Contaminated drinking water is one of the main health concerns in the world, especially within developing countries. And the greatest contaminant that health officials have to deal with, which affects and slowly poisons over 100 million people around the world, is arsenic.
A Worldwide Concern
Groundwater pollution from arsenic is a serious problem and it’s not caused by what you probably suspect it is. Sure, some amount of industrial pollution likely contributes to the issue, but arsenic is a common element in the Earth’s crust in general.
On average, the concentration of arsenic within 1 kilogram of soil is about 5 milligrams. That might not sound like much, but the capability of arsenic to leach through rock and into surrounding water systems is a huge problem. Things like mining and even just digging holes in general can exacerbate this process.
In places like India and Bangladesh, villagers will often dig wells to access groundwater and to otherwise store the water that is available to them. But wells that are improperly lined with ill-fitting stone (sometimes without any lining at all) allow pollutants such as arsenic to come through and contaminate the entire water supply.
This same sort of situation happens with rivers just from general erosion and places without proper filtration systems for river water have seen disastrous consequences. Access to and distribution of small scale arsenic filters have helped alleviate some of the problems, but it is still a serious concern for millions of people.
From Rivers To Sponges
With all this information in hand, it better allows one to understand the depth of importance of what Tel Aviv University has discovered. In a study published in Nature Communications last week, they discussed a specific species of marine sponge (Theonella swinhoei) that they had been investigating in the Red Sea.
This sponge has a species of Entotheonella bacteria that endosymbiotically inhabits it. While inside of its sponge host, the bacteria helps to protect its host from metal poisoning, such as from arsenic and barium, an also common water contaminant.
Bacteria in general had already been known to assist with cycling of organic material like carbon and nitrogen throughout the sponges, but this is the first time they’ve been found to have an influence on the more dangerous trace elements.
A Filter Friend
When tested, it was found that the sponges appeared to have an extreme amount of arsenic and barium accumulated within their tissues, 8,600 micrograms and 13,400 micrograms respectively. And this was in a sea where these elements are normally only found in amounts of 2 to 10 micrograms.
To answer how the sponges were doing this and surviving, one must look at their companion bacteria. All the various types of symbiotic bacteria in T. swinhoei make up more than half of its entire body weight, with photosynthetic bacteria on its exterior and other kinds inside of it.
But the Entotheonella bacteria were the key, making up 3.25% of the sponge’s mass. The bacteria themselves have arsenic and barium making up 6% and 12% of their entire cellular mass.
Minerals For You And Me
Further research showed that these bacteria engage in biomineralization of the elements, converting them into spherical granules of minerals inside of the cell itself. Barium is converted into the mineral barite and arsenic is turned into crystalline calcium arsenate. There is also some leftover calcium sulfide phosphate from the processes.
Looking into the granules, it appears that the bacteria primarily focuses on barite conversion, with that making up 87% of the crystals and calcium arsenate only 7%. But, either way, Entotheonella is one of the very few bacteria know of that is able to intracellularly convert arsenic and literally the only one known to convert barium into barite.
This hyper-accumulation and storage of these two elements is what keeps the sponge healthy and it turns the arsenic and barium into a completely inert, unreactable state.
The Solution To Pollution, Or Some Of It
The next research step being undertaken is to determine what enzymes the bacteria uses to accomplish this mineralization and if they can be exploited. Another side research angle is to see if the bacteria can be successfully cultivated away from its sponge host and used as a filtration system for arsenic and barium contamination of water.
Either way, this discovery is exciting for biology and health sciences and hopefully will result in a reproducible biological method to combat toxic contamination of groundwater around the world.
Photo CCs: Arsenforurenet jord på collstropgrunden i Brabrand, 2010-09-30 (Arsenic soil pollution) from Wikimedia Commons
