How metal-munching microbes help the rare, toxic element tellurium circulate in the environment

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by Owen Peter Missen, Barbara Etschmann, Jeremiah Shuster, Joël Brugger and Stuart Mills, The Conversation

New technologies often mean elements start moving through the environment in new ways. Take lead plumbing: it helped provide access to fresh water for the masses, but left a toxic legacy that remains to this day.

As we transition away from , we are turning to technologies reliant on rare elements that had few uses in the past. One of these is tellurium, an element found in an increasing number of solar panels.

How do we anticipate the potential pitfalls of a dramatic increase in the flux of tellurium through the biosphere? And how do we secure safe and reliable supplies of this commodity?

To start answering these questions, we traveled to an abandoned gold mine in Mexico—and discovered how metal-munching microbes are moving this elusive element through the environment.

Elements on the move

Tellurium is as rare as gold in Earth’s crust, with only around 1 milligram in each metric ton of average crustal rock. The silvery substance was discovered only in 1783, and until recently its main claim to fame was the fact it can make you smell unpleasantly like garlic if you handle it.

Tellurium is often found in . Despite gold’s famous reputation for durability, over the past 15 years we have discovered the precious metal is remarkably mobile in the environment—even growing in trees.

Microbes and organic material on the surface of native gold (left) and tellurium (right) contribute to active cycling of these rare elements. Newly formed tellurium nanoparticles are highlighted in the yellow circles. Credit: Missen et al.

It turns out certain microbes can effectively munch on gold, slowly transforming gold nuggets into chemical forms that can move through the environment. These mobile gold compounds (particularly ones that can dissolve in water) are quite toxic: only a few metal-resistant microbes can thrive in the unique micro-environment found on the surface of a grain of gold.

Can tellurium move like gold?

We wanted to test whether microbes can cycle tellurium through the environment in the same way they do for gold. We used natural ore deposits to do this, but this gives us information about what would happen if tellurium-rich materials were dumped by humans.

Finding a suitable site was a challenge. Since high tellurium content is associated with high gold content, most tellurium deposits close to the surface (such as those near Kalgoorlie, Western Australia) have been mined out a long time ago.

Eventually our quest led us to Moctezuma in Mexico, where there is a small former gold mine that is exceptionally rich in tellurium.

Metallic tellurium in the fresh ore (left) oxidises to colourful minerals near the surface (green emmonsite in the middle panel). Further away from the vein, tellurium can still be detected (right), but does not form its own minerals. Credit: Missen et al.

At the mine, we studied ores and soils away from the main vein of gold and tellurium. We found tellurium was moving away from the richest ore, and discovered the first evidence of natural tellurium nanoparticles on the surface of pieces of native tellurium.

This discovery is significant because nanoparticles play a special role in the environment, as they have different properties compared to macro-particles. For example, they tend to be more reactive than larger particles, and they may be toxic in their own right.

The tellurium nanoparticles we found appeared very similar to gold nanoparticles that have previously been found on the surface of gold grains.

Nanoparticles and microbes

We also showed that gold and tellurium have rather different modes of transport in soils and groundwater.

In in-vitro experiments, some microbes present in gold- or tellurium-rich environments are able to excrete nanoparticles of the metals dissolved in the growth medium, thereby detoxifying their environment. On the left, a Serratia cell shows many gold particles on the cell surface (lighter blobs); on the right, a cross-section through a Rhodococcus cell shows needle-like particles of tellurium growing in (arrow) and around the cell. Credit: Missen et al. / Presentato et al.

Gold particles can be carried a long way in rivers, for example. However, tellurium metal oxidizes quickly when exposed to air, forming highly soluble—and toxic—compounds. Hence, there is no physical transport of grains of tellurium in metallic form.

The movement of tellurium is also limited by reaction with common minerals in soils. This is a good thing, since tellurium’s limited mobility keeps concentrations in groundwater low, and hence limits toxic effects.

In our latest research published in the Journal of Hazardous Materials Letters, we have detected tellurium nanoparticles in the soil of Moctezuma, away from the metal-rich outcrops.

Because metallic tellurium nanoparticles are highly reactive and not expected to survive for long in soils, this discovery provides the strongest evidence yet that microbes are actively helping to cycle this rare element through the environment. Tellurium in these soils in most likely subject to a dynamic cycle of oxidation and dissolution followed by reduction and precipitation, all controlled by microbial activity.

A schematic summary of gold (on the left) and tellurium (right) cycling. Credit: Ella Lausberg

Cleaner mining

We are only now beginning to understand how microbes cycle “exotic” elements such as tellurium. Understanding these “biogeochemical” processes is important to understand how elements move in our landscapes. We can then assess potential risks, and design efficient mitigation strategies.

This understanding can also aid in developing more sustainable mining (and recycling) technologies. Around Moctezuma, at least, microbes effectively separate from in soils.

Innovative solutions will be required to address our planet’s need to generate more energy more sustainably, and cleaning up mine product processing to better separate all potential commodity elements is just one of these ways.

More information:
Owen P. Missen et al, Natural nanoparticles of the critical element tellurium, Journal of Hazardous Materials Letters (2022). DOI: 10.1016/j.hazl.2022.100053

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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How metal-munching microbes help the rare, toxic element tellurium circulate in the environment (2022, November 15)
retrieved 16 November 2022
from https://phys.org/news/2022-11-metal-munching-microbes-rare-toxic-element.html

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Calls for a ‘one-child policy’ in India are misguided at best, and dangerous at worst

Hexbyte Glen Cove

Credit: Pixabay/CC0 Public Domain

India will surpass China as the country with the world’s largest population in 2023, according to the United Nations World Population Prospects 2022 report.

The UN also projects the has reached eight billion as of Tuesday.

As early as March 2022, reports circulated on Chinese social media that India’s population had already surpassed China’s, though this was later dispelled by experts.

Women in India today are having fewer than their mothers had. But despite a lower fertility rate, the country’s population is still growing.

The idea the country should adopt something like China’s former “one-child ” has been moving from the fringe to the political mainstream.

But the notion that India should emulate China’s past population policies is misguided at best, and dangerous at worst.

Both countries are struggling with the legacy of harsh population policies, and stricter population controls in India could have disastrous consequences for women and minority communities.

Given Australia’s growing ties to India, it should be concerned about what population policy could mean for the erosion of democratic norms in India.

Unintended consequences

India implemented the world’s first national family planning program in 1952. The birthrate began to drop, but only gradually, and family sizes remained stubbornly high. The government then implemented widespread forced sterilization particularly of Muslims and the urban poor, especially during “The Emergency” years of 1975-77.

After the founding of the People’s Republic of China in 1949, infant mortality dropped significantly. Between 1950 and 1980, China’s population almost doubled. The “one-child policy”—limiting births per couple through coercive measures—was implemented in the early 1980s, and fertility dropped dramatically.

In both India and China, these population policies had unintended consequences.

In China, the government found that once dropped, they were faced with an aging population. Even after relaxing control policies to allow all couples to have two children in 2015, and three children in 2021, birth rates remain low, particularly among the urban middle class favored by the government.

In both countries, skewed caused by sex selective abortions have led to a range of social problems, including forced marriages and human trafficking.

China has found that despite reversing course, it cannot undo this rapid demographic transition. Urban, middle-class couples face mounting financial pressure, including the cost of raising children and of caring for the elderly. While the government has encouraged “high quality” urban women to give birth, rural and minority women are still discouraged from having more children.

As in China, in some states in India, women’s education and their aspirations for their children have contributed to lower birth rates. Like China, these states now face an aging population. Birth rates in other states with high Muslim populations have also declined, but at a slower rate.

Unfair impact

Despite declining , some politicians have advocated for the adoption of something like China’s former one-child policy in with large Muslim populations. These calls have less to do with demographic reality, and more to do with majoritarian Hindu nationalist concerns around Muslim and “lower-caste” fertility.

The worry here is that the coming population milestone will push India to adopt knee-jerk population policies. These could in turn unfairly affect women and minorities.

Four Indian states with large Muslim populations have already passed versions of a “two-child policy”. What’s more, built into many of these policies are incentives for families to have just one child. And in 2021, a senior government minister proposed a national “one-child” policy.

Like past control policies, they’re targeted at Muslim and lower-caste families, and illustrate a broader Hindu nationalist agenda with anti-democratic tendencies.

As happened at the height of China’s , Indians could lose government jobs and more if such laws were passed at the national level. Some Indian states and municipalities have already legislated that people with more than two children are ineligible for government jobs and to stand for political office.

The irony is that India’s birth rate and the size of families are decreasing because of women’s own reproductive choices. Many women are getting surgical contraception after having two children (or after having a son).

However, financial inducements for doctors and the means poorer women are pressured to undergo these procedures.

In other words, the trend in India is towards smaller families already. As the 2022 UN report itself notes, no drastic intervention from the state is required.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Citation:
Calls for a ‘one-child policy’ in India are misguided at best, and dangerous at worst (2022, November 15)
retrieved 15 November 2022
from https://phys.org/news/2022-11-one-child-policy-india-misguided-dangerous.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

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International research team cracks chemical code on how iodine helps form clouds

Hexbyte Glen Cove

The Cosmics Leaving Outdoor Droplets (CLOUD) experiment at CERN, Geneva uses an ultraclean chamber facility to study how gases form new particles (nucleation), and grow to affect cloud formation. The primary goal of CLOUD is to understand the influence of galactic cosmic rays (GCRs) on aerosols and clouds, and their implications for climate. Credit: CERN

An international team led by CU Boulder researchers has cracked the chemical code driving the formation of iodine particles in the atmosphere, revealing how the element contributes to increased cloud cover and depletes molecules in the Earth’s protective ozone layer.

The research, conducted at the world’s largest particle physics laboratory, the European Organization for Nuclear Research (CERN), was published today in the journal Nature Chemistry. It’s the first time that any experiment in the world has demonstrated the mechanism for how the gas-phase form of iodine—known as iodic acid—forms, and suggests it has an significant role in atmospheric particle formation.

It comes at a time when atmospheric iodine is increasing globally, with current levels triple what they were 70 years ago. Researchers hope that this new knowledge on iodine’s atmospheric interactions can be added to global atmospheric and climate models to help scientists better understand its environmental impacts—such as increased cloud cover, which could exacerbate global warming-related thinning of Arctic sea ice.

“This paper establishes a link between the sources of iodine, how they are emitted into the atmosphere, and particle formation, which through subsequent growth, seeds clouds,” said Rainer Volkamer, co-lead author on the paper, professor of chemistry at CU Boulder and fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES). “That link didn’t exist before, and now we have established that link at the molecular level.”

This missing mechanical link between iodine sources and atmospheric particle formation is a multi-step process. First iodine oxide radicals bond with themselves, then react with ozone and water to make iodic acid, with (singlet) oxygen and hypoiodous acid as co-products.

Iodine is a common and highly reactive element that forms radical species which undergo rapid chemical reactions lasting seconds to minutes in the atmosphere. Most iodine found in the atmosphere comes from the ocean—where it exists as iodide, also present in table salt. Its three-fold increase in the atmosphere over the past 70 years is linked to an increase in anthropogenic air pollution: as harmful, ground-level ozone reacts with the ocean-based iodide, it releases volatile iodine gasses to the atmosphere.

While iodine has been studied for 150 years, it is only in the past two decades that researchers such as Volkamer have revealed its important role within the atmosphere. In 2020, Volkamer and CU Boulder and CIRES researchers published research showing how iodine reaches the stratosphere and eats away at the ozone that protects the planet from harmful UV radiation.

“Iodine is the new kid on the block, among other halogens, that play into the recovery of the ozone layer,” said Volkamer.

Iodine is a common and highly reactive element, which can increase cloud cover and destroy ozone as a result of its chemical interactions. Scientists now understand how ionic acid (HIO3) forms in the atmosphere. Credit: Henning Finkenzeller

DisCERNing chemical processes

To study this missing link, the research team turned to CERN, home to the pristine conditions required to observe and collect data on these particles. Here, an experiment known as CLOUD (Cosmics Leaving Outdoor Droplets) has become the world’s leading laboratory experiment to study the remaining poorly understood aspects of aerosol and cloud formation.

Volkamer’s research group, the Atmospheric Trace Molecule Spectroscopy (ATMOSpec) Lab, is one of only three universities in the U.S. (along with Caltech and Carnegie Mellon University) who are part of this collaboration, along with 16 European partners.

“This is the only such experiment that exists in the world,” said Volkamer. “It’s an honor to be part of the collaboration and to be leading it in the context of a study like this one.”

In the CLOUD chamber at CERN, the researchers had access to a laboratory environment with perfect control over conditions like temperature, pressure, humidity, ozone concentration, and iodine concentration, as well as access to different light sources resembling different aspects of the solar spectrum.

By setting up this artificial, indoor atmosphere where certain reactions may or may not happen, the scientists could accurately gather data on iodine chemical reactions that form and grow particles.

“This is a great example of experiments and computations coming together to answer a question that neither of them could have answered on their own,” said Theo Kurten, co-lead author on the study and professor of chemistry at the University of Helsinki.

To determine whether what they observed in the laboratory translated to the real world, they also tested their findings in the air surrounding the Maïdo observatory on Réunion Island in the southern Indian Ocean—a free of much of the influence of human activity—and were able to corroborate their laboratory results.

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