Eight persons returning after a day-long picnic were killed and seven others were injured when their pick-up van collided head on with a truck in West Bengal's Nadia district on Sunday, police said.The accident occurred around 5.30 p.m. at Jugpur Bazar on National Highway 34.The injured have been admitted in a local hospital.Four of the injured were in serious condition, said Nakashipara police station officer-in-charge Mukul Mia.The victims were returning after a picnic party at Bethuadahari.