Federal investigators say a former tenant of a Boise apartment complex may be the source for the mercury that prompted a full-scale cleanup now in its seventh day.

Environmental Protection Agency crews began removing the hazardous metal last week after children were found playing with it outside the complex. Officials estimate they have recovered between 12 and 14 ounces of mercury, and on Tuesday began ripping up a concrete driveway and sidewalk to lower mercury levels.

EPA officials say the search continues for the former tenant neighbors contend had mercury, a poison especially harmful to children.

The cleanup could cost between $100,000 and $200,000. (AP)