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Mystery of arsenic release into groundwater solved


New York: Stanford scientists have solved an important mystery about where the microbes responsible for releasing dangerous arsenic into groundwater in Southeast Asia get their food.

Groundwater in many countries, including India, China, Bangladesh, Myanmar and Vietnam, contains concentrations of arsenic 20 to 100 times greater than the World Health Organisation’s (WHO) recommended limit.

Arsenic is bound to iron oxide compounds in rocks from the Himalayas and gets washed down the major rivers and deposited in the lowland basins and deltas.

Scientists know that in the absence of oxygen, some bacteria living in those deposited sediments can use arsenic and iron oxide particles as an alternative means of respiration.

When they do this, however, the microbes separate the arsenic and iron oxides and transfer the toxin into underlying groundwater.

The mystery in this system, though, is an obvious source of energy that the microbes can tap to fuel the separation process.

“The question that really limits our ability to come up with predictive models of groundwater arsenic concentrations is how and why does the food they use vary across the landscape and with sediment depth,” said professor Scott Fendorf from Stanford.

In their study, Fendorf and his team found that mixing sediments collected from different depths in vials with artificial groundwater revealed that the oxygen-deprived bacteria living in the upper few feet of permanent wetlands were releasing arsenic.

However, water mixed with sediments gathered from the same shallow layers of seasonal wetlands was arsenic free.

The Stanford scientists hypothesized that bacteria residing in the shallow layers of seasonal wetlands were eating all of the digestible plant material during dry periods when sediments are exposed to air and the microbes have access to oxygen.

As a result, no food is left for the microbes when the floods returned, rendering them unable to cleave arsenic particles from iron oxides.

“The arsenic-releasing bacteria living in the shallow regions of seasonal wetlands are ‘reactive’ carbon limited – that is, they don’t release arsenic into the water because there isn’t enough carbon available in a form they can use,” Fendorf explained.

The findings have large-scale implications for projecting changes in arsenic concentrations with land development in South and Southeast Asia and for the terrestrial carbon cycle.

“If you change the hydrology of a region by building dams or levies that change the course of the water, or if you change agricultural practices and introduce oxygen or nitrate into sediments where they didn’t exist before, that will alter the release of arsenic,” Fendorf said.

The findings were published in the journal Nature Geosciences.


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WHO: Nearly 1 Billion People Risk Hearing Loss by 2050

Problems resulting from hearing loss are expected to rise because of a growing and aging population - a population that is expected to reach 9 billion by 2050

An 85-year-old Nepalese man is seen fitted with a hearing aid, in Kathmandu, Nepal, April 12, 2017. VOA

On the occasion of World Hearing Day, Saturday, the World Health Organization (WHO) is warning one in 10 people globally, or more than 900 million, are at risk of disabling hearing loss by 2050 unless preventive action is taken now.

The World Health Organization reports 466 million people around the world currently suffer from disabling hearing loss. The annual cost to countries in direct health services and lost productivity resulting from this disability is estimated at $750 billion.

Problems resulting from hearing loss are expected to rise because of a growing and aging population – a population that is expected to reach 9 billion by 2050.

ALSO READ: Heart Surgery In Infants May Cause Deafness

Shelly Chadha, a technical officer in the WHO’s Department of Prevention of Deafness and Hearing Loss, says the rise in the aging population does not mean that an increase in hearing loss is inevitable. She says there are many factors besides aging that affect hearing.

hearing loss
In cases where hearing loss is unavoidable, the WHO says people can be helped through technologies such as hearing aids and surgically implanted electronic cochlear implants. Pexels

“These may be factors such as infectious diseases, which we may encounter in childhood – rubella or mumps, meningitis or ear infections. There may be factors such as exposure to loud sounds, to loud music or noise at workplaces. Many of these causes are preventable, and by addressing them, we can reduce or minimize the risk of hearing loss,” Chadha said.

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The WHO reports about 60 percent of hearing loss in children can be prevented. Measures include immunizing children against infectious diseases, screening and treating chronic ear infections, avoiding the use of drugs harmful to hearing, and controlling exposure to loud sounds and music.

It says these devices are of great benefit to the hard-of-hearing because they make it possible for them to better communicate and socialize with others. (VOA)

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