Bangladesh arsenic poisoning mystery solved

A team from the Massachusetts Institute of Technology may have solved one of the great environmental disaster riddles of the last 30 years -- where did the arsenic that has poisoned between two and 25 million people in Bangladesh come from?

In a paper from this week’s edition of the journal Nature Geoscience, engineers from MIT, Harvard and the Bangladesh University of Engineering and Technology in Dhaka, Bangladesh offer a new potential source -- tens of thousands of human-dug ponds.

The ponds were dug over the past 50 years to provide dirt so home could be sited on high ground and so flood barriers could be built.

Using chemical tracers, the researchers show that when organic carbon settles at the bottom of these ponds, it seeps underground where microbes consume it. This creates a chain of biochemical events that causes naturally occurring arsenic to dissolve out of the sediment and into the ground water.

Tragically, international health agencies in the 1970s began a successful push to get villagers to dig shallow tube wells for water, to stop the spread of cholera and other water-borne bacterial diseases that came from drinking pond and river water. Upwards of 40% of those wells are now contaminated with arsenic.

Beginning in the late 1970s the country was struck with severe, widespread arsenic poisoning. The immediate symptoms are violent stomach pains, vomiting, diarrhea, convulsions and cramps. Over the longer term, serious skin diseases can result.

Scientists at MIT and Harvard also estimate that the in the end the exposure will result in 125,000 cases of skin cancer, and 3,000 deaths from internal cancers.

The researchers found that when rice fields are irrigated with this arsenic-laden water, the rice filtered arsenic out of the water system. So one solution is to dig wells for drinking water below the level of the ponds. Another would be to put shallow wells under rice fields which naturally filter the arsenic.

They estimate that by replacing 31% of the wells in the country with deeper wells the health effects of the arsenic could be reduced by 70%.

By Elizabeth Weise
Photo: Installing a pore-water sampler into the soil of a rice field. (Sarah Jane White, Nature)

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Water mission returns first data

By Jonathan Amos
Science reporter, BBC News

Smos builds up its map data in strips as it sweeps around the Earth

Europe's latest Earth observation satellite has returned its first data.

Smos was launched earlier this month on a quest to help scientists understand better how water is cycled around the Earth.

The spacecraft will make the first global maps of the amount of moisture held in soils and of the quantity of salts dissolved in the oceans.

The data will have wide uses but should improve weather forecasts and warnings of extreme events, such as floods.

"Smos is performing like a dream," said Dr Yann Kerr, a lead investigator on the mission from the Centre for the Study of the Biosphere from Space (Cesbio), Toulouse, France.

"Everything went as clockwork and exactly as expected or better up to now. We did not expect to have images so soon," he told BBC News.

The European Space Agency's (Esa) Soil Moisture and Ocean Salinity (Smos) satellite was launched on 2 November.

The mission will run for three years in the first instance

After its initial check-out in orbit, its sole instrument - an interferometric radiometer called Miras - was sent live on Tuesday this week.

The first publicly released image on this page has not been properly calibrated by researchers but they say it proves the instrument is in good shape.

Miras is some eight metres across; it has the look of helicopter rotor blades.

It measures changes in the wetness of the land and in the salinity of seawater by observing variations in the natural microwave emission coming up off the surface of the planet.

It does this through 69 antennas positioned on a central structure and along the lengths of its three arms.

Generally speaking, the "colder" (blue) the "temperature brightness" of the microwave signal, the saltier the water and the wetter the soil; but a lot of processing will be needed before any real values can be attached to the measurements coming down from Smos.

"Moreover, there seem to be radio frequency interferences (RFIs) over China, western Russia and parts of Europe (the reddish stripes)," explained Dr Kerr.

"We will have to tune the reconstruction algorithm before we can reduce or address these."

Scientists were well aware before launch that RFIs might be a problem. Smos is operating in the so-called L-band (21cm) which is supposed to be protected, but pre-flight testing established known interference hotspots, such as airports.

The 315m-euro ($465m; £280m) Smos programme, although led by Esa, has with significant input from French and Spanish interests. The satellite is expected to operate for at least three years.

The amount of water retained in soils varies between about 5% and 50%

This will cover most conditions from 'bone dry' to 'mud bath'

Smos sees the entire range with an accuracy of 4% at the 50km scale

Natural salinity in water covers the range from near zero to 30%

Drinking water might be one extreme; salt lakes would be the other extreme

Smos is seeking sea waters which are typically in the 3-3.5% range

This needs high accuracy (0.01-0.02%). Maps are at the 200km scale

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Water found in lunar impact probably came from comets

Volatiles, including hydrocarbons known to be present in comets, have been detected in lunar material kicked up by NASA's LCROSS mission (Image: T.A.Rector/I.P.Dell'Antonio

by Dana Mackenzie, Houston

The mystery of where the moon's water came from may soon be solved. Evidence from NASA's LCROSS mission suggests much of it was delivered by comets rather than forming on the surface through an interaction with the solar wind.

In October, the mission crashed two impactors – a spent rocket stage and a few minutes later, the LCROSS spacecraft itself – into a crater near the moon's south pole. The spacecraft snapped images and took spectra of lunar debris kicked up by the rocket's impact and found that it contained the unmistakable signs of water.

Previous missions have also found hints of lunar water but its source has not been clear. One idea is that it forms when hydrogen atoms from the solar wind latch onto oxygen atoms in the lunar soil, creating hydroxyl and water.

But now, the evidence is mounting in favour of an alternative explanation – comet impacts. The data was discussed this week at the Lunar Exploration Analysis Group meeting, a gathering of 160 lunar scientists in Houston, Texas.

'Dirty iceballs'

The first line of evidence comes from compounds that vaporise readily, called volatiles. LCROSS found spectral signs of volatiles containing carbon and hydrogen – likely methane and ethanol – as well as others such as ammonia and carbon dioxide. "It appears that we impacted into a very volatile-rich area," LCROSS principal scientist Tony Colaprete told the conference.

These compounds should have been mostly lost to space billions of years ago, when the moon coalesced from the debris of an impact between the Earth and a Mars-sized object. Water formed through an interaction with the solar wind would therefore be relatively pure – and free of volatiles.

But comets, which are thought to have been responsible for many of the moon's impact scars, are "dirty iceballs" known to contain volatiles such as methane. "If you can nail down the source of the water [on the moon], that could tell us a lot about the cometary history of the moon for the last couple of billion years," says Larry Taylor of the University of Tennessee.

High concentrations

The second line of evidence pointing to comets comes from the amount of water detected. The solar wind is expected to form water in minute amounts, amounting to concentrations of no more than 1 per cent in the lunar soil.

LCROSS team members are still analysing the data, but calculations suggest the concentration of water is higher than that. "The data are consistent with a total hydrogen content in the range of several per cent," says Colaprete.

Beyond their link to comets, volatiles generated excitement at the meeting because of their value as a resource for human spaceflight. While water is important for survival on the moon, it is the water's hydrogen that can be used as rocket propellant.

The possibility of finding compounds like ethanol and methane, which can be used as fuel directly, makes the economic case for returning astronauts to the moon even sweeter. "LCROSS has given us our ticket back to the moon," says Noah Petro of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

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