The environmental services company Clean Harbors Inc. said it has agreed to buy Safety-Kleen Inc., an oil recycler whose clients include NASCAR, for $1.25 billion, in a deal that will increase the Norwell company’s sales and profits by about 50 percent.

Clean Harbors has specialized in the field of collecting and disposing of hazardous waste since the 1980s, ­expanding significantly over that time. In what its chief executive, Alan S. McKim, called a “landmark event” for the company, the addition of Safety-Kleen launches Clean Harbors into the ­profitable oil re-refining business.