NUSA DUA (AFP) -- Millions of discarded mobile phones and computers are posing a ""major challenge"" to human health, the chief of the United Nations Environment Program said on Thursday.

Achim Steiner told a UN conference on waste management on the Indonesian resort island of Bali that 20 million mobile phones were thrown away each year in China.
Meanwhile, the global number of personal computers was expected to double to two billion by 2015.
""The rapid growth and rapid redundancy of all this equipment ... represents a major challenge to the international community in terms of human health and the environment,"" he said.
He said 20 to 50 million tons of electronics waste was produced every year -- enough to load a train that would stretch around the world.
""The growth in electronics is unlikely to abate any time soon, especially as disposable incomes rise in the rapidly developing and developing economies.""
Much of this waste was ending up in landfills usually in developing countries in Africa and Asia, where it leaks chemicals and heavy metals into the environment, Steiner said.
""This is effectively long-distance dumping,"" he said.
The disposal of massive numbers of unwanted electronics goods has been a key focus of the five-day meeting of parties to the 1992 Basel Convention on waste management that began Monday.
More than 1,000 delegates from 170 countries are taking part in the talks to review the impact of hazardous waste on human health and livelihoods.
The Basel Convention is an international treaty that regulates the global trade in hazardous waste and aims to minimize its generation and movement across borders.
Participants were expected to adopt a ""Bali Declaration"" aimed at highlighting the importance of health and waste management to global development strategies, such as reducing poverty.