Aurélie Ciutat

Effects of bioturbation on cadmium transfer and distribution into freshwater sediments.

To investigate bioturbation effects on cadmium (Cd) fluxes from overlying water to sediments, indoor microcosms were developed. The bioturbating organisms were freshwater tubificid worms. Three experimental conditions were studied during 56 d. The three conditions were contaminated water column ([Cd]: 20 microg/L) with or without worms and uncontaminated water column with worms. Cadmium vertical profiles were determined in the pore water and in the sediments, based on six layers (0-0.5, 0.51, 1-2, 2-3, 3-5, 5-12 cm). Dissolved oxygen, manganese, sulfate, and particulate manganese were measured. Bioturbation was analyzed using conservative fluorescent particulate tracers. Bioturbation increased Cd flux into the sediments by close to a factor of two. Scavenging of Cd was more efficient in the bioturbated sediments because particles and adsorption sites for Cd were renewed at the sediment-water interface. Tubificids also increased the thickness of the Cd-enriched layer. Metals adsorbed on particles at the sediment surface were distributed by bioadvection, which predominated the mixing processes. Bioturbation also modified the vertical profiles of dissolved and particulate manganese and dissolved sulfate but not the profiles of dissolved oxygen. These results indicate that the advective transport of particles by bioturbation and their subsequent modification by redox reactions accelerates the trapping of metals in sediments.

Impact of gold nanoparticles on zebrafish exposed to a spiked sediment.

Abstract Increasing use of metallic nanomaterials is likely to result in release of these particles into aquatic environments; nevertheless it is unclear whether these materials present a hazard to aquatic organisms. The impact of contaminated sediment containing 14-nm gold nanoparticles (AuNPs) was investigated in the zebrafish Danio rerio exposed for 20 days to two concentrations, 16 and 55 µg/g dry weight. AuNPs were released from the sediment to the water column, and during this period the mean concentrations of AuNP in the filtered water fraction were 0.25 ± 0.05 and 0.8 ± 0.1 µg/L, respectively. A similar experiment with ionic gold contamination was simultaneously performed to obtain a positive control. AuNP exposure triggered various effects in fish tissues including modifications of genome composition, shown using a random amplified polymorphic DNA-PCR genotoxicity test. Expression of genes involved in oxidative stress, mitochondrial metabolism, detoxification and DNA repair were also modulated in response to AuNP contamination. Gold altered neurotransmission, since brain acetylcholine esterase activity increased for both tested doses of AuNP but not for ionic gold. Gold accumulation in fish tissues demonstrated the lower bioavailability of AuNP compared to ionic Au, and underlined the higher toxic potential of the nanoparticle form.

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

Abstract 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.

Do trace metal contamination and parasitism influence the activities of the bioturbating mud shrimp Upogebia cf. pusilla

Mud shrimp are considered as among the most influential ecosystem engineers in marine soft bottom environments because of their significant bioturbation activity and their high density. These organisms play a key role on the physical structure of sediments through intense sediment reworking activity and also deeply influence geochemical properties of sediments via frequent bioirrigation events. The influence that mud shrimp have on the environment is related to the magnitude of bioturbation processes and subsequently depends on their physiological condition. In natural environments, several factors act together and influence the well-being of organisms. Among them, the deleterious role of parasites on the physiology and the behavior of their host is well established. Aquatic organisms are also subject to pollutants released by anthropogenic activities. However, the effect of both stressors on the fitness and bioturbation activity of mud shrimp has never been investigated yet. We conducted a 14-day ex-situ experiment to evaluate the influence of trace metal contamination (cadmium Cd) and parasitism infestation on the gene expression (molecular endpoint) and sediment reworking activity (behavioral endpoint) of the mud shrimp Upogebia cf. pusilla. At completion, mud shrimp exhibited substantial Cd bioaccumulation, with parasitized organisms showing a significantly lower contaminant burden than unparasitized specimens. Cadmium contamination induces modifications of gene expression in both unparasitized and parasitized organisms. We report an antagonistic effect of both stressors on gene expression, which cannot be fully explained by a lower Cd bioaccumulation. At the behaviour level, parasitism seems to reduce the sediment reworking activity of mud shrimp, while Cd contamination appears to stimulate this activity. This study highlights that the effects of multiple stressors may be quite different from the effects of each stressor considered individually. It should also motivate for more studies evaluating the influence of multiple stressors on different endpoints encompassing various levels of organization.