It is expected that the rapid expansion of nanotechnology will bring many potential benefits. However, initial investigations have demonstrated that nanomaterials may adversely affect human health and the environment. By increasing the application of nanoparticles, protection of the human respiratory system from exposure to airborne nanoparticles and ultrafine particulates has become an emerging health concern. Available research has demonstrated an association between exposure to ambient airborne particulates and ultrafine particles and various adverse heath effects including increased morbidity and mortality. Nanomaterial structures are more likely to be toxic than the same materials of conventional sized samples and can be inhaled more deeply into the lungs. While the respiratory tract is considered as the primary target organ for inhaled nanoparticles, recent research has demonstrated that extrapulmonary organs are also affected. The very small size distribution and large surface area of nanoparticles available to undergo reactions may play a significant role in nanotoxicity, yet very little is known about their interactions with biological systems. This review explores the possible underlying toxicity mechanisms of nanoparticles following inhalational exposure. Nanoparticles differ from the same conventional material at a larger scale in physical, chemical and biological characteristics; therefore it is critical to recognize the potential risk of nanoparticle exposure using appropriate toxicity test methods. Current advances and limitations of toxicity assessment methods of nanoparticles are discussed highlighting the recent improvements of in vitro screening tools for the safety evaluation of the rapidly expanding area of nanotechnology.
Novel engineered nanoparticles (NPs), nanomaterial (NM) products and composites, are continually emerging worldwide. Many potential benefits are expected from their commercial applications; however, these benefits should always be balanced against risks. Potential toxic effects of NM exposure have been highlighted, but, as there is a lack of understanding about potential interactions of nanomaterials (NMs) with biological systems, these side effects are often ignored. NPs are able to translocate to the bloodstream, cross body membrane barriers effectively, and affect organs and tissues at cellular and molecular levels. NPs may pass the blood–brain barrier (BBB) and gain access to the brain. The interactions of NPs with biological milieu and resulted toxic effects are significantly associated with their small size distribution, large surface area to mass ratio (SA/MR), and surface characteristics. NMs are able to cross tissue and cell membranes, enter into cellular compartments, and cause cellular injury as well as toxicity. The extremely large SA/MR of NPs is also available to undergo reactions. An increased surface area of the identical chemical will increase surface reactivity, adsorption properties, and potential toxicity. This review explores biological pathways of NPs, their toxic potential, and underlying mechanisms responsible for such toxic effects. The necessity of toxicological risk assessment to human health should be emphasised as an integral part of NM design and manufacture.
Exposure to occupational and environmental contaminants is a major contributor to human health problems. Inhalation of gases, vapors, aerosols, and mixtures of these can cause a wide range of adverse health effects, ranging from simple irritation to systemic diseases. Despite significant achievements in the risk assessment of chemicals, the toxicological database, particularly for industrial chemicals, remains limited. Considering there are approximately 80,000 chemicals in commerce, and an extremely large number of chemical mixtures, in vivo testing of this large number is unachievable from both economical and practical perspectives. While in vitro methods are capable of rapidly providing toxicity information, regulatory agencies in general are still cautious about the replacement of whole-animal methods with new in vitro techniques. Although studying the toxic effects of inhaled chemicals is a complex subject, recent studies demonstrate that in vitro methods may have significant potential for assessing the toxicity of airborne contaminants. In this review, current toxicity test methods for risk evaluation of industrial chemicals and airborne contaminants are presented. To evaluate the potential applications of in vitro methods for studying respiratory toxicity, more recent models developed for toxicity testing of airborne contaminants are discussed.
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