Distribution of Cr, As, Se, Ag, Cd, Ba, Hg, and PB in Pacific Ocean ferromanganese nodules.
Fifty-five bulk ferromanganese nodule samples from the Pacific Ocean were analyzed for total content of Cr, As, Se, Ag, Cd, Ba, and Hg. Concentrations of Pb and other metals had been determined previously for the same samples. Cadmium and barium are correlated positively with Mn, Ni, Cu and Zn, and negatively with Fe, CO, As, and Pb. Cadmium seems to occur primarily in the 10 a manganate phase of the nodules, whereas Ba occurs at least partly in the form of barite. Chromium probably occurs in the sediments incorporated within the nodules and is correlated positively with As and Si and negatively with Mn. Arsenic and mercury are correlated with Fe, and As is also correlated positively with CO and Pb and negatively with Mn, Ni, Cu, and Zn. Arsenic and mercury are associated presumably with the iron oxide phases. Like CO, they are especially concentrated in regions characterized by seamounts and may be of volcanic origin. Silver and selenium showed no clear trends. Concentrations of the toxic elements in nodules from the region between the Clarion and Clipperton fracture zones, where deep ocean mining is most likely to occur, can be compared with the maximum levels allowed by the U.S. Environmental Protection Agency (EPA) if a solid is not to be considered a toxic waste. Concentrations of Cr, Ag, and Hg are so low that they are of no environmental concern. Levels of As, Cd, and Ba are borderline. Since Se and Pb are the most likely elements to make the rejects toxic, further studies should pay particular attention to these elements.