Using plants as bio-scavangers of metal toxins in water and soil.
Posted on December 16th, 2013

Chandre Dharmawardana

Last October when I was in Colombo I gave several talks in symposia on Kidney disease, one of which was at the Gannoruwa Instittute of agriculture, while another symposium was at the Professional Institute in Colombo. I also raised this question of water hayacinth-like plants (water hayacynth, Japan jabara, lotus root etc), or even Murunga, and their capacity to extract and concentrate toxins from polluted water. This point has been raised by many others as well.

In principle, such plants can be used to “clean the water”. In practice this is NOT TRUE.  What do you do with the plants that have now collected all the toxic  heavy metals? Are you going to put the plants back into the soil, or disperse them in the ecosphere, or burn them? None of them will work as the pollution will just go back to the water table. You have to physically bury them in deep pits, or compound them in bitumin, or drop them in the ocean — all costly steps. So Dr. Yapa, a well respected  scientist previously at  Sri Jayawardenapure University, has looked at the problem partially, but has not discussed the final steps.

The same issue of getting rid of the waste matter arises with the reverse-osmosis process advocated in seminars by various  people and various NGOs like Sarvodaya. When 1000 litres of water are purified using reverse osmosis, 200 litres of highly polluted water remains in the reverse-osmosis machine. Now, where do you dump that water ? Do you dump it back to the soil? That will not do.

What we need to do is to cut the problem at the source. The source is the fertilizer runoff from the hill country, coming along the Mahaweli, and polluting all the water bodies connected to the mahaweli via the “accelerated mahaweli” project, and other similar irrigation projects which link agriculture and drinking water.

These problems did not exist prior to 1977. After the “open economy”
fertilizer sales became unregulated. The problem is not with the fertilizer, but with excess use where 5 to 10 times the required amount is used, and this gets washed off to our rivers like the Mahaweli, and end up in the drinking water. Testing form cadmium, arsenic etc in the drinking water shows no significant amounts of these ions, (as the WHO study found), because the culprit is not those ions, but the excessive fertilizer run off made up of phosphate, potassium, nitrate etc. The fertilizer runoff adds to the already hard water in the Rajarata. The resulting high salinity (i.e, the ionicity) of  the water destroys the inner layers of the kidney, just as brakish  water corrodes anything. Once the kidney is corroded, the small amounts of As, Cd etc., that are always found in any environment enters the body and the body accumulates them, just as the kidneys do. The resulting kidney desease ultimately killes the patients. When you analyze their organs, they too are found to have accumulated As, Cd, etc, just as some plants (that do not have the capacity to filter out the toxins) do.

So,fertilizer should be controlled by the agriculture department. The govenment should issue  to the farmers only the recommended amount of fertilizer (as was done in the 1970s) and stop the free sale of fertilizers. Then, after a few monsoons, the soil will be clear of the contamination.

The majority of plants don’t have special fitration mechanisms like the kidneys. So such plants can be used as a means of monitoring the water as it is easy to analyse in the laboratory, the more concentrated toxin present in the plant. I pointed this out in my talks at Gannoruwa and Colombo, and of course, this is not a completely new idea and I am sure other have thought of it. But trying to use them for cleaning all the water in the rajarata ecosystem is, in my view, not feasible and extremely expensive. In any case, we want to grow paddy or vegetables, and not japan jabara or Salvinia.

 The sale of fertilizers should be controlled, and fertilizer subsidies should also be stopped . The money saved can be used to help the affected farmers. If the excess use of fertilizer is used, we also save foreign exchange, and regain our pure water system. The digging and selling of  Eppawala phosphates should be stopped as the soil is already over saturated with phosphate.

5 Responses to “Using plants as bio-scavangers of metal toxins in water and soil.”

  1. Lorenzo Says:


    Will the govt. do it?

  2. Vijendra Says:

    Chandre is absolutely right in that the source of the water contamination by fertilizer run off should be controlled rather than waiting to clean up the water down stream.

    Having said that, the water already polluted may also need cleaning up, if feasible. There is a lot of know how on the getting rid of slag and sludge available, particularly in the mining industry. As you may be aware, even radioactive waste is being rendered safe for disposal under special conditions, by encapsulating it in cement blocks. Of course, it is vital to stop the material getting into the water in the first instance, just as the saying goes, “a stitch in time saves nine”.

    Those using fertilizer must be educated so that they will use the right type and amount of water after having carried out soil tests, so that they will not only get the best bang for the buck, but also will not pollute our waters. It is nice to see that Chandre has spent time and effort to educate our local people while he is on holiday in SL. We certainly have good brains in SL. I hope our own local university researchers are actually doing some research concerning this problem of “Rajarata kidney disease” and not waiting just twiddling their thumbs until “foreign experts” from WHO come and provide solutions our local problems.

  3. Vijendra Says:

    I am sorry for an error in my post above. The third paragraph, first sentence should read as follows.

    “Those using fertilizer must be educated so that they will use the right type and amount of fertilizer after having carried out soil tests, so that they will not only get the best bang for the buck, but also will not pollute our waters by exceeding the real requirements.”

  4. Fran Diaz Says:

    Mr Chandre Dharmawardana’s article is the best I have read on the subject, certainly the most concentrated and pragmatic article.

    I myself wrote about the Reverse Osmosis method as it is best method known to clean already contaminated water. The waste water produced along with contaminants is usually sent into the rest of the waste water system of the city or town. Some smaller cities and towns in USA have the Reverse Osmosis method used for the entire city or town. I have no idea what they do with the large amounts of contaminated water resulting from such methods – I guess it is put into the sea or lakes, which is not the right way to do things. Once in the sea or lakes, the contaminants will pollute the fish and other life and plants there. In some parts of the world, the larger fish like Tuna are already carriers of Mercury. Mercury poisoning is deadly to human beings. On a another related topic, we still use Mercury amalgam in our teeth calling it ‘silver fillings’. The newer ‘white fillings’ are much safer.

    We agree that use of fertilizer and pesticides ought to be highly regulated by the government. Should the larger users of fertilizers &/or Pesticides require a permit or license ? All must be trained users.

    Harmless Organic fertilizers can be made locally and is bound to be very popular. It will prove to be a lucrative business. There are also other ways to control pests, through crop rotation, and use of herbs being the more popular methods. There are other ancient methods used by the Sinhale for pest control.

    But is is curious that even heavy fertilizer/pesticide run offs from the Central Province can contaminate the water table of adjoining Provinces without affecting the CP people at all.

  5. Ben Silva Says:

    Thank you Prof. Dharnawardana for this article. The problems caused by agrochemicals will be far more than that caused by terrorism and it will last longer. The best solution may be to harvest and store rain water for consumption. Reverse osmosis will create highly toxic waste that will eventually go back into the environment. Harmful agro chemicals should be banned and enforced properly. People need to be educated about the harmful effect of certain agro chemicals. THOSE THAT DAMAGE THE ENVIRONMENT OUGHT TO BE FINED.

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