Toxicity evaluation of natural and synthetic phenanthrenes in aquatic systems

Seven natural 9,10-dihydrophenanthrenes were isolated from the common reed Juncus effusus by means of chromatographic processes and identified by spectroscopic means. Furthermore, mimics of natural isolated compounds were synthesized to try to evaluate the influence of functional groups on the dihydrophenanthrene skeleton. Syntheses of compounds were based on the cross-coupling of 1-(2-iodo-5-methoxy)phenyl-ethanol with variously substituted iodobenzenes by zerovalent nickel. All the chemicals were tested to evaluate their effects on freshwater organisms from different trophic levels. Toxicity tests were performed on reducers (the bacterium Escherichia coli); producers (the alga Raphidocelis subcapitata, previously known as Selenastrum capricornutum); and consumers including a rotifer (Brachionus calyciflorus), a cladoceran (Daphnia pulex), and an anostracan (Thamnocephalus platyurus). Results suggested no one organism was uniquely sensitive to the chemicals tested. Toxicity depended on the kind and position of substituents on the aromatic skeleton.     

Bayesian modelling of daphnid responses to time-varying cadmium exposure in laboratory aquatic microcosms

Experiments were carried out to test the effects of cadmium on five aquatic species in 2-L indoor freshwater/sediment microcosms. Experimental data were collected over 21 days in static conditions, i.e. the microcosms evolved without water renewal. Because of speciation, the total cadmium concentration in water decreased with time. Here we present a focus on Daphnia magna responses. For the three life history traits we considered (survival, growth and reproduction), mathematical effect models were built based on threshold stress functions involving no effect concentrations (NECs). These models took the time-varying conditions of exposure into account through a time-recurrent formalism. Within a Bayesian framework, four kinds of data were fitted simultaneously (exposure, survival, growth and reproduction), using an appropriate error model for each endpoint. Hence, NECs were determined as well as their associated estimation uncertainty. Through this modelling approach, we demonstrate that thresholds for stress functions can be successfully inferred even in experimental setup more complex than standard bioassays.     

Development of a coupled metal speciation-fate model for surface aquatic systems

A coupled metal transport and speciation model (TRANSPEC) has been developed for surface aquatic systems that explicitly considers the influence of metal speciation on fate. The TRANSPEC, which is general to most metal and surface aquatic systems, is constructed by sequentially coupling the speciation/complexation module (in this application MINEQL+) with the fugacity/aquivalence approach for the fate calculations. This model formulation increases the mechanistic detail, predictive power, and fidelity to reality of current fugacity-aquivalence fate models for metals by estimating aqueous speciation and complexation, rather than relying on empirically derived partition coefficients. A pseudo-steady state version of TRANSPEC was used to simulate Zn dynamics in Ross Lake (Flin Flon, MB, Canada) that received elevated metal and organic matter inputs for over 50 years. Field studies revealed that ZnS forms soluble ZnL, Zn2+, and ZnSO4(0) increasing pore water concentrations when surficial sediments turn oxic during fall. The model results for three seasonal scenarios suggest that Zn remobilization is driven by resuspension of insoluble ZnS and the contribution of diffusion is negligible, even during fall when ZnS dissolves to increase the concentration of soluble species under oxic conditions in the sediments. The low diffusive flux is due to the binding of Zn to colloidal dissolved organic matter (DOM) for which sediment-water diffusion is relatively slow, a result that was obtained as a result of considering metal speciation in the fate calculations.     

A micelle inhibition model for the bioavailability of polycyclic aromatic hydrocarbons in aquatic systems

A mathematical model was developed to quantify micelle suppression on the bioavailability of hydrophobic organic compounds in aquatic systems. The model was based on a three-compartment dynamic system in which the hydrophobic compounds are taken up and eliminated by organisms with an equilibrium partitioning between water and micelle. The model was validated against data obtained from in vitro studies of the bioaccumulation of naphthalene, anthracene, and chrysene into the gills of the freshwater mussel (Ellipto complanata) in the presence of a surfactant (Tween 80). The model predictions agreed well with the experimental results for all three chemicals. Sensitivity analyses were performed to examine model responses to the surfactant parameters. From the model, we derive an equation for a bioconcentration factor in aquatic surfactant systems to predict the maximum concentration of polycyclic aromatic hydrocarbons (PAHs) in aquatic organisms. From these results, we also propose a micelle inhibition factor for bioconcentration that is a function of the surfactant concentration, critical micelle concentration, and partition coefficient of hydrophobic compounds between water and micelle. Knowledge of these parameters may improve understanding of the partitioning of PAHs into organisms in the presence of surfactants.     

Toxic effects and bioaccumulation of cadmium in the aquatic oligochaete Tubifex tubifex

Although Tubifex tubifex (Oligochaeta, Tubificida) has been proposed as a test organism for ecotoxocological studies, very few data concerning sublethal toxicity and bioaccumulation are available on this worm. The aims of this work were to assess the toxicity of cadmium, one of the most toxic metals frequently encountered in polluted areas, on T. tubifex and the ability of the worm to accumulate this metal. Acute toxicity was analyzed by measurement of the 96-h LC(50) and daily survival rates. Results indicated that T. tubifex undergoes an adaptation period to Cd, the duration of which decreases with increasing Cd concentration. The various parameters affecting toxicity are discussed. Sublethal toxicity was studied by scanning electron microscopy. Observations revealed that Cd induced autotomy of the caudal region and mucus production. Autotomy is proposed as a criterion for sublethal toxicity. The results of bioaccumulation studies revealed that Cd is highly and rapidly taken up by the worm, suggesting involvement of efficient detoxification mechanisms. Consequently, the ability to accumulate large amounts of Cd may represent a potential toxicological risk to predators of the worm if Cd is accumulated in bioavailable forms.     

Syngerism between dissolved oxygen and cadmium toxicity in five species of aquatic insects.

Continuous-flow bioassays were employed to determine the relationship between dissolved oxygen and cadmium upon five species of aquatic insects, as measured by survival and the amount of cadmium found within the insect. Results indicate the toxicity of cadmium increases as the dissolved oxygen concentration increases. This may be explained by an observed increase in the amount of cadmium found in the insect as the dissolved oxygen concentration increases. Oxygen consumption has been reported to increase as the dissolved oxygen concentration increases (Petty, 1967; Ericksen, 1963; Fox et al., 1937). In this study, using a fixed cadmium concentration, the amount of cadmium found in the insect also increased with an increase in the dissolved oxygen. Therefore, cadmium absorption may be coupled to metabolism.     

Toxicology and ecotoxicology of persistent organic microcontaminants in aquatic systems

Persistent organic pollutants (POP) are a heterogeneous group of chemicals widely distributed in the aquatic environment. Some classes cause adverse effects in the biota at minute concentrations, persist in the environment for a long time, and bioaccumulate in animal tissues. Several strategies exist today to monitor their levels and evaluate their effects in the environment. Particularly, some interesting approaches have recently been developed in the field of biomarkers, although much work seems to be required to study the relationships between toxic responses at different levels of the biological organization of interest and concentration levels in tissues.     

Behavior of trifluralin in aquatic model ecosystems

Conclusions These data illustrate the variation that can be obtained when using different model ecosystem designs in studying the behavior of pesticides in the aquatic ecosystem. These differences were probably related to the rapid metabolism and degradation of soil-incorporated trifluralin in the first experiment and to the continuous input of trifluralin in the second experiment. A very important difference between the two ecosystems was the toxic effect of trifluralin on the algae and fish during the second experiment. We believe that the risks of trifluralin in the aquatic ecosystem are greatest when there is a continuous input of tribluralin. With an occasional soil-incorporated input, the degradation processes would minimize this risk.     

Metamorphosis of two amphibian species after chronic cadmium exposure in outdoor aquatic mesocosms

Amphibian larvae at contaminated sites may experience an alteration of metamorphic traits and survival compared to amphibians in uncontaminated conditions. Effects of chronic cadmium (Cd) exposure on the metamorphosis of American toads (Bufo americanus) and southern leopard frogs (Rana sphenocephala) were determined. The two species were reared separately from shortly after hatching through metamorphosis in outdoor mesocosms (1,325-L polyethylene cattle tanks) that simulated natural ponds and enhanced environmental realism relative to the laboratory. Both species exhibited a decrease in survival with increasing initial nominal aqueous Cd concentration. Cadmium treatment did not influence mass at metamorphosis for either species when survival was included as a covariate, but increased the age at metamorphosis for the American toads. The whole body Cd content of metamorphs increased with aqueous Cd treatment level for both species, and the American toads tended to possess more elevated residues. Cadmium quickly partitioned out of the water column and accumulated in and altered the abundance of the tadpoles' diet. Cadmium-contaminated sites may produce fewer metamorphs, and those that survive will metamorphose later and contain Cd. Interspecific differences in the response variables illustrate the importance of testing multiple species when assessing risk.     

Ultrastructural and biochemical effects of cadmium on the aquatic fern Marsilea minuta Linn

The uptake of cadmium by cultured vegetative clones of the aquatic fern Marsilea minuta was studied in a static experimental bioassay system as functions of dose and period of exposure. The pathomorphological manifestations of Cd toxicity, as studied by transmission electron microscope, indicated damage to chloroplasts and tonoplasts as well as electron opaque granular deposits. Preliminary evidence based on molecular sieving chromatography showed the formation of two cadmium-binding proteins of 78 and 33 kDa in the leaf tissue under cadmium stress.     

Selenium teratogenesis in natural populations of aquatic birds in Central California

The frequency and types of malformations are described that were encountered during the spring of 1983 in a natural population of aquatic birds exposed to agricultural drainwater ponds and food items containing high concentrations of selenium in central California. A total of 347 nests of aquatic birds containing 1,681 eggs was selected for study at Kesterson Reservoir located in the Kesterson National Wildlife Refuge (NWR), Merced County, California. Embryos collected during incubation or from eggs that failed to hatch were examined to determine the age at death and presence of malformations. Embryonic death was generally high; approximately 17–60% of the nests of different species contained at least one dead embryo. The incidence of malformed embryos was also high; approximately 22–65% of the nests where at least two embryos were examined contained abnormal embryos. American coots (Fulica americana) and black-necked stilts (Himantopus mexicanus) experienced the highest incidence of malformed embryos. For all species, the average percentage of eggs containing dead or live abnormal embryos was 16.1 whereas the average percentage containing live abnormal embryos was 10.7. Multiple gross malformations of the eyes, brain, and feet were often present. Brain defects included hydrocephaly and exencephaly. Eye defects included both unilateral and bilateral anophthalmia and microphthalmia. Eye and foot defects with ectrodactyly and swollen joints were the most common in coots. Beak defects also occurred frequently and most often included incomplete development of the lower beak of ducks (Anas spp.) and stilts. Wing and leg defects were most prevalent in stilts and ducks, with ectromelia and amelia most prevalent in stilts. Other malformations occurring at lower frequencies included enlarged hearts with thin ventricular walls, liver hypopiasia, and gastroschisis. Based upon simultaneous examination of a control population of aquatic birds of the same species and published studies, the incidences of embryonic mortality and deformities were 9–30 times greater than expected. The role of the form of selenium responsible for teratogenesis in laboratory studies is discussed.     

Influence of tetrachloroethylene on the biota of aquatic systems: Toxicity to phyto- and zooplankton species in compartments of a natural pond

This study was designed to determine the effects of tetrachloroethylene on the phyto- and Zooplankton community at initial concentrations of 1.2 and 0.44 mg/L in separated compartments of an experimental pond. Measurements in the surrounding water were made simultaneously to detect possible effects of compartmentalization. Residues as low as 0.1 mg/L could be analyzed 5 days (low dose) and 38 days (high dose) post application. In all applied biotopes, a lethal effect on the Daphnia population was detected. The phytoplankton community showed an increase of relative abundance and a decrease in species diversity. Studies of the frequency distribution of six selected phytoplankton species demonstrated the total elimination of at least four species from the treated compartments. In spite of different dosing, only weak differences could be found in toxic effects between the low and high dosed compartments. No significant chemical-induced effect was observed on the physico-chemical properties of the treated water.     

Metal interactions within the kidney,gill, and digestive gland of the clam,Mercenaria mercenaria,following laboratory exposure to cadmium

Mercenaria mercenaria were exposed to 0.1 g Cd/ml seawater (¹⁰⁹Cd + stable carrier) for either (1) periods of 1 hr to 31 days, or (2) a period of 3 days followed by depuration in clean seawater for 2 to 64 days. Cd accumulated at increasing rates in the kidney, but at decreasing rates in all other organs of the clam during the laboratory exposure period. Measurement of total Cd levels confirmed that¹⁰⁹Cd was accumulated by the clam tissues and not simply exchanged. The overall rate of Cd accumulation was significantly greater (P < 0.05) for the kidney than for the gill, mantle, digestive gland, pericardial gland, adductor, or remaining viscera, but not significantly different among the other organs (P > 0.05). No loss of Cd or other detectable metals occurred even after 64 days depuration. The degree to which Cd accumulated in the kidney, gill, and digestive gland did not correlate with the concentrations of other metals already present in these organs (except with Zn in the digestive gland). Negative correlations between different metal concentrations were never observed. Comparison of metal interaction patterns between the kidney, gill, and digestive gland indicates that each organ relies on different mechanisms for sequestering metals.