The influence of dissolved organic carbon on the potential bioavailability and toxicity of metals to tropical freshwater biota

Melanie Trenfield (2012). The influence of dissolved organic carbon on the potential bioavailability and toxicity of metals to tropical freshwater biota PhD Thesis, School of Medicine, The University of Queensland.

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Author Melanie Trenfield
Thesis Title The influence of dissolved organic carbon on the potential bioavailability and toxicity of metals to tropical freshwater biota
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2012
Thesis type PhD Thesis
Supervisor Jack Ng
Barry Noller
Scott Markich
Rick van Dam
Total pages 203
Total colour pages 18
Total black and white pages 185
Language eng
Subjects 050206 Environmental Monitoring
050204 Environmental Impact Assessment
Abstract/Summary The influence of DOC on the toxicity of U and Al to three Australian tropical freshwater species (for U: the northern trout gudgeon, Mogurnda mogurnda, the green alga, Chlorella sp. and the green hydra, Hydra viridissima and Al: the cladoceran Moinodaphnia macleayi, Chlorella sp. and Hydra viridissima) was investigated. Two DOC sources were assessed: (i) Suwannee River fulvic acid standard (SRFA) and (ii) local DOC sourced from Sandy Billabong water, Northern Territory, Australia. The influence of SRFA on U toxicity was studied at 0, 1, 5, 10 and 20 mg/L DOC in synthetic Magela Creek water (SMCW). Uranium toxicity to M. mogurnda (96-h survival) was approximately four times lower in SMCW containing 20 mg/L DOC than SMCW devoid of DOC (the concentration that results in 50% survival relative to the control response (LC50), increased from 1550 to 7200 μg/L). Chlorella sp. (72-h population growth rate) was the most sensitive of the organisms to U, with toxicity being reduced 16 fold in the presence of 20 mg/L DOC compared with 0 mg/L DOC (an increase in IC50 from 40 to 650 μg/L). For H. viridissima (96-h population growth), U toxicity was reduced seven fold with the addition of 20 mg/L DOC (the IC50 increased from 65 to 470 μg/L). For E. gracilis an additional 20 mg/L DOC in the form of SRFA, reduced U toxicity by three to five-fold (an increase in IC50 from 57 to 254 μg/L. Uranium toxicity in Sandy Billabong water (SBW) assessed at 0, 1, 5 and 10 mg/L DOC showed U toxicity was halved for M. mogurnda and H. viridissima at 10 mg/L DOC compared to DOC-free water (M. mogurnda IC50 increased from 1730 to 3100 μg/L and the IC50 for H. viridissima increased from 50 to 113 μg/L). For Chlorella sp. in SBW containing 10 mg/L DOC there was a 12-fold reduction in U toxicity IV compared to toxicity in DOC-free test waters (the IC50 increased from 13 to 150 μg/L). Mechanistic studies exposing the unicellular eukaryote Euglena gracilis to U at background DOC in the presence of a reactive oxygen stress (ROS) probe, indicated U toxicity (inhibition of cell growth and cell death) may be linked to U-induced oxidative stress. ~15% of E. gracilis cells exposed to 60 μg/L U, fluoresced in the presence of an ROS probe and at 1 mg/L U, this proportion increased to ~23%. Chemical characterisation of Sandy Billabong fulvic acid (SBFA) and SRFA (elemental composition, molecular weight and proportion of functional groups) found they were similar, but differences in acidity of the FAs led to initial conclusions that SBFA had a weaker proton binding affinity than SRFA. The equilibrium constant for U-SRFA (log K of 6.8) was adapted to a log K of 4.94 for SBFA, based on the differences in acidity of the FAs. HARPHRQ speciation calculations suggested the decrease in U toxicity with increasing DOC was primarily due to a decrease in UO2 2+ and UO2OH+ through complexation with each DOC source. SBW was initially predicted to complex less U than SRFA. For SBW, HARPHRQ predictions of U-DOC complex were within 4% of measured UDOC using flow field-flow fractionation combined with inductively coupled plasma mass-spectroscopy (FFF-ICP-MS). Results suggest that in billabong surface water containing 10 mg/L DOC and 90 μg/L U, around 10% of U could be bound as UDOC. However revised speciation modelling suggested this could be as high as 80%. The toxicity of Al was assessed at pH 5 in the presence of each DOC source at 1, 2, 5 and 10 mg/L DOC. H. viridissima was most sensitive to Al. In the presence of SRFA at 10 mg/L DOC, the toxicity of Al to M. macleayi, Chlorella sp. and H. V viridissima was reduced up to 8-fold compared to its toxicity at 1 mg/L DOC. In SBW containing 10 mg/L DOC, Al toxicity was reduced up to 4-fold compared to Al toxicity at 1 mg/L DOC. Of the test organisms, Chlorella sp. showed the most pronounced response to DOC in terms of reduction in Al toxicity. Decreased Al toxicity was best attributed to a decrease in Al3+ and AlOH2+ through complexation by DOC. Speciation modelling suggested almost 100% of Al could be bound to FA in billabong surface water containing 10 mg/L DOC and 100 μg/L Al. Attempts to experimentally quantify differences in Al complexation by each of the DOC sources (using cation exchange and chromatography techniques) were inconclusive. However the difference in the influence of the DOC sources on U and Al toxicity highlights the need to incorporate a local DOC source for metal toxicity studies where possible.
Keyword Dissolved organic carbon
Additional Notes Colour: I, 29,30,51,59,60,61,80,81,97,105,114,133,137,139,143,144,145 Landscape: 42,158-164, 171-189

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Created: Fri, 20 Apr 2012, 13:37:56 EST by Mrs Melanie Trenfield on behalf of Library - Information Access Service