Toxicity of herbicides to the marine microalgae Tisochrysis lutea and Tetraselmis sp.

Pesticides are ubiquitous in the catchments of the Great Barrier Reef (GBR) and regularly discharge into the nearshore waters. Effective management of pesticides requires suitable water quality guideline values (WQGVs), and further ecotoxicological data for many pesticides are needed to improve the reliability of environmental risk assessments. To help address this issue, toxicity thresholds were determined to two species of tropical marine microalgae Tisochrysis lutea and Tetraselmis sp. for a suite of herbicides detected in the GBR. Photosystem II (PSII) herbicides significantly reduced growth with no effect concentration (NEC) and 10% effect concentration (EC10) values spanning two orders of magnitude from 0.60 µg L-1 for diuron to 60 µg L-1 for simazine across both species. However, growth was insensitive to the non-PSII herbicides. The NEC/EC10 thresholds for most herbicide-microalgae combinations were greater than recent WQGVs intended to protect 99% of species (PC99); however, metribuzin was toxic to T. lutea at concentrations lower than the current PC99 value, which may have to be revisited. The toxicity thresholds for alternative herbicides derived here further inform the development of national and GBR-specific WQGVs, but more toxicity data is needed to develop WQGVs for the > 50 additional pesticides detected in catchments of the GBR.

Methods for estimating no-effect toxicity concentrations in ecotoxicology.

A range of new statistical approaches is being developed and/or adopted in ecotoxicology that, when combined, can greatly improve the estimation of no-effect toxicity values from concentration-response (CR) experimental data. In particular, we compare the existing no-effect-concentration (NEC) threshold-based toxicity metric with an alternative no-significant-effect-concentration (NSEC) metric suitable for when CR data do not show evidence of a threshold effect. Using a model-averaging approach, these metrics can be combined to yield estimates of N(S)EC and of their uncertainty within a single analysis framework. The outcome is a framework for CR analysis that is robust to uncertainty in the model formulation, and for which resulting estimates can be confidently integrated into risk assessment frameworks, such as the species sensitivity distribution (SSD). Integr Environ Assess Manag 2024;20:279-293. © 2023 Commonwealth of Australia and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Derivation of toxicity thresholds for gas condensate oils protective of tropical species using experimental and modelling approaches.

Toxicity thresholds for dissolved oil applied in tropical ocean risk assessments are largely based on the sensitivities of temperate and/or freshwater species. To explore the suitability of these thresholds for tropical habitats we experimentally determined toxicity thresholds for eight tropical species for a partially weathered gas condensate, applied the target lipid model (TLM) to predict toxicity of fresh and weathered condensates and compared sensitivities of the tropical species with model predictions. The experimental condensate-specific hazard concentration (HC5) was 167 µg L-1 total aromatic hydrocarbons (TAH), with the TLM-modelled HC5 (78 µg L-1 TAH) being more conservative, supporting TLM-modelled thresholds for tropical application. Putative species-specific critical target lipid body burdens (CTLBBs) indicated that several of the species tested were among the more sensitive species in the TLM database ranging from 5.1 (coral larvae) to 97 (sponge larvae) µmol g-1 octanol and can be applied in modelling risk for tropical marine ecosystems.

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.

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.

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.

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.

Additive pressures of elevated sea surface temperatures and herbicides on symbiont-bearing foraminifera.

Elevated ocean temperatures and agrochemical pollution individually threaten inshore coral reefs, but these pressures are likely to occur simultaneously. Experiments were conducted to evaluate the combined effects of elevated temperature and the photosystem II (PSII) inhibiting herbicide diuron on several types of symbiotic algae (diatom, dinoflagellate or rhodophyte) of benthic foraminifera in hospite. Diuron was shown to evoke a direct effect on photosynthetic efficiency (reduced effective PSII quantum yield ΔF/F'(m)), while elevated temperatures (>30 °C, only 2 °C above current average summer temperatures) were observed to impact photosynthesis more indirectly by causing reductions in maximum PSII quantum yield (F(v)/F(m)), interpreted as photodamage. Additionally, elevated temperatures were shown to cause bleaching through loss of chlorophyll a in foraminifera hosting either diatoms or dinoflagellates. A significant linear correlation was found between reduced F(v)/F(m) and loss of chlorophyll a. In most cases, symbionts within foraminifera proved more sensitive to thermal stress in the presence of diuron (≥ 1 µg L(-1)). The mixture toxicity model of Independent Action (IA) described the combined effects of temperature and diuron on the photosystem of species hosting diatoms or dinoflagellates convincingly and in agreement with probabilistic statistics, so a response additive joint action can be assumed. We thus demonstrate that improving water quality can improve resilience of symbiotic phototrophs to projected increases in ocean temperatures. As IA described the observed combined effects from elevated temperature and diuron stress it may therefore be employed for prediction of untested mixtures and for assessing the efficacy of management measures.

Symbiont-specific responses in foraminifera to the herbicide diuron.

The effects of the photosystem II (PSII) herbicide diuron was assessed on thirteen tropical foraminifera hosting diatom, dinoflagellate, red or green algae endosymbionts. Inhibition of photosynthesis (reduced ΔF/F(m)(')) by diuron depended on both symbiont type and test ultrastructure, with greatest sensitivity observed for diatom- and chlorophyte-hosting species (24h IC(25) 2.5-4µg L(-1)). Inhibition kinetics was slow (24-48h until maximum inhibition) in comparison with corals, suggesting structural differences may influence herbicide uptake and transport. Although foraminifera were generally less sensitive to direct effects of diuron (inhibition ΔF/F(m)(')) than other marine phototrophs, damage to PSII (reduction F(v)/F(m)) occurred at concentrations lower than observed for other organisms (24h IC(25) 3-12µg L(-1)). Damage to PSII was highly light dependent and occurred at very low light intensities indicating limited photoprotective capacity. The high diversity, widespread occurrence and relative sensitivity make foraminifera good bioindicator organisms to evaluate phytotoxic stress on coral reefs.

Real-time automated measurement of Xenopus leavis tadpole behavior and behavioral responses following triphenyltin exposure using the multispecies freshwater biomonitor (MFB).

The present study examines whether behavior of Xenopus laevis tadpoles, when measured with the multispecies freshwater biomonitor (MFB), can be a sensitive and practical parameter for quantification of behavioral effects induced by toxic compounds. The MFB system is capable of automated simultaneous recording and integration of different types of movement over time. Basic tadpole behavior was studied under standard ambient temperature and colder conditions. At lower temperatures the time spent on low frequency behavior such as swimming and ventilation decreased, while at higher frequency movements associated with subtle tail tip oscillations it increased. Changes in behavior were also studied during the process of metamorphosis when both the morphology and physiology of tadpoles change. In the course of metamorphosis the tadpoles decreased the time spent on swimming and increased tail tip oscillations, especially in the period shortly before and during metamorphic climax. Additional experiments were performed to investigate whether the MFB could be used to quantify behavioral effects of exposure to a toxic compound. A 48 h exposure to a sublethal concentration of 1.25 microg L(-1) triphenyltin (TPT) significantly increased low frequency behavior, whereas 5 microg L(-1) TPT significantly reduced this type of behavior while the number of periods of total inactivity increased. One week after transferring the animals to clean water, registered behavior of tadpoles in the highest TPT group (5 microg L(-1)) was normal again for this developmental stage. The results show that the MFB can be used as a new tool for automated registration of sublethal toxic effects on tadpole behavior including recovery.