Every cell phone or computer contains only a small amount of gold. But due to an ever-expanding electronics industry, according to statistics by the World Gold Council, these sectors consume more than 6 percent of the gold produced globally.

But the five biggest smartphone manufacturers on the European market – Samsung, Apple, Research in Motion, Nokia, and HTC – cannot guarantee that they are not using gold mined by children, a new reportby a Danish research group says.

This is disturbing news.

As documented by Human Rights Watch, hazardous child labor is common in small-scale gold mining in countries such as Mali, Ghana, and Tanzania. Children risk life and limb as they work underground in unstable shafts, carry back-breaking loads, and crush rocks. They regularly use toxic mercury to separate the gold from the ore.

In Mali, I spoke to “Mohamed,” a boy who said he was 12 years old and had dropped out of school. He had been working in mining for years, and explained to me that, “When you leave the mining site, and you arrive home, everything hurts, particularly the chest and the back.” He used mercury, which he obtained from a local trader, but was unaware of the health risks it carries. Mohamed climbed into 30-meter deep pits to mine. One such pit collapsed on his fellow miners, who had to be rescued.

At least Mohamed is still alive. A boy miner in Ghana, Abroso, was not so lucky. Abroso, aged 17, died in April this year when a wall in his pit collapsed. His aunt showed me his picture – he had a young, happy face.

Companies along the gold supply chain have a responsibility to ensure that none of the gold they buy has been mined by children. In recent years, companies have made increased efforts to avoid buying “conflict gold,” but they have paid far less attention to the issue of child labor. The new report highlights this important obligation and exposes the limits of companies’ due diligence procedures – with leading brands unable to state whether their gold was sourced from Ghana or Mali, where child labor in small-scale gold mining is common.

If we want our smartphones to be free of child labor, the producers will have to develop smarter due diligence procedures that reach all the way down to the origin of the gold – the mine.