When the bomb, containing plutonium 239 manufactured at Hanford, exploded over Nagasaki a cloud formed and traveled northeast over the Nishiyama district, home of the cities' reservoir. Black rain is a term used by the survivors of the bombings in Japan to describe the nuclear fallout that ensued. In 1946 the area 15 kilometers east of Nagasaki had more residual radiation than the hypo-center of the blast. There are still high levels of Hanford manufactured plutonium 239 and censium in the Nishiyama reservoir area. In 1995 the bodies of Nishiyama residents were found to have unusually high levels of cesium-137. This is believed to be from the cesium fallout that was stored and consumed in the plants and vegetables grown in personal gardens.

References

http://www.idealist.ws/atomicclock.php

http://books.google.com/books?id=2-zsny77v5kC&pg=PA40&lpg=PA40&dq=Nishiyama+black+rain&source=bl&ots=A1ZoFKMPnT&sig=noIF49RzXb-vn0WQCaxwZ1bU_oU&hl=en&ei=KUiyS-_yJ6LgtAPkvYjMBA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CA0Q6AEwAjgK#v=onepage&q=Nishiyama%20black%20rain&f=false