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NNadir

(33,368 posts)
Wed Aug 11, 2021, 11:54 PM Aug 2021

Bacterial driven mechanism for tellurium transport from discarded solar cells in landfills.

The paper I'll discuss in this post is this one: Tellurite Adsorption onto Bacterial Surfaces (Jennifer L. Goff, Yuwei Wang, Maxim I. Boyanov, Qiang Yu, Kenneth M. Kemner, Jeremy B. Fein, and Nathan Yee Environmental Science & Technology 2021 55 (15), 10378-10386).

I think it should be pretty clear, stripped of delusions anyway, that all of the cheering for the solar industry for the last half a century has had no effect whatsoever on climate change. If you haven't noticed, as I have, the whole planet is on fire. That hasn't stopped such cheering, of course, but reality is reality and it is a fact that the rate of degradation of the atmosphere is accelerating, not ameliorating.

Besides the popular lie we tell ourselves that solar energy will save the day, there is a related lie we tell ourselves that involves the widespread belief that solar cells are environmentally benign.

This paper suggests otherwise for a particular solar technology; similar considerations apply to other solar technologies.

The paper refers to the mobilization of tellurium, defined as an "emerging contaminant" via proteomic interactions with bacteria, common organisms in landfills.

A cartoon about what's going on in the paper:



From the introduction:

Tellurium (Te) is a chalcogen used in photovoltaic technologies for the production of low-cost cadmium telluride (CdTe) solar cells(1) and the disposal of CdTe solar panels contributes to environmental contamination when soluble Te is released from buried waste.(2?4) Upon decommissioning and disposal of CdTe photovoltaic devices, Te undergoes redox transformations that form dissolved tellurite [Te(IV), TeO32–] and tellurate [Te(VI), TeO42–] in landfill leachate.(2,3) Tellurite is more toxic than tellurate to the microorganisms involved in biodegradation, and the accumulation of tellurite in landfill leachate causes the inhibition of acetoclastic and hydrogenotrophic methanogenesis.(4) Because tellurite is also toxic to humans,(5,6) there is significant interest in understanding its environmental fate(7,8) and transport to drinking water sources.(2?4)
Microbial interactions can alter the chemical speciation of tellurite in the environment.(9) Diverse microorganisms are able to reduce tellurite to elemental tellurium [Te(0)] and precipitate nanoparticulate Te rods and spheres.(10?12) Microbes also uptake tellurite into their cells,(13?15) where it interacts with intracellular thiols and depletes cytoplasmic reservoirs of glutathione.(16,17) Furthermore, experimental studies with other organisms have shown that tellurite binds to proteins(18) and reacts with cellular enzymes that contain sulfhydryl functional groups.(19)

Bacterial cell surfaces are known to harbor sulfhydryl functional groups(20,21) that adsorb environmental contaminants,(22?25) including selenium (Se),(26) a chalcogen that is chemically similar to Te. A recent spectroscopic investigation by Yu et al.(26) revealed that selenite [Se(IV), SeO32–] binds to bacterial surface thiol sites via the formation of R1S–Se–SR2 organo-selenium complexes. Thiol site densities on bacterial surfaces are generally low, but sulfhydryl-selenium complexes are significantly more stable than Se adsorbed to carboxyl and phosphoryl functional groups.(27) Thus, at environmentally relevant contaminant concentrations, sulfhydryl functional groups on cell surfaces can control bacterial adsorption reactions.(28) Currently, the molecules on bacterial surfaces that host reactive sulfhydryl functional groups are poorly understood, and the adsorption of tellurite onto bacterial cells has not been characterized.

The objective of this study was to examine the mechanism of tellurite binding onto bacterial surfaces. Because tellurite reacts with sulfhydryl-containing molecules,(29,30) and the common soil bacterial species Bacillus subtilis is known to produce cell surface sulfhydryl sites,(21,23,26) we selected B. subtilis to test the hypothesis that bacterial tellurite adsorption is controlled by cell surface thiols...

...The results indicate that sulfhydryl-containing molecules in extracellular polymeric substances (EPS) play a key role in tellurite adsorption onto bacterial surfaces...


There is a rather detailed report on the experimental procedures which I will not repeat in detail here, as I haven't much time for detailed discussion.

The authors did not utilize discarded solar cells as the model for the concentrations at which they tested, but rather modeled their work on the known tellurium concentrations associated with silver and gold mine tailings in Japan, and tellurium concentrations measured near a nickel refinery in the UK.

The cells were treated with disodium telluride, similar to the chemical species one would expect to leach from cadmium telluride.

The determination of the proteome of the Bacillus subtilis strain 168 utilized in the experiment was not determined experimentally, but rather the proteome was downloaded from Uniprot as FASTA text files and the cysteine residues therein were counted. This is a relatively simple procedure. I've done it lots of times myself. If you've worked with Uniprot using mass spectrometry to confirm results, it's incredibly accurate.

They considered the sequences of 739 bacterial proteins.

The authors also used a program with which I'm not familiar, CELLO, to localize the proteins within the bacterial cell walls.

Cool...

Some results:

Reaction of aqueous tellurite with B. subtilis cells resulted in the loss of dissolved tellurium from solution (Figure 1). Adsorption experiments showed that the concentration of adsorbed tellurite increased linearly with the aqueous tellurite concentration with a Kd value of 19.5 ± 5.4 L kg–1. To test if sulfhydryl sites are involved in tellurite adsorption, the membrane-impermeable thiol-specific probe qBBr was used to block the sulfhydryl sites on the bacterial surface. The adsorption isotherms showed significantly less tellurite adsorption by qBBr-treated cells compared to untreated cells. The partition coefficient of the qBBr-treated cells was Kd = 6.6 ± 2.6 L kg–1. The decrease in the tellurite binding constant was attributed to tellurite binding to low-affinity sites on the bacterial surface due to the loss of sulfhydryl complexation on the qBBr-treated cells...


Figure 1:



The caption:

Figure 1. Tellurite adsorption isotherms. Adsorption of tellurite (Te[IV]) on to untreated Bacillus subtilis cells ( ● ) ; cells treated with resin to desorb surface attached EPS ( ? ) ; and cells treated with qBBr to block surface thiol sites ( □ ). All experiments conducted at pH = 7.2.


Another picture involving tellurium speciation using two x-ray absorption techniques, XANES and EXAFS





The caption:

Figure 2. Te K-edge XAS of Te standards and Te adsorbed to B. subtilis. (A) XANES spectra. Arrows indicate the position and amplitude of the white lines for the different Te species; (B) k2-weighed ? (k) EXAFS spectra; (C) Fourier transform of the EXAFS data in the range ?k = 2.5–10.5 Å–1; (D) Shell-by-shell fits of the EXAFS data. Letter designations (A–G) correspond to the EXAFS model listed in Table 1. The ball-and-stick models to the right illustrate the starting tellurite ion and the structure of the binding of the adsorbed Te atoms bound to S-based groups in the biomass.


Table 1 is rather technical, but for completeness, is below:



The caption:

N, R, and ?^(2_ are coordination number, radial distance, and Debye-Waller factor, respectively, for each path used in the fit. ?E is the energy shift relative to the calculated Fermi level. DF = degrees of freedom in the fit, i.e., the difference between the number of independent data points and the number of fit parameters (data were fit between R + ? = 1.1–2.2 Å for Na2-tellurite, 1.5–3.0 Å for metallic Te, 1.0–3.8 Å for TeO2, 1.5–3.0 Å for the Te(IV)-thiol and Te-biomass data). The R-factor is the fractional misfit of the data relative to its amplitude, and is a goodness-of-fit indicator. More details on these fit parameters can be found in FEFFIT’s documentation(43).

bThe amplitude suppression factor S02 was determined to be 0.93 based on the fit of this standard where the O coordination is known to be 3.0; this S02 was then used in all other fits to refine the coordination numbers.

cDue to the overlapping contributions in this spectral region there was significant correlation between the coordination number and the Debye–Waller factor of this shell, so the latter was fixed to the value shown to stabilize the fit.

dThe ?E variables for the two O shells were constrained to be the same.


Another figure:





The caption:

Figure 3. Protein and thiol content of B. subtilis EPS. (A) Protein concentration in EPS; (B) Thiol content of EPS collected from early stationary phase cultures. (C) Surface site concentrations of cells with intact EPS (+EPS) and cells with EPS removed (?EPS). Error bars represent the standard deviation of triplicate measurements.


The authors argue that the tellurium adhering to the surface of bacterial walls will not be transported into cells, killing them:

Bioenvironmental Implications

The adsorption of Te(IV) and formation of stable RS–Te–SR components in the EPS are expected to affect bacterial Te(IV) uptake and microbial Te interactions. Previous studies of microbial Te(IV) reduction have largely focused on the chemical reactions that occur after Te enters the cells(16,17,64,65) and have neglected the mechanisms that control Te(IV) binding to the cell surface. Microorganisms can import tellurite into the cell and reduce Te(VI) to Te(0).(13,14) In environmental microbial systems, cell surface adsorption and uptake of tellurite are likely to co-occur to varying degrees depending on EPS production. Our results suggest that microorganisms that produce thiol-rich EPS would bind a significant portion of tellurite outside of the cell, thus limiting the translocation of Te into the cytoplasm and potentially mitigating the deleterious effects of tellurite uptake...


They conclude:

...Finally, our findings have important implications for understanding the environmental fate of Te adsorbed to bacterial surfaces. If high-affinity tellurite binding sites on bacteria are associated with loosely attached molecules on the cell surface, then the adsorbed organo-tellurium components can be released into aqueous solution as soluble organic matter when the EPS is destabilized. The attachment of EPS to cells is controlled, in part, by electrostatic interactions.(68) Thus, changes in environmental factors such as pH, salinity, and groundwater composition can trigger EPS detachment from the cell surface and render the organo-tellurium species mobile for transport. Of particular interest is the stability of cysteine-rich proteins in the EPS which have high thiol site densities and likely have the greatest contribution to tellurite binding. The results of our study indicate that quantification of these sulfhydryl-containing molecules and the incorporation of protein-specific complexation reactions into surface complexation models will enable better predictions of how bacterial adsorption affects tellurite transport in landfills and other contaminated sites.


Solar cells can be expected to become landfill in about 20-25 years, and since their massive production has only provided trivial energy, the expectation of increasing their distribution by orders of magnitude will involve massive amounts of distributed electronic waste on a scale dwarfing the already intractable amounts of this waste.

Note that the release of tellurium from cadmium telluride will also mobilize cadmium, the toxicity of which is also connected with cysteine residues in zinc proteins important for respiration.

Have a nice day tomorrow.
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Bacterial driven mechanism for tellurium transport from discarded solar cells in landfills. (Original Post) NNadir Aug 2021 OP
II-VI based solar cells are hardly a significant part of the market Effete Snob Aug 2021 #1
I specifically stated that this form of solar garbage was only one such case. NNadir Aug 2021 #3
There are just too many people consuming more than they need. alfredo Aug 2021 #2
My solar panels and electric cars won't save the world? That's so sad. hunter Aug 2021 #4
We are culling our own herd alfredo Aug 2021 #5
 

Effete Snob

(8,387 posts)
1. II-VI based solar cells are hardly a significant part of the market
Thu Aug 12, 2021, 12:10 AM
Aug 2021

Please don't pretend that II-VI cells are representative of photovoltaics generally. That's ridiculous.

If you'd like to have a reality-based discussion, please refer to page 22 of this report from the Fraunhofer Institute on the state of the PV market since 1980:

https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/Photovoltaics-Report.pdf

As any idiot can see, the peak year for ALL thin-film technologies (of which CdTe is one) was 1988, at 30%. ALL of the remaining 70% that year was either polycrystalline silicon or monocrystalline silicon.

Currently, ALL thin film technologies are less than 5% of production.

Now, what share of that thin film category is CdTe? Page 23 - a little more than half, with the rest being amorphous Si, and Copper Indium (Gallium) Selenide.

TLDR for non-techies - the OP is about a contaminant found in a relatively insignificant and shrinking share of the photovoltaic market, involving a PV technology which is generally used in specialized applications, and is quite unlike the sorts of solar panels you see for general purpose use.

NNadir

(33,368 posts)
3. I specifically stated that this form of solar garbage was only one such case.
Thu Aug 12, 2021, 12:33 AM
Aug 2021

Any idiot can see, in my opinion, that all the cheering for mass intensive solar garbage has failed to address climate change.

After 50 years of insipid excuses and diversion of attention, solar electricity does not produce 3 exajoules of the more than 600 exajoules of energy humanity produces each year.

That's a fact. Facts matter.

The reason is physics, it's extremely low and environmentally unsustainable energy to mass ratio and the requirement for redundancy.

Maybe, just maybe, while cheering for copper indium gallium selenide, anyone cheering for this crap should look into the world supply of indium. One may also be interested in its toxicology of this element, except if one is involved in defending the indefensible. The search terms (Indium "Lung Disease" ) produces over 2800 hits on Google scholar in less than one second. 131 papers on this issue have been published in 2021.

But considering that would involve seriousness.

Indium is defined by many international scientific organizations as a critical element:

https://www.acs.org/content/acs/en/greenchemistry/research-innovation/endangered-elements/indium.html

Given that the solar industry has been trivial for half a century of cheering for it, and given the expenditure of trillions of dollars on the solar fantasy for no result, and given that it is already useless in addressing climate change, any attempt to expand it using indium is immediately doomed to failure.

In general, people cheering for the production of electronic waste couldn't care less about these kinds of issues. They expect that this is a problem for poor people in the third world who will be tasked with "recycling" this electronic garbage.

The fact remains solar industry has done nothing to address climate change, is doing nothing to address climate change, and will do nothing to address climate change.

As noted in the OP, the world is on fire, and for me, as an old man, it comes after many decades of hearing how solar energy would save us. Color me unimpressed.

It is well known to any serious person involved in industrial ecology that continuous systems are thermodynamically and environmentally superior to discontinuous systems. It is wasteful in the extreme to require two systems to do what one can do more reliably, with lower mass intensity.

But of course, the cited paper was published in the current issue of a major environmental scientific journal which I've been reading for decades. Rather than write to me to complain about the fact that I take it seriously, why not write to the authors of the paper itself, which can be found at the link, and tell them how stupid they are for raising this point.

The text in my post comes from their paper after all.

Have a nice day tomorrow.

alfredo

(60,065 posts)
2. There are just too many people consuming more than they need.
Thu Aug 12, 2021, 12:14 AM
Aug 2021

Keep it in your pants and put your credit card away.

When we were concerned with nuclear obliteration, some said we will not go out with a bang, but with a whimper. A third end could be unheard mournful last words muttered in a respirator.

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