A cross-species and model comparison of the acute toxicity of nanoparticles used in the pigment and ink industries

A major user of nanoparticles (NPs) is the pigment and ink industry, where NPs are incorporated into numerous products (e.g. paints, food, plastics, printers, personal care products, and construction materials). Assessment of NP toxicity requires potential impacts on human health and the environment to be evaluated. In this study, we examined the toxicity of a range of NPs, of varied physico-chemical properties, used in the pigment and ink industries including silver (Ag), iron oxide (Fe₂O₃), titanium dioxide (TiO₂), aluminium oxide (Al₂O₃), zinc oxide (ZnO), cobalt aluminium oxide (CoAl₂O₄) and cadmium selenide/zinc sulphide (CdSe/ZnS) quantum dots (QDs). Acute toxicity exerted by this NP panel to mammalian cells in vitro (macrophages, hepatocytes and alveolar epithelial cells) and aquatic environmental organisms (Raphidocelis subcapitata Daphnia magna, Lumbriculus variegatus) was investigated. For mammalian cells, cytotoxicity was assessed 24 h post exposure, at concentrations ranging from 1 to 125 μg/ml using the LDH and WST-1 assays. The aquatic toxicity of the NP panel was assessed according to OECD protocols (201, 202, 315), up to 96 h post exposure. Rats were exposed to selected NPs via intratracheal instillation (62 μg) and the pulmonary inflammatory response quantified 24 h post exposure. This cross-species comparison revealed that Ag, QDs and ZnO NPs were consistently more toxic than the other NPs tested. By looking across mammalian and aquatic ecotoxicological models we obtained a better understanding of the sensitivity of each model, and thus which models should be prioritised for selection in the future when assessing the mammalian and ecotoxicity of NPs, and in particular when screening the toxicity of a panel of NPs. We recommend that macrophage and daphnia models are prioritised when assessing the mammalian toxicity and ecotoxicity of NPs, respectively, due to their increased sensitivity, compared to the other models tested. Of interest is that the in vitro and invertebrate models used were able to predict the toxic potency of the NPs in rodents, and thus our approach has the potential to enhance the implementation of the 3Rs principles in nanotoxicology and reduce reliance on rodent testing when assessing NP safety. By identifying hazardous NPs the data obtained from this study can feed into the selection of (low toxicity) NPs to use in products and will also contribute to the safe design of future generations of NPs used by the pigment and ink industries.