Experimental evidence for ²³⁴Th bioaccumulation in three Antarctic crustaceans: Potential implications for particle flux studies

234Th is considered a valuable and useful tracer of oceanic biogeochemical processes occurring over timescales of days to weeks. While the geochemical behaviour of this radionuclide in the marine environment is well known, relatively few studies have explored its interactions with biota. To better understand biologically related 234Th dynamics, bioaccumulation of 234Th from the dissolved phase and its subsequent retention in small Antarctic crustaceans (the isopod Natatolana oculata and the amphipods Orchomenella ultima and Uristes stebbingi) was determined under controlled laboratory conditions. Despite morphological and behavioural differences, all three species displayed comparable concentration factors (CF >= 80) and very long retention of 234Th (biological half-life not significantly different from infinity). From 16% (isopod) to 49% (both amphipods) of accumulated 234Th was associated with the animal soft parts, which is substantial when compared with reported values for other particle-reactive transuranic elements. The relevance of zooplankton as a potential modulator of 234Th distribution in the water column is discussed in light of these findings. CF-based computations suggest that, for typical zooplankton biomass, biologically mediated interactions with particle flux models can be neglected. In contrast, in waters with very high crustacean biomass, such as krill schools, 234Th distribution in the water column would be largely determined by these organisms. In such waters the biological compartment should be addressed as it could confound the reliability of vertical particle flux assessment using 234Th as a proxy

Sorption-desorption kinetics and toxic cell concentration in marine phytoplankton microalgae exposed to Linear Alkylbenzene Sulfonate

Linear Alkylbenzene Sulfonates (LAS) are ubiquitous surfactants. Traces can be found in coastal environments. Sorption and toxicity of C12-LAS congeners were studied in controlled conditions (2-3500 µg C12LAs/L) in five marine phytoplanktonic species, using standardized methods. IC50 values ranged from 0.5 to 2 mg LAS/L. Sorption of 14C12-6 LAS isomer was measured at environmentally relevant trace levels (4 µg/L) using liquid scintillation counting. Steady-state sorption on algae was reached within 5 h in the order dinoflagellate > diatoms > green algae. The sorption data, fitted a L-type Freundlich isotherm, indicating saturation. Desorption was rapid but a low LAS fraction was still sorbed after 24 h. Toxic cell concentration was 0.38 +/- 0.09 mg/g for the studied species. LAS toxicity results from sorption on biological membranes leading to non-specific disturbance of algal growth. Results indicate that LAS concentrations in coastal environments do not represent a risk for these organisms

Effects of PCBs on reactive oxygen species (ROS) production by the immune cells of <i>Paracentrotus lividus</i> (Echinodermata)

The impact of four PCB congeners: 3,3',4,4'-tetrachlorobiphenyl (IUPAC congener #77), 3,3',4,4',5-pentachlorobiphenyl (IUPAC #126), 2,2',4,4',5,5'-hexachlorobiphenyl (IUPAC #153) and 3,3',4,4',5,5'-hexachlorobiphenyl (IUPAC #169) was investigated on the reactive oxygen species (ROS) production by coelomocytes of the echinoid Paracentrotus lividus, an important species in marine benthic ecosystems. PCBs were found to increase ROS production and to delay the time of peak production. These effects were stronger on bacteria-stimulated cells and were congener-specific: coplanar congeners (#77, 126 and 169) had more effect than the non-coplanar PCB #153. Among coplanar congeners, PCB #169 showed dose-dependent effects whereas PCB #77 and 126 were more toxic at high and low doses, respectively. The relative immunotoxicity of the different PCB congeners is discussed in the light of their structural properties and biological affinities

Biokinetics of zinc and cadmium accumulation and depuration at different stages in the life cycle of the cuttlefish <i>Sepia officinalis</i>

Bioaccumulation of 65Zn and 109Cd by the cuttlefish Sepia officinalis L. was studied at different stages of its life cycle, i.e. in embryos, juveniles and adults, following exposures via sea water, sediments and food. Cuttlefish eggs efficiently accumulated both elements from seawater with bioconcentration factors of 79 for 65Zn and 46 for 109Cd after 11 d exposure. Most of the radiotracers were found in the capsule membrane of the eggs, demonstrating that the capsule acts as a shield to protect embryos against metals. Juveniles and adults efficiently bioconcentrated both radiotracers from seawater, with the muscular tissues containing 84% of the total 65Zn and 62% of the total 109Cd. Loss kinetics followed a single exponential function for 65Zn, while for 109Cd loss was best described by a double exponential model. Biological half-lives for elimination were ca. 2 mo for both elements. After 29 d depuration in uncontaminated seawater, 76 to 87% of the radiotracers were found in the digestive gland. For both elements, the dissolved phase can be considered as a significant source of accumulation. In an experiment with radiolabelled sediments, transfer factors were very low, even after 29 d exposure. Food-chain transfer experiments demonstrated that both juveniles and adults assimilated 65Zn and 109Cd very efficiently. Moreover, loss of ingested radiotracers was much slower than elimination of 65Zn and 109Cd taken up from seawater, indicating a very strong retention of dietary Cd and Zn by juvenile as well as by adult cuttlefish. As with direct uptake from seawater, ingested radiotracers were mainly found in the digestive gland, with fractions reaching 82% for 65Zn and 97% for 109Cd after 29 d depuration. These tracer experiments indicate that (1) food is the likely primary pathway for Zn and Cd bioaccumulation in S. officinalis, and (2) the digestive gland plays a major role in the subsequent storage and presumed detoxification of these elements regardless of the uptake pathway