Scientists are only just beginning to understand the potential risks associated with releasing nanomaterials into the environment. These include potentially harmful effects on soil and water organisms. Despite growing evidence of potential harm, a new study suggests that globally hundreds of thousands of tonnes of nanomaterials are already being released into our soils, water and atmosphere.
In May, a group of US scientists published the first global assessment of the likely emissions of engineered nanomaterials (ENMs) into the environment and landfills. It was estimated that in 2010, 260,000–309,000 tonnes of global ENM production ended up in landfills (63–91%), soils (8–28 %), water bodies (0.4–7 %), and the atmosphere (0.1–1.5 %). According to the authors, more accurate estimates of ENM emissions were hampered by the lack of available data on use.
This demonstrates the need for a mandatory register of nanomaterial use − to help regulators determine the quantities and types of nanomaterials currently being produced. This is vital to not only characterise the risk associated with nanomaterial pollution, but also to develop successful strategies to prevent it.
Potential impacts on soil organisms
According to the study, emissions to soils represent up to about a quarter of the material flows, mostly from the disposal of biosolids (i.e. materials from waste water treatment plants) onto agricultural land. This is concerning, since laboratory experiments have indicated that nanomaterials could potentially harm beneficial soil microbes and the digestive systems of earthworms − essential engineers in maintaining soil.
In Australia, we currently produce approximately 300,000 dry tonnes of biosolids annually. Approximately 55% is applied to agricultural land and around 30% is disposed of in landfill or stockpiled. The remaining 15% is used in composting, forestry, land rehabilitation or incinerated.
A recent study by Dutch research institute Alterra found that exposure to certain nanoparticles damaged the health of earthworms. The study by Merel van der Ploeg found that exposure to soil laced with carbon nanoparticles showed a “significant” effect, including slower population growth, increased mortality and tissue damage.
“The same characteristics which make nanoparticles useful in many products, such as chemical reactivity and persistence, cause concern about their potential adverse health effects,” stated Van der Ploeg.
However, since this experiment was conducted in the lab its results can’t be reliably extrapolated to field conditions. Further research is needed to determine what impact nanoparticles in biosolids might have on earthworms under more realistic exposure scenarios.
Another recent study by Colman et al. found an adverse impact on plants and microorganisms in a long-term field experiment following the application of sewage biosolids containing a low dose of nano-silver. The nano-silver treatment led to changes in microbial community composition, biomass, and extracellular enzyme activity, as well as affecting some of the above ground plant species. It also led to an increase in nitrous oxide (N2O) fluxes. This is significant − since nitrous oxide is a notorious greenhouse gas, with 296 times the global warming potential of carbon dioxide. It is also the dominant stratospheric ozone depleting substance. The results also suggest that while nano-silver may be transformed in biosolids through oxidation and sulfidation, it may still have an impact on plants and microbes.
A recent review looking at the environmental factors that affect the biological activity of silver, copper oxide and zinc oxide nanoparticles concluded that the anti-microbial activity of certain nanomaterials can damage beneficial microbes and “modify important aspects of metabolism of microbes and plants at sub-lethal levels”. The scientists observed that the bioreactivity of nanomaterials is likely to vary significantly depending on the soil type. Therefore predicting the potential toxicity and evaluating the risks associated with nanoparticles in soil will be difficult to achieve − even with the most sophisticated equipment.
Soil microorganisms are at the foundation of our entire food chain. Funding research to understand the ways in which nanomaterials affect these organisms, and taking steps to avoid the contamination of agricultural land with nanomaterials, should be urgent priorities for the government.
Nanoparticles in the food chain
Another disturbing finding from the Colman study was that several plant species were able to take up silver from nano-silver in soils. This suggests a potential route for nano-silver from sewage waste to get into the food chain.
The impact that soils contaminated with nano zinc oxide (ZnO) and cerium oxide (CeO2) had on soybean crops was the focus of another recent study. According to the authors:
“The results provide a clear, but unfortunate, view of what could arise over the long term:
(i) for nano-ZnO, component metal was taken up and distributed throughout edible plant tissues;
(ii) for nano-CeO2, plant growth and yield diminished, but also
(iii) nitrogen fixation — a major ecosystem service of leguminous crops — was shut down at high nano-CeO2 concentration.
Juxtaposed against widespread land application of wastewater treatment biosolids to food crops, these findings forewarn of agriculturally associated human and environmental risks from the accelerating use of MNMs [Manufactured Nanomaterials].”
The scientists emphasised the need to make nanomaterials sparingly bioavailable by design and to manage waste streams to prevent the crop-damaging soil buildup of toxic nanomaterials.
More evidence of the uptake of nanomaterials by plants was revealed in a study published earlier this year by Hernandez-Viezcas et al. This tracked the uptake of zinc oxide and cerium oxide (CeO2) nanoparticles by soybeans. The scientists found nano cerium oxide − used in internal combustion processes, sunscreens, gas sensors and cosmetic creams − in the edible part of the soybean,. They concluded that their data suggests that cerium oxide nanoparticles “can reach the food chain and the next soybean plant generation.”
Effects on aquatic organisms
The fact that as much as 7% of nanomaterial emissions end up in water bodies is also of concern given their potential toxicity to aquatic organisms. A recent review of the toxicity of silver, copper oxide and zinc oxide nanoparticles on aquatic organisms found that they were toxic to fish, algae and crustaceans. The study concluded that “the discharge or leaching of biocidal nanomaterials to surface waters may pose threat to aquatic species” and that “this aspect of life cycle of nanomaterials could be controlled either at the level of ‘safe by design’ or, if applicable, by regulated discharge / disposal.”
Urgent regulatory action is needed
In 2004 the United Kingdom’s Royal Society recommended that given the evidence of serious nanotoxicity risks, nanomaterials should be treated as new chemicals and subject to new safety assessments before being allowed in consumer products. It also recommended that releases of nanomaterials to the environment should be avoided as far as possible until it could be demonstrated that the benefits outweighed the risks.
From reading the government’s literature on nanotechnology safety and regulations you’d be forgiven for thinking the government was already effectively regulating these risks. In a 2011 publication, the then Department of Innovation, Industry, Science and Research stated “to keep us safe, regulators adapt their methods of analysis or risk assessment to take account of the specific challenges posed by the qualities of the material or product being assessed. This gives regulators enough flexibility in their current risk assessment approaches to consider issues that are specifically relevant to nanotechnology and nanomaterials.”
However, despite the rhetoric, the overwhelming majority of nanomaterials remain effectively unregulated. While our national chemicals regulator NICNAS (the National Industrial Chemicals Notification and Assessment Scheme) has introduced regulation for nano forms of new chemicals, nano forms of existing chemicals still remain unregulated. Although many nanomaterials now in commercial use pose greater toxicity risks than the same materials in larger particle form, if a substance has been approved in bulk form, it remains legal to sell it in nano form.
There is no requirement for new safety testing; product labelling to inform consumers, workers or employers; or new occupational exposure standards or mitigation measures to protect workers or to ensure environmental safety. Incredibly, there is not even a requirement for manufacturers to notify regulators that they are using nanomaterials.
Despite, and perhaps because of this regulatory vacuum, nanomaterials are already being used in thousands of consumer products and are making their way into waste streams and the environment. Yet scientists are only just beginning to understand what the potential implications of this could be.
The US based Institute for Agriculture and Trade Policy recently produced a report which calls for an immediate moratorium on fertilising with biosolids from sewage treatment plants near nanomaterial fabrication facilities. The Institute argues that a moratorium would give researchers time to determine whether nanomaterials in soil can be made safe and to research alternatives to building soil heath, rather than depending on fertilisation with biosolids.
Regulators also need to be able to properly quantify the scale of the problem. A mandatory register of nanomaterial use would help regulators determine the quantities and types of nanomaterials currently being produced. This is vital both to characterise the risk associated with nanomaterial pollution, and to develop successful strategies to prevent it.
This year the European Commission announced that it will conduct an impact assessment on a EU-wide nanomaterials registry. Meanwhile, our federal government has refused to take similar action here. A recent study commissioned by the government concluded that the feasibility of implementing a similar system here was “questionable”, despite the fact that other countries such as France are in the process of doing it.
