Review of nanomaterial aging and transformations through the life cycle of nano-enhanced products

Abstract

In the context of assessing potential risks of engineered nanoparticles (ENPs), life cycle thinking can represent a holistic view on the impacts of ENPs through the entire value chain of nano-enhanced products from production, through use, and finally to disposal. Exposure to ENPs in consumer or environmental settings may either be to the original, pristine ENPs, or more likely, to ENPs that have been incorporated into products, released, aged and transformed. Here, key product-use related aging and transformation processes affecting ENPs are reviewed. The focus is on processes resulting in ENP release and on the transformation(s) the released particles undergo in the use and disposal phases of its product life cycle for several nanomaterials (Ag, ZnO, TiO2, carbon nanotubes, CeO2, SiO2 etc.). These include photochemical transformations, oxidation and reduction, dissolution, precipitation, adsorption and desorption, combustion, abrasion and biotransformation, among other biogeochemical processes. To date, few studies have tried to establish what changes the ENPs undergo when they are incorporated into, and released from, products. As a result there is major uncertainty as to the state of many ENPs following their release because much of current testing on pristine ENPs may not be fully relevant for risk assessment purposes. The goal of this present review is therefore to use knowledge on the life cycle of nano-products to derive possible transformations common ENPs in nano-products may undergo based on how these products will be used by the consumer and eventually discarded. By determining specific gaps in knowledge of the ENP transformation process, this approach should prove useful in narrowing the number of physical experiments that need to be conducted and illuminate where more focused effort can be placed.

Nanomaterials Release from Nano-Enabled Products

“…Sun et al claimed that NMs use in polymer reinforcement represented the main production of carbon nanotubes (CNT, 84.1%, >300 tons/year in EU) and fullerenes (45.9%) and an important application field of other nanosized materials such as TiO 2 (3.6%, >500 tons/year in EU), ZnO (2%, >1,000 tons/year in EU) or Ag (3.3%) [9]. Similarly, Kalinina has reported plastic reinforcement as one of the main uses of nano-SiO 2 , estimating around 1,500 tons/ year in EU [8,10]. These studies also report the penetration of NMs in ceramic and metallic materials.…”

“…It means that different NMs in the same matrix can have similar characteristics once released [8]. However, due to photodegradation, hydration and hydrolysis processes, NMs can be modified and released with surface modifications (e.g., TiO 2 surface hydration or CNT oxidation).…”

“…It is very difficult to quantify, or even estimate, the levels of nanocomposite (NC) production and the amounts of every NM that are being used due to the lack of official registers and the mistrust of the companies in giving any type of information Insulation Surface, embedded [7][8][9]. Anyway, all the attempts to estimate annual production of NMs point to NCs as one of the most important application fields, mainly as plastic reinforcers (which include the packing industry).…”

“…Thus, the processes to study NM release can be very similar to the ones accepted and standardized to study material performance by traditional ageing. Most literature in the field is focused on two types of degradation processes, UV ageing/weathering and machining abrasion, while literature reporting migration due to contact with liquids is still very scarce [8,39]. These processes intend to simulate the release that occurs in different scenarios: in outdoor applications where NCs are exposed to sunlight, temperature and/or rain exposure; in NCs contacting to any type of liquid such as the ones for packaging or engineered tissue applications; and in NCs subject to abrasion forces such as in machinery applications.…”

Paradigms on landfill mining: From dump site scavenging to ecosystem services revitalization

“…There is an urgent need for broad and integrated studies that address the risks of engineered nanomaterials and other emerging pollutants, including their impacts on the waste composition, to consider them for landfill mining and recovery of valuables (Tolaymat et al 2015) as well as the recovery potential of nanomaterials itself. In the context of assessing potential risks of engineered nanoparticles, life cycle thinking can represent a holistic view on the impacts of nanomaterials through the entire value chain of nanoparticles containing products from production, through use, and finally to disposal (Mitrano et al 2015). …”