Assessing human bioaccessibility of trace contaminants in size-fractionated red mud, derived precipitates and geopolymeric blocks

The objective of this study was to provide insight into hwnan exposure to trace contaminants bearing red mud, derived precipitates and geopolymeric blocks due to inhalation contact and/or hand-to-mouth ingestion. The in vitro bioaccessibility behavior of trace contaminants was investigated with the PBET （Physiologically based extraction test）, ALF （artificial lysosomal fluid） and MGS （modified Gamble＇ solution） methods. The results showed that total contents of trace contaminants and operation parameters, such as pH and chelating properties of simulated gastrointestinal phases （PBET）, played a joint role in controlling the bioaccessibility efficacy for size-fractionated red mud particles. As for airborne particles （ 〈 38 μm size fractions）, trace contaminants concentrations extracted by MGS was significantly higher than those by ALF. Additionally, higher bioaccessibility （PBET） values ofCu, Pb, Zn, As, V and U were obtained from red mud derived precipitates compared with those of red mud itself. Even though short-term and long-term leaching values of trace contaminants were relatively lower in the prepared geopolymeric blocks, the health risk could be significantly higher due to the more pronounced bioaccessibility characteristics.

Trace Metal Contamination of Water in the Lubumbashi River Basin, Kafubu, Kimilolo and Kinkalabwamba Rivers in Lubumbashi City, Democratic Republic of Congo

Concentrations of fifteen trace metals including Aluminum （Al）, Vanadium （V）, Chromium （Cr）, Manganese （Mn）, Iron （Fe）, Strontium （Sr）, Molybdenum （Mo）, Silver （Ag）, Cadmium （Cd）, Tin （Sn）, Caesium （Cs）, Barium （Ba）, Lead （Pb）, Bismuth （Bi） and Uranium （U） were investigated in water samples collected from sixteen sampling locations in the Lubumbashi river basin and five locations in Kafubu, Kimilolo and Kinkalabwamba rivers during February, March and April 2016. Chemical analyses of the samples were carried out using ICP-MS （Inductively Coupled Plasma-Mass Spectrometer）. Water pH was determined using a pH-meter and pH values ranged from 4.2 to 7.8. The highest mean trace metal levels of water were 5,515.816 ）μg·L^-1, 166.925μg·L^-1, 3.898μg·L^-1 and 1.879μg·L^-1 for Al, Ba, Cr and U, respectively in Kashobwe river, 2,419.522 μg·L^-1 and 17.994 μg·L^-1 for Fe and Cd, respectively in Kafubu river at its confluence with Lubumbashi rivers, 1,408.136μg·L^-1 for Mn in Kafubu river 1.36 kilometer downward its confluence with Naviundu river, 222.406 μg·L^-1 and 0.092 μg·L^-1 for Sr and Cs, respectively in Kamalondo river 60 meters from the GCM-Lubumbashi （General of Quarries and Mines-Lubumbashi） smelter, 140.294μg·L^-1, 12.063 μg·L^-1 and 0.008μg·L^-1 for Pb, V and Bi, respectively in Munua river, 3.544 μg·L^-1 for Ag in Kabulameshi river, 1.49 μg·L^-1 for Mo in Kafubu river and 0.081μg·L^-1 for Sn in Tshondo river. The mean concentrations of Al, Cd, Fe, Mn and Pb in water of many rivers and the channel exceeded the maximum admissible limits of the WHO （World Health Organization）, USEPA （United States Environmental Protection Agency） and EU （European Union） drinking-water standards. Trace metal contamination of water of the studied rivers, channel and springs might be partially attributed to natural processes, unplanned urbanization, poor waste management and mostly to abandoned and ongoing mining and ore processing activities in Lubumbashi city.

Trace Metal Contamination of Water in Naviundu River Basin, Luano and Ruashi Rivers and Luwowoshi Spring in Lubumbashi City, Democratic Republic of Congo

Aluminum （AI）, Vanadium （V）, Chromium （Cr）, Manganese （Mn）, Iron （Fe）, Strontium （Sr）, Molybdenum （Mo）, Silver （Ag）, Cadmium （Cd）, Tin （Sn）, Caesium （Cs）, Barium （Ba）, Lead （Pb）, Bismuth （Bi） and Uranium （U） concentrations were investigated in water samples from fifteen sampling locations in Naviundu river basin, Luano and Ruashi rivers and Luwowoshi spring in Lubumbashi city during February, March and April 2016. Chemical analyses of the samples were carried out using Inductively Coupled Plasma-Mass Spectrometer. Water pH was determined using a pH-meter and mean pH values ranged from 4.2 to 5.8. The highest mean levels of Al （5,961.954 μg·L^-1）, Pb （472.287 μg·L^-1）, V （21.014 μg·L^-1）, Cr （8.185μg·L^-1）, U （4.163μg·L^-1） and Bi （0.012 μg·L^-1） were recorded in Chemaf （Chemicals of Africa） hydrometallurgical plant effluent, those of Mn （29,714.593 μg·L^-1）, Sr （374.377μg·L^-1）, Cd （11.358μg·L^-1） and Cs （0.107μg·L^-1） in Naviundu river at Cimenkat （Katanga＇s Cement Factory） exit, those of Fe （14,258.9 μg·L^-1） and Ba （307.641μg·L^-1） in Luano river and those of Ag （2.669 μg·L^-1）, Mo （0.559 μg·L^-1） and Sn （0.325 μg·L^-1） were respectively noted in Foire channel, Naviundu river under bridge on Kasenga road and Kalulako river. The concentrations of Cd in Naviundu river at Cimenkat exit （11.358 μg·L^-1）, Chemaf bydrometallurgical plant effluent （9.697μg·L^-1）, Naviundu river under bridge on De Plaines Avenue （6.95 μg·L^-1） and Kalulako river （3.229 μg·L^-1）, Pb concentrations in Chemaf hydrometallurgical plant effluent （472.287 μg·L^-1） as well as the AI, Fe and Mn concentrations recorded in most waters in this study exceeded the WHO （World Health Organization） maximum permissible limits for drinking water. The metal contamination of waters of the studied rivers, channel and spring might be partially attributed to natural processes, unplanned urbanization and poor waste management, and mostly to abandoned and ongoing mining and ore processing activities in Lubumbashi city.

Mechanistic insights for efficient inactivation of antibiotic resistance genes: a synergistic interfacial adsorption and photocatalytic-oxidation process

Advanced oxidation processes(AOPs) have been applied to address multiple environmental concerns including antibiotic resistance genes(ARGs). ARGs have shown an increasing threat to human health,and they are either harbored by antibiotic-resistant bacteria(ARB) or free in the environment.However, the control of ARGs has been substantially limited by their low concentration and the limited knowledge about their interfacial behavior. Herein, a novel AOP catalyst, Ag/TiO_(2)/graphene oxide(GO),combined with a polyvinylidene fluoride(PVDF) ultrafiltration membrane was designed with a synergistic interfacial adsorption and oxidation function to inactivate ARGs with high efficiency in both model solutions and in secondary wastewater effluent, especially when the residue concentration was low.Further analysis showed that the mineralization of bases and phosphodiesters mainly caused the inactivation of ARGs. Moreover, the interfacial adsorption and oxidation processes of ARGs were studied at the molecular level. The results showed that GO was rich in sp^(2) backbones and functional oxygen groups,which efficiently captured and enriched the ARGs via p-p interactions and hydrogen bonds. Therefore,the photogenerated active oxygen species attack the ARGs by partially overcoming the kinetic problems in this process. The Ag/Ti O2/GO catalyst was further combined with a PVDF membrane to test its potential in wastewater treatment applications. This work offers an efficient method and a corresponding material for the inactivation and mineralization of intra/extracellular ARGs. Moreover, the molecularlevel understanding of ARG behaviors on a solid–liquid interface will inspire further control strategies of ARGs in the future.