Illegally high levels of poisonous heavy metals found in rice grown in southern China have highlighted a lack of openness among officials charged with environmental protection and food safety, activists said this week.
Authorities in the southern province of Guangdong took the unprecedented step last week of naming rice producers whose products contained "excessive amounts" of cadmium, amid growing public pressure for transparency over the scandal.
Of 18 batches of rice tested during quarterly spot-checks, eight were found to contain excessive amounts of the carcinogenic heavy metal, the Global Times newspaper reported on Tuesday.
Samples of the tainted rice were taken from two college canteens and two other restaurants in the provincial capital, Guangzhou, and revealed readings of between 0.21 and 0.4 milligrams of cadmium per kilogram, in excess of a national limit of 0.2 milligrams, the paper said.
However, expert studies revealed as early as 2011 excessive cadmium levels in around 10 percent of rice sold across China.
Sichuan-based environmental activist Yang Yong said the rice had likely been contaminated by the water used to irrigate the rice paddies in which it is grown.
"Heavy metals can be found in water and in soil, and can be transferred into food," Yang said. "This can have a huge impact as it accumulates in the human body."
According to Xue Shikiu, a water resources management expert at the University of Florida, there are three main sources of heavy metal contamination of crops.
"The first is from natural minerals which permeate into the water supply through weathering," Xue said. "The second is from industrial pollution, and the third is pollution from various sources during agricultural production."
Some media reports focused on recent investigations in Hunan, which also revealed higher-than-permitted levels of heavy metals in rice grown near the Dongting Lake.
Experts told local media that local farmers' fertilization of the fields could be a factor.
Landfill trash for compost
A recent investigation by RFA's Cantonese Service in Guangdong found that local farmers were using trash from nearby landfill sites as compost, mixing it together with commercial fertilizers, and spreading it on their fields.
Footage obtained by RFA showed spent batteries, which contain heavy metals, spread around on fields of green, leafy vegetables.
According to Yang Yong, the contamination in Hunan could be linked to China's biggest center for phosphate mining, on the border with nearby Guizhou.
"There are large amounts of heavy metals in the wastewater and slurry produced by the phosphate mining industry," Yang said.
Official information lacking
But he said that expert opinions are often guesswork amid a widespread lack of official information about levels of pollution and possible causes of contamination.
"They very rarely make information public, and their laboratory work and testing procedures aren't reliable, either," Yang said.
"Basically, the general public has zero information on this issue ... and sometimes such information is regarded as a state secret by the authorities."
"People should be very concerned about this situation."
Worsening levels of air and water pollution, as well as disputes over the effects of heavy metals from mining and industry, have forced ordinary Chinese to become increasingly involved in environmental protection and protest, according to a 2013 report from the Friends of Nature group.
Many ordinary citizens have been prompted into action by China's environmental crisis, sparking a rise in "mass incidents" linked to pollution, while environmental groups have raised growing concerns over the falsification of pollution testing and environmental impact assessments.
Campaigners say that China has an exemplary set of environmental protection legislation, but that close ties between business and officials mean that it is rarely enforced at a local level.
Reported by Shi Shan for RFA's Mandarin Service and by Bi Zimo for the Cantonese Service. Translated and written in English by Luisetta Mudie.