To test the response of the freshwater bivalve Pyganodon grandis (formerly Anodonta grandis) to increased metal exposure in the field, we transferred specimens (8 cm length; 4–6 years old) from a less to a more contaminated lake in the mining area of Rouyn-Noranda, in northwestern Québec. The transplanted bivalves were maintained in open enclosures placed in the bottom sediments of the contaminated lake. Up to 16 individuals were removed from pairs of enclosures at times t = 0 (June 1990), 5, 14, 30, 60, 90, and 400 d; tissue concentrations of metallothionein (MT) and metals were monitored over time. Measurements on control molluscs enclosed in their lake of origin showed that enclosure per se had no apparent effect on tissue [MT] or tissue metal levels, but did decrease shell growth. Metallothionein levels in specimens transplanted to the more contaminated lake showed a slow but steady increase with time; in contrast, MT levels in the control populations showed only modest seasonal fluctuations. The increase in MT over time in the transplanted bivalves was closely correlated with a similar slow increase in soft tissue [Cd]. We conclude that MT in the freshwater bivalve P. grandis is a promising biochemical indicator of metal exposure.

To examine links between the metallothionein (MT) status of an organism and its general health, we transplanted adult specimens of the freshwater bivalve Pyganodon grandis (formerly Anodonta grandis) from a less to a more contaminated lake in the mining area of Rouyn-Noranda, in northwestern Québec. The transplanted bivalves were maintained in open enclosures placed in the bottom sediments of the contaminated lake; in addition, indigenous specimens were maintained in control enclosures in their lake of origin. Up to 16 individuals were removed from pairs of enclosures at times t = 0 (June 1990), 5, 14, 30, 60, 90, and 400 d. Excised gill tissue was analyzed for metallothionein, Cd, Cu, Zn, Ca, and malondialdehyde (MDA), a product of lipid peroxidation. Metal partitioning in the gill cytosol, as determined on a subset of gill samples from transplanted molluscs, changed markedly during the experiment. After 400 d, Cd was present in the low molecular weight fraction of the gill cytosol, and symptoms of cellular toxicity were detected in the transplanted molluscs (elevated [MDA] and [Ca]). At the whole organism level, the marked transplanted bivalves grew more slowly over the 400-d experiment than did marked control bivalves in Lake Opasatica, and their condition index deteriorated over time.

Deleterious effects of environmental contaminants could be due to enhanced prooxidant forces overcoming antioxidant defences. Before practical biomarkers based on free radical biology will be generally accepted and validated in situ, additional research is required concerning normal physiological and environmental influences on the relevant systems. The aims of this study were to evaluate in situ the importance of oxyradical production in the presence and absence of pollutants and to characterize some antioxidant systems in Mytilus edulis L. Specimens of M. edulis L. were transplanted from a reference site (Franquelin) to Bale Comeau (Bale des Anglais), on the North shore of the St. Lawrence maritime estuary, where are found aluminium and pulp and paper plants. An oxidative stress was observed in mussels submitted to a chronic exposure in the polluted environment. Variations of proand anti-oxidant molecules involved in oxidative processes were related in part to seasonal and physico-chemical influences. Catalase activity, malondialdehyde and glutathione concentrations will be useful as biomarkers of stress in situ since they react to anthropogenic influence and to abiotic factors such as emersion period and temperature.

In an attempt to improve our understanding of the transfer process of organic mercury (mainly methyl mercury) from the prey to the consumer, the uptake of mercury in edible muscle of shrimps, Panda/us borealis, from contaminated mussels used as food supplies was studied. Shrimps bioaccurnulated rapidly mercury in their abdominal muscle when submitted to a highly contaminated diet (6 11g Hg g-1 ) but biomagnification was not observed and Hg concentration in shrimps never exceeded 1.81J.g g-1 . The assimilation efficiency during the uptake period was estimated to about 42%.When shrimps received moderately contaminated diet (2.5-2.91J.Q Hg g-, a two-stage bioaccumulation process was observed in which mercury concentration began to increase in shrimp muscle after 15 days of contaminated diet and at the end of the experiment it seemed to level off. This process can be represented by a two-compartment conceptual model in which mercury is first eliminated and/or accumulated in the compartment 1 (digestive organs) and then transferred to the compartment 2 (abdominal muscle) following a mechanism and under conditions not yet clearly understood. The use of selenium biologically incorporated into the diet had no apparent effect on the uptake of mercury.

Blood prolactin (PRL) variations have been linked to temperature and osmotic changes in several species. The latter factors are here explored to better understand blood PRL responses frequently induced during physical exercise. Since body heat generated by exercise can lead to marked body fluid shifts, it was postulated that PRL changes observed during exercise could be associated with variations in body temperature and/or blood osmolality (OSM). A wide range (38.5–40.5°C) of rectal temperatures (Tr; used here to appreciate core temperatures) were theoretically selected and randomly assigned as targets to male runners. Measured by thermistor probe, target Tr were obtained by a combination of factors: (a) ↑ heat production by treadmill running, and (b) ⇓ heat losses by appropriate clothing (⇓ evaporation) in warmed (⇓ radiation) and hypo ventilated (⇓ convection) laboratory conditions. For each subject, target Tr was attained not prior to 30 min after initiation of running, and had to be maintained for at least 10 min, for a mean ( ± SD) running time of 52.6 ± 10.0 min. In a first protocol, hypohydration was provoked in 26 runners (23.9 ± 4.7 years) by total restriction of water intake. In a second protocol (10 different runners: 22.3 ± 3.3 years), euhydration was maintained by water intake (20 ml/kg body weight). Venous blood was sampled at rest before and immediately after the run. PRL was assayed by RIA; OSM was measured by freezing point depression; sodium was analyzed by flame photometry. At rest, before the heat-producing exercise, mean PRL values were 9.4 ± 3.4 ng/ml for both eu/hypohydrated groups. In the hypohydrated runners, exercise-induced hyperthermia was significantly (r = 0.82; p < 0.0005) associated with blood PRL responses. Moreover, these changes in Tr were also significantly (r = 0.54; p < 0.0025) related to changes in OSM, the latter variations being mostly explained (78 %) by the accompanying hypernatremia. In the euhydrated group of runners, the hyperthermic exercise failed to induce significant changes in OSM (r = 0.22; p > 0.15) and, as expected, variations in blood sodium levels were also not significant under these conditions. However, hyperthermic running in these iso-osmolar conditions did not prevent blood PRL levels from rising (r = 0.77; p < 0.0005). It was thus concluded that, in male trained runners, exercise-induced blood PRL responses could be derived more from thermic than from osmolar stresses.