Public Health

Current understanding of potential toxicity of engineered nanomaterials to aquatic microorganisms is limited for risk assessment and management. Here we evaluate if the MetPLATE™ test can be used as an effective and rapid screening tool to test for potential aquatic toxicity of various metal-based nanoparticles (NPs). The MetPLATE bioassay is a heavy metal sensitive test based on β-galactosidase activity in Escherichia coli. Five different types of metal-based NPs were screened for toxicity: (1) citrate coated nAg (Citrate-nanosilver), (2) polyvinylpyrrolidone coated nAg (PVP-nAg), (3) uncoated nZnO, (4) uncoated nTiO2 and (5) 1-Octadecylamine coated CdSe Quantum Dots (CdSe QDs); and compared with their corresponding ionic salt toxicity. Citrate-nAg was further fractionated into clean Citrate-nAg, unclean Citrate-nAg and permeate using a tangential flow filtration (TFF) system to eliminate residual ions and impurities from the stock Citrate-nAg suspension and also to differentiate between ionic- versus nano-specific toxicity. Our results showed that nAg, nZnO and CdSe QDs were less toxic than their corresponding ionic salts tested, while nano- or ionic form of TiO2 was not toxic as high as 2.5 g L− 1 to the MetPLATE™ bacteria. Although coating-dependent toxicity was noticeable between two types of Ag NPs evaluated, particle size and surface charge were not adequate to explain the observed toxicity; hence, the toxicity appeared to be material-specific. Overall, the toxicity followed the trend: CdCl2 > AgNO3 > PVP-nAg > unclean Citrate-nAg > clean Citrate-nAg > ZnSO4 > nZnO > CdSe QDs > nTiO2/TiO2. These results indicate that an evaluation of β-galactosidase inhibition in MetPLATE™ E. coli can be an important consideration for rapid screening of metal-based NP toxicity, and should facilitate ecological risk assessment of these emerging contaminants.► MetPLATE bioassay was evaluated as a rapid screening tool for nanotoxicity. ► Five different metal nanoparticles were tested for potential aquatic toxicity. ► Evaluated nanoparticles were less toxic than their respective ionic salts. ► Nano-TiO2, including its ionic form, was non-inhibitory to MetPLATE. ► Results show MetPLATE can be considered a rapid screening tool for nanotoxicity.

With rising valuation of mineral commodities, mining has been envisioned as a profitable industry regardless of many challenges it entails. This comprehensive review provides the state of knowledge about several aspects of the metal mining industry, including (a) the basic mining processes with reasons for mine closure, (b) the potential environmental and human health impacts associated with mining, (c) the potential techniques for impact mitigation, (d) the latest production statistics for the base and precious metals with identification of currently operational major metal mines for different countries, and (e) how mining activities are regulated in different nations. Finally, the authors provide critical appraisal on the debatable issue of mining and sustainability to stimulate thoughts on how metal mining can be made sustainable, and suggest a path forward. Issues of Metal Mining: A Review 2353 explorations for mining and subsequent use of the metalliferous minerals do not seem to cease down. 1 Because of their inherent characteristics, such as malleability, ductility, good conductivity of heat and electricity, and durability, metals serve many purposes. 1 From bases of skyscrapers to ordinary homes, from automobile body parts to robust engines, from tailors' sewing needles to surgeons' scalpels, and from common household utensils to heavy duty machineries, all use metals in one form or the other. For alchemists, many metals serve as catalysts to facilitate the chemical reactions. Precious metals, such as gold, silver, and platinum, in bullion have great economic value. To meet the global demand of materials and energy for ever-growing human populations and to maintain better living standards, mining has been envisioned as a dependable source of many metallic minerals. With the recent growing hype for sustainable society, metal mining industry-the only source for almost two thirds of the mostly used metallic elements-is also anticipated to offer potential for sustainable development. Basically, metals are of two types-base metals and precious metals. Base metals are defined in many ways. Mining and economics define base metals as inexpensive, non-ferrous metals but not the precious metals. It includes copper, lead, zinc, and nickel. 5 The U.S. Customs and Boarder Protection defines base metals under Harmonized Tariff Schedule (HTS) as iron and steel, thallium. The Oxford dictionary, on the other hand, defines a base metal as a common metal that is not considered precious, such as copper, tin, or zinc. Usually base metals are relatively reactive and form oxides. In contrast, precious metals are relatively less reactive, rarely available and highly expensive such as gold, silver, and platinum. 6 This review follows the HTS definition for base metals.

Mechanism underlying nanotoxicity has remained elusive. Hence, efforts to understand whether nanoparticle properties might explain its toxicity are ongoing. Considering three different types of organo-coated silver nanoparticles (AgNPs): citrate-coated AgNP, polyvinylpyrrolidone-coated AgNP, and branched polyethyleneimine-coated AgNP, with different surface charge scenarios and core particle sizes, herein we systematically evaluate the potential role of particle size and surface charge on the toxicity of the three types of AgNPs against two model organisms, Escherichia coli and Daphnia magna. We find particle size, surface charge, and concentration dependent toxicity of all the three types of AgNPs against both the test organisms. Notably, Ag + (as added AgNO 3 ) toxicity is greater than each type of AgNPs tested and the toxicity follows the trend: AgNO 3 N BPEI-AgNP N Citrate-AgNP N PVP-AgNP. Modeling particle properties using the general linear model (GLM), a significant interaction effect of primary particle size and surface charge emerges that can explain empirically-derived acute toxicity with great precision. The model explains 99.9% variation of toxicity in E. coli and 99.8% variation of toxicity in D. magna, revealing satisfactory predictability of the regression models developed to predict the toxicity of the three organo-coated AgNPs. We anticipate that the use of GLM to satisfactorily predict the toxicity based on nanoparticle physico-chemical Science of the Total Environment 468-469 (2014) 968-976 j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v characteristics could contribute to our understanding of nanotoxicology and underscores the need to consider potential interactions among nanoparticle properties when explaining nanotoxicity.

Biologically, two species within a genus are more similar (e.g., morphologically and genetically) in many respects than two other species belonging to different genera. Despite the long history of ecotoxicology and efforts to understand interspecies variability in sensitivity to environmental contaminants, choosing representative species for screening potential toxicity of the environmental contaminants, be it the conventional toxicants such as the dioxins or the emerging contaminants such as the manufactured nanomaterials, has remained challenging. More challenges have, however, confronted the emerging nano-research community-a highly diverse community of researchers ranging from those with expertise involved in tailoring nanomaterial properties for desired applications to others engaged in identifying whether nanomaterial is a hazard and poses risk to environmental health and safety (EHS)-in discerning the mechanistic basis of toxicity, including both the intrinsic and extrinsic factors that could potentially modulate toxicity, of the manufactured nanomaterials on various biological organisms.

Current understanding of potential toxicity of engineered nanomaterials to aquatic microorganisms is limited for risk assessment and management. Here we evaluate if the MetPLATE™ test can be used as an effective and rapid screening tool to test for potential aquatic toxicity of various metal-based nanoparticles (NPs). The MetPLATE bioassay is a heavy metal sensitive test based on β-galactosidase activity in Escherichia coli. Five different types of metal-based NPs were screened for toxicity: (1) citrate coated nAg (Citrate-nanosilver), (2) polyvinylpyrrolidone coated nAg (PVP-nAg), (3) uncoated nZnO, (4) uncoated nTiO 2 and (5) 1-Octadecylamine coated CdSe Quantum Dots (CdSe QDs); and compared with their corresponding ionic salt toxicity. Citrate-nAg was further fractionated into clean Citrate-nAg, unclean Citrate-nAg and permeate using a tangential flow filtration (TFF) system to eliminate residual ions and impurities from the stock Citrate-nAg suspension and also to differentiate between ionic-versus nano-specific toxicity. Our results showed that nAg, nZnO and CdSe QDs were less toxic than their corresponding ionic salts tested, while nano-or ionic form of TiO 2 was not toxic as high as 2.5 g L − 1 to the MetPLATE™ bacteria. Although coating-dependent toxicity was noticeable between two types of Ag NPs evaluated, particle size and surface charge were not adequate to explain the observed toxicity; hence, the toxicity appeared to be material-specific. Overall, the toxicity followed the trend: CdCl 2 > AgNO 3 > PVP-nAg> unclean Citrate-nAg > clean Citrate-nAg > ZnSO 4 > nZnO> CdSe QDs > nTiO 2 / TiO 2 . These results indicate that an evaluation of β-galactosidase inhibition in MetPLATE™ E. coli can be an important consideration for rapid screening of metal-based NP toxicity, and should facilitate ecological risk assessment of these emerging contaminants.