Toxic chemical build-up in NCP, upcountry soils:

Cadmium poison threat looms

by Dr. Sarath Amarasiri

Cadmium is a Class 1 carcinogen according to the International Agency for Research on Cancer of the World Health Organization, and is also a well known nephrotoxin, meaning that it could impair kidney functions.

The WHO and the Ministry of Health concluded that cadmium is a risk factor for the Chronic Kidney Disease of unknown Etiology (CKDu) from a joint study they conducted in 2011 and 2012.

The Sri Lankan public needs to be informed about the presence of cadmium in the environment. Sri Lankan scientists need to urgently engage in research on the subject and, we need to invest sufficiently in a cadre of environmental scientists as a matter of high priority.

Much of the information given here is from published literature. The sources can be provided to interested readers via email.

Drinking water

Even in the early 1950s most of the people living in Anuradhapura district drank surface water mainly from the large number of small tanks that existed in most of the villages. It is after the Mahaveli river diversion that many people shifted to drinking well water. At present almost every farm family in Systems B and C has its own well. Many living in the cities in the district have access to pipe-borne water. It can be said that there is hardly a publication in the last five years that reported values of cadmium in drinking water that exceeded the safe limit of 0.003 mg/litre stipulated by the Sri Lanka Standards Institute (SLSI). Most of the values were less than 0.002 mg/litre.

It is likely that the cadmium content in ground water is mostly due to geogenic factors (geological processes). The anthropogenic cadmium (due to human activity) such as from triple superphosphate fertilizer (TSP) that is added to the soil surface, has to travel a long distance through top soil, sub soil, decomposing rock and other materials before reaching ground water.

In this journey the soluble cadmium can be rendered sparingly soluble. It is therefore not surprising that cadmium levels in ground water are low.

In fact many studies in other countries have shown that cadmium hardly moves below a depth of about 40 cm from the soil surface..

Although drinking water cadmium levels are lower than the SLSI limit at present, there is no guarantee that this situation will last for a long time. There is published information showing that the phosphorus levels in some of the reservoirs in Anuradhapura and Polonnaruwa districts have increased five fold from the values reported fifty years ago. This is perhaps mainly due to the use of excessive amounts of phosphate fertilizer in the upcountry. If phosphorus in the reservoir waters have increased and are increasing, it follows that although cadmium is low at present, it too may be increasing, given that all phosphate fertilizers contain cadmium.

It is not only the current values of cadmium in drinking water that have to be taken note of, but also the rate of change. The country should continuously monitor the content of potential toxins in all water bodies whether they are likely to be the causal factor of CKDu or not.

Cadmium in soil

There is hardly any published information regarding high levels of cadmium in soils reported from any part of the world arising from geogenic factors . Much of the contamination has been shown to be anthropogenic. New Zealand had a very serious cadmium contamination of their pasture lands in the 1980s that resulted in a severe crisis in the livestock industry. Investigations revealed that it was caused by the use of high-cadmium containing phosphate fertilizers manufactured from Nauru rock phosphate.

Many vegetable growing farmers in the upcountry have been adding 8-10 times the Department of Agriculture chemical fertilizer recommendation for over two decades. The main reasons for this unfortunate situation include the extremely high profits from cultivating potato and other vegetables, very low prices of subsidised chemical fertilizers and a complete breakdown of a well established agricultural extension service.The combined effect of these factors has led to the rapid build-up of soil phosphorus to an extent probably not found elsewhere in the world. More details of this agronomic, economic and environmental disaster are described in a book by the writer published in 2015 by the National Water Supply and Drainage Board (Ref 1).

Lakmalie Wijeratne in her MPhil Thesis submitted to the Postgraduate Institute of Agriculture, University of Peradeniya, (titled Soil and Crop Contamination by Toxic Trace Elements) has reported the Olsen phosphorus values of a number of soil samples collected from the upcountry and lowcountry vegetable growing lands. This is a measure of phosphorus in soil that is available for plant growth. It hardly exceeds 20 mg/kg in uncultivated lands. A value of 30-40 mg/kg soil is normally considered adequate for crops. The research findings indicated that vegetable growing farmers have added excessive amounts of phosphate-containing fertilizers in the upcountry and the low country.

There is hardly a phosphate fertilizer in the world that does not contain cadmium. The quantity however, varies widely from 3 mg/kg in Florida rock phosphate in USA to over 100 mg/kg in Nauru. There is published evidence from Australia, New Zealand and many countries in Europe showing that elevated levels of cadmium in soils have arisen from the application of phosphate fertilizers over long periods of time.

The MPhil research referred to above gives the cadmium content of soil samples collected from vegetable cultivating lands in the upcountry and the lowcountry.

In the upcountry 18 samples were studied from Seetha Eliya, Kandapola, Haputale, Bogahakumbura and Rahangala. The average cadmium value was 1.21 mg/kg. The uncultivated soil had only 0.51 mg/kg cadmium.Twenty two locations were studied at Bandaragama and Wellampitiya in the low country. The average cadmium value was 1.10 mg/kg soil. The corresponding value for uncultivated soil was 0.03 mg/kg. One could conclude from these studies that soil cadmium content of vegetable cultivated lands has increased in the upcountry and the lowcountry in recent times.

These results suggest strongly that the build-up of cadmium in soils of some areas in Sri Lanka has been caused by the addition of high levels of phosphate containing fertilizers, as has been observed in many other countries.

More than half a dozen factors can affect the cadmium content of the soil solution. They include; soil minerals, soil clays, low molecular weight organic acids, iron and aluminium oxides, chloride from potash fertilizer and irrigation water, sewage sludge and phosphate fertilizer. Research conducted on soil cadmium with respect to its chemistry and dynamics in tropical countries is scarce.

Cadmium in vegetables

The same MPhil research reports the cadmium content of above ground parts of a number of vegetables grown in the upcountry and lowcountry.

The cadmium content of carrot, cabbage, leek and lettuce ranged from 0.30 to 2.71 with an average value of 0.93 mg/kg.

The cadmium content of kang kung, mukunuwenna, sarana, spinach, thampala and gotukala was determined from 18 locations in Wellampitiya and Bandaragama in the low country. The values ranged from 0.17 to 1.10 with an average value of 0.47 mg/kg. Much of the cadmium of vegetables is very likely coming from the application of TSP fertilizer, cow dung and poultry litter.

Many countries have regulations in place to prohibit entry of high-cadmium containing fertilizers. It is only In 1988 that the Sri Lanka Standards Institute (SLSI) issued a Circular stating that phosphate fertilizers containing more than 5 ppm (parts per million) cadmium will not be permitted into the country.

Prior to that Sri Lanka may have imported hundreds of thousands of tonnes of cheap TSP fertilizer containing even more than 100 ppm cadmium because it was not illegal to do so.

However, there are publications that indicate that during the period 1988-2012 TSP fertilizer bags at different locations in the country contained 23.5, 30.8, 39.5 and 46.1 ppm cadmium, not withstanding the SLSI regulations, arousing suspicions that high cadmium containing phosphate fertilizers may have been imported illegally to Sri Lanka even up to the recent past.