New York -- The Institute of Scrap Recycling Industries (ISRI) is helping New York City officials ensure that all recyclable material removed from the World Trade Center site is recycled through the proper channels, following numerous reports that organized crime families were stealing the metal for profit.

Most of the recyclable material now is being sent to the Fresh Kills landfill in Staten Island, where investigators inspect the material and send it to a contracted scrap processor.

ISRI has asked government officials to provide lists of all companies that have contracts with the city to remove recyclable materials from the site.

Meantime, New York city officials have hired four private investigation firms to monitor work at the site, and the Manhattan district attorney's office is conducting a grand jury probe into organized crime-related truckers who allegedly stole tons of scrap metal and sold it, instead of transporting it to Fresh Kills.

According to an ABCNews.com report, at least five of the trucking companies being used to haul wreckage from the site are on a list of city vendors involved in alleged corruption or have ties to organized crime.

"We don't have any firm information about continuing violations along these lines," New York City investigation commissioner Ed Kuriansky told ABCNews.com, "but we want to ensure it doesn't happen."