Markey touts response to BP oil spill in second ad

The ad highlights his efforts to get BP to put a camera focused on the oil gushing into the ocean after one of its oil rigs exploded in the Gulf of Mexico.

"When BP tried to avoid responsibility, Massachusetts Congressman Ed Markey put the so-called 'spill cam' online. Ed Markey uncovered the extent of the damage and when BP executives lied, Ed Markey held them accountable," a narrator says in the ad, over shots of oil-soaked water and animals, as well as a shot of oil spewing into the ocean.

"I'm Ed Markey and I approved this message, because I believe polluters must pay," Markey says at the end.

Markey also led an investigation into BP's claims following the spill, charging that the company was downplaying the severity of the spill.  BP ultimately pleaded guilty to felony manslaughter, environmental crimes and obstruction of Congress. The company paid $4.5 billion.

But Markey has not given up the fight. Last year, he urged Republicans to hold hearings on a report on the spill.

And it's one of the strongest arguments he has in his pursuit of the seat vacated by Secretary of State John Kerry (D). Markey is known as a leader on environmental issues in Congress, and this new ad is a way for him to tout his work on the issue.

Markey's first ad also focused on his policy work, highlighting his support for increased gun control measures.

He'll face Rep. Stephen Lynch (D-Mass.) in the April 30 Democratic primary. Three Republican contenders are facing off for their party's nomination, but the seat is likely to remain in Democratic hands.