Assessing the risk of sediment-associated nickel exposure to benthic marine biota in Southeast Asia and Melanesia

The Southeast Asia and Melanesia (SEAM) region has extensive nickel-rich lateritic regoliths formed from the tropical weathering of ultramafic rocks. As the global demand for nickel continues to rise, these lateritic regoliths are increasingly being exploited for their economic benefit. Mining of these lateritic regoliths contributes to the enrichment of coastal sediments in trace metals, especially nickel. A review of tropical estuarine and marine ecotoxicity data for nickel highlighted the absence of sediment ecotoxicity data, benthic test species and the associated sediment toxicity test methods required to assess the potential impacts of sediment nickel exposure to benthic biota of SEAM. The aim of this thesis was to use a multiple lines of evidence approach to provide a robust evidence-base and risk assessment tools applicable for informing environmental risk assessment of nickel-rich estuarine and marine sediments within the SEAM region. A whole sediment bioassay based on sub-lethal effects was adapted for use with the tropical benthic marine diatom Ceratoneis closterium (Chapter 3). Effects data relevant to the SEAM region were then derived for three nickel-spiked sediments and two field-contaminated sediments. No toxicity based on chlorophyll-a concentration was observed in the sediment with the highest total organic carbon content (5%) (72-h 10% effect concentration (EC10) \u3e4,300 mg/kg dilute-acid extractable concentration of nickel). The sediments without significant total organic carbon content (1%) were toxic above 950 mg/kg dilute-acid extractable nickel (72-h EC10). The tropical benthic snail Nassarius dorsatus was also investigated for its suitability for developing a whole-sediment bioassay but was found to be relatively tolerant to dissolved nickel exposure (juvenile 21-d lowest observable effect concentration (LOEC) based on scavenging ability endpoint of 380 g Ni/L). It was concluded that a species relevant to SEAM with greater sensitivity to nickel is required to provide greater confidence that using a whole-sediment bioassay as a line of evidence in sediment quality assessment will identify sediments likely to have adverse effects. This research highlighted the need for a more strategic approach for selecting species to develop new bioassays or alternative tools for investigating contaminated sediments in the absence of sensitive whole-sediment toxicity test methods relevant to the SEAM region