KOLKATA, 13 FEB: The state public health engineering (PHE) department has invited experts from across the world to tour the four districts affected by arsenic seeking suggestions for the use of modern technology to tackle the problem. Apart from visiting the four districts ~ North 24-Parganas, Nadia, Murshidabad and South 24-Parganas ~ experts will also visit the three districts partially-affected by arsenic ~ Bankura, Purulia and West Midnapore.