A recent study has revealed that more than half the snails fished out of southern Hong Kong waters contained excessive levels of toxic metals. The study conducted by researchers of the City University urged people to eat fewer shellfish. But the Hong Kong department of health said they were generally safe. Margaret Chan Fung, director of health, says: "Only a small proportion of shellfish was found to contain unacceptable limits of toxic metals. We can't conclude that all shellfish have excessive levels of toxic metals. We also have to look into the selection method of the study