How two-in-one shampoos work, the genes that we share with trees, and the link between polonium and cancer from cigarettes
Tobacco leaves contain polonium-210, which is linked to lung cancers among smokers. Photograph: Mark Wilson/Getty
Q If shampoo is designed to wash stuff out of your hair, how can "shampoo with conditioner" possibly work? asks Clifton Hughes
A Shampoo removes oil and dirt from your hair so at first glance it makes an odd bedfellow for conditioners, which provide an oil-based protective coating that allows hair fibres to slip over each other and hence reduce tangling.
However, as Dr Jeni Thomas of P&G explains, the answer lies in some clever chemistry. Shampoos are based on jekyll-and-hyde molecules that, when ionised, have a negatively-charged water-loving end and an uncharged oil-loving end. When they come into contact with dirty hair, the oil-loving tails cluster around the grime and bundle it up, leaving the water-loving ends sticking out. When water is applied, it readily carries away the shampoo and the dirt that it has bundled up.
So what about two-in-one products? In a nutshell many products make use of silicone oils, like dimethicone, that can lubricate the hair. These conditioning agents are suspended as tiny droplets in a matrix composed of ethylene glycol distearate. Hence the silicone oil is just a bystander in the lathering process: when the two-in-one product is applied to the hair, the oil-loving end of the shampoo molecules bundle up the dirt and grease in the hair. But as water is splashed on to rinse off the shampoo, the water breaks down the ethylene glycol distearate matrix and the silicone oil droplets are released. These droplets form complexes with positively charged long-chain molecules (called cationic polymers) that are also in the mix, however these complexes are not very soluble in water, and so are deposited on the hair. The cationic polymers of the complex protect the delicate wet hair and aid the deposition of the silicone oil. As the hair dries, this silicone oil spreads out over the hair fibre and leaves hair smooth, shiny and combable.
Q Do people and trees share any DNA? If so, are there any estimates as to how much? asks Phil Hore
A As Dr James Schnable, assistant professor at the University of Nebraska, explains: "The last common parent of animals and plants lived between 1.1 and 1.8bn years ago." But the clues to the past remain. "There are still many genes in plants (including trees) and animals (including humans) that are related to each other.
"Related genes do not have identical DNA sequences, however, they show enough similarity that we can tell the two genes shared a common parent millions or billions of years ago." But just how many of our genes are "related" to those of the greenery? "Different estimates suggest that between 40-55% of the genes in the human genome are related to genes found in plants," says Schnable.
"However, because genes are only a small part of the total genome in any species, the percentage of the total DNA shared between a human and a tree is quite small and will vary a lot depending on the tree species. The genome of a pine tree is seven times as large as our own human genome, while the genome of a papaya tree is only 1/10th as large as the human genome," he says.
Q Increasing numbers of wind farms are taking energy out of air flows across the globe. Is it possible this is affecting the normal tracking of the jet stream resulting in the recent changes in weather patterns? asks Sue Hammler
A As Dr Axel Kleidon from the Max Planck Institute for Biogeochemistry explains, the energy harnessed by wind turbines is unlikely to disrupt air flows high in the atmosphere.
"Wind turbines certainly take energy out of the winds, energy that is otherwise removed by friction near the surface. When large wind farms take out energy, this would certainly affect the surface and alter the environment," he says. "Yet they are unlikely to impact jet streams that are far removed from the surface."
However, as Kleidon says, the energy removed by the wind farms is only a fraction of the energy taken out of the wind by friction close to the surface. "To put things in proportion, about 3.4 gigawatts of electricity was on average generated by wind turbines during 2012, while about a hundred times as much was lost by friction over the UK," he says.
Q A recent article in the Guardian said polonium collects in tobacco leaves. Could that polonium account for most of thecancer attributed to tobacco? asks Emiliano Zapata
A Tobacco leaves – and hence cigarettes – do indeed contain polonium-210, a radioactive isotope that hit the headlines in 2006 when ex-spyAlexander Litvinenko was poisoned with a dose that was apparently slipped into his tea. That cigarette smoke contains polonium-210 wasreported in the 1960s. In soil, naturally occurring radium-226 (a decay product of uranium) undergoes a decay pathway that leads to lead-210 and hence polonium-210. Calcium phosphate fertilisers, often used on tobacco plants, that are contaminated with such radionuclides are also a source of polonium-210. As well as taking up radioactive elements from the soil through their roots, tobacco plants may also trap them from their air by means of tiny, sticky hairs and pores on their leaves.
Polonium-210 emits alpha particles (helium nuclei) as it decays, which have a high energy and can damage DNA, for example by deletation of segments, and cause cell death. When cigarette smoke is inhaled, these substances accumulate in localised areas within the lungs. Studies over the years have looked at the effects of this radiation on the lungs. Areport from 1982 suggested that smoking one and a half packets of cigarettes a day for a year exposes the lungs to a radiation dose that is equal to having 300 chest x-rays over 12 months, however a more recentstudy revised this to 28 chest x-rays in a year for a smoker who consumed 20 cigarettes a day for 12 months. A study from the 1970s found exposing the lungs of hamsters to polonium-210 can give rise to cancers, suggesting it could do the same in humans.
Most interestingly, the levels of polonium-210 found to induce tumours in these rodents was less than a fifth of that a smoker would inhale over 25 years if they consumed two packets a day.
While polonium-210 is one of many carcinogens that enter the lungs through smoking, it has been linked to a shift in the type of lung cancersseen in smokers over recent decades – a trend that appears to correlate with an increase in the use of calcium phosphate fertilisers.
US Figures estimate that 80-90% of lung cancer deaths are caused by smoking, however it is difficult to estimate what proportion might be down to the polonium-210 alone.
The authors of one 2011 paper estimate that polonium-210 could be responsible for "120 to 138 deaths per 1,000 regular smokers over a 25-year period" while another estimates the direct risk to be four cases of lung cancer per 10,000 smokers per year.
No comments:
Post a Comment