Many Guangzhou residents have been worried and angry for more than a week after being told that nearly half the rice they buy from local markets may contain excessive levels of cadmium, a carcinogenic heavy metal.
The city's Food and Drug Administration said on May 16 that it had checked 18 batches of rice between January and March and had found cadmium levels in eight of them exceeded the national food safety standard.
But it declined to disclose any information about the tainted rice, such as where it was produced and by which brands. The food-safety watchdog said it was "inconvenient" to share the information with the public but did not explain why.
The cover-up sparked a national outcry. Even some state-owned media criticised the regulator, saying the refusal to disclose the information was a crime.
After coming under a great deal of pressure, the watchdog disclosed the names of the rice producers last Saturday, but still refused to detail the amount of tainted rice sold.
The Guangzhou case is merely the tip of the proverbial iceberg in showing how reluctant mainland officials are to allow open access to government data.
The Regulations on Open Government Information, introduced by Beijing in 2007, say all levels of local government should make their non-classified information public.
The regulations set clear standards for the format authorities should follow when publishing and organising the data on their websites, because of concerns that members of the public would otherwise be unable to find the information they were looking for.
But six years later, mainland officials remain reluctant to publicise such information.
For instance, a requirement of the 2007 regulations is that different government departments should publish their non-classified information in specified catalogues.
But an ongoing study of government transparency in Guangdong shows that such data, which is supposed to include local environmental protection reports and real-time food-safety data, remains largely missing from many county government websites.
Last week, the group conducting the research - including this writer, University of Hong Kong students, and an open-data expert - spent two days investigating the websites of 27 Guangdong counties, focusing on their environmental protection information.
The results were disappointing.
We could only find vague documents called "Government Open Information Annual Reports" - regular reports by the environmental watchdogs that set ambitious goals but seldom provide any solid information.
Some county governments failed to follow Beijing's basic standard when setting up their "open government" webpages. They placed all the documents from various departments in one catalogue and provided a substandard search service.
Another problem is that many documents provided online are outdated.
But not all county officials were incapable of enacting Beijing's instructions.
Huaiji, a county in western Guangdong, had posted several dozen weekly air-quality reports online since early last year.
The reports were very simple, only mentioning the air pollution index and not explaining how it was calculated.
But it is data relevant to residents' daily lives that should be shared with them.
After opening up to foreign investors for more than three decades, the authorities are now releasing more data to the public.
To be sure, there are at least two major obstacles that officials need to overcome in making government data more transparent.
First, officials who fail to disclose key information that can significantly affect the public should be punished. The 2007 regulations include guidelines on this but the terms are very vague. But if officials can always escape punishment, no one will really follow the rules.
Second, and most importantly, the public should be encouraged to request whatever government information they need. The degree of public participation is an important criterion the World Bank uses to evaluate government transparency.
After all, governments do not generally change themselves without external pressure - meaning from the public.