It Really is a Very Small Thing!
A new batch of papers on nanoparticles suggests that it is time to revisit this topic. The last library on nanoparticles was in 2010. Since then, I’ve avoided thinking about them and haven’t really missed them. In fact, coming up with a clever title for the library just reinforced how much more I miss Robin Williams and how much more he contributed to our society than nanoparticles, in particular nano silver. But that is article #,2 and I am getting ahead of myself. For those too young, or for whatever reason, Nanu Nanu was a stock part of Robin William’s vocabulary; it was how he said good bye on the show Mork and Mindy (see for yourself on Hulu).
This library starts with a paper that has modeled the potential environmental concentrations of the range of nano materials in large scale use. The authors included titanium, zinc, silver, and carbon nano tubes and fullerenes in their model. They accounted for a wide range of uses for these materials, including composites, plastics, glass, ceramics and light bulbs. For these uses, landfill disposal was the primary pathway considered. For cosmetics, coatings, cleaning agents and dietary supplements, wastewater treatment was the primary pathway. For textiles, landfill disposal and wastewater treatment were both considered. From that abbreviated list of types of products you can understand that, right now, these materials are ubiquitous. Figure 1 of this paper is the most useful for me, as it includes diagrammed results of where the different types of particles end up. For titanium, silver and zinc particles, the thickest arrow goes to the WWTP. There is also a table that shows the predicted changes in concentration in biosolids and biosolids amended soils for the different materials. The authors conclude that such particles are not a significant risk for land application of biosolids.
From here, I thought that it would be useful to go to an article that considers whether the use of these nanomaterials actually yields any benefits. We figured out way too late that all of those antimicrobials really don’t help at all. So, maybe we ought to start the evaluation process earlier with these nanomaterial compounds.
The second article is a life cycle assessment of silver nanomaterials in clothing. It turns out that the real benefits from silver nanomaterials in clothing are only realized if you end up washing the clothing less. It also turns out that my summer obsession with line drying clothes (I have to admit here that I still use the dryer for socks and towels) is a really good thing. Now, I am not sure, and the authors couldn’t find any data on this, but something tells me that, nano silver or not, you are still likely to wash your socks after every wearing. After about 100 washings, all the silver is gone, and so likely is the matching sock, or you have long since gotten holes in them.
For the next paper, I was going to add one of the two new papers showing the awful environmental risks of land applied biosolids with nanomaterials. Both are in good journals, both by respected authors:
Chen et al., 2015. Toxicogenomic Responses of the Model Legume Medicago truncatula to Aged Biosolids Containing a Mixture of Nanomaterials (TiO2, Ag, and ZnO) from a Pilot Wastewater Treatment Plant. Environ. Sci. Tech. 49:8759-8768.
Judy et al. 2015, Nanomaterials in Biosolids Inhibit Nodulation, Shift Microbial Community Composition, and Result in Increased Metal Uptake Relative to Bulk/Dissolved Metals. Environ. Sci Tech. 49:8751-8758
I am happy to provide both if you want. But both fall prey to the traditional and longstanding practice of using experimental conditions that have no relation to the real world. Both used biosolids from the same baby erected for research treatment plant and both used materials where all of the metals in question were introduced to the system as nano materials and then biosolids were applied at 20 year max loading rates.
Instead of going with these two new papers, I opted to go with an earlier paper that followed a similar research approach but skipped the treatment plant part all together. Paper #3 added the nano materials directly to soil and found toxicity. The authors added zinc and cerium nanomaterials and found Zn uptake by soybeans and end of nodulation as a result of the cerium. Very high profile journal and very certain that agricultural production as we know it will end as a result of nanomaterials in biosolids.
Paper #4 is actually a letter responding and objecting to the methods used in article #3. The objections include the methods used in the study and the conclusions drawn from the data. The first author of the letter is also the first author of paper #5. In paper #5, the authors actually monitored the fate of Zn nanoparticles in wastewater including anaerobic digestion and biosolids stabilization. What they found was that during digestion the Zn in the nanoparticles ceases to be nano Zn and becomes just regular old Zn, the kind that we have studied for decades now and recognize as a plant nutrient.
I am happy to send any and all of these articles for your reading pleasure. Alternatively, you can just read this blurb and then spend the extra time watching Mork and Mindy reruns. I can promise you that will be a lot more fun.
Sally Brown University of Washington