TiO2 and algae, and that nano-TiO2 could significantly reduce the existing metal AEs from algae. More attention should be paid to the potential roles of nano-TiO2 in disturbing metal assimilation in the environmental risk assessments of nanoparticles.

In this study, we measured trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in water and sediment from representative sites of Taihu Lake, with focus on the analysis of trace metal accumulation in Corbicula fluminea (bivalve). The results showed that the quality of water in Taihu Lake was generally good and the correlation was not found between Cu bioaccumulation in C. fluminea and the concentration in water and sediment. Thus, using the stable isotope tracer method, we studied Cu uptake from the water phase, the assimilation of Cu from the food phase, and the efflux of Cu in vivo by C. fluminea. The result revealed that this species exhibited a relatively lower efflux rate constant of Cu compared with other zoobenthos species. Using a simple bioenergetics-based kinetic model, Cu concentrations in the C. fluminea were calculated with the measured efflux rate. We put forward a novel method, which was taking the influence of biological kinetic on metal bioaccumulation into account to explain the field survey data.

Titanium dioxide (TiO2) nanoparticles are widely used in water treatments, yet their influences on other contaminants in the water are not well studied. In this study, the aqueous uptake, assimilation efficiency, and toxicity of two ionic metals (cadmium-Cd, and zinc-Zn) in a freshwater zooplankton, Daphnia magna, were investigated following 2 days pre-exposure to nano-TiO2. Pre-exposure to 1 mg/L nano-TiO2 resulted in a significant increase in Cd and Zn uptake from the dissolved phase. After the nano-TiO2 in the guts were cleared, the uptake rates immediately recovered to the normal levels. Concurrent measurements of reactive oxygen species (ROS) and metallothioneins (MTs) suggested that the increased metal uptake was mainly due to the increased number of binding sites provided by nano-TiO2 presented in the guts. Consistently, pre-exposure to nano-TiO2 increased the toxicity of aqueous Cd and Zn due to enhanced uptake. Our study provides the evidence that nano-TiO2 in the guts of animals could increase the uptake and toxicity of other contaminants.

This study examines the potential hazard of an individual nanomaterial on the Cu biotoxicity to aquatic organisms. Daphnia magna in the absence or presence of nano-TiO2 was exposed to Cu. Maintaining nano-TiO2 at a safe concentration cannot eliminate its potential hazard. The biomarkers superoxide dismutase, catalase, and Na+/K+-ATPase in D. magna were measured. Cu in the presence of nano-TiO2 induced higher levels of oxidative stress and physiological damage because of the sorption of Cu. Nano-TiO2 also caused Na+/K+-ATPase inhibition possibly by impeding the Na+/K+ transfer channel. The correlations among the biomarkers, mortality, and accumulation further showed that the overloading reactive oxygen species generation caused by nano-TiO2 contributed to deeper oxidative stress and physiological regulation, thereby causing greater toxic injury.

Titanium dioxide nanoparticles (nano-TiO(2)) are now widely applied in consumer products, and the dispersion of nano-TiO(2) may adsorb metals and modify their behavior and bioavailability in the aquatic environment. In the present study, the aqueous uptake, dietary assimilation efficiency (AE), and efflux rate constant (k(e)) of two toxic metals (cadmium-Cd, and zinc-Zn) adsorbed on nano-TiO(2) in a freshwater zooplankton Daphnia magna were quantified. The biokinetics was then compared to daphnids that were exposed only to dissolved metals as controls. The aqueous uptake of Cd and Zn involved an initial rapid uptake and then an apparent saturation, and the uptake of metals was accompanied by an ingestion of nano-TiO(2). The AEs of Cd and Zn adsorbed on nano-TiO(2) were 24.6 ± 2.4-44.5 ± 3.7% and 30.4 ± 3.4-51.8 ± 5.0%, respectively, and decreased with increasing concentrations of nano-TiO(2). Furthermore, the difference between the AEs of Cd and Zn indicated that the desorption of Cd and Zn from nano-TiO(2) may have occurred within the gut of daphnids. With the use of algae as carrier, the AEs of Cd and Zn adsorbed on nano-TiO(2) were significantly higher than those of Cd and Zn directly from nano-TiO(2). The efflux rate constants of Cd and Zn adsorbed on nano-TiO(2) in the zooplankton were significantly lower than those of Cd and Zn not adsorbed on nano-TiO(2). Our study shows that the uptake and retention of toxic metals is enhanced when they are adsorbed on nano-TiO(2), and suggests more attention be paid to the potential influences of nano-TiO(2) on the bioavailability and toxicity of other contaminants.

The acute toxicity of engineered nanoparticles (NPs) in aquatic environments at high concentrations has been well-established. This study demonstrates that, at a concentration generally considered to be safe in the environment, nano-TiO2 remarkably enhanced the toxicity of copper to Daphnia magna by increasing the copper bioaccumulation. Specifically, at 2mgL−1 nano-TiO2, the (LC50) of Cu2+ concentration observed to kill half the population, decreased from 111μgL−1 to 42μgL−1. Correspondingly, the level of metallothionein decreased from 135μgg−1 wet weight to 99μgg−1 wet weight at a Cu2+ level of 100μgL−1. The copper was found to be adsorbed onto the nano-TiO2, and ingested and accumulated in the animals, thereby causing toxic injury. The nano-TiO2 may compete for free copper ions with sulfhydryl groups, causing the inhibition of the detoxification by metallothioneins.