Mineralogy of metal contaminated estuarine sediments, Derwent estuary, Hobart, Australia: implications for metal mobility

Abstract

The mobility, bioaccessibility and transfer pathways of metals and metalloids in estuarine sediments have been the focus of much detailed research. However, to date, few studies have examined the mineralogical siting of metals and metalloids in such sediments. This is despite the fact the mineralogy of sediments is an important factor that controls which and how much of a particular metal is released to pore waters and overlying water columns. This study reports on the mineralogical siting of metals in contaminated estuarine sediments, Hobart, Australia, and aims to evaluate the mobility of metals in the contaminated substrates. Mineralogical, mineral chemical and bulk chemical analyses demonstrate that the sediments contain very high levels of several metals and metalloids. The contaminated sediments have concentrations of zinc (Zn), lead (Pb), copper (Cu) and cadmium (Cd) ranging from 0.55 to 4.23 wt%, 0.16 to 0.70 wt%, 415 to 951 mg/kg and 23 to 300 mg/kg, respectively. Franklinite and lesser sphalerite are the main repositories of Zn, whereas much of the Pb and Cu is hosted by sulfides, organic matter and undetermined iron (Fe) oxides. While the release of contaminant loads from franklinite through dissolution is likely to be insignificant, even small releases of metals from the highly contaminated sediments can still cause the deterioration of local water quality. The contaminated sediments represent long-term sources of metal pollutants, particularly Zn, to local waters. This study demonstrates that mineralogical analyses are a vital tool to recognise the potential mobility of trace metals in estuarine environments.

河口沉积物中金属和非金属的流动性、生物可接近性及运移通道一直是很多研究的重心。然而，到目前为止，很少研究涉及这种沉积物中的金属和非金属的矿物定位，尽管事实上沉积物的矿物学特征是一种重要的控制排放到地下水和上层水体中的金属种类和金属量的因素。该研究报道了澳大利亚Hobart受污染河口沉积物中金属的矿物定位，其目标是检测受污染基底中金属的流动性。矿物学、矿物化学和大量化学分析显示，沉积物中若干种金属和非金属的含量很高。污染沉积物中锌、铅、铜和镉的含量范围分别为0.55-4.23wt%、0.16-0.70wt%、415-951mg/kg及23-300mg/kg。锌铁尖晶石和稍少的闪锌矿是锌的主要载体，而大量铅和铜含于硫化物、有机物和氧化铁中。虽然从锌铁尖晶石经溶解作用释放出的污染物可能量很少，但尽管这样，从高度污染的沉积物中释放出的少量金属也会造成当地水质的下降。污染的沉积物代表了金属污染物（特别是锌）长久地进入当地水体。该研究显示，矿物学分析对识别河口环境中微量金属的潜在流动性很关键。

KEY WORDS:

• zinc
• franklinite
• sequential leach
• lead
• copper
• metal siting
• mineralogy
• contamination
• Derwent estuary.

关键词:

• 锌
• 锌铁尖晶石
• 顺序浸淋
• 铅
• 铜
• 金属定位
• 矿物学
• 污染
• Derwent 河口

ACKNOWLEDGEMENTS

The authors thank the following people: Mark Stalker (Veolia Services) for donation of time and equipment during the sampling of the Derwent sediments; John Gibson and Kerrie Swadling for use of the hammer corer; Ashley Townsend, Ian Little and Jay Thompson for conducting the compositional analyses on the samples and aiding in the composition of the methods section; Sandrin Feig and Karsten Goemann for their aid in the microprobe and SEM analyses and aiding in composition of the methods section; Selina Wu for the SWIR analyses; Anita Parbhakar-Fox and Nathan Fox for XRD analyses targeting jarosite; Stafford McKnight for QXRD analyses; Bernd Lottermoser and Ashley Townsend invaluable comments on early drafts of the manuscript; Nick Ramshaw, Todd Milne and James Burke of Nystar Hobart for their aid in detailing the past practises of the smelter; Christine Coughanowr and Jason Whitehead for their edits of the manuscript. Thank you also to Tony Morrison and an unnamed reviewer whose insightful comments greatly increased the quality of this manuscript. We also thank Karsten Goemann, Bernd Lottermoser and Janina Micko for their translation of the sequential leach method into English.

Notes

Table modified from that used by Scheinost et al. (2002).

() indicate that the metals were not analysed for and are estimated using the sum of the percentages of the other analyses such that the total equals 100%. ^a1 M NH₄NO₃; ^b1 M NH₄OAc (pH 6); ^c0.1 M NH₃OHCl + NH₄OAc (pH 6); ^d0.025 M NH₄-EDTA (pH 4.6); ^e0.2 M NH₄-oxalate (pH 2.6); ^f0.1 M ascorbic acid + 0.2 M NH₄-oxalate (pH 2.6); ^gdigested using a HF-sulfuric acid digestion in the PicoTrace high pressure digestion system.