Alicia C. Hogan

Aquatic toxicity of magnesium sulfate, and the influence of calcium, in very low ionic concentration water

The toxicity of magnesium sulfate (MgSO(4)), and the influence of calcium (Ca), were assessed in very soft freshwater (natural Magela Creek water [NMCW]) using six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Moinodaphnia macleayi, Hydra viridissima, and Mogurnda mogurnda). The study involved five stages: toxicity of MgSO(4) in NMCW, determination of the toxic ion, influence of Ca on Mg toxicity, toxicity of MgSO(4) at an Mg:Ca mass ratio of 9:1, and derivation of water quality guideline values for Mg. The toxicity of MgSO(4) was higher than previously reported, with chronic median inhibition concentration (IC50)/acute median lethal concentration (LC50) values ranging from 4 to 1,215 mg/L, as Mg. Experiments exposing the 3 most sensitive species (L. aequinoctialis, H. viridissima, and A. cumingi) to Na(2)SO(4) and MgCl(2) confirmed that Mg was the toxic ion. Additionally, Ca was shown to have an ameliorative effect on Mg toxicity. For L. aequinoctialis and H. viridissima, Mg toxicity at the IC50 concentration was eliminated at Mg:Ca (mass) ratios of < or =10:1 and < or =9:1, respectively. For A. cumingi, a 10 to 30% effect persisted at the IC50 concentration at Mg:Ca ratios <9:1. The toxicity of MgSO(4) in NMCW at a constant Mg:Ca ratio of 9:1 was lower than at background Ca, with chronic IC50/acute LC50 values from 96 to 4,054 mg/L, as Mg. Water quality guideline values for Mg (to protect 99% of species) at Mg:Ca mass ratios of >9:1 and < or =9:1 were 0.8 and 2.5 mg/L, respectively. Magnesium can be toxic at concentrations approaching natural background levels, but toxicity is dependent on Ca concentrations, with exposure in very low ionic concentration, Ca-deficient waters posing the greatest risk to aquatic life.

Toxicity and metal speciation characterisation of waste water from an abandoned gold mine in tropical northern Australia

The decommissioned Mount Todd gold mine, located in the wet-dry tropics of northern Australia, consists of a large waste water inventory and an acid rock drainage problem, which has the potential to impact upon freshwater ecosystems of the Edith River catchment. The toxicity of retention pond 1 (RP1) water was determined using six local freshwater species (duckweed, alga, cladoceran, snail, hydra and a fish). RP1 water was very toxic to all species, with the percentage dilution of RP1 water inhibiting 10% of organism response (IC10), or lethal to 5% of individuals (LC5), ranging from 0.007 to 0.088%. The percentage dilution of RP1 water inhibiting 50% of organism response (IC50), or lethal to 50% of individuals (LC50), ranged from 0.051% to 0.58%. Based on chemical analyses and geochemical speciation modelling of the test waters, Cu, Zn and Al were the most likely toxic components at acidic dilutions (i.e. > or =1%), while Cu and Zn were the most likely toxic components at 0.1% RP1 water, where pH was 6.5. Species sensitivity distributions (SSDs) were used to predict dilutions of RP1 water that would protect or unacceptably affect the downstream aquatic ecosystems. A dilution ratio of 1 part RP1 water to 20000 parts Edith River water (0.005% RP1 water) was calculated to be required for the protection of at least 95% of species. This information can be used in conjunction with field chemical and biological data to better predict the ecological risks of RP1 waste water downstream of the Mount Todd mine.

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.

Ecotoxicology of Highly Treated Mine Waters: Lessons from an Australian Mine

Abstract Mining operations commonly treat mine water prior to discharging it to the environment. Results of biological toxicity tests and Toxicity Identification Evaluations have shown that environmental risks can still exist for these highly treated waters. We present examples for mine waters that were treated using high density sludge–microfiltration–reverse osmosis and brine concentration processes. While such treatment substantially reduces the primary toxicity of the water, three key factors that could affect environmental consequences may arise or persist: (1) residual contaminants may still be at toxic concentrations, (2) the bioavailability of residual contaminants may increase, and (3) the treated water may be nutrient or major ion deficient. Appropriate strategies for the management of these treated waters should consider that toxicity or other water quality risks may still exist and that these will differ from those of the untreated water.ZusammenfassungBergwerke reinigen normalerweise ihr Grubenwasser bevor es in den Vorfluter abgegeben wird. Die Ergebnisse von toxikologischen Tests sowie von Untersuchungen zur Toxizität zeigen, dass diese gut gereinigten Grubenwasser nach wie vor Umweltrisiken darstellen können. Wir präsentieren Beispiele von Grubenwässern die mittels Dickschlamm-Mikrofiltration-Umkehrosmose sowie weiterer Aufkonzentrierung des Konzentrats gereinigt wurden. Diese Prozesse verringern die ursprüngliche Toxizität des Wassers deutlich. Es kann jedoch dazu kommen, dass drei wichtige, umweltrelevante Faktoren entstehen oder bestehen bleiben: 1) Restverunreinigungen können in noch toxischen Konzentrationen vorliegen, 2) die Bioverfügbarkeit der Restverunreinigungen wird erhöht und 3) das Wasser kann einen Mangel an Nährstoffen oder Hauptionen aufweisen. Entsprechende Strategien für das Management dieser gereinigten Wässer sollten daher berücksichtigen, dass diese nach wie vor Toxizität oder Risiken aufweisen können, die sich von denen des ungereinigten Wassers unterscheiden.ResumenLas operaciones mineras usualmente tratan las aguas de minas antes de su descarga en el medio ambiente. Los resultados de ensayos de toxicidad biológica y evaluaciones de identificación de toxicidad (TIE) han mostrado que los riesgos ambientales pueden seguir existiendo en las aguas altamente tratadas. En este trabajo presentamos ejemplos sobre aguas de minas que fueron tratadas usando lodo de alta densidad-microfiltración-ósmosis reversa (HDS/MF/RO) y procesos de concentración de salmuera (BC). Mientras que tales tratamientos reducen substancialmente la toxicidad primaria del agua, tres factores principales que podrían traer consecuencias ambientales pueden persistir: 1) contaminantes residuales pueden aún estar en concentraciones tóxicas, 2) la biodisponibilidad de los contaminantes residuales puede incrementarse y, 3) el agua tratada puede ser deficiente en nutrientes o en iones. Estrategias apropiadas para el manejo de estas aguas tratadas deberían considerar que la toxicidad o los riesgos de calidad de agua pueden existir y que ellos diferirán de los que tiene el agua sin tratamiento.抽象采矿产生的矿井废水必须经过处理达标才能向环境排放。但是,生物毒理试验和毒理识别评价(TIE)表明矿井废水经深度处理后可能仍存在环境风险。本文研究了矿井废水经过高密度污泥-微滤-反渗膜(HDS/MF/RO)和卤水浓缩(BC)深度处理后的生态毒理学特征。虽然该处理工艺已经大幅消除了废水的毒性,但是处理后废水可能产生环境影响的三个关键因素仍然存在:(1) 残留污染物浓度可能仍处于毒性范围;(2) 残留污染物的生物药效可能增大;(3) 被处理水可能富含营养也可能主离子缺失。合理的水处理方案应该考虑水的毒性或其它水质风险依然存在,应该考虑处理前后毒理的变化。

Development and implementation of a site‐specific water quality limit for uranium in a high conservation value ecosystem

Water quality guideline values (GVs) are a key tool for water quality assessments. Site-specific GVs, which incorporate data relevant to local conditions and organisms, provide a higher level of confidence that the GV will protect the aquatic ecosystem at a site compared to generic GVs. Site-specific GVs are, therefore, considered particularly suitable for sites of high sociopolitical or ecological importance. The present paper provides an example of the refinement of a site-specific GV for high ecological value aquatic ecosystems in Kakadu National Park, Northern Territory, Australia, to improve its site specificity and statistical robustness, thereby increasing confidence in its application. Uranium is a contaminant of concern for Ranger U mine, which releases water into Magela Creek and Gulungul Creek in Kakadu National Park. A site-specific GV for U has been applied, as a statutory limit, to Magela Creek since 2004 and to Gulungul Creek since 2015. The GV of 6 μg/L U was derived from toxicity data for 5 local species tested under local conditions. The acquisition of additional U data, including new information on the effect of DOC on U toxicity, enabled a revision of the site-specific U GV to 2.8 μg/L U and an ability to adjust the value on the basis of environmental concentrations of DOC. The revised GV has been adopted as the statutory limit, with the regulatory framework structured so the GV requires adjustment based on DOC concentration only when an exceedance occurs. Monitoring data for Magela Creek (2001-2013) and Gulungul Creek (2003-2013) downstream of the mine show that dissolved U has not exceeded 1 μg/L. Integr Environ Assess Manag 2017;13:765-777.

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.

Hydra viridissima (green Hydra) rapidly recovers from multiple magnesium pulse exposures

The time taken for organisms to recover from a pulsed toxicant exposure is an important consideration when water quality guidelines are applied to intermittent events in the environment. Organisms may appear to have recovered by standard toxicity testing methods but could carry residual toxicant or damage that may make them more sensitive to subsequent pulses. Such cumulative effects may render guidelines underprotective. The present study evaluated recovery of the freshwater cnidarian Hydra viridissima following multiple pulse exposure to magnesium (Mg). The H. viridissima were exposed to 4-h pulses of 790 mg/L and 1100 mg/L separated by 2-h, 10-h, 18-h, 24-h, 48-h, and 72-h recovery periods. Twenty-four-hour pulses of 570 mg/L, 910 mg/L, and 940 mg/L were separated by 24-h, 96-h, and 168-h recovery periods. All treatments showed similar or reduced sensitivity to the second pulse when compared with the single pulse, indicating that full recovery occurred prior to a second pulse-exposure. Five variations of equivalent time-weighted average concentrations were used to compare sensitivity of Hydra with various pulse scenarios. The sensitivity of the organisms to the multiple pulses was significantly lower than the time-weighted average continuous exposure response in 3 of the 4 scenarios tested, indicating that the Hydra benefited from interpulse recovery periods. The findings will be utilized alongside those from other species to inform the use of a site-specific, duration-based water quality guideline for Mg, and they provide an example of the use of empirical data in the regulation of toxicant pulses in the environment.

Failure of Hydra populations to develop tolerance, indicates absence of toxicity from a mining whole-effluent

The green hydra, Hydra viridissima, exists in water bodies on the Project Area ofthe Ranger Uranium Mine (RUM) in northern Australia, which contain concentrations of magnesium (Mg), higher than those reported to cause toxicity from the Environmental Research Institute of the Supervising Scientist (eriss) laboratory toxicity tests. McCuLLOUGH (2006) reported a lowest-observed-effectconcentration (LOEC) for H. viridissima of 4.6 mg L Mg, (present as MgS04), which represented a population growth rate decrease of approximately 30% relative to the control response. The same study found that toxicity was due to Mg and not so4. However, CORBETT (1996) reported the presence of H. viridissima in water bodies on the RUM Project Area containing Mg concentrations above this LOEC, and theoretically high enough to severely impact population growth (i.e., 10-20 mg L-1). The disparity between the eriss laboratory and field results raised the question of how H. viridissima could exist in these contaminated environments. lnteractions between chemical compounds in complex mixtures can result in antagonistic effects that reduce toxicity (WARNE 2003). In addition, however, adaptation of aquatic organisms exposed to elevated contaminant concentrations can occur (DIXON & SPRAGUE 1981, GALE et al. 2003). The presence of H. viridissima in the contaminated water bodies could potentially be explained by one or both of these factors. This study sought to determine whether H. viridissima from a water body containing elevated Mg exhibited increased tolerance to Mg by comparing their responses to those of H. viridissima from eriss laboratory stock. We exposed cultures from both populations to a series of concentrations of (l) contaminated billabong water from the RUM Project Area, and (2) Mg-spiked natural creek water.