Abstract
Humans are typically exposed to environmental contaminants’ mixtures that result in different toxicity than exposure to the individual counterparts. Yet, the toxicology of chemical mixtures has been overlooked. This work aims at assessing and comparing viability and cell cycle of A549 cells after exposure to single and binary mixtures of: titanium dioxide nanoparticles (TiO2NP) 0.75–75 mg/L; cerium oxide nanoparticles (CeO2NP) 0.75–10 μg/L; arsenic (As) 0.75–2.5 mg/L; and mercury (Hg) 5–100 mg/L. Viability was assessed through water-soluble tetrazolium (WST-1) and thiazolyl blue tetrazolium bromide (MTT) (24 h exposure) and clonogenic (seven-day exposure) assays. Cell cycle alterations were explored by flow cytometry. Viability was affected in a dose- and time-dependent manner. Prolonged exposure caused inhibition of cell proliferation even at low concentrations. Cell-cycle progression was affected by TiO2NP 75 mg/L, and As 0.75 and 2.5 μg/L, increasing the cell proportion at G0/G1 phase. Combined exposure of TiO2NP or CeO2NP mitigated As adverse effects, increasing the cell surviving factor, but cell cycle alterations were still observed. Only CeO2NP co-exposure reduced Hg toxicity, translated in a decrease of cells in Sub-G1. Toxicity was diminished for both NPs co-exposure compared to its toxicity alone, but a marked toxicity for the highest concentrations was observed for longer exposures. These findings prove that joint toxicity of contaminants must not be disregarded.
Highlights
Nanotechnology is an innovative scientific and economic growth area with exponential production, due to its multidisciplinary applications and economic importance
With the foreseeing increased exposure of humans to legacy and emerging contaminants, a thorough understanding of the potential toxicity resulting from acute and long-term exposure to unintentional mixtures of these contaminants is required. This affirmation is supported by the results presented in this study showing that, even at low concentrations, mixtures of As, Hg, TiO2NP and CeO2NP may result in different toxicity to A549 cell line than the individual counterparts, after long-term exposure
It is noteworthy to mention that, according to the results presented in Figure 10A, the sub-G1 phase caused by exposure to a concentration of 20 μg/L Hg alone is significantly decreased by co-exposure with CeO2NP, indicating a possible long-term protective effect of this material in A549 cells
Summary
Nanotechnology is an innovative scientific and economic growth area with exponential production, due to its multidisciplinary applications and economic importance. Nanoparticles (NPs) can be found in everyday products and, humans are inevitably and constantly exposed to them [1,2] Despite their versatile application and benefits, the effect and impact of NPs on the environment and public health is still uncertain [3]. In the environment, NPs co-exists as complex mixtures, with different types of contaminants and toxic species, such as metal(loids) [4]. Two of the possible scenarios are: (1) NPs may adsorb the contaminant decreasing its availability, resulting in a reduction of contaminant uptake by organisms; or (2) NPs can act as “Trojan Horses” facilitating the transport into cells or organisms, increasing the cellular dose and amplifying the toxic effect of the contaminant. The deleterious effect could be caused by either NPs or the other contaminants, or even in a synergistic way [11,12]
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