Particle size distribution and metal content of suspended particulate matter in river and coal mine-affected water from the Fitzroy River Basin, Central QLD, Australia

This preliminary study aimed to characterise suspended particulate matter (SPM) from sites within a coal mining region of the Fitzroy River Basin, Central Queensland. SPM transported downstream may contain potential metal contaminants. Comparisons of SPM from the study area and from coal mine- affected water (CMAW) that is released into this freshwater system, have not been reported. Sampling sites included an upstream location (“Ref” site) where no coal mining has ever occurred, a CMAW holding dam, as well as five sites (2, 3, 5a, 5b and 6) that were progressively downstream of several coal mines. Sites were not controlled for prominent land uses, i.e. agriculture or cattle grazing. Samples were only collected from flowing waters. No mines were releasing CMAW at the time of the study (March 2015). SPM samples were collected on large diameter in-line filters. Nitric acid digests of samples and blanks were analysed for metals using ICP-MS. Particle size diameters of the SPM from the CMAW and from sites 2, 5a, 5b and 6 were determined using laser diffraction (no reliable readings for “Ref” (TSS=23 mg/L) and site 3 (TSS=17 mg/L) were obtained). The concentration ranges (mg/kg) of particulate metals were greater in the CMAW sample than in the six river water site samples, although the filter digestion method requires further validation. Site 2 (TSS = 69.0 mg/L) had the lowest concentration of metals and the largest particles (D10=14.3µm, D50=65.4 µm and D90=289 µm). Sites 5a (TSS= 170 mg/L) and 5b (TSS=174 mg/L) - the head and tail waters of a weir - exhibited similar PSD (D10, 50, 90 = 0.295, 0.828, 7.76 µm and 0.299, 0.860, 11.5 µm, respectively). The PSD of the CMAW was: D10=1.96, D50=12.0 and D90=222µm. Mixing studies in the laboratory using the CMAW sample and river water (site 5b) are being conducted to elucidate further the changes that may occur during a CMAW release into the receiving river.