What is the difference in meaning between these two sentences?

Question

He went on to talk about pollution

vs.

He went on talking about pollution

Answer 1

The first means that he was talking about something else and turned the subject to pollution.

The second means that he had talked about pollution, and continued to do so.

Answer 2

As per the definition of Oxford Dictionaries, "go on to do something" means "​to do something after completing something else". e.g., "After her early teaching career she went on to become a doctor."

https://www.oxfordlearnersdictionaries.com/definition/english/go-on-to-do

"He went on to talk about pollution." It means that he talked about pollution after he had talked about something else.

As per the definition of Oxford Dictionaries, "go on doing something" means "​to continue an activity without stopping". e.g., "He said nothing but just went on working."

https://www.oxfordlearnersdictionaries.com/definition/english/go-on-doing

"He went on talking about pollution." It means that he continued to talk about pollution without stopping".