Seasonal responses of macroinvertebrate assemblages to magnesium in a seasonally flowing stream

Macroinvertebrates can be highly sensitive to elevated salinity in freshwater environments, and are known to respond to saline discharges. Magnesium (Mg) is a mine-related contaminant and is a potential environmental risk to a seasonally-flowing, receiving water stream in Kakadu National Park, located in the wet-dry tropics of Australia. The macroinvertebrate assemblage in the stream in the was characterised at four hydrographic phases, from early wet season flow to early dry season pools at flow cessation. On each of the four occasions representing the respective phases, individuals from the most abundant macroinvertebrate species present were collected and acutely exposed to a range (up to 19) of Mg concentrations under laboratory conditions. Sensitivity of taxa to Mg ranged between 39 mg/L Mg (Caenidae: Tasmanocoenis spp.) and 4400 mg/L Mg (Dytiscidae: Clypeodytes feryi), based on the 50% Lethal Concentration (LC50). Characterisation of the macroinvertebrate assemblage at each hydrographic phase indicated the seasons when Mg-sensitive species were present. Whilst no statistical differences in measures of seasonal sensitivity were found, the macroinvertebrate assemblages present during the early flow period had higher Mg-sensitivity than the assemblages present during other hydrographic phases. This could be attributed to the greater relative proportions of Mg-sensitive taxa (e.g. Ephemeroptera) present at early flow compared to greater relative proportions of more Mg-tolerant taxa (C. feryi and Hydacarina spp.) present during later hydrograph phases, especially periods of lower, or no, flow.

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.

Elevated Magnesium Concentrations Altered Freshwater Assemblage Structures in a Mesocosm Experiment

Magnesium (Mg) is a mining-related contaminant in the Alligators Rivers Region of tropical northern Australia. A mesocosm experiment was used to assess Mg toxicity to aquatic freshwater assemblages. Twenty-five 2700-L tubs were arranged, stratified randomly, on the bed of Magela Creek, a seasonally flowing, sandy stream channel in the Alligator Rivers Region of northern Australia. The experiment comprised 5 replicates of 4 nominal Mg treatments, 2.5, 7.5, 23, and 68 mg L^-1 , and a control. Phytoplankton biomass, and diatom, zooplankton, and macroinvertebrate assemblages present in the treatment tubs were sampled before and after Mg addition. A significant negative relationship between phytoplankton biomass and Mg was observed 4 wk after Mg addition as measured by chlorophyll a concentrations (r²  = 0.97, p = 0.01). This result was supported by reductions in some major phytoplankton groups in response to increasing Mg concentrations, in the same experiment and from independent field studies. There was a significant negative relationship between zooplankton assemblage similarity (to control) and Mg concentrations (r²  = 0.96, p = 0.002). Seven weeks after Mg addition, macroinvertebrate assemblages were dominated by 3 microcrustacean groups (Ostracoda, Cladocera, and Copepoda), each reaching maximum abundance at intermediate Mg concentrations (i.e., unimodal responses). The responses of phytoplankton and zooplankton were used to derive assemblage effect concentrations (Mg concentrations resulting in x% of the assemblage change [ECx]). Magnesium concentrations resulting in assemblage EC01 values were <3 mg L^-1 . Together with candidate guideline values from other laboratory- and field-based lines of evidence, the mesocosm EC01 values were incorporated into a weight-of-evidence framework for a robust regulatory approach to environmental protection. Environ Toxicol Chem 2020;39:1973-1987. © 2020 Commonwealth of Australia. Published by Wiley Periodicals LLC on behalf of 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.

Response of the Native Springtail Parisotoma insularis to Diesel Fuel-Contaminated Soils Under Field-Realistic Exposure Conditions at Subantarctic Macquarie Island

A number of sites contaminated by petroleum hydrocarbons from past fuel spills are currently undergoing remediation on subantarctic Macquarie Island (under the jurisdiction of Tasmania, Australia). To assess the environmental risks these spills pose, and to establish remediation targets and guideline values, toxicity data for a range of native biota are required. The availability of data for local biota is limited, especially for soil invertebrates, which are critical to soil health. To examine the response of naturally occurring soil invertebrate communities to fuel contamination, intact soil cores from a range of soil types were collected along an organic carbon (OC) gradient. Organic carbon was factored into the toxicity assessment due to its toxicity-modifying potential. Soil cores were spiked with Special Antarctic Blend diesel, to mimic a fresh fuel spill at the soil surface. Springtails were the most abundant taxa, with the community heavily dominated by the native species Parisotoma insularis. This species was sensitive to fuel contamination (EC20 48 mg/kg, CI 5-188), irrespective of soil organic content. This study is the first to derive critical effect concentrations (CECs) for a subantarctic springtail species and provides important data that will be incorporated into future derivation of site-specific soil quality guideline values for fuels for Macquarie Island soils and the broader subantarctic region. Integr Environ Assess Manag 2019;15:565-574. © 2019 SETAC.

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.

Freshwater chronic ammonia toxicity: A tropical-to-temperate comparison

The chronic toxicity of ammonia to tropical freshwater species is understudied, and thus data on temperate species have been used to derive water quality guideline values for tropical regions. Such practices may lead to underprotective guideline values due to differences in toxicities observed between tropical and temperate species. In addition, the presence of ammonia in low-ionic-strength waters may also result in higher toxicity, and studies on this factor are limited. The present study assessed the toxicity of ammonia to 6 tropical freshwater species in low-ionic-strength waters. Because ammonia toxicity varies depending on the pH and temperature, test water pH concentrations were maintained at approximately pH 6.0 ± 0.3 at temperatures between 27.5 and 30 °C. Low-effect chronic inhibition concentrations were derived for the following species: Chlorella sp. 66 mg L^-1 ; Lemna aequinoctialis 22 mg L^-1 ; Hydra viridissima 1.8 mg L^-1 ; Moinodaphnia macleayi 27 mg L^-1 ; Amerianna cumingi 17 mg L^-1 ; and Mogurnda mogurnda 5.4 mg L^-1 total ammonia nitrogen. Two of the species tested (a cnidarian and a fish species) were among the most sensitive reported anywhere within their taxonomic group. Chronic ammonia datasets representing toxicity estimates for temperate and tropical species were plotted and compared using species sensitivity distributions. The results indicate that the differences in chronic toxicity observed between tropical and temperate species were likely due to the low ionic strength of the waters to which tropical species were exposed, rather than any inherent physiological differences between species from tropical and temperate regions. This finding suggests that tropical waters of low ionic strength may be at a higher risk from ammonia compared with other freshwater ecosystems. Environ Toxicol Chem 2019;38:177-189. © 2018 Commonwealth of Australia. Published by Wiley Periodicals, Inc. on behalf of SETAC.

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.

Modeling the pH-ammonia toxicity relationship for Hydra viridissima in soft waters with low ionic concentrations

There are limited data concerning the toxicity of ammonia in fresh soft waters. Ammonia toxicity is largely dependent on pH and temperature. The US Environmental Protection Agency (USEPA) has derived equations to adjust species toxicity estimates based on changes in pH and temperature. It has been reported that the pH-ammonia toxicity relationship, derived by the USEPA, may differ in waters with low ionic concentrations because of the absence of potentially ameliorative ionic constituents. The present study aimed to assess the pH-ammonia toxicity relationship for the tropical green hydra, Hydra viridissima, across a range of pH values in a natural water with low ionic content. Ammonia toxicity to H. viridissima was assessed at a pH range between 6.0 and 8.5 and temperature 27.5 ± 1 °C. Test solution pH was maintained using a pH buffer. The resulting median effect concentrations ranged from 9.62 (7.95-11.65) mg L^-1 total ammonia nitrogen at pH 6.0 to 0.64 (0.50-0.81) mg L^-1 total ammonia nitrogen at pH 7.9. The results indicated that increasing pH increased the sensitivity of H. viridissima to ammonia. The pH dependence equation derived by the USEPA accurately described the relationship between pH and ammonia toxicity for H. viridissima. However, when the model parameters for the generic pooled relationship were used, the fit was less accurate (r²  = 0.66), indicating that the generic pooled pH-dependence equations may not be appropriate for use with this species. Environ Toxicol Chem 2018;37:1189-1196. © 2017 SETAC.

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.

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.

Toxicity of diesel contaminated soils to the subantarctic earthworm Microscolex macquariensis

Several fuel spills have occurred on subantarctic Macquarie Island (54°30' S 158°57' E) associated with storing fuel and generating power for the island's research station. The Australian Antarctic Division began full-scale, on-site remediation of these sites in 2009. To develop appropriate target concentrations for remediation, acute and chronic tests were developed with the endemic earthworm, Microscolex macquariensis, using avoidance, survival, and reproduction as endpoints. Uncontaminated low (3%), medium (11%), and high (38-48%) carbon content soils from Macquarie Island were used to examine the influence of soil carbon on toxicity. Soils were spiked with Special Antarctic Blend (SAB) diesel and used either immediately to simulate a fresh spill or after four weeks to simulate an aged spill. Earthworms were sensitive to fresh SAB, with significant avoidance at 181 mg/kg; acute 14-d survival median lethal concentration (LC50) of 103 mg/kg for low carbon soil; and juvenile production median effective concentration (EC50) of 317 mg/kg for high carbon soil. Earthworms were less sensitive to aged SAB than to fresh SAB in high carbon soil for juvenile production (EC50 of 1,753 and 317 mg/kg, respectively), but were more sensitive for adult survival (LC50 of 2,322 and 1,364 mg/kg, respectively). Using M. macquariensis as a surrogate for soil quality, approximately 50 to 200 mg SAB/kg soil would be a sufficiently protective remediation target.