Copper toxicity to blue mussel embryos (Mytilus galloprovincialis): The effect of natural dissolved organic matter on copper toxicity in estuarine waters
Graphical abstract
Introduction
Estuarine environments are productive ecosystems with high ecological, economic and cultural value (Williams and Hall, 1999). The health of these ecosystems is, however, subjected to constant deterioration by influences such as pollution from urbanisation, industrialization and agricultural intensification (Williams and Hall, 1999), which makes it important to assess and quantify associated risks to aquatic organisms. Of special concern is the increase in chemical pollutants such as trace metals in estuaries (Buck and Bruland, 2005). Copper is one example. Copper serves as either an essential micronutrient to marine organisms, or as a toxicant when exceeding a critical concentration (Brand et al., 1986). The window between sufficiency and toxicity can be narrow and early life stages are usually the most vulnerable to Cu-toxicity (Fitzpatrick et al., 2008; Jakimska et al., 2011).
Chemical speciation is the driving factor for understanding Cu-bioavailability (i.e., fraction of copper in the aquatic system bioavailable for uptake by biota) and toxicity to aquatic organisms (Van Briesen et al., 2010). Cu-toxicity is directly related to the bioavailable Cu-concentration ([Cu′]) (Huang et al., 2003; Hassler et al., 2004, Hassler et al., 2007), which according to the biotic ligand model (BLM) is the concentration of free hydrated Cu-ions ([Cuf]) and Cu weakly complexed by inorganic ligands ([CuXIN]), such as Cl−, OH− and SO4−2 (Luoma, 1983; Campbell et al., 2002; Semeniuk et al., 2015), rather than the total dissolved Cu-concentration ([CuT]) present in solution (Luoma, 1983; Huang et al., 2003; Hassler et al., 2004, Hassler et al., 2007). The BLM integrates the concept of bioavailability to evaluate actual metal-toxicity risks (lethal and sub-lethal effects) to exposed aqueous biota (Niyogi and Wood, 2004; Smith et al., 2015) and, therefore, greatly improves the ability to generate site-specific ambient water quality criteria (AWQC) for metals in the natural environment (US EPA, 2002; Niyogi and Wood, 2004; Smith et al., 2015). The most mature BLM, and recently incorporated into the updated AWQC, is that for the toxicity of Cu (US EPA, 2007). The BLM also recognises that bioavailable metal concentrations in the water column are strongly mediated by geochemical conditions (Sander et al., 2015), which are highly variable both temporally and spatially within tide-dominated estuarine systems (Cloern and Nichols, 1985).
In estuarine waters, metal speciation is mainly influenced by changes in salinity and dissolved organic carbon (DOC) quantity and quality (Cooper et al., 2014; Deruytter et al., 2015). Alteration in these three parameters, typical for tidal environments, can alter metal complexation processes and bioavailability to aquatic organisms (Huang et al., 2003; Buck and Bruland, 2005; Grosell et al., 2007; Cooper et al., 2014). At present, the effects of rapid fluctuations in salinity, DOC-concentration and/or the nature of DOC on Cu-speciation in estuaries have not been assessed (Grosell et al., 2007). In constant conditions, several experiments have demonstrated (1) nonlinear and potentiating effects of increasing salinity on Cu-toxicity to various aquatic organisms instead of the toxicity decrease that is expected based on speciation processes (i.e., complexation and competition with cations) (Grosell et al., 2007; Deruytter et al., 2015), and (2) a proportionality between DOC-concentration and Cu-toxicity (Arnold et al., 2009, Arnold et al., 2010; Deruytter et al., 2013, Deruytter et al., 2015). These studies (Rosen et al., 2005; Arnold et al., 2009, Arnold et al., 2010; Deruytter et al., 2013, Deruytter et al., 2015; Bosse et al., 2014) illustrate, however, substantial differences in Cu-sensitivity for M. galloprovincialis embryos with [Cu48-h-EC50] (mortality and malformation as the half-maximal response of the embryos) between 65 and 547 nM. Changes with salinity in embryo osmoregulatory physiology as well as differences in DOC-sources and/or DOC-Cu-reactivities with salinity are thought to be responsible for these ambiguous Cu-toxicity results (Grosell et al., 2007; De Polo and Scrimshaw, 2012; Cooper et al., 2014; Deruytter et al., 2013, Deruytter et al., 2015).
It is well established that Cu has a high affinity for binding to some constituents that make up DOC, a process which prevents or attenuates Cu-uptake by, and Cu-toxicity to, aquatic organisms (Cooper et al., 2014). Cu-binding constituents of natural DOC are mainly humic substances (HS) from allochthonous (i.e., terrestrial input including stormwater and wastewater (DePalma et al., 2011; Mahmood, 2017)) and autochthonous (i.e., organic carbon formed in the aquatic environment) sources (Arnold et al., 2009; Cooper et al., 2014; Abualhaija et al., 2015; Nogueira et al., 2017) with allochthonous DOC being more protective against Cu-toxicity than autochthonous DOC (Cooper et al., 2014; Mahmood, 2017; Nogueira et al., 2017). The different Cu-binding affinities of the different Cu-binding species of DOC render DOC-source and related DOC-quality more important in determining Cu-complexation processes in the natural aquatic environment than DOC-concentration (Cooper et al., 2014; Deruytter et al., 2015). Thiols, known to emanate from reducing marine sediments or produced by marine organisms, may represent a second component of the Cu-binding ligand pool in estuarine and oceanic waters (Whitby and Van den Berg, 2015; Whitby et al., 2017). All in all, little is known regarding the effect of (1) different DOC-fractions on Cu-speciation, or (2) salinity on DOC-Cu-reactivity, which impedes comparison between eco-toxicological studies and prevents precise risk assessments for Cu in saline environments.
The focus of the present study was thus to assess the combined effect of natural DOC and salinity on Cu-toxicity in estuarine waters using a 48-h bioassay of blue mussel embryos (Mytilus galloprovincialis). Mytilus galloprovincialis is common and widely distributed internationally and is found in the intertidal zone of New Zealand (Gardner, 2004). Although not an estuarine species, M. galloprovincialis is known to be tolerant of a range of salinities (12 to 38 (Bayne, 1976)), and is used internationally for toxicity testing (ASTM, 1997). Given the lack of explicit Cu-speciation measurements in estuarine eco-toxicological studies, special emphasis was put on the measurement of Cu-speciation rather than a modelling approach. Cu-speciation parameters were determined using adsorptive cathodic stripping voltammetry (AdCSV) with salicylaldoxime (SA) as the complexing agent or anodic stripping voltammetry (ASV). Consequently, the present study builds on earlier research by Nadella et al. (2009), Arnold et al. (2010), and Deruytter et al. (2013 and 2015), thereby contributing to an integrated picture of Cu-speciation processes in estuarine environments to improve the BLM and associated Cu-risk assessments.
Section snippets
Materials and methods
The experiments were conducted collaboratively by the University of Otago and NIWA (Hamilton). All preparation, experiments and assessments followed the NIWA standard protocol for bivalve embryo-larval toxicity testing as described in Williams and Golding (2008) and elsewhere (American Society for Testing and Materials (ASTM), 1997). The protocol was modified to create trace-metal-clean working procedures in all stages of sampling and laboratory work (Arnold et al., 2009; Powell, 2015).
Statistical analysis
One 48-h-EC50 Cu-value ([Cu48-h-EC50]) was derived for each salinity-DOC-treatment, using embryo survival data for a given Cu-concentration (n = 5) for all 9 Cu-concentrations in the pre-test and 6 Cu-concentrations in the full-test prior to using the Log-normal Probit or the Trimmed Spearman-Karber method embedded in the Comprehensive Environmental Toxicity Information System software package (CETIS v1.7.0.2, Tidepool Scientific Software). If a concentration-dependent-response was observed
Physicochemical parameters
The majority of nutrient concentrations for the mixed test solutions within the full-test (Table A.3) were consistent with the anticipated values based on the end-member concentrations (Table 1), except for samples C, D, and G. Nutrient data for the pre-test is only available for control solutions as sample volume restricted the analysis of test solutions (Table A.3).
At t48 the mean temperature was 21.9 ± 0.1 °C, pH was 7.8 ± 0.1, and DO was 7.4 ± 0.1 mg/L for the pre-test solutions (Table
Discussion
To date several studies (Rosen et al., 2005; Arnold et al., 2009, Arnold et al., 2010; Deruytter et al., 2013, Deruytter et al., 2015; Bosse et al., 2014) illustrated substantial differences in the Cu-sensitivity for M. galloprovincialis embryos with 48-h-EC50 Cu-values between 65 and 547 nM. This ~8.4-fold discrepancy in the Cu-toxicity was explained by differences in DOC-concentration, DOC-origin, and varying salinity in the test media (Arnold et al., 2009; Nadella et al., 2009), but chemical
Conclusion and recommendations
Overall, this study highlights the importance of measuring Cu-speciation parameters when determining Cu-toxicity in the aquatic environment (Cooper et al., 2014). [Cu′] (sum of Cu2+ and CuXIN) along with measurements of [L], DOC-quality, and salinity are good predictors of 48-h-EC50 Cu-values and are thus critical to obtain an integrated picture of Cu-speciation and associated processes in natural waters - which may otherwise be misinterpreted when only [CuT] and/or [Cu2+] is measured. Further,
Acknowledgements
RZ received a doctoral scholarship from the University of Otago. This study was also supported in part by the Ministry of Business, Innovation and Employment (MBIE) grant to the National Institute of Water and Atmospheric Research (NIWA) for the “Management of Cumulative Effects of Stressors on Aquatic Systems” programme (Contract No: C01X1005). The authors thank and acknowledge David Barr, Dr. Rob Middag and Dr. Malcom Reid from the University of Otago for their technical support. The IAEA is
References (92)
- et al.
Competition between copper and iron for humic ligands in estuarine waters
Mar. Chem.
(2015) - et al.
Dissolved organic carbon in a large macrotidal estuary (the Humber, UK): behaviour during estuarine mixing
Mar. Pollut. Bull.
(1999) - et al.
Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues
Anal. Chim. Acta
(2009) - et al.
Copper bioavailability and toxicity to Mytilus galloprovincialis in Shelter Island Yacht Basin, San Diego, CA
Mar. Pollut. Bull.
(2014) - et al.
Reduction of marine phytoplankton reproduction rates by copper and cadmium
J. Exp. Mar. Biol. Ecol.
(1986) - et al.
Intercomparison of voltammetric techniques to determine the chemical speciation of dissolved copper in a coastal seawater sample
Anal. Chim. Acta
(2000) - et al.
Copper speciation in San Francisco Bay: a novel approach using multiple analytical windows
Mar. Chem.
(2005) - et al.
Metal bioavailability to phytoplankton—applicability of the biotic ligand model
Comp. Biochem. Physiol. C Toxicol. Pharmacol.
(2002) - et al.
Polarographic determination of half-wave potentials for copper-organic complexes in seawater
Mar. Chem.
(1999) - et al.
Effects of dissolved organic matter and reduced sulphur on copper bioavailability in coastal marine environments
Ecotoxicol. Environ. Saf.
(2011)
A new cathodic stripping voltammetric method for determining organic copper complexation in seawater
Mar. Chem.
The relative sensitivity of sperm, eggs and embryos to copper in the blue mussel (Mytilus trossulus)
Comp. Biochem. Physiol. C Toxicol. Pharmacol.
Influence of the type of titration and of data treatment methods on metal complexing parameters determination of single and multi-ligand systems measured by stripping voltammetry
Anal. Chim. Acta
Toxicity of copper to the green alga, Chlamydomonas reinhardtii (Chlorophyceae), as affected by humic substances of terrestrial and freshwater origin
Aquat. Toxicol.
Comparison of the linear van den Berg/Ružić transformation and a non-linear fit of the Langmuir isotherm applied to Cu speciation data in the estuarine environment
Mar. Chem.
Physiology is pivotal for interactions between salinity and acute copper toxicity to fish and invertebrates
Aquat. Toxicol.
Copper complexation by thiol compounds in estuarine waters
Mar. Chem.
Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)
Mar. Chem.
Bioavailability of trace metals to aquatic organisms—a review
Sci. Total Environ.
Distribution and potential sources and sinks of copper chelators in the Sargasso Sea
Deep Sea Res. A Oceanogr. Res. Pap.
Toxicity of dissolved Cu, Zn, Ni and Cd to developing embryos of the blue mussel (Mytilus trossulus) and the protective effect of dissolved organic carbon
Comp. Biochem. Physiol. C Toxicol. Pharmacol.
ProMCC: an all-in-one tool for trace metal complexation studies
Mar. Chem.
Complexation of iron (III) by natural organic ligands in the Central North Pacific as determined by a new competitive ligand equilibration/adsorptive cathodic stripping voltammetric method
Mar. Chem.
The effect of natural organic ligands on trace metal speciation in San Francisco Bay: implications for water quality criteria
Mar. Chem.
Acquisition of organically complexed copper by marine phytoplankton and bacteria in the northeast subarctic Pacific Ocean
Mar. Chem.
Strong copper complexation in an organic-rich estuary: the importance of allochthonous dissolved organic matter
Mar. Chem.
Using biotic ligand models to predict metal toxicity in mineralized systems
Appl. Geochem.
Evidence for copper-binding humic substances in seawater
Mar. Chem.
Standard guide for conducting static acute toxicity tests starting with embryos of four species of bivalve molluscs. E 724-94
Effects of dissolved organic carbon on copper toxicity: implications for saltwater copper criteria
Integr. Environ. Assess. Manag.
A comparison of the copper sensitivity of two economically important saltwater mussel species and a review of previously reported copper toxicity data for mussels: important implications for determining future ambient copper saltwater criteria in the USA
Environ. Toxicol.
A comparison of the copper sensitivity of six invertebrate species in ambient salt water of varying dissolved organic matter concentrations
Environ. Toxicol. Chem.
Technical Rationale for Changes to the Method for Deriving Australian and New Zealand Water Quality Guideline Values for Toxicants
Copper in the Ocean Environment
The organic complexation of iron and copper: an intercomparison of competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) techniques
Limnol. Oceanogr. Methods
Organic ligands—a key control on trace metal biogeochemistry in the ocean
Front. Mar. Sci.
Time scales and mechanisms of estuarine variability, a synthesis from studies of San Francisco Bay
Hydrobiologia
Influence of salinity and dissolved organic carbon on acute Cu toxicity to the rotifer Brachionus plicatilis
Environ. Sci. Technol.
Production of extracellular Cu complexing ligands by eucaryotic phytoplankton in response to Cu stress
Limnol. Oceanogr.
Challenges for the development of a biotic ligand model predicting copper toxicity in estuaries and seas
Environ. Toxicol. Chem.
The combined effect of dissolved organic carbon and salinity on the bioaccumulation of copper in marine mussel larvae
Environ. Sci. Technol.
Salinity and dissolved organic carbon both affect copper toxicity in mussel larvae: copper speciation or competition cannot explain everything
Environ. Toxicol. Chem.
Salinity, dissolved organic carbon, and interpopulation variability hardly influence the accumulation and effect of copper in Mytilus edulis
Environ. Toxicol. Chem.
Biotic ligand model of the acute toxicity of metals. 1. Technical basis
Environ. Toxicol. Chem.
Trace metal cycling in the Whau Estuary, Auckland, New Zealand
Environ. Chem.
Cited by (34)
Release of adsorbed copper and carbon during Fe(Ⅱ) catalytic conversion of ferrihydrite-humic acid coprecipitation under acidic condition: Mechanism and properties
2023, Journal of Environmental Chemical EngineeringIntegrative assessment of biomarker responses in Mytilus galloprovincialis exposed to seawater acidification and copper ions
2022, Science of the Total Environment