Deuterium toxicity does exist, but you’d have to ingest a hell of a lot of it, not trace amounts via breathing. The symptoms mimic radiation poisoning, although since deuterium isn’t radioactive, it isn’t actually that.

deuterium poisoning

https://en.wikipedia.org/wiki/Heavy_water#Effect_on_biological_systems

Deuterium is toxic (in high concentrations) to multicell animals as it changes the angle of.the hydrogen bonds which is key to cellular replication and enzyme prodcution. However you would have to drink all d2o instead of h2o for about a week to begin to notice (need 25-50% of body water). Blocking cellular replication is similar to what chemotherapy does so would.be like bad chemo...eventually the dose is so large it is not useful Cancer drug.

There is also mentions of dizziness and impact on vestibular system (senses) but not the wiki article does not expand on this and the linked article just mentions nystagmus (involuntary eye movements)
https://ui.adsabs.harvard.edu/abs/1974Natur.247..404M/abstract

https://en.m.wikipedia.org/wiki/Heavy_water

Interestingly there is also a theory it may affect circadian cycles in some insects https://www.ncbi.nlm.nih.gov/pmc/articles/PMC433660/ (which could impact sleep pattern in humans)

All in all it looks like the writers may have looked into it afterall.

Yeah when you have "refinarey", mysterious signal, it was well hinted, then acts of sabotage it did seem that way and when the other victim was focussed on jestisoning the gas from the nacel seemed even more certain

I mean, I think it's just reality-adjacent technobabble and you've got to accept it as plausible in universe. Tritium is a real thing used in nuclear fission but it's not so rare that you should don robotic arms and go on a crime spree to get some. On a more Star Trek adjacent topic, protostars are a real thing but (at least as far as we know) you can't shove them in a box to travel ludicrous speed.

@deweydecibel @ValueSubtracted

That's frankly what caught my attention, even as I was watching the episode. The decision turns out to have been right, but on thin-to-nonexistent justification.

They could have fixed that by analyzing the signals in her brain in such a way that they could actually show to Pike.

The Bussards are an emergency backup system for use when fuel replenishment via tanker is not possible, and are not normally active.

From the TNG Technical Manual (for the Galaxy class, but one can safely assume operations haven’t changed that much):

In the event a deuterium tanker cannot reach a Galaxy class starship, the capability exists to pull low-grade matter from the interstellar medium through a series of specialized high-energy magnetic coils known collectively as a Bussard ramscoop. Named for the twentieth-century physicist and mathematician Robert W. Bussard, the ramscoop emanates directional ionizing radiation and a shaped magnetic field to attract and compress the tenuous gas found within the Milky Way galaxy. From this gas, which possesses an average density of one atom per cubic centimeter, may be distilled small amounts of deuterium for contingency replenishment of the matter supply. At high relativistic speeds, this gas accumulation can be appreciable, though the technique is not recommended for long periods for time-dilation reasons (See: 6.2). At warp velocities, however, extended emergency supplies can be gathered.

[my emphasis]

In those three places there are the qualifiers “in the event…”, “contingency” and “emergency”, which indicate that the Bussard collectors are only activated when needed and are not always on.

The reason is simple: the amount of deuterium that can be gathered is usually in negligible amounts unless you’re in proximity to a dense source of the element, like in a nebula. So it’s just not energy efficient to keep the collectors on all the time.

Half of all TNG episodes started with them being amazed looking at a relatively common phenomena. Those old scientists were just passionate about their job.