Cuts, bruises, infections and fights with wild pigs and dogs are daily occupational hazards for 13-year-old Yashoda and 10-year-old Rukrnini. Along with their mother, aunt, grandmother and 12,000 other women and children from their slum in Pune, India, the sisters set off early each morning for nearby rubbish dumps, where they earn their living recycling others' trash.

Up to 2 per cent of the developing world's urban population survives by scavenging. They come from the most disadvantaged and vulnerable segments of society. Each day 20,000 waste pickers scour every square metre of Calcutta's municipal dumps, sorting and collecting bottles, cardboard, plastic, metal and other materials for reuse and resale. This scene is recreated each day in rubbish sites from Cairo and Manila to Lagos, Lima and Baghdad.

Work-related disease, injury and social stigma all take their toll - in Mexico City, dumpsite pickers have a life expectancy of 39 years, compared with 67 years for the general populace. Pay generally varies but rarely rises above $2 a day (one notable exception is Beijing, where rubbish pickers make three times the salary of university professors).

Encouragingly, scavenger cooperatives are springing up across Latin America and Asia to empower the poor, combat exploitation and reward entrepreneurial initiative. Once organized, many groups are able to negotiate reasonable prices for their goods from middlemen and even win contracts from local governments. In Colombia, a non-governmental organization called the Fundación Social helps rubbish pickers to form cooperatives and provides grants, loans and legal and business advice to newly formed ventures. Similar networks are in place in Argentina, Brazil, India, Indonesia, Mexico and the Philippines.