Potential health risk assessment through ingestion and dermal contact arsenic-contaminated groundwater in Jianghan Plain, China.

Groundwater contamination with high arsenic (As) levels has caused serious health problem in Jianghan Plain. This study presents a framework to evaluate the results and their probable influencing factors of non-carcinogenic risk and carcinogenic risk in Shahu Village. An appropriate health risk assessment for residents exposing to As through ingestion and dermal contact pathways is also discussed in the paper. Hazard quotient (HQ) and target cancer risk (TR) are adopted to compute the non-carcinogenic and carcinogenic effects for residents, respectively. Monte Carlo simulation technique is used to quantify the uncertainty of the risk assessment. The assessment results show that the HQs and TRs of 10-m-deep and 25-m-deep wells exhibit seasonal variations with higher values in rainy season and lower values in dry season. The HQ values exceeding 1 at the depths of 10 (from 0.09 to 23.21 m) and 25 m (from 0.29 to 130.55 m) account for 61 and 94%, respectively, which associate with the As contents distribution in the aquifer sediments. The estimated TR values at the depths of 10 (from 3.86E-05 to 1.04E-02) and 25 m (from 1.32E-04 to 5.87E-02) exceeding the highest acceptable standard (10-4) account for 95 and 100%, respectively. Comparison of the two exposure pathways, the ingestion exposure contributes much more than the dermal contact exposure for both non-carcinogenic risk and carcinogenic risk. The results of sensitivity analysis indicate that a more accurate measurement and better definition of probability distributions for As concentration in the groundwater can increase the accuracy of health risk assessment in Jianghan Plain. The findings demonstrate the importance of the drinking water safety, and the government should take measures to ensure the drinking water safety.

Characterization of spent nickel-metal hydride batteries and a preliminary economic evaluation of the recovery processes.

UNLABELLED: Valuable metal materials can be recovered from spent nickel-metal hydride (NiMH) batteries. However, little attention has been paid to the metal compositions of individual components of NiMH batteries, although this is important for the selection of the appropriate recycling process. In this study, NiMH batteries were manually disassembled to identify the components and to characterize the metals in each of these. A preliminary economic analysis was also conducted to evaluate the recovery of valuable metals from spent NiMH batteries using thermal melting versus simple mechanical separation. The results of this study show that metallic components account for more than 60% of battery weight. The contents of Ni, Fe, Co, and rare earth elements (REEs) (i.e., valuable metals of interest for recovery) in a single battery were 17.9%, 15.4%, 4.41%, and 17.3%, respectively. Most of the Fe was in the battery components of the steel cathode collector, cathode cap, and anode metal grid, while Ni (>90%) and Co (>90%) were mainly in the electrode active materials (anode and cathode metal powders). About 1.88 g of REEs (Ce, La, and Y) could be obtained from one spent NiMH battery. The estimated profits from recovering valuable metals from spent NiMH batteries by using thermal melting and mechanical processes are 2,329 and 2,531 USD/ton, respectively, when including a subsidy of 1,710 USD/ton. The findings of this study are very useful for further research related to technical and economic evaluations of the recovery of valuable metals from spent NiMH batteries. IMPLICATIONS: The spent nickel-metal hydride (NiMH) batteries were manually disassembled and their components were identified. The metals account for more than 60% of battery weight, when Ni, Fe, Co, and rare earth elements (REEs) were 17.9%, 15.4%, 4.41%, and 17.3%, respectively, in a single battery. The estimated profits of recovering valuable metals from NiMH batteries by using thermal melting and mechanical processing are 2,329 and 2,531 USD/ton, respectively, when including a subsidy of 1,710 USD/ton. These findings are very useful to develop or select the recovery methods of valuable metals from spent NiMH batteries.

Optical Characterization of Strong UV Luminescence Emitted from the Excitonic Edge of Nickel Oxide Nanotowers.

NiO had been claimed to have the potential for application in transparent conducting oxide, electrochromic device for light control, and nonvolatile memory device. However, the detailed study of excitonic transition and light-emission property of NiO has rarely been explored to date. In this work, we demonstrate strong exciton-complex emission of high-quality NiO nanotowers grown by hot-filament metal-oxide vapor deposition with photoluminescence as an evaluation tool. Fine and clear emission features coming from the excitonic edge of the NiO are obviously observed in the photoluminescence spectra. A main excitonic emission of ~3.25 eV at 300 K can be decomposed into free exciton, bound excitons, and donor-acceptor-pair irradiations at lowered temperatures down to 10 K. The band-edge excitonic structure for the NiO nanocrystals has been evaluated and analyzed by transmission and thermoreflectacne measurements herein. All the experimental results demonstrate the cubic NiO thin-film nanotower is an applicable direct-band-gap material appropriate for UV luminescence and transparent-conducting-oxide applications.

Dynamic factor analysis for estimating ground water arsenic trends.

Drinking ground water containing high arsenic (As) concentrations has been associated with blackfoot disease and the occurrence of cancer along the southwestern coast of Taiwan. As a result, 28 ground water observation wells were installed to monitor the ground water quality in this area. Dynamic factor analysis (DFA) is used to identify common trends that represent unexplained variability in ground water As concentrations of decommissioned wells and to investigate whether explanatory variables (total organic carbon [TOC], As, alkalinity, ground water elevation, and rainfall) affect the temporal variation in ground water As concentration. The results of the DFA show that rainfall dilutes As concentration in areas under aquacultural and agricultural use. Different combinations of geochemical variables (As, alkalinity, and TOC) of nearby monitoring wells affected the As concentrations of the most decommissioned wells. Model performance was acceptable for 11 wells (coefficient of efficiency >0.50), which represents 52% (11/21) of the decommissioned wells. Based on DFA results, we infer that surface water recharge may be effective for diluting the As concentration, especially in the areas that are relatively far from the coastline. We demonstrate that DFA can effectively identify the important factors and common effects representing unexplained variability common to decommissioned wells on As variation in ground water and extrapolate information from existing monitoring wells to the nearby decommissioned wells.

Immobilization and encapsulation during vitrification of incineration ashes in a coke bed furnace.

A real-scale coke bed furnace system has been successfully applied to vitrify the incineration ashes into glassy slags. The object of this research was to evaluate the effect of the system on the immobilization of metal species in the slag. Ashes and slag specimens were tested to identify their metal phase distribution following a sequential extraction procedure. The mobility of Al, Ca, Cd, Cr, Mg, Mn and Pb was noticeably reduced by vitrification. An important implication is the reduction of Cr(6+) to Cr(3+) along with its immobilization with this coke bed furnace. The Ni and Zn contents were relatively low in slag, indicating that their availability of mobile phases in ashes was reduced during vitrification. The XRD analyses identified the major crystalline phase in slag as åkermanite, which is inert and helpful in metal immobilization. The phase distribution analysis also contributed to verify that the incorporation of Ca and Mg enhanced the encapsulation in the slag matrix. The low oxygen content in slag made the structure of silicate resistant to the proton-promoted attack and also enhanced the mobility reduction of matrix elements (Ca, Mg and Al) in the moderately reducible phase and also contributed to the immobilization of other metal species. However, the properties of slag also deserve further studies to ensure its long-term stability and safety.

Metal behavior during vitrification of incinerator ash in a coke bed furnace.

In this study, municipal waste incinerator ash was vitrified in a coke bed furnace system and the behavior of metals was investigated. Coke and lime were added to provide heat which facilitated vitrification. Ash contributed more than 90% of metal (except for Ca) input-mass. Metal species with low boiling points accounted for the major fraction of their input-mass adsorbed by air pollution control devices (APCDs) fly ash. Among the remaining metals, those species with light specific weights in this furnace tended to be encapsulated in slag, while heavier species were mainly discharged by ingot. Meanwhile, the leachability of hazardous metals in slag was significantly reduced. The distribution index (DI) was defined and used as an index for distribution of heavy metals in the system. A high DI assures safe slag reuse and implies feasibility of recovering hazardous heavy metals such as Cr, Cu, Fe, Pb and Zn. The vitrification in a coke bed furnace proved to be a useful technology for the final disposal of MSW incinerator ash. The heavy metals are separated into the slag, ingot and fly ash, allowing safe reuse of the slag and possible recovery of the metals contained in the ingot and ash fractions.

Fate of polycyclic aromatic hydrocarbons during vitrification of incinerator ash in a coke bed furnace.

Fate of polycyclic aromatic hydrocarbons (PAHs) during the vitrification of fly ash and bottom ash from the municipal waste incinerator in a coke bed furnace was investigated. In this system, both coke and lime were added to enhance the melting reaction. The major PAH sources in this system were ash and coke, which respectively contributed 97% and 3% of PAHs in the input-mass. During vitrification process, low molecular PAHs (LM-PAH, 2-3-ring), median molecular PAHs (MM-PAH, 4-ring) and high molecular PAHs (HM-PAH, 5-7-ring) mass respectively accounted for >99%, >99% and 84% of the output-mass emitted as the stack flue gas; while those discharged from the slag were <1%, <1% and 16%, respectively. The O/I (output-mass/input-mass) ratio of LM-, MM- and HM-PAHs were 0.063, 0.002 and <0.001, respectively. The high distribution in flue gas and O/I ratio of LM-PAHs is reasonable since they are more easily evaporated, hence difficult to be removed by air pollution control devices. On the contrary, the HM-PAHs, having lower vapor pressure, primarily stays mainly in slag. Based on the 21 total PAH content in feeding ash and slag, the reduction efficiency of the coke bed furnace was >99.9%. To minimize the risk of secondary pollution, the efficiency of coke bed furnace should be improved to reduce the PAH emission into ambient air.