brand logo

Toxic elements in dry zone paddy soil have little impact on CKDu rates: Studies 

22 Dec 2021

  • National/international researches note most levels of trace elements in rice/rice growing soils within acceptable levels
BY Ruwan Laknath Jayakody  Hundreds of studies carried out by various national and international researchers thus far have confirmed that the impact of toxic elements in rice or rice paddy soils on the incidence of chronic kidney disease of undetermined origin (CKDu) in the dry zone of Sri Lanka is negligible, as most of the levels of trace elements in rice or rice growing soils are within the acceptable levels, Senior Professor in Geology at the Peradeniya University’s Science Faculty’s Geology Department, Prof. Rohana Chandrajith claimed. This observation was made by him in his capacity as an Associate Editor of the Ceylon Journal of Science’s Editorial Board in an editorial on “Paddy farming, fertiliser, and CKD with an undetermined origin” which was published in the Ceylon Journal of Science 50 (4) in December 2021.   CKDu, according to Chandrajith, S. Nanayakkara, K. Itai, T.N.C. Aturaliya, C.B. Dissanayake, T. Abeysekera, K. Harada, T. Watanabe and A. Koizumi’s “CKD of uncertain aetiology in Sri Lanka: geographic distribution and environmental implications”, is devastating agricultural communities in many other countries in the tropical equatorial belt, not solely Sri Lanka. The disease is reported to affect farming workers such as paddy farmers in Asia and sugarcane workers in Latin America, who work in hot and humid climates. In certain areas in the dry zone of Sri Lanka, over 10% of adult farming communities are affected by this new form of kidney disease, per P. Vlahos, S.L. Schensul, N. Nanayakkara, Chandrajith, L. Haider, S. Anand, K.T. Silva and J.J. Schensul’s “Kidney progression project: Protocol for a longitudinal cohort study of progression in CKD of unknown aetiology in Sri Lanka”.  After identifying this new entity of kidney disease in the mid-1990s, a large number of research studies, Chandrajith noted, have been published describing clinical, pathological, geo environmental, and socio economic aspects of the disease and they proposed over 65 possible aetiological factors; yet the risk factors hitherto remain inconclusive.  Dehydration and environmental exposure to toxic trace elements such as Cadmium (Cd), and Lead (Pb) have been considered, Chandrajith observed, as possible aetiological factors for the emergence of CKDu that is widespread in certain pockets in the dry zone areas. Based on the histo pathological (the diagnosis and study of diseases of the tissues) studies, the epidemic of CKDu is considered, per Chandrajith, as a phenotypic (relating to the observable characteristics of an individual resulting from the interaction of its genotype [an individual’s collection of genes] with the environment) environmentally induced disease that may contribute from environmental, occupational, and social factors.  Since the majority of these patients are involved in rice farming-related activities, few studies have argued that, Chandrajith mentioned, the application of agrochemicals could be the cause behind CKDu, although it is much debated. Since contaminated rice can be a vehicle of toxic elements, rice grains, rice growing soils, and fertilisers were investigated in detail during the last few years. Modern agriculture in Sri Lanka mainly depends on the use of fertilisers and pesticides that can, Chandrajith added, affect the soil quality detrimentally while severe deterioration in the soil quality may lead to the permanent degradation of land productivity. Rice farmers in the dry zone are believed to, Chandrajith reported, use an excessive amount of agrochemicals and in wrong blends.  Nitrogen (N) and phosphates (PO₄³⁻) can adversely affect the soil water system in areas where paddy farming is widespread, Chandrajith elaborated. In Sri Lanka, chemical and mineral-based fertilisers are widely used in rice cultivation. Urea (CO[NH2]2), Ammonium Sulfate ([NH₄]₂SO₄), Triple Superphosphate (TSP), and Muriate of Potash (MOP) are regularly used in paddy farming. TSP contains the major plant nutrient Phosphorus (P) but also consists of many other trace elements of which some are toxic, according to Dissanayake and Chandrajith’s “Phosphate mineral fertilisers, trace metals and human health”. “In general, the apatite (a group of phosphate minerals) mineral structure may include heavy metals (metallic chemical elements that have a relatively high density and are toxic or poisonous at low concentrations) such as Arsenic (As), Cd, Chromium (Cr), Mercury (Hg), Pb, Selenium (Se), Uranium (U), and Vanadium (V). Additionally, certain heavy metals can be introduced as impurities from Sulfuric Acid and Phosphoric Acid that are used in the manufacturing processes of TSP. Therefore, the long term application of agrochemicals may result in the accumulation of trace metals in agricultural fields”.  According to Chandrajith, their recent investigations indicated that the content of trace elements in mineral-based fertilisers such as TSP is higher than in chemical fertilisers. “In general, trace metals such as Zinc (Zn), Nickel (Ni), Copper (Cu), Iron (Fe), Titanium (Ti), Strontium (Sr), and Manganese (Mn) are available in elevated concentrations in TSP. For instance, impurities in TSP fertilisers in Sri Lanka were found to contain up to 46.1 milligrams per kilo (mg/kg) of Cd by S. Balasooriya, S. Diyabalanage, S.K. Yatigammana, O.A. Ileperuma and Chandrajith’s ‘Major and trace elements in rice paddy soils in Sri Lanka with special emphasis on regions with endemic CKDu’,” Chandrajith further explained.  Per Chandrajith, the problem is compounded by the fact that very low quality fertilisers are imported into Sri Lanka due to the absence of proper control mechanisms.  “Although fertilisers are used excessively in paddy farming, islandwide surveys carried out recently (Balasooriya et al., R.T. Rubasinghe, S.K. Gunatilake and Chandrajith’s ‘Climatic control of major and trace elements in paddy soils from the wet and dry regions of Sri Lanka’), indicated that rice paddy soils are not exceptionally contaminated with heavy metals. In these studies, 102 soils samples collected from the main climatic zones, namely, the wet and dry zones, including CKDu hotspots, were analysed for their trace element contents. Although As, Cd, and Pb contents are moderately enriched in both climatic zones with respect to their background levels, the geo accumulation index assorted that the paddy soils were uncontaminated to moderately contaminated, implying that rice paddy soils are not alarmingly contaminated with toxic trace elements.  “Higher P levels were noted in paddy soils from CKDu hotspots in the dry zone. The long term application of TSP, organic fertiliser, and animal manure leads to the accumulation of P in rice paddy soils. Similarly, 17 to 298 mg/kg of P with a mean of 156 mg/kg were also found in the highly agricultural regions of Nuwara Eliya in E.A.G.S. Amarawansha and S.P. Indraratne’s ‘Degree of P saturation in intensively cultivated soils in Sri Lanka’, indicating the availability of extractable P in both rice and vegetable soils. In general, the need for Olsen (a Phosphate extraction method) extractable P for optimum crop production is less than 30 mg/kg while it has been proved that some plants perform well under higher (48 mg/kg) P in soil, per J.P. Kirthisinghe, D. Kumaragamage and F. Sultanbava’s ‘Evaluation of site specific fertiliser recommendation for cauliflower in two locations in Sri Lanka’. Nearly 60% of paddy soil and 46% of garden soils in the CKDu hotspot of Wilgamuwa showed higher extractable P content than the 48 mg/kg cut-off, per Balasooriya et al.,” Chandrajith further elaborated.  In order to provide sufficient nutrients to the soils which are regularly used for cultivation, it is, Chandrajith explained, required to add fertilisers as otherwise the crop yield becomes drastically depleted. Without an excessive yield, the requirement of foods to feed millions cannot be fulfilled. It is well known that most Sri Lankan farmers use higher than recommended amounts of fertiliser, intending thereby to improve the economic benefits.  “Therefore, controlling the use of fertilisers for crops needs to be thoroughly monitored by the responsible authorities. Most importantly, the regular and continuous monitoring of fertilisers imported to the country is important, particularly for mineral-based fertilisers. In addition, soils in rice paddy and other agricultural fields need to be monitored regularly, thereby providing for the required nutrient levels to be recommended,” Chandrajith concluded.


More News..