N-(phosphonomethyl)glycine a widely used herbicide better known as glyphosate, could be helping carry heavy metals toxic to kidneys, occurring naturally and in agro-chemicals such as phosphate fertilizer, the researchers said.
Chronic kidney disease of unknown etiology (CKDu) first appeared in Sri Lanka's rice growing areas in the north central province in the 1990s and has been spreading into other areas including the South, with over 20,000 estimated deaths so far.
Glyphosate was originally used as a de-scaling agent to clean out calcium and other mineral deposits in hot water systems, the study said. De-scaling agents tie themselves to on metals like Calcium and Magnesium and makes them water soluble.
It was later sold as a herbicide by US-based Monsanto under the brand name 'Round up' and was under patent until 2000. By 2012 China became the largest producer of glyphosate in the world.The mystery kidney disease is mostly found in areas with 'hard' ground water (water containing Calcium, Magnesium, Strontium and Iron and other chemicals) except in Sri Lanka's northern province where the ground water is also hard.
But in the Northern Province agro-chemical use was banned until the end of a civil war to prevent them being used to make bombs until a few years ago and there was no CKDu epidemic there yet, providing evidence to a recent agro-chemical link, the paper said.
Other researchers have earlier found Arsenic in hair and nails of victims and even healthy individuals in the affected areas.
The researchers cite findings saying the affected rice growing areas are naturally rich in heavy metals including Nickel, Chromium, Cobalt and others.
Triple-super-phosphate (TSP) fertilizer used in farming was also found to contain heavy metals and Arsenic.
"...[W]ithin a couple of weeks after the spraying of glyphosate farmers apply triple phosphate (TSP) to the paddy fields," the researchers said.
"Recent findings have shown that the TSP available in Sri Lanka is contaminated with significant amounts of Cd (Cadmium), Cr (Cromium), Ni (Nickel) and Pb (lead).
"Furthermore, it was also found that TSP used in Sri Lanka is a very rich source of arsenic."
The paper cited anecdotal reports of shallow wells that have become increasingly contaminated and being abandoned by farmers.
The disease was also not found in people drinking from natural springs which had no hard water and pipe-borne water.
The chemical could also be ingested into the body through other ways.
The researchers said farmers in Sri Lanka do not use protective gear and glyphosate is also dissolved in hard water before spraying. They have detected Glyphosate in their urine after spraying.
The compound can be breathed in and get into the body through the skin after dissolving in sweat, the paper said.
Other research had found Cadmium and Arsenic in rice and tobacco grown in Sri Lanka. Farmers also ate rice as a staple and also chewed tobacco.
"The phosphorous atom in the phosphonic group in the glyphosate/AMPA molecule can possibly be replaced by As (Arsenic)," the researchers said.
"Following dermal and respiratory absorption of glyphosate, it can form complexes with nephrotoxic metals and As derived from rice, vegetables and tobacco within the circulation."
A similar epidemic has been found in Andra Pradesh in India where the ground water was also hard. But hard water is not usually associated with kidney toxicity. In Sri Lanka also, though hard water has not received much attention earlier.
"The inability to detect glyphosate-metal complexes using the commonly used analytical methods may have deterred the investigators in both Sri Lanka and Andra Pradesh from looking further into the role of these compounds in CKDu," the researchers said.
The authors had used a special Enzyme Linked Immuno-Sorbent Assay (ELISA) test to detect these glyphosate-metal complexes.
The researchers said glyphosate being advertised as a magic week killer which was environmentally friendly and degraded quickly may have led to it being ignored.
Further animal studies were needed but it was not done due to a Buddhist philosophy in Sri Lanka, the paper said.
The findings may also help solve mystery diseases in other countries, the researchers suggested.
A similar kidney disease has also been found among farmers in Central America's pacific coastline including El Salavador, Nicaragua and Costa Rica.
"The disease is common in sugarcane cultivating areas in CA (Central America) where some of them previously used to grow cotton," the paper said.
"Both sugarcane and rice belong to the grass family and need a comparatively higher amount of agrochemicals in large-scale cultivation.
"Glyphosate is the leading pesticide used in El Salvador as well. If we apply the same hypothesis to explain the CKDu in CA it can logically explain the occurrence of disease among male farm workers in pacific coastal line."
Other reports have suggested that agro-chemical use in Sri Lanka is the highest in the world.
The Island newspaper quoted Shanthi Mendis, a professor at World Health Organization who also studied the disease as saying that Sri Lanka had to probe the issue as quickly as possible and develop remedies.
The newspaper quoted WHO/UN data which said Sri Lanka used 471 units of agro-chemicals, the highest in the world, made up of 187 Units of pesticides, which was also the highest in the world and 284 units of fertilizer, which was the 8th highest in the world.
Others were; Bangladesh (431U), Jamaica (397U), Dominican Republic (358U), Costa Rica (357U) and El Salvador (355U).
Sri Lanka had a state policy of pushing rice production especially after 1977, when vast areas of forest were cut down for r with massive irrigation projects to support it. The state also subsidizes chemical fertilizer in an unprecedented scale.
Domestic food prices are also kept high through import taxes and carbohydrate consumption other than rice is discouraged through high taxes which affect poor people most.