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Effect of Silver Nanoparticles on Plant Growth

Nanoparticles are becoming increasingly used as materials in over 2000 consumer products due to their unique chemical, physical and electrical properties. A nanometer is one billionth of a meter and nanoparticles can be 1-100 nm in size. Silver nanoparticles are used for their antibacterial properties in many every day products such as food storage containers, air filtration systems and bandages. Nanomaterials are structures, devices, and systems at the nanometre scale. They are fast becoming an important material that can range from better and faster electronics to more efficient fuel usage, drug discovery and stronger, more resistant materials (Whatmore, 2006).
The demand for engineered nanomaterials is a rapidly growing industry which was expected to reach a market size of approximately 2.6 trillion dollars by 2015 (Lee et al., 2010), however there is little knowledge on whether nanomaterials have an adverse effect on the environment or to human health and what the extent of these effects could be. Engineered nanoparticles have a wide range of chemical, physical and electrical properties such as conducting heat with low resistance and being stronger and lighter than other bulk materials (Tolaymat et al., 2017). The broad number of products that contain nanomaterials for consumers may lead to the release of an increased quantity of engineered nanoparticles in to the environment, which display different physiochemical properties than larger materials. (Geisler-Lee et al., 2012). While the benefits of nanomaterials are broadcasted, their potential effects to the environment and to human health from their widespread use in consumer products are just becoming recognized. (Hoet et al., 2004).

There are a number of ways that nanoparticles can be released in to the environment as shown in Figure 1. There are a number of different entry points for engineered nanomaterials into the environment, including wastewater treatment plant (WWTP) effluent, and WWTP sludge, however, it is difficult to estimate the relevant concentrations of nanoparticles that will be released in to the environment (Maurer-Jones et al., 2013).
Once nanoparticles enter the environment there can be movement throughout the environment. One way this could happen is through food webs. If nanoparticles are consumed by organisms on a low trophic level thy may begin to accumulate in organisms at higher trophic levels. One of the challenges for working out the dangers associated with nanomaterial release in to the environment is the concern related to how clear our knowledge of how the properties of nanomaterials change once they interact with the environment. Also, nanoparticle properties can be affected by conditions, such as soil chemistry, pH, and organic matter. (Darlington et al., 2009)
One of these effects to the environment could be the release of nanomaterials, through different pathways, in to bodies of water including lakes, rivers, and streams which could also cause run off in to soils and in to the air. Recent research (Das et al., 2012) showed that AgNPs rapidly but temporarily inhibited natural bacterioplankton production. Nanoparticles can affect biological behaviour at the cellular, subcellular and protein levels of a plant.
The effect of nanomaterials on plant species is a topic that is being widely researched however there is still no conclusive answer on whether nanomaterials, specifically silver nanoparticles, have a negative impact on plant species, however metallic engineered nanoparticles may have stimulatory and inhibitory effects on plants. Arabidopsis thaliana is widely used in scientific research and was used in this study to further investigate the effects of silver nanoparticles on germination of seeds and also chlorophyll fluorescence after treatment with differing concentrations of nanomaterials.
The silver nanoparticles used in this experiment were capped with PVP; this is because capped nanoparticles are less likely to aggregate in the solution over time and are more stable than uncapped nanoparticles (Tejamaya et al., 2012). Due to this a control of PVP had to be used to show that the capping had no effect on the plant species itself.
Two mutations of A. thaliana seed were used in this experiment to test the effects of silver nanoparticles. The two sizes of silver nanoparticles were dissolved in distilled water which also meant that distilled water had to be used as a control to show that, on its own, it had no effect on the plant germination. Silver nitrate was also used at differing concentrations as a third control to show any differences between nanoparticles and as silver nitrates can be reduced, with PVP as a stabilizer, to synthesize silver nanoparticles (Samadi et al., 2010). As silver nanoparticles are smaller in size than silver nitrate particles, there will be a higher abundance of nanoparticles within the solution at a given concentration than silver nitrates.
The effect of silver nanoparticles on plant species is important due to the many ways that nanoparticles can be dispersed in the environment. Relatively few studies have investigated the toxicological and environmental effects of engineered nanoparticles (Smita et al., 2012). However, the concentrations used in this experiment would generally be higher than the concentrations of these nanoparticles in the environment, although accurate concentrations in the environment are still not fully known. This is because their concentration in the environment will depend on factors such as the amount of the material released over time. The nanoparticles may become physically or chemically altered by environmental conditions such as temperature and salinity of water and also these factors may alter the form of the nanoparticles, exposure, and transport through the environment. There is still concern over the potential impacts of engineered nanoparticles in the environment on aquatic and terrestrial organisms. Although some data indicates that current risks of engineered nanoparticles in the environment may be low, what we know of the potential impacts of engineered nanoparticles in the environment is still limited. There is still a demand for continued work to further understand the exposure levels for engineered nanoparticles in environmental systems and try and further our knowledge on the significance of these levels in terms of the environment which is what has been addressed in this project (Boxall et al., 2007).
A similar study was carried out by (Obaid, 2016) which evaluated the impact of capped silver nanoparticles on terrestrial and aquatic plants, one of the terrestrial plants being A. thaliana . In this study chlorophyll fluorescence and gaseous exchange of the plants were measured to analyse the effects of the capped silver nanoparticles. The study showed that the capped silver nanoparticles displayed varying toxicity to the plants at higher concentrations, with particular interest to how they effected the germination of A. thaliana, with inhibition of germination at a concentration of 100mg/l of capped silver nanoparticles. The outcome of this study found that there are many factors that have significance on the toxicity of silver nanoparticles which includes exposure method, released ions, plant species, light intensity and growth mediums. However the concentrations used in the study by (Obaid, 2016), much like the concentrations used in this project, are exaggerated and concentrations as high as these will not be present in the environment as yet although it is important to test high concentrations due to large quantities of nanoparticles being used in every day products therefore such concentrations may be present in the environment in the very near future.

The Green Revolution: History, Impact and Future

Plants are an essential part of lives on the planet and a crucial source of economic prosperity for almost every country. They provide directly or indirectly almost all the food of man and animals. They also supply industrial raw material, for instance, timber, paper, rubber, products for the chemical industries such as starch, sugars, oils and fats, energy in the form of fuel wood, starch and sugars which are sources of ethanol, methanol, etc., and massive numerous valuable drugs, fragrances and other fine chemicals. Plant growth also has a massive influence on environment. Because of all these roles, Policymakers should be continually developing policies for the use of plants to protect the earth’s environment and to feed the growing populations.(1)
The Historical Phenomenon (Green revolution) The term “Green Revolution” has begun to be used in 1960s refers to the renovation of agricultural practices by some Third World countries, particularly in Asia and Latin America, beginning in Mexico in the 1940s. Because of the use of high-yielding varieties (HYVs) of wheat and rice which increase food crop production. Green revolution technologies spread worldwide in different terms as “agricultural revolution” and “seed-fertilizer revolution”, which led to a substantial increase in the amount of calories produced per acre of agriculture in 1960s.(light green, H2)
The green days of the Green Revolution (History and Development) In 1970 the American botanist, Norman Borlaug, Director of the Division for Wheat Cultivation at the International Maize and Wheat Improvement Center or CIMMYT in Mexico, was awarded the Nobel Peace Prize. He was honoured for having set in motion a worldwide agricultural development, later to be called the ‘Green Revolution’ (light green). In the 1940s, N. Borlaug began conducting research in Mexico and developed new disease resistance high-yield varieties of wheat. By combining Borlaug’s wheat varieties with new mechanized agricultural technologies, Mexico was able to produce more wheat than was needed by its own citizens, leading to its becoming an exporter of wheat by the 1960s. Prior to the use of these varieties, the country was importing almost half of its wheat supply.(net)
Due to the success of the Green Revolution in Mexico, its technologies spread worldwide in the 1950s and 1960s. The United States for instance, imported about half of its wheat in the 1940s but after using Green Revolution technologies, it became self-sufficient in the 1950s and became an exporter by the 1960s.(net)
A renovation of the history of the Green Revolution shows that the international agricultural research institutes played an important role in progressing of using Green Revolution technologies. Such as, in 1959, the CIMMYT instituted in Mexico, which was founded by the Ford and Rockefeller Foundations, and the Mexican government provided the land. Also, in 1960, the International Rice Research Institute (IRRI) in Manila, which was joint effort of the Ford and Rockefeller Foundation Several more international institutes were established and funded by government agencies as the World Bank and the US Agency for International Development (USAID). After that, in 1971, all the international agricultural research institutes were brought under the umbrella of the Consultative Group on International Agricultural Research (CGIAR).(4)
The development was based on the genetic improvement of particularly productive plants. Borlaug’s so-called “miracle wheat” doubled and tripled yields in short period of time. Similar increases were soon achieved with maize and, at the (IRRI), with rice (IR8) that produced more grain per plant when grown with irrigation and fertilizers.(2)
The success of the newly developed strains appeared limitless. They were introduced in several Asian countries in 1965, and, by 1970, these strains were being cultivated over an area of 10 million hectares. Within three years, Pakistan ceased to be dependent wheat imports from the United States. Sir Lanka, the Philippines, and number of African and South American countries achieved record harvests. India, which had just avoided a severe famine in 1967, produced enough grain within five years to support its population, and became one of the world’s leading rice producers.(2) Despite the success of the Green Revolution in increasing yields per hectare in India, this success has largely bypassed Africa. The reasons for this include the fact that both wheat and rice are relatively unimportant staple crops in Africa; that Africa’s main staples of maize, sorghum, millet, and cassava have experienced only modest productivity gains; and that Africa’s infrastructure is not sufficiently well developed to support significant agricultural change
The witness of the Green Revolution (Plant Technologies) Agricultural technology development can be characterised as passing from primarily “land-related” technologies, through mechanisation to bio-chemical technologies (associated with new varieties and relatively large amount of agro-chemicals). It is now moving towards a “bio-technology’ phase. (green p 72)
The crops developed throughout the Green Revolution were high yield varieties (HYVs), which means they were domesticated plants in high response to chemical fertilizers and produce more grain per plant when grown with irrigation.( H2)
They were insensitive to photoperiodicity and matured in about 110 days rather than 180 days; it was thus possible to grow two or even three crops in a year. The yield potential of these varieties was greater in the temperate regions of Asia and in the dry season in the monsoon region than in the humid tropics, because of the longer hours of sunshine and hence the greater potential photosynthesis available to the plant. (H2)
The terms often used with these plants that make them successful are harvest index, photosynthate allocation, and insensitivity to day length. The harvest index refers to the above ground weight of the plant. During the Green Revolution, plants that had the largest seeds were selected to create the most production possible. After selectively breeding these plants, they evolved to all have the characteristic of larger seeds. These larger seeds then created more grain yield and a heavier above ground weight.
This larger above ground weight then led to an increased photosynthetic allocation. By maximizing the seed or food portion of the plant, it was able to use photosynthesis more efficiently because the energy produced during this process went directly to the food portion of the plant.
Finally, by selectively breeding plants that were not sensitive to day length, researchers like Borlaug were able to double a crop’s production because the plants were not limited to certain areas of the globe based solely on the amount of light available to them.
Benefits

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