Heavy Metal Contamination from Landfills in Coastal Marine Sediments: Kiribati and New Zealand.

Abstract

Landfill leachates are a concern in the Pacific Region where they may contribute contaminants to the coastal marine environment. Poor waste management and pollution of coastal waters are amongst the major environmental problems in Kiribati, particularly in South Tarawa. An investigation of areas adjacent to coastal landfill sites; Betio, Kiribati and Auckland, New Zealand was undertaken. The Kiribati case study investigated metal contamination in marine sediments at an operational landfill while the New Zealand study was adjacent to a coastal landfill decommissioned in the 1970s. Surficial sediments (top 15 cm) were collected along transects. At both the New Zealand and Kiribati sites, 3 transects adjacent to the landfill and 1 control transect were sampled. The sediments were analyzed for particle size distribution, organic matter content, and Cd, As, Cr, Cu, Pb, Hg, Ni and Zn concentrations. The pH was also measured.

The Kiribati study site had a groundwater pH of 7.14 - 8.85, and sediment materials were dominated by sand with a low organic matter content (1.60 - 2.21 %). At the Kiribati sites Cd, As, and Ni were below the detection limits. The Cr, Cu, Pb and Zn concentrations were lower at the Kiribati control transect than the landfill transects. Cr level decreased away from the landfill indicating the landfill as a possible source. However, Cu and Zn did not show any distribution pattern suggesting other potential sources (port and shipwrecks) may have contributed to the elevated levels. At the Kiribati landfill and control transects the Cr, As, Cd, Cu, Pb, Ni, and Zn concentration were below the Effects Range-Low (ERL) and the threshold Effects levels (TEL) of the Sediment Quality Guidelines (SQCs) of the National Oceanographic and Atmospheric Administration (NOAA) and the Florida Department of Environmental Protection, indicating no potential adverse ecological effects on the biota. At the Kiribati control site the Cr, As, Cd, Cu, Pb, Ni and Zn concentrations were within the background ranges published for clean reef sediment but the concentration at the landfill transects exceeded the background ranges. The concentration of mercury at both the control and landfill transects in Kiribati exceeded the Effects Range-Median (ERM) and the Probable Effects Level (PEL) of the SQGs indicating potential adverse ecological effects on the local benthic communities.

The New Zealand study site sediments had a pH of 6.22 - 7.24, and comprised up to 90 % clay/silt, with an organic matter content of 5 - 22 %. At the New Zealand landfill transects Arsenic concentrations decreased away from the landfill indicating the landfill as a possible source. Other metals such as Cr did not show a pattern of distribution along the transects, or with depth, suggesting that the landfill was not the only source of these metals. There was a weak correlation between organic matter content, particle size distribution, and metal enrichment.

At the New Zealand site, there were no marked differences in metal concentrations between the landfill and control transects suggesting the landfill was not the only source of metals and that the wider urban or industrial run-off may have contributed. All the metal concentrations, except Hg and Zn, exceeded the ERL and the TEL values indicating the potential for adverse ecological effects of metals on the benthic communities. At the New Zealand site the Hg and Zn concentrations exceeded both the ERM and PEL of the SQGs and are considered highly contaminated.