Effects of heavy metals on the nitrogen metabolism of the aquatic moss Fontinalis antipyretica L. ex Hedw. A 15N tracer study

The assessment of pollution in aquatic systems necessitates an accurate indication of toxicity of heavy metals for organisms and ecosystems. We used the stable nitrogen isotope 15N to estimate the influence of the heavy metals Cd, Pb and Zn on the synthesis of nitrogen-containing fractions in the aquatic moss Fontinalis antipyretica. This method permits conclusions concerning inhibitory effects of these heavy metals on the assimilation of nitrogen and the biosynthesis of amino acids and proteins. The moss was exposed to metal concentrations of 25-500 microM over a period of 5-10 days. 15N abundance of exposed plants was compared with that of control plants. Similar to a loss of vitality determined using a fluorometric assay, a decrease of the 15N abundance in the N fractions of Fontinalis antipyretica was measured in dependence on the metal concentration. Nevertheless, the individual inhibition by the distinct metals was different, so that the following order of toxicity was derived: Cd > Pb > Zn.     

Biomonitoring of sporadic acidification of rivers on the basis of release of preloaded cadmium from the aquatic bryophyte Fontinalis antipyretica Hedw

A technique is proposed for biomonitoring of sporadic acidification events in rivers. Individuals of the bioindicator species are pre-incubated with a chemical marker, then transplanted to the test location for the period of interest, then analysed for marker content; acidification events are inferred on the basis of the degree of reduction in marker concentration. To assess the validity of the proposed technique, we performed laboratory trials with the aquatic bryophyte Fontinalis antipyretica Hedw. as bioindicator species, and cadmium (Cd) as marker. The bryophytes were pre-incubated with a Cd solution, obtaining saturation concentrations in the extracellular compartment and near-saturation concentrations in the intracellular compartment. In a first series of experiments, Cd-preloaded bryophyte apices were maintained for 1-30 h in water of different pH; the results clearly indicated that the amount of Cd released is dependent on pH. In a second series of experiments, Cd-preloaded bryophyte apices were maintained for 1-24 h in water with various combinations of pH and aluminium (Al) concentration (Al being a highly toxic element that is typically mobilized in acid waters). In these experiments, pH again had a marked effect on the amount of Cd released, while Al concentration had no consistent effects. To facilitate data analysis, Davidson-type equations were fitted to the results of the second series of experiments, allowing prediction of medium acidity on the basis of Cd concentration remaining in the extracellular and intracellular compartments.     

Antioxidant enzyme activities as affected by trivalent and hexavalent chromium species in Fontinalis antipyretica Hedw

The detoxification mechanisms of the aquatic moss, Fontinalis antipyretica Hedw., exposed to Cr was analyzed. In addition, the influence of Cr salts (as Cr nitrate, chloride and potassium bichromate) on these mechanisms has also been studied. The activity of antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1.), catalase (EC 1.11.1.6.), ascorbate peroxidase (APX, EC 1.11.1.11.), guaiacol peroxidase (GPX, EC 1.11.1.7.) and glutathione reductase (GR, EC 1.6.4.2.) increased in plants treated with Cr concentrations ranging from 6.25x10(-5) to 6.25mM when given as Cr(NO(3))(3). Antioxidant enzymes responded to the other two salts CrCl(3) and K(2)Cr(2)O(7) only with Cr concentrations higher than 6.25x10(-2)mM. Glutathione level and GSSG/GSH ratio also responded to Cr exposure but no dose-effect relationship could be observed. Moreover, two unknown thiol compounds were observed in mosses exposed to the highest Cr concentrations. Effects on chlorophyll contents and chlorophyll a/b ratios were also shown even at low Cr concentrations. Our results indicated that environmentally realistic concentrations of Cr could lead to impairment of the cellular activity towards F. antipyretica and that Cr(III), when present as a nitrate salt, was as harmful as Cr(VI).     

Modelling the extra and intracellular uptake and discharge of heavy metals in Fontinalis antipyretica transplanted along a heavy metal and pH contamination gradient

Samples of the aquatic bryophyte Fontinalis antipyretica Hedw. were transplanted to different sites with the aim of characterizing the kinetics of the uptake and discharge of heavy metals in the extra and intracellular compartments. The accumulation of metals in extracellular compartments, characterized by an initial rapid accumulation, then a gradual slowing down over time, fitted perfectly to a Michaelis-Menten model. The discharge of metals from the same compartment followed an inverse linear model or an inverse Michaelis-Menten model, depending on the metal. In intracellular sites both uptake and discharge occurred more slowly and progressively, following a linear model. We also observed that the acidity of the environment greatly affected metal accumulation in extracellular sites, even when the metals were present at relatively high concentrations, whereas the uptake of metals within cells was much less affected by pH.     

Fluoride toxicity to aquatic organisms: a review

Published data on the toxicity of fluoride (F-) to algae, aquatic plants, invertebrates and fishes are reviewed. Aquatic organisms living in soft waters may be more adversely affected by fluoride pollution than those living in hard or seawaters because the bioavailability of fluoride ions is reduced with increasing water hardness. Fluoride can either inhibit or enhance the population growth of algae, depending upon fluoride concentration, exposure time and algal species. Aquatic plants seem to be effective in removing fluoride from contaminated water under laboratory and field conditions. In aquatic animals, fluoride tends to be accumulated in the exoskeleton of invertebrates and in the bone tissue of fishes. The toxic action of fluoride resides in the fact that fluoride ions act as enzymatic poisons, inhibiting enzyme activity and, ultimately, interrupting metabolic processes such as glycolysis and synthesis of proteins. Fluoride toxicity to aquatic invertebrates and fishes increases with increasing fluoride concentration, exposure time and water temperature, and decreases with increasing intraspecific body size and water content of calcium and chloride. Freshwater invertebrates and fishes, especially net-spinning caddisfly larvae and upstream-migrating adult salmons, appear to be more sensitive to fluoride toxicity than estuarine and marine animals. Because, in soft waters with low ionic content, a fluoride concentration as low as 0.5 mg F-/l can adversely affect invertebrates and fishes, safe levels below this fluoride/l concentration are recommended in order to protect freshwater animals from fluoride pollution.     

Acute and chronic toxicity of benzotriazoles to aquatic organisms

Purpose

Resulting from their intensive use as corrosion inhibitors in aircraft deicing and anti-icing fluids (ADAF) and for silver protection in dishwasher detergents benzotriazoles (BTs) are widespread in European surface waters. The current study aimed on an ecotoxicological characterization of 1H-benzotriazole (1H-BT) and 5-methyl-1H-benzotriazole (5MBT).

Methods

Acute and chronic OECD guideline tests were conducted with primary producers (Desmodesmus subspicatus, Lemna minor) and two daphnia species (Daphnia magna, Daphnia galeata) to characterize the hazard of these chemicals. Additionally, the estrogenic activity of both BTs was analyzed in vitro using a recombinant yeast estrogen screen (YES).

Results

Both BTs revealed significant effects in acute and chronic experiments, but exhibited no estrogenic activity in the YES. The algal growth test displayed an inhibited cell number increase with effect concentration (EC) values of EC₁₀ 1.18 and 2.86?mg?l^-1 for 1H-BT and 5MBT, respectively. In the Lemna test, EC₁₀ values were 3.94?mg?l^-1 (1H-BT) and 2.11?mg?l^-1 (5MBT). D. magna was also affected with EC₅₀ (48?h) values of 107?mg?l^-1 for 1H-BT and 51.6?mg?l^-1 for 5MBT. D. galeata was more sensitive with an EC₅₀ (48?h) of 14.7?mg 1H-BT l^-1 and 8.13?mg 5MBT l^-1. In the 21-day reproduction tests with D. magna, the EC₁₀ for 5MBT was 5.93?mg?l^-1 while 1H-BT showed no adverse effects. D. galeata turned out to be more sensitive in the chronic study with EC₁₀ values of 0.97?mg?l^-1 for 1H-BT and 0.40?mg?l^-1 for 5 MBT.

Conclusion

Because BTs are regularly found in the aquatic environment at lower ??g l^-1 concentrations reflecting their persistence and poor elimination during wastewater treatment processes, a preliminary risk assessment was conducted. There is little indication that BTs pose a risk for aquatic ecosystems at current exposure levels during most of the year. However, it cannot be excluded that in winter with a higher usage of ADAFs environmental concentrations may well exceed the level that is considered safe for aquatic organisms.     

Calculating the aquatic toxicity of hydrocarbon mixtures

For acute toxicity to aquatic organisms, individual hydrocarbons are equally toxic on the basis of their internal molar concentration within the organism. The differences in measured toxicities among hydrocarbons lies with differences in their equilibrium partitioning behavior between water and the organism. For complex hydrocarbon mixtures, an additional complication of partitioning between the bulk hydrocarbon and the water is encountered. Equations are developed for calculating the water concentration of components of complex hydrocarbon mixtures. Using gasoline as an example, a method is presented for first calculating the concentration of gasoline components in water after equilibration with different gasoline volumes and then, the component toxicities are used to estimate the gasoline volume causing 50% mortality to aquatic organisms.     

A novel approach to predict aquatic toxicity from molecular structure

The main aim of the study was to develop quantitative structure-activity relationship (QSAR) models for the prediction of aquatic toxicity using atom-based non-stochastic and stochastic linear indices. The used dataset consist of 392 benzene derivatives, separated into training and test sets, for which toxicity data to the ciliate Tetrahymena pyriformis were available. Using multiple linear regression, two statistically significant QSAR models were obtained with non-stochastic (R2=0.791 and s=0.344) and stochastic (R2=0.799 and s=0.343) linear indices. A leave-one-out (LOO) cross-validation procedure was carried out achieving values of q2=0.781 (scv=0.348) and q2=0.786 (scv=0.350), respectively. In addition, a validation through an external test set was performed, which yields significant values of Rpred2 of 0.762 and 0.797. A brief study of the influence of the statistical outliers in QSAR's model development was also carried out. Finally, our method was compared with other approaches implemented in the Dragon software achieving better results. The non-stochastic and stochastic linear indices appear to provide an interesting alternative to costly and time-consuming experiments for determining toxicity.     

Data ranges in aquatic toxicity of chemicals

A significant problem for effect assessment of aquatic ecosystems arises from the large ranges of toxicity data, which can be found in different databases and literature. Here, ranges are given for the aquatic toxicity of 27 high production volume chemicals. Based on these illustrative examples and on the current literature on uncertainty in aquatic effect assessment, toxicity ranges are discussed for their possible causes (variation in experimental condition, species, endpoint, time) and ways to handle them (safety factors). Implications and recommendations on the procedure of risk analysis of chemical substances are drawn. Two main requirements for a comprehensive risk assessment are identified, which often play a minor role in current practice (as they are often neglected) as well as in scientific discussion (as they are meant to be trivial). First, data quality must be checked critically before applying any result of a toxicity test. Secondly, experimental data should take into account different species and acute as well as chronic data. If these aspects are considered in risk analysis, which is common practice in ecotoxicology but not always in the context of practical applications in risk engineering, a more comprehensive picture of the environmental toxicity of a chemical substance can be obtained.     

A microcosm system to evaluate the toxicity of the triazine herbicide simazine on aquatic macrophytes

This study evaluates the effects of the triazine herbicide simazine in an outdoor pond microcosm test system that contained two submerged rooted species (Myriophyllum spicatum and Elodea canadensis) and two emergent rooted species (Persicaria amphibia and Glyceria maxima) over a period of 84 days. Simazine was applied to the microcosms at nominal concentrations of 0.05, 0.5 and 5 mg/L. General biological endpoints and physiological endpoints were used to evaluate herbicide toxicity on macrophytes and the algae developing naturally in the system.Concentration-related responses of macrophytes and algae were obtained for the endpoints selected, resulting in a no observed ecologically adverse effect concentration (NOEAEC) at simazine concentrations of 0.05 mg active ingredient/L after 84 days. E. canadensis was the most negatively affected species based on length increase, which was consistently a very sensitive parameter for all macrophytes. The experimental design presented might constitute a suitable alternative to conventional laboratory single-species testing.     

Assessing the toxicity of organophosphorous pesticides to indigenous algae with implication for their ecotoxicological impact to aquatic ecosystems

This study aimed to determine the toxicity of three organophosphorous pesticides, chlorpyrifos, terbufos and methamidophos, to three indigenous algal species isolated from local rivers and algal mixtures. The diatom Nitzschia sp. (0.30–1.68 mg L^?1 of EC₅₀ -the estimated concentration related to a 50% growth reduction) and the cyanobacteria Oscillatoria sp. (EC₅₀ of 0.33–7.99 mg L^?1) were sensitive to single pesticide treatment and the chlorophyta Chlorella sp. was the most tolerant (EC₅₀ of 1.29–41.16 mg L^?1). In treatment with the mixture of three pesticides, Chlorella sp. became the most sensitive alga. The antagonistic joint toxic effects on three indigenous algae and algal mixtures were found for most of the two pesticide mixtures. The results suggested that mixture of pesticides might induce the detoxification mechanisms more easily than the single pesticide. The synergistic interactions between terbufos and methamidophos to algal mixtures and between methamidophos and chlorpyrifos to Nitzschia sp. indicated methamidophos might act as a potential synergist. Differential sensitivity of three families of algae to these pesticides might result in changes in the algal community structures after river water has been contaminated with different pesticides, posing great ecological risk on the structure and functioning of the aquatic ecosystem.     

Nitrate toxicity to aquatic animals: a review with new data for freshwater invertebrates

Published data on nitrate (NO3-) toxicity to freshwater and marine animals are reviewed. New data on nitrate toxicity to the freshwater invertebrates Eulimnogammarus toletanus, Echinogammarus echinosetosus and Hydropsyche exocellata are also presented. The main toxic action of nitrate is due to the conversion of oxygen-carrying pigments to forms that are incapable of carrying oxygen. Nitrate toxicity to aquatic animals increases with increasing nitrate concentrations and exposure times. In contrast, nitrate toxicity may decrease with increasing body size, water salinity, and environmental adaptation. Freshwater animals appear to be more sensitive to nitrate than marine animals. A nitrate concentration of 10 mg NO3-N/l (USA federal maximum level for drinking water) can adversely affect, at least during long-term exposures, freshwater invertebrates (E. toletanus, E. echinosetosus, Cheumatopsyche pettiti, Hydropsyche occidentalis), fishes (Oncorhynchus mykiss, Oncorhynchus tshawytscha, Salmo clarki), and amphibians (Pseudacris triseriata, Rana pipiens, Rana temporaria, Bufo bufo). Safe levels below this nitrate concentration are recommended to protect sensitive freshwater animals from nitrate pollution. Furthermore, a maximum level of 2 mg NO3-N/l would be appropriate for protecting the most sensitive freshwater species. In the case of marine animals, a maximum level of 20 mg NO3-N/l may in general be acceptable. However, early developmental stages of some marine invertebrates, that are well adapted to low nitrate concentrations, may be so susceptible to nitrate as sensitive freshwater invertebrates.     

A comparison of acute toxicity of biodiesel, biodiesel blends, and diesel on aquatic organisms

The increased demand of alternative energy sources has created interest in biodiesel and biodiesel blends; biodiesel is promoted as a diesel substitute that is safer, produces less harmful combustion emissions, and biodegrades more easily. Like diesel spills, biodiesel can have deleterious effects on the aquatic environments. The effect of neat biodiesel, biodiesel blends, and diesel on Oncorhynchus mykiss and Daphnia magna was evaluated using acute toxicity testing. Static nonrenewal bioassays of freshwater organisms containing B100, B50, B20, B5, and conventional diesel fuel were used to compare the acute effects of biodiesel to diesel. Mortality was the significant end point measured in this study; percent mortality and lethal concentration (LC50) at different exposure times were determined from the acute toxicity tests performed. Trials were considered valid if the controls exhibited > 90% survival. Based on percentage of mortality and LC50 values, a toxicity ranking of fuels was developed.     

Statistical evaluation of chronic toxicity data on aquatic organisms for the hazard identification: the chemicals toxicity distribution approach

Presently, in the Globally Harmonised System of Classification and Labelling of Chemicals the classification of substances for long-term effects to aquatic life is based on acute toxicity in combination with degradation and/or bioaccumulation potential. Recently an OECD Working Group was created to develop the classification scheme to accommodate chronic toxicity data related to aquatic organisms for assigning a chronic hazard category. This study focuses on a new approach for setting chronic toxicity cut-off values based on Chemicals Toxicity Distributions (CTDs). A CTD is obtained through statistical fitting of the data used by regulatory bodies for setting hazard-based classifications. The CTDs were made using the lowest aquatic NOEC value of each chemical. A review of different toxicological sources reporting acute aquatic toxicities was carried out. Initially, the data were arranged according to the specific source and distributions for key taxonomic groups (i.e. fishes, crustaceans and algae) were evaluated separately. In most cases, no significant departures from normality were observed. Thereafter, a compiled database containing >900 values was developed and the CTDs were constructed for each taxonomic group. Significant deviation from normality (P < 0.05) was observed in the fishes and crustaceans' CTDs. However, this deviation was apparently produced by the presence of only seven values with NOECs <1 x 10(-5) mg l(-1), while high correlation between the data and the normal scores (r-values>or= 0.989) indicated that the data were samples from normal distributions. From these observations, potential cut-off values would allow quantitative estimations of the percentage of chemicals falling into each specific category. This approach results in a simple classification hazard scheme where most chemicals are covered in one of the categories, allowing a clear distribution of the chemicals among three categories for chronic toxicity.