GALVESTON, Tex.  As the search continued here for people killed or stranded by Hurricane Ike, the authorities said Monday that they were faced with much larger challenges than simply clearing roadways and restoring electricity before they could let residents back onto this debris-strewn island.

The sludge left in homes and on roads as floodwaters recede represents a “toxic soup” of mud, human waste, asbestos, lead and gasoline that poses serious health risks and must be removed before people return, they said.

Homes must be inspected for structural damage and for leaks before natural gas service can be restored.

And before debris can be hauled away, hazardous material has to be separated from what can be sent to recycling centers, burned or chipped into mulch.