Vol.:(0123456789) 1 3 Environmental Chemistry Letters https://doi.org/10.1007/s10311-020-01033-6 REVIEW Toxicity of metal and metal oxide nanoparticles: a review Ayse Busra Sengul 1  · Eylem Asmatulu 2 Received: 22 August 2019 / Accepted: 7 June 2020 © Springer Nature Switzerland AG 2020 Abstract Nanotechnology has recently found applications in many felds such as consumer products, medicine and environment. Nano- particles display unique properties and vary widely according to their dimensions, morphology, composition, agglomeration and uniformity states. Nanomaterials include carbon-based nanoparticles, metal-based nanoparticles, organic-based nano- particles and composite-based nanoparticles. The increasing production and use of nanoparticles result in higher exposure to humans and the environment, thus raising issues of toxicity. Here we review the properties, applications and toxicity of metal and non-metal-based nanoparticles. Nanoparticles are likely to be accumulated in sensitive organs such as heart, liver, spleen, kidney and brain after inhalation, ingestion and skin contact. In vitro and in vivo studies indicate that exposure to nanoparticles could induce the production of reactive oxygen species (ROS), which is a predominant mechanism leading to toxicity. Excessive production of ROS causes oxidative stress, infammation and subsequent damage to proteins, cell mem- branes and DNA. ROS production induced by nanoparticles is controlled by size, shape, surface, composition, solubility, aggregation and particle uptake. The toxicity of a metallic nanomaterial may difer depending on the oxidation state, ligands, solubility and morphology, and on environmental and health conditions. Keywords Nanotechnology · Nanoparticles · Metal nanoparticles · Toxicity mechanism · Reactive oxygen species Introduction Nanotechnology has become one of the most rapidly grow- ing areas of science and technology in the USA as well as other parts of the world. It has led to the increased produc- tion and applications of nanomaterials in a wide range of felds such as automotive, biomedical, cosmetics, defense, energy and electronics. The global market for nanotechnol- ogy products and applications was valued at $39.2 billion in 2016 and is expected to reach $90.5 billion in 2021 (McWil- liams 2016). The nanomaterial is defned as a material with any exter- nal dimension in the nanoscale or having an internal struc- ture or surface structure in the nanoscale, approximately 1–100 nm size range (ISO 2015). They may be in the form of nanoparticles, nanofbers, nanotubes, nanocomposites and nanostructured materials. Figure 1 shows the classif- cation of nanostructure materials according to dimensions, morphology, composition, agglomeration and uniformity states. Nanoparticle agglomeration, size and surface reac- tivity, along with shape and size, need to be considered when choosing health and environmental regulations for new materials (Asmatulu et al. 2013; Asmatulu 2013). Nanopar- ticles have been used in many products due to their unique physicochemical properties, which include a large surface- to-volume ratio, extremely small size and size-dependent optical properties (Sajid et al. 2015). For example, cobalt nanoparticles have gained great interest in biomedical- related felds such as drug delivery and magnetic resonance imaging (Ansari et al. 2017). Silica nanoparticles are used in chemical and electronic industries, building materials, foods, and the biomedical and biotechnological felds (Kaphle et al. 2018; Zhou et al. 2019). Titanium dioxide and zinc oxide nanoparticles are frequently used as suncare products to minimize the unwanted skin whitening efect and to pro- vide high UV protection efcacy and pleasant skin aesthetics (Stark et al. 2015). Although the uses of nanoparticles have contributed signifcant advantages in many areas, nanoparticles raise * Eylem Asmatulu e.asmatulu@wichita.edu 1 Department of Civil and Construction Engineering, Kennesaw State University, Kennesaw, GA 30144, USA 2 Department of Mechanical Engineering, Wichita State University, 1845 Fairmount Street, Wichita, KS 67260, USA