主播大秀

Matthew Bannister talks to Dr Max Holmes, who has travelled to some of the remotest places in the world to analyse river water. He heads the Global Rivers Observatory at the Woods Hole Research Centre in Massachusetts.

The 主播大秀's Tahir Qadiry meets 22-year-old Sahar Parniyan. She carved out a successful career as a TV actress in Afghanistan - but when two of her colleagues were killed, she began to fear for her own life. She eventually left the country and has now settled in the UK.

We also hear from Syrian singer Yahya Hawwa. He grew up in exile, and first made his name as a religious singer. But when the Syrian uprising began, he started writing protest songs, which have been taken up by the rebels.

And as a painting known as "The Green Lady" (by Russian artist Vladimir Tretchikoff) sells at auction for a million pounds, we meet the woman who sat for the portrait: Monika Pon-su san. She is now in her late seventies and lives in South Africa.

On Witness, we hear from Albert Hofmann, the Swiss scientist who took the first ever acid trip. He took LSD by accident.