Engineered nanomaterials in the context of global element cycles†
Environmental nanomaterials researchers are challenged to discern relevant use and release scenarios of engineered nanomaterials (ENMs). Here, we evaluated ENMs within the framework of global anthropogenic element cycles. To provide a bird's-eye view of the status and scale of nanotechnologies, we constructed a multifaceted framework to discern industrial relevance by employing metrics, such as technology readiness level, annual production volumes, synthetic efficiencies, and projected annual market growth rates across twenty-five ENMs. For eight detailed element cycles (Ce, Ag, Zn, Al, Co, Cu, Ni, and Fe), ENMs had a minor influence on anthropogenic element cycling (2 × 10−6 to 2% of total extracted ore), while nSiO2 represents 3–25% of Si metal mined. Production volumes represent only a portion of the material mined for nanomaterial synthesis; synthetic yields for metal, metalloid, and metal oxide nanomaterials were high (typically greater than 90%), while carbon-based nanomaterials have dramatically lower synthetic efficiencies (8–33%). Finally, technology readiness levels indicated that carbon-based nanomaterials have a diverse suite of current applications, whereas metal and metalloid-oxide applications are more limited in number. Several markets continue to grow, particularly quantum dots (58% projected annual growth from 2015–2025). Probing the vast nanomaterial space en masse serves to focus environmental health and safety efforts on materials that are most industrially relevant to biogeochemical processes, and this article is first to consider ENMs within the framework of anthropogenic element cycling of bulk materials at the global level.