Bioaccumulation of PCBs in the sea urchin Paracentrotus lividus: seawater and food exposures to a 14C-radiolabelled congener (PCB#153)

Adult Paracentrotus lividus were exposed to a 14C-labelled PCB congener (PCB#153) using two different exposure modes: (1) the surrounding sea water and (2) the food (viz. the phanerogam Posidonia oceanica and the brown alga Taonia atomaria). Uptake kinetics from water and loss kinetics after single feeding were followed in four body compartments of the sea urchins (body wall, spines, gut and gonads). Results indicate that PCB bioaccumulation in P. lividus varies from one body compartment to another, with the exposure mode and the nature of the food. The echinoids accumulate PCB#153 more efficiently when exposed via water than via the food (the transfer efficiency is higher by one order of magnitude). Target body compartments of PCB#153 were found to be body wall and spines when individuals were exposed via water, and gut when they were exposed via food. It is concluded that P. lividus is an efficient bioaccumulator of PCB and that it could be considered as an interesting indicator for monitoring PCB contamination in the marine environment.

Bioaccumulation of PCBs in the cuttlefish Sepia officinalis from seawater, sediment and food pathways

The cuttlefish Sepia officinalis was selected as a model cephalopod to study PCB bioaccumulation via seawater, sediments and food. Newly hatched, juvenile cuttlefish were exposed for 17 days to environmentally realistic concentrations of (14)C-labeled 2,2',4,4',5,5'-hexachlorobiphenyl (PCB#153) (18 ng PCB l(-1) seawater; 30 ng PCB g(-1) dry wt sediments; Artemia salina exposed to 18 ng PCB l(-1) seawater). Accumulation of PCB#153 was followed in three body compartments: digestive gland, cuttlebone and the combined remaining tissues. Results showed that (1) uptake kinetics were source- and body compartment-dependent, (2) for each body compartment, the accumulation was far greater when S. officinalis was exposed via seawater, (3) the cuttlebone accumulated little of the contaminant regardless of the source, and (4) the PCB congener showed a similar distribution pattern among the different body compartments following exposure to contaminated seawater, sediment or food with the lowest concentrations in the cuttlebone and the highest in the remaining tissues. The use of radiotracer techniques allowed delineating PCB kinetics in small whole organisms as well as in their separate tissues. The results underscore the enhanced ability of cephalopods to concentrate organic pollutants such as PCBs, and raise the question of potential risk to their predators in contaminated areas.

Relative importance of dissolved and food pathways for lead contamination in shrimp

The relative importance of dissolved and food pathways and the influence of food type in the bioaccumulation and retention of lead in the shrimp Palaemonetes varians were examined using a radiotracer method. Shrimp were exposed to 210Pb-labelled seawater or fed two types of 210Pb-labelled food, viz. mussels or worms. The amount of radiotracer accumulated by shrimp was examined over a 7-day period, followed by a 1-month and a 7-day depuration period for the dissolved and food source, respectively. Steady state in the uptake was reached after 2 days exposure to dissolved lead, with a resultant estimated concentration factor of 98+/-3. Transfer factors following ingestion of contaminated mussels and worms were lower than unity for both food types, with lead transfer from worms being significantly higher than that from mussels. Accumulation of dissolved Pb by shrimp was found to occur mainly through adsorption on the exoskeleton with a minor accumulation in the internal tissues probably resulting from the intake of seawater for osmoregulation. In contrast, lead taken up from contaminated food was readily absorbed and bound in the internal tissues of P. varians. Although the transfer of lead to P. varians through the ingestion of contaminated food was low (TF<1%), it still represented 4 to 8% of the lead content in the prey which is a significant additional contribution of lead to the shrimp body burden. Independent of food type, following ingestion of contaminated food, approximately 23-27% of total lead accumulated in shrimp was located in the edible parts (e.g. muscle). Therefore, the food pathway is suggested to be a significant contributor to the lead transfer to humans through ingestion of contaminated shrimp. After exposure to contaminated food, lead loss kinetics were described by a two-component model, whereas Pb loss following direct uptake from seawater was best described by a three-component model. The additional compartment representing 64% of total Pb retained and characterized by a turnover<10 min, corresponded to lead weakly adsorbed on the exoskeleton and incorporated in the hepatopancreas. Nevertheless, a significant fraction of lead accumulated from the dissolved (2%) and food (52-57%) pathways remained irreversibly retained in the tissues, suggesting that this organism could also serve as an effective long-term bioindicator of lead contamination in marine waters.

210Po and 210Pb cycling in a hydrothermal vent zone in the coastal Aegean sea

To quantify the potential enhancement of naturally-occurring 210Po and 210Pb that may result from the high sulfur-reducing and sulfur-oxidizing regimes associated with hydrothermal vents, sinking particles from both inside and outside vent areas and benthic molluscs grazing on or living near bacterial mats in the vent zone were collected off Milos Island (Aegean Sea) and analyzed for their 210Po and 210Pb content. There was no significant difference in the range of 210Po specific activities measured in particulate material collected by sediment traps in a control area and in the vent area; the resultant 210Po levels were of the same order of magnitude as literature values reported for other Mediterranean coastal areas. 211Pb levels in sinking particles from the control site tended to be higher than those measured in the vent zone, as demonstrated by the lower 210Po/210Pb ratios observed in particles from the control site. Nevertheless, these 210Pb levels were also comparable with similar 210Pb data reported for the northwestern Mediterranean Sea. The 210Po and 210Pb vertical particulate fluxes were, on average, higher in the vent zone as a consequence of the higher particle flux. This observation indicates that vents can indirectly control the flux of these natural radionuclides by affecting the types and amount of particles produced in hydrothermal areas. The 210Po levels measured in a gastropod and a bivalve living on or near the microbial mat in the vent zone were higher than values reported for non-vent gastropods and bivalves from the NW Mediterranean Sea, an observation which suggests that an enhanced food chain transfer of 210Po may occur in the vicinity of vents off Milos Island. Nevertheless, the lack of a general enhancement of 210Po and 210Pb in the marine particulate samples collected indicates that any input of these radionuclides through venting activity may have a minimal effect in the surrounding environment.

Bioaccumulation and retention of lead in the mussel Mytilus galloprovincialis following uptake from seawater

Bioaccumulation of lead in the mussel Mytilus galloprovincialis from 210Pb-labeled bulk seawater (dissolved and particulate pathways combined) was examined over 21 days. The lead bioaccumulation factor (BAF) at equilibrium was estimated to be 211 +/- 10 ml g-1. This value was two orders of magnitude lower than BAFs reported in the literature for other trace metals in this bivalve indicating that lead is not efficiently accumulated by mussels from bulk seawater. The resultant lead distribution in mussels was 49 +/- 10% in soft tissues and 46 +/- 16% in the shell suggesting similar uptake rates (Bq day-1) in both compartments throughout the exposure. Total elimination for lead in mussels was adequately described by a short-term compartment with a biological half-life for loss of 1.4 +/- 0.3 days and a long-term compartment which released lead only very slowly (Tb1/2 = 2.5 +/- 0.7 months). No difference was noted for lead elimination rates in shell and in soft parts. When experimentally exposed to lead under conditions representative of natural environmental lead levels in water, including both that in the dissolved phase and in the food, the shell compartment was shown to contain the major fraction of the total lead accumulated by mussels. Therefore mussels may be considered as good bioindicators of lead contamination accumulated from the dissolved rather than from the particulate source. Furthermore, the relatively slow uptake and the long depuration half-life of lead will limit the ability of mussels to accurately record short-term variations in lead concentrations in the surrounding waters, a fact which should be taken into consideration in order to define the appropriate sampling frequency for mussels used in biomonitoring programs involving lead.