I had to look up the cause, and it was because it used a high Nickel alloy for the tool steel.
I had not associated Nickel as particularly harmful, but... it's relatively nasty in regards to human health (particularly when inhaled in even small amounts).
So I was curious and scrolled down to page 81 in the linked document on this post - they do a fairly thorough walk through of the potential harms, and it's worth reading for the folks who do this at home.
I've copied the relevant regulatory warnings from the document here:
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¹Nickel salts (e.g., Ni sulphate, Ni sulphamate) carry the following human health hazard classifications under GHS: (Global Harmonized System): Acute Tox. 4 (H302: Harmful if swallowed and H332: Harmful if inhaled), Skin Irrit. 2 (H315: Causes skin irritation), Resp. Sens. 1 (H334: May cause allergy or asthma symptoms or breathing difficulties if inhaled), Skin Sens. 1 (H317: May cause an allergic skin reaction), Repr. 1B (H360: May damage fertility or the unborn child, developmental effects), Muta. 2 (H341: Suspected of causing genetic defects), Carc. 1A (H350: May cause cancer by inhalation route only), and STOT Rep. Exp. 1 (H372: Causes damage to respiratory tract through prolonged or repeated inhalation exposure). Nickel metal carries the following human health hazard classifications under GHS: Skin Sens. 1 (H317: May cause an allergic skin reaction), Carc. 2 (H350: May cause cancer by inhalation route only), and STOT Rep. Exp. 1 (H372: Causes damage to respiratory tract through prolonged or repeated inhalation exposure).