The Ram 2500 has earned the dubious distinction of being rated the world's least eco-friendly vehicle, topping the list for 2014's "dirty dozen."

Comprising solely American and European makes, the top 12 environmentally dirtiest cars for this year also include models from Ford, Mercedes-Benz and Lamborghini, Forbes reported.

The American Council for an Energy-Efficient Economy names the cleanest and dirtiest vehicles when it comes to environmental impact.

The Smart for Two Electric Drive took the top spot for eco-friendly cars with a record rating of 59 points. No Japanese brands were among the top 12 dirtiest cars; instead, automakers like Toyota and Honda dominated the earlier released eco-friendly list.

Green Score ratings are determined based on a vehicle's fuel economy and emissions, Forbes said. Tailpipe emissions can hold "health-damaging and smog-forming airborne pollutants like hydrocarbons, nitrogen oxide, particulate matter, carbon monoxide and formaldehyde, as well as greenhouse gases like carbon dioxide, nitrous oxide and methane," according to Forbes.

In comparison with the Smart for Two's score of 59, the Ram 2500 pickup earned just 18 points. The Chrysler model is closely followed on the dirty list by the Bugatti Veyron with a score of 19 and Ford's E-150 Wagon FFV, the Bentley Mulsanne and the Mercedes-Benz G63 AMG, each of which earned 21 points.

Some Ram 2500 models were recalled late last year after crashes and injuries.

Chrysler recalled around 1.2 million Ram trucks to fix front-end issues that could cause future steering problems. The automaker announced three recalls on Nov. 8, according to a company statement. One of the recalls covered approximately 294,000 Ram 2500 and 3500 trucks released for the 2008 through 2012 model years.

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