Complex sentence: 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.
Split into simpler sentences: In 1990 Dartford contained some of spoiled land resulting from extractive industries. Cement-dust pollution from local cement works was a regular subject of complaint in the local press throughout the 20th century.