This seedling kind of reminds me of a sick little E.T. all ghost-white and pitiful. But what you see there is diatomaceous earth. It's not a chemical; it's actually the crushed cell walls of unicellular algae. Diatoms live in water and when they die they sink to the bottom and form a crust of diatomaceous earth.
The powder is actually made up of lots of jagged edges from the perspective of a tiny little insect. The powder has a dessicating effect on insects that spend too much time in it. It's not pleasant, I know. But I put it on potatoes, tomatoes, and eggplant to keep flea beetles from killing the seedlings. I use it for a short period of time in the spring before my plants are flowering. Once it rains, it's useless, so it's pretty labor intensive in that you must reapply it after each rain.
Over the years I've continued to use it because it keeps the flea beetles from killing or devastating seedlings. I haven't heard too many people talk about using it. I know it's pretty horrible to breathe on a regular basis. It's fairly cheap. I feel better using it than just about any other pest control (besides structural things and crop rotation).
I put my eggplant seedlings in the ground one afternoon and by the next day all of the leaves looked like they'd been shot with a shot gun. The flea beetles were hitting them pretty hard, so I've been dusting them regularly. They've managed to put out two or three healthy leaves each. When they've got a good healthy start, I'll back off and hope the plants can weather a little munching.