Reanalysis of uranium toxicity data for selected freshwater organisms and the influence of dissolved organic carbon.

The present study reanalyzed 46 existing uranium (U) chronic toxicity datasets for four freshwater species to generate consistent toxicity measures and explore relationships between U toxicity and key physicochemical variables. Dissolved organic carbon (DOC) was consistently the best predictor of U toxicity based on 10% inhibitory concentration (IC10) and median inhibitory concentration (IC50) values, with water hardness also being a significant co-predictor of IC50 concentrations for one species. The influence of DOC on acute and chronic U toxicity was further characterized using existing data for five species, and was found to vary depending on species, DOC source, and exposure duration (acute vs chronic). The slopes of the relationships between DOC and (normalized) acute and chronic U toxicity were modeled using cumulative probability distributions. From these, slopes were selected for which to correct acute or chronic U toxicity values or hazard estimates based on the aquatic DOC concentration. The fifth percentiles of these cumulative probability distributions for acute and chronic exposure data were 0.064 and 0.090, respectively, corresponding to a 6.4 and 9.0% reduction in U toxicity relative to the toxicity at the base DOC concentration for each 1 mg/L increase in DOC concentration (over the DOC range 0-30 mg/L). Algorithms were developed to enable the adjustment of U toxicity values and U hazard estimates, depending on DOC concentrations. These algorithms will significantly enhance the environmental relevance of water quality/risk assessments for U in fresh surface waters.

Effects of alumina refinery wastewater and signature metal constituents at the upper thermal tolerance of: 1. The tropical diatom Nitzschia closterium.

Ecotoxicological studies, using the tropical marine diatom, Nitzschia closterium (72-h growth rate), were undertaken to assess potential issues relating to the discharge from an alumina refinery in northern Australia. The studies assessed: (i) the species' upper thermal tolerance; (ii) the effects of three signature metals, aluminium (Al), vanadium (V) and gallium (Ga) (at 32°C); and (iii) the effects of wastewater (at 27 and 32°C). The critical thermal maximum and median inhibition temperature for N. closterium were 32.7°C and 33.1°C, respectively. Single metal toxicity tests found that N. closterium was more sensitive to Al compared to Ga and V, with IC(50)s (95% confidence limits) of 190 (140-280), 19,640 (11,600-25,200) and 42,000 (32,770-56,000) µg L(-1), respectively. The undiluted wastewater samples were of low toxicity to N. closterium (IC(50)s>100% wastewater). Environmental chemistry data suggested that the key metals and discharge are a very low risk to this species.

Uranium toxicity and speciation during chronic exposure to the tropical freshwater fish, Mogurnda mogurnda.

The effects of chronic uranium (U) exposure on larval Northern trout gudgeon, Mogurnda mogurnda, were assessed in two experiments using a newly-developed 28d survival and growth toxicity test. Significant effects were observed in both tests, but toxicity was markedly higher in Test 2 than Test 1. The LC50s for Tests 1 and 2 were 2090microgL(-1) and 1070microgL(-1), respectively. Larval growth IC10s for Tests 1 and 2 were 860microgL(-1) and 660microgL(-1) (dry weight), and 1160microgL(-1) and 850microgL(-1) (length), respectively. Uranium speciation modelling showed that a lower pH in Test 2 (mean of 6.0) compared to Test 1 (mean of 6.7) resulted in a greater proportion of free uranyl ion (UO(2)(2+)), the predominant bioavailable form of U. A higher dissolved organic carbon concentration (DOC) in Test 2 (4.2mgL(-1)) compared to Test 1 (2.1mgL(-1)) resulted in a higher proportion of U-DOC in Test 2, but this was insufficient to counter the effect of pH on the proportion of UO(2)(2+). The difference in U toxicity between the two tests could be explained by normalising for UO(2)(2+); the concentrations of UO(2)(2+) at the LC50s for Tests 1 and 2 were calculated to be 13.3 and 13.7microgL(-1), respectively. Finally, the results of this study, and comparisons with other studies suggest that U toxicity to M. mogurnda appears to be as much, if not more, a function of exposure water quality and feeding regime, as exposure duration.

Low power vs standard power transpupillary thermotherapy in patients with age-related macular degeneration and subfoveal choroidal neovascularization ineligible for photodynamic therapy.

AIM: To assess the effect of standard power vs low power transpupillary thermotherapy (TTT) in patients with active subfoveal choroidal neovascularization secondary to age-related macular degeneration ineligible for photodynamic therapy (PDT) by original treatment of age-related macular degeneration with photodynamic therapy (TAP) study group recommendations. METHODS: Retrospective review of 79 patients with active predominantly occult subfoveal choroidal neovascularization or predominantly classic subfoveal choroidal neovascularization but Snellen visual acuity <20/200. All patients were treated with TTT administered via a Mainster wide field fundus contact lens with a retinal power/diameter coefficient of 248 mW/mm in the standard power (n=27) and 181 mW/mm in the low power group (n=52). The primary outcome was stabilization (<1 Snellen line change) or improvement (two or more Snellen lines) in visual acuity. Clinical and fluorescein angiographic resolution of overlying exudation was documented. RESULTS: At 24 month follow-up, 17 patients (63%) in the standard power and 36 patients (69%) in the low power group achieved stable or improved vision. Improved vision (mean three lines) was observed in 22% of the standard power and 23% of the low power group. Overlying exudation was reduced clinically with minimal or no leakage on fluorescein angiogram in 85% of standard power and 90% of low power group. Subgroup analysis in the low power group demonstrated a visual benefit in patients with subfoveal lesions, which had any classic component. CONCLUSIONS: Low power TTT is as effective as standard power in stabilizing or improving vision and reducing overlying exudation in patients with active subfoveal choroidal neovascularization ineligible for PDT.

The development of marine Toxicity Identification Evaluation (TIE) procedures using the unicellular alga Nitzschia closterium.

Unicellular algae are highly sensitive to a wide range of toxicants and have been used extensively in ecotoxicological testing. This, along with their ability to grow in very small test volumes over short test durations, make them ideal test organisms for use in Toxicity Identification Evaluations (TIEs). Despite this, microalgae have not previously been used in marine TIE studies. In this study, the marine diatom Nitzschia closterium was shown to be a highly suitable test organism after modification of the standard test protocol to reduce test volumes to 6 mL and test duration to 48 h. The alga was tolerant to the chemicals used in phase I of the standard USEPA TIE protocol, and physical TIE manipulations had no effect on algal growth. The cation exchange procedure, however, inhibited algal growth, while the anion exchange procedure stimulated growth, making these two procedures unsuitable for use with this species. Of the buffers trialed for the graduated pH procedure, 0.01 M PIPES buffer was found to be suitable for buffering at pH 7 because it maintained the required pH over the duration of the test and did not affect the growth or sensitivity of the algae to one reference toxicant (copper). A trial TIE on a secondary-treated sewage effluent for discharge into coastal waters showed that the developed protocols could successfully be used to identify ammonia as the major toxicant in the effluent.