“…They either exist freely in nature or are artificial (Griffin et al, 2018). Examples of NPs which exist naturally include organic compounds (such as viruses, bacteria, proteins, and polysaccharides) and inorganic compounds (such as natural dust, aluminosilicates, and iron oxyhydroxides), which are produced by volcanic eruptions, microbial processes, weathering, and wildfires (Griffin et al, 2018;Purev, 2016). However, it remains unknown how long NPs have existed in nature.…”