Toxicity of Zinc to Aquatic Life in Tropical Freshwaters of Low Hardness.

Zinc (Zn) is a metal of potential concern for a uranium mine whose receiving waters are in the World-Heritage listed Kakadu National Park in northern Australia. The chronic toxicity of Zn was assessed using seven tropical species in extremely soft freshwater from a creek upstream of the mine. Sensitivity to Zn was as follows (most sensitive to least sensitive based on 10% effect concentrations [EC10s]): mussel Velesunio angasi > gastropod Amerianna cumingi > fish Mogurnda mogurnda > cladoceran Moinodaphnia macleayi > green hydra Hydra viridissima > green alga Chlorella sp. > duckweed Lemna aequinoctialis, with EC10s (<0.45 µm filtered fraction) ranging from 21 to 320 µg/L Zn and EC50s ranging from 52 to 1867 µg/L Zn. These data were used to inform the risk assessment for the rehabilitation of the mine-site and contribute to the global Zn dataset. Environ Toxicol Chem 2023;42:679-683. © 2023 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2023 SETAC.

Development of a Site-Specific Guideline Value for Copper and Aquatic Life in Tropical Freshwaters of Low Hardness.

Copper (Cu) is a contaminant of potential concern for a uranium mine whose receiving waters are in the World Heritage-listed Kakadu National Park in northern Australia. The physicochemical characteristics of the freshwaters in this region enhance metal bioavailability and toxicity. Seven tropical species were used to assess the chronic toxicity of Cu in extremely soft freshwater from a creek upstream of the mine. Sensitivity to Cu was as follows: Moinodaphnia macleayi > Chlorella sp. > Velesunio sp. > Hydra viridissima > Amerianna cumingi > Lemna aequinoctialis > Mogurnda mogurnda. The 10% effect concentrations (EC10s) ranged from 1.0 µg/L Cu for the cladoceran Moinodaphnia macleayi to 9.6 µg/L for the fish M. mogurnda. The EC50s ranged from 6.6 µg/L Cu for the mussel Velesunio sp. to 22.5 µg/L Cu for M. mogurnda. Geochemical modeling predicted Cu to be strongly bound to fulvic acid (80%-99%) and of low bioavailability (0.02%-11.5%) under these conditions. Protective concentrations (PCs) were derived from a species sensitivity distribution for the local biota. The 99% PC (PC99), PC95, PC90, and PC80 values were 0.5, 0.8, 1.0, and 1.5 µg/L Cu, respectively. These threshold values suggest that the current Australian and New Zealand default national 99% protection guideline value for Cu (1.0 µg/L) would not provide adequate protection in freshwaters of low hardness, particularly for this area of high conservation value. The continuous criterion concentration predicted by the Cu biotic ligand model for conditions of low pH (6.1), low dissolved organic carbon (2.5 mg/L), low hardness (3.3 mg/L), and 27 °C was 0.48 µg/L Cu, comparable with the PC99. Consideration of the natural water quality conditions of a site is paramount for protective water quality guidelines. Environ Toxicol Chem 2022;41:2808-2821. © 2022 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2022 SETAC.

Assessing the Toxicity of Mine-Water Mixtures and the Effectiveness of Water Quality Guideline Values in Protecting Local Aquatic Species.

Six tropical freshwater species were used to assess the toxicity of mine waters from a uranium mine adjacent to a World Heritage area in northern Australia. Key contaminants of potential concern for the mine were U, Mg, Mn, and total ammonia nitrogen (TAN). Direct toxicity assessments were carried out to assess whether the established site-specific guideline values for individual contaminants would be protective with the contaminants occurring as mixtures. Metal speciation was calculated for contaminants to determine which were the major contributors of toxicity, with 84 to 96% of Mg predicted in the free-ion form as Mg2+ , and 76 to 92% of Mn predicted as Mn2+ . Uranium, Al, and Cu were predicted to be strongly bound to fulvic acid. Uranium, Mg, Mn, and Cu were incorporated into concentration addition or independent action mixture toxicity models to compare the observed toxicity in each of the waters with predicted toxicity. For >90% of the data, mine-water toxicity was less than predicted by the concentration addition model. Instances where toxicity was greater than predicted were accompanied by exceedances of individual metal guideline values in all but one case (i.e., a Mg concentration within 10% of the guideline value). This indicates that existing individual water quality guideline values for U, Mg, Mn, and TAN would adequately protect ecosystems downstream of the mine. Environ Toxicol Chem 2021;40:2334-2346. © 2021 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2021 SETAC.

Development of a Sublethal Chronic Toxicity Test for the Northern Trout Gudgeon, Mogurnda mogurnda, and Application to Uranium, Magnesium, and Manganese.

Many international guidance documents for deriving water quality guideline values recommend the use of chronic toxicity data. For the tropical fish northern trout gudgeon, Mogurnda mogurnda, 96-h acute and 28-d chronic toxicity tests have been developed, but both tests have drawbacks. The 96-h toxicity test is acute and has a lethal endpoint; hence it is not a preferred method for guideline value derivation. The 28-d method has a sublethal (growth) endpoint, but is highly resource intensive and is high risk in terms of not meeting quality control criteria. The present study aimed to determine the feasibility of a 7-d larval growth toxicity test as an alternative to the 96-h survival and 28-d growth tests. Once the method was successfully developed, derived toxicity estimates for uranium, magnesium, and manganese were compared with those for other endpoints and tests lengths within the literature. As a final validation of the 7-d method, the sensitivity of the 7-d growth endpoint was compared with those of 14-, 21-, and 28-d exposures. Fish growth rate, based on length, over 7 d was significantly more sensitive compared with existing acute toxicity endpoints for magnesium and manganese, and was similarly sensitive to existing chronic toxicity endpoints for uranium. For uranium, the sensitivity of the growth endpoint over the 4 exposure periods was similar, suggesting that 7 d as an exposure duration is sufficient to provide an indication of longer term chronic growth effects. The sensitivity of the 7-d method, across the 3 metals tested, highlights the benefit of utilizing the highly reliable short-term 7-d chronic toxicity test method in future toxicity testing using M. mogurnda. Environ Toxicol Chem 2021;40:1596-1605. © 2021 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2021 SETAC.

Acute and chronic toxicity of magnesium to the early life stages of two tropical freshwater mussel species.

Magnesium (Mg) is a common contaminant in mine water discharges. Although Mg is an essential element in biological processes, increased concentrations from anthropogenic sources can stress aquatic ecosystems. Additionally, studies evaluating the effects of Mg on north Australian freshwater species have indicated that in very soft waters there is a high risk to some species. Freshwater mussels are an ecologically and culturally important taxon in many freshwater environments, but knowledge of their sensitivity to Mg is limited. In the present study, the acute and chronic sensitivity of two freshwater mussel species, Velesunio angasi and an undescribed Velesunio species, to Mg was assessed (using MgSO4) on their early life stages, larval glochidia and post-parasitic juveniles. Acute 24-h exposures with glochidia generated a mean median lethal (LC50) toxicity estimate of 284mg/L for the five tests with V. angasi, and a mean LC50 of 300mg/L for the three tests with Velesunio sp. Mean chronic 14-d toxicity estimates resulting in 50% (EC50) and 10% (EC10) growth rate reductions for juveniles were 241 and 88mg/L respectively for the three tests with V. angasi juveniles, and 232 and 87mg/L respectively for the three tests with Velesunio sp. juveniles. The results represent the first acute and chronic Mg toxicity data for tropical freshwater mussels, and indicated that V. angasi and Velesunio sp. exhibited similar sensitivity and were moderately sensitive to Mg when compared to other tropical species. These results are a valuable contribution to the small existing dataset for Mg toxicity to tropical freshwater species, which can be used to inform water management in areas where Mg is a contaminant of concern, and ensure the protection of these taxa.

Chronic ammonia toxicity to juveniles of 2 tropical Australian freshwater mussels (Velesunio spp.): Toxicity test optimization and implications for water quality guideline values.

Freshwater mussels play key roles in aquatic ecosystems, but are experiencing a global decline. Although studies have reported high acute sensitivity of mussels to some contaminants, chronic toxicity data are lacking for deriving high-reliability water quality guideline values. Ammonia is a contaminant of potential concern in some catchments of tropical northern Australia, where freshwater mussels are important ecological and cultural components. The extremely soft waters (hardness < 5 mg/L) of these environments can result in increased toxicity of many contaminants including ammonia, and regionally relevant tropical guideline values are needed to adequately protect these unique ecosystems. An optimized 14-d toxicity test protocol was used to assess the chronic toxicity of ammonia for 2 species, the lotic Velesunio sp. and the lentic Velesunio angasi. Ammonia exposures were conducted at pH 6.0 and 27 ± 0.5 °C to represent local environmental conditions, using shell length growth rate as the endpoint. Chronic toxicity estimates indicated high sensitivity to ammonia, with mean median effect concentrations (in total ammonia nitrogen) being 7.0 mg/L for V. angasi from the semi-urbanized Lake Bennett, 9.2 mg/L for V. angasi from Sandy Billabong, and 11.3 mg/L for Velesunio sp. from Gulungul Creek. When the 10% effect concentration values were compared with other chronic ammonia data (normalized to pH 7.0 and 20 °C), Velesunio spp. were found to be more sensitive than 8 of 16 other temperate and 7 of 9 tropical invertebrate and fish species. These chronic toxicity estimates will be used to further inform regionally relevant and site-specific guideline values. Environ Toxicol Chem 2019;38:841-851. © 2019 Commonwealth of Australia. Published by Wiley Periodicals Inc. on behalf of SETAC.

Integrating laboratory and field studies to assess impacts of discharge from a uranium mine and validate a water quality guideline value for magnesium.

Magnesium (Mg) is a primary contaminant in mine water discharges from the Ranger Uranium Mine (north Australia). Site-specific water quality guideline values (WQGVs) for Mg have been derived from laboratory and field studies. Contaminated groundwater with elevated electrical conductivity and metals (Mg, Mn, U, SO4 , and Ca) was detected flowing from the mine site into adjacent surface waters. This provided an opportunity to investigate the protectiveness of the Mg WQGV by conducting an integrated laboratory and field study. A direct toxicity assessment (DTA) of the groundwater was conducted with local tropical freshwater species: duckweed (Lemna aequinoctialis), green hydra (Hydra viridissima), and the aquatic snail Amerianna cumingi. An in situ toxicity assessment was carried out in the creek receiving diluted groundwater by use of the same species of snail, to aid interpretation of laboratory-derived data. The toxicity of the contaminated groundwater was higher than Mg-only toxicity testing for H. viridissima, with other elevated metals and major ions contributing to toxicity. However, for duckweed and snail, the contaminated groundwater was less toxic than the Mg-only testing. In situ snail monitoring supported laboratory exposures, showing no effect on reproduction of A. cumingi exposed to an average of approximately 5 mg/L Mg; however, a very small effect was noted closer to the groundwater source, probably associated with other contaminants. The minimal toxicity observed for L. aequinoctialis and A. cumingi, despite the elevated Mg, can be explained by the high calcium (Ca) concentration of the water and the potential amelioration of metal toxicity. The extent of Ca amelioration of Mg toxicity was organism dependent. This study affirms the proposed environmental rehabilitation standard of 3 mg/L Mg for surface waters with a Ca concentration typical of water from this mine site. Integr Environ Assess Manag 2019;15:64-76. © 2018 SETAC.

Assessing chronic toxicity of aluminium, gallium and molybdenum in tropical marine waters using a novel bioassay for larvae of the hermit crab Coenobita variabilis.

A novel bioassay is presented that allows for the estimation of the chronic toxicity of contaminants in receiving tropical marine environments. Relevant procedures to identify contaminants of concern and evaluate hazards associated with contamination in these environments have long remained inadequate. The 6-day bioassay is conducted using freshly hatched planktonic larvae of the hermit crab Coenobita variabilis and is targeted at generating environmentally relevant, chronic toxicity data. The developmental endpoint demonstrated consistently high control performance and was validated through the use of copper as a reference toxicant. In addition, the biological effects of aluminium, gallium and molybdenum were assessed. The endpoint expressed high sensitivity to copper (EC10 = 24 µg L-1) and moderate sensitivity to aluminium (EC10 = 312 µg L-1), whereas gallium and molybdenum elicited no obvious effects, even at high concentrations (EC10 > 6000 µg L-1), providing valuable information on the toxicity of these elements in tropical marine waters for derivation of water quality guidelines or testing of compliance limits.

Water quality guideline values for aluminium, gallium and molybdenum in marine environments.

Revised water quality guideline values (WQGVs) are presented for the metals aluminium (Al), gallium (Ga) and molybdenum (Mo) in receiving marine environments. These elements are commonly found in elevated concentrations in alumina refinery waste streams, yet current WQGVs fail to accurately assess the environmental risk. Here, chronic biological effects data we have generated over the course of several years were combined with toxicity data from the open literature to construct species sensitivity distributions (SSDs) which enabled the computation of revised WQGVs for Al, Ga and Mo in marine environments. These procedures are in accordance with internationally recommended derivation procedures, and newly computed WQGVs may be incorporated in regulatory frameworks aimed at sustainable exploitation of environmental resources and ongoing protection of the marine estate. Where the available datasets allowed such distinction, separate SSDs were constructed for temperate and tropical environments and zone-specific WQGVs derived. Extrapolated from the SSDs, WQGVs of 56 µg Al L-1, 800 µg Ga L-1 and 3.88 mg Mo L-1 (in the 0.45-µm filtered fraction) for 95% species protection were recommended for implementation in both temperate and tropical receiving environments. Currently, there is insufficient validation to separate the tropical from the temperate data and in most cases, application of the generic WQGVs is recommended.

Assessing the chronic toxicity of nickel to a tropical marine gastropod and two crustaceans.

The mining and processing of nickel ores from tropical regions contributes 40% of the global supply. The potential impact of these activities on tropical marine ecosystems is poorly understood. Due to the lack of ecotoxicity data for tropical marine species, there is currently no available water quality guideline value for nickel that is specific to tropical species. In this study, we investigated the toxicity of nickel to three tropical marine invertebrates, the gastropod Nassarius dorsatus, the barnacle Amphibalanus amphitrite, and the copepod Acartia sinjiensis. All toxicity tests used chronic endpoints, namely larval growth, metamorphosis (transition from nauplii to cyprid larvae) and larval development for the snail, barnacle and copepod respectively. Toxicity tests were carried out under environmentally relevant conditions (i.e. 27-30ᵒC, salinity 34-36‰, pH 8.1-8.4). Copper was also tested for quality assurance purposes and to allow for comparisons with previous studies. The copepod was the most sensitive species to nickel, with development inhibited by 10% (EC10) at 5.5 (5.0-6.0) µg Ni/L (95% confidence limits (CL)). Based on EC10 values, the gastropod and barnacle showed similar sensitivities to nickel with growth and metamorphosis inhibited by 10% at 64 (37-91) µg Ni/L and 67 (53-80) µg Ni/L, respectively. Based on existing data available in the literature, the copepod A. sinjiensis is so far the most sensitive tropical marine species to nickel. This study has provided high quality data which will contribute to the development of a water quality guideline value for nickel in tropical marine waters. A species sensitivity distribution of chronic nickel toxicity used the data generated in this paper supplemented by available literature data, comprising 12 species representing 6 taxonomic groups. A 5% hazard concentration (HC5) was determined as 8.2 µg/L Ni.

Acute ammonia toxicity to the larvae (glochidia) of the tropical Australian freshwater mussel Velesunio spp. Using a modified toxicity test protocol.

Ammonia is recognized as a major pollutant worldwide, originating from natural and anthropogenic sources. Studies have reported that freshwater mussels are among the most sensitive taxa to ammonia, but few data are available on ammonia toxicity for the early life stages of freshwater mussels from tropical regions. We report on the modification of a 24-h acute toxicity test protocol for tropical freshwater mussels and application of the test using ammonia. Velesunio spp. from 3 different sites were used to assess the toxicity of ammonia at a targeted pH of 6.0 and a water temperature of 27.5 °C, which were the average annual values for some slightly to moderately acidic, soft water (3-6 mg/L as CaCO3 ) creeks of tropical northern Australia. The valve closure responses of mussel glochidia (larvae) to a sodium chloride solution were used to measure the survival endpoint. Acute toxicity estimates indicate that tropical Velesunio spp. were highly sensitive to ammonia, with 24-h exposures to ammonium sulfate generating median lethal concentration estimates ranging from 6.8 to 14.2 mg/L total ammonia nitrogen, which, when adjusted to pH 7 and 20 °C, were among the highest sensitivities yet reported for any freshwater mussel species, and among the highest in sensitivity for any tropical taxon. These toxicity estimates can contribute to the derivation or refinement of ammonia guideline values for freshwater ecosystems globally. Environ Toxicol Chem 2018;37:2175-2187. © 2018 SETAC.

Assessing the chronic toxicity of copper and aluminium to the tropical sea anemone Exaiptasia pallida.

The world's most productive bauxite mines and alumina refineries are located in tropical or sub-tropical regions. The discharge water from alumina refineries can contain elevated aluminium (Al, <0.45µm fraction), from 30 to 1000µg/L. There is a need for additional information on the toxicity of Al to aquatic organisms to improve the environmental regulation and management of alumina refinery operations in tropical coastal regions. A 14-d chronic toxicity test was developed for the tropical sea anemone Exaiptasia pallida. Asexual reproduction and growth rates of E. pallida were assessed using the number of lacerates produced and oral disc diameter. The comparative sensitivity of E. pallida was assessed through exposure to a commonly-used reference toxicant, copper (Cu) at 28°C, with asexual reproduction toxicity estimates of 10% (EC10) and 50% (EC50) effect concentrations, calculated as 8.8µg/L (95% confidence limits (CL): 1-18µg/L) and 35µg/L Cu (95% CL: 30-39µg/L), respectively. Growth rate was a suitable additional endpoint (EC50=35µg/L Cu, 95% CL: 23-49µg/L). The EC10 and EC50 for Al (total fraction, based on reproduction) at 28°C were 817µg/L (95% CL: 440-1480µg/L) and 2270µg/L (95% CL: 1600-3900µg/L), respectively. The toxicity of Cu and Al was also assessed at 24°C and 31°C, representing average year-round water temperatures for sub-tropical and tropical Australian coastal environments. Changing the temperature from 28°C to 24°C or 31°C resulted in up to 45% less reproduction of anemones and increased their sensitivity to Cu (EC50s at 24°C=21µg/L, 95% CL: 17-26µg/L and at 31°C=23µg/L, 95% CL: 21-25µg/L). Sensitivity to Al was reduced at 24°C with an EC50 of 8870µg/L (95% CL: 6200-NC). An EC50 for Al at 31°C could not be calculated. This test is a reliable and sensitive addition to the suite of standardised tests currently developed for tropical marine species.

A novel bioassay using the barnacle Amphibalanus amphitrite to evaluate chronic effects of aluminium, gallium and molybdenum in tropical marine receiving environments.

A need exists for appropriate tools to evaluate risk and monitor potential effects of contaminants in tropical marine environments, as currently impact assessments are conducted by non-representative approaches. Here, a novel bioassay is presented that allows for the estimation of the chronic toxicity of contaminants in receiving tropical marine environments. The bioassay is conducted using planktonic larvae of the barnacle Amphibalanus amphitrite and is targeted at generating environmentally relevant, chronic toxicity data for water quality guideline derivation or compliance testing. The developmental endpoint demonstrated a consistently high control performance, validated through the use of copper as a reference toxicant. In addition, the biological effects of aluminium, gallium and molybdenum were assessed. The endpoint expressed high sensitivity to copper and moderate sensitivity to aluminium, whereas gallium and molybdenum exhibited no discernible effects, even at high concentrations, providing valuable information on the toxicity of these elements in tropical marine waters.

Increasing uranium exposure durations to the aquatic snail Amerianna cumingi does not result in lower toxicity estimates.

Reproductive inhibition (egg production) of the aquatic snail Amerianna cumingi over 4 d has been used to derive toxicity estimates for toxicants of concern in tropical Australia. Toxicity estimates from this test have been used as chronic data points in species sensitivity distributions (SSDs) for deriving site-specific guideline values. However, revised guidance for the Australian and New Zealand Water Quality Guidelines advises that test durations for adult macroinvertebrates should be ≥14 d to be considered chronic. Hence, to strengthen the data set underpinning the site-specific guideline value for uranium (U) in Magela Creek, which receives water from the Ranger Uranium Mine in northern Australia, the toxicity of U to A. cumingi was compared after 4 d, 9 d, and 14 d. Daily U concentrations were measured because of expected U loss during testing, providing extensive chemical analyses of the U exposure during the toxicity tests. Comparison of the U concentrations causing 50% reproductive inhibition (IC50) after 4 d, 9 d, and 14 d showed no difference in toxicity (4 d IC50 = 161 µg L-1 , confidence interval = 133-195; 9-d IC50 = 151 µg L-1 , confidence interval = 127-180; 14-d IC50 = 153 µg L-1 , confidence interval = 29-180). The present study provides evidence that test durations of <14 d are suitable for assessing chronic toxicity to U for this species and supports the use of the 4-d toxicity estimate in the SSD for U. Environ Toxicol Chem 2016;35:2851-2858. © 2016 Commonwealth of Australia.

A chronic toxicity test for the tropical marine snail Nassarius dorsatus to assess the toxicity of copper, aluminium, gallium, and molybdenum.

Chronic toxicity test methods for assessing the toxicity of contaminants to tropical marine organisms are generally lacking. A 96-h chronic growth rate toxicity test was developed for the larval stage of the tropical dogwhelk, Nassarius dorsatus. Growth rates of N. dorsatus larvae were assessed following exposures to copper (Cu), aluminium (Al), gallium (Ga), and molybdenum (Mo). Exposure to Cu at 28 °C validated the sensitivity of the test method, with 10% (EC10) and 50% (EC50) effect concentrations of 4.2 µg/L and 7.3 µg/L Cu, respectively. The EC10 and EC50 values for Al (<0.45-µm filtered fraction) at 28 °C were 115 µg/L and 185 µg/L, respectively. The toxicity of Cu and Al was also assessed at 24 °C and 31 °C, representing average year-round water temperatures for subtropical and tropical Australian coastal environments. At 24 °C, the growth rate of control larvae was reduced by 52% compared with the growth rate at 28 °C and there was an increase in sensitivity to Cu (EC50 = 4.7 µg/L) but a similar sensitivity to Al (EC50 = 180 µg/L). At 31 °C the control growth rate increased by 35% from that measured at 28 °C and there was reduced sensitivity to both Cu and Al (EC50s = 8.5 µg/L and 642 µg/L, respectively). There was minimal toxicity resulting from Ga (EC50 = 4560 µg/L) and Mo (no effect at ≤7000 µg/L Mo). Environ Toxicol Chem 2016;35:1788-1795. © 2015 SETAC.

Manganese toxicity to tropical freshwater species in low hardness water.

Elevated manganese (Mn) is a common contaminant issue for mine water discharges, and previous studies have reported that its toxicity is ameliorated by H(+), Ca(2+), and Mg(2+) ions. In the present study, the toxicity of Mn was assessed in a high risk scenario, that is, the slightly acidic, soft waters of Magela Creek, Kakadu National Park, Northern Territory, Australia. Toxicity estimates were derived for 6 tropical freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Moinodaphnia macleayi, Hydra viridissima, and Mogurnda mogurnda). Low effect chronic inhibition concentration (IC10) and acute lethal concentration (LC05) values ranged between 140 µg L(-1) and 80,000 µg L(-1), with 3 of the species tested (M. macleayi, A. cumingi, and H. viridissima) being more sensitive to Mn than all but 1 species in the international literature (Hyalella azteca). A loss of Mn was observed on the final day for 2 of the H. viridissima toxicity tests, which may be a result of the complex speciation of Mn and biological oxidation. International data from toxicity tests conducted in natural water with a similar physicochemistry to Magela Creek water were combined with the present study's data to increase the sample size to produce a more reliable species sensitivity distribution. A 99% protection guideline value of 73 µg L(-1) (33-466 µg L(-1)) was derived; the low value of this guideline value reflects the higher toxicity of Mn in slightly acidic soft waters.

Aluminium, gallium, and molybdenum toxicity to the tropical marine microalga Isochrysis galbana.

There is a shortage of established chronic toxicity test methods for assessing the toxicity of contaminants to tropical marine organisms. The authors tested the suitability of the tropical microalga Isochrysis galbana for use in routine ecotoxicology and assessed the effects of 72-h exposures to copper (Cu, a reference toxicant), aluminium (Al), gallium (Ga), and molybdenum (Mo), key metals of alumina refinery discharge, on the growth of I. galbana at 3 temperatures: 24 °C, 28 °C, and 31 °C. The sensitivity of both I. galbana and the test method was validated by the response to Cu exposure, with 10% and 50% effect concentrations (EC10 and EC50) of 2.5 µg/L and 18 µg/L, respectively. The EC10 and EC50 values for total Al at 28 °C were 640 µg/L and 3045 µg/L, respectively. The toxicity of both Cu and Al at 24 °C and 31 °C was similar to that at 28 °C. There was no measurable toxicity from dissolved Ga exposures of up to 6000 µg/L or exposures to dissolved Mo of up to 9500 µg/L. Solubility limits at 28 °C for the dissolved fractions (<10 kDa) of Al, Ga, and Mo were approximately 650 µg/L Al, >7000 µg/L Ga, and >6000 µg/L Mo. In test solutions containing >650 µg/L total Al, dissolved and precipitated forms of Al were present, with precipitated Al becoming more dominant as total Al increased. The test method proved suitable for routine ecotoxicology, with I. galbana showing sensitivity to Cu but Al, Ga, and Mo exhibiting little to no toxicity to this species.

Toxicity of magnesium pulses to tropical freshwater species and the development of a duration-based water quality guideline.

Six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Hydra viridissima, Moinodaphnia macleayi, and Mogurnda mogurnda) were exposed to 4-h, 8-h, and 24-h Mg pulses in natural creek water. Magnesium toxicity to all species increased with exposure duration; however, the extent of increase and the nature of the relationship differed greatly between species. Based on median inhibitory concentrations (IC50s), and compared with continuous exposure data from a previous study, the increase in toxicity with increasing exposure duration from 4 h to continuous (72-144 h) ranged from approximately 2-fold for Chlorella sp. and H. viridissima to greater than 40-fold for A. cumingi. Moreover, the form of the relationship between Mg toxicity and duration ranged from linear or near-linear to exponential for different species. The life-stage at which M. macleayi was exposed was important, with cladocerans pulsed at the onset of reproductive maturity being approximately 4 times more sensitive (based on IC50s) than younger than 6-h-old neonates. Species sensitivity distributions were constructed for the 4-h, 8-h, and 24-h pulse durations, from which 99% species protection guideline values (95% confidence limits [CLs]) of 94 (6.4-1360) mg/L, 14 (0.5-384) mg/L, and 8.0 (0.5-144) mg/L Mg, respectively, were derived. These values were plotted against exposure duration (h) and polynomial interpolation used to derive a guideline value for any pulse duration within the range assessed.

Dissolved organic carbon reduces uranium toxicity to the unicellular eukaryote Euglena gracilis.

The influence of dissolved organic carbon (DOC), in the form of Suwannee River fulvic acid (SRFA), on uranium (U) toxicity to the unicellular eukaryote, Euglena gracilis (Z strain), was investigated at pH 6. In a background medium without SRFA, exposure of E. gracilis to 57 µg L(-1) U resulted in a 50% reduction in growth (IC(50)). The addition of 20 mg L(-1) DOC (as SRFA), reduced U toxicity 4 to 5-fold (IC(50) increased to 254 µg L(-1) U). This reduction in toxicity was also evident at more sensitive effect levels with a 10% reduction in growth (IC(10)) occurring at 5 µg L(-1) U in the background medium and at 17 µg L(-1) U in the SRFA medium, respectively. This amelioration of toxicity with the addition of SRFA was linked to a decrease in the bioavailability of U, with geochemical speciation modelling predicting 84% of U would be complexed by SRFA. The decrease in bioavailability of U in the presence of SRFA was also evident from the 11-14 fold reduction in the cellular concentration of U compared to that of E. gracilis in the background medium. Stepwise multiple linear regression analyses indicated that UO(2)(2+) alone explained 51% of the variation in measured U toxicity to E. gracilis. Preliminary U exposures to E. gracilis in the presence of a reactive oxygen species probe, suggest exposure to ≥60 µg L(-1) U may induce oxidative stress, but this endpoint was not considered to be a sensitive biological indicator.

Dissolved organic carbon reduces the toxicity of aluminum to three tropical freshwater organisms.

The influence of dissolved organic carbon (DOC) on the toxicity of aluminum (Al) at pH 5 (relevant to acid mine drainage conditions), to the tropical green hydra (Hydra viridissima), green alga (Chlorella sp.), and cladoceran (Moinodaphnia macleayi) was assessed. Two DOC sources, a natural in situ DOC in soft billabong water (SBW) and Suwannee River fulvic acid (SRFA) standard, were compared. The order of sensitivity of the test organisms to dissolved Al (0.1 µm fraction) was Hydra viridissima > Moinodaphnia macleayi > Chlorella sp. with DOC reducing dissolved Al toxicity most for Hydra viridissima. However, colloidal or precipitated Al may contribute indirectly to the toxicity for M. macleayi and Chlorella sp. The toxicity of dissolved Al was up to six times lower in test waters containing 10 mg L(-1) DOC (in the form of SRFA), relative to toxicity observed at 1 mg L(-1) DOC. In contrast, the toxicity of Al was up to two times lower in SBW containing 10 mg L(-1) DOC, relative to water containing 1 mg L(-1) DOC. The increased ability of SRFA in reducing Al toxicity was linked to its greater affinity for complexing Al compared with the in situ DOC. This has important implications for studies that use commercial standards of humic substances to predict Al toxicity in local environments. Speciation modeling demonstrated that Al(3+) and AlOH(2+) provided a strong relationship with toxicity. An empirical relationship is provided for each organism that can be used to predict Al toxicity at a given Al and DOC concentration.