Abstract
Metals are bound to a different phase in sediment and that speciation reflects their bioavailability for an organism. The speciation of Cu and Ni in sediment in Benoa Bay, Bali was not well investigated. Thus, this study was aimed to determine Cu and Ni speciation in sediment from Benoa Bay, Bali and to assess their mobility. Sediment samples were collected from 11 observation points (stations) in Benoa Bay in March 2017. Modified BCR (Community Bureau of Reference) protocol was applied to extract different Cu and Ni species in the sediment namely metal associated with carbonate fraction (F1), iron/manganese oxide (F2), organic and sulfides (F3) and mineral (F4). The result revealed that Cu was dominantly associated with mineral (>50% of Cu in F4), therefore, Cu resembled the lithogenic origin. Opposite, Ni was associated with carbonate and iron/manganese oxide almost in all observation points indicating anthropogenic origin. Risk assessment code (RAC) was computed to determine the possibility of that Cu and Ni to be released. The computation of RAC indicated Cu was at low-risk level and Ni was at a medium to high-risk level to be released. However, the total Cu and Ni were below sediment quality guideline so the level of metals was at a minimum possibility to stimulate adverse effect to an organism. The spatial distribution of Ni in the bay reflected the anthropogenic source thus the activity should be well managed to control the contamination.