A bit of googlework found this:
http://www.rfreitas.com/Astro/SearchIcarus1983.htm
Nothing was found, but the faintest they searched was 14th
magnitude. I have no idea what the size would be of a sooty, dull
black object at L5 that was 14th magnitude. I know that 14th
magnitude isn't very bleedin' bright, like some people I've met.

http://www.creationscience.com/Asteroids2.html
This is an interesting site, wherein it is claimed that Noah's Flood
created the asteroids and comets. (!?!?)

http://www.asme.org/events/flight/hiten.shtml
A Japanese spacecraft named Hiten actually looped through L4 and L5,
looking for concentrations of dust. None were found.

http://www.google.com/search?hl=en&q=l5+trapped
The Google page itself. Includes links to a lot of articals about
back pain.

So, the stuff has been looked for and not found, but there might
still be something there. It might still be worth looking, but big
chunks are out.

>Includes links to a lot of articles about back pain.<

Here's a version without the back-pain stuff.
http://www.google.com/search?hl=en&lr=&safe=off&q=l5+OR+l4+trapped+-
lumbar&btnG=Search

Right - looks like any big stuff is out.

Thanks for the search.

--- In spacesettlers@yahoogroups.com, "Xenophile"