The effect of humic acid on uptake/adsorption of copper by a marine bacterium and two marine ciliates

Effects of natural organic matter on the joint toxicity and accumulation of Cu nanoparticles and ZnO nanoparticles in Daphnia magna

Various modern products have metallic nanoparticles (MNPs) embedded to enhance products performance. Technological advances enable nowadays even multiple hybrid nanoparticles. Consequently, the future co-release of multiple MNPs will inevitably result in the presence of MNP mixtures in the environment. An important question is if the responses of mixtures of MNPs can be dealt with in a similar way as with the responses of biota to mixtures of metal salts. Moreover, natural organic matter (NOM) is an important parameter affecting the behavior and effect of MNPs. Herein, we determined the joint toxicity and accumulation of copper nanoparticles (CuNPs) and zinc oxide nanoparticles (ZnONPs) in Daphnia magna in the absence and presence of Suwannee River natural organic matter (SR-NOM), compared to the joint toxicity and accumulation of corresponding metal salts. The results of toxicity testing showed that the joint toxicity of CuNPs + ZnONPs was greater than the single toxicity of CuNPs or ZnONPs. The joint toxic action of CuNPs + ZnONPs was additive or more-than-additive for D. magna. A similar pattern was found in the toxicity of the mixtures of Cu- and Zn-salts from the literature data. The presence of SR-NOM had no significant impact on the joint toxicity of CuNPs + ZnONPs. The calculated component-specific contribution to overall toxicity indicated that SR-NOM increased the relative contribution of dissolved ions released from the MNPs to the toxicity of the binary mixtures at high-effect concentrations of individual MNPs. Moreover, dissolved Zn-ions released from the ZnONPs were found to dominate the joint toxicity of CuNPs + ZnONPs in the presence of SR-NOM. Furthermore, the results of the accumulation experiment displayed that the presence of SR-NOM significantly enhanced the accumulation of either CuNPs or ZnONPs in D. magna exposed to the MNP mixtures.

Removal of low levels of Cu from ongoing sources in the presence of other elements - Implications for remediated contaminated sediments

Mesocosms were used to investigate the effects of Cu influx, alone and in the presence of other elements, on sediments remediated by active caps, passive caps, and in situ treatment. Competitive interactions between Cu and other elements were investigated because contaminants often co-occur. Elements in surface water remained at significantly lower concentrations in mesocosms with apatite and mixed amendment caps than in mesocosms with passive sand caps or uncapped sediment. Element concentrations in Lumbriculus variegatus were significantly higher in untreated sediment than in active caps and significantly related to element concentrations in sediment measured by DGT probes. The cumulative toxicity of Cu mixed with other elements was greater than the toxicity of Cu alone in treatments without active caps, but the ability of active caps to control Cu was not affected by the presence of other elements. Active caps can protect remediated sediments by reducing bioavailable elements in ongoing contamination.

Speciation and bioavailability of dissolved copper in different freshwaters: comparison of modelling, biological and chemical responses in aquatic mosses and gammarids

Biological and chemical measurements were performed in mesocosms to investigate the bioavailability of copper, with a greater emphasis on the effects of competing ions and copper speciation. Measurements were achieved in three different natural waters for two aquatic species (Gammarus pulex and Fontinalis antipyretica) along a copper gradient concentration: natural concentration, spiked at 5 and 15 μg L(-1). Aquatic mosses exhibited high enrichment rates that were above the background levels compared to gammarids. The accumulation of copper in F. antipyretica is better correlated to the weakly complexed copper concentrations measured using differential pulse anodic stripping voltammetry (DPASV) and diffusive gradient in thin film (DGT) than to the free copper concentration measured using an ion selective electrode (ISE). In unspiked natural waters, the presence of dissolved organic ligands strongly controls the metal speciation and consequently largely minimised the impact of competing cations on the accumulation of Cu in mosses. Furthermore, the BioMet Biotic Ligand Model (BLM) successfully describes the site-specific copper bioaccumulation for the freshwater mosses studied. However, the comparison of the results with a previous study appears to indicate that the adsorption/desorption of Cu in mosses is impacted by seasons. This highlights a limit of the BioMet model in which the physiological state of aquatic organisms is not considered. No toxic effect of Cu exposure on lipid peroxidation was observed in the mosses and gammarids regardless of the site and the concentration considered. However, the oxidative stress measured in the mosses via their guaiacol peroxidase (GPX) activity increased in the case where internalised Cu reached maximal values, which suggests a threshold effect on the GPX activity.

Modeling the effect of water chemistry on the bioaccumulation of waterborne cadmium in zebra mussels

The present study aims at investigating the effects of Zn, Ca, and dissolved organic carbon (DOC) on the waterborne Cd bioaccumulation of a freshwater bivalve (Dreissena polymorpha). Mussels were exposed for 48 h at 3 µg/L of Cd in different media. Their physiological activities were assessed by separately measuring the filtration rate in the same exposure water. Increased Zn (from 3 to 89 µg/L) and Ca (from 37 to 131 mg/L) concentrations in water led to a threefold and sevenfold reduction of Cd bioaccumulation, whereas the effect of DOC varied greatly depending on its concentration. At low DOC concentrations (from 0.2 to 1.1 mg/L), the uptake of Cd increased, whereas at higher concentrations (from 1.1 to 17.1 mg/L), the uptake decreased. The filtration activity was not strongly influenced by either Zn or Ca concentration, whereas it was modified in enriched DOC media in the same manner as Cd uptake. A competitive model was built to predict the waterborne uptake rate constant of Cd (k (u)) as a function of Zn and Ca concentrations in the water. Over the range of DOC concentrations we tested, organic matter was shown to influence Cd bioaccumulation in two ways: by modifying Cd speciation and thus its bioavailability and its interaction with the biological membrane, and by affecting the mussel's physiology and therefore its sensitivity to metal. The present study provides a useful means of adjusting the toxicokinetic constant to the water's physicochemical characteristics and proposes a unifying model that takes into account the different geochemical and biological influences on bioaccumulation.

Natural DOM affects copper speciation and bioavailability to bacteria and ciliate

This study aimed to investigate the influence of natural dissolved organic materials (DOM) on copper speciation (total dissolved, particulate, and free Cu2+ ions) and bioavailability during a two-level experimental microbial food chain. Bacteria were used as the first trophic level, and Paramecium caudatum (protozoan) as the second. The organisms were obtained from a freshwater reservoir and kept under controlled laboratory conditions. Three experimental treatments were performed: exposure of the organisms to copper in the absence of DOM, exposure to DOM in the absence of copper, and exposure to both copper and DOM. Freshwater medium containing natural DOM and copper at a total dissolved concentration of 1.8 x 10(-6) mol L(-1) was furnished to bacteria, which was further used as food to the protozoan. The results showed that after bacterial growth, DOM concentration decreased as quantified by total organic carbon determinations. At the same time, free Cu2+ ions concentration increased in the medium. A lower copper concentration was detected in both microorganisms in the presence of DOM. We conclude that natural DOM reduced copper accumulation in the organisms on the first and second trophic levels, thus reducing the entrance of copper into the aquatic microbial food chain.

The effects of Anabaena spiroides exopolysaccharides on copper accumulation in an aquatic food chain

The influence of Anabaena spiroides exopolysaccharides (EPS) on copper speciation (total dissolved, particulate and free Cu(2+) ions) and bioavailability in aquatic organisms was investigated. Bacteria were used as the first trophic level, Paramecium caudatum (protozoan) as the second and the copepod cyclopoid Metacyclops mendocinus as the third level. The organisms were obtained from a freshwater reservoir and held under continuous laboratory controlled conditions. Freshwater media containing EPS excreted by A. spiroides (10mgL(-1)) and copper (1.0x10(-6)molL(-1)) were used for bacteria growth. Contamined bacteria were used as food source to protozoan, which was further furnished to copepods. The results showed a reduction of EPS concentration during bacteria growth and also a smaller copper accumulation by microorganisms in the presence of EPS. We concluded that A. spiroides exopolysaccharides have reduced copper entrance into the experimental aquatic microbial food chain.

Toxicity of dissolved Cu, Zn, Ni and Cd to developing embryos of the blue mussel (Mytilus trossolus) and the protective effect of dissolved organic carbon

Marine water quality criteria for metals are largely driven by the extremely sensitive embryo-larval toxicity of Mytilus sp. Here we assess the toxicity of four dissolved metals (Cu, Zn, Ni, Cd) in the mussel Mytilus trossolus, at various salinity levels while also examining the modifying effects of dissolved organic carbon (DOC) on metal toxicity. In 48 h embryo development tests in natural seawater, measured EC50 values were 6.9-9.6 microg L(-1) (95% C.I.=5.5-10.8 microg L(-1)) for Cu, 99 microg L(-1) (86-101) for Zn, 150 microg L(-1) (73-156) for Ni, and 502 microg L(-1) (364-847) for Cd. A salinity threshold of >20 ppt (approximately 60% full strength seawater) was required for normal control development. Salinity in the 60-100% range did not alter Cu toxicity. Experimental addition of dissolved organic carbon (DOC) from three sources reduced Cu toxicity; for example the EC50 of embryos developing in seawater with 20 mg C L(-1) was 39 microg Cu L(-1) (35.2-47.2) a 4-fold increase in Cu EC50. The protective effects of DOC were influenced by their distinct physicochemical properties. Protection appears to be related to higher fulvic acid and lower humic acid content as operationally defined by fluorescence spectroscopy. The fact that DOC from freshwater sources provides protection against Cu toxicity in seawater suggests that extrapolation from freshwater toxicity testing may be possible for saltwater criteria development, including development of a saltwater Biotic Ligand Model for prediction of Cu toxicity.

The effects of humic substances on copper toxicity to Ceriodaphnia silvestrii Daday (Crustacea, Cladocera)

A major question in the field of ecotoxicology is how DOM affects copper accumulation and toxicity in planktonic organisms; copper acute toxicity and bioaccumulation in Ceriodaphnia silvestrii were investigated in the presence and absence of humic substances (HS) under controlled laboratory conditions. Copper was determined as free Cu2+ ions in the media and total copper in the animals; metal ion buffers were used for ion selective electrode calibration, extending the lower detection limit to 10(-11) mol l(-1). Groups of 20 adult females of similar sizes were exposed (24 h) to a range of nominal copper concentrations. Based on total added copper, LC50 was 4.4 x 10(-8) mol l(-1) without HS, whereas with 20 mg l(-1) HS, it was 25 times higher (1.1 x 10(-6) mol l(-1)). Based on free Cu2+ ions LC50 was statistically similar either with (2.8 x 10(-8) mol l(-1)) or without HS (3.3 x 10(-8 )mol l(-1)). The present results showed that natural DOM reduced copper toxicity and that free Cu2+ ions correlates to the bioavailable fraction to zooplankton. Nevertheless, copper bioaccumulation by C. silvestrii was similar either in the presence or absence of humic substances, suggesting that C. silvestrii regulates its body copper content up to 3.0 x 10(-8) mol l(-1) free Cu2+ ions in the media. The organisms were not able to deal with higher free Cu2+ ions concentrations in the media.

Complexation of Cadmium and Copper by Fluvial Humic Matter and Effects on Their Toxicity

The effects of humic acids and fulvic acids isolated from the River Arno (Italy) on the bioavailability and toxicity of cadmium and copper were assessed in relation to changes in their speciation. Measurements of the complexing capacity of solutions containing these organic ligands were carried out by a titration procedure followed by DPASV and toxicity tests were carried out using lysosomes isolated from rat liver. The complexing capacity of the physiological medium containing about 13 mg/L of humic acids, expressed as ligand concentrations, was 0.30 and 0.072 micromol/L for cadmium and copper respectively; the corresponding conditional stability constants were 4.2 x 10(11) and 1.3 x 10(8) (mol/L)-1. The complexing capacities of the solution containing the same amount of fulvic acids were 0.33 and 0.164 micromol/L for cadmium and copper respectively, the conditional stability constants were 3.2 x 10(11) and 2.4 x 10(7) (mol/L)-1. The humic acids reduced the toxicity of cadmium by about 5 times: the EC50 changed from 4.4 to 20.4 micromol/L. The dose effect curve of copper presented a bi-sigmoid trend and two EC50 values can be determined: The EC50(1) in the presence of humic acids changed from 2.0 to 3.1 micromol/L, while the EC50(2) increased from 22.3 to 45.3 micromol/L. The fulvic acids reduced the cadmium toxicity by about the same amount as humic acids, from 4.4 to 18.6 micromol/L, but they had no effect on copper toxicity. Analysing the chemical speciation of cadmium and copper in the presence of humic components and under toxicity test conditions we can say that the appreciable decrease of EC50 is not related to changes in their speciation; we can hypothesize that this is due to different processes, as well as to blocking of the lysosomal membrane. On the basis of the shape of the dose-effect curves obtained for cadmium and copper respectively, we can say that the toxic effects of the two metals are different and we can hypothesize that copper could exercise its toxic activity by inhibiting the ATP-driven proton pump and the function of the Cl- selective channel.

Copper accumulation by bacteria and transfer to scallop larvae

A bacterial copper-resistant strain was isolated from a hatchery-conditioned adult of the scallop Argopecten purpuratus and was identified as Vibrio sp. according to its physiological characteristics. The lowest concentration of Cu2+ required for its complete inhibition in VNSS medium was 50 microg ml(-1). The Vibrio strain was found to accumulate copper, exhibiting cellular and loosely bound copper levels of 201.14 and 493.21 microg g(-1) dry weight, respectively, after 24 h of incubation in VNSS medium supplemented with 15 microg ml(-1) of Cu2+, with cellular concentration factors of 10.17 and 14.35 after 12 and 24 h of exposure. When a scallop larvae culture was exposed to a concentration of 6.46 x 10(2) CFU ml(-1) of Cu-enriched Vibrio, they accumulated 20.42 +/- 1.12 and 30.96 +/- 1.85 microg Cu2+ g(-1) dry weight after 12 and 24 h, respectively. This study suggests that bacterial copper accumulation could be very active in marine environments increasing the occurrence of copper transfer to marine food chains.

Predicting copper toxicity in estuarine and marine waters using the Biotic Ligand Model

The Biotic Ligand Model (BLM) has proven efficient in predicting the toxicity of a variety of metals to freshwater organisms. Consequently, the US EPA has proposed its use for calculating freshwater copper criteria. This study evaluates the BLM for use in estuarine and marine waters. Studies were conducted using the bivalve, Mytilus sp. and 48-h embryo-larval development chronic estimator test methods. These are the most sensitive taxa and test in the US EPA saltwater copper criteria database. Samples from five locations around the USA were tested. There is a strong relationship between measured and BLM predicted copper EC50s (log transformed data, r(2)=0.76, p<0.001, n=44). The BLM predicted within a factor +/-2 of measured EC50s in 41 of 44 cases. However, the BLM tends to predict lower EC50s when measured EC50s are approximately < or =10 microg Cu/L. This may be due to limitations of the metal-dissolved organic matter interaction model.

Polychlorinated biphenyls and organochlorine pesticides in human adipose tissue and breast milk collected in Hong Kong

Contamination from persistent organic pollutants is a pervasive global problem that urgently demands global concern and action. In the present study, concentrations of organochlorine (OC) pesticides and polychlorinated biphenyls (PCBs) were determined in 37 samples of female adipose tissue collected in Hong Kong hospitals. Among the pollutants analyzed, DDTs (2.79 ng/g fat), HCHs (0.72 ng/g fat), and PCBs (0.19 ng/g fat) were prominent compounds in most of the adipose tissue. p,p'-DDE and hexachlorinated biphenyls were found in all samples, whereas heptachlor epoxide and dieldrin were found only in some samples. An estimation of toxic equivalency concentration (TEQ) due to dioxin-like coplanar PCBs was also performed. The estimated TEQ(PCBs) was 2.01 pg/g fat. This study also compared our previous results obtained from the milk samples of the same donors. Significant correlations are obtained for DDTs and HCHs between milk and adipose tissue. Detailed review of available information concerning OC pesticides and PCBs in different ecological compartments indicated that bioconcentration and biomagnification of these contaminants are common phenomena of the Pearl River Delta region, which has undergone rapid socioeconomic change in the past 20 years. It is suggested to establish a regional organization in order to coordinate the monitoring of persistent organic pollutants in the region.

Comparison of diffusive gradients in thin films and equilibrium dialysis for the determination of Al, Fe(III) and Zn complexed with dissolved organic matter

The distinction between 'free' metals and organically complexed metals in aqueous solutions is important for research involving the mobility or bioavailability of metals in the environment. In this study, the applicability of equilibrium dialysis (molecular weight cut-off = 1000 Da) and diffusive gradients in thin films (DGT) to determine 'free' Al, Fe(III) and Zn in four forest soil solutions was compared. The 'free' metals as measured by both methods, consist of hydrated metal cations and soluble inorganic metal complexes. In addition, dialysis measures any organic complexes < 1000 Da and DGT measures a portion of smaller labile organic complexes. The four soil solutions were prepared by water extraction of an organic soil horizon (H) from a Fimic Anthrosol, and contained either 20 or 75 mg C/l dissolved organic matter at pH 4.0 and pH 7.0. To test the performance of both methods and optimize experimental volume and time, experiments using metal nitrate solutions were carried out. In the solutions at pH 4.0, no significant differences in average 'free' metal contents were found for Al, Fe(III) or Zn. This makes DGT a viable alternative for equilibrium dialysis for the study of the complexation of all three metals in acidic soils. At pH 7.0, again no significant difference between both methods were found for Al and Fe(III), but the DGT results for Zn were significantly higher. This was likely caused by labile organic complexes that were only detected by DGT.