Tuesday, April 22, 2014

Deep Down and Dirty: the Science of Soil.

This is such a brilliantly crafted programme http://www.bbc.co.uk/iplayer/episode/b040y925/Deep_Down_and_Dirty_The_Science_of_Soil/, that I decided to summarise its contents here (along with a few comments of my own). The microscopic photography is just amazing, revealing the structural components of soil in intricate detail: grains of sand, silt and clay, and the creatures that live in it, most of which are invisible to the naked eye: nematodes, protozoa, mites, bacteria, fungi etc. It is through its soil that the world springs into life, in this eponymous season, awakening from a winter torpor. Originally the Earth was barren rock, but was transformed into a vibrant living planet by soil. So where did the soil come from and why is it so important? What is it that gives soil its amazing life-generating force? In a forest, everything is supported by what is inherently in the ground, whereas in a human-tended garden or farm, fertilizers are added to replenish what is lost from the soil. In the forest too, those nutrients must also be replaced, but this is largely accomplished through the symbiotic balance of natural processes.

The forest floor is covered with leaf litter from last season's life. Plants cannot use this to grow on, because the fallen leaves are too tough to be broken down and digested: thus, any nutrients they contain are locked within them. Samples taken using a soil-corer reveal intact leaf litter as a top layer, but below that is a much darker layer where the particles are smaller and much more broken down, and below this is topsoil. The different layers are described as soil horizons and collectively as the soil profile. Below this, the individual components disappear, so that the trapped nutrients are ultimately released into the soil. The key organism for breaking down the leaf litter is a fungus: strictly, mycelium - the vegetative part of the fungus - which we often observe as fine, white threads that grow out from dead wood, leaves etc. The mycelium releases enzymes to break down wood or leaves. Fungi are the only organisms on Earth that can decompose wood. As the fungus breaks down the wood and leaves, a rich material called humus is formed.

The fungus also feeds an entire world that we are not normally aware of, called the soil food web, consisting of millions of tiny creatures, all of which are dependent on the nutrients released by the fungus. There may be half a million different species of organisms in the soil, including bacteria, nematodes, protozoa, mites (arthropods), tardigrades (water bears), and rotifers (with a tail that appears to revolve like a wheel). As they eat, and are eaten themselves, along with their excrement, these creatures disperse nutrients that were initially released by the fungi. Breaking down all these tough materials is too hard a job for the fungi to do alone, and earthworms are their greatest ally. The earthworm has been called an ecosystem engineer. There may be two million earthworms in an average field. Charles Darwin studied earthworms for over 40 years, fascinated by the question of why they are so important in soil. While the majority of the organisms in the soil are invisible, it is not necessary to make recourse to a microscope to determine the health of the soil food web, since the abundant presence of earthworms is a clear indicator that all its members are present in mutual harmony.

Earthworms dig burrows in the soil, which provide air for everything that lives there, they digest dead leaves, unlocking their trapped nutrients, and they excrete the black-brown material that is a visible component of the soil. Worm-casts are frequently visible on the soil surface: calling-cards from the nocturnal adventures of earthworms. Nothing is faster than an earthworm in breaking down plant matter, and in an average field one and a half tonnes of plant matter are processed every year. Yet they look like a simple fleshy tube, so what's going on inside the worm? It turns out that the worms are full of bacteria, and so the worm ingests the leaves and the bacteria finish the job of breaking down the plant matter. The worm produces mucous/sugars that the bacteria like to feed on, and the conditions inside the worm of moisture and pH are ideal to support the bacteria. Inside the worm the concentration of bacteria is 1,000 times greater than exists in soil. There is more life within the soil than on and over the ground above it. A complex system of animals, fungi and bacteria work to cycle nutrients from the dead to the living and keep the soil fertile to support the life above. Soil is maintained fertile by the continual creation of new soil.

This amazing synergy occurs in the upper layers of the soil, and we might ask whether soil consists only of plant material? By taking soil and heating it very hot with a blowtorch flame, it is found that some 30% of its mass burns-off, i.e. that from organic matter, leaving 70% which is the mineral component. The soil particles disintegrate as the organic matter is lost. On looking at depths below the topsoil, exposed from a landslip, the profile of layers (soil horizon) is visible. At the top, there is topsoil, roots etc., but on going successively further down, the dark organic material is seen to disappear, and the deeper layers consist mainly of fragments from the underlying rock. Finally there is bedrock, which is the foundation of soil development.

The largest soil particles are sand (seen as round grains, of millimeter to sub-millimeter dimensions), while the smallest particles are clay (of nanometer size); silt is of an intermediate particle size (of the order of microns). In relative terms, if a sand grain were the size of a beach-ball, a clay particle would be a pinhead. The particular composition of a soil determines the behaviour of that soil and most importantly how it supports life. By comparing three cylinders, filled respectively with sand, silt and clay, water is seen to percolate relatively quickly through sand, but only very slowly through clay, while the silt is somewhere in-between. This demonstrates drainage, or how well water can move through different kinds of soil. Within the clay, the gaps where water can penetrate are exceptionally small, hence the tortuous movement of water through it. Indeed, using scanning electron microscopy, it is apparent that in a clay the particles are so small that there are no defined spaces between them, whereas there are clear gaps between the sand and silt particles that water can move through.

Particles of clay have tremendously greater surface areas than those of silt or sand, and also carry a surface electric charge. This means that nutrients and water are attracted and held to the clay surface, from where they can be taken up by plant roots. There is a compromise, in that if there is too much clay, the soil acts like a sponge and quickly becomes waterlogged, while the water runs through sand too quickly, leaving the soil dry. An ideal soil has all three components, with adequate but not too rapid drainage, and enough clay to retain nutrients and water. In an ideal soil, all three components work together, to support the microbes etc. that live within it. Good soil can support all plant life on earth.

How did the very first soil come to exist? In the past, glaciers would have scoured rock clean of any previous soil. What could begin to break up something as seemingly permanent as rock? Water pooled in the rock fissures and expanded when it froze, providing sufficient force to break the rock apart - this is called physical weathering. Next is the process of chemical weathering which starts with rain, which is slightly acidic from dissolved CO2, and thus can dissolve the limestone component of the rock. When the limestone is dissolved, sediments remain. The sediments are not yet soil, but it is the growth of lichens on the rock that begins the process of soil formation in earnest. A lichen may be thought of as a fungus and an algae in one body. The fungal part of a lichen can chemically attack the rock, by the excretion of an acid. Over time, generations of lichen grow one on the other, the new on the dead, while the dead remains form organic matter and when this mixes with the sediment, soil results.

From barren limestone, the processes of weathering and biological activity generate soil. The different regions show that in some cases the process is just beginning, whereas in others it has been ongoing for thousands of years. Soil is the boundary where the barren rocks meet the riot of life above. The whole provides a complex ecosystem, where life creates soil, breaking down organic matter and forcing rock apart, and yet that life is dependent on the same soil for shelter, nutrition, habitat and anchorage. A delicate balance therefore exists in the life of the soil: challenge one and you challenge the other. However, a new and mighty force has impacted on the soil: Humankind. We have mined soil, built on it, farmed on it, and in places drained it. Our actions have had consequences we never imagined.

In East Anglia the fen-land has been drained into the sea, using dykes. As the U.K. population grew, rivers and lakes were drained to plant crops. It had been long known that when land was drained, it tended to sink. Holme Fen is the largest lowland birch woodland in the UK, and on the edge of the former Whittelsey Mere basin. In 1851, the mere was drained, with the result that the raised bog, reedbed and fen habitat, which would have surrounded the mere, dried out and collapsed over time leading to the formation of the birch dominated woodland of Holme Fen http://www.naturalengland.org.uk/ourwork/conservation/designations/nnr/1006079.aspx. The dramatic illustration of the degree to which that land has sunk is the Holme Fen Post, which was set at ground level in 1850, but is now 4 metres above ground level! It is fortunate that even after drainage, the land remained too wet for ploughing and, over most of the site, the peat currently retains a depth of around 3 metres.

Peat forms in wetland environments, and is waterlogged, acidic and low in oxygen. In combination, these factors impede the rate of decomposition of organic matter, which accordingly accumulates. Plants grow using CO2 from the air, and so if their remains are not decomposed when they die, they build up, providing a "carbon sink". Once the water is removed, oxygen enters the soil allowing bacteria and fungi to breathe and the organic matter is decomposed; hence, formerly stored carbon is being released into the atmosphere as CO2. It is thought that fens are losing about 4 million cubic meters of peat = 1-1.5 million tones of CO2/year, with thousands of years worth of captured carbon being converted to CO2 in a mere period of decades.

Increasing populations led to greater areas of land being turned over to the plough. Intensive farming can lead to nutrient depletion, ploughing and tilling can destroy the soil structure, while heavy irrigation can increase the toxicity of soil. These are all contributors to soil degradation, making it susceptibile to erosion from wind and water. By the 1930s, vast swathes of land had been turned over to food production from Canada down to Texas, which led to the infamous dust bowls. Intensive farming had weakened the structure of the soil so it couldn't hold itself together, and when it dried out it simply blew away. 100 million acres of land were affected, as a result of which 200 million people were driven off the prairies. The potential problem is far more severe now that there are 7 billion of us on the planet, or more than the total number of humans who had ever lived, up to the beginning of the 20th century, and we are over-cultivating the soil, to produce ever more food. When we talk about an impending food crisis, it is really a soil crisis that confronts us.

A farmer at Ross on Wye was brought to the brink of ruin, since massive gullies opened up in his field. The problem was that the soil had been weakened by intensive farming, and was simply washed away by the rain, taking his  asparagus crop with it. The soil was exposed the whole time, and to avoid water standing around the crop, he planted it up and down in rows, so that the water ran off, but carried soil with it, producing gullies that became ever deeper, on down the slope. Water erosion has proved to be a devastating problem in the U.K. We have had five sequentially very severe years of storms, culminating in the storms of 2013 when the U.K. suffered unprecedented rainfall, leaving regions such as the Somerset Levels inundated for months http://ergobalance.blogspot.co.uk/2014/02/flooding-on-somerset-levels-and.html.

A raindrop has a certain mass and an associated kinetic energy, which causes breakdown at the soil surface. Extreme rainfall events mean larger drop-sizes with higher kinetic energy and more damage to the soil surface, which exacerbates runoff. By planting on the diagonal, not up and down in rows, and planting grass between the plants, runoff is slowed down. A surprisingly effective innovation is to put straw over the ground, as a mulch, which takes the energy out of the raindrops directly and acts as a blanket to absorb some of the water and slow down the runoff. When the ground is left bare, raindrops hit the earth with sufficient force to break up the soil. Runoff water soon begins to form and carries soil way. The straw absorbs the impact from the raindrops and the runoff is vastly reduced. It is remarkable that something so low-tech as straw is as effective as this, and while these ideas are beginning to spread, commitment and effort to change and adapt will prove critical to preserving the soils.

Sunday, April 20, 2014

Wheat Rust: "The Death of Grass"?

In an echo of "The Death of Grass", the 1956 novel whose theme is the progressive razing of the world's food production by a marauding and mutating virus, with apocalyptic consequences for humankind http://ergobalance.blogspot.co.uk/2012/01/death-of-grass.html, the spectre of "wheat rust" is now raised. Wheat rust is said to be a similarly devastating condition, in fact a fungus, described as the "polio of agriculture", which has spread from Africa to South and Central Asia, the Middle East and Europe, causing severe yield losses of the most important staple crop next to rice http://www.independent.co.uk/news/uk/home-news/wheat-rust-the-fungal-disease-that-threatens-to-destroy-the-world-crop-9271485.html. In writing his novel, Sam Youd, using the pseudonym John Christopher, may have been inspired by the major epidemic of wheat rust that engulfed the North American wheat belt in the 1950s, in which 40% of the harvest was destroyed. In 1999, in Uganda, the disease resurfaced, due to mutation of the fungus, despite millions of pounds that have been spent in creating rust-resistant strains of wheat. It is thought that some 90% of all types of wheat in Africa are vulnerable to wheat rust.

Properly termed "wheat leaf rust" http://en.wikipedia.org/wiki/Wheat_leaf_rust, this is a fungal disease that affects wheat, barley and rye stems, leaves and grains, with crop yields being further diminished by dying leaves which feed the fungus. The pathogen is Puccinia rust fungus: P.triticina causes 'black rust', P.recondita causes 'brown rust' and P.striiformis causes 'yellow rust'. While farmers have used strain selection over centuries to improve wheat yields, so doing to provide disease-resistant crops has proved equally important in maintaining adequate crop production. The use of a single resistance gene against various pests and diseases plays a major role in resistance breeding for cultivated crops, and many single genes for leaf rust resistance have been identified.

Wheat leaf rust spreads via airborne spores, of which 5 different kinds are produced over the life cycle: uredospores, teleutospores, and basidiospores develop on wheat plants and pycnidiospores and aeciospores develop on the alternate hosts. Moisture is a key element for successful germination, for which optimum conditions are 100% humidity and a temperature of 15-20 degrees Centigrade. Within 10 – 14 days of infection, the fungi begin to sporulate and symptoms become visible on the wheat leaves, while the plants are entirely without symptoms prior to sporulation. In the Asian subcontinent, the spores cannot survive the hot dry weather but are re-introduced year on year from the Himalayas or surrounding hills, originating, so it is thought, from Berberis spp, Thalictrum flavum and Muehlenbergia huglet, which is a major cause of bread moulds.

Rust epidemics have been compared to a forest fire, in that once they take hold, the loss of crops is rapid and widespread, since millions of wind-borne spores are produced by the fungus, each of which has the capacity to initiate a fresh infection. The race is on to find new disease-resistant seed varieties of wheat, for which the legacy nations are better provided than developing countries such as those in Africa. A central part of this strategy is the use of Genetically Modified (GM) crops, including cloning resistance from wild grasses and barley, as opposed to using ever more virulent chemical pesticides. Mathematical models are being developed to predict potential outbreaks of wheat rust in African and Middle Eastern nations, to determine which may be most vulnerable.

Part of the problem is blamed on climate change, and the spread of two types of the fungus is thought to be a result of its adaptation to a warmer environment. Thus, outbreaks have been born in regions with no history of the disease, stretching from North Africa to South Asia, transmitted via spores carried by wind and through the soil. Such crop infestations can be added to the nexus http://ergobalance.blogspot.co.uk/2014/04/the-soil-land-water-climate-honey-bees.html of other afflictions upon the human capacity to survive and thrive, and most likely are exacerbated by modern industrialised agriculture and its practice of monoculture cropping. By default or more desirably by design, humankind may find itself steered onto the path of agro-ecology, regenerative agriculture and permaculture http://www.ncbi.nlm.nih.gov/pubmed/23469709, and away from a global food production system which is patently unsustainable.

Sunday, April 06, 2014

The Soil, Land, Water, Climate, Honey Bees, Oil, Food Nexus: Peak Soil.

There is a tendency for humans to perceive ill occurrences as separate events, rather as the Biblical plagues of Egypt: water into blood, frogs, lice, wild animals or flies, deceased livestock, boils, storms of fire, locusts, darkness and death of the firstborn. Scientists now believe that the latter are historically true, but they were in fact all results of a single cause: not the wrath of a punitive God, but climate change http://www.telegraph.co.uk/science/science-news/7530678/Biblical-plagues-really-happened-say-scientists.html. Modern humans are aware of contemporary global menaces: a changing climate, peak oil, a dodgy economy that could collapse at any moment, and the extinction of honey bees, but relatively few of us know that the world's productive soils are also under threat. What has been most noticeable is that the price of food and fuel has increased markedly over the past decade, during when we have also experienced an economic crash. We fear another such shock, even amid whispers of "growth", which can only be expected to be of a slow stuttering kind, since we cannot significantly grow our rate of production of resources. Thus, the price of a barrel of crude oil has more than trebled since 2004, while global production has practically flat-lined at around 75 million barrels a day over that same period, leading to the view that we have reached the ceiling of our oil supply http://www.rsc.org/chemistryworld/2014/02/peak-oil-not-myth-fracking.

Given that all components of human civilization are inextricably linked to petroleum, either as a chemical feedstock or a fuel, if we cannot elevate our production rate of oil, nor can we grow the global economy. The fundamental fragility of the human condition, however, is more profound, since we are steadily using-up Mother Earth's bestowal to us of fertile soil. This has been dubbed "peak soil" http://www.theguardian.com/environment/earth-insight/2013/jun/07/peak-soil-industrial-civilisation-eating-itself in analogy with "peak oil", and while the two phenomena are not of the same kind, they are connected, as indeed are all the elements listed in the title of this article: soil, land, water, climate (change), honeybees, oil and food. Alice Friedmann wrote, in the context of the unsustainable nature of growing land-based crops and producing biofuels from them: http://greatchange.org/bb-alcohol1-friedemann.html

"Iowa has some of the best topsoil in the world, yet in the past century it's eroded from an average of 18 inches to less than 10 inches (Pate 2004, Klee 1991). When topsoil reaches 6 inches or less (the average depth of the root zone in crops), productivity drops off sharply (Sundquist 2005). Soil erodes geologically at a rate of about 400 pounds of soil per acre per year (Troeh 2005). But on over half of America's best crop land, the erosion rate is 11,000 pounds per acre, 27 times the natural rate, and double that on the worst 7% of cropland (NCRS 2006), partly because farmers aren't paid to conserve their land, and partly because hired farmers wrench every penny of profit they can on behalf of short-sighted owners."

This is deeply disturbing, all the more so because rates of erosion that are in excess of the natural rate of soil formation are not restricted to Iowa, but are a global feature http://www.soilerosion.net/doc/what_is_erosion.html. According to a report by the World Resources Institute (WRI) some 20% of the world's cultivated areas are afflicted by land degradation http://pdf.wri.org/great_balancing_act.pdf, and in order to feed Humankind over the next 40 years, food production must be increased by 60%. This conclusion is drawn, in part, from the expectation that another 2.5 billion people will be added to the current number of just over 7 billion of us, and that a rising middle class will have greater expectations of their diet, particularly in wanting to eat more meat. The amount of food that is wasted is another consideration, and combining this factor with population increase suggests a daily gap between the demand for food and what is likely to be available by 2050 of 900 calories (kilocalories) per capita.

Many of the limitations to meeting such a testing challenge are those implicit to the modern industrialised agricultural system per se. The factors involved are complex and inseparable, in short providing a nexus. The impact of climate change adds further weight to the problem, and seven clear courses of action have been identified, by which we might adapt to ensure food security into the future http://cgspace.cgiar.org/bitstream/handle/10568/10701/Climate_food_commission-SPM-Nov2011.pdf?sequence=6. 24% of anthropogenic greenhouse gas emissions are from agricultural activities, including methane from livestock, nitrous oxide from fertilizers, carbon dioxide from running tractors and combine harvesters etc. and from changes in land use. Furthermore, 70% of all human water consumption is claimed by agriculture. In the last 40 years, 20 million square kilometers of land have suffered degradation, which accounts for around 15% of the total land area of the Earth, while 30% of the originally available cropland is now unproductive. As noted for Iowa, the degradation of topsoil is occurring many times faster than the rate at which soil is generated by Nature, which may take 500 years to form just an inch of it http://www.theecologist.org/blogs_and_comments/commentators/other_comments/2150973/peak_soil_act_now_or_the_very_ground_beneath_us_will_die.html.

There is an increasing pressure on water supplies too, which may begin to struggle in meeting demand in the food basket regions of the Americas, west and east Africa, central and eastern Europe, Russia, the Middle East and south and south-east Asia, within only 12 years http://pdf.wri.org/great_balancing_act.pdf. As alluded earlier, the costs of both fuel and food have risen markedly over the past decade: food prices follow oil prices because oil and gas are involved at all principal stages in the food production and distribution chain. The World Bank has proposed restricting oil prices as a means to mitigating food price increases http://www-wds.worldbank.org/external/default/WDSContentServer/IW3P/IB/2013/05/21/000158349_20130521131725/Rendered/PDF/WPS6455.pdf There appears little doubt that oil prices will remain high, and most likely rise considerably, since the global oil supply will increasingly be provided from unconventional sources, e.g. producing shale oil by fracking, tar sands  and (ultra)deepwater drilling, all of which have poorer net energy returns than does conventional crude oil http://www.rsc.org/chemistryworld/2014/02/peak-oil-not-myth-fracking. Indeed, were the price of oil not as high as it is currently, no one would bother to produce it from such expensive and demanding sources. There is also the critical question of how high an oil price the economy can bear, before it falls into recession and finally collapses http://www.rawstory.com/rs/2013/12/23/former-bp-geologist-peak-oil-is-here-and-it-will-break-economies/

According to the U.S. National Agriculture Statistics there has been a decline from about 6 million bee-hives in 1947 to 2.4 million in 2008, representing a reduction by 60% http://ecowatch.com/2013/06/11/worldwide-honey-bee-collapse-a-lesson-in-ecology/. Over the past 10 years, beekeepers in both the U.S. and Europe have reported annual hive losses of 30%, and last winter losses of 50% in the U.S. were not uncommon, with worst case examples of 80-90% http://www.theguardian.com/environment/earth-insight/2013/jun/07/peak-soil-industrial-civilisation-eating-itself. Since one third of all food crops rely on bees to pollinate them, if this "bee-collapse" continues, the effect on world food production could be calamitous. Various causes have been brought culpable for killing the bees, including pesticides, parasitic mites, intensive monoculture farming methods and urban development. The nexus of components that we have identified is totally at odds with providing sufficient food for a population of 9.5 billion by 2050 and maybe 11 billion by 2100 http://www.un.org/en/development/desa/population/

The various ills we have described are (as already alluded to) outcomes of the industrial nature of monoculture farming, since it frets the ecology but does not restore it, including the soil itself. Alternatively, methods of regenerative agriculture and permaculture have been advanced http://www.ncbi.nlm.nih.gov/pubmed/23469709. The latter help to rebuild the soil, making it more fertile through increasing its soil organic matter content (SOM), including establishing a healthy network of microbes and other creatures to live in it (the soil food web), thus securing fertility and crop productivity. Such methods of ecological food production can be done on a more local scale, and the food consumed closer to where it is grown, largely obviating the necessity for an extensive transportation/distribution system powered by oil-refined fuels. They are further less intensive in their demand for other inputs, such as water, fertilizers, pesticides and herbicides. By keeping the soil covered throughout the year, it is substantially protected from erosion, while the increase in SOM improves the soil structure so that it can absorb water more effectively and allow aquifers to recharge, thus mitigating both water shortages and flooding. It is likely that a reduced use of pesticides, through reintroducing biodiversity, might help to bring the bees back too.


Thursday, March 20, 2014

Eating Small: Applications and Implications for Nanotechnology in Agriculture and the Food Industry.



The following will be published next month in the journal Science Progress http://www.sciencereviews2000.co.uk/view/journal/science-progress, which I am an editor of - so, this is a preview!


1. Introduction.

That synthesis might be undertaken by the direct manipulation of atoms was suggested by Richard Feynman in 1959, although term "nano-technology"1 was not coined until 1974, by Norio Taniguchi. In 1986, K. Eric Drexler published his book Engines of Creation: The Coming Era of Nanotechnology, which contained the notion of a nanoscale "assembler" with the capacity to build copies of itself and other items, by atomic level manipulation. The groundbreaking invention, in 1981, of the scanning tunnelling microscope (STM) demonstrated that individual atoms could be visualised, and the technology was further developed to physically move adsorbed atoms and molecules around on a surface2. Notable examples2 demonstrated for publicity purposes are the sign-writing of "IBM" using 35 xenon atoms on a Ni(110) surface, and of "2000" using 47 CO molecules on a Cu(211) surface, by researchers in the eponymous organisation, to auger in the new millennium. Considerably larger molecules can also be moved using an STM tip, for example 1,4-diiodobenzene and biphenyl, which have been towed around on  copper surfaces. The tunnelling electrons may also be used to initiate chemical reactions, the products of which can be subsequently manipulated over the surface, so providing proof of chemical change having occurred, e.g. the conversion of iodobenzene to biphenyl. As a definition, nanotechnology (nanotech) can be described as the manipulation of matter over an atomic, molecular, and supramolecular dimension. Molecular nanotechnology is the intention of manipulating atoms and molecules, so to create macroscale products. The prefix “nano” is derived from the Greek word meaning “dwarf”. The U.S. National Nanotechnology Initiative3 defines nanotechnology as, “the manipulation of matter with at least one dimension in the range 1—100 nanometers (nm)”, where quantum mechanical effects become increasingly important as the smaller end of the range is accessed. It is critical that the particular materials, and devices made from them, should possess properties that are different from the bulk (micrometric or larger) materials, as a consequence of their small size, which may include enhanced mechanical strength, chemical reactivity, electrical conductivity, magnetism and optical effects (e.g. Figure 1).

One nm is one billionth, or 10−9, of a meter, which in relative size to a meter is about the same as that of a marble to the Earth.4 Placed in a different context, an average man's beard grows about one nm in the time it takes him to lift the razor to his face.4 The lower limit is set by the size of atoms, which are the fundamental building blocks of nanotechnology devices, while the upper limit is of a more arbitrary quality but is of the dimension at which the particular phenomena of the quantum realm begin to appear, which are essential to the nano-device. A device that is merely a miniaturised form of an equivalent macroscopic version does not conform to nanotechnology, lacking these particular phenomena, but is classified under the heading microtechnology.5 In regard to the fabrication of nanodevices, we find the "bottom-up" approach, where materials and devices are constructed from molecular components which self-assemble via molecular recognition, while in the "top-down" approach, nano-objects are built from larger entities, not involving control at an atomic level.6

The plural forms "nanotechnologies" and "nanoscale technologies" thus refer to the many and various aspects, devices and their applications that have in common this scale of the quantum realm. Indeed, there are multifarious potential applications of nanoscale materials, including industrial and military uses, as attested by the investment of $3.7 billion, by the U.S. National Nanotechnology Initiative, $1.2 billion by the European Union and $ 750 million in Japan.1 It may be that nanotechnology can provide advances in medicine, electronics, biomaterials, energy production and, as is the subject of this article, in agriculture and more broadly in the food industry. On the other hand, nanotechnology raises many of those same issues as when any new technology is inaugurated, e.g. concerns about the toxicity and environmental impact of nanomaterials,1 and their potential effects on global economics, in addition to speculation over potential doomsday scenarios (“grey goo”), most emphatically dramatised by the late Michel Crighton in his novel Prey7. The Royal Society's report on nanotechnology contains examples of some of the definitions and potential implications of nanotechnologies.8 Commercial products, so far, are limited1 to bulk applications of nanomaterials, rather than atomic scale synthesis, e.g. the use of silver nanoparticles as a bactericide, nanoparticle-based transparent sunscreens, and stain-resistant textiles based on carbon nanotubes.The aspects embraced by nanotechnology are broad, and there is much work and concern over the large-scale employment of engineered nanoparticles (ENMs) and their effects on the environment, agriculture, and plants, and the humans who consume them directly. Moreover, as this short survey attempts to indicate, there is also now a considerable body of work in the applications of nanoscale technology to agriculture and the food industry. Indeed, an ACS Select was recently published on this topic9.Thus may be provided novel sensors intended to improve the quality and safety of food, along with methods of packaging that will amend the storage and delivery of foodstuffs. 

According to the researchers and stakeholders, revolutionary advances can be anticipated during the next 10-15 years, principally through a convergence of nanotechnology, biotechnology and agricultural and environmental sciences, of which the following have been listed9:

•development of nanotechnology-based foods with lower calories and less fat, salt, and sugar while retaining flavour and texture;
•nanoscale vehicles for effective delivery of micronutrients and sensitive bioactives;
•re-engineering of crops, animals, and microbes at the genetic and cellular level;
•nanobiosensors for detection of pathogens, toxins, and bacteria in foods;
•identification systems for tracking animal and plant materials from origination to consumption;
•integrated systems for sensing, monitoring, and active response intervention for plant and animal production;
•smart field systems to detect, locate, report, and direct application of water;
•precision and controlled release of fertilizers and pesticides;
•development of plants that exhibit drought resistance and tolerance to salt and excess moisture; and
•nanoscale films for food packaging and contact materials that extend shelf life, retain quality, and reduce cooling requirements.


2. Nanotechnology in agriculture.
 
2.1 Precision Farming.

Precision farming aims to maximise output (i.e. crop yields) while minimising input (i.e. fertilisers, pesticides, herbicides, water etc). Computers, global satellite positioning systems, and remote sensing devices are all employed in the monitoring of highly localised environmental conditions, so to determine whether crops are growing at maximum efficiency or any specific problems, and their precise location. The input of fertilizers and water use can be optimised, resulting in lower production costs and potentially greater production. The amount of waste from agriculture can also be reduced, further minimising its environmental impact. Real-time monitoring may be achieved through linking nanotechnology-enabled sensor devices with a GPS system. By dispersing nanosensors throughout a field, soil conditions and crop growth could be continuously monitored. A wi-fi system has been introduced in one of the Californian vineyards, Pickberry, in Sonoma County , for which the initial cost is justified since it enables the best grapes to be grown, to produce finer wines, to be sold at a premium price10.

2.2 Smart Delivery Systems.

Many of the pesticides that were in widespread use during the second half of the 20th Century, have been banned on account of their toxicity. As an alternative means to maintain adequate crop yields, Integrated Pest Management systems have been introduced, which employ a blend of traditional methods of crop rotation and biological pest control methods. However, it is thought that nanoscale “smart” devices might be employed, e.g. to identify plant health dysfunctions before they have advanced sufficiently to become visible to the farmer, and even to provide a remedial response to them. Such devices might therefore act both as an early warning system and as a curative. Chemical agents, such as fertilizers, pesticides and herbicides, might thus be delivered by targeted and controlled means, in fact similar to drug-delivery systems in nanomedicine. The deployment of these agents has been revolutionised through methods of encapsulation and controlled release, e.g. in formulations containing nanoparticles in the 100—250 nm size range with improved water solubility. (thus increasing their activity). Alternatively, suspensions of 200—400 nm nanoparticles (nanoemulsions) - either water or oil-based – may be readily incorporated in a variety of media (gels, creams, liquids, etc.), with multiple advantages. The Primo MAXX® plant growth regulator, which if applied before the impacts of heat, drought, disease or traffic are manifest, has been shown to strengthen the physical structure of turfgrass, allowing it to cope with such stresses throughout the growing season.10

Marketed under the name Karate®ZEON, is a rapid-release microencapsulated product containing  lambda-cyhalothrin (a synthetic insecticide related to natural pyrethrins) which bursts, to discharge its contents, on contact with leaves.10 A more targeted agent is the appositely named “gutbuster”, which releases its active agent from an capsulated form when it encounters alkaline environments, as pertains in the stomachs of some insects.10 Smart fertiliser and pesticide delivery systems are being researched, employing nanoparticles, with the ultimate goal to release their contents, either slowly or quickly, in response to particular environmental changes, such as magnetic fields, heat, moisture, etc. Through such nanodevices, a more efficient use of water, pesticides, herbicides and fertilizers might be engendered, so to create a more environmentally friendly and less polluting version of agriculture.

Researchers at Cornell University have produced microscopic fluorescent probes or “nanobarcodes” with which to label multiple pathogens on a farm. The intention is to develop a portable on-site detector that can be used by non-specialists. Scientists at Purdue University developed a nanosensor that reacts with the hormone auxin (essential for root growth and the establishment of seedlings). An electrical signal is generated when the interaction occurs, so that, in principle, the concentration of auxin at various regions of the root can be determined. It is thus possible to ascertain whether auxin is absorbed or released by the surrounding cells, thus aiding an understanding of the way plant roots adapt to their environment, which is a critical factor especially in marginal soils.11 Biotechnology and nanotechnology have been connected in the form of synthetic crystalline DNA sequences that are able to self-assemble into a collection of three-dimensional triangular forms. The crystals have small cohesive sequences (“sticky ends”) that can specifically bind another molecule. A lattice structure can be formed, when multiple helices are attached through single-stranded sticky ends, which extends in six different directions, thus creating a three-dimensional crystal. It is thought that important crops might be improved by organizing and linking carbohydrates, lipids, proteins and nucleic acids to these crystals.11 Chemically-coated 3 nm diameter mesoporous silica nanoparticles (MSN), have been used to provide containers to delivered genes into plants, by a team at Iowa State University. The plant is activated by the coating to absorb the particles through its cell walls, where the genes are emplaced and activated very precisely, so eliminating any undesirable effects of toxicity. DNA has been successfully introduced to tobacco and corn plants by means of this method.11

2.4 Other Developments in the Agricultural Sector due to Nanotechnology.

Nanotechnology can offer routes to added value crops or environmental remediation, for example, particle farming may provide nanoparticles by growing plants in defined soils, to be subsequently employed industrially. As an example, when alfalfa plants are grown in soil containing gold nanoparticles, the latter are absorbed via the plant roots and which accumulate in the body of the plant. When the plants are harvested, the gold nanoparticles can be recovered by mechanical separation.18 The U.S.-based firm, Argonide, is employing 2 nm diameter aluminium oxide nanofibres (NanoCeram) in water purifying filters, which can remove viruses, bacteria and protozoan cysts from water that is contaminated with them.10 The German chemical group BASF has targeted a substantial proportion of its $105 million nanotechnology research fund to water purification techniques. The French utility company Generale des Eaux has also developed its own Nanofiltration technology in collaboration with the Dow Chemical subsidiary Filmtec. Ondeo, the water unit of French conglomerate Suez, has meanwhile installed what it calls an ultrafiltration system, with holes of 0.1 microns in size, in one of its plants outside Paris.10 Altairnano are using a device termed “Nanocheck” which contains lanthanum nanoparticles that can absorb phosphates from aqueous environments, e.g. to prevent the growth of algae in ponds, swimming pools with a future market for commercial fish ponds, to reduce the currently high costs of removing algae from them.10 Contaminated soil and groundwater may be “cleaned” by the action of iron nanoparticles, which can catalyse the oxidation of organic pollutants such as trichloroethene, carbon tetrachloride, dioxins, and PCBs to form simpler and less toxic carbon compounds. Iron oxide nanoparticles have been shown to be highly effective in binding and removing arsenic from groundwater, a significant health problem in West Bengal and Bangladesh, where there are naturally high concentrations of arsenic present in the soils and groundwater.10 In the U.S., there are of the order of 150,000 underground storage tank egresses, along with a considerable number of landfills, abandoned mines, and industrial sites that might be cleaned-up using nanoparticles.10

2.4 Nanoparticles and Recycling Agricultural Waste.

Nanotechnology finds applications11 in agricultural waste prevention, particularly in the cotton industry. Some of the cellulose or the fibres that arise when cotton is processed into fabrics and garments, are either discarded as waste or they may be taken-up into making  low-value products such as cotton wool or wadding. However, using an electrospinning method, 100 nm diameter cotton fibres can be produced, which are able to absorb fertilizers or pesticides very effectively, so permitting their later targeted application in agriculture. Cellulosic feedstocks are now regarded as a viable means for producing biofuels, and research is underway to nano-engineer enzymes for the simple and cheap conversion of cellulose from waste plant residues into ethanol. When rice husk is burned to produce thermal energy, a by-product is high-quality nanosilica, which can be processed in the fabrication of glass and concrete, thus converting a troublesome waste product into useful materials.

3. Nanotechnology in the Food Industry.

That the potential for nanotechnology in the food industry is limited only by human ingenuity is made clear by the aforementioned recent ACS Select on the subject9. The widening prospect to design and operate on the nanoscale accords that more engineered nanomaterials (ENMs) will ultimately find their way onto our farms, into our supermarkets, onto our plates and into our bodies. There had been some lack of will to disclose their activities in “nanofood”, but a number of companies have more lately been explicit in their intentions to introduce the technology, e.g. in smart packaging, on demand preservatives, and interactive foods. The latter concept centres around having thousands of nanocapsules containing flavour or colour enhancers, or added nutritional elements (such as vitamins), in the food, which would remain dormant until their release and activation was triggered by the consumer10. Thus, consumers would be able to modify food, according to their particular nutritional requirements or preferences. Kraft foods have established a consortium involving 15 different universities to research into applications of nanotechnology for the creation of interactive foods. The consortium further intends to develop smart foods, containing nanocapsules which will be ingested with food, but remain dormant until activated: thus, nutrients can be released to counter any deficiencies as detected by nanosensors. To be characterised as nanofood, it is necessary that nanotechnology methods or materials must feature at in the creation of the food at some point in its cultivation, production, processing, or packaging. It does not mean that the foodstuff will be created or modified at the atomic level, which for the foreseeable future will remain the stuff of science fiction.

3.1 Packaging and Food Safety.

Food is packaged in films principally to prevent it from going dry, and to protect it from external moisture and oxygen. In the future, nanotechnology may provide smart packaging systems with the ability to mend small holes or tears, react to changes in particular environmental conditions, such as temperature and moisture concentration, and signal to the customer when the food has become contaminated. An “electronic tongue” is being developed for inclusion in packaging, with an array of nanosensors that are specific for the detection of gases that accompany the spoiling of food, which cause colour changes in the sensor strip - an unambiguous signal that the food has “gone off”. The Durethan KU2-2601 packaging film has been produced by Bayer Polymers, containing silica nanoparticles, with improved properties of weight, mechanical strength and heat resistance. The particles provide a highly effective barrier against the intrusion of oxygen, and the loss of water, so prolonging the life of foodstuffs. When beer is stored in plastic bottles, a reaction occurs between the alcohol and the plastic, resulting in a greatly diminished shelf-life, such that shipping beer in this way is not practical, despite the advantages of reduced weight over glass bottles, and lower cost. However, a nanocomposite has been developed, containing clay nanoparticles, called Imperm, from which bottles can be made. The nanocomposite structure both reduces the loss of CO2 from the beer and keeps oxygen out, extending the shelf-life to around 6 months.10 Antimicrobial films have been produced by Kodak, that can absorb oxygen from the contents of the package, so lengthening the shelf-life of food. The NanoBioluminescence Detection Spray contains a luminescent protein which specifically binds to the surface of microbes, e.g. salmonella and E. coli. On binding, a visible glow is emitted, providing an instant signature of bacterial contamination, the degree of which is in proportion to the intensity of the glow. EU researchers in the Good Food Project have developed a portable nanosensor that can be used in field situations, e.g. on-farm, abattoir, during transportation, processing or at the packaging point. Thus, food can be tested for chemicals, pathogens and toxins there and then, avoiding the need to send samples away to analytical laboratories10.

The BioFinger device, developed with funding from the European Union, employs a cantilever, the tip of the which is coated with specific molecules that can bind to others, e.g. on the surface of bacteria, whereupon the tip bends and resonates. Since the cantilevers are incorporated on a disposable microchip, the device is easy to carry around.10 By means of the “lotus effect” (lotus leaves are coated with nanoscale wax pyramids which cause water to form beads and run off them) a dirt-repelling packaging material has been fabricated at the University of Bonn, intended for use in abattoirs and meat processing plants. The bactericidal properties of silver nanoparticles are well known12, and they are used to coat the inside of some washing machines, particularly those that run at temperatures well below the “boil wash”. However, it has been shown that magnesium oxide and zinc oxide nanoparticles are highly effective at destroying microorganisms, which clearly are much cheaper to make, and it is thought they might revolutionise food packaging materials.10 Radio Frequency Identification (RFID) technology is used in many areas of the food industry, e.g. for stock control in retail outlets, and to ensure better efficiency in the supply chain. The technology, first developed for military use over half a century ago, employs a tag with microprocessors with an antenna for the transmission of signals to a wireless receiver: thus, the journey of an item can be traced from the warehouse to the consumer, giving the advantage over bar codes, that line-of-sight is not necessary, and many hundreds of tagged-items can be read per second. A nanofood consortium has been created which aims  to: develop sensors which can almost instantly reveal whether a food sample contains toxic compounds or bacteria; to develop anti-bacterial surfaces for machines involved in food production; to develop thinner, stronger and cheaper wrappings for food; and the creation of food with a healthier nutritional composition.10 The Centre for Advanced Food Studies (LMC), which is an alliance of Danish institutions working in food sciences, proposed that the food science thematic priority in the Seventh Framework Programme (FP7) should address six specific areas13:

- basic understanding of food and feed for intelligent innovation;
- systems biology in food research;
- biological renewal in the food sector/biological production;
- technology development;
- nutrigenomics;
- consumer needs-driven innovation and food communication.

It is believed by LMC that a focus on these fields would force an interdisciplinary and holistic approach, adding that possible risks, health, the environment and ethical issues should be incorporated into each of the priority areas. Following a foresight exercise on nanoscience, food researchers in Denmark hold the opinion that they are well placed to participate in international projects. Recommendations for significant increases in funding were made, and seven research areas were prioritised, as a result of the exercise, four of these LMC consider are relevant to food science: biocompatible materials; nanosensors and nanofluidics; plastic electronics; and nanomaterials with new functional properties.

3.2 Food Processing

A critical feature in the area of “on demand” foods is the development of nanocapsules which are to be included in food to deliver nutrients to cells as necessary. Nanoparticles may also be added to existing foods so that nutrients are absorbed more effectively. In Western Australia, a major bakery has incorporated nanocapsules containing tuna fish oil (a source of omega-3 fatty acids) into bread: these have the advantage that the capsules only release their contents when in the stomach, so that the taste of fish oil, which some people find unpleasant, is avoided10. Nano-sized Self-assembled Liquid Structures (NSSL) are employed, in the form of ca 30 nm diameter expanded micelles with nutrients or “nutraceuticals” contained within the aqueous interior, including lycopene, beta-carotene, lutein, phytosterols, CoQ10 and DHA/EPA. The particles have the trade-name, Nutralease, and allow the nutraceuticals to enter the bloodstream from the gut more easily than from normal foodstuffs. NSSL is marketed by Shemen Industries to deliver Canola Activa oil, which competes for bile solubilisation, and is claimed to reduce the body’s cholesterol intake by 14%. 50 nm coiled nanoparticles, called nanocochelates, have been developed by Biodelivery Sciences International, for the enhanced delivery of nutrients such as vitamins, lycopene, and omega fatty acids, with no influence on the food’s colour or taste. As a result of the above, the “super foodstuffs” concept is brought closer to becoming real, with potential manifold benefits, e.g. more energy, better cognitive functions, improved immune function, and anti-aging protection. A new product by the name of NanoCeuticals, which is a colloid (or emulsion) of particles of less than 5 nm in diameter, has been brought out by Royal BodyCare, who claim that it will scavenge free radicals, increase hydration and balance the body’s pH. A nanoceramic has been marketed by the Oilfresh Corporation (U.S.) which, as a result of its large surface area, prevents the oxidation and agglomeration of fats in deep fat fryers, thus extending the useful life span of the oil. The amount of oil used in restaurants and fast food shops is thus reduced by half, and since the oil heats up faster, there is a further saving in the amount of energy used for cooking.10

NovaSOL Sustain, developed by Aquanova (Germany), is a technology which incorporates two separate substances that are active for fat reduction (CoQ10) and satiety (alpha-lipoic acid) into micelles of ca 30 nm diameter, and is said to provide a novel approach to intelligent weight management. The NovaSol technology has been further employed to produce a vitamin E preparation, called SoluE, that does not cloud liquids, and a similar material containing vitamin C, called SoluC. Since the NovaSOL protects its contents from stomach acids, it can be used for the introduction of other dietary supplements.10 The Woodrow Wilson International Center for Scholars in the US has produced a consumer database of marketed nanotechnology and has so far identified more than 15 items which have a direct relation to the food industry14. A lifeycle analysis15 has been made of nanocellulose, which is increasingly being used in food packaging and encapsulation applications.

Efforts have been made to provide a more stable environment from which to deliver eugenol, which is present in “oil of cloves”, and is a popular preservative in the food industry, with antibacterial, antifungal and antioxidant properties. Normally, eugenol (Figure 2) is relatively sensitive to oxygen heat and light, which tend to degrade it, but when encapsulated as an inclusion complex in cyclodextrin (Figure 3), it is much more stable16.

4. Potential Environmental Health and Toxicological Issues.

From the ACS Select on nanotechnology in food and agriculture9, we may draw attention to the following subjects. Despite the attractiveness of using QSAR approaches to the determination of the econanotoxicological effects of ENMs, the complexity of the real environmental situation, e.g. many different kinds of organism and of material types, render the relationships difficult to apply because of a lack of reliable experimental data17. As an alternative, high-output screening combined with dynamic energy budget models is proposed18. Irrespective of the origin of the ENMs, i.e. whether they are deliberately introduced as part of an agricultural strategy, or present as contaminants, it is critical to know what effects they may have on the growth of plants. Thus, when wheat shoots were grown in sand that had been amended with silver nanoparticles, their growth was demonstrated to be stunted in a dose-dependent manner19. When Arabidopsis thaliana was exposed to CeO2 nanoparticles at a concentration of 250 parts per million (ppm), a significant increase in plant biomass was found, but as the concentration was increased to 500-2000 ppm, plant growth was decreased by up to 85% in a fashion that was dose-dependent20. Different effects were observed with In2O3 nanoparticles20. Although the environmental concentrations of ENMs are generally low, there is a risk that they may bioaccumulate in plants. Thus, it has been demonstrated that copper oxide nanoparticles will accumulate in maize plants, translocating from the roots to the shoots, and back again21. To explore the possibility of tropic transfer (movements of pollutants up the food chain), soil was inoculated with gold nanoparticles, and indeed, while the latter could be transferred to earthworms and thence to bullfrogs, the concentrations decreased by two orders of magnitude in each step22. It was shown that children may have the highest level of exposure to TiO2 nanoparticles, which are in relatively high concentrations in “candy products”23. Silica ENMs were found to enter the gut epithelium, after digestion in the stomach, alerting to a potential problem that requires further investigation24.
            Although nanoscale technology shows much promise in the food industry and in agriculture, its development must be done sustainably, and it is governments who will contribute substantially to this development25, mainly through existing regulations. Notwithstanding that, during the past decade, much effort has gone into the environmental health and toxicological Issues of ENMs, considerable uncertainly still remains, for which the following topics may be highlighted9:

measurement and metrology of ENMs in complex matrixes;
•environmental fates and transformation of currently known ENMs and ever increasing number of newENMs;
•nanobio interface between ENMs with human body and ecosystem species;
•exposure and full life cycle assessment;
•risk assessment and management of diverse uses of ENMs;
•safety by design; and
•sustainable nanomaterials and nanomanufacturing.

Nanoinformatics is an emerging field of research, for the design, data integration and communication of information regarding ENMs. Methods to predict the econanotoxicology of ENMs need major development and it appears probable that high-throughput, high-content screening methods will prove useful in assessing the safety of nanomaterials. I note a much cited review of the environmental and health effects of nanoparticles, of both natural and artificial origin26.

References.
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(4) Kahn, J. (2006) Nanotechnology. National Geographic (June): 98–119.
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(6) Rodgers, P. (2006) Nanoelectronics: Single file. Nature Nanotechnology. doi:10.1038/nnano.2006.5.
(7) Crichton, M. (2006) Prey. Harper Collins, New York. ISBN-13: 978-0007796427.
(8) http://royalsociety.org/policy/publications/2004/nanoscience-nanotechnologies/
(9) Chen, H., Seiber, J.N. and Hotze, M. (2014) ACS Select on Nanotechnology in Food and Agrculture: A Perspective on Implications and Applications. J. Agricul. and Food Chem. 62, 1209-1212.
(10) Joseph, T. and Morrison, M. (2006) Nanotechnology in Agriculture and Food. Nanoforum Report. ftp://ftp.cordis.europa.eu/pub/nanotechnology/docs/nanotechnology_in_agriculture_and_food.pdf
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(13) http://cordis.europa.eu/news/rcn/24345_en.html
(14) http://www.nanotechproject.org/cpi/
(15) Li, Q., et al. (2013) Nanocellulose life cycle assessment. ACS Sustainable Chem. Eng. 1, 919−928.
(16) Kayaci, F., Ertas, Y.and  Uyar, T. (2013) Enhanced thermal stability of eugenol by cyclodextrin inclusion complex encapsulated in electrospun polymeric nanofibers. J. Agric. Food Chem. 61, 8156−8165.
(17) Kahru, A. and Ivask, A. (2012) Mapping the dawn of nanoecotoxicological research. Acc. Chem. Res., 46, 823−833.
(18) Holden, P. A. et al. (2012) Ecological nano-toxicology: integrating nanomaterial hazard considerations across the subcellular, population, community, and ecosystems levels. Acc. Chem. Res. 46, 813−822
(19) Dimkpa, C. O. et al. (2012) Silver nanoparticles disrupt wheat (Triticum aestivum L.) growth in a sand matrix.Environ. Sci. Technol. 2012, 47, 1082−1090.
(20) Ma, C.et al. (2013) Physiological and molecular response of Arabidopsis thaliana (L.) to nanoparticle cerium and indium oxide exposure. ACS Sustainable Chem. Eng.
1, 768−778.
(21) Wang, Z. et al. (2012) Xylem- and phloem-based transport of CuO nanoparticles in maize (Zea mays L.). Environ. Sci. Technol. 46, 4434−4441.
(22) Unrine, J. M. et al. (2012) Trophic transfer of Au nanoparticles from soil along a simulated terrestrial food chain. Environ. Sci. Technol. 46, 9753−9760.
(23) Weir, A. et al. (2012) Titanium dioxide nanoparticles in food and personal care
products. Environ. Sci. Technol. 46, 2242−2250.
(24) Peters, R. et al. (2012) Presence of nano-sized silica during in vitro digestion of foods containing silica as a food additive. ACS Nano. 6, 2441−2451.
(25) Bergeson, L. L. (2013) Sustainable nanomaterials: emerging governance systems. ACS Sustainable Chem. Eng. 1, 724−730.
(26) Buzea, C. et al. (2007) Nanomaterials and nanoparticles: Sources and toxicity. Biointerphases 2(4), MR17-MR172. http://arxiv.org/ftp/arxiv/papers/0801/0801.3280.pdf
(27) Rhodes, C.J. (2010) Solar Energy - Principles and Possibilities. Sci. Prog. 93, 37-112.

Captions to figures:

Figure 1. A photograph and representative spectrum of photoluminescence from colloidal CdSe quantum dots excited by UV light. The absorption and consequent fluorescence, moves to higher energies and hence toward the blue end of the visible spectrum, as the particle size decreases27http://upload.wikimedia.org/wikipedia/commons/5/57/CdSeqdots.jpg Credit: NASA.
Figure 2. Molecular structure of eugenol http://upload.wikimedia.org/wikipedia/commons/8/86/Eugenol2.svg
Figure 3. Space filling model of β-cyclodextrin. http://upload.wikimedia.org/wikipedia/commons/9/92/Beta-cyclodextrin3D.png