Late last month, local media reported a study conducted by a sixth-grade student, who found a florescent brightener (bleach) in 12 of the 16 samples of mushrooms bought locally. Driven in part by the media's thirst for sensation, we saw the more or less hyped headlines that more than 93 per cent of mushrooms sold in local markets had been treated with the harmful chemical to give them a fresh look.

The Beijing municipal administration for industry and commerce was quick to respond. But the response stopped at a terse statement that mushrooms in the local markets were safe, and the simple comment that the primary school student's survey was "not scientific".

But they did not publish the findings of their own survey until challenged to disclose relevant information. The official survey, said to be based on random sampling (132 samples in total), showed 97.73 percent of the mushrooms sold locally passed safety checks.

But that has failed to dispel the clouds of suspicion. Instead of a sigh of relief, we heard more questions about authenticity - how could their findings be so different?

Worse, the local industry and commerce authorities suffered a near-complete loss of public confidence in a contest with an 11-year-old sixth grader. In an online poll conducted by a website, more than 1,100 people chose to believe the primary school student, and only 8 percent said they believed the industry and commerce department.

The problem is no longer about toxic mushrooms. It is more about whether our official watchdogs are worth our trust. That the well-staffed and well-equipped official agencies whose full-time job is to regulate the market have been displaced by a sixth grader in issuing an alert - florescent brightener was also found in the official probe - should not be taken simply as an embarrassment.

It may be groundless speculation to suspect that the authorities have intentionally played down the problem out of "stability concerns". But many people tend to trust the 11-year-old, saying he was under no pressure to lie or conceal. There may be a number of variables responsible for the divergent findings. But unless convincing clarifications are made, there is little chance of the local industry and commerce administration escaping a loss of credibility.

Right now, people in Beijing desperately need evidence of their watchdog's reliability. A truthful account of the safety of mushrooms is the least they deserve.

The official conclusion must be put to stringent scrutiny because we cannot afford a watchdog giving false assurances on safety.

The author is a senior writer for China Daily.