Stuart L. Simpson

Uptake and internalisation of copper by three marine microalgae: comparison of copper-sensitive and copper-tolerant species

Although it has been well established that different species of marine algae have different sensitivities to metals, our understanding of the physiological and biochemical basis for these differences is limited. This study investigated copper adsorption and internalisation in three algal species with differing sensitivities to copper. The diatom Phaeodactylum tricornutum was particularly sensitive to copper, with a 72-h IC50 (concentration of copper to inhibit growth rate by 50%) of 8.0 microg Cu L(-1), compared to the green algae Tetraselmis sp. (72-h IC50 47 microg Cu L(-1)) and Dunaliella tertiolecta (72-h IC50 530 microg Cu L(-1)). At these IC50 concentrations, Tetraselmis sp. had much higher intracellular copper (1.97+/-0.01 x 10(-13)g Cu cell(-1)) than P. tricornutum (0.23+/-0.19 x 10(-13)g Cu cell(-1)) and D. tertiolecta (0.59+/-0.05 x 10(-13)g Cu cell(-1)), suggesting that Tetraselmis sp. effectively detoxifies copper within the cell. By contrast, at the same external copper concentration (50 microg L(-1)), D. tertiolecta appears to better exclude copper than Tetraselmis sp. by having a slower copper internalisation rate and lower internal copper concentrations at equivalent extracellular concentrations. The results suggest that the use of internal copper concentrations and net uptake rates alone cannot explain differences in species-sensitivity for different algal species. Model prediction of copper toxicity to marine biota and understanding fundamental differences in species-sensitivity will require, not just an understanding of water quality parameters and copper-cell binding, but also further knowledge of cellular detoxification mechanisms.

The influence of sediment particle size and organic carbon on toxicity of copper to benthic invertebrates in oxic/suboxic surface sediments

The use of sediment quality guidelines to predict the toxicity of metals in sediments is limited by an inadequate understanding of exposure pathways and by poor causal links between exposure and effects. For a 10-d exposure to Cu-spiked sediments, toxicity to the amphipod Melita plumulosa was demonstrated to occur through a combination of dissolved and dietary Cu exposure pathways, but for the bivalves Spisula trigonella and Tellina deltoidalis, toxicity occurred primarily by exposure to dissolved Cu. For relatively oxidized sediments that had moderate amounts of organic carbon (2.6-8.3% OC), silt (20-100% <63-µm particles) but low acid-volatile sulfide (AVS), acute toxicity thresholds for the three species were derived based on the OC-normalized Cu concentration of the less than 63-µm sediment fraction. For all three species, no effects were observed at concentrations below 10 µg/L dissolved Cu (in pore water and overlying water) or below 12 mg Cu/g OC (for <63 µm sediment). For sediments with silt/OC properties of 20/0.5, 50/1, or 70/4%, the particulate Cu-based threshold equated to 60, 120, or 480 mg Cu/kg, respectively. For oxic/suboxic sediments in which AVS is not limiting metal availability, sediment quality guidelines of this form will provide adequate protection against toxicity and improve the prediction of effects for sediments with varying properties.

Oxidation of acid-volatile sulfide in surface sediments increases the release and toxicity of copper to the benthic amphipod Melita plumulosa

Acid-volatile sulfides (AVS) are an important metal-binding phase in sediments. For sediments that contain an excess of AVS over simultaneously extracted metal (SEM) concentrations, acute or chronic effects should not result from the metals Cd, Cu, Ni, Pb and Zn. While AVS phases may exist in surface sediments, the exposure to dissolved oxygen may oxidize the AVS and release metals to more bioavailable forms. We investigated the role of oxidation of AVS, and specifically copper sulfide phases, in surface sediments, in the toxicity to juveniles of the epibenthic amphipod, Melita plumulosa. Sediments containing known amounts of copper sulfide were prepared either in situ by reacting dissolved copper with AVS that had formed in field sediments or created in sediments within the laboratory, or by addition of synthesised CuS to sediments. Regardless of the form of the copper sulfide, considerable oxidation of AVS occurred during the 10-d tests. Sediments that had a molar excess of AVS compared to SEM at the start of the tests, did not always have an excess at the end of the tests. Consistent with the AVS-SEM model, no toxicity was observed for sediments with an excess of AVS throughout the tests. However, the study highlights the need to carefully consider the changes in AVS concentrations during tests, and that measurements of AVS and SEM concentrations should carefully target the materials to which the organisms are being exposed throughout tests, which in the case of juvenile M. plumulosa is the top few mm of the sediments.

Demonstrating the appropriateness of developing sediment quality guidelines based on sediment geochemical properties.

The pool of bioavailable metals in sediments is typically much smaller than the total metal concentration and is strongly influenced by metal-binding with acid-volatile sulfide (AVS), particulate organic carbon (OC), and iron and manganese oxide solid phases. We have investigated how the properties of relatively oxidized sediments influence the exposure and effects of copper on the survival and growth rate of the deposit-feeding benthic bivalve Tellina deltoidalis. Growth rate was a much more sensitive end point than survival. Toxic effects to growth were consistently observed in sediment where both pore water and overlying water copper concentrations were below the effect threshold for dissolved copper. Decreases in growth of the bivalve were largely attributable to dietary exposure to sediment-bound copper, as the organism was observed to actively feed on fine materials from the sediment surface. For sediments with the same total copper concentrations, effects were less for sediments with greater concentrations of fine particles (<63 μm sediment) or particulate organic carbon (OC). Based on the concentration-response relationship, a no-effect value of 5.5 mg <63 μm Cu g(-1) OC for growth of T. deltoidalis was calculated. The results confirm the appropriateness of using OC-normalized copper concentration in the <63 μm sediment fraction to develop sediment quality guidelines (SQGs) that vary with sediment properties. For sediments where the amount of AVS is not sufficient to bind metals in non bioavailable forms, the metal-binding capacity provided by OC and iron and manganese oxyhydroxides associated with the fine sediments considerably reduced metal bioavailability. These sediment properties should be considered when assessing the risks posed by metal-contaminated sediments.

Sub-lethal effects of copper to benthic invertebrates explained by sediment properties and dietary exposure

The next generation of sediment quality guidelines (SQGs) requires better established causal links between the chronic exposure and effects of metals from both dissolved and dietary sources. The potential for dietary exposure from sediment metals to cause toxic effects to benthic invertebrates is strongly influenced by the metal-binding properties of the sediments. For relatively oxidized sediments, sublethal effects of copper to the epibenthic deposit-feeding amphipod, Melita plumulosa, and the benthic harpacticoid copepod, Nitocra spinipes, were investigated. Effects on reproduction were strongly influenced by the properties of the sediments and sediment-bound copper was found to be the major contribution to the toxicity. For sediments with the same total copper concentrations, effects were less for sediments with greater concentrations of fine particles (<63 μm sediment) or particulate organic carbon (OC). The OC-normalized copper concentration in the <63 μm sediment fraction provided a single effects threshold for all sediment types. For M. plumulosa and N. spinipes, the 10% effect concentrations (EC10s) were 5.2 and 4.8 mg <63 μm Cu g(-1) OC. These chronic EC10s indicate that a SQG of 3.5 mg <63 μm Cu g(-1) OC, that was previously proposed based on a species sensitivity distribution of acute no effects thresholds data for 12 benthic organisms, will be protective for these species. The study confirms the appropriateness of using SQGs that vary with sediment properties and that SQGs of this form provide adequate protection for metal exposure via both dissolved and dietary exposure pathways.

Performance and sensitivity of rapid sublethal sediment toxicity tests with the amphipod Melita plumulosa and copepod Nitocra spinipes

Sublethal whole-sediment toxicity tests are an important tool for assessing the potential effects of contaminated sediments. However, the longer duration required for evaluating potential chronic effects may increase endpoint variability and test costs compared to survival endpoints. In the present study we compare the performance and sensitivity to contaminants of 10-d sublethal sediment toxicity tests with the amphipod Melita plumulosa and harpacticoid copepod Nitocra spinipes. For both tests, sublethal effects were consistently observed when sediment contaminant concentrations exceeded sediment quality guideline (SQG) concentrations. The response of these bioassays in metal-contaminated sediments was shown to conform ideally with respect to the mean SQG quotient calculated on the basis of the Australian and New Zealand lower SQG trigger value, with toxicity being observed only in those sediments where the mean quotient exceeded one. Better predictions of nontoxicity were obtained when dilute acid-extractable rather than total metal concentrations were used. Using the upper SQG, toxicity frequently occurred at mean quotients below one. The effects were generally consistent with predictions from the acid-volatile sulfide and simultaneously extracted metal model. Effects on reproduction of M. plumulosa were detected for sediments that did not cause effects on survival and highlighted the environmental relevance and importance of using these sublethal endpoints. When using four replicates for M. plumulosa and five replicates for N. spinipes, the endpoint variability (standard error) was less than 10%. Variations in sediment particle size and organic carbon content did not affect endpoint variability. Both species are relatively easily cultured in the laboratory, and the estimated effort and cost of achieving the sublethal endpoints is 1.5 times that of the acute survival test endpoints.

Geochemical influences on metal partitioning in contaminated estuarine sediments

Stormwater runoff has resulted in heavy metal contamination throughout much of the Port Jackson estuary, Sydney, Australia. Metal partitioning was investigated in the benthic estuarine sediments of Iron Cove, an off-channel embayment of Port Jackson. Contamination was greatest near the stormwater canal, where sediments were anoxic and contained high concentrations of sulfide in the porewater. Away from the canal a layer of non-cohesive, sub-oxic surficial sediment containing high dissolved iron was found overlaying a more cohesive substratum. At all sites, porewater Cd, Cu, Ni, Pb and Zn were <2.5 g L–1, and negligible metal release was observed upon sediment resuspension. According to water quality guidelines, the ecological risk posed by dissolved metals from the Iron Cove sediments is low. Estimated fluxes of Cd, Cu, Ni, Pb and Zn from the sediments were calculated to be <0.2 mol m–2 day–1. The rapid oxidation then hydrolysis of iron(II) in porewaters caused a drop in pH and the formation of iron hydroxide precipitate. These processes may affect dissolved metal concentrations; hence, oxidation of samples must be avoided during sampling and extraction procedures. Sediment-bound zinc was the metal most easily mobilized.

In Situ–Based Effects Measures: Considerations for Improving Methods and Approaches

Abstract In situ-based effects measures have gained increased acceptance as a means to improve the link between cause and effect in aquatic ecotoxicological studies. These approaches have primarily been employed where more conventional laboratory tests with field collected samples and routine in-field community surveys have failed to provide reasonable answers with respect to causes of toxicity, primary routes of contaminant exposure, and what constitutes ecotoxicologically relevant contaminant levels, at least at a site-specific level. One of the main advantages provided by in situ tests compared to more conventional field-based monitoring approaches is that they provide better control over stressor exposure to a defined population of test animals under natural or near-natural field conditions. In situ techniques can also be used to avoid artifacts related to sampling, transport and storage of contaminated water and sediment intended for laboratory-based toxicity assessment. In short, they can reduce the need for laboratory to field extrapolation and, when conducted properly, in situ tests can provide improved diagnostic ability and high ecological relevance. This paper provides suggestions and considerations for designing in situ studies, choosing test species and test endpoints, avoiding or minimizing test artifacts, best addressing some of the limitations of in situ test techniques, and generally improving the overall quality of the in situ approach chosen.

Development and application of a rapid amphipod reproduction test for sediment-quality assessment.

Melita plumulosa is an epibenthic, detritivorous amphipod native to eastern Australia that has been adopted as a test organism for toxicity evaluations of contaminated estuarine sediments. In the present study, a 13-d amphipod reproduction test was developed that encompasses gametogenesis, fertilization, and embryo development before hatching. The primary endpoints for the test are fecundity (measured as the number of embryos per individual surviving female) and a fecundity index (fecundity multiplied by the stage of embryo development). This new test has been employed to scrutinize the sediments from a metal-contaminated coastal lagoon. Lake Macquarie (NSW, Australia) is a large, saltwater lagoon that has received metal pollution over many decades, leading to a concentration gradient of trace metals, including Pb, Zn, Cd, and Cu, in the sediments. Within one of the northern bays (Warners Bay), the concentrations of these metals either border on or exceed sediment quality guideline values prescribed by Australian and New Zealand Guidelines for Fresh and Marine Water Quality. In trials with the 13-d amphipod reproduction test, Warners Bay sediments significantly reduced fecundity in the test species. Subsequent tests with clean sediments spiked singly with Pb, Zn, or Cu indicated that no single metal was responsible for the observed toxicity in the field sediments. However, sediments spiked with various combinations of Pb, Zn, Cd, and Cu indicated that Zn in combination with one or more of the other metals was responsible for the reproductive toxicity observed in Warners Bay sediments. In all these tests, measured metal concentrations in overlying water and pore water were low, thus confirming that the observed effects on reproduction could be attributed to dietary exposure to metals.

Influence of the choice of physical and chemistry variables on interpreting patterns of sediment contaminants and their relationships with estuarine macrobenthic communities

A primary objective of contaminated sediment risk assessments is to identify if contaminant enrichment is eliciting an ecological response. Using complementary environmental and biotic datasets, we examined five scenarios with respect to: dataset complexity; metal extraction; normalisation of organics; the inclusion/exclusion of acid-volatile sulfide data, and iron and manganese concentrations. Spatial distributions of abiotic variables were examined by principal components analysis, with canonical correspondence analysis used to examine the total and partitioning of biological variation. Metals were the dominant contaminant and explained the largest proportion of variation in the macrobenthic data. Extraction procedure and carbon normalisation of organics had little influence on the overall analysis. Porewater metal data was essential for interpretation, with excess of acid-volatile sulfide over simultaneously extractable metals being a poor surrogate. In the canonical correspondence analyses, the inclusion of Fe/Mn accentuated the covariation between the ecological and contaminant variables. Multimodel comparisons aided interpretation by emphasising specific relationships among environmental variables and their interactions with the biotic data. Furthermore, for future examinations of the described system, the findings can be used to reduce the collection of redundant environmental variables or variables that are poorly correlated with changes in macrobenthic assemblages.