The organisation that campaigns for protection of the environment tested a small selection of vegetables, mostly green leafy vegetables and others like tomatoes that tend to absorb pesticides, sold in the Parknshop and Wellcome supermarkets between November 2005 and March 2006.
More than 70 per cent of the 55 samples contained pesticide residues, and 30 per cent (17 samples) of these exceeded 'international standards', it said in a statement last week.
One Choi Sum sample collected in a Wellcome store was found to have pesticide residues at 240 times the EU standard.
Greenpeace said it also discovered banned pesticides including DDT, HCH and Lindane in five of the samples.
"In one tomato sample from Parknshop, five different pesticides, including an illegal type Lindane, were found," said the organisation's food safety assistant campaigner Chow Yuen Ping.
Almost 80 per cent of the vegetables sold in Hong Kong come from mainland China, particularly from Guangdong province, so the report raises once again the problematic issue of China's pesticide use.
"We decided to test supermarket products because consumers tend to trust the quality of products coming from supermarkets and their sales are expanding very fast," a Greenpeace spokesman told AP-Foodtechnology.com.
"But our results show that pesticides are still a problem," he said.
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 Qingdao-based food analysis laboratory, said the Greenpeace findings are "nothing new".
"I'm not at all surprised by the results but it's a question of interpretation," he told AP-Foodtechnology.com.
Depending on which vegetables are tested for which pesticides, it is not difficult to find residues on Chinese farm produce, he explained.
However Chapple believes that farmers may be using illegal pesticides unknowingly, while DDT could be coming from the environment and contaminating soil.
"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.
The Greenpeace report looks set to put additional pressure on Chinese suppliers by increasing scrutiny of vegetables imported into Hong Kong. Both Hong Kong's government and the two supermarkets concerned by the tests have said they will step up testing.
On Sunday, Wallace Lau, Hong Kong's principal of health, welfare and food bureau said food inspectors and customs officials will now require every truck crossing the border to submit samples for pesticide testing.
Currently tests are only carried out on between 70 to 80 per cent of vehicles crossing into Hong Kong at Man Kam To, near the border with Shenzen, according to a government official, quoted by Bloomberg.
But both Greenpeace and Chapple are critical of the quick testing method carried out at the border, which cannot analyse samples for all kinds of pesticides.
"Instead there should be selective testing as early as possible, prior to harvesting, and as near to the farm as possible," said Chapple.
Greenpeace said there is "an urgent need for Parknshop to expand their farm-checking and surveillance system to non-leafy vegetables such as tomatoes" while Wellcome should implement "a full-scale reform on their monitoring in order to identify and fix the loopholes".
It added that Wellcome, owned by Dairy Farm International Holdings, a unit of Jardine Matheson Holdings, has already stopped using one of its mainland Chinese suppliers as a result of the report.
Greenpeace is currently testing samples from vegetables sold in mainland China, with results expected in coming months.