Metal pollution in Wellington Harbour

Abstract

Sediment traps, located on the Wellington harbour floor, as well as five storm drain catchments were sampled for metal content. Included in the catchments, were their outlets on the periphery of the harbour basin. The samples were analysed for total metal content using x-ray fluorescence spectrometry and acid digestion followed by inductively coupled plasma-mass spectrometry. Bioavailable metal content was determined by extraction with 0.1 mol L-1 acetic acid. High values of Pb and Zn were found in the storm drain catchments and outlets, decreasing to elevated background rock levels in the centre of the harbour. Enhanced lead levels in the Evans Bay trap probably result from close proximity to a major road. The high values of Cu, Ba and in some cases As found in the catchments and outlets decreased to background rock levels in the harbour. Most sites exhibited background rock levels of the other metals and major elements. A comparison of As, Cr, Cu, Pb, Ni and Zn concentration averages with sediment quality guidelines, indicate that all sediment traps were below the biological probable effects levels (PEL). However the Kaiwharawhara catchment exceeded the PEL for As, Pb and Zn, while its outlet exceeded the PEL only for Pb and Zn. The Inner City and Basin Reserve catchments exceeded the PEL with As, Cu, Pb and Zn, and in the later catchment Ni values were also high. The Lambton Harbour outlets, draining these two catchments exceeded the PEL for Cu, Pb, Zn and especially As. The Miramar catchment exceeded the PEL in all six metals, with Pb and Zn being especially high. The Evans Bay outlet exceeded the level only for As, Cu, Pb and Zn. Highest overall values were recorded in Boulcott Street adjacent to the cathedral. High levels of Pb (4605 ppm), Cu (2981 ppm) and Zn (3572 ppm) may have been caused by cathedral renovations which were ongoing at the time of sampling. The highest values in the storm drain outlets were at the Overseas Passenger Terminal in Lambton Harbour. Arsenic (296 ppm), Cu (418 ppm), Pb (2158 ppm) and Zn (1508 ppm) levels were all higher than the PEL, while Cr and Ni were marginally below the PEL. The proximity of a marina and the high density of traffic along Cambridge and Kent Terrace probably accounted for the high Pb levels. A comparison of the current results with those of earlier studies show that the harbour sites display similar concentrations for most metals, although a slight decrease has occurred in Cr (at each site) and Ni at Evans Bay. However an increase has occurred in Cu, Pb and Zn levels at Lambton Harbour and Kaiwharawhara. As no temporal variations of metal concentrations in the sediment traps were detected, the averages for each trap can be used as an accurate baseline for comparison with future studies.