Predicting toxicity in marine sediment in Taranto Gulf (Ionian Sea,Southern Italy) using Sediment Quality Guidelines and a battery bioassay

The goal of this study was to assess coastal marine pollution in the Mar Piccolo and Taranto Gulf (Ionian Sea, Southern Italy) by combining chemical and toxicological data in order to compare and integrate both approaches. Pollutants levels, traditionally, have limited ability to predict adverse effects on living resources. Moreover, in order to provide information on the ecological impact of sediment contamination on aquatic biota Numerical Sediment Quality Guidelines (SQGs) and sediment toxicity bioassays were carefully recommended. In this study ERL (effect range low)/ERM (effect range medium value) and TEL (threshold effect level)/PEL (probable effect level) guidelines have been used. Bioassays were performed with two species of amphipods Gammarus aequicauda and Corophium insidiosum, one species of isopod Idotea baltica and bivalve Mytilus galloprovincialis larvae. The TEL/PEL analysis suggested that, especially for stations 1 and 2, sediments in Mar Piccolo should contain acutely toxic concentrations of metals. In particular Hg content, in station 1, was about 17 times PEL value. 96 h LC₅₀ and 48 h EC₅₀ values were estimated for cadmium, copper and mercury in these species using the static acute toxicity test. M. galloprovincialis larvae was more sensitive than other species to all the reference toxicants tested (EC₅₀ determined for cadmium copper and mercury were of 0.59, 0.11 and 0.01 mg/l respectively). Significant differences in sensitivity of species tested to all reference toxicants (ANOVA p < 0.001) were recorded. Bioassays with these species allowed to estimated sediment toxicity from the different studied sites. On the basis of results obtained a good agreement was reported between chemical data and response of the biological endpoints tested.     

Individual and combined effects of cadmium and copper on the growth response of Chlorella vulgaris

The individual and combined effects of cadmium and copper on the growth response of the green alga, Chlorella vulgaris, were examined. The effects of pH alone, and in combination with copper were also evaluated. An increase in cadmium and copper concentrations caused a significant reduction in the growth of C. vulgaris cells, and the corresponding EC₅₀ values were 1.02 and 4.01 mg L⁻¹, respectively. For a pH range of 2–7, the inhibitory effect due to increased copper concentrations (coupled with the resulting drop in pH) was significantly higher than the impact due to increased acidity (by addition of HCl) alone. At lower metal concentrations (5 mg L⁻¹ Cu + < 2 mg L⁻¹ Cd or 2.5 mg L⁻¹ Cd + < 4 mg L⁻¹ Cu), a combination of copper and cadmium appeared to have a stronger inhibitory effect on cell growth than that of a single metal. In contrast, at higher metal concentrations (5 mg L⁻¹ Cu + > 2 mg L⁻¹ Cd or 2.5 mg L⁻¹ Cd + > 4 mg L⁻¹ Cu), the effect of a single metal exhibited a significantly stronger effect compared to a combination of the two metals. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 347–353, 1999     

ISTA13‐catecholamine toxicity and metabolism in the ciliated protozoan,Tetrahymena pyriformis

A high throughput culture methodology of unicellular eukaryote Tetrahymena pyriformis, strain GL were used for the determination of catecholamines toxicity and their metabolism. Catecholamines exhibited acute toxicity to Tetrahymena cells where dopamine and L ‐DOPA showed higher toxic potential of EC₁₀ (0.39 and 0.63 mg/L, respectively) and EC₂₀ (1.1 and 1.0 mg/L, respectively). All the testing catecholamines were highly degradable in the PPY‐medium due to the oxidizing environment during incubation. They were also naturally synthesized and released by Tetrahymena cells into the culture medium and increasingly accumulated with time where as noradrenalin demonstrated significant results. Cells were exposed with physiological concentration (0.12 mg/L) and one higher concentration (8.0 mg/L) of catecholamines, resulting noradrenalin depletion and in vivo generation of a metabolite in response to dopamine with higher concentration treatment. This dopamine metabolite was relatively nonpolar compared with the catecholamines and was eluted later from the reverse phase C‐18 column. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2009.     

Multilaboratory evaluation of 15 bioassays for (eco)toxicity screening and hazard ranking of engineered nanomaterials: FP7 project NANOVALID

Within EU FP7 project NANOVALID, the (eco)toxicity of 7 well-characterized engineered nanomaterials (NMs) was evaluated by 15 bioassays in 4 laboratories. The highest tested nominal concentration of NMs was 100?mg/l. The panel of the bioassays yielded the following toxicity order: Ag?>?ZnO?>?CuO?>?TiO_2?>_?MWCNTs?>?SiO_2?>_?Au. Ag, ZnO and CuO proved very toxic in the majority of assays, assumingly due to dissolution. The latter was supported by the parallel analysis of the toxicity of respective soluble metal salts. The most sensitive tests/species were Daphnia magna (towards Ag NMs, 24-h EC_50?=_?0.003?mg Ag/l), algae Raphidocelis subcapitata (ZnO and CuO, 72-h EC_50?=_?0.14?mg Zn/l and 0.7?mg Cu/l, respectively) and murine fibroblasts BALB/3T3 (CuO, 48-h EC_50?=_?0.7?mg Cu/l). MWCNTs showed toxicity only towards rat alveolar macrophages (EC_50?=_?15.3?mg/l) assumingly due to high aspect ratio and TiO₂ towards R. subcapitata (EC_50?=_?6.8?mg Ti/l) due to agglomeration of TiO₂ and entrapment of algal cells. Finally, we constructed a decision tree to select the bioassays for hazard ranking of NMs. For NM testing, we recommend a multitrophic suite of 4 in vitro (eco)toxicity assays: 48-h D. magna immobilization (OECD202), 72-h R. subcapitata growth inhibition (OECD201), 30-min Vibrio fischeri bioluminescence inhibition (ISO2010) and 48-h murine fibroblast BALB/3T3 neutral red uptake in vitro (OECD129) representing crustaceans, algae, bacteria and mammalian cells, respectively. Notably, our results showed that these assays, standardized for toxicity evaluation of “regular” chemicals, proved efficient also for shortlisting of hazardous NMs. Additional assays are recommended for immunotoxicity evaluation of high aspect ratio NMs (such as MWCNTs).     

Toxicity of nanoparticles of ZnO, CuO and TiO2 to yeast Saccharomyces cerevisiae

The aim of this study was to evaluate the toxic effect of nanosized ZnO, CuO and TiO₂ to Saccharomyces cerevisiae – a widely used unicellular eukaryotic model organisms in molecular and cell biology. The effect of metal oxide nanoparticles, their bulk forms and respective ionic forms were compared. The bioavailable Zn²⁺ and Cu²⁺ ions in the growth medium were quantified by recombinant microbial sensors.Nano and bulk TiO₂ were not toxic even at 20000 mg/l. Both, nano and bulk ZnO were of comparable toxicity (8-h EC₅₀ 121–134 mg ZnO/l and 24-h EC₅₀ 131–158 mg/l). The toxicity was explained by soluble Zn-ions as proved by the microbial sensor. However, nano CuO was about 60-fold more toxic than bulk CuO: 8-h EC₅₀ were 20.7 and 1297 mg CuO/l and 24-h EC₅₀ were 13.4 and 873 mg/l, respectively. The increase in toxicity of both CuO formulations at 24th hour of growth was due to the increased dissolution of copper ions from CuO over time. Comparison of EC₅₀ values of nano CuO, bulk CuO and Cu²⁺ with bioavailable copper concentrations in the growth medium showed that the solubilized Cu-ions explained only about 50% of the toxicity of both, nano and bulk CuO. To our knowledge, this is the first study that evaluates the toxicity of ZnO, CuO and TiO₂ nanoparticles to S. cerevisiae.     

Cadmium sulfide nanoparticles trigger DNA alterations and modify the bioturbation activity of tubificidae worms exposed through the sediment

To address the impact of cadmium sulfide nanoparticles (CdS NPs) in freshwater ecosystems, aquatic oligochaete Tubifex tubifex were exposed through the sediment to a low dose (0.52?mg of 8?nm in size of CdS NPs/kg) for 20 days using microcosms. Cadmium (Cd) was released from the CdS NPs-contaminated sediment to the water column, and during this period the average concentrations of Cd in the filtered water fraction were 0.026?±?0.006?µg/L in presence of oligochaetes. Similar experiments with microparticular CdS and cadmium chloride (CdCl₂) were simultaneously performed for comparative purposes. CdS NPs exposure triggered various effects on Tubifex worms compared to control, microsized and ionic reference, including modification of genome composition as assessed using RAPD-PCR genotoxicity tests. Bioaccumulation levels showed that CdS NPs were less bioavailable than CdCl₂ to oligochaetes and reached 0.08?±?0.01?µg Cd/g for CdS NPs exposure versus 0.76?±?0.3?µg Cd/g for CdCl₂ exposure (fresh weight). CdS NPs altered worm’s behavior by decreasing significantly the bioturbation activity as assessed after the exposure period using conservative fluorescent particulate tracers. This study demonstrated the high potential harm of the CdS nanoparticular form despite its lower bioavailability for Tubifex worms.     

The influence of humic acid on the toxicity of nano‐ZnO and Zn2+ to the Anabaena sp.

This study explored the effects of humic acid (HA) on the toxicity of ZnO nanoparticles (nano‐ZnO) and Zn²⁺ to Anabaena sp. Typical chlorophyll fluorescence parameters, including effective quantum yield, photosynthetic efficiency and maximal electron transport rate, were measured by a pulse‐amplitude modulated fluorometer. Results showed that nano‐ZnO and Zn²⁺ could inhibit Anabaena sp. growth with the EC₅₀ (concentration for 50% of maximal effect) of 0.74 ± 0.01 and 0.3 ± 0.01 mg/L, respectively. In the presence of 3.0 mg/L of HA, EC₅₀ of nano‐ZnO increased to 1.15 ± 0.04 mg/L and EC₅₀ of Zn²⁺ was still 0.3 ± 0.01 mg/L. Scanning electron microscopy observation revealed that HA prevented the adhesion of nano‐ZnO on the algae cells due to the increased electrostatic repulsion. The generation of intracellular reactive oxygen species and cellular lipid peroxidation were significantly limited by HA. Nano‐ZnO had more damage to the cell membrane than Zn²⁺ did, which could be proven by the malondialdehyde content in Anabaena sp. cells. © 2014 Wiley Periodicals, Inc. Environ Toxicol 30: 895–903, 2015.     

Influence of some experimental factors on metal toxicity to Selenastrum capricornutum

Toxic effects of Cd⁺⁺, Cu⁺⁺, and Zn⁺⁺ on Selenastrum capricornutum were evaluated in various experimental conditions in order to determine the influence of the composition of the test medium and of the concentration of the algal biomass on the toxicity of metals to algae. Four media recommended in different standard methods (International Standards Organisation, U.S. Environmental Protection Agency, Organisation for Economic Cooperation and Development, AFNOR) were compared. Results of algal bioassays showed that the sensitivity of algae during the exponential growth phase was not influenced by the concentration of macronutrients in the medium. On the contrary, the numeration of the algal suspensions tested appeared determinant as the toxicity decreased when the quantity of algal inoculum was increased: with inocula of nearly 3 × 10⁴, 2.5 × 10⁵, 6 × 10⁵, and 3 × 10⁶ cells/mL at t = 0, the corresponding EC₅₀ were 46, 80, 110, and up to 300 μg/L for cadmium, 10, 65, 105, and 280 μg/L for copper, and 90, 163, 225, and 365 μg/L for zinc. Modifications in the speciation forms of the metal induced by a rapid increase of the pH could be responsible for part of this decreased toxicity.     

A pilot study of heavy metal concentration in various environments and fishes in the Upper Sakarya River Basin,Turkey

In this study, concentration of lead, cadmium, copper, cobalt, nickel, and manganese were measured in water, sediment, and fish (Cyprinus carpio and Barbus plebejus) samples at the upper Sakarya river basin in Sept. 1995–1996 period. Also, physical parameters of selected stations in the Sakarya river were measured. Mean concentrations of lead, cadmium, copper, nickel, and manganese differed between water, sediment, and fish samples by seasons. Mean concentrations of lead, cadmium, and cobalt increased in sediment samples in October and August. In water samples only cadmium and cobalt increased in October whereas lead and copper increased in August. Also, high levels of manganese concentrations were detected in water and sediment samples and fish tissue during the study. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 367–373, 1999     

Combined toxicity of dissolved mercury with copper, lead and cadmium on embryogenesis and early larval growth of the Paracentrotus lividus sea-urchin

The individual and combined toxicity of dissolved mercury, copper, lead and cadmium has been investigated by using the Paracentrotus lividus sea-urchin embryo-larval bioassay. Embryogenesis success and early larval growth have been recorded after incubation of fertilised eggs in seawater, both with single metals and binary combinations of Hg with every other metal. For individual metals the ranking of toxicity was Hg > Cu > Pb > Cd, with EC₅₀ values of 21.9, 66.8, 509 and 9240g/l, respectively. Lowest observed effect concentrations (LOEC) for early larval growth were approximately three times lower than the EC₅₀ values for Hg, Cu and Pb, and more than two orders of magnitude lower for Cd, emphasizing the danger of underestimating toxicity when only lethal effects are recorded. Marking & Dawson's additive indices ranged from 0.10 to 0.19, indicating additive effects with a slight trend to synergism, which was statistically significant for the Hg–Pb combination only. Hayes' additive indices were within the margins considered acceptable to describe additive interactions.     

Acute toxicity evaluation of olive oil mill wastewaters: A comparative study of three aquatic organisms

Acute toxicity of olive mill wastewaters (traditional and continuous processes) collected from different regions of Portugal was evaluated using three test species (Vibrio fischeri formerly Photobacterium phosphoreum, Thamnocephalus platyurus, and Daphnia magna) and correlated with several physical and chemical parameters. Acute toxicity of these effluents, expressed in LC₅₀ or EC₅₀, ranged from: 0.16 to 1.24% in Microtox test, 0.73 to 12.54% in Thamnotoxkit F test, and 1.08 to 6.83% in Daphnia test. These values reflect the high toxicity of the olive mill wastewaters to all test species. Statistical analysis of the results shows a high correlation between the two microcrustacean bioassays. Microtox test did not correlate significantly with the other bioassays used. A significative correlation (p≤0.05) could also be established between L(E)C₅₀ obtained in the microcrustacean tests and some physicochemical parameters of the effluent. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 263–269, 1999     

A test battery approach to the ecotoxicological evaluation of cadmium and copper employing a battery of marine bioassays

Heavy metals are ubiquitous contaminants of the marine environment and can accumulate and persist in sediments. The toxicity of metal contaminants in sediments to organisms is dependent on the bioavailability of the metals in both the water and sediment phases and the sensitivity of the organism to the metal exposure. This study investigated the effects of two metal contaminants of concern (CdCl₂ and CuCl₂) on a battery of marine bioassays employed for sediment assessment. Cadmium, a known carcinogen and widespread marine pollutant, was found to be the least toxic of the two assayed metals in all in vivo tests. However, CdCl₂ was found to be more toxic to the fish cell lines PLHC-1 and RTG-2 than CuCl₂. Tisbe battagliai was the most sensitive species to both metals and the Microtox^® and cell lines were the least sensitive (cadmium was found to be three orders of magnitude less toxic to Vibrio fischeri than to T. battagliai). The sensitivity of Tetraselmis suecica to the two metals varied greatly. Marine microalgae are among the organisms that can tolerate higher levels of cadmium. This hypothesis is demonstrated in this study where it was not possible to derive an EC₅₀ value for CdCl₂ and the marine prasinophyte, T. suecica. Conversely, CuCl₂ was observed to be highly toxic to the marine alga, EC₅₀ of 1.19 mg l^?1. The genotoxic effect of Cu on the marine phytoplankton was evaluated using the Comet assay. Copper concentrations ranging from 0.25 to 2.50 mg l^?1 were used to evaluate the effects. DNA damage was measured as percent number of comets and normal cells. There was no significant DNA damage observed at any concentration of CuCl₂ tested and no correlation with growth inhibition and genetic damage was found.     

Influence of salinity on metal toxicity to Ulva pertusa

The present study was undertaken to establish the effect of salinity on the toxicity of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) to Ulva pertusa, with inhibition of spore release used as the endpoint. The optimal salinity for maximal spore release for U. pertusa was found to be between 20 and 40 psu. Comparisons between toxicity of metals, as measured by EC₅₀, was shown to be in the descending order of Cu>Cd>Pb=Zn, which is similar to the toxicity of metals to algae, in general. When salinity was decreased from 30 to 20 psu, the EC₅₀ values for Cd toxicity to the inhibition of spore release in U. pertusa decreased from 261 to 103 g·L^?1, whereas increased salinity from 30 to 40 psu increased the EC₅₀ from 261 to 801 g·L^?1. Similarly, EC₅₀ values for Cu toxicity were 52 g·L^?1 at 20 psu, 99 g·L^?1 at 30 psu, and 225 g·L^?1 at 40 psu, and for Zn toxicity were 720 g·L^?1, 1,074 g·L^?1 and 1,520 g·L^?1, at 20, 30 and 40 psu, respectively. In contrast, no salinity dependent change in EC₅₀ values was apparent for Pb, with no significant differences in EC₅₀ values at under the three different salinity regimes. In general, lower salinity (20 psu) induced a significant decrease in percent spore release of U. pertusa as estimated by a decrease in EC₅₀ values, while higher salinity (40 psu) reduced the toxicity of metals as shown by an increase EC₅₀ values. These findings enable one to predict that any additional increase in pollution status would result in a pronounced reduction in the distribution of U. pertusa in brackish and estuarine waters.     

Glutathione modifies the toxicity of triethyltin and trimethyltin in C6 glioma cells

It has been demonstrated that exposure to mercury or cadmium compounds causes alterations in the glutathione system in a model glial cell line, C6. Here we report that two organic tin compounds, triethyltin (TET) and trimethyltin (TMT), are also toxic to these cells with EC₅₀ values for cell death of c. 0.02 μM and 0.8 μM respectively. Exposure for 24 h to either of these compounds at sub-toxic concentrations caused increases in the amount of reduced glutathione (GSH) per cell. Increases in glutathione-S-transferase enzyme activity were also demonstrated after TET or TMT exposure. This suggests that glutathione increases occur in glial cells after toxic insults below that required to cause cell death, possibly acting as a protective mechanism. To test whether GSH plays a role in organotin-induced cell death we manipulated GSH in the culture media or via intracellular GSH and looked at the effects on sensitivity to TET or TMT toxicity. Adding GSH to the culture media did not protect the cells. Depletion of intracellular GSH with buthionine-[S,R] sulphoximine did not alter cytotoxicity of TET or TMT. However, pre-treatment with (−)-2-oxo-4-thiazolidine carboxylic acid (OTC), which increases intracellular GSH levels, protected the cells against both compounds. The EC₅₀ for TMT was increased from 0.77 to 1.8 μM, a 2.3-fold shift, whereas the EC₅₀ for TET was increased >20-fold, from 0.022 to 0.47 μM. One interpretation of these results is that GSH protects cells against the toxicity of organic tin compounds without reacting directly with them to any significant extent. Under conditions where GSH is depleted, additional protective mechanisms may be active. Received: 26 May 1997 / Accepted: 21 October 1997     

Development of a chronic toxicity structure–activity relationship for alkyl sulfates

Much of the historical data regarding the toxicity of alkyl sulfate (AS) surfactants to aquatic organisms have been compromised due to excessive loss of the parent material via biodegradation and precipitation—processes especially important during chronic tests. To minimize these issues, a novel flow-through system for Ceriodaphnia dubia was developed and acute and chronic toxicity data were obtained for several AS structures. Acute toxicity increased linearly with increased alkyl chain length (CL) from C12AS to C16AS. However, a parabolic response was observed for reproduction where toxicity increased with alkyl chainlength from C12AS to C14AS, but decreased with increased chain length from C14AS to C18AS. Soluble vs precipitated forms of AS contribute to the parabolic relationship. A quadratic approach using the chronic end points no observed effect concentration, lowest observed effect concentration, maximum acceptable toxicant concentration, EC₅₀, and EC₂₀ yielded the best fit for EC₂₀ (R²=0.99). Quantitative structure–activity relationships for AS, based on acute toxicity alone, overpredict chronic toxicity at chainlengths greater than C14AS. Use of the quadratic model [EC₂₀(M)=5.12×10⁻⁷(CL)²−1.49×10⁻⁵(CL)+11.1×10⁻⁵] is advocated for use in environmental risk assessment. © 1997 John Wiley & Sons, Inc. Environ Toxicol Water Qual 12 : 295–303, 1997     

Influence of temperature and soil moisture on the toxic potential of clothianidin to collembolan Folsomia candida in a tropical field soil

Climate change can alter the toxic effects of pesticides on soil invertebrates. However, the nature and magnitude of the influence of climatic factors on clothianidin impacts in tropical soils are still unknown. The influence of increasing atmospheric temperature and the reduction in soil moisture on the toxicity and risk of clothianidin (seed dressing formulation Inside FS^®) were assessed through chronic toxicity tests with collembolans Folsomia candida in a tropical field soil (Entisol). The risk of clothianidin for collembolans was estimated using the Toxicity-Exposure Ratio (TER) approach. Organisms were exposed to increasing clothianidin concentrations at 20, 25 and 27?°C in combination with two soil moisture conditions (30 and 60% of the maximum water holding capacity—WHC). The effect of temperature and soil moisture content on clothianidin toxicity was verified through the number of F. candida juveniles generated after 28 days of exposure to the spiked soil. The toxicities estimated at 25?°C (EC₅₀__30%WHC?=?0.014?mg?kg^?1; EC_{50_60%WHC}?=?0.010?mg?kg^?1) and 27?°C (EC_{50_30%WHC}?=?0.006?mg?kg^?1; EC_{50_60%WHC}?=?0.007?mg?kg^?1) were 2.9–3.0-fold (25?°C) and 4.3–6.7-fold (27?°C) higher than those found at 20?°C (EC_{50_30%WHC}?=?0.040?mg?kg^?1; EC_{50_60%WHC}?=?0.030?mg?kg^?1), indicating that clothianidin toxicity increases with temperature. No clear influence of soil moisture content on clothianidin toxicity could be observed once the EC₅₀ values estimated at 30% and 60% WHC, within the same temperature, did not significantly differ. A significant risk was detected in all temperatures and soil moisture scenarios studied, and the TER values indicate that the risk can increase with increasing temperatures. Our results revealed that temperature could overlap with soil moisture in regulating clothianidin toxicity and reinforce the importance of including climatic factors in the prospective risk assessment of pesticides.

     

Biodegradability and microbial toxicity of aircraft fuel system icing inhibitors

In a pollution prevention and chemical substitution effort, the U.S. Air Force and Navy formed a joint initiative to find safer, more environmentally acceptable jet fuel system icing inhibitors (FSII) for military aircraft. Standard biochemical oxygen demand (BOD) analysis and variations of the BOD procedure were used as simple screening tools to evaluate the potential for aquatic biodegradation and microbial toxicity of proposed FSIIs. This laboratory evaluation of biological properties allows prediction of the biotreatability of the chemicals in wastewater treatment plants, and their potential application as biocides at higher concentrations. The current FSII, diethylene glycol monomethyl ether (DiEGME) was evaluated along with two new candidate compounds, dipropylene glycol and glycerol formal. At a low concentration (3.5 mg/L), DiEGME exerted a BOD₅ of about 27% of theoretical oxygen demand. Test concentrations of ≥7 mg/L had decreasing oxygen consumption rate and extent, typical of a material with potential aquatic microbial toxicity. Dipropylene glycol began to moderately degrade only after more than 3 weeks exposure to microorganisms obtained from raw sewage. Glycerol formal showed no signs of biodegradation during a 5-week test period. In a simple microbial toxicity test DiEGME was most toxic, dipropylene glycol was moderately toxic, and glycerol formal showed little toxicity. At low concentrations (7 mg/L), none of the chemicals significantly inhibited microbial activity (P=0.34). ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 383–390, 1999     

Interactions of CuO nanoparticles with the algae Chlorella pyrenoidosa: adhesion,uptake, and toxicity

The potential adverse effects of CuO nanoparticles (NPs) have increasingly attracted attention. Combining electron microscopic and toxicological investigations, we determined the adhesion, uptake, and toxicity of CuO NPs to eukaryotic alga Chlorella pyrenoidosa. CuO NPs were toxic to C. pyrenoidosa, with a 72?h EC₅₀ of 45.7?mg/L. Scanning electron microscopy showed that CuO NPs were attached onto the surface of the algal cells and interacted with extracellular polymeric substances (EPS) excreted by the organisms. Transmission electron microscopy (TEM) showed that EPS layer of algae was thickened by nearly 4-fold after CuO NPs exposure, suggesting a possible protective mechanism. In spite of the thickening of EPS layer, CuO NPs were still internalized by endocytosis and were stored in algal vacuoles. TEM and electron diffraction analysis confirmed that the internalized CuO NPs were transformed to Cu₂O NPs (d-spacing, ～0.213?nm) with an average size approximately 5?nm. The toxicity investigation demonstrated that severe membrane damage was observed after attachment of CuO NPs with algae. Reactive oxygen species generation and mitochondrial depolarization were also noted upon exposure to CuO NPs. This work provides useful information on understanding the role of NPs–algae physical interactions in nanotoxicity.     

Sediment contaminants and microtox toxicity tested in a direct contact exposure test

Limnic and brackish water sediments were tested in a modified contact exposure bioluminescence test, the Microtox test. A variety of chemical constituents were analyzed in the sediments such as metals, chlorinated pesticides, and polychlorinated biphenyls. Sulfur in the common elemental form and pore water hydrogen sulfide were also analyzed. The measured effect in the Microtox toxicity test was correlated with the various chemical parameters to determine the origin of the toxic effect. Based on multivariate data anlaysis, a group of metals including Cu, Zn, Pb, and Cd were correlated positively with the Microtox toxicity tested in the direct contact test. Similarly, but to a lesser extent sulfur, hydrogen sulfide, and the pesticides p,p′-DDT and p,p′-DDD were also correlated. Other pesticides and all the analyzed polychlorinated biphenyls were poorly, if at all, correlated with the toxicity of the samples. In a comparison with the Microtox toxicity of the pure compounds, it was found that, of the analyzed and tested compounds, Zn, Pb, Cu, and elemental sulfur were present in amounts high enough to produce an effect in the test system. This calculation was, however, based on the assumption (unrealistic) that the total amount of a compound in the sediment was available in the test. On the other hand, the metals Cd, Cr, and Ni were found at concentrations of a few percent or less of their EC₅₀ concentrations in the Microtox test of the sediment, γ-Hexachlorocyclohexane and p,p′-DDT were also far less than the concentration required to give an effect in the test system. The pore water content of hydrogen sulfide was also too small to affect the test organism at the EC₅₀ dilution and, similarly, the fraction of the toxicant in the remaining aqueous phase in the sediment after separation of the pore water. Thus only the three metals Zn, Pb, and Cu, and elemental sulfur, were found in concentrations that would give an effect in the test system (0.68–398 times the effect), provided that the substances were available for the organisms. Consequently, elemental sulfur, Zn, Pb, and Cu were indicated as causing the effect in the Microtox test of sediments and not a series of other metal ions, nor tested chloropesticides or chlorinated biphenyls. © 1996 by John Wiley & Sons, Inc.     

Toxicity and critical body residues of Cd, Cu and Cr in the aquatic oligochaete Tubifex tubifex (Müller) based on lethal and sublethal effects

The aim of the present study was to estimate critical body residues (CBRs) of three metals [cadmium (Cd), copper (Cu), chromium (Cr)] in the aquatic oligochaete Tubifex tubifex based on lethal (LBR) and sublethal effects (CBR), and to discuss the relevance of the exposure to sediment for deriving CBR. Toxicity parameters (LC₅₀, EC₅₀, LBR₅₀ and CBR₅₀) were estimated for each metal by means of data on survival and on several sublethal variables measured in short-term (4 days), water-only exposures and in long-term, chronic (14 and 28 days) exposures using metal-spiked sediment. Sublethal endpoints included autotomy in short-term exposure, as well as reproduction and growth in chronic bioassays. LBR₅₀ and CBR₅₀ were 3–6 times higher in sediment than in water-only exposure to Cd and about 2–11 times higher for Cu, depending on the measured endpoint; however, for Cr these parameters varied only by a factor of 1.2. Cu and Cr LBR₅₀ and CBR₅₀ values in 96 h water-only exposure were very similar (survival 2.39 μmol Cu g^?1 dw, 2.73 μmol Cr g^?1 dw; autotomy 0.53 μmol Cu g^?1 dw, 0.78 μmol Cr g^?1 dw). However, in metal-spiked sediments, 28 d CBR₅₀ values for autotomy, reproduction and growth ranged 6.76–29.54 μmol g^?1 dw for Cd, 3.88–6.23 μmol g^?1 dw for Cu, 0.65 μmol g^?1 dw for Cr (calculated only on total number of young). Exposure conditions (time and presence/absence of sediment) seem to be influential in deriving metal CBR values of Cd and Cu, while appear to be irrelevant for Cr. Thus, CBR approach for metals is complex and tissue residue–toxicity relationship is not directly applicable so far.