First of all there are the unburned remnants of the uranium/plutonium core (and even thermonukes start with a fission core). Say, about 15-20 pounds of that, and it is pretty benign stuff unless someone breathes it. Generally it gets washed out of the atmosphere and settles out in the environment, like lead.
Then there are the "burned" components. They are isotopes of middle-weight elements, stuff like argon, iodine, barium, cesium, potassium and so on. Most will be radioactive and will disintegrate into other middle-weight elements, many of which continue to be radioactive. The problem with these is that some are preferentially absorbed into body tissues, like iodine into the thyroid gland, potassium into nerves, and cesium into muscles, where their radioactivity can become unusually damaging. They will all eventually decay, but that time can be long in human life terms.
Then there is the bomb case and other thing that were close enough to the blast to be irradiated with the blast of neutrons emanating in the instant of the blast. These aren't themselves radioactive to begin with, but absorption of neutrons can make them radioactive in a process called activation. A spectacular example of this occurs in a ocean blast, of which the US did 5 during testing in the 20th century. Water doesn't activate hardly at all, but the sodium in sea salt does. It becomes violently radioactive, but decays rapidly, to decay almost entirely within a month. After a sea blast, there is a lot of short term, very damaging radioactivity, but it drops off fast.
All these things together can be termed fallout when they are dragged into the air by the blast convection and spread over a wide area. The amounts are usually measured in a few pounds, and all radioactive materials decay over time. These can be called "toxins", though most aren't chemical toxins in the traditional meaning of the word (a few, like elemental uranium, are heavy metal toxins like arsenic and lead, besides being radioactive).
Thankfully, major water and air components (hydrogen, oxygen, nitrogen) all require multiple captured neutrons before they become radioactive, so they are largely are untouched by a nuke blast, though the random, rare atom can become radioactive.
Then there are the "burned" components. They are isotopes of middle-weight elements, stuff like argon, iodine, barium, cesium, potassium and so on. Most will be radioactive and will disintegrate into other middle-weight elements, many of which continue to be radioactive. The problem with these is that some are preferentially absorbed into body tissues, like iodine into the thyroid gland, potassium into nerves, and cesium into muscles, where their radioactivity can become unusually damaging. They will all eventually decay, but that time can be long in human life terms.
Then there is the bomb case and other thing that were close enough to the blast to be irradiated with the blast of neutrons emanating in the instant of the blast. These aren't themselves radioactive to begin with, but absorption of neutrons can make them radioactive in a process called activation. A spectacular example of this occurs in a ocean blast, of which the US did 5 during testing in the 20th century. Water doesn't activate hardly at all, but the sodium in sea salt does. It becomes violently radioactive, but decays rapidly, to decay almost entirely within a month. After a sea blast, there is a lot of short term, very damaging radioactivity, but it drops off fast.
All these things together can be termed fallout when they are dragged into the air by the blast convection and spread over a wide area. The amounts are usually measured in a few pounds, and all radioactive materials decay over time. These can be called "toxins", though most aren't chemical toxins in the traditional meaning of the word (a few, like elemental uranium, are heavy metal toxins like arsenic and lead, besides being radioactive).
Thankfully, major water and air components (hydrogen, oxygen, nitrogen) all require multiple captured neutrons before they become radioactive, so they are largely are untouched by a nuke blast, though the random, rare atom can become radioactive.