The Guardian has obtained data showing diesel cars from four major car manufacturers are emitting significantly more pollution on the road than in their regulatory tests. Tests conducted by the company Emissions Analytics show that models of Mercedes-Benz, Honda, Mazda and Mitsubishi all emit far more toxic pollution than previously thought. This comes as Volkswagen CEO Michael Horn apologized for the emissions cheating scandal in his testimony to Congress Thursday.

Michael Horn: “On behalf of our company and my colleagues in Germany, and me personally, I would like to offer a sincere apology—sincere apology—for Volkswagen’s use of a software program that served to defeat the regular emissions testing regime.”

The Guardian reported similar revelations about higher pollution emissions from cars made by Renault, Nissan, Hyundai, Citroën, Fiat, Volvo and Jeep last week. Nick Molden, whose company has tested the cars, said: “The issue is a systemic one.”