Tag Archives: arsenic


There are arsenic-breathing microbes in the tropical Pacific, a new study finds

Arsenic is generally viewed as a life-ending element, but new research shows how some organisms rely on it to breathe.


Image credits fdecomite / Flickr.

Certain microorganisms in the Pacific Ocean respire arsenic, according to a new study from the University of Washington. The findings are quite surprising as, although arsenic-based respiration has been documented in ancient and current organisms, it is extremely rare on the planet. Moreover, ocean water just doesn’t have that much arsenic, to begin with.

Doing without

“We’ve known for a long time that there are very low levels of arsenic in the ocean,” said co-author Gabrielle Rocap, a UW professor of oceanography. “But the idea that organisms could be using arsenic to make a living—it’s a whole new metabolism for the open ocean.”

The team analyzed Pacific seawater samples taken from water layers at depth intervals where oxygen is almost absent. Given the lack of oxygen here, organisms had to adapt and seek other sources of energy, the team writes. The results are interesting and may become very important in our understanding of marine ecosystems, as these areas — known as oxygen-deficient zones, ODZs or oxygen minimum zones, OMZs — will likely expand under climate change, according to other recent research.

The most common alternatives to oxygen that biology draws upon today are nitrogen and sulfur. However, previous research carried out by Jaclyn Saunders, this paper’s first author, suggested that arsenic might also do the trick. She was curious to see whether this was the case, which spurred the present paper.

The samples used in this study were collected during a 2012 research cruise to the tropical Pacific, off the coast of Mexico. Analysis of eDNA material recovered from the samples showed two genetic pathways that process arsenic-based molecules to extract energy. Two different forms of arsenic seem to be targeted by these pathways, leading the authors to believe that we’re looking at two organisms that cycle arsenic back and forth between the different forms. Which, as far as ecosystems are concerned, is quite a nifty trick.

“Thinking of arsenic as not just a bad guy, but also as beneficial, has reshaped the way that I view the element,” said Saunders, who did the research for her doctoral thesis at the UW and is now a postdoctoral fellow at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology.

While arsenic might be beneficial, it’s certainly not very popular. Only about 1% of the microbe population in the samples seems to breathe arsenic, judging by the ratios of genetic material. Most likely, these strains are loosely-related to arsenic-breathing microbes found in hot springs or contaminated sites on land. Saunders recently collected samples from the same region and is now trying to grow the arsenic-breathing marine microbes in a lab in order to study them more closely.

“Right now we’ve got bits and pieces of their genomes, just enough to say that yes, they’re doing this arsenic transformation,” Rocap said. “The next step would be to put together a whole genome and find out what else they can do, and how that organism fits into the environment.”

“What I think is the coolest thing about these arsenic-respiring microbes existing today in the ocean is that they are expressing the genes for it in an environment that is fairly low in arsenic,” Saunders said. “It opens up the boundaries for where we could look for organisms that are respiring arsenic, in other arsenic-poor environments.”

Arsenic respiration is most likely a ‘retro’ type of respiration, passed down over the eons. When life first sprung up on Earth, oxygen was very scarce both in the air and in the ocean (as oxygen is very reactive and forms chemical bonds readily). Until photosynthesizing plants became widespread, there simply wasn’t enough output of this gas to maintain any meaningful levels available for organisms to use up. As such, early life had to use something else for energy — and arsenic was likely common in the oceans at that time.

Climate change may, sadly, breathe new life into arsenic-breathing life. Low-oxygen regions are projected to expand as thermal imbalances shift water currents, and dissolved oxygen is also predicted to drop across the board in marine environments.

The paper “Complete arsenic-based respiratory cycle in the marine microbial communities of pelagic oxygen-deficient zones” has been published in the journal Proceedings of the National Academy of Sciences.

Credit: Pixabay.

Water wells serving 2 million Americans could be contaminated with high levels of Arsenic

Credit: Pixabay.

Credit: Pixabay.

Some 44 million Americans source their water from domestic wells, most of which are unregulated. According to a new paper appearing in Environmental Science & Technology, roughly two million of them could be exposed to high levels of arsenic in the water. The toxic chemical is naturally occurring, being widely distributed in the earth’s crust.

A silent, odorless, and tasteless health threat

Arsenic is naturally present at high levels in the groundwater of a number of countries and, when it appears in inorganic compounds, can be highly toxic to all living organisms. Long-term exposure to arsenic from drinking water or food has been linked to a wide range of health problems such as cancer or skin lesions. Arsenic poisoning is also associated with cardiovascular disease, neurotoxicity, and diabetes. The most recent research also found that low-level exposure to arsenic, while usually not dangerous, can affect fetal growth or lead to pre-term birth in pregnant women.

People are constantly exposed to arsenic. We normally take in small amounts in the air we breathe, the water we drink, and the food we eat. It’s even widely used in some medicines. Over a certain threshold, however, arsenic can become poisonous. Most arsenic compounds have no smell or taste, so usually, you can’t tell if arsenic is in the air, food, or water.

Cities and towns that use centralized water systems employ filtering that keeps the arsenic out but as far as private water wells are concerned, arsenic monitoring is entirely the responsibility of the owners.

Joseph D. Ayotte and colleagues at the U.S. Geological Survey and the U.S. Centers for Disease Control and Prevention set out to assess arsenic exposure from private water wells on a national level.

The scientists built a model which incorporates a huge dataset comprising tens of thousands of arsenic measurements from wells across the US. This sophisticated model takes into account the facts that can increase or decrease arsenic concentration such as regional and seasonal rainfall, geology, and aquifer chemistry.

Arsenic concentrations from 20 450 domestic wells in the U.S. were used to develop a logistic regression model of the probability of having arsenic >10 μg/L (“high arsenic”), which is presented at the county, state, and national scales. Credit: Environmental Science and Technology.

Arsenic concentrations from 20 450 domestic wells in the U.S. were used to develop a logistic regression model of the probability of having arsenic >10 μg/L (“high arsenic”), which is presented at the county, state, and national scales. Credit: Environmental Science and Technology.

The Environmental Protection Agency (EPA) has set a threshold concentration for arsenic in water wells at 10 micrograms per liter. However, some 2.1 million people living the United States could be drinking water contaminated with arsenic whose concentration crosses this threshold. Hotspots are largely concentrated in New England, the upper Midwest, the Southwest, and southern Texas.

“Additionally, by predicting to all of the conterminous U.S., we identify areas of high and low potential exposure in areas of limited arsenic data. These areas may be viewed as potential areas to investigate further or to compare to more detailed local information,” the authors concluded.

Many of these people are largely unaware of the health risks they’re subjecting themselves by sourcing water from unregulated, unmonitored wells. Homeowners are advised to immediately monitor the various chemical concentration found in their water wells if they haven’t done this already. The authors of the study also recommend government officials and policymakers to step up awareness programs and develop new mitigation strategies.

Villagers high in the Andes have developed a genetic tolerance to arsenic

For centuries, arsenic was the go-to poison in the high circles of Europe, either to knock out political foes or to simply eliminate people on the dastardly way to a high state position; it was odourless, tasteless, and until 1830 – when chemist James Marsh developed a test – impossible to detect. Thankfully, we’re dealing with much less intentional arsenic poisoning today, but unfortunately, we’re dealing with much more accidental poisoning. Recently, scientists discovered a population that developed natural immunity to arsenic, high in the Andes.

Image: Wikimedia/Guigue

The dominant basis of arsenic poisoning is from ground water that naturally contains high concentrations of arsenic. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning from drinking water. At high doses, the metal can cause vomiting, convulsions and eventually results in coma  and can even be fatal. Low exposures over a longer period of time have been linked to liver and cardiovascular diseases, diabetes, skin lesions and cancer.

There is no cure or treatment for chronic exposure to arsenic, so any clue would be much welcome in the fight against this issue which plagues so many people world wide. Researchers from Sweden say they have identified a population in Argentina that has evolved a genetic mutation, which enables them to naturally inactivate arsenic toxicity, at least to some extent..

“They metabolise arsenic faster and to a less toxic form compared to an American or Westerner,” the study’s lead author, Karin Broberg, a geneticist at Karolinska Institutet, a medical university in Sweden, told NPR. “This is the first evidence of human adaptation to a toxic chemical.”

Archaeologists had previously found 7,000 year old mummies with traces of arsenic in their hair, so this led scientists to believe that the population had been living in a contaminated area for very many generations, something which seems to have gradually created a specific adaptation. The research team performed a genome wide survey on a group of 124 Andean women, and analyzed their urine to see how well they metabolize arsenic.

They found a significant difference in the way they are able to metabolize arsenic; basically, they are not affected by chronic exposure to it (or are less affected). The exact date at which this evolutionary trigger took place remains unknown, but this phenomenon might new insights regarding not only how we can fight arsenic poisoning – but how resistance to such substances occurs genetically.

Journal Reference: Carina M Schlebusch, Lucie M Gattepaille, Karin Engström, Marie Vahter, Mattias Jakobsson and Karin Broberg. Human Adaptation to Arsenic-Rich Environments. doi: 10.1093/molbev/msv046



Debunking Arsenic life: bacterium prefers phosphorous after all

Remember when, in 2010, we told you about a team of researchers which claimed they found a bacteria that feasts on arsenic, instead of phosphorous? The study has spurred quite the discussion, receiving a lot of both criticism and praise, but seeming to be, ultimately, incorrect (as this other study also claims). Dan Tawfik, who studies protein function at the Weizmann Institute of Science in Rehovot, Israel, put the final nail in the theory’s coffin.

The main ingredients for life

Oh well…

Currently, life as we know it requires six elements to survive (CHNOPS): Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur. Practically over 98% of all dry organic matter is made from these elements. Arsenic is chemically somewhat similar to sulfur, but it’s actually very poisonous to most life, so finding a bacteria that relies on it to survive could essentially change the way we understand life itself; obviously this is a big thing.

After the initial momentum passed, the theory started losing ground and started being attacked, so that after a year, few believed it to be correct. The bacteria, (GFAJ-1 microbe) became boring. But biology is never boring – life is never boring, and a key question remained: how does GFAJ-1 differentiate between nearly identical molecules of phosphate (PO43-) and arsenate (AsO43-).

Arsenic vs phosphorous: a chemical bond

Professor Dan Tawfik and his team dug deep and found what makes bacteria attach to phosphorous molecules and avoid arsenic ones, suggesting that a single chemical bond holds the key.

“This work provides in a sense an answer to how GFAJ-1 (and related bacteria) can thrive in very high arsenic concentrations,” say Tobias Erb and Julia Vorholt of the Swiss Federal Institute of Technology in Zurich, co-authors of the latest paper, who were also co-authors on a follow-up paper that cast doubt on the initial arsenic-life claims.

The team analyzed five types of phosphate-binding protein from four different bacteria species; out of four, two were resistant to arsenic and two were highly sensitive to it. In order to study just how good these bacteria are at differentiating between molecules, they were placed in a solution with a set amount of phosphate and different concentrations of arsenate for 24 hours and then checked which molecules they naturally bound to.

When 50% of the proteins ended up bound to arsenate, it was clear the ability to differentiate had been overwhelmed. Even when there was 500 times more arsenic than phosphorous molecules, all four species were still able to differentiate and bound to the right molecules. As a matter of fact, the one from Mono Lake, which sparked the original study, was able to do so even at arsenate excesses of up to 4,500-fold over phosphate.

Tawfik says that he was shocked by how good bacteria are at extracting the necessary phosphorous while rejecting the deadly arsenic; however, this doesn’t show bacteria is arsenate-free.

“It just shows that this bacterium has evolved to extract phosphate under almost all circumstances.”

Arsenate monster actually hates arsenate

The Arsenate monster, as the GFAJ-1 bacteria was jokingly called by some biologists actually goes to a huge amount of effort to actually avoid arsenic – clearly showing that it doesn’t like the element inside its cytoplasm.

Felisa Wolfe-Simon, lead author on the original Science paper and now at Lawrence Berkeley National Laboratory in Berkeley, California showed an extremely positive fair play attitude, explaining “represents the kind of careful study that really helps the community”. However, we mustn’t reject novel ideas such as the one she proposed – it’s this kind of study which push the scientific boundaries most, be it to confirm or disprove them.

Scientific source

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA

New study debunks preposterous claims of arsenic-thriving bacteria

In 2010, a NASA study published in the journal Science heralded the discovery of a bacteria, called GFAJ-1, which the authors at the time claimed it substitutes arsenic for phosphorus to survive. This contravened with the elemental recipe for life, where phosphorus is essential, stirring a wave of controversy within scientific community, as it would mandate a reformulation of the basic requirements for life on Earth. Recently, two separate and independent studies found that the claims were erroneous, disproving the paper.

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA.

The bacterium was found in Mono Lake, California. The lake doesn’t have any outlet to the ocean, which has lead along many thousand of years to an unusually salty body of water with high arsenic and mineral levels. Thus, a totally unique ecosystem was also formed. It’s  these truly unique conditions that sparked NASA’s interest, as it resembles patches of Mars or even early Earth.

In the lake, scientists discovered the GFAJ-1 bacteria, which was found to be able to survive despite having arsenic in its DNA and cell membranes instead of phosphorus – a controversial claim, by all means.

Science has found that there are six critical elements indispensably required for life: carbon, hydrogen, nitrogen, oxygen, phosphorous and sulphur. Arsenic, though rather similar to sulphur, is not only missing from the aforementioned list, but poisonous for most living organisms. So, you can imagine what kind of uprising the claim that an organism which incorporates poison into its DNA stirred into the scientific community at the time. It had alien written all over it, and enthusiasts were quick to jump on the bandwagon.

From extraterrestrial back to terrestrial

The claim had to be confirmed by other separate, independent studies before it could have been deemed as a discovery. Two were recently published, both of which found flaws in the original paper.

One of the papers found that the bacterium was not really replacing phosphorus with arsenic throughout its DNA, but “may sometimes assimilate arsenate into some small molecules in place of phosphate.” The other paper tackled another significant claim; in the original paper from 2010, the authors stressed that the phosphor present in the samples was simply too low to accommodate life at all. The group, lead by Tobias Erb from the Institute of Microbiology, found that organism was incapable of surviving without some amount of the substance.

Some scientists, and science journalists alike, were quick to bash the authors of the original paper, lead by Felisa Wolfe-Simon of NASA’s Astrobiology Institute. Phrases like “bad science”, “sloppy research” and the likes were thrown a lot these past few days. I, for one, don’t agree. While I believe that the research could have been checked and even interpreted a lot more conservative, the finding is still important due to the very nature of this extraordinary organism. All the worse was for the better, if you’d like to see the half full side of the glass, since more attention has been directed towards it.

GFAJ-1 is a veritable extremophile. A survivor. It “is likely adept at scavenging phosphate under harsh conditions, which would help to explain why it can grow even when arsenic is present within the cells,” one of the journal entries reads; and what follows couldn’t better resonate with my own thoughts:

“The scientific process is a naturally self-correcting one, as scientists attempt to replicate published results,” it added.

Both studies were published in the journal Science.

source: 1 and 2

coal ash

New toxic coal ash pollutant sites listed by environmental group

coal ash The U.S. Environmental Protection Agency, in collaboration with the  independent Environmental Integrity Project, have identified 20 new sites in the US contaminated with toxic coal ash, raising the number to a current total of 157 sites nationwide, whose water supplies and soil ares contaminated.

Coal ash is the waste which results from coal combustion, filled with arsenic, selenium, lead, cadmium and mercury, all of these heavy metals are toxic for the soil, local fauna and man from a certain level. Typically, this waste has to be disposed of properly in ponds with liners and covers, however these new discovered sites have all been dumped directly in complete disregard.

In 19 out of 20 sites, arsenic and other toxic metals water contamination has reached levels far exceeding the allowed limit impossed by the Safe Drinking Water Act. The 20th site showed contaminated soil with arsenic 900 times the federal screening level for site cleanups.

Those involved in coal ash clean-ups have only common sense and a deep respect for nature to guide them along, since most US states don’t have a clear policy, neither requiring any construction standards or  monitoring, nor cleanup requirements. It’s very nice to hear certain states put so much faith in their local industries’ civil ethics, however like most of the time when there aren’t any laws, complemented with criminal charges against its offenders, people will always take the easier, cheaper way. Maybe this is why half of the US’s coal ash is dumped in an uncontrolled, highly pollutant manner, according to the released report.

The pollution report coincides as the EPA is struggling to decide whether to regulate the ash as a hazardous material. You might wonder why this kind of extremely evident environmental hazard hasn’t been regulated until now. Well, it seems there are many interests at stake, as a number of congressmen, whose political affiliations I’d like to chose not to disclose (we’re an apolitical publication),  are trying to block the stricter regulation from happening.

reuters  | image credit