Public Lab Research note

A proposal for a way to remediate indoor silica dust

by marlokeno | December 23, 2015 02:49 23 Dec 02:49 | #12539 | #12539

I want to see if diatoms and a bio-bubbler can help reduce indoor silica dust.

proposal for mitigating indoor silica dust

After reading #eustatic’s ingenious bubbler for improving indoor air [ see: ], it occurred to me that algae, specifically, diatoms, a/k/a brown algae, could be used in a similar way to mitigate indoor silica. Diatoms eat silica and use it to build their cells.

My proposal is to create a bubbler like the one #eustatic made for his office; but one with a larger surface area of water in order to increase light exposure to help diatoms/brown algae thrive. An infusion of diatoms will substitute for the water plant. An aquarium should do for the initial experiment, and grow lights for brown algae photosynthesis. In addition, I plan to add some water plants, goldfish, and maybe a little dirt to help provide other nutrients for the diatoms.

My hope is that the diatoms will absorb the crystalline silica dust found in homes near frack sand mines and trans-load facilities.. Also, I hope that grow lights will be strong enough to enable the diatoms to thrive.

If this works, the residents should be able to scoop out the brown scum in order to get rid of silica and allow light through for continuing growth photosynthesis. The literature I read indicates that brown algae/diatoms like lots of light, even though there are some species which live underground

The diatoms/brown algae can easily be acquired from local ponds near frack sand mines which have to clean up brown algal growths several times a growing season. Diatoms/brown algae usually grow in a boom/bust cycle, as mining does.

In addition, the person who volunteered to host the experiment has a Dylos, which measures pm levels in the air. So if the diatom bubbler works, I hope to see lower pm when it is operating, and lower pm readings than in other areas of the house. Of course, indoor dust/ pm levels are influenced by HVAC systems in the house, the wood-burning stove, cooking & baking, and so forth.

Given the difficulties of measurement, I propose to set up the same equipment in my house, which is in an area where it is believed that there is less silica dust. There is certainly less household dust at our house than the frack sand country house. In addition, last winter, the sand country house had visible dust lying on top of the snow, which is a common sight near frack sand mines. Many people left a bucket out and collected sand from snowfall, but this was not taken seriously by town governments or the WDNR.

The fish pond in the sand country house has a lot of brown scum, a phenomenon which only began when frack sand mining began. The water in the pond has been tested last summer and high silica levels were verified; Also, there were silica deposits at the bottom. Therefore, I think it a reasonable assumption that there are silica eating brown algae/diatoms present. Of course, to go beyond a trial, that assumption needs to be verified. I’m hoping to enlist the department of health and/or university extension if preliminary results look promising.

Fun fact: Diatoms and kelp are both brown algae.

My attempt and results

We plan to attempt this in the beginning of January.

Questions and next steps

I wonder what other nutrients the diatoms will need in addition to silica. I wonder whether room temperature is warm enough for plenty of diatom growth. I wonder if the bubbler will be enough to introduce silica into the water. Perhaps dust falling from room air will also get in the water..

Why I'm interested

I'm interested because a number of people near the sand mines/transloads have developed asthma and some other medical problems that silica dust can cause. Children appear more vulnerable to asthma than adults; but I don't have good statistical evidence of changes in asthma rates of any group. The picture here is an aerial view I photographed of the transload facility in Augusta, Wisconsin. IMG_9264.JPG


dope graphic

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@eustatic -the graphic comes from a 1996 OSHA campaign, under then-sect'y of Labor, Robert Reich, who resigned in '97, he wrote, to spend more time with his family.

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I hate to be pessimistic, but even a medium efficiency supply air filter is probably more effective in removing the dangerous particles (respirable, < 4 µm). You need both a high flow (0.5 to 2 times the room volume per hour) and a high collection efficiency in the range 0.2 - 4 µm. Bubblers tend to be quite inefficient under 1 - 2 µm. An additional problem is that there are many indoor particle sources that could confound your experiment (candles, cooking, vacuuming etc). However, the bubbler might remove water soluble VOCs which might be a good thing! I also think that the diatoms will have a hard time to digest the crystalline quarz, for the same reasons the substance is dangerous to mammals. Really sorry but I wish you good luck with future projects! (I have 20 years of experience in the IAQ and epidemiology field.)

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Thanks for sharing your expertise, @martenskram. I didn't know that bubblers were inefficient under 1-2 µm. Your information about flow & particles, especially the following-

"You need both a high flow (0.5 to 2 times the room volume per hour) and a high collection efficiency in the range 0.2 - 4 µm. Bubblers tend to be quite inefficient under 1 - 2 µm."- is especially helpful-because I'm hoping to get the diatoms to eat very fine, possibly ultra-fine particles that a room air filter can't trap."

And you're right, I have no way to account for dusts made by baking, vacuuming and other household dust sources. Both of the above issues worry me.

On the other hand, my understanding is that diatoms can metabolize silica, unlike mammals. I have 2 reasons for thinking this: 1) (Anecdotal) Fish ponds near the silica mine & transload grow a lot of brown algae/ diatoms now during warmer months, which never happened before the mining started. The remedy for brown algae on fishpond and aquarium sites was to reduce the silica in the water 2) Concerning diatoms, and their consuming silica, wikipedia wrote: " Diatom cells are contained within a unique silica cell wall comprising two separate valves (or shells). The biogenic silica that the cell wall is composed of is synthesised intracellularly by the polymerisation of silicic acid monomers... ...In the open ocean, the condition that typically causes diatom (spring) blooms to end is a lack of silicon. Unlike other nutrients, this is a major requirement solely of diatoms, so it is not regenerated in the plankton ecosystem as efficiently as, for instance, nitrogen orphosphorus nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus)." from:

Since diatoms need silica to build their cell walls, I've been hoping they might help remove silica from the air.

So I'm still curious about diatoms and silica dust. Home air filters that I googled filter particles down to 0.3 microns. And on the chance this might filter out some very fine & ultra-fine particles, I think it's worth trying. It's important to me to keep trying because I know a woman near here who has filters all over her house, and continues to have asthma and bronchial problems which disappear when she goes out of state to visit family or travel.

I'll change goals for this experiment, and make the goal to see if more diatoms grow in a tank with a bubbler than in a tank without a bubbler. That may mean changing the experiment to 2 households with the same equipment other than the bubbler, and comparing diatom growth in each. If they thrive at all under grow lights, as I hope.

Then, if, & this a very big if, diatoms grow more in the tank with the bubbler, there remains the problem of sorting out whether the bubbling helped the diatoms grow better, or the presence of silica in the water. The only way I can think of to begin with water that is without diatoms is to use distilled water. Maybe treated tap water would be ok; the water where the homes have a silica dust problem, are using untreated well water.

Second, while I'll use the Dylos to measure particulates, listing date, weather & household activities that day, I'm not going to do other measurements. If someone knows a good technique with which I can get better data, please let me know.
I've been following the twists and turns of outdoor dust monitoring by @mathew and others, e.g. this recent post:

Thanks again for helping me think through this.


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If bubbling room air through an aquarium removes some dust from the air (including some silica dust) then growing diatoms in the water is not required. The silica dust will be trapped in the water and can be disposed of (I guess silica is dangerous to us only when it is suspended in the air). The trick is to force a room full of air through the water every hour or so, so a floor to ceiling tube (e.g., 4" PVC pipe) might be more appropriate than an aquarium. If the bubbling will not remove the finest particles, some other method will be needed to remove those particles. That other method might also remove all the larger particles, so the bubbling may be superfluous.

If you want to test whether diatom growth is stimulated by silica removed from the air which bubbles through water, then:

1) determine that there is silica dust in your air,
2) establish that diatoms will grow in your aquarium,
3) establish that diatom growth is stimulated by added silica (a separate experiment),
4) grow diatoms in two similar aquaria,
5) bubble air through both aquaria,
6) filter the air that enters one of the aquaria (so no dust enters that aquarium),
7) quantify the amount of diatom growth in each aquarium,
8) replicate the experiment until you have some confidence that your result is real.


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Thanks to Chris for some lucid suggestions. I have some questions, and ideas for improvements after reading your post.

Question: I don't understand why it is necessary to circulate the volume of all the room air every hour, if formaldehyde can be remediated with a bubbler/plant. I'm wondering whether the flow of the room's volume of air every hour is enough to create air currents that change things. Probably it doesn't matter in a house with cooking and vacuuming activities, as @martenskram wrote.

Your point that the bubbler alone may be sufficient to mitigate dusts is something that needs to be included. So a first experiment without the diatoms will improve the experiment.

In the interests of brevity, I didn't include all the information that I have. Silica dust has been well-documented outside the residence. I quote from part of the report: "There was indeed a presence of respirable (<4 um) and fine (<2.5 um) crystalline silica particles, as seen in a phase-contrast microscope analysis ..." That is from a report from a local university laboratory. Respirable silica dust outside gets inside. Documenting silica indoors is important; at present, the best solution that I can think of is to measure dust indoors and outdoors. I will measure dust quantities of all dusts, inside and out with the Dylos. Concerning diatoms, part of this trial will be to see if diatoms will grow under artificial lighting. As diatoms do grow in indoor aquaria, I'm hopeful. Fortunately, it is well-established in biology that silica is a necessary nutrient for diatoms.

Filtering air to the control aquarium and simultaneously using a bubbler could help add rigor. I'm not sure how to do that; presumably the intake air to the bubbler would need to be filtered first ? My plan for now is to use a control aquarium at a site where there is less silica in the air. Maybe the experiment at both sites should be repeated at both sites with a commercial HEPA air filter.

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I'm unsure about the claims, but at least one vaccuum company advertises that its unit can 'wash' the air. Of course, the unit moves a larger volume of air and the unit costs $2000++, but i do believe they would have some specs on how long it takes to clean a room...

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Very neat idea -- I guess I agree with Chris that it may not matter if diatoms metabolize the silica, if the silica is already transfered from the bubbled air into the water -- it could just accumulate at the bottom of the water vessel. I think it could be hard to tell in the pond you mention whether diatoms are involved or not -- would it look different if they were or were not involved in capturing silica? I guess I don't know much about it.

I wonder if you can run the whole thing as an experiment in a sealed chamber like a bucket or sealed fish tank, and monitor the silica dust levels (sorry, the Dylos can detect the relevant silica? I really don't know much about it) -- so you'd, in Test A:

  • turn on the sensor, measure a baseline
  • introduce silica dust into the chamber, see a spike on the sensor readout
  • start the bubbler, watch if the sensor readout drops and how fast

Then you'd repeat the whole thing with no bubbler, ideally in the same conditions, as Test B (temperature, humidity, airflow). And back and forth a few times so you are sure that A and B are different no matter which you run first.

I'd leave the bubbler in the chamber for both tests to be sure it's the actual bubbles that make the difference. Maybe even leave the pump going for both, where the difference would be only that it's not bubbling, and the vibration and airflow of the pump itself isn't part of it (esp. since the pump has a crude filter in it).

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In these experiments, the bubbler will increase the humidity in the chamber or room. That alone could reduce the dust in the air (by dampening the dust?). So it might be hard to know if the silica was being removed into the bubbler water or not. But if bubbling reduces dust, then mission accomplished. As long as the humidity does not remove your wallpaper.


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@cfastie, @warren, @eustatic, and @martenskram- Thanks for your help clarifying ideas & procedures. As it's winter and cold, indoor air is often desert dry. So I'm not worried about the wallpaper yet, Chris. And if humidity lowers the dust level, that would be great. Scott, not many people around here can afford ++$2000. Median household income in the area is ~ $44,000. One reason for using diatoms is that they probably make cleaning up silica much less hazardous. Dead diatoms=diatomaceous earth, which is a non-crystalline, amorphous form of silica. The living diatoms form a brown mat on the ponds near silica sites. One variety is called "brown snot." I assume live diatoms likewise have cell walls of amorphous silica. An IARC monograph states: "Crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1) Amorphous silica is not classifiable as to carcinogenicity to humans (Group 3)." Accessed 2016-Jan 11 from:

[Notice the authors say "...from occupational sources." This was used as the justification that the WI DNR gave for saying that silica in ambient air had never been shown to be dangerous. The only evidence of hazard came from studies of occupational sources. My opinion is that if an unsafe occupational level is established, where a person breathes for 8 hours a day, then the unsafe level for 24 hours a day of ambient air exposure should be 1/3 of the occupational level.]

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