Health risk assessment of arsenic from blended water in distribution systems

Fe-based layered double hydroxides for removing arsenic from water: sorption-desorption-regeneration

Since the presence of arsenic in the waters of the world causes serious health effects on people, it is very important to remove it. Layered double hydroxides have a high surface area and high anion exchange capacity, and because of this feature, it is a potential adsorbent to remove arsenic. For regeneration and reuse of adsorbents, researchers in some limited studies have used agents such as acids and alkalis. Media replacement accounts for approximately 80% of the total operational and maintenance costs. In this paper, an adsorption/desorption/regeneration study was carried out with MgFeHT to determine the desorption properties of the adsorbent and to examine its reusability. The best alkaline desorption solution was determined from two different alkaline solutions: NaOH and KH₂PO₄. As(V) adsorption capacity of the MgFeHT at different pH (3-12) using the arsenic aqueous solution (with 2,000 μg As(V)/L) was evaluated. For the adsorption process, the experimental data are fitted well with the pseudo-second-order kinetic model and the Langmuir model. Moreover, the concentration of 2,000 μg/L arsenic was reduced to below the legal limit determined by the WHO (<10 μg/L). The regeneration studies were conducted on the adsorptive media used in the arsenic removal system. The regeneration efficiency of As(V) was maintained 98.5% for four regeneration cycles using 0.5 M NaOH. MgFeHT was successfully regenerated with an aqueous solution of NaOH and was reused with a small loss of sorption efficiency.

Arsenic: Geochemical distribution and age-related health risk in Italy

This study is the first attempt to evaluate occurrence, distribution and potential health impacts of As at a national scale in Italy. In various environmental matrices, As geochemical distribution was investigated and carcinogenic and non-carcinogenic risks were assessed with respect to different exposure routes and age groups. Both deterministic and probabilistic methods were used to determine the health risks. Geochemical mapping at a sub-continental scale provided a useful tool to spatially represent As concentration and the critical areas posing a health threat to inhabitants. The results show that significant As concentrations in tap water and soil (up to 27.20 μg/l and 62.20 mg/kg, respectively) are mainly governed by geological features. In the central parts of Italy, where alkaline volcanic materials and consequently high levels of As occur, the residents are prone to health issues. Daily exposure to As in tap water is unparalleled playing an important role in the potential cancer and non-cancer risks. The Incremental Lifetime Cancer Risk for skin cancer and also lung and bladder cancer associated with tap water ingestion interestingly shows that (i) almost 80% of the computed values fall above the internationally accepted benchmark value of 1 × 10^-5; (ii) majority of the data exceed the acceptable risk proposed by most jurisdictions, such as that of Italian law (1 × 10^-6). Further, geographical variation of health risk highlights high carcinogenic and non-carcinogenic risk associated with water ingestion for those living in the northern Alps (including the city of Trento) and the central and southern Italy (including the capital Rome and the cities of Napoli and Catanzaro). According to the results, application of the probabilistic method which considers variability and uncertainty is preferred to the deterministic approach for risk assessment. The sensitivity analysis showed that As concentration in drinking water and exposure duration are the factors with the greatest impact on the outcome of risk assessment (for all age groups). The results of the current study may be a good starting point for authorities to urgently decide about the needed policy actions in order to prevent the adverse health effects and to reduce the human health risk due to As exposure.

Using disability-adjusted life years to estimate the cancer risks of low-level arsenic in drinking water

Recent studies have shown that long-term exposure to low-level arsenic (<10 μg/L) may cause human health problems. However, the induced cancer risks and differences among multisite cancers have not been well-understood. In this study, the concentrations of low-level arsenic in drinking water in XP city, Northwest China were investigated. A health risk assessment was carried out for different age groups and exposure pathways based on Monte Carlo simulations and disability-adjusted life years (DALYs). The measured arsenic levels were in the range of 7.61-9.25 μg/L with a mean of 8.23 μg/L. For the public, the average total lifetime cancer risk was 3.87 × 10^-4, and the total DALYs estimation for all age groups was 20.58 person-year. The average individual DALYs lost was 3.35 × 10^-5 per person-year (ppy), which was 33.5 times the reference value (1.00 × 10^-6 ppy). The mortality burden had a considerably larger contribution (97.31%) to the total disease burden, and the 60-65-year age group exhibited the largest DALYs lost. Skin cancer exhibited the largest burden of 2.15 × 10^-5 ppy, followed by lung cancer (1.20 × 10^-5 ppy). This study might be useful for potential strategies of risk control and management in XP drinking water.

Concentrations and potential health risks of strontium in drinking water from Xi'an, Northwest China

Information about the concentrations of strontium (Sr(II)) in drinking water in China and the corresponding health risks to Chinese residents is lacking. This study investigated Sr(II) in drinking water through a monthly sampling campaign in twelve locations in Xi'an, Northwest China. A health risk assessment for different age groups and exposure pathways were carried out by Monte Carlo simulation. The results show Sr(II) concentrations of 0.06-1.69 mg/L in all drinking water samples, which exceeded the minimum reporting level (MRL) of 0.3 μg/L. Also, one sample exceeded the health reference level (HRL) of 1500 μg/L. Higher Sr(II) levels were recorded in groundwater supply zones and springs, and more potential changes in Sr(II) occurred in distribution pipes transporting groundwater. The non-carcinogenic risk associated with Sr(II) exposure via drinking water was less than 1, indicating no significant health risk to the residents of Xi'an. As the first attempt to provide information on the health risks of Sr(II) in drinking water in China, findings from this study can be useful for the development of potential strategies for risk control and management.

Estimating and comparing the cancer risks from THMs and low-level arsenic in drinking water based on disability-adjusted life years

To determine the priority hazard in drinking water, disability-adjusted life years (DALYs) method was used to evaluate the disease burden induced by trihalomethanes (THMs) and low-level arsenic through multiple exposure routes based on the two-year sampling from drinking water in Xi'an city, Northwest China. The average concentrations of chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (TBM) and arsenic were 12.67 μg/L, 1.42 μg/L, 0.60 μg/L, 0.13 μg/L and 1.00 μg/L, respectively, and the total lifetime cancer risks for all THMs and arsenic were 8.54 × 10^-6 and 4.02 × 10^-5, which were 8.54 and 40.2 times of the negligible risk level (1.00 × 10^-6), respectively. The DALYs estimation showed that the total DALYs lost for all age groups was 32.62 person-year, and the average individual DALYs lost was 4.77 × 10^-6 per person-year (ppy), which was 4.77 times of the reference level (1.00 × 10^-6 ppy). About 72.07% of the total disease burden was due to arsenic, which was considered to be the priority hazard in Xi'an drinking water. The age group of 75-80 years was found to be most vulnerable to the induced cancer risk, and skin cancer had the highest disease burden (2.24 × 10^-6 ppy). Due to the relatively high incidence rates of lung cancer and skin cancer, most DALYs lost for males were 2-4 times to that for females in the same age group. Oral ingestion made the most contribution (88.58%) to the total disease burden, followed by inhalation of THMs (11.30%), whereas dermal absorption showed negligible risk (0.12%). As the first to compare the cancer risks of arsenic and THMs to the public in DALYs in China, this study might be useful for potential strategies of risk control and management of hazardous agents in drinking water.

Water quality characteristics and corrosion potential in blending zones in X city drinking water distribution system

Blended water, always existing in a drinking water distribution system (DWDS) with different sources, can cause some unintended results, including corrosion and/or release of corrosion by-products. Although some studies have specially focused on the blended water in DWDSs, the water quality characteristics, variations, and mechanisms for corrosion and metal release have not been fully understood. This study aims to examine the characteristics and evaluate the corrosion potential of blended water in X city DWDS using four indices of Langelier saturation index (LSI), Ryznar stability index (RSI), Puckorius scaling index (PSI), and calcium carbonate precipitation potential (CCPP). Physical and chemical analysis showed that the values of pH, total dissolved solids (TDS), sulfate (SO₄^2-), and chloride (Cl^-) in blended water were always at acceptable levels, while some free residual chlorine concentrations fell outside the regulatory standards (≥ 0.05 mg/L) with the minimum of 0.01 mg/L. Most parameters except pH varied in large ranges with maximum to minimum ratios (MMRs) over 2.25. The mean values of the LSI, RSI, PSI, and CCPP indices were - 0.44, 8.65, 8.79, and - 1.95 mg/L CaCO₃, respectively, indicating that the blended water was slightly corrosive. For the three zones, Z2 had the highest mean levels of TDS (320.84 mg/L), alkalinity (188.70 mg/L CaCO₃), SO₄^2- (13.69 mg/L), Cl^- (36.37 mg/L), calcium hardness (Ca²⁺) (28.99 mg/L), and magnesium hardness (Mg²⁺) (15.22 mg/L) and the lowest mean level of dissolved oxygen (DO) (6.72 mg/L). Thus, the corrosion potential in Z2 was the lowest with the LSI, RSI, PSI, and CCPP values of - 0.17, 8.11, 8.08, and 2.87 mg/L CaCO₃, respectively. During a year, the corrosion in blended water was more serious in winter with the LSI, RSI, PSI, and CCPP indices of - 0.79, 9.25, 9.37, - 7.54 mg/L CaCO₃, respectively. The water corrosivity reached the minimum level in summer (LSI - 0.12, RSI 8.05, PSI 8.03, and CCPP 5.22 mg/L CaCO₃) owing to the decrease of DO concentrations and the increase of temperature and groundwater supplies with higher alkalinity. During rainy season, the concentrations of TDS, alkalinity, SO₄^2-, Cl^-, Ca²⁺, and Mg²⁺ in blended water were reduced by 41.05%, 40.48%, 35.83%, 47.48%, 23.47%, and 55.73%, respectively, resulting in the increase of water corrosivity. More decreases of water parameters were recorded in Z2 (TDS, 221.80 mg/L; alkalinity, 139.50 mg/L CaCO₃; SO₄^2-, 9.97 mg/L; Cl^-, 13.74 mg/L; Ca²⁺, 7.10 mg/L; and Mg²⁺, 11.37 mg/L), because most groundwater from No. 5 WTP was pumped paretic water with more variations of water quality by rainfall. Moreover, it was suggested that Mg²⁺ should be considered in the corrosion indices, and the corrosion tendency of blended water could be reduced by adjusting the levels of pH, alkalinity, Ca²⁺, and Mg²⁺. The results of this research may pave the way for several opportunities to improve the management and corrosion prevention of blended water.