Black substance appearing in fridge

[fan-of-fans]

We have a 1995 Kenmore (made by GE) top freezer fridge. A while back I noticed a small amount of black dirt-like residue on the top left shelf. I took everything out of the fridge including the shelves last month and did the annual deep clean. A few days ago I looked in there and noticed this black dirt was in a line down the back wall of the fridge and on the right shelf also were several spots of it. Looking closer, on the bottom of the box where the controls are, there is a metal plate on the bottom with holes. It seems this black dirt stuff is coming from there.

Any idea what this is? Never seen it before until the last year or so.

 

[cfz2882]

foam strip crumbling?

could be some foam weatherstrip is crumbling and producing the particles?...I have a 1991 GE built Kenmore

 

[arbilab]

Mold likes to be black.