Recycling is supposed to be good for the environment. But if it’s not carried out properly, certain kinds of recycling  notably the dismantling of electronic circuit boards, which contain lead, zinc, copper and other metals  can cause environmental harm.

It can also be dangerous to human health, as a new study of electronics recycling in China shows.

Anna O. W. Leung and Ming H. Wong of Hong Kong Baptist University and colleagues went to the town of Guiyu in southeastern China, home to a cottage industry of family-run recycling workshops. These are typically set up inside homes, where family members melt the tin-lead solder on the boards to remove chips and other components for sale, with only small household fans for ventilation.

The researchers collected surface dust samples in and around these workshops, at local markets and schools and in other nearby residential areas.

As reported in Environmental Science and Technology, they found extremely elevated levels of lead, zinc and other metals in the workshops. Lead levels, for example, were up to 2,400 times commonly accepted optimum levels.