Mercury Accumulation in Sediments of the Ala Wai Canal and in Soils and Stream Sediments of the Central Honolulu Watershed

Abstract

In this study we determined the historical trend of both natural and anthropogenic sources of mercury deposition as preserved in anoxic estuarine sediments of the Ala Wai Canal, an estuary situated within a heavily urbanized area of Honolulu. Analysis of sediments from the Ala Wai Canal revealed that the total mercury content is highest at the Ala Wai Yacht Harbor (0.054-2.810 ug/g) and decreases exponentially toward the most distal portion of the canal (0.009-0.237 ug/g). In contrast, the mercury content of soil and stream samples taken from the central Honolulu watershed ranges from only 0.001 to 0.058 ug/g. This pattern suggests tidal transport of mercury into the canal from the Ala Wai Yacht Harbor. A chronological analysis of core samples shows a peak in mercury concentrations in the late 1950s, which corresponds to the use of antifouling paints on boats in the harbor and is the probable source of the majority of the mercury found in the Ala Wai Canal. High mercury accumulation ends in the early 1970s in two of the cores investigated, suggesting that antifouling paint-based accumulation ceased rapidly after the U.S. Environmental Protection Agency (EPA) ban. An exception is noted in a comparatively smaller peak coincident with 1986, the last year of a 3-yr intense fire-fountaining period of the ongoing Pu'u '0'o eruption of nearby Kilauea Volcano.