Graph neural networks-enhanced relation prediction for ecotoxicology (GRAPE).

Exposure to toxic chemicals threatens species and ecosystems. This study introduces a novel approach using Graph Neural Networks (GNNs) to integrate aquatic toxicity data, providing an alternative to complement traditional in vivo ecotoxicity testing. This study pioneers the application of GNN in ecotoxicology by formulating the problem as a relation prediction task. GRAPE's key innovation lies in simultaneously modelling 444 aquatic species and 2826 chemicals within a graph, leveraging relations from existing datasets where informative species and chemical features are augmented to make informed predictions. Extensive evaluations demonstrate the superiority of GRAPE over Logistic Regression (LR) and Multi-Layer Perceptron (MLP) models, achieving remarkable improvements of up to a 30% increase in recall values. GRAPE consistently outperforms LR and MLP in predicting novel chemicals and new species. In particular, GRAPE showcases substantial enhancements in recall values, with improvements of ≥ 100% for novel chemicals and up to 13% for new species. Specifically, GRAPE correctly predicts the effects of novel chemicals (104 out of 126) and effects on new species (7 out of 8). Moreover, the study highlights the effectiveness of the proposed chemical features and induced network topology through GNN for accurately predicting metallic (74 out of 86) and organic (612 out of 674) chemicals, showcasing the broad applicability and robustness of the GRAPE model in ecotoxicological investigations. The code/data are provided at https://github.com/csiro-robotics/GRAPE.

Advantages of model averaging of species sensitivity distributions used for regulating produced water discharges.

Produced water (PW) generated by Australian offshore oil and gas activities is typically discharged to the ocean after treatment. These complex mixtures of organic and inorganic compounds can pose significant environmental risk to receiving waters, if not managed appropriately. Oil and gas operators in Australia are required to demonstrate that environmental impacts of their activity are managed to levels that are as low as reasonably practicable, for example, through risk assessments comparing predicted no-effect concentrations (PNECs) with predicted environmental concentrations of PW. Probabilistic species sensitivity distribution (SSD) approaches are increasingly being used to derive PW PNECs and subsequently calculating dilutions of PW (termed "safe" dilutions) required to protect a nominated percentage of species in the receiving environment (e.g., 95% and 99% or PC95 and PC99, respectively). Limitations associated with SSDs include fitting a single model to small (six to eight species) data sets, resulting in large uncertainty (very wide 95% confidence limits) in the region associated with PC99 and PC95 results. Recent advances in SSD methodology, in the form of model averaging, claim to overcome some of these limitations by applying the average model fit of multiple models to a data set. We assessed the advantages and limitations of four different SSD software packages for determining PNECs for five PWs from a gas and condensate platform off the North West Shelf of Australia. Model averaging reduced occurrences of extreme uncertainty around PC95 and PC99 values compared with single model fitting and was less prone to the derivation of overly conservative PC99 and PC95 values that resulted from lack of fit to single models. Our results support the use of model averaging for improved robustness in derived PNEC and subsequent "safe" dilution values for PW discharge management and risk assessment. In addition, we present and discuss the toxicity of PW considering the paucity of such information in peer-reviewed literature. Integr Environ Assess Manag 2024;20:498-517. © 2023 Commonwealth Scientific and Industrial Research Organisation. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Applicability of Chronic Multiple Linear Regression Models for Predicting Zinc Toxicity in Australian and New Zealand Freshwaters.

Bioavailability models, for example, multiple linear regressions (MLRs) of water quality parameters, are increasingly being used to develop bioavailability-based water quality criteria for metals. However, models developed for the Northern Hemisphere cannot be adopted for Australia and New Zealand without first validating them against local species and local water chemistry characteristics. We investigated the applicability of zinc chronic bioavailability models to predict toxicity in a range of uncontaminated natural waters in Australia and New Zealand. Water chemistry data were compiled to guide a selection of waters with different zinc toxicity-modifying factors. Predicted toxicities using several bioavailability models were compared with observed chronic toxicities for the green alga Raphidocelis subcapitata and the native cladocerans Ceriodaphnia cf. dubia and Daphnia thomsoni. The most sensitive species to zinc in five New Zealand freshwaters was R. subcapitata (72-h growth rate), with toxicity ameliorated by high dissolved organic carbon (DOC) or low pH, and hardness having a minimal influence. Zinc toxicity to D. thomsoni (reproduction) was ameliorated by both high DOC and hardness in these same waters. No single trophic level-specific effect concentration, 10% (EC10) MLR was the best predictor of chronic toxicity to the cladocerans, and MLRs based on EC10 values both over- and under-predicted zinc toxicity. The EC50 MLRs better predicted toxicities to both the Australian and New Zealand cladocerans to within a factor of 2 of the observed toxicities in most waters. These findings suggest that existing MLRs may be useful for normalizing local ecotoxicity data to derive water quality criteria for Australia and New Zealand. The final choice of models will depend on their predictive ability, level of protection, and ease of use. Environ Toxicol Chem 2023;42:2614-2629. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Acute and chronic toxicity of manganese to tropical adult coral (Acropora millepora) to support the derivation of marine manganese water quality guideline values.

Adult corals are among the most sensitive marine organisms to dissolved manganese and experience tissue sloughing without bleaching (i.e., no loss of Symbiodinium spp.) but there are no chronic toxicity data for this sensitive endpoint. We exposed adult Acropora millepora to manganese in 2-d acute and 14-d chronic experiments using tissue sloughing as the toxicity endpoint. The acute tissue sloughing median effect concentration (EC50) was 2560 µg Mn/L. There was no chronic toxicity to A. millepora at concentrations up to and including the highest concentration of 1090 µg Mn/L i.e., the chronic no observed effect concentration (NOEC). A coral-specific acute-to-chronic ratio (ACR) (EC50/NOEC) of 2.3 was derived. These data were combined with chronic toxicity data for other marine organisms in a species sensitivity distribution (SSD). Marine manganese guidelines were 190, 300, 390 and 570 µg Mn/L to provide long-term protection of 99, 95, 90, and 80 % of marine species, respectively.

Adult Corals Are Uniquely More Sensitive to Manganese Than Coral Early-Life Stages.

Manganese (Mn) is an essential element and is generally considered to be one of the least toxic metals to aquatic organisms, with chronic effects rarely seen at concentrations below 1000 µg/L. Anthropogenic activities lead to elevated concentrations of Mn in tropical marine waters. Limited data suggest that Mn is more acutely toxic to adults than to early life stages of scleractinian corals in static renewal tests. However, to enable the inclusion of sufficient sensitive coral data in species sensitivity distributions to derive water quality guideline values for Mn, we determined the acute toxicity of Mn to the adult scleractinian coral, Acropora muricata, in flow-through exposures. The 48-h median effective concentration was 824 µg Mn/L (based on time-weighted average, measured, dissolved Mn). The endpoint was tissue sloughing, a lethal process by which coral tissue detaches from the coral skeleton. Tissue sloughing was unrelated to superoxidase dismutase activity in coral tissue, and occurred in the absence of bleaching, that is, toxic effects were observed for the coral host, but not for algal symbionts. We confirm that adult scleractinian corals are uniquely sensitive to Mn in acute exposures at concentrations 10-340 times lower than those reported to cause acute or chronic toxicity to coral early life stages, challenging the traditional notion that early life stages are more sensitive than mature organisms. Environ Toxicol Chem 2023;42:1359-1370. © 2023 Commonwealth Scientific and Industrial Research Organisation. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The Influence of Oil-in-Water Preparations on the Toxicity of Crude Oil to Marine Invertebrates and Fish Following Short-Term Pulse and Continuous Exposures.

Following an oil spill, accurate assessments of the ecological risks of exposure to compounds within petroleum are required, as is knowledge regarding how those risks may change with the use of chemical dispersants. Laboratory toxicity tests are frequently used to assess these risks, but differences in the methods for preparation of oil-in-water solutions may confound interpretation, as may differences in exposure time to those solutions. In the present study, we used recently developed modifications of standardized ecotoxicity tests with copepods (Acartia sinjiensis), sea urchins (Heliocidaris tuberculata), and fish embryos (Seriola lalandi) to assess their response to crude oil solutions and assessed whether the oil-in-water preparation method changed the results. We created a water-accommodated fraction, a chemically enhanced water-accommodated fraction, and a high-energy water-accommodated fraction (HEWAF) using standard approaches using two different dispersants, Corexit 9500 and Slickgone NS. We found that toxicity was best related to total polycyclic aromatic hydrocarbon (TPAH) concentrations in solution, regardless of the preparation method used, and that the HEWAF was the most toxic because it dispersed the highest quantity of oil into solution. The TPAH composition in water did not vary appreciably with different preparation methods. For copepods and sea urchins, we also found that at least some of the toxic response could be attributed to the chemical oil dispersant. We did not observe the characteristic cardiac deformities that have been previously reported in fish embryos, most likely due to the use of unweathered oil, and, as a consequence, the high proportion of naphthalenes relative to cardiotoxic polycyclic aromatic hydrocarbon in the overall composition. The present study highlights the need to characterize both the TPAH composition and concentration in test solutions when assessing oil toxicity. Environ Toxicol Chem 2022;41:2580-2594. © 2022 SETAC.

A generic environmental risk assessment framework for deep-sea tailings placement.

Deep-sea tailings placement (DSTP) involves the oceanic discharge of tailings at depth (usually >100 m), with the intent of ultimate deposition of tailings solids on the deep-sea bed (>1000 m), well below the euphotic zone. DSTP discharges consist of a slurry of mine tailings solids (finely crushed rock) and residual process liquor containing low concentrations of metals, metalloids, flotation agents and flocculants. This slurry can potentially affect both pelagic and benthic biota inhabiting coastal waters, the continental slope and the deep-sea bed. Building on a conceptual model of DSTP exposure pathways and receptors, we developed a stressor-driven environmental risk assessment (ERA) framework using causal pathways/causal networks for each of eight pelagic and benthic impact zones. For the risk characterisation, each link in each causal pathway in each zone was scored using four levels of likelihood (not possible, possible, likely and certain) and two levels of consequence (not material, material) to give final risk rankings of low, potential, high or very high risk. Of the 246 individual causal pathways scored, 11 and 18 pathways were considered to be of very high risk and high risk respectively. These were confined to the benthic zones in the mixing zone (continental slope) and the primary and secondary deposition zones. The new risk framework was then tested using a case study of the Batu Hijau copper mine in Indonesia, the largest DSTP operation globally. The major risk of DSTP is smothering of benthic biota, even outside the predicted deposition zones. Timescales for recovery are slow and may lead to different communities than those that existed prior to tailings deposition. We make several recommendations for monitoring programs for existing, proposed and legacy DSTP operations and illustrate how georeferenced causal networks are valuable tools for ERA in DSTP.

The influence of salinity on the chronic toxicity of shale gas flowback wastewater to freshwater organisms.

The potential environmental risk associated with flowback waters generated during hydraulic fracturing of target shale gas formations needs to be assessed to enable management decisions and actions that prevent adverse impacts on aquatic ecosystems. Using direct toxicity assessment (DTA), we determined that the shale gas flowback wastewater (FWW) from two exploration wells (Tanumbirini-1 and Kyalla 117 N2) in the Beetaloo Sub-basin, Northern Territory, Australia were chronically toxic to eight freshwater biota. Salinity in the respective FWWs contributed 16% and 55% of the chronic toxicity at the 50% effect level. The remaining toxicity was attributed to unidentified chemicals and interactive effects from the mixture of identified organics, inorganics and radionuclides. The most sensitive chronic endpoints were the snail (Physa acuta) embryo development (0.08-1.1% EC10), microalga (Chlorella sp. 12) growth rate inhibition (0.23-3.7% EC10) and water flea (Ceriodaphnia cf. dubia) reproduction (0.38-4.9% EC10). No effect and 10% effect concentrations from the DTA were used in a species sensitivity distribution to derive "safe" dilutions of 1 in 300 and 1 in 1140 for the two FWWs. These dilutions would provide site-specific long-term protection to 95% of aquatic biota in the unlikely event of an accidental spill or seepage.

Modelling the attenuation of flowback chemicals for a soil-groundwater pathway from a hypothetical spill accident.

Flowback water from shale gas operations contains formation-derived compounds, including trace metals, radionuclides, and organics. While accidental releases from storage tanks with flowback water are low-probability events if multiple containment barriers are put in place, they cannot be entirely excluded. Here the natural attenuation potential of deep unsaturated zones and groundwater was explored using predictive modelling involving a hypothetical leak from a storage tank. Actual chemical concentrations from flowback water at two shale gas wells with contrasting salinity (12,300 and 105,000 ppm TDS) in the Beetaloo Sub-basin (Northern Territory, Australia) served as input to the one-dimensional HYDRUS model for simulating chemical transport through the unsaturated zone, with groundwater at 50 and 100 m depth, respectively. Subsequent chemical transport in groundwater involved the use of a three-dimensional analytical transport model. For a total of 63 chemicals the long-term attenuation from dilution and dispersion in unsaturated sediments and groundwater was calculated. Predicted environmental concentrations for aquatic receptors were compared with no-effect levels of individual chemicals to derive risk quotients (RQ) and identify chemicals of no concern to ecosystem health (i.e. RQ <1). Except for salinity and radium-228 in one of the two wells, RQ < 1 for all other chemicals. The initial approach considered testing of toxicity to individual chemicals only. When direct toxicity assessments (DTAs) were used to account for effects of chemical mixtures, the required DTA-derived safe dilution factor for 95% species protection was 1.8 to 2.5 times higher than the dilution factor accounting for dispersion and dilution only. Accounting for biodegradation, sorption and radioactive decay decreased chemical concentrations in unsaturated sediments to safe levels using the DTA for all chemicals. The study highlighted the importance of incorporating DTA in chemical risk assessments involving complex chemical mixtures. Improved understanding of fate and transport of flowback chemicals will help effectively manage water-quality risks associated with shale gas extraction.

A Comparison of Short-Term and Continuous Exposures in Toxicity Tests of Produced Waters, Condensate, and Crude Oil to Marine Invertebrates and Fish.

Petroleum hydrocarbons can be discharged into the marine environment during offshore oil and gas production or as a result of oil spills, with potential impacts on marine organisms. Ecotoxicological assay durations (typically 24-96 h) used to characterize risks to exposed organisms may not always reflect realistic environmental exposure durations in a high-energy offshore environment where hydrocarbons are mixed and diluted rapidly in the water column. To investigate this, we adapted 3 sensitive toxicity tests to incorporate a short-term pulse exposure to 3 petroleum-based products: a produced water, the water-accommodated fraction (WAF) of a condensate, and a crude oil WAF. We measured 48-h mobility of the copepod Acartia sinjiensis, 72-h larval development of the sea urchin Heliocidaris tuberculata, and 48-h embryo survival and deformities of yellowtail kingfish Seriola lalandi, after exposure to a dilution series of each of the 3 products for 2, 4 to 12, and 24 h and for the standard duration of each toxicity test (continuous exposure). Effects on copepod survival and sea urchin larval development were significantly reduced in short-term exposures to produced water and WAFs compared to continuous exposures. Fish embryos, however, showed an increased frequency of deformities at elevated concentrations regardless of exposure duration, although there was a trend toward increased severity of deformities with continuous exposure. The results demonstrate how exposure duration alters toxic response and how incorporating relevant exposure duration to contaminants into toxicity testing may aid interpretation of more realistic effects (and hence an additional line of evidence in risk assessment) in the receiving environment. Environ Toxicol Chem 2021;40:2587-2600. © 2021 CSIRO. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Metabarcoding Reveals Changes in Benthic Eukaryote and Prokaryote Community Composition along a Tropical Marine Sediment Nickel Gradient.

The Southeast Asia and Melanesia region has extensive nickel (Ni)-rich lateritic regoliths formed from the tropical weathering of ultramafic rocks. As the global demand for Ni continues to rise, these lateritic regoliths are increasingly being exploited for their economic benefit. Mining of these regoliths contributes to the enrichment of coastal sediments in trace metals, especially Ni. The present study used high-throughput sequencing (metabarcoding) to determine changes in eukaryote (18s v7 recombinant DNA [rDNA] and diatom-specific subregion of the 18s v4 rDNA) and prokaryote (16s v4 rDNA) community compositions along a sediment Ni concentration gradient offshore from a large lateritized ultramafic regolith in New Caledonia (Vavouto Bay). Significant changes in the eukaryote, diatom, and prokaryote community compositions were found along the Ni concentration gradient. These changes correlated most with the dilute-acid extractable concentration of Ni in the sediments, which explained 26, 23, and 19% of the variation for eukaryote, diatom, and prokaryote community compositions, respectively. Univariate analyses showed that there was no consistent change in indices of biodiversity, evenness, or richness. Diatom richness and diversity did, however, decrease as sediment acid extractable-Ni concentrations increased. Threshold indicator taxa analysis was conducted separately for each of the 3 targeted genes to detect changes in taxa whose occurrences decreased or increased along the acid extractable-Ni concentration gradient. Based on these data, 46 mg acid extractable-Ni/kg was determined as a threshold value where sensitive species began to disappear. In the case of the estuarine sediments offshore from lateritized ultramafic regolith in New Caledonia, this is recommended as an interim threshold value until further lines of evidence can contribute to a region-specific Ni sediment quality guideline value. Environ Toxicol Chem 2021;40:1894-1907. © 2021 SETAC.

Development of a bioavailability-based risk assessment framework for nickel in Southeast Asia and Melanesia.

Nickel laterite ore deposits are becoming increasingly important sources of Ni for the global marketplace and are found mainly in tropical and subtropical regions, including Indonesia, the Philippines, Papua New Guinea, Cuba, and New Caledonia. There are few legislatively derived standards or guidelines for the protection of aquatic life for Ni in many of these tropical regions, and bioavailability-based environmental risk assessment (ERA) approaches for metals have mainly been developed and tested in temperate regions, such as the United States and Europe. This paper reports on a multi-institutional, 5-y testing program to evaluate Ni exposure, effects, and risk characterization in the Southeast Asia and Melanesia (SEAM) region, which includes New Caledonia, Papua New Guinea, the Philippines, and Indonesia. Further, we have developed an approach to determine if the individual components of classical ERA, including effects assessments, exposure assessments, and risk characterization methodologies (which include bioavailability normalization), are applicable in this region. A main conclusion of this research program is that although ecosystems and exposures may be different in tropical systems, ERA paradigms are constant. A large chronic ecotoxicity data set for Ni is now available for tropical species, and the data developed suggest that tropical ecosystems are not uniquely sensitive to Ni exposure; hence, scientific support exists for combining tropical and temperate data sets to develop tropical environmental quality standards (EQSs). The generic tropical database and tropical exposure scenarios generated can be used as a starting point to examine the unique biotic and abiotic characteristics of specific tropical ecosystems in the SEAM region. Integr Environ Assess Manag 2021;17:802-813. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Empirical Bioavailability Corrections for Nickel in Freshwaters for Australia and New Zealand Water Quality Guideline Development.

Bioavailability-based approaches have been developed for the regulation of metals in freshwaters in several countries. Empirical multiple linear regression (MLR) models have been developed for nickel that can be applied to aquatic organisms. The MLR models have been compared against the use of previously developed biotic ligand models (BLMs) for the normalization of an ecotoxicity dataset compiled for the derivation of a water quality guideline value that could be applied in Australia and New Zealand. The MLR models were developed from data for a number of specific species and were validated independently to confirm their reliability. An MLR modeling approach using different models for algae, plants, invertebrates, and vertebrates performed better than either a pooled MLR model for all taxa or the BLMs, in terms of its ability to correctly predict the results of the tests in the ecotoxicity database based on their water chemistry and a fitted species-specific sensitivity parameter. The present study demonstrates that MLR approaches can be developed and validated to predict chronic nickel toxicity to freshwater ecosystems from existing datasets. The MLR approaches provide a viable alternative to the use of BLMs for taking account of nickel bioavailability in freshwaters for regulatory purposes. Environ Toxicol Chem 2021;40:113-126. © 2020 SETAC.

Application of Bioavailability Models to Derive Chronic Guideline Values for Nickel in Freshwaters of Australia and New Zealand.

There has been an increased emphasis on incorporating bioavailability-based approaches into freshwater guideline value derivations for metals in the Australian and New Zealand water quality guidelines. Four bioavailability models were compared: the existing European biotic ligand model (European Union BLM) and a softwater BLM, together with 2 newly developed multiple linear regressions (MLRs)-a trophic level-specific MLR and a pooled MLR. Each of the 4 models was used to normalize a nickel ecotoxicity dataset (combined tropical and temperate data) to an index condition of pH 7.5, 6 mg Ca/L, 4 mg Mg/L, (i.e., approximately 30 mg CaCO3 /L hardness), and 0.5 mg DOC/L. The trophic level-specific MLR outperformed the other 3 models, with 79% of the predicted 10% effect concentration (EC10) values within a factor of 2 of the observed EC10 values. All 4 models gave similar normalized species sensitivity distributions and similar estimates of protective concentrations (PCs). Based on the index condition water chemistry proposed as the basis of the national guideline value, a protective concentration for 95% of species (PC95) of 3 µg Ni/L was derived. This guideline value can be adjusted up and down to account for site-specific water chemistries. Predictions of PC95 values for 20 different typical water chemistries for Australia and New Zealand varied by >40-fold, which confirmed that correction for nickel bioavailability is critical for the derivation of site-specific guideline values. Environ Toxicol Chem 2021;40:100-112. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The Diffusive Gradients in Thin Films Technique Predicts Sediment Nickel Toxicity to the Amphipod Melita plumulosa.

The geographical shift of nickel mining to small island countries of the Southeast Asia and Melanesia region has produced a need to assess the environmental risk associated with increased sediment nickel exposure to benthic estuarine/marine biota. Chemical measurements of nickel concentration and potential bioavailability, including the use of diffusive gradients in thin films (DGT), were compared to effects on 10-d reproduction of the epibenthic estuarine/marine amphipod Melita plumulosa in nickel-spiked sediments and field-contaminated sediments with different characteristics. The 10% effect concentrations (EC10s) for amphipod reproduction ranged from 280 to 690 mg/kg total recoverable nickel, from 110 to 380 mg/kg dilute acid-extractable nickel, and from 34 to 87 µg Ni/m2 /h DGT-labile nickel flux. Nickel bioavailability was lower in sediments with greater total organic carbon, clay content, and percentage of fine particles. Measurements of DGT-labile nickel flux at the sediment-water interface integrated exposure to nickel from porewater, overlying water, and ingested sediment exposure pathways and were found to have the strongest relationship with the biological response. At most, there was a 29% reduction in 10-d M. plumulosa reproduction relative to the control when exposed to nickel from field-contaminated sediments collected from nickel laterite mining regions of New Caledonia. The DGT technique can be used as a complementary tool to measure the bioavailability of nickel in estuarine/marine sediments, especially sediments that are in nickel laterite mining regions where there are no or few toxicity data available for determining biological effects on local species. Based on the combined data set of the 3 nickel-spiked sediments a DGT-labile nickel EC10 threshold of 50 (30-69) µg Ni/m2 /h was determined. Environ Toxicol Chem 2021;40:1266-1278. © 2020 SETAC.

Effects of dissolved nickel and nickel-contaminated suspended sediment on the scleractinian coral, Acropora muricata.

Intensification of lateritic nickel mining in Southeast Asia and Melanesia potentially threatens coastal ecosystems from increased exposure to nickel and suspended sediment. This study investigated the response of Acropora muricata when exposed to either dissolved nickel, clean suspended sediment or nickel-contaminated suspended sediment for 7 days, followed by a 7-d recovery period. Significant bleaching and accumulation of nickel in coral tissue was observed only after exposure to high dissolved nickel concentrations and nickel-spiked suspended sediment. No effect on A. muricata was observed from exposure to a particulate-bound nickel concentration of 60 mg/kg acid-extractable nickel at a suspended sediment concentration of 30 mg/L TSS. This study demonstrates that bioavailability of nickel associated with suspended sediment exposure plays a key role in influencing nickel toxicity to corals. These findings assist in assessments of risk posed by increasing nickel mining activities on tropical marine ecosystems.

Toxicity of dissolved and precipitated forms of barium to a freshwater alga (Chlorella sp. 12) and water flea (Ceriodaphnia dubia).

Barium is present at elevated concentrations in oil and gas produced waters, and there is no international water quality guideline value to assess the potential risk of adverse effects to aquatic biota. Sulfate concentration largely controls the solubility of barium in aquatic systems, with insoluble barium sulfate (barite) assumed to be less bioavailable and less toxic than dissolved barium. We exposed aquatic biota to dissolved barium only and to a mixture of dissolved and precipitated barium. The chronic dissolved barium 48-h growth rate inhibition effect concentrations, (EC10 and EC50) for the tropical freshwater alga Chlorella sp. 12 were 40 mg/L (27-54 mg/L 95% confidence limits [CL]), and 240 mg/L (200-280 mg/L 95% CL), respectively. The acute EC10 and EC50 values for 48-h immobilization of the water flea (Ceriodaphnia dubia) by dissolved barium were 14 mg/L (13-15 mg/L 95% CL) and 17 mg/L (16-18 mg/L 95% CL), respectively. Chlorella sp. 12 was significantly more sensitive to precipitated barium than to dissolved barium, whereas the opposite seemed likely for C. dubia. Ceriodaphnia dubia was predicted to be chronically sensitive to dissolved barium at concentrations measured in produced waters and receiving waters, based on a predicted chronic EC10 of 1.7 mg/L derived from the acute EC50/10. Further chronic toxicity data that account for barium toxicity in dissolved and precipitated forms are required to derive a barium guideline for freshwater biota. Environ Toxicol Chem 2018;37:1632-1642. © 2018 SETAC.

Toxicity of nickel to tropical freshwater and sediment biota: A critical literature review and gap analysis.

More than two-thirds of the world's nickel (Ni) lateritic deposits are in tropical regions, and just less than half are within South East Asia and Melanesia (SEAM). With increasing Ni mining and processing in SEAM, environmental risk assessment tools are required to ensure sustainable development. Currently, there are no tropical-specific water or sediment quality guideline values for Ni, and the appropriateness of applying guideline values derived for temperate systems (e.g., Europe) to tropical ecosystems is unknown. Databases of Ni toxicity and toxicity tests for tropical freshwater and sediment species were compiled. Nickel toxicity data were ranked, using a quality assessment, identifying data to potentially use to derive tropical-specific Ni guideline values. There were no data for Ni toxicity in tropical freshwater sediments. For tropical freshwaters, of 163 Ni toxicity values for 40 different species, high-quality chronic data, based on measured Ni concentrations, were found for just 4 species (1 microalga, 2 macrophytes, and 1 cnidarian), all of which were relevant to SEAM. These data were insufficient to calculate tropical-specific guideline values for long-term aquatic ecosystem protection in tropical regions. For derivation of high-reliability tropical- or SEAM-specific water and sediment quality guideline values, additional research effort is required. Using gap analysis, we recommend how research gaps could be filled. Environ Toxicol Chem 2018;37:293-317. © 2017 SETAC.

Aquatic live animal radiotracing studies for ecotoxicological applications: Addressing fundamental methodological deficiencies.

The use of live animal gamma radioisotope tracer techniques in the field of ecotoxicology allows laboratory studies to accurately monitor contaminant biokinetics in real time for an individual organism. However, methods used in published studies for aquatic organisms are rarely described in sufficient detail to allow for study replication or an assessment of the errors associated with live animal radioanalysis to be identified. We evaluate the influence of some important methodological deficiencies through an overview of the literature on live aquatic animal radiotracer techniques and through the results obtained from our radiotracer studies on four aquatic invertebrate species. The main factors discussed are animal rinsing, radioanalysis and geometry corrections. We provide examples of three main techniques in live aquatic animal radiotracer studies to improve data quality control and demonstrate why each technique is crucial in interpreting the data from such studies. The animal rinsing technique is also relevant to non-radioisotope tracer studies, especially those involving nanoparticles. We present clear guidance on how to perform each technique and explain the importance of proper reporting of the validation of each technique for individual studies. In this paper we describe methods that are often used in lab-based radioecology studies but are rarely described in great detail. We hope that this paper will act as the basis for standard operating procedures for future radioecology studies to improve study replication and data quality control.