In June 2017 the top-selling premium pet food company, Blue Buffalo, was hit with a class-action lawsuit from pet parents alleging their food contained unsafe levels of lead (between 140 ppb and 840 ppb - parts per billion). For comparison, the State of California requires bottled water to contain no more than 5 ppb. You can learn more about this lawsuit here. UPDATE: A judge dismissed this lawsuit in 2018 because of a technicality - Blue Buffalo had already settled a class-action lawsuit for false advertising and apparently couldn't be sued again!
About the same time, in July 2017, a report came out from thecleanlabelproject.com showing that the presence of heavy metals may not be confined to the #1 brand. Of the 71 different brands of premium and grocery store dog and cat foods they tested an overwhelming majority contained more lead, mercury and cadmium than is allowed in US drinking water.
More recently both Champion Pet (Orijen/Acana) and Solid Gold have been hit with class-action lawsuits claiming their foods had elevated levels of heavy metals in dog and cat food. You can learn more about these lawsuits here:
What should pet parents do?
Thecleanlabelproject concluded that dog foods containing sea-based ingredients were more likely to contain high levels of heavy metals. Others theorize that heavy metal contamination is linked to the purchase of ingredients from countries with lax pollution control standards (countries like China where many pet food companies source their ingredients). Unfortunately, there is no clear answer here, so the best bet is to go with a company that regularly tests their foods for the presence of heavy metals and discloses the results.