Children of the Black Hole

His skin is caked in toxic black soot, his lungs poisoned - and, at the end of the day, he'll wash in one of the world's most polluted rivers.

Biplob is five years old. Others working alongside him in a bamboo and corrugated iron shack are a little older. Mugba is seven, Dania 10.

This is the Black Hole in the Bangladesh capital Dhaka - a huddle of riverside factories where children work taking apart old batteries for recycling.

They don't go to school. Instead, for 50 hours a week and a wage of £1, they bash away at the batteries with metal mallets. After the batteries are taken apart, the insides are heated in furnaces to separate the lead, mercury, zinc and cadmium.

But the children have no face masks - meaning the toxic fumes quickly fill their lungs. Life expectancy in Bangladesh is 50. But these kids will be lucky to see 30. Exposure to mercury and lead causes nausea, chest pains and, in extreme cases, seizure and coma.

And there's another danger - the Buriganga river yards from the factory. It's full of waste and sewage and its waters give you diarrhoea, hepatitis and typhoid. Yet it's here the kids wash themselves after a shift in the factory - and to escape the 40degC heat.

Just as relentless are the deliveries of old batteries. As soon as they arrive on carts, factory boss Agba unloads them. He has to work quickly because in a week the carts will be back to collect the recycled parts ready for shipping to China, where they are used in cheap clocks and radios.

Agba is stuck in the same cycle of poverty as his workers. His own daughter Poppy, 10, works at the factory. "I'd prefer for her to go to school but I have no choice," he says. "Her mother is ill so Poppy has to help so we have money for food. We try to teach her at home but often we're too tired after work. I wish there was another way but this is the life we have."

It's a miserable existence - and precarious too. The Black Hole is one of a dwindling number of battery factories in Bangladesh.

Falling demand means fewer firms are bothering to recycle batteries. Agba says: "You work week to week and hope the delivery arrives. But part of me wishes they would stop. Then perhaps I'd have to find some other way to make money."

'Working without masks choking, toxic fumes fill their tiny lung'