A. Wagner, A.P. White, M.C. Tang, S. Agarwal, T.A. Stueckle, Y. Rojanasakul, K.A. Sierros, R.K. Gupta, C.Z. Dinu
West Virginia University,
United States
Keywords: nanoclay, nanocomposites, toxicity, safety implementation
Summary:
Nanoclays are layered mineral silicates that originate from the clay fraction of the soil and are readily available, as well as inexpensive. Upon organic modification, generally with quaternary ammonium compounds, nanoclays can be incorporated into polymers to form nanocomposites with increased strength, barrier properties, and UV dispersion capabilities, allowing for an increased usage in industrial areas such as food packaging or medical devices. However, little information is available on the toxicity of nanoclay or nanoclay-containing systems, as well as their end of life cycle byproducts. Considering that upon usage, nanoclay-containing systems or nanocomposites likely undergo incineration via municipal solid waste plants to be then disposed in the landfilled and considering that during the incineration and disposal there is the possibility of human interaction during the route of inhalation, there is a need to understand their toxicological profiles and predict ways to circumvent their deleterious effects. Herein, we designed a systematic study to investigate the physico-chemical properties of nanoclay systems, both pristine and organically modified nanoclays, along with an associated nanocomposite, in their as-received forms, mimicking the manufacturing stage, and in their thermally degraded forms, mimicking end of life cycle stage. We then correlated such properties to potential, induced toxicity to lung epithelial cells, used to model inhalation toxicity. Material properties were determined via microscopical and spectroscopical techniques, while toxicity was determined via in vitro cellular assays using discrete time point assays as well as real-time monitoring. Model in vivo systems were also used to assess long term human exposure and viable toxicological pathways. Our data and analysis showed that the organic modifier played a large role in the material properties and ultimately influenced toxicity, with the organic modifier generally displaying increased toxicity, dependent on the modifier composition. Further, loss of the organic modifier via thermal degradation caused for changes in the physico-chemical properties of the nanoclays or nanocomposites, resulting in a general, decreased toxicity profiles for cellular or in vivo systems, relative to the as-received nanoclays. Finally, the thermally degraded nanocomposite also displayed similar toxicological profiles relative to the thermally degraded nanoclays, solely. Based on these results, detection and mitigation strategies should be implemented in areas of manufacturing and disposal of nanoclay and their related systems to thus reduce worker inhalation hazards. Further investigations are also recommended in order to explore the pathways that will lead to safe-by-design manufacturing of such nanomaterials as well as optimization of their implementation or disposal strategies.