Shipment of waste from country to country can also involve dumping waste into the ocean. Ocean dumping has been a problem since the 19th century. In the United States, it was legal to dump industrial waste into the ocean until the Ocean Dumping Act was passed in 1972. During the years of 1970 and 1980 alone, it was estimated that 25 million tons of waste including scrap metal, chemicals, and acids were dumped into the ocean. Ocean dumping can lead to eutrophication which depletes the oxygen from the water, in turn killing marine life. Ocean dumping is placed into three lists: Gray List, Black List, and White List.