Nyodene D chemical in White Noise is not real but is fictional. The substance doesn't exist in real chemical world.

Don DeLillo created a fictional toxin chemical as one of the primary contexts of his book. In the novel, the chemical is said to be a whole bunch of things that have been mixed that are the byproducts and waste material of the insecticide manufacturer.

He presents the toxin as a chemical that can cause tumors in healthy rats when examined. The creator makes symptoms of toxin as nausea, skin irritation, sweaty hands, and vomiting, along with persistent feelings of déjà vu, which are eventually replaced by coma, convulsions, and miscarriages. 

Though the toxin reaction sounds much more dangerous for the present world, we still need to remember that the toxin only exists in an imaginary world.

Don got all his inspiration for the poison from a real-life event he saw on television. Don's only motive for creating this kind of toxicity in his novel is for people to be alert for those situations.

Due to this toxin, people seem to have a mass panic situation. People immediately follow the route of government-assigned places. But the impact of the symptoms and the eventual loss of life due to the toxins make people do unimaginable things that makes them question their morality.

People are so engrossed in the morality of society people throw away the facade of morality when it comes to the way of survivability. And we can see such examples in the novel.

The second part of the novel is depicted as an Airborne Toxic Event. The connection of both parts is related to morality.

The first part of the novel shows Jack, a college professor who specializes in the field of Hitler Studies but is also frequently wonderer and fearful of demise. It is "Waves and Radiation," where readers are introduced to Murray Jay Siskind, a friend of Jack's and a fellow professor at the college.

Both Jack and Murray discuss the theory of dying, supermarkets, and other topics, along with the morality of the human being. With the start of the toxic event, Jack, who is afraid of the end forced to choose between his morality and his fear of extinction above life. 

Even when his sons believe the danger of the toxic explosion event is massive and the family needs to evacuate, he puts his morality first, talking about him being a professor and a chair of the department who cannot flee from events such as toxic accidents. 

Jack had thought that the event of the accident was a minor issue until they received a government warning for the harmful impact of the toxic that had gone airborne. Only after the warning he believes that the event is not minor and decides to leave his morality when the survivability kicks in.

This event in the second part of the novel links to the first part, showing that the man who is obstinate about morality can change in front of the loss of life.