Nanoparticles down the drain

With significant amounts of nanomaterials now entering markets, it’s clearly worth worrying about what’s going to happen these materials after disposal – is there any danger of them entering the environment and causing damage to ecosystems? These are the concerns of the discipline of nano-ecotoxicology; on the evidence of the conference I was at yesterday, on the Environmental effects of nanoparticles, at Birmingham, this is an expanding field.

From the range of talks and posters, there seems to be a heavy focus (at least in Europe) on those few nanomaterials which really are entering the marketplace in quantity – titanium dioxide, of sunscreen fame, and nano-silver, with some work on fullerenes. One talk, by Andrew Johnson, of the UK’s Centre for Ecology and Hydrology at Wallingford, showed nicely what the outline of a comprehensive analysis of the environmental fate of nanoparticles might look like. His estimate is that 130 tonnes of nano-titanium dioxide a year is used in sunscreens in the UK – where does this stuff ultimately go? Down the drain and into the sewers, of course, so it’s worth worrying what happens to it then.

At the sewage plant, solids are separated from the treated water, and the first thing to ask is where the titanium dioxide nanoparticles go. The evidence seems to be that a large majority end up in the sludge. Some 57% of this treated sludge is spread on farmland as fertilizer, while 21% is incinerated and 17% goes to landfill. There’s work to be done, then, in determining what happens to the nanoparticles – do they retain their nanoparticulate identity, or do they aggregate into larger clusters? One needs then to ask whether those that survive are likely to cause damage to soil microorganisms or earthworms. Johnson presented some reassuring evidence about earthworms, but there’s clearly more work to be done here.

Making a series of heroic assumptions, Johnson made some estimates of how many nanoparticles might end up in the river. Taking a worst case scenario, with a drought and heatwave in the southeast of England (they do happen, I’m old enough to remember) he came up with an estimate of 8 micrograms/litre in the Thames, which is still more than an order of magnitude less than that that has been shown to start to affect, for example, rainbow trout. This is reassuring, but, as one questioner pointed out, one still might worry about the nanoparticles accumulating in sediments to the detriment of filter feeders.

3 thoughts on “Nanoparticles down the drain”

  1. One way to increase production of a socially responsible commodities is for an exchange to offer a new contract. I’m windering for the purposes of nanoparticles, if the science is in on some of them enough for this to be contemplated? If silver nanoparticles are most anti-bacterially effective at 45nm diameters, and we can only make them at 50nm using current processes, it would make sense to wait standardizing the contracts. Is the optimal “cell-membrane ripping” diameter of Ag/Au/Cu nanoparticles known?
    Same issue for the pollution absorbing properties of TiO2 particles and the salts Amminex is toying with to store solid-state hydrogen as a dry brick.
    Guess the nanoparticle safety concerns would want to be cleared up before issuing a NYMEX contract.

  2. What is the possiblity of nanoparticles entering the repertory system of animals and humans, being carried by wind currents or normal airflow?

    I would assume under the right circumstances this could cause some serious health hazards (entering into bodily tissues not prepared to rid themselves of foreign objects of such small size).

  3. Given that all of the UK sewage sludge applied to land goes through a stabilisation process – usually anaerobic digestion – it would seem sensible to look at the effects of this process on the aggregation of nanoparticulate TiO2…and any effects of the nanoparticulates on the biological process too.


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