A few years ago a newspaper report (Sunday Times, 2013) stated that Sri lankan rice took second place in a twelve-country list of rice containing high amounts of the toxic metal known as cadmium. Many people even now claim that Sri Lankan rice has excess cadmium (Cd), and that this must be a recent problem because “our fore-fathers” ate three meals of rice with no Cd toxicity showing up.
In my view, the actual circumstances are very different. There has probably always been cadmium in our soil, and in our rice. Yet it is quite safe to eat, for a number of reasons, as seen from a most recent study of the chemical components in rice published by researchers in the geology department of the Peradeniya University led by Prof. Rohan Chandrajith and by Dr. S. Premarathne of the agriculture department. In the Geology department study they compared the cadmium dietary load for residents of the dry zone (DZ), intermediate zone and the wet zone (WZ). In fact WZ-rice is found to have more cadmium than DZ-rice.
This study shows that although there seems to be significantly more Cadmium per kilo of rice than the safe limit stipulated by regulatory agencies like the WHO, there is also a thousand times more Zinc (Zn) in the rice. Now, it is known that Zn completely inhibits the toxic action of Cadmium. An excellent simply worded review of Cadmium toxicity and mitigation by zinc is given in the following link: ARL : Cadmium Toxicity
For instance, oysters and other sea foods containing quite high amounts of cadmium are allowed to be sold in European markets as long as they have an access of Zn. Having a thousand-fold excess of Zn atoms over each Cadmium atom is like having a thousand guards to keep check of a single criminal. Zn is good for the human body in the amounts present in rice and other food stuffs of Sri Lanka. In fact, a recent study by S. Premaratne (Ph.D thesis, Dept of agriculture, University of Peradeniya) shows that not only rice, but most Sri Lankan vegetables have this protective shield of Zn in them, when ever there is cadmium in them.
Hence, because of the presence of Zn, all varieties of Sri Lankan rice are probably very safe. Another
substance which competes with cadmium and nullifies its toxicity is selenium. The Peradeniya team has shown that Sri Lankan rice has not only Zn with its well-known protective action, but also selenium.
Further more, all the cadmium in rice cannot be absorbed by the body, because usually more than half the cadmium is in a form that is not available to the body. Such bio-unavailable cadmium is excreted out of the system. So only about 50% of the cadmium content in rice is relevant, and this is in any case neutralized by the presence of zinc and selenium.
In my view, the Cadmium in our soil may not be anything new, and is a result of geological processes. It could have been there even in ancient times, but with a “protective shield” due to the presence of Zn in the rice, just as it is the case today. In 2013 we did not know that there were such protective shields (i.e., presence of Zn and Se) in our rice. Hence there has been much speculation and even worry that there is a definite health risk all over Sri Lanka due to dietary intake of cadmium via rice and other foods. In fact the WHO and NSF (national science foundation) sponsored study (2013) of kidney disease in the North Central Province speculated that the kidney-disease epidemic may be linked to ingestion of cadmium-containing food. At that time it was not known that Sri lankan foods contained zine, i.e., a protective element against cadmium toxicity.
In my view, recent studies, and especially the recent work of the Peradeniya geology and agriculture researchers have done much to dissipate such fears.
Please remember that prior to this cadmium scare, there was much fan fare about there being arsenic in Sri Lankan rice, and this was even claimed to be a communication to the effect by God Natha. However, subsequent research has shown that there is no significant amount of arsenic in our soil or water, even in the Rajarata villages stricken with chronic kidney disease.
What about cadmium contaminated “cheap” fertilizers brought into Sri Lanka? Let us consider as an example, a shipment contained, say, 50 milli-grams of Cd per kilo of fertilizer (while the allowed amount is an order of magnitude smaller).
It is normal to apply 25 kilos of fertilizer per hectare of land. If the fertilizer is spread into the soil to a depth of 15 cm, the total soil volume is 1.5 trillion liters. Its dry weight would be roughly 0.5 trillion kilos.
The total amount of cadmium per kilo will be (25×50) mg of cadmium divided by the soil dry weight. Thus we find that even a sample of “highly cantaminated fertilizer” only adds 2500 nanograms of cadmium per kg of dry soil. This is thousand of times smaller than the WHO threshold for soil contamination with cadmium, and it should take five to ten centuries for the soil to become Cd-toxic via the application of fertilizers. Note that if we allow for monsoonal wash away and other effects, it will take even longer to have any ecological impact. Hence the claim sometimes made, that cadmium in soil is a recent problem due top the use of cheap contaminated fertilizers is completely untenable.
So, in my view, Sri Lanka rice is safe to eat, and even good to eat as its ingestion is accompanied by the ingestion of adequate amounts of zinc and selenium into the body.
A majority of scientists and Nephrologists do not believe that there is a “cadmium threat” in Sri Lanka although there may be some long-term hazard. They believe that the kidney disease rampant in the North Central provice is casued by the consumption of contaminated water in shallow household wells used by poor farmers who live at a significant distance from reservoirs (Weva), rivers and irrigation canals. Those who use use water from tanks, rivers and canals do not contract kidney disease, although they consume the same rice and vegetables as those farmers who use their own well water and get kidney disease. Hence a small program of providing water to farmers where rain water is harvested has been introduced and seems to be a successful method.
However, only a few rainwater storage tanks have been installed so far due to lack of funds, as much of the government funding has gone to the installation of expensive reverse-osmosis (RO) machines. The cost of each such installation is sufficient to help about 200 times as many affected people via the rainwater collection project.