Environmental campaign group Greenpeace attacked the Hong Kong food safety authority last week for failing to improve testing for pesticides in fruit and vegetables imported from mainland China.
The group reported in April that it had found high levels of pesticide contamination in fruit and vegetables on sale in Hong Kong retailers.
Last week it revealed similar results for samples taken from three supermarkets in the southern China province of Guangzhou.
Between November 2005 and April 2006, Greenpeace said it had found 25 per cent of vegetable and fruit samples collected from Vanguard, ParknShop and Carrefour stores were contaminated by banned pesticides.
More than 70 per cent of tomatoes tested were found to have the banned pesticide Lindane, and almost 40 per cent of the samples had a mix of three or more types of pesticides.
Greenpeace said the test results showed that illegal pesticide is still widely used in agriculture over the region.
Furthermore, because Hong Kong imports most of its vegetables from Guangdong province, the government needs to increase its testing, said Chow Yuen Ping, assistant campaigner for food safety at Greenpeace.
"The government has admitted flaws and loopholes in the monitoring system and the need to establish a traceability system for vegetable produce. However, no further action has been taken, not even publicizing the list of accredited farms exporting vegetable produce to Hong Kong. This is not acceptable," said Chow.
Greenpeace claims that the mainland government has been more transparent way by posting a list of accredited farms to its website.
Intake of an excessive amount of pesticides can lead to acute intoxication while long time exposure can cause chronic poisoning. Many pesticides have also been identified as potential carcinogens.
China, with the lowest amount of land per person than anywhere else in the world aside from India, is under constant pressure to maximise productivity at farms. Use of pesticides is therefore significant but a weak licensing system for the chemicals and poor availability of information to farmers have contributed to numerous pesticide poisonings over the years.
John Chapple, manager of Sinoanalytica, a independent food analysis laboratory based in Qingdao, China, says depending on which vegetables are tested for which pesticides, it is not difficult to find residues on Chinese farm produce.
However Chapple believes that farmers may be using illegal pesticides unknowingly.
"There are very poor information systems for China's farmers," he said, adding that the recommended time between the application of pesticides and harvesting varies between regions, complicating the guidelines.
Export markets are however becoming ever more wary of pesticide residue, with Japan introducing new standards next month that go further than any other country.
Greenpeace also wants Hong Kong's recently established Centre for Food Safety to monitor fruit being imported from China. Unlike vegetables, fruit does not have to pass through the Man Kam To Food Safety Office across the border and there is no other monitoring of the produce.
The Centre for Food Safety said in a statement that it would "follow up reports that some vegetables in retail outlets contain excessive pesticide residue".
It added that the standards adopted in Hong Kong for the monitoring of pesticide residue in food commodities mainly followed those set by the international body, the Codex Alimentarius Commission, and criticized the tests done by Greenpeace which selected only parts of the vegetable.
"Tests should be conducted on the whole edible portion of the vegetable, which is the testing method adopted by the centre in monitoring pesticide residue in vegetables," the statement said.