Short-term toxic effects of chlorobenzenes on broadbean (Vicia faba) seedlings

The root growth, changes in Superoxide dismutase (SOD, EC 1.15.1.1) activity, malonyldialdehyde (MDA) and total soluble protein level of broadbean (Vicia faba) seedlings were researched at different soil concentrations of chlorobenzene (CB), 1,2,4-trichlorobenzene (TCB) and hexachlorobenzene (HCB). The results showed that root growth of seedlings was interrupted after 5d of 50–200 μg · g⁻¹ TCB treatment. During a 3 d of recovery period, root growth was, however, restored to some extent although there was a delay in returning to the control level. The total soluble protein content in seedlings increased with TCB concentration and duration of exposure. Effect of TCB stress on SOD activity in seedlings displayed a significant dose-effect relationship for 1–5 d of 50–200 μg · g⁻¹ treatment. When broadbean seedlings were placed in clean tap water for 3 d following exposure to 5 d of TCB stress to clear tap water for 3 d, SOD activity at 50 μg · g⁻¹ TCB recovered towards control level (P> 0.05) while a significant increase in SOD activity was observed at 100 and 200 μg · g⁻¹ TCB compared to control (P< 0.05). The experiments also revealed that a significant increase of MDA level in seedlings occurred after 3 and 5 d of 100 and 200 μg · g⁻¹ TCB treatment (P< 0.05 andP< 0.01), and there was a positive correlation between TCB concentration and MDA level. All the above results showed that SOD activity and MDA level of broadbean seedlings might be proposed as the biomarkers for short-term TCB contamination in soil. Compared to TCB, the toxicity of 50−1000 μg · g⁻¹ CB or HCB in soil to broadbean seedlings was not observed after a 3 d exposure.

     

Resuspension of algal cells by benthivorous fish boosts phytoplankton biomass and alters community structure in shallow lakes

1. Positive effects of fish on algal biomass have variously been attributed to cascading top‐down effects and to nutrient enrichment by fish excretion. 2. Here, we used a combination of field and laboratory approaches to test an additional hypothesis, namely that the physical resuspension of settled algal cells by fish enhances algal biomass and alters community composition. 3. A multi‐lake survey showed that phytoplankton biomass and the fraction of motile algae increased with the concentration of inorganic suspended solids. This correlation could not be explained by wind‐induced resuspension because of the small size of the lakes. 4. In an enclosure experiment, chlorophyll‐a concentration, phytoplankton abundance and inorganic suspended solids increased significantly in the presence of Cyprinus carpio (common carp), but only if the fish had access to the sediment. No such effects were seen when a net prevented carp reaching the sediment. 5. The effects of enhanced nutrients and reduced zooplankton grazing as a result of fish feeding could not (fully) explain these observations, suggesting that the resuspension by carp of settled algae from a surface film on the sediment was the major factor in the outcome of the experiment. 6. An increase in diatoms and green algae (organisms with a relatively large sedimentation velocity) only in enclosures where carp could reach the sediment supported this view. 7. Several lines of evidence indicate that fish‐induced resuspension of algal cells from the sediment is an important mechanism that affects phytoplankton biomass and community composition in shallow lakes.     

Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material

The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0–1 cm) and three times lower in the middle layer (1–3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3–10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We␣conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were␣no␣indications of any group adjusting their vertical position behaviourally as a response to predation threat.     

Laboratory test of suspended sediment effects on short‐term survival and swimming performance of juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus,Mitchill, 1815)

Tested was the hypothesis that juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) would exhibit no response in short‐term survival or swimming performance when exposed to varying concentrations of suspended sediment simulating dredge plumes in waterways where this species may be impacted by dredging operations. Sediment collected from Savannah Harbor, South Carolina, USA was used to simulate a worst‐case scenario. Juvenile sturgeon were contained for a 3‐day period in flow‐through aquaria, with limited opportunity for movement, in sediment of varying concentrations (100, 250 and 500 mg L^?1 total suspended solids [TSS]) mimicking prolonged exposure to suspended sediment plumes near an operating dredge. Of the 90 fish exposed, 86 (96%) survived the test. Of the four fish that died, one was exposed to 250 TSS and three to 500 TSS. Swimming performance results indicated that nearly all fish were positively rheotactic. Critical swim speeds (U_crits) were moderate, whether measured as absolute values (21–31 cm s^?1) or as relative values (1.4–2.1 body lengths s^?1), with no significant differences among treatments (F < 0.83, P ≥ 0.4874). Behavior was dominated by contact‐based locomotion and station‐holding. Absence of substantial or significant immediate effects on survival and swimming performance suggest that impacts of sediment plumes in nature, where fish have freedom of movement and the power to escape rapidly, are minimal.     

Diversity of dechlorination pathways and organohalide respiring bacteria in chlorobenzene dechlorinating enrichment cultures originating from river sludge

Anaerobic reductive dechlorination of hexachlorobenzene (HCB) and three isomers of tetrachlorobenzene (TeCB) (1,2,3,4-, 1,2,3,5- and 1,2,4,5-TeCB) was investigated in microcosms containing chloroaromatic contaminated river sediment. All chlorobenzenes were dechlorinated to dichlorobenzene (DCB) or monochlorobenzene. From the sediment, a methanogenic sediment-free culture was obtained which dechlorinated HCB, pentachlorobenzene, three TeCB isomers, three trichlorobenzene (TCB) isomers (1,2,3-, 1,2,4- and 1,3,5-TCB) and 1,2-DCB. Dechlorination involved multiple pathways including the removal of doubly flanked, singly flanked and isolated chlorine substituents. 454-pyrosequencing of partial bacterial 16S rRNA genes amplified from selected chlorobenzene dechlorinating sediment-free enrichment cultures revealed the presence of a variety of bacterial species, including Dehalobacter and Dehalococcoides mccartyi, that were previously documented as organohalide respiring bacteria. A genus with apparent close relationship to Desulfitobacterium that also has been associated with organohalide respiration, composed the major fraction of the operational taxonomic units (OTUs). Another major OTU was linked with Sedimentibacter sp., a genus that was previously identified in strict co-cultures of consortia reductively dehalogenating chlorinated compounds. Our data point towards the existence of multiple interactions within highly chlorinated benzene dechlorinating communities.     

Short-term toxic effects of chlorobenzenes on broadbean (Vicia faba) seedlings

The root growth, changes in superoxide dismutase (SOD, EC 1.15.1.1) activity,malonyldialdehyde (MDA) and total soluble protein level of broadbean (Vicia faba) seedlings were researched at different soil concentrations of chlorobenzene (CB), 1,2,4-trichlorobenzene (TCB) and hexachlorobenzene (HCB). The results showed that root growth of seedlings was growth was, however, restored to some extent although there was a delay in returning to the control level. The total soluble protein content in seedlings increased with TCB concentration and duration of exposure. Effect of TCB stress on SOD activity in seedlings displayed a significant were placed in clean tap water for 3 d following exposure to 5 d of TCB stress to clear tap water (P＜0.05). The experiments also revealed that a significant increase of MDA level in seedlings was a positive correlation between TCB concentration and MDA level. All the above results showed that SOD activity and MDA level of broadbean seedlings might be proposed as the biomarkers for short-term TCB contamination in soil. Compared to TCB, the toxicity of 50-1000 μg · g-1 CB or HCB in soil to broadbean seedlings was not observed after a 3 d exposure.     

Study on the mechanism of interference of 3,4,3',4'-tetrachlorobiphenyl with the plasma retinol-binding proteins in rodents

The mechanism of plasma retinol reduction in rodents by 3,4,3',4'-tetrachlorobiphenyl (TCB) was investigated by radioimmunochemical analysis of the amounts of circulating and hepatic retinol-binding protein (RBP) and transthyretin (TTR) in exposed and control animals. Plasma RBP concentrations were markedly reduced in C57BL/Rij mice (50%) at 4 days, in DBA/2 mice (37-41%) at 4 and 8 days, and in Sprague-Dawley rats (58%) at 2 days after exposure to TCB. These reductions paralleled the time course of reduction of plasma retinol after exposure to TCB. Hepatic RBP concentrations were somewhat increased in TCB-treated animals, especially in the C57BL/Rij mouse and Sprague-Dawley rat. However, the release of hepatic RBP into the circulation was not blocked by TCB treatment, as analysed in vitamin A deficient rats. In addition, the amount of plasma TTR was in the normal range in TCB-treated rats. The dissociation constants of the RBP-TTR complex as analysed by polarization of fluorescence appeared to be significantly increased (from 0.5 x 10(-7) M-1 to 2.4 x 10(-7) M-1) in the presence of a TCB metabolite, isolated from plasma of TCB-treated rats. In addition, the estimated number of binding sites for RBP on the TTR molecule was reduced (from 2.8 to 1.7 sites) upon treatment of TTR with the TCB metabolite. These data support the hypothesis that plasma retinol reduction by TCB might result from a weakening of the RBP-TTR complex, in the presence of the TCB metabolite bound to the TTR.     

Is reduction of the benthivorous fish an important cause of high transparency following biomanipulation in shallow lakes?

Experimental reduction of the fish stock in two shallow lakes in The Netherlands shows that such a biomanipulation can lead to a substantial increase in transparency, which is caused not only by a decrease in algal biomass, but also by a decrease in resuspended sediment and detritus. A model was developed to describe transparency in relation to chlorophyll-a and inorganic, suspended solids (resuspended sediment). With the use of this model it is shown that more than 50% of the turbidity in these shallow lakes before biomanipulation was determined by the sediment resuspension, mainly caused by benthivorous fish. Another analysis reveals that the concentration of inorganic suspended solids and the biomass of benthivorous fish are positively correlated, and that even in the absence of algae a benthivorous fish biomass of 600 kg ha⁻¹ can reduce the Secchi depth to 0.4 m in shallow lakes. In addition, it is argued that algal biomass is also indirectly reduced by removal of benthivorous fish. Reduction of benthivorous fish is necessary to get macrophytes and macrophytes seem to be necessary to keep the algal biomass low in nutrient-rich shallow lakes. It is concluded that the impact of benthivorous fish on the turbidity can be large, especially in shallow lakes.     

Enclosures study of trophic level interactions in the mesotrophic part of Lake Balaton

Enclosures, open to the bottom sediments and to the atmosphere, containing about 17 m³ of lake water in the mesotrophic area of Lake Balaton, were used to elucidate the role of the benthivorous fish bream (Ambramis brama L.) in the lake during 1984–1986.Throughout the whole period water was less transparent in the enclosure containing fish, which strongly influenced the concentrations of suspended solids and chlorophyll a.Both phytoplankton biomass and production readily responded to nutrient increase in the enclosure with fish. In 1985 diatoms were replaced by cyanobacteria whereas in 1986, at a lower fish stocking, a shift in algal structure towards chlorophytes was observed.Egested organic substances and the resuspension of sediment particles by fish increased bacterial production.     

Short-term toxic effects of chlorobenzenes on broadbean (<Emphasis Type="Italic">Vicia faba</Emphasis>) seedlings

The root growth, changes in Superoxide dismutase (SOD, EC 1.15.1.1) activity, malonyldialdehyde (MDA) and total soluble protein level of broadbean (Vicia faba) seedlings were researched at different soil concentrations of chlorobenzene (CB), 1,2,4-trichlorobenzene (TCB) and hexachlorobenzene (HCB). The results showed that root growth of seedlings was interrupted after 5d of 50–200 μg · g^?1 TCB treatment. During a 3 d of recovery period, root growth was, however, restored to some extent although there was a delay in returning to the control level. The total soluble protein content in seedlings increased with TCB concentration and duration of exposure. Effect of TCB stress on SOD activity in seedlings displayed a significant dose-effect relationship for 1–5 d of 50–200 μg · g^?1 treatment. When broadbean seedlings were placed in clean tap water for 3 d following exposure to 5 d of TCB stress to clear tap water for 3 d, SOD activity at 50 μg · g^?1 TCB recovered towards control level (P> 0.05) while a significant increase in SOD activity was observed at 100 and 200 μg · g^?1 TCB compared to control (P< 0.05). The experiments also revealed that a significant increase of MDA level in seedlings occurred after 3 and 5 d of 100 and 200 μg · g^?1 TCB treatment (P< 0.05 andP< 0.01), and there was a positive correlation between TCB concentration and MDA level. All the above results showed that SOD activity and MDA level of broadbean seedlings might be proposed as the biomarkers for short-term TCB contamination in soil. Compared to TCB, the toxicity of 50?1000 μg · g^?1 CB or HCB in soil to broadbean seedlings was not observed after a 3 d exposure.     

Control of foraging behavior of individuals within an ecosystem context: the clam Macoma balthica,flow environment,and siphon-cropping fishes

Macoma balthica (L.), an abundant clam, ubiquitous in temperate estuaries across the North Atlantic, is known to practice both alternative basic modes of feeding available to seafloor invertebrates. It either holds its feeding organ, the siphon, at a fixed position just above the sediment surface to filter out food particles suspended in the overlying water or else extends and moves its siphon around to vacuum up deposited food particles on the sediment surface. Previous laboratory experiments have established an understanding of the role of current flow in dictating the choice of whether suspension or deposit feeding will be used by marine invertebrates with the facultative flexibility to choose. Faster flows imply greater fluxes of suspended particles so that the energetic rewards of suspension feeding are enhanced. Slower flows imply reduced renewal rates of suspended foods in the bottom boundary layers and enhanced deposition of food particles on the seafloor so that a switch to deposit feeding is favored. Like early optimal foraging theory, this understanding is based on energetic considerations alone without incorporation of broader implications of how population interactions such as predation and competition influence individual foraging behavior. Feeding behavior of Macoma balthica is influenced in the Neuse River estuary by both hydrodynamics and siphon-cropping by juvenile demersal fishes. Under conditions of identical concentrations of suspended particulates in the water column and organic contents of surface sediments, Macoma exhibited much higher levels of deposit feeding where currents were slower. In addition, exclosure and fish inclosure experiments demonstrated that juvenile demersal fishes influence feeding behavior of Macoma by cropping exposed siphons and inducing reduction in deposit-feeding activity. Effects of croppers were substantial in early to midsummer, when juvenile fish abundances were greatest in trawl samples from this estuarine nursery and before the growing fish exhibited ontogenetic changes in diet away from early concentration on bivalve siphons. Field experiments in which siphon-cropping fish were caged at varying distances off the bottom failed to detect any effective behavioral avoidance by Macoma of cropping in response to proximity of fish. One might have hypothesized that under high risk of cropping, Macoma would switch to suspension feeding and away from deposit feeding, the feeding method entailing more risk of losses to croppers because of greater siphon activity and greater extension of siphons on the sediment surface. Consequently, partial predation by siphon-cropping fishes greatly reduces deposit-feeding activity by Macoma balthica during summer as an apparent direct effect of disfigurement and reduction of siphons, the organ required for efficient deposit feeding. Information on current flows alone would not suffice to predict feeding behavior of this marine invertebrate: the influence of partial predation must also be included.     

Influence of food‐web structure on the biodegradability of lake sediment

1. Sediment plays a key role in internal nutrient cycling and eutrophication in lakes. However, studies focusing on the efficiency of the biomanipulation techniques for improving the control of primary producers have rarely examined the effects of changes in food‐web structure on the sediment biochemical composition and biodegradability. 2. In a 1‐year experiment conducted in large replicated mesocosms, we tested how the absence or presence of a zooplanktivorous fish (roach, Rutilus rutilus) affected the elemental composition and the potential biodegradability of recently deposited sediment in a eutrophic system. The potential biodegradability of these sediments was assessed in laboratory microcosms by measuring the production of CO₂ during 44‐day incubations. 3. The potential biodegradability of recently deposited sediment from the fish treatment was 60% higher than that from the fishless treatment. This higher biodegradability was corroborated by a higher annual loss of sediment in fish enclosures (36%) than in fishless ones (16%). Annual losses of carbon, nitrogen and organic phosphorous were higher for sediment from fish enclosures. 4. Carbon and nitrogen contents of sediment were higher for the fish treatment. In contrast, the sediment C/N ratio, one of the proxies used to estimate sediment biodegradability, did not differ between treatments. No relationship was observed between elemental composition of sediment and its potential biodegradability. This latter appeared to be more probably dependent on the biochemical composition of the sediment and especially on the content of labile compounds such as proteins, sugars and polyunsaturated fatty acids. The use of sterols as biomarkers revealed an important degradation by microorganisms of 1‐year‐old sediment from both fish and fishless treatments. 5. Our results revealed that fish biomanipulations might favour clear water states not only through a stronger top–down control on phytoplankton but also through a lower biodegradability of sediment reducing internal nutrient cycling.     

Depuration kinetics of hexachlorobenzene in the clam, Macoma nasuta

1. The depuration rate constant for [14C]hexachlorobenzene (HCB) in the clam, Macoma nasuta, was determined following a short-term exposure to HCB contaminated seawater. 2. Depuration was not correlated with ventilation volume, nor did the amount of sediment ingested during depuration have a significant effect. 3. The half-life for HCB in M. nasuta was estimated to be 16 days with a bioconcentration factor of 3490 (wet weight basis).     

Effects of two prototypic polychlorinated biphenyls (PCBs) on lipid composition of rat liver and serum

Mature male Sprague-Dawley rats received a single IP injection of either 2,2',4,4',5,5'-hexachlorobiphenyl (HCB), 3,3',4,4'-tetrachlorobiphenyl (TCB) (300 microm/kg) in corn oil (10 ml/kg) or the corn oil vehicle alone, and were killed four days later after having been fasted overnight. The vehicle control group consisted of rats which were allowed free access to feed as well as pair-fed animals. Lipid analyses were conducted on liver, hepatic microsomes and serum. TCB- (but no HCB-) treatment resulted in a statistically significant increase in total liver lipids and triglycerides. Liver phospholipids remained unchanged. Both PCBs increased the cholesterol and phospholipids content of the liver microsomal fraction. Serum lipids measured were not statistically different from control values. While HCB had little effect on the fatty acid composition of liver lipids, TCB caused an increase in C 18:1 (n-9) and a decrease in C 20:4 (n-6). Both PCBs increased C 18:0 in the hepatic microsomal fraction, but TCB also decreased C 16:0. Neither PCB altered the fatty acid composition of serum total lipids. These data are consistent with the concept that specific alterations in lipid metabolism are dependent on the structure of the PCB.     

Pathways of Increased Water Clarity After Fish Removal from Ventura Marsh; a Shallow, Eutrophic Wetland

We investigated the pathways by which water clarity increases following fish removal by evaluating the effects of a benthivorous fish reduction in a large, shallow, eutrophic, wetland in a predominately agricultural watershed in Iowa, U.S.A. Phytoplankton was phosphorus limited prior to manipulation. After a substantial fish removal was obtained, water clarity increased as a result of decreased suspended sediment and phytoplankton biomass. Trophic cascading, mitigated by release from fish predation and decreased physical interference from suspended sediments, appears to determine water clarity. Inorganic suspended solids declined immediately after fish were removed but the biomass of Daphnia and Ceriodaphnia did not increase until a few weeks after fish removal. High grazing by zooplankton likely reduced phytoplankton biomass during the height of the clear-water phase. Phytoplankton appeared to be limited by zooplankton grazing for approximately two months before reverting to bottom-up control. An increase in suspended sediment and/or increased predation pressure on zooplankton, due to the return of juvenile carp, appears to account for the decline of larger-bodied zooplankters and the switch back to bottom-up control. Macrophyte diversity and density increased substantially after the initiation of the clear-water phase.     

Tubifex tubifex as a link in food chain transfer of hexachlorobenzene from contaminated sediment to fish

Sediments contaminated with poorly water-soluble organic chemicals pose a risk to aquatic food chains. Sediment-associated chemicals can be accumulated by endobenthic, sediment-ingesting invertebrates. Some tubificid species – or other benthic annelids – serve as food for benthivorous fish, which thereby ingest the sediment-borne chemicals and may accumulate contaminant concentrations far higher than from water exposure only, and transfer them to organisms of higher trophic levels. For measurement of biomagnification, a sediment based food chain was developed and established in the laboratory. The two-step food chain included the sediment-dwelling freshwater oligochaete Tubifex tubifex (Müller) as a representative species of benthic infauna. The three-spined stickleback (Gasterosteus aculeatus, Linné), a small teleost fish which often feeds primarily on benthic invertebrates, served as a model predator. Spiked artificial sediment and reconstituted water as the overlying medium were used. Experiments were performed using ¹⁴C-labelled hexachlorobenzene, a hydrophobic pollutant as a model compound. To examine the influence of benthic prey on the bioaccumulation of the test substance in the predator, fish were exposed to spiked water, spiked sediment, pre-contaminated prey organisms, or combinations of these exposure routes. The results of these experiments indicate that for hexachlorobenzene, the presence of contaminated Tubifex tubifex as a food source in combined exposure leads to significantly higher accumulation in fish than exposure to single pathways.     

Ecosystem-level effects of bioturbation by the tadpole shrimp <Emphasis Type="Italic">Lepidurus packardi</Emphasis> in temporary pond mesocosms

An example of ecosystem engineering gaining attention in aquatic systems is bioturbation, the disruption of sediment at the water–sediment interface due to burrowing and foraging. One consequence of bioturbation can be increased turbidity from suspended sediment, which generally inhibits macrophyte growth and reduces ecosystem functioning. Conversely, bioturbation may promote invertebrate species richness by unearthing dormant cysts. Temporary-pond crustaceans are not widely regarded as agents of bioturbation, but on the basis of aquaria observations we hypothesized that certain taxa can disturb the sediment and create highly turbid water. We tested this hypothesis by removing crustaceans from mesocosms lined with vernal pool soil. Compared to this treatment group, mesocosms containing crustaceans had extremely high turbidity from suspended sediment, as well as reduced total macrophyte cover. We also found clear compositional differences in macrophyte communities between treatments, driven largely by differences in water physicochemistry, including turbidity. Regression analysis linked most of the bioturbation to the endangered notostracan Lepidurus packardi Simon 1886, which was a strong predictor of turbidity in our mesocosms. We also found a trend toward increased crustacean species richness in our mesocosms in the presence of this taxon. An analysis of published data from King et al. (1996) suggests that this trend may extend to natural vernal pools. Overall, our results suggest that L. packardi may have large effects on vernal pool communities, likely mediated in part through its disturbing of the sediment.     

The effects of hexachlorobenzene on circulating levels of adrenal steroids in the ovariectomized rat

Hexachlorobenzene (HCB), is a global pollutant that resists degradation and possesses a propensity to bioaccumulate. However, the effect of HCB on adrenal function remains largely unknown. Thus, circulating levels of adrenal steroids in HCB-exposed (0.0, 1.0, 10.0, or 100.0 mg/kg/day—for 30 days by gavage) adult ovariectomized Sprague–Dawley rats (N = 32) were investigated. A terminal blood sample was collected for HCB residue analysis, and levels of circulating progesterone (P₄), corticosterone (CS), and aldosterone (ALD) were quantified. Mean serum CS levels were significantly (P = 0.02) reduced by HCB exposure, starting with the lowest dose group (1.0 mg/kg/day for 30 days), whereas no differences in mean serum P₄ and ALD levels were observed. Since it has been argued that the rodent possesses the ability to produce small amounts of cortisol and that levels of this glucocorticoid are altered in pathological states, serum cortisol (C) levels were also measured. Circulating levels of C were significantly lower (P < 0.05) in the highest dose group compared with controls. The presence of C in serum was confirmed by reverse-phase HPLC. These data suggest that even at the lowest dose studied, HCB exposure induces alterations in steroidogenesis of cells of the adrenal cortex inner zone.     

Involvement of Cd Bioaccumulation in Spinal Deformities Occurrence in Natural Populations of Mediterranean Killifish

The aim of this study was to investigate the possible influence of environmental exposure to cadmium (Cd) on the spinal deformities occurrence in the Mediterranean killifish, Aphanius fasciatus (Pisces: Cyprinodontidae). For this purpose, some indicators of skeletal bone mineralization, Cd, and calcium (Ca) concentrations in spinal column as well as bioaccumulation of Cd from the water and the sediment have been compared in normal and deformed fish collected from polluted (S1) and nonpolluted (S2) areas in the Gulf of Gabès in Tunisia. When compared to the normal fish, the deformed fish showed signs of spinal column demineralization such as significant decrease in the ash weight/dry weight ratio, percentage of nonorganic components content, and Ca concentration. Cd concentrations in spinal column and liver were significantly higher in deformed fish than in normal fish. A highly significant negative correlation (r = −0.915, p < 0.01) between Cd and Ca concentrations was noted in spinal column of deformed fish. Bioaccumulation factors of Cd in the liver from the water and the sediment in deformed fish were also significantly higher (p < 0.0001) than in normal fish from S1 and S2. These findings suggest that the ability to accumulate large amount of Cd may represent a potential risk to induce spinal deformities in natural populations of Mediterranean killifish.     

The influence of Corophium volutator abundance on resuspension

Two experiments were performed to test the hypothesis that Corophium volutator affects the turbidity of water in estuaries through active resuspension of sediment. One experiment was done in a flume system under different flow velocities, and one in aquaria. A diatom film developed at the sediment surface in both experiments before Corophium was added. This diatom film was supposed to have a stabilising effect on the sediment. In both experiments, the concentration of suspended solids in the water column increased with the density of Corophium individuals. No effect of flow velocity on suspended solids concentration was found. This indicates that, in our flume experiment, active resuspension by Corophium was more important than physical resuspension, at least at low flow velocity (<20 cm s^-1) and in the presence of a diatom film. The critical erosion threshold decreased with increasing Corophium density in the aquarium experiment, indicating that indirect effects of Corophium grazing may become more important at high levels of bottom shear stress. The implications of our findings for suspended solids concentration in estuarine systems are discussed.