Co-occurrence profiles of trace elements in potable water systems: a case study

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.

Effects of chloride on corrosion scale compositions and heavy metal release in drinking water distribution systems

Variations in water chemistry may lead to the release of harmful heavy metals in drinking water distribution systems (DWDSs). In this study, the effects of chloride on the release of heavy metals such as Fe, Mn, As, Cr, Mo, V, Sr, and Co were examined using steel and cast iron pipe loops. After chloride was added, the relative contents of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and siderite (FeCO3) in pipe scales increased, but the contents of magnetite (Fe3O4) decreased. The most prevalent compounds were α-FeOOH and γ-FeOOH. When the chloride levels were increased, the effluent concentrations of Fe, Mn, As, Cr, Mo, V, Sr, and Co significantly increased. These heavy metals were released presumably because of the destabilization and dissolution of corrosion scales induced by chloride and adsorption site competition. Strong positive correlations were also observed between Fe&Mn, Fe/Mn&As, Fe/Mn&Cr, Fe/Mn&Mo, Fe/Mn&V, Fe/Mn&Sr, and Fe/Mn&Co, indicating the co-release of Fe, Mn, and other metals. This study may be helpful for the potential strategies on avoidance of heavy metal release and improvement of water supply security.

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.

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 SO₄^2- 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.

Integrating Transcriptomics and Free Fatty Acid Profiling Analysis Reveal Cu Induces Shortened Lifespan and Increased Fat Accumulation and Oxidative Damage in C. elegans

Nowadays, human beings are exposed to Cu in varieties of environmental mediums, resulting in health risks needing urgent attention. Our research found that Cu shortened lifespan and induced aging-related phenotypes of Caenorhabditis elegans (C. elegans). Transcriptomics data showed differential expression genes induced by Cu were mainly involved in regulation of metabolism and longevity, especially in fatty acid metabolism. Quantitative detection of free fatty acid by GC/MS further found that Cu upregulated free fatty acids of C. elegans. A mechanism study confirmed that Cu promoted the fat accumulation in nematodes, which was owing to disorder of fatty acid desaturase and CoA synthetase, endoplasmic reticulum unfolded protein response (UPRER), mitochondrial membrane potential, and unfolded protein response (UPRmt). In addition, Cu activated oxidative stress and prevented DAF-16 translocating into nuclear with a concomitant reduction in the expression of environmental stress-related genes. Taken together, the research suggested that Cu promoted aging and induced fat deposition and oxidative damage.

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.

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.

Disinfection by-products in Croatian drinking water supplies with special emphasis on the water supply network in the city of Zagreb

The occurrence of disinfection by-products (DBPs) was investigated in 48 drinking water systems across Croatia. Eleven DBPs were studied: chlorite (ClO₂^-), chlorate (ClO₃^-), four trihalomethanes (THMs), and five haloacetic acids (HAAs). Furthermore, an intensive sampling program was conducted in the distribution system in the city of Zagreb where, aside from DBP analyses, natural organic matter (NOM) was characterized using fluorescence spectroscopy. In the drinking waters examined across Croatia, DBP values were found in the range from 0.7 μg/L to 32.8 μg/L for THMs, below LOQ to 17.2 μg/L for HAAs (primarily di- and trichloroacetic acids), below LOQ to 720 μg/L for ClO₂^- and below LOQ to 431 μg/L for ClO₃^-. The results obtained showed higher chlorite concentrations in the systems treated with hypochlorite compared to systems treated with chlorine dioxide. DBPs in the Zagreb distribution network were generally low (the average values were below 6 μg/L and 2 μg/L for total THM and total HAA respectively). In contrast to our observations throughout Croatia, dibromoacetic acid (DBAA) was found to be the predominant HAA within Zagreb, most likely due to the degradation of chlorinated carboxylates (di-/tri-chloroacetic) in the network. Characterization of NOM by Parallel Factor Analysis (PARAFAC) fluorescence spectroscopy across the Zagreb network showed distinct temporal variations arising from groundwater inputs, as evident from variable humic-, tyrosine-, and tryptophan-like peaks. Statistical correlations between fluorescence data and DBPs highlight its potential for monitoring the presence of DBPs in distribution networks.

Associations between urinary cadmium levels, blood pressure, and hypertension: the ESTEBAN survey

Cadmium is inconsistently associated with blood pressure (BP) and hypertension. Our study focuses to understand the association between urinary cadmium levels, blood pressure, and hypertension in a French representative sample. Our study included 2015 subjects from the ESTEBAN survey (2014-2015) with measured urinary cadmium. Associations between natural logarithm-transformed cadmium levels and BP (systolic (SBP) and diastolic blood pressure (DBP)) were performed by adjusted linear regression models. Associations between cadmium and hypertension were performed by adjusted logistic regression models. Models were stratified by gender, smoking habits, body mass index (BMI), and kidney function categories. Men present higher SBP (131.7 vs. 121.5 mmHg, p < 0.0001) and DBP (78.9 vs. 74.7 mmHg, p < 0.0001) in comparison to women. Creatinine-adjusted urinary cadmium levels (0.48 vs. 0.39 μg/L, p < 0.0001) were higher in hypertensive subjects. Nevertheless, no difference was observed after adjustment for age, gender, and smoking habits. No correlation between urinary cadmium, BP, and hypertension was observed in overall population. Stratified models showed inverse correlations between urinary cadmium and hypertension among obese (OR = 0.39, 95% CI [0.21-0.57], p = 0.0009), chronic kidney function (OR = 0.68 95%CI [0.75-0.97], p = 0.003), and current smokers (OR = 0.78, 95% CI [0.64-0.92], p = 0.04). A correlation between urinary cadmium levels, BP, and hypertension is observed in subpopulations. Nevertheless, directions and significance of these associations differs by gender, BMI, smoking, and kidney function categories.

Characterization and release profile of (Mn, Al)-bearing deposits in drinking water distribution systems

Inorganic contaminants accumulation in drinking water distribution systems (DWDS) is a great threat to water quality and safety. This work assessed the main risk factors for different water pipes and discovered the release profile of accumulated materials in a full scale distribution system frequently suffered from water discoloration problem. Physicochemical characterization of pipe deposits were performed using X-ray fluorescence, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The metal release profile was obtained through continuous monitoring of a full-scale DWDS area. The results showed that aluminum and manganese were the main metals of deposits in nonmetallic pipes, while iron was dominant in iron-based pipe corrosion scales. Manganese primarily existed as MnO₂ without well crystalline form. The relative abundance of Mn and Fe in deposits changed with their distance from the water treatment plant. Compared with iron in corrosion scales, Mn and Al were more labile to be released back into bulk water during unidirectional flushing process. A main finding of this work is the co-release behavior of Mn and Al in particulate form and significant correlation exists between these two metals. Dual control of manganese and aluminum in treated water is proposed to be essential to cope with discoloration and trace metal contamination in DWDS.

Cadmium body burden, hypertension, and changes in blood pressure over time: results from a prospective cohort study in American Indians

American Indian communities are at greater risk of hypertension and cardiovascular disease than the general US population and are exposed to greater cadmium levels. However, cadmium's effect on blood pressure is unclear. This study assesses the association between baseline urinary cadmium and longitudinal changes in blood pressure in American Indian communities. Cadmium was measured in 3047 baseline urine samples from Strong Heart Study participants from three geographic areas. Longitudinal changes in blood pressure across three study visits (1989-1999) were modeled using linear mixed models by baseline log urinary cadmium to creatinine ratio. Hypertension risk was evaluated using interval-censored survival analysis. Higher levels of urinary cadmium at baseline were associated with faster rates of increase in diastolic and systolic blood pressure (P [trend] = .001 and .02, respectively). The estimated change in diastolic and systolic blood pressures per year was 0.18 mm Hg (0.05-0.31) and 0.62 mm Hg (0.37-0.87) in the upper quintile of cadmium level compared with -0.11 mm Hg (-0.24 to 0.02) and 0.21 mm Hg (-0.04 to 0.46) in the lowest, respectively. A one-unit increase in log-transformed urinary cadmium was associated with 10% greater hypertension risk (95% confidence interval: 1.01-1.20). In conclusion, blood pressure of individuals with greater baseline levels of urinary cadmium increased at a faster rate relative to those with lower levels.