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  • Writer's pictureAllan Dyen-Shapiro

On the Everglades part 4: Sulfate and methylmercury

Back in my scientist days, I had a colleague at the U. of Georgia with a fascinating and important idea. He had been told of a genetic pathway in bacteria that detoxified and volatilized methylmercury. Methylmercury is a potent neurotoxin. Indeed, a disease, called the Danbury Shakes, was named after a hat making plant in Danbury, Connecticut, where the workers and people who lived around the plant all suffered from poisoning from this toxin. This scientist proposed (and ultimately did) the cloning of these genes and expressing them in cottonwood trees (in the roots). So, all you have to do is plant the plants, the mercury is changed into a less toxic form and it flies away into the atmosphere.

Sounds great, right?

Now try phrasing it as evil scientist wants to plant transgenic crops that are going to send poisonous mercury into the atmosphere so it can rain down on you. A bit of a marketing nightmare. The company he formed out of a biotech park puttered along for a few years with his former employees coming in over their weekends as volunteers because they thought it was so important to be able to clean up mercury pollution that they kept putting their hearts and souls into the project. To no avail. Eventually, the town of Danbury agreed to let them come in and try this as long as they did it at the scientists' own expense. I just Googled; the company still hasn't gotten financing.

The irony is that mercury is already raining down from the sky. It has been discovered in the Everglades, it's at high enough levels to make fish inedible and to endanger wildlife, and it is all coming from the rain. The major source of airborne mercury is burning of coal. Coal fired power plants have very tall smokestacks, so the effluent is sent into the atmosphere and travels long distances. Most of the mercury in the Everglades is coming from China.

So, all one has to do to remediate this is to wean the Chinese from their major energy source, right? Fat chance of that happening in my lifetime.

Actually, no. There is something local that should be done that will reduce methylmercury levels in the Everglades to where it is not an environmental problem, or at least no worse of a problem than for anywhere else in the world. And it's completely feasible. So, why hasn't this solution hit the bumper stickers of cars that also sport Bahai aphorisms and Bernie Sanders stickers?

Because understanding it requires some knowledge of biochemistry. Let me walk you through this. Those of you who have read my first three posts are aware that dry conditions have prevailed in the eastern Everglades, and that the ecosystem there is seriously imperiled (see post #1). The dry soil becomes oxidized due to exposure. This oxidized soil is excellent substratum for sulfate reducing bacteria. When also exposed to mercury, sulfate/mercury complexes form in these bacteria that increase the bioavailability of mercury to the methyl transferase enzymes that make methylmercury (the potent neurotoxin).

So, where does the sulfate come from? You guessed it: backpumping of water from Big Sugar's lands into Lake Okeechobee. Some of the sulfate is legacy, having been deposited a long time ago, some is natural, some is from current pollution.

But aren't there stormwater treatment areas just south of Lake O? Yes, there are. And these do a wonderful job of removing phosphates. Indeed they are the reason the low phosphate ecosystems where water has been dumped (e.g., Biscayne Bay, Florida Bay) are coming back (see my post #2 in this series). They are a completely artificial ecosystem that the water management district made, choosing plants that are very good at taking up the phosphate. In fact, these are almost 100% effective.

For phosphate. They weren't designed to remediate sulfate pollution. Only 20% of the sulfate run-off is captured.

So, part A of the solution: when the new reservoirs everyone agrees are needed south of Lake O are built, plant plants that are good at taking up sulfate. Easy.

So, you say, couldn't sugar cane producers also reduce their use of sulfur amendments to the soil so there isn't so much sulfate run-off? Again, the answer is yes. Agronomists have found that due to changes in soil composition, sulfur addition is no longer effective in contributing to plant growth on these farms. In essence, what you would be saying to a sugar cane grower is to stop spending their own money on something that is not only a waste of their money but also causing them a public relations problem. (I might even be so bold as to say that you could sneak in a mention of destroying the Everglades if you wanted.)

Growers listen when they are presented with hard data. I used to live in Delaware. Phosphate overload in the soil was running off into the Chesapeake Bay and causing toxic algal blooms. The nutrient management experts in the flagship state agricultural university were told by the governor to get their data together and present field studies to the farmers. And you know what? If you tell a farmer that they are wasting their money, prove it to them with data, and then tell them there might be fines coming if they don't stop wasting their money, they listen!

The news focuses on the two major growers of sugarcane, but there are a lot of minor ones. Could the state ag extension service get this data together and make a nice PowerPoint to show the farmers? Again, in my eyes, an easy solution.

Last piece of the puzzle: dilution. Flood the area with fresh water, the soil will no longer be as oxidized, and the concentration of sulfate in the ecosystem will be diluted. Okay, wait for it, I get to use my Biochemistry Ph.D. again here: enzymes display saturation kinetics. The transporters (permeases) that transport sulfate into bacterial cells don't operate to any great extent unless there is a sufficiently high concentration of sulfate (mass of sulfate per volume of water). It's not the absolute level of sulfate that matters as much as the concentration. Most non-scientists naively expect a linear dose-reponse: more bad thing means more bad effect. It's not that way at all if an enzyme is governing the process. More of the bad thing doesn't do much of anything until you reach a certain concentration, then it is linear, then the effect is maximal after that point. Look up Michaelis-Menten kinetics on Wikipedia if you'd like a more in depth explanation.

So, all that is needed is some land south of Lake O, where new stormwater treatment areas could be built south of reservoirs that would also serve for flood control, with the water then being directed into the eastern Everglades. Actually, that's called the Everglades Restoration Project. And it's stalled. Because the state doesn't have control of the necessary pieces of land.

And to answer why, I finally have to turn to politics. For those of you who know me well and are amused by my getting four posts into this series without mentioning politics (or four posts of any sort out onto the Internet without mentioning politics), it's coming in blog post #5.

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