いろいろとみなさんからアドバイスをいただきまして、アメリカ人に
も聞いてみました。
The word you are looking for in the case of dust or most
dropped components would be 'debris.'
This is a French word (but used commonly in English) which
means 'trash.' It is a more proper
word than trash. Dropped components would be 'obstacles' if
they were liable to cause something
(a head or subsequent part) to collide with them or cause
future misplacements.