With 18 million tonnes, a remote island turns into plastic junkyard

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Plastic debris on Henderson Island in Pacific Ocean

The beaches of Henderson Island, an uninhabited island in the South Pacific Ocean about 5,000 km away from the nearest population centre, are heavily littered with plastic waste. The beaches have an estimated 38 million plastic debris items weighing 17.6 tonnes.

The largest of the four islands of the Pitcairn Island group, Henderson Island is a Unesco World Heritage Listed site. Since it is uninhabited, its ecology is largely untouched by humans.

With 671 plastic items per sq metre on the surface of the beaches, the island has the highest density of plastic waste reported from anywhere in the world. And the amount of plastic waste on the island is ever growing with about 27 new plastic items per metre getting accumulated on a daily basis; in the North Beach of the Island alone, about 3,570 items get deposited daily. The results were published in the journal Proceedings of the National Academy of Sciences.

crab-OptimizedIn 2015, the researchers enumerated over 53,000 plastic items and arrived at an estimate of 37 million items littered on the beach. And alarmingly, even the 37 million plastic items may be an underestimation.  The reason: the team could not sample plastic waste buried below 10 cm from the surface and particles below 2 mm size and those found in the cliff areas and rocky coastline were not sampled.

With plastic waste disintegrating, smaller items were predominant, with microplastic accounting for 62% of items found in the Henderson Island.

The Henderson Island is located ion the western boundary of the South Pacific Gyre, a known plastic-accumulation zone for debris carried from South America (27%) or deposited by fishing boats.

“The plastic waste creates a physical barrier and contributes to a reduction in the number of sea turtles laying attempts, lower density of shoreline invertebrate communities and increased hazard of entanglement of coastal-nesting seabirds,” they write.

“Research has shown that more than 200 species are known to be at risk from eating plastic, and 55 per cent of the world’s seabirds, including two species found on Henderson Island, are at risk from marine debris,” Dr Jennifer Lavers from the University of Tasmania, Australia and the first author of the paper says in a release.

With the 17.6 tonnes of plastic waste found on the island accounting for only about 2 seconds of global production of plastic, the amount of waste that would get accumulated even in remote islands is bound to increases and further impact the exceptional natural beauty and biodiversity of these islands.

Bengaluru researchers mimic nature to produce richer colours

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(From left) Prof. Rajesh Ganapathy, Chandan Mishra and Prof. Ajay Sood have taken the first step to make crystalline materials that produce structural colours by scattering light

In a novel approach that mimics nature, Bengaluru-based researchers have designed crystalline materials that selectively scatter specific colours of light. Dyes and pigments produce colour predominantly through selective absorption of light. But scattering of light by particles which are arranged in an ordered, periodic pattern produces structural colour, which gives butterfly wings their colour and sheen.

The backlit colour display of a mobile or laptop monitor becomes difficult to read under intense light. But if the front panel were to be made of structural colour then the ambient light would become a source of colour. By producing crystals that scatter wavelengths corresponding to  red, green and blue light, structural colours can be used in place of the conventional LED and LCD monitors, too.

In nature, nanosized particles and colloids are responsible for producing structural colours. Compared with atoms, colloidal particles are 10,000 times bigger, and, so, conventional lab techniques to move the particles over long distances to form an ordered, periodic pattern have been riddled with problems.

The novel approach adopted by researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) and Indian Institute of Science (IISc) has overcome the challenge of transporting the particles to target sites; the size and symmetry of the growing crystallites are also controlled. The results were published in the journal Proceedings of the National Academy of Sciences.

structural colours can be used in place of the conventional LED and LCD monitors.“We need some mechanism which will drive the particle in a given direction to a long distance. We solved this by creating an energy gradient on the surface of a Moiré pattern. The energy gradient dictates where the colloidal particle should go and nucleate and grow in an ordered fashion,” says Chandan K. Mishra from the Chemistry and Physics of Materials Unit, JNCASR, and the first author of the paper.

To produce the Moiré pattern the researchers first imprinted an optical grating (which has linear trenches drilled on a glass surface) on a soft polymer. Rotating the optical grating at a small angle and repeating the imprinting on the soft polymer led to the creation of a geometrical pattern. The Moiré pattern with channels of non-uniform depth was the template on which the colloidal particles get deposited at specific sites in an orderly pattern.

“There is an energy gradient within the geometric pattern which drives the particles to the desired locations,” says Prof. Ajay Sood of the Department of Physics, IISc and a coauthor of the paper. The energy gradient comes from the variation in the depth of the channels and the presence of small particles driving the colloidal particles to the specific sites in the pattern.

In the presence of smaller particles (which are added along with the colloidal particles), the colloidal particles are attracted towards the channel wall. “Since the channel has a gradient in depth, the smaller particles drive the colloidal particles to the deeper portions of the channel where the particle is surrounded by tall ridges on either side.  This is the final resting place of the colloidal particle. If all the particles come to this point they form a crystal,” says Prof. Rajesh Ganapathy from JNCASR and one of the corresponding authors of the paper.

The nucleation initially begins at the sites where the ridges have maximum height and then progressively spreads to sites where the channel height is less. The distance between two nucleation sites is predetermined to scatter a particular colour, for instance, red.

The process is repeated with colloidal particles of a different size which will grow into crystals with a different separation distance between them (periodicity). Due to a different separation distance the crystals will then scatter light of a different wavelength. “Our eventual goal is to make these patterns and drop particles of three different sizes at the same time and the Moiré pattern will decide where each particle size should go and form crystals that scatter red, green and blue wavelength,” says Prof. Ganapathy. “What we have done is the first step — controlling the colloidal self-assembly using the Moiré pattern.”

Published in The Hindu on December 18, 2016

Thanks to air pollution, magnetic particles found in the brain

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Magnetite nanoparticles are toxic to the brain tissue as they generate reactive oxygen species.

The effects of air pollution on human health has gone up by a few notches with the discovery of large number of rounded magnetite nanoparticles of about 18 nanometres in diameter (and maximum of 150 nm) in the frontal cortex tissue of the brain of 37 people. The people studied were 3-92 years old and lived in Mexico City and Manchester, U.K. The results are published today (September 6) in the Proceedings of the National Academy of Sciences. 

This is the first time rounded magnetic nanoparticles occurring along with other transition metals, such as platinum, nickel, and cobalt have been reported in the brain of human beings.

Airborne particles less than 200 nanometres can enter the brain directly through the olfactory nerve. The nanoscale magnetite particles can respond to external magnetic fields and are toxic to the brain tissue as they have been implicated in the generation of reactive oxygen species. Enhanced reactive oxygen species production in the brain is casually linked to neurogenerative diseases such as Alzheimer’s.

Magnetite particles are ubiquitous in airborne-particulate matter and are caused due to combustion of iron-rich particles and friction-heating (brake pads). “Magnetite can arise from combustion of many types of organic matter, depending on heating temperature and atmosphere, and source of iron content,” they write. Besides, industrial and vehicles, open fires or poorly sealed stoves used for cooking and/or heating can produce magnetite nanoparticles. The combustion-derived magnetite particles can range in size from less than 5 nanometre to 1 micrometer.

“Increased metals content and Alzheimer’s disease neuropathological hallmarks have been found in young human brains exposed to high airborne particulate matter PM2.5 concentrations in Mexico City,” the write. Since only about 5 per cent of Alzheimer’s is directly inherited, other factors such as environmental factors and/or gene/environment interactions may be playing a huge role in initiating and/or promoting Alzheimer’s.

But it yet to be firmly established that magnetite from air pollution can indeed be a critical factor in the development of Alzheimer’s. Particularly because more number of cases should be seen and at an early ages in places where magnetite pollution in air is more. It is also not clear yet whether size, number, mineralogy and associated chemical species of particulate matter contributes most to toxic effects.

Less risk of skin cancer if exposed to UV radiation in the morning: Nobel Laureate Aziz Sancar

“If you really must go to a tanning booth, do it in the morning,” Aziz Sancar, from the University of North Carolina, Chapel Hill, U.S., who shared the Nobel Prize in Chemistry with two others — Tomas Lindahl of Francis Crick Institute and Clare Hall Laboratory, Hertfordshire, U.K. and Paul Modrich of Howard Hughes Medical Institute and Duke University School of Medicine, Durham, U.S. — told New Scientist.

Dr. Sancar’s advice was based on studying how a mouse’s circadian rhythms affect its ability to repair DNA damage caused by UV radiation in the morning.

Unlike mice, humans are diurnal and hence one can expect the opposite results in humans — greater ability to repair DNA damage caused by UV radiation in the morning.

Dr. Sancar was awarded the Nobel Prize for mapping nucleotide excision repair — the mechanism that cells use to repair UV damage to DNA. According to a Nobel Prize release, people born with defects in this repair system will develop skin cancer if they are exposed to sunlight. The cell also utilises nucleotide excision repair to correct defects caused by mutagenic substances, among other things.

His observation was based on a study undertaken in mice. The results of a study published in the Proceedings of the National Academy of Sciences in November 2011 found that the time of day of exposure to UV radiation is a “contributing factor” to skin cancer development in mice and “possibly in humans.”

He and his colleagues arrived at this conclusion based on fact that the mechanism that cells use to repair UV damage to DNA (excision repair rate) exhibits daily rhythmicity in mouse skin. In the case of mice, the ability to repair UV damage to DNA was minimum in the morning and maximum in the afternoon/evening.

As a result, mice exposed to UV rays (280-320 nm) at 4 am, when the cells ability to repair UV damage to DNA (excision repair activity) was at its lowest developed skin cancers at a “faster rate” and at about “fivefold higher frequency” compared with mice that were exposed to UV rays at 4 pm, when the excision repair activity was at its peak.

“We conclude that time of day of exposure to UV radiation is an important determinant in the carcinogenicity of UV radiation,” notes the paper. Since the human clock is identical to the mouse but is opposite in phase (diurnal vs nocturnal), the “susceptibility of humans to UV radiation-induced skin cancers is likely to exhibit a daily rhythm as well.”

“In mouse skin there is more DNA replication and less repair in the morning and less replication and more repair in the evening. Because UV-induced skin cancers arise from mutagenic replication of epidermal keratinocyte DNA, the same UV dose is more carcinogenic in early morning hours than when given in the early evening hours,” they note.

In the paper, Dr. Sancar “predicts” that humans are less likely to develop skin cancer if exposed to UV radiation in the morning. The authors have gone so far as stating that “it might be advisable for humans, to the extent possible, to restrict their occupational, therapeutic, recreational, and cosmetic UV radiation exposure to the morning hours.

They add a note of caution by stating that the phase of circadian rhythm is not the uniform in all people but varies between individuals. And hence any recommendation for best times for UV radiation exposure should be based on individual’s circadian rhythm. However, with rare exceptions, humans on the whole are diurnal and hence are most likely to have maximum repair capacity in the morning hours. “We suspect that by restricting UV radiation exposure to morning hours would reduce the risk of skin cancer in humans,” they write.

It is well known that the circadian clock is known to affect the onset and severity of a few other common diseases such as asthma and cardiovascular incidents.

Published in The Hindu on October 7, 2015

Fixed nitrogen: Mars was once habitable

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Curiosity has found evidence of indigenous nitrogen in the form of nitrates in aeolian deposits. – Photo: NASA

The Mars rover Curiosity has for the first time found evidence of indigenous nitrogen in the form of nitrate in aeolian deposits and in two mudstone deposits on the red planet. This discovery has great implications for habitability and, “specifically for the potential evolution of a nitrogen cycle at some point in Martian history.”

The results were published a few days ago in the journal Proceedings of the National Academy of Sciences (PNAS).

At first, Curiosity found indirect evidence of water that was once present on Mars, and then found true indicators of water that existed as rivers and lakes. The evidences unequivocally showed the presence of fresh water that was neither acidic nor salty.

In December last year, Curiosity detected wafts of methane in the Martian air. On Earth, methane is largely produced by living organisms. The detections indicated that the gas is present at about 1 part per billion in the Martian atmosphere, or 4,000 times less than in Earth’s.

The detection of nitrate in aeolian samples and two mudstone samples drilled from a relict lakebed suggests “widespread atmospheric deposition” of nitrogen gas.

The detection of nitrate in samples of different kinds (aeolian deposits and mudstone) is quite likely due to nitrogen fixation to nitrate as a result of thermal shock either from impact or volcanic plume lightning. Immaterial of the route in which the nitrogen fixation had taken place, the very presence of fixed nitrogen would have facilitated the development of “primitive nitrogen cycle” on the Martian surface. In turn, this would have provided a “biochemically accessible source of nitrogen.”

Much like water, nitrogen is essential for life. After all, it forms the building blocks of larger molecules like DNA, RNA and protein. But nitrogen has to be fixed for it to take part in chemical reactions essential for creation of life. Both on Earth and Mars, atmospheric nitrogen is in the form of nitrogen gas (N2) where two nitrogen atoms combine and do not easily react with other molecules.

Earlier studies have found nitrogen gas to constitute around 2 per cent of the Martian atmosphere.

Curiosity detected the bulk of nitrogen in the form of nitric oxide. According to the scientists, the nitric oxide quite likely indicates a mineralogical sink for atmospheric nitrogen gas before being fixed as nitrate (NO3). The estimated abundance of nitrates in the aeolian sample is about 110-300 ppm and vary in the two mudstone samples — 70-260 ppm and 330-1,100 ppm.

Nitrogen has to be fixed to become biochemically available. On Earth, certain organisms carry out this process of fixing atmospheric nitrogen. On Mars, lightning and/or thermal shock would have played a role.

The scientists state that the presence of fixed nitrate suggests that the first half of the Martian cycle was established at some point. But in the absence of near-surface life in Mars after some 3.5 billion years ago, the cycle of releasing the fixed nitrogen to atmosphere did not take place. As a result, the fixed nitrogen accumulated as nitrate in the rocks. On Earth, nitrogen returns to the atmosphere by de-nitrification via biological activity.

In the Atacama Desert, organisms have little role to play in nitrogen fixation; the fixation takes place through an abiotic process. Since the hyperarid climate is not quite conducive for biological activity, the nitrogen fixed as nitrates is not lost to the atmosphere through the de-nitrification process.

Published in The Hindu on March 26, 2015

Mangroves in Florida expanding poleward

Adding to the growing evidence of climate change-induced poleward migration and/or expansion of many fish and terrestrial plant species, a paper published recently in the Proceedings of the National Academy of Sciences (PNAS) journal has found a massive expansion of mangroves in Florida. The expansion has been to an extent of more than 3,000 acres over a 28-year period — 1984 to 2011.

By default, mangroves are restricted to the tropical areas as they cannot tolerate the extreme cold events that are so very typical of the temperate zone. Therefore, the massive expansion of mangroves in the temperate zone of Florida during the last three decades is proof of climate change’s role.

“These increases [expansion] correspond to decrease in the frequency of extreme cold events in this region,” notes Kyle Cavanaugh of the Smithsonian Environmental Research Centre, Smithsonian Institute, U.S. Dr. Cavanaugh is the first author of the paper.

Aside from pointing out the poleward expansion, the study has highlighted another important parameter — the “dynamics of mangrove” coverage. The authors have found that the 26.75 degree N latitude plays a critical role.

While there was an increase in the mangrove coverage north of this latitude, there was “little or small decrease” in the area south of this latitude. The increase in mangrove coverage north of 26.7 degree N was about 4,200 acres; the area south of this latitude had reduced by about 1,164 acres. “The 26.75 degree N [is] a breakpoint in the relationship between latitude and change in mangrove area,” they write.

According to the authors, the reason for this strange concomitant expansion/reduction in mangrove coverage boils down to extreme cold events — days colder than -4 degree C. Minus four degree C is the physiological temperature limit of mangrove survival.

The region north of 26.75 degree N latitude had registered an increase in coverage as there was a “significant decrease” in the frequency of extreme cold events during the last three decades, they note. Such extreme cold events are “rare or nonexistent” in the region south of this latitude.

The impact of extreme cold event (days colder than -4 degree C) has been well documented by the hard-free winter of 1989 to 1990 — the cold event decreased the mangrove area. It took about nine years for the mangroves to reach the pre-1989 levels.

The authors rule out the role of temperature increase in bringing about an expansion. It is true that the mean winter temperatures had risen at seven of eight coastal weather stations in the study area. But if overall warming was indeed the factor for the expansion, then an overall increase in coverage should have been observed both north and south of this latitude. According to them, no other factor like rainfall and urban or agricultural land use could account for this strange trend. Only a reduction in the extreme cold events could.

“It is likely that cold thresholds act as a barrier to the poleward extension of mangroves in other parts of the world,” they write. “Relatively small future decrease in the frequency of extreme cold events could lead to further increase in mangrove cover near the current poleward limit of mangrove forests in Florida.”

Unlike terrestrial plants, a change in the type of vegetation cover would be relatively rapid in the case of mangroves as water is far superior to wind and animals in dispersing plants.

Published in the Hindu on January 2, 2014

“Functional” blood vessels made from stem cells

A team of scientists has been able to engineer “stable and functional” blood vessels in mice using induced pluripotent stem (iPS) cells taken from humans. The blood vessels lasted for 280 days in the brain of the mice. The scientists are from Massachusetts General Hospital, Boston, and Harvard Stem Institute, Harvard University.

The skin cells of healthy people and those with Type I diabetes were used to produce iPS cell lines, and, in turn, the blood vessels. The results of the study are published online on July 16, 2013 in the Proceedings of the National Academy of Sciences (PNAS) journal.

This work is proof of concept demonstration that vascular precursor cells — endothelial precursor cells and mesenchymal precursor cells from iPS cells — can be used to engineer blood vessels. While endothelial cells form the inner lining of blood vessels, mesenchymal cells provide structural stability.

3 specific markers

“The method of deriving these two cells from iPS cells was by using three specific markers. The way we did it enabled us to engineer blood vessels in vivo [inside the mice] using sophisticated microscopy and mouse models,” said Dr. Rekha Samuel, Professor of Pathology at the Centre for Stem Cell Research, CMC, Vellore, Tamil Nadu. She was in Boston as a post-doctoral fellow in Dr. Rakesh K. Jain’s (one of the co-authors) laboratory with a DBT fellowship.

Clinical applications will become possible only once the safety and body’s immune response to the lab-created vessels are studied in detail.

Engineered construct

To begin with, the two precursor cells (endothelial precursor cells and mesenchymal precursor cells) are mixed in a particular material in the lab. “This proteinaceous material provides the environment for the two cells to grow and connect in a dish,” explained Dr. Samuel. “This is called engineered construct.”

The engineered construct was then transferred onto the brain and dorsal skin of the mice and visualised with a microscope through a glass cover slip. It was also subcutaneously injected into the backs of the animals. The mice with subcutaneously injected construct were sacrificed (killed) after two weeks. Even within this short period, it had formed blood vessels and connected with the animals’ vessels. The presence of mouse RBCs in the engineered vessels is proof that blood had flowed through them.

More permeable vessels

“We were able to study the construct in the brain non-invasively every day for 280 days,” she said. “It allowed us to measure the functionality of the construct and understand the differences between the vessels of the host and the construct.” For instance, the engineered vessels were more permeable compared with vessels of the mice. In the case of skin, the construct was studied for 30 days. “Endothelial cells are different in different organs. [Hence], vessels with organ-specific endothelial cells are needed,” stressed Dr. Samuel. “So we need the best way to create the vessels to make it translational [taking it to clinical use].”

This study holds great promise to restore blood flow, especially in the case of Type II diabetic patients with ischemia in the foot. According to her, about 20 patients with diabetic foot problems are seen per week at CMC, of which, four end up in amputation.

Published in The Hindu on July 16, 2013