Some of Dartford's key industries, including brewing, paper-making, flour milling and the manufacture of cement, suffered extreme decline in the 20th century, causing redundancies and unemployment. Swanscombe Cement Works (now redeveloped into Bluewater shopping centre) was closed by Blue Circle in 1990. This industry had been an economic boon to the area, but left behind a lot of derelict land and pollution. In 1990 Dartford contained around of spoiled land resulting from extractive industries, and cement-dust pollution from local cement works was a regular subject of complaint in the local press throughout the 20th century.