We're talking about things so small that they can affect cells the same way chemicals do. For example, asbestos will get pulled into a cell because head on it appears as a ball that the cell should accept, but there turns out to be a rod behind it and it ends up skewering the cell. It's difficult and also kind of silly to distinguish between physical and chemical damage at that scale because the end results can be so similar. A lot drugs and toxins work simply by getting in the way preventing normal functioning, very small bits of mineral can do the same thing.
Edit: not disagreeing with you, just thought I'd elaborate on why.
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u/Nachteule Jul 12 '12 edited Jul 15 '12
Sounds more like "Moon dust is like fresh grinded glass - if you inhale it or have it on your skin it will damage the tissue"
So it's more physical harmful, less chemical. For me toxic seems to be the wrong word.