Safety issues relating to nanomaterials for construction applications - Nanotechnology in Eco-efficient Construction - page 149

TNF- in the lungs and bronchoalveolar lavage fl uid of exposed workers

(Xia et al. , 2008).

α

7.5 Future trends and conclusions
With increased attention on MNM health hazards, there has been a need
to develop new methods for toxicity profi ling, safer manufacturing proce-
dures, and 'greener' MNMs as alternatives to more harmful materials. While
engineered nanomaterials provide many benefi ts to 'green' construction,
uncertainty remains about the long-term effects of nano-enhanced struc-
tures. In this context, it will be important to ensure MNMs are not released
into the environment until these MNMs are proven harmless. Or course,
the ultimate goal is to use safe, next generation MNMs for future construc-
tion projects. Ultimately, methods for predicting MNM toxicity a priori
must be explored. Since no defi nitively hazard-free nanomaterial presently
exists, there is much work to be done in this area to alleviate public concern
and move forward with new nano-enabled construction.

7.5.1 Nanomaterial toxicity and green nanomaterials

Our ability to generate safer MNMs will depend on our understanding of
the toxicological liabilities of current MNMs, our ability to tie toxicological
liabilities to MNM properties, and design of greener MNM, which are
devoid of any toxicological liability while building on our conclusions. A
prime example of this approach is the design of environmentally friendlier,
'greener' metal oxide MNMs (Meng et al. , 2009). One of the main toxicity
paradigms of metal oxide MNMs is oxidative stress (Xia et al. , 2006). For
example, it has been shown that the overlap of conduction band energy
( E ( c )) levels with the cellular redox potential ( 4.84 eV) is strongly

correlated to the ability of various nanoparticles to induce oxygen radicals,
oxidative stress, and infl ammation (Zhang et al. , 2012).
Iron doping is one way to tune down the toxicity of ZnO particles, which
are notorious for their ability to generate ROS through ion shedding. The
addition of 1-10% iron results in ZnO particles which are less soluble,
which in consequence are less toxic in the rodent lung and towards zebrafi sh
embryos. We can be hopeful that we will see many more examples of
greener MNMs in the years to come.
Taking MNM production from 'green by trial and error' to 'green by
design' requires us to be able to predict MNM toxicity a priori . Such a pre-
diction of MNM toxicity will depend on our ability to generate a nanostruc-
ture activity relationship (nano-SAR) (Liu et al. , 2012) in which MNM
toxicity properties are correlated with MNM descriptors (Zhang et al. ,
2012). This nano-SAR will provide models of the toxicity profi le of an MNM

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