Improvement of methodological and data background for life cycle assessment of nano-metaloxides

Engineered nanomaterials (ENMs) introduction into consumer products and the increasing amount of ENM product has led to concerns. Based on this, an all-inclusive environmental assessment method of the potential impacts from these is needed. Life cycle assessment (LCA) is an assessment method that considers the whole life cycle of a product or system and is able to quantify impacts from a wide range of impact categories.

In theory LCA is the needed tool, but still there is a limited amount of LCAs performed on ENM products and there are concerns raised on how to apply such a tool on an emerging technology. The aim of the PhD project was to investigate the status and improvement potential of LCA of ENMs. This was done through three sub-aims: • Review current possibilities and limitations of applying LCA on ENM products. • Improve the limitation in ENM production data inventory by presenting novel data from an industrial case study of metal (-oxide) ENM products. • Improve the LCA limitation of ecotoxicity assessment by developing freshwater ecotoxicity characterisation factors for chosen metal (-oxide) ENMs.

By reviewing the scientifically published LCA studies of ENMs it was concluded that there are several challenges. Firstly the LCAs are limited to the first part of the life cycle, the cradle-to-gate. The main reason for this is that the data and approaches for assessing the remainder of the life cycle are not there.

Industrial data inventories are missing, e.g. the data for production of ENMs is often from lab-scale testing and also being reused in different LCA studies. This means that a too limited amount of data is publicly available. Further, issues are also seen on the functional unit setting, as the ENM enhanced functionalities in products are to a lesser extent included.

This provides an unfair comparison, as production of ENM products leads to higher environmental impacts than conventional products. The potential release of ENMs from a product is commonly not dealt with in the reviewed LCAs, mainly due to the missing (eco-) toxicity LCA characterisation factors and actual release measurements from products.

Based on the review a central part of the improvement could be done by addressing the functional unit, data inventory and ENM freshwater ecotoxicity CFs. In order to derive freshwater (European continent) ecotoxicity CFs, at midpoint level, of metal (-oxide) ENMs a fate and effect model was setup. The fate was based on peri-kinetic aggregation (Brownian motion), ortho-kinetic aggregation (fluid motion), differential settling (sedimentation), resuspension and dissolution of ENMs.

The effect part was based on three freshwater trophic levels (algae, daphnia and fish), as in standardized toxicity testing. The results for the engineered nanoparticle (ENP) geometric mean ranges of 1-100 nm and 801- 1000 nm in nominal diameter sizes, were 4.81E+01 (1-100 nm, α=0.01) to 2.05E-02 (801- 1000 nm, α=1), 1.48E-01 (1-100 nm, α=0.01) to 6.27E-05 (801-1000 nm, α=1), and 7.49E+00 (1-100 nm, α=0.01) to 3.20E-03 (801-1000 nm, α=1) PAF·m3 ·day/kg for Ag, TiO2, and ZnO ENMs, respectively.

In terms of toxicity level the derived CFs show that Ag>ZnO>TiO2. The CFs can be applied, but should be considered interim. A LCA case study was performed on five ENM products, where novel industrial production data was presented along with showing the result differences when applying different functional unit approaches.

The LCA case study comparison was based on whether to use ENM or conventional additives (e.g. to enhance the antibacterial properties of a product). The functional units were set according to products equality and to targeted enhanced functionality/property. Results of the study showed that by setting the functional unit according to the targeted functionality some ENM products can environmentally outperform the conventional based products, in terms of predicted environmental impacts.

In the end, a 1 % ENM products release to freshwater was assumed in the case study. The results showed that the ENM release freshwater ecotoxicity contributes with a low impact in relation to the current conventional aquatic ecotoxicty assessment in LCA that does not consider ENM release. In conclusion, the project showed that LCA needs overhauling and particularly in relation to the issues broached in this project.

By not addressing these, the reliability of one’s LCA of ENMs would be significantly compromised.