Hydrogen Sulfide layers in water

[Tamara Thomsen]

Because of several recent posts on this site I felt compelled to share my experiences with hydrogen sulfide layers. I don’t mean to scare anyone but here it goes: 

My first experience with hydrogen sulfide was working on a scientific expedition several years ago to the blue holes of the Bahamas.  The layer was thin- maybe 6 inches- and looked like a whispy cloud that was sandwiched at about 100 feet deep in between distinct layers of water coming from different water sources.  I was told not to dwell too long in or near the layer.  I quickly moved below the layer, conducted my assigned work and returned to the surface.  Upon surfacing, I noticed that all of the chrome was burned off of my regulator, the brass on my equipment clips was tarnished, and my soft gear retained an odor of rotten eggs.

The next site we visited had a thick, red layer of hydrogen sulfide of about a foot thick.  My assignment was to collect animals that lived and hunted near the layer, it was thought that several of these were breath holders and would live below the layer, but hunt above (and vice versa).  Spending more time near the layer dragging a plankton net, I noticed more prevalently the rotten egg smell and my exposed skin tingled quite a bit.  But by the end of the dive I didn’t notice the egg smell anymore.  I learned later that the nearest cousin (chemically speaking) is hydrogen cyanide a neurotoxin that is trans-dermal i.e. soaks in through your skin. 

After conducting these type of dives with varying exposures- some elongated dives on rebreather- for the duration of 2 weeks I noticed other effects.  Because of my prolonged exposure it was as if I had gotten an expensive chemical peel- most of the skin on my face and hands peeled away and my sense of smell was altered and had become very acute.  I would get out of the water and feel dizzy for several hours before recovering.

I found out later after talking to a friend in NEDU (Navy Experimental Diving Unit) that has done trials with this stuff, that over 25 ppt will affect a human nervous system in air, but in water there are little or no studies.  You actually stop smelling the rotten eggs after 10 ppt- but again this is in air- so who knows about in water!  So you can’t always rely on the smell as an indicator….

Hydrogen sulfide is formed not only because of decaying material or in swamps, but can also be the result of mining, and other industries.  Anyway, because of the mention of a possible hydrogen sulfide layer now at Devils Lake and the one that is below 135 feet in Fortune Pond, I thought that my experience would be of interest and help you decide how to plan for it. 

Safe diving....
Tami

[matt t.]

How long did the effects last, and were there any permanent effects from this stuff? Also, did they at least replace your regluator? 

[Tamara Thomsen]

The effects for me only lasted a couple of hours after the dives- headache and dizziness- but this was after nearly 2 weeks of daily exposure that I began to develop these symptoms. The skin thing was no more than a sunburn or chemical peel would be, but made my skin very sensitive. 

I'm not saying don't dive at Fortune Pond or Devil's Lake- I dive there.  I also have no idea about the concentrations in the water at these places either.  I'm just saying be aware of what you are getting yourself into.  Nothing is ever mentioned about H2S in basic scuba, or tech classes or even in cave diver courses.  I think that all that I ever heard was a VERY breif mention in my Introductory Cave course- don't dwell in an H2S layer because it will eat your gear and you'll smell bad when you get out.... 

I couldn't believe that my gear looked so bad after so little exposure, but I guess that it has everything to do with the concentration.  I'll try to post pictures a little later.  BTW, no, I didn't get my reg. replaced- but I didn't ask either because I wanted to be invited back on other projects- didn't want to rock the boat....  Chrome is pretty superficial anyway.

[Chris H]

I've experienced the sulfur taste/smell at Redgranite Quarry as well.  Not recently, but it has been a while since I've been to the bowels of the quarry to see the crane and all of the other mining equipment still sitting upright in 237' of water.   :  >  ;D

[LKunze]

Thanks for the info Tami.  Several of the Cuyuna pits near Brainerd MN have the Hydrogen Sulfide layer... or what some of us like to call the Rootbeer layer.  The layer seems to change from year to year and pit to pit at varying depths and in some cases it has been close to 10 feet thick.  It's strange because often times if you go through it the water is gin clear below the layer but no ambient light is able to penetrate it. 

[codecruncher]

This page on Seasonal Lake Stratification I found pretty interesting and mentions hydrogen sulfide.



Excerpt:
During summer stagnation the lake bottom can become anoxic (i.e., without oxygen) and anaerobic bacteria begin to decompose organic material without the aid of dissolved oxygen.  If dead algae accumulate at a faster rate than bacteria decompose the organic matter, sediment deposited in the lake will be rich in organics.  This is likely because without thorough mixing to provide the surface water with nutrients from the bottom, the algae eventually begin to limit the available nutrients in the epilimnion. Lack of available nutrients can cause large die-offs of algae, adding to the organic matter on the lake bottom.  Frequently, anaerobic bacteria produce hydrogen sulfide gas (H2S), so the organic-rich sediment may have the odor of “rotten eggs”.

How does the H2S gas end up becoming a floating layer in the water column instead of simply escaping into the air on the surface?

[Tamara Thomsen]

Here are a couple photos that I took of collecting and diving around the hydrogen sulfide layers in the Bahamas, and my gauge (minus the chrome) after only one dive.  It's scary to think of what it's doing to your body!

[Maka]

Thanks Tami,

I wonder how different the effects are in salt water vs. fresh. 

[Tamara Thomsen]

From my experience, the hydrogen sulfide layers settle in between layers of water with differing densities.  In the Bahamas we were finding it at layers with different salinities(sea water on bottom and brackish on top).  If I remember correctly from quarries that I have experienced this in, it may be associated with a thermocline and the water density diferences due to the termperature differential (however so slight) may be what is trapping the gas in the water column.  For those of you that have expereinced this effect more recently, you'll have to confirm or deny this for me.  This may answer both questions (JohnF and Maka) that are up and unanswered. 

What we have to our advantage here in the north, is that a majority of us that punch through these layers are wearing drysuits, possibly dry gloves, hoods, etc.  We have little skin exposed directly to the water at best! 

[Chris H]

I just looked up Hydrogen Sulfide in the Merck Index and this blurb seems most appropriate as reasons we see what we see.  Temperature is Celsius
 
One gram H2S dissolves in 187 ml water at 10°, in 242 ml water at 20°, in 314 ml water at 30°; in 94.3 ml abs alcohol at 20°; in 48.5 ml ether at 20°. Sol in glycerol, gasoline, kerosene, carbon disulfide, crude oil. Water solns of H2S are not stable, absorbed oxygen causes the formation of elemental sulfur, and the solns become turbid rapidly.

From this I would gather that whatever is producing the gas, is likely at the bottom, as is the cold water where the gas is more soluble in the water.  Once it is in the water, the elemental sulfur crashes out and forms dark water.   I’m guessing here, but I think turnover of lakes, depending on conditions would be a likely cause for the change in position of this layer, or a portion of it, in the water column.

Additionally, Tami’s described symptoms are listed with the overexposure symptoms in the Merck Index.   This stuff isn’t very nice, so don’t swim in it if you have the choice.

Caution: Highly toxic irritant and chemical asphyxiant; overexposure can be fatal. Insidious poison, since sense of smell may be fatigued and fail to give warning of high concns. Direct contact with gas may cause irritation of eyes and respiratory tract resulting in keratoconjunctivitis, photophobia, lacrimation, corneal opacity; rhinitis, laryngitis, cough, bronchopneumonia. Direct contact with solution may cause skin irritation, erythema. Potential symptoms of overexposure by inhalation include salivation, GI disturbances; giddiness, headache, vertigo, confusion, unconsciousness; tachypnea, tachycardia, sweating, fatigue. Exposure to very high vapor concentrations may result in systemic intoxication leading to paralysis of respiratory center of brain, apnea and sudden collapse. See Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams & Wilkins, Baltimore, 5th ed., 1984) Section III, pp 198-202; NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 170.