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Friday, October 27, 2006

Beating Arsenic in Bengal and Bangladesh

Arsenic in groundwater is a severe problem in West Bengal and in Bangladesh, where it is estimated to cause 200,000 to 270,000 deaths per year. [Other regions are also affected, including Argentina, Chile, China, India, Mexico, Taiwan, Thailand and the United States of America.]

In humans, arsenic causes arsenicosis which causes skin problems including skin cancer, bladder, kidney and lung cancer, disease to the blood vessels of the legs and feet which can lead to gangrene, and is suspected to contribute to diabetes, high blood pressure, and reproductive disorders. [Source WHO] The WHO's Guideline Value for arsenic in drinking water is 0.01 mg /litre.

The problem of arsenic in drinking water can be tackled by harvesting rainwater - a strategy routinely advocated in permaculture.

Arsenic also affects agriculture in two ways: arsenic is drawn into plants contaminating the plant; and arsenic is drawn up instead of phosphorus, which is a major limiting factor in plant growth. The result is a plant that has a degree of toxicity and is stunted due to lack of phosphorus. When groundwater irrigation is utilised in areas with arsenic contamination, these problems appear.

The use of swales, or water-harvesting ditches on contour, is the most cost effective type of earthworks for capturing water. It also reduces or eliminates the need for groundwater irrigation.

Additionally, endomycorrhyzal fungi can be employed to help alleviate the arsenic problem. Plants with the endomycorrhyzal fungi Glomus mosseae have been show to reduce plant uptake of arsenic and increase the uptake of phosphorus as reseach by the University of Aberdeen recently shows:
Arsenic (As) contamination of irrigation water represents a major constraint to Bangladesh agriculture. While arbuscular mycorrhizal (AM) fungi have their most significant effect on P uptake, they have also been shown to alleviate metal toxicity to the host plant. This study examined the effects of As and inoculation with an AM fungus, Glomus mosseae, on lentil (Lens culinaris L. cv. Titore). Plants were grown with and without AM inoculum for 9 weeks in a sand and terra green mixture 50:50 v/v and watered with five levels of As (0, 1, 2, 5, 10 mg As L-1 arsenate). Inoculum of Rhizobium leguminosarum b.v. Viceae strain 3841 was applied to all plants. Plants were fed with modified Hoagland solution (1/10 N of a full-strength solution and without P). Plant height, leaf number, pod number, plant biomass and shoot and root P concentration/offtake increased significantly due to mycorrhizal infection. Plant height, leaf/ pod number, plant biomass, root length, shoot P concentration/offtake, root P offtake and mycorrhizal infection decreased significantly with increasing As concentration. However, mycorrhizal inoculation reduced As concentration in roots and shoots. This study shows that growing lentil with compatible AM inoculum can minimise As toxicity and increase growth and P uptake.
Also see More Evidence of Mycorrhizal Fungi as Arsenic Beater.


Scott A. Meister said...

Looks like this is a major problem in the U.S. too. It seems to me, that pumping of underground water, combined with pesticide use, and pesticide run-off into rivers and streams, is a recipe for disaster.

There’s some interesting info here...along with maps of contamination.

“The main sources of arsenic in the environment are either natural or man-made. The natural sources include naturally existing minerals/ores (such as pyrites), soils which usually are sinks for the weathered form of arsenic compounds, and mineral-rich geothermal waters. The man-made sources are usually the industrial effluents, which may be direct discharge of arsenic compounds into soil, water, air (which results in atmospheric deposition of arsenic). Such industries include copper smelters (See smelter on Ruston Point, Tacoma, Superfund Site), pesticide and wood preservative manufacturers, among many others.”

DJEB said...

I should add something that would be useful for permaculturists:

If you use sawdust in composting, do not use it from pressure treated lumber. The lumber is not "treated " with "pressure." It is dunked in a solution of chromated copper arsenate.

I mentioned that arsenicosis regularly includes cancer. Well, chromium is also a human carcinogen.

Scott A. Meister said...

Excellent point DJEB, and I'd like to add to that.

It's also a good idea NOT to use treated lumber for fence posts or vine-posts, for this will result in arsenic leaching into the surrounding soil, as they have discovered in the vineyards around Marlborough wine-country in New Zealand.

story here...

Instead of using treated lumber...I suggest people use another kind of durable hard wood like my favorite, maclura pomifera, otherwise known as Osage Orange (see story on the Top 10 Fuel Trees elsewhere on this blog).
Harvest fence posts/vine-posts outdoor furniture lumber and fuel wood from sustainably managed, coppiced or pollarded hard wood trees, and you'll be able to reduce your arsenic risk, while also extending the life of the trees which do other healthy things for us, the soil, the air, and water management anyway.
There's some serious use stacking! You could even go a step further and make a mixed hard-wood planting with various other nitrogen fixers or fruit trees on a swale!

Scott A. Meister said...

By the way, although I like the idea of using Mycorrhizal fungi/mycelium to help plants reduce uptake of Arsenic and Heavy Metals. I have some questions. Perhaps I just missed something. If so, please point it out, but...

I'm interested in what happens to the toxic substances.
Although Mycorrhizal fungi can reduce plant uptake of toxic substances such as Heavy Metals and Arsenic...aren't the substances still there...just taken up by the fungi/
Or do the Mycorrhizal fungi/mycelleum lock it up and render it inert?

If they aren’t rendered inert, it might make sense to combine Mycorrhizal fungi with a swale system which, as we witnessed in Jordan, seemed de-salinate the soil by washing it through.
I guess, what I'm suggesting is that the Mycorrhizal fungi would simply buy you time while the swale system "flushes" the soil...therefore actually de-toxing the productive horizons of the soil (unless it's actually rendered inert).
But if it's not rendered inert, even with the flush from the swale...where does it go? Just deeper into the soil, and perhaps out of the way of interfering with plant/animal life (for the time being)?

DJEB said...

It is not clear what is going on in each case.

Button mushrooms (Agaricus bisporus) accumulate cadmium (as do other Agaricus species). Oyster mushrooms do not accumulate as much in the same conditions. (Both of these are saprophytic mushrooms.) It seems that some mycorrhizal fungi acccumulate asenic (As), but don't transmute that to the plants.

Glomus species here are helping to keep arsenic out of the plants, but there is no mention of it being locked up permanently.

With Jordan, it is my understanding that the fungi naturally occuring on the site locked up the salt rather than it being washed through. It seems likely, however, that swales would contribute to salt being washed through the soil on land where it would usually sheet off.

You're right. For areas with arsenic problems, swales would help in reducing levels. It would also get people away from using ground water for irrigation - a practice that compounds the problem.

In one way, the mycelium do "buy you time," but they do do much more than just guard against As. There is, as meantioned, the problem of plants taking up As instead of P, but the fungi help with that. Under normal, healthy soil conditions, however, mycorrhizae assist plants in the uptake of minerals and they help protect against disease in the plants. The plants, in turn, provide the fungi with photosynthates.

My hidden message in all these stories on fungi it that we should leave the soil in it's natural state. And if it is not in it's natural state (say after years of agricultural use), then we need to return it to that state for plants to be healthy.

Scott A. Meister said...

"we should leave the soil in it's natural state. And if it is not in it's natural state (say after years of agricultural use), then we need to return it to that state for plants to be healthy."

I think I know what you're saying here...but I would venture to add that it's our job as humans to assist nature in achieving it's most productive natural state and then become good managers of it's health from that point on...for plants to be healthy, as well as ourselves, and our environment.

(soils natural state can be both productive and not-so productive, depending on the site)

The task for us then(as far as soil and plant life are concerned) is finding out exactly what nature's most productive state actually is.

This gets into the complexities of soil-biodiversity, climate, terrain, landscape, age of the soil, etc. etc.

However, Permaculture does give us a great many good ideas for this and it's exactly this topic that I'm writing about now, and will hopefully post here very soon.

Nature has it's fixes for all of our human screw-ups...and mycorrhizal fungi are just one of nature's little helpers that we can use to our advantage.

DJEB said...

Yes. Keep in mind that the survival of some species depends on environments that are less than optimal. For example, plants that only thrive in salted conditions, or land lacking in nitrogen, to give two examples. But we can certainly benefit from taking land that we have degraded and repairing that, making the soil optimal for the most number of species.

I look forward to your post.

I should note that I keep writing on mycelium because the field is now exploding. We are learning more and more each month about them. I'll no doubt be writing about actinomycetes when we start to learn more of their benefits or more about protozoa, or more about...