For every tonne of chemical effluents that factories dump into China’s rivers and lakes, a comparable amount of harmful waste finds its way into this country’s water bodies from green fields and farmhouses.

A first of its kind pollution survey has found that farms have contributed as much to a growing pollution crisis in China as its famously unclean factories and industries.

The study, released by the Ministry of Environment and Forests this week, indicated that widespread agricultural pollution caused by the overuse of fertilizers has led to a level of pollution far higher than what has been previously stated in official reports.

But the survey also found that pollution levels in China will peak earlier than expected, said officials.

China’s “national pollution census” is the first official attempt to map and assess the scale of the pollution problem, which has progressively worsened along with the unprecedented economic growth unleashed by economic reforms three decades ago.

The census, which took two years to complete and involved more than 5,70,000 people, studied 6 million sources of industrial, residential and agricultural waste from all over China.

Its findings have challenged conventional wisdom on the causes of the pollution problem, and have also underscored the difficulties the government faces in addressing it, said officials and environmental analysts.

The study, which used data collected in 2007, found levels of pollution were far higher than what has been stated in earlier government reports. For instance, the discharge of chemical oxygen demand (COD), which reflects water pollution, was estimated at 30.3 million tonnes. This was more than double the level stated in a 2007 government report, which measured COD at 13.8 million tonnes.

Part of the reason for the discrepancy was that the impact of agricultural pollution had not been accounted for in earlier estimates, said Zhang Lijun, Vice-Minister for Environmental Protection.

Agricultural sources were found to account for 43.7 per cent of all COD discharge. The pollution stems from widespread overuse of fertilizers, with farmers using 40 per cent more fertilizers than required, according to a recent Greenpeace report.

The use of fertilizers and pesticides has enabled China to increase grain production eight times in the past four decades. But the use of nitrogen fertilizers has increased by 55 times, and has begun to seriously impact water pollution, the Greenpeace study found.

Mr. Zhang said the prevention and control of pollution from agricultural sources had now become China’s “top priority for environmental protection to resolve the problem of water pollution in China at the root”.

Among the survey’s more positive findings was that China’s pollution levels are expected to peak earlier than expected, according to Wang Yuqing, director of the national office for the consensus.

He said pollution levels had started falling following the restrictions imposed under the Eleventh Five Year Plan (2006-10), and that the levels would peak when the per capita income reached $3,000.

China’s per capita income, according to official figures, was $2,770 in 2008.

Environmental groups welcomed the government’s efforts to map the pollution problem for the first time, but called for stricter pollution targets.

“But it’s only the first step,” said Sze Pang Cheung, a campaign director at Greenpeace. “The Chinese government should use the statistics as the benchmark to prioritise the country’s biggest pollution issues, review current measures and policies, and set up more stringent pollution control targets in the twelfth five-year plan.”

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