In the protected Calanques National Park, where turquoise blue water sparkles in the sun, extensive work has begun to clean up the southern coastline of Marseille, which has been contaminated for two centuries by various industrial activities. The greyish deposits clash with the idyllic landscape of limestone rocks bordering the Mediterranean. These materials, known as slag and containing high levels of lead and arsenic, are residues from former factories that were used as road fill for the construction of roads and car parks during the 20th century. IMAGES AND SOUNDBITES