Trace metal contamination of soils and sediments in the Port Kembla area, New South Wales, Australia

Transcription

1 University of Wollongong Thesis Collections University of Wollongong Thesis Collection University of Wollongong Year 2009 Trace metal contamination of soils and sediments in the Port Kembla area, New South Wales, Australia Yasaman Jafari University of Wollongong Jafari, Yasaman, Trace metal contamination of soils and sediments in the Port Kembla area, New South Wales, Australia, Master of Environmental Science - Research thesis, School of Earth & Environmental Sciences - Faculty of Science, University of Wollongong, This paper is posted at Research Online.

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3 Chapter 3 Materials and Methods 3.1 Sample Collection: Core samples: Three core samples were collected from undisturbed northern parts of Lake Illawarra (Figure 3.1) using a petrol operated vibracore and tetra-pod extraction system. Samples were placed in a cool room for about two weeks at 4 C to minimize sample degradation prior to analysis Grab Samples: Ninety five topsoil samples were collected within four regions (Port Kembla, Warrawong, Lake Heights and Cringila) across the Illawarra, NSW, between July and December 2008, using a small spade to take suitable representative amounts of soil, (Figure 3.1). The study area is situated 80 km south of Sydney, NSW, and was home to a copper smelter (which ceased operation in July 2003), steelworks and fertilizer plant among other lighter industry. Previous studies have indicated soil contamination, primarily in the nearby urban areas surrounding the copper smelter (Beavington, 1973; Martley et al., 2004). The Port Kembla area was chosen for this study due to its location downwind from the industrial complex in an urban setting. Samples were collected from open grassed areas, roadside and other potential sources of metal contamination. Furthermore, four, four and one sample(s) were collected from Permian basalt, Permian sandstone and a Tertiary basalt dyke respectively, to determine natural background trace element levels. Soil texture varied from sand to silty loam, sandy clay loam to clay Sample preparation and analysis: Laboratory techniques: In the laboratory, cores were measured and a brief description of sedimentary characteristics of the cores was prepared, noting distinct changes in colour, the type of sediment and shells present. Cores 1 and 2 were divided into one-centimetre intervals from 33

4 Figure 3.1: Sample locations in the study area. The area north of the geological boundary is underlain by Permian basalt whereas the area south of the line represents Permian sedimentary rocks. 34

5 the top 50 cm length of each core. Thereafter, twelve and five additional samples were taken from the remainder of the cores 1 and 2, respectively, especially where marked changes in composition were noted including higher amounts of clay and shell particles. Core 3 was divided into one-centimetre intervals up to 50 cm length of the core and twocentimetre intervals to 85 cm length of the core. Thereafter, four more samples were taken from the rest of the core containing typical shell assemblage (core photos in Appendix 2). Samples were placed in polyethylene lined aluminium containers and placed in an evaporating oven at 80 C for a period of 3 days to ensure that samples were completely dry. Grab samples were placed in polyethylene lined aluminium containers after a quick search to remove plant parts and rocks and put in an evaporating oven at 80 C for a period of a few days to ensure that samples were perfectly dry. Samples were then removed from the oven and crushed using a tungsten carbide TEMA mill until the sediment was crushed to an homogenous powder. Samples were recovered from the TEMA and placed in re-sealable sterile bags. Between the crushing of the samples, the TEMA was washed with tap water and dried with paper towel and a dryer. This was completed in order to prevent cross-contamination of samples. Production of a homogenous powder is important for XRF analysis in order to minimize systematic error with respect to particle effects Grain Size Analysis: A portion of each soil sample collected in the field was kept in a plastic bag in order to prevent the samples from drying. Using a Mastersizer 2000 particle size analyser and its software, small quantities of soil were then analysed to establish the percentage of sand (63µm-2000µm), silt (3.9µm-63µm) and clay (< 3.9µm) present within each soil sample, taking three readings and averaging these to provide an average for each soil sample Trace element analysis using X-Ray Fluorescence Spectrometry: Approximately 5.5 grams of crushed, fine, homogenous powder was combined with about 10 drops of polyvinyl alcohol binder in a paper cup using a wooden coffee stirrer. 35

6 After mixing, the sediment was placed in an hydraulic press where the sediment was pressed at 2500 p.s.i forming a robust pellet. The pellets were left to oven dry at 80 C for a period of up to 2-3 days and then weighed. Each sample was placed into the chamber of an energy dispersive X-ray fluorescence spectrometer, where they were analysed against a suite of calibration standards Bioavailability experiments: Dilute Hydrochloric Acid Extraction: First, all laboratory glassware was cleaned with nitric acid, rinsed with deionised water, rinsed with 0.1 mol/l HCl and rinsed again with distilled water followed by drying. About 25 ml of 0.1 mol/l HCl were added to 2.5 g of each soil sample in a 50 ml centrifuge tube. The tubes were screw capped and shaken for 15 minuets on an end-overend shaker and then, centrifuged for about 20 minutes. Thereafter, the supernatant of each tube was decanted into a 50 ml propylene bottle through a pre-washed filter paper for XRF analysis (Page et al., 1982). EDTA Extraction Protocols: A 0.05 mol/l EDTA extractant was prepared as an ammonium salt solution as follows: in a fume cupboard, ±0.05 g of EDTA free acid were added to 800±20mL distilled water and partially dissolved by stirring in 130±5 ml of saturated ammonia solution. The addition of ammonia was continued until all the EDTA was dissolved. The obtained solution was diluted with water to 9.0 ± 0.5 L and the ph was adjusted to 7.00 ± 0.05 by addition of a few drops of ammonia as appropriate. Then the solution was diluted with distilled water to L, well mixed and stored in borosilicate glassware. Extractions were carried out according to the following procedure: All laboratory glassware was initially cleaned with nitric acid, rinsed with distilled water, rinsed with 0.05mol/L EDTA, and rinsed again with distilled water and dried. Then, 25 ml of 0.05 mol/l EDTA were added to 2.5 g of each soil sample in a 50 ml centrifuge tube. The tubes were screw capped and shaken for 15 minutes on an end-overend shaker before being centrifuged for another 20 minutes. The supernatant from each 36

7 tube was decanted into a 50 ml propylene bottle through a pre-washed filter paper for XRF analysis (Quevauviller et al., 1998) GIS map for sample locations: Latitude and longitude of each sample location were taken in the field using a Garmin GPS72, the Australian Geodetic 66 Datum and UTM UPS. These data were added onto a GIS map through the ArcGIS Desktop program to obtain exact locations for each sampling site (Figure 1.2) Normalised trace element concentrations in sediment samples: Trace metal concentrations in each sediment core were normalised to the portion of silt and clay (C m = metal concentration in 100% mud) using Excel software to show more uniform patterns for assessing metal concentrations in the cores. C m = Measured metal conc. * 100 (100 sand %) Statistical Analysis: Correlation coefficient analyses were applied using the Excel software in order to determine the strength of association between parameters analysed in the samples. The parameters include trace metal concentrations, rubidium concentrations and grain size. Strong associations (i.e., higher values close to one) between parameters define linear relationships, which can be used to indicate that compared components hold a close association to each other. This can be used to indicate whether components like metal species originate from the same source (e.g., industrial discharges) or diffuse sources (e.g., urban runoff, McGinn, 2001). 37