In Mauritania, it is thought that up to 600,000 men, women and children, or 20% of the population, are slaves, and that many of them are used as bonded labour. Slavery in Mauritania was made illegal in August 2007. In Niger, there is also much slavery. A Nigerian study has found that more than 800,000 people are slaves, almost 8% of the population. Child slavery has commonly been used when making cash crops and mining. According to the United States Department of State, more than 109,000 children were working on cocoa farms alone in Côte d'Ivoire (Ivory Coast) in 'the worst forms of child labour' in 2002.