The effects of polystyrene microbeads (micro-PS; mix of 2 and 6 μm; final concentration: 32 μg L(-1)) alone or in combination with fluoranthene (30 μg L(-1)) on marine mussels Mytilus spp. were investigated after 7 days of exposure and 7 days of depuration under controlled laboratory conditions. Overall, fluoranthene was mostly associated to algae Chaetoceros muelleri (partition coefficient Log Kp = 4.8) used as a food source for mussels during the experiment. When micro-PS were added in the system, a fraction of FLU transferred from the algae to the microbeads as suggested by the higher partition coefficient of micro-PS (Log Kp = 6.6), which confirmed a high affinity of fluoranthene for polystyrene microparticles. However, this did not lead to a modification of fluoranthene bioaccumulation in exposed individuals, suggesting that micro-PS had a minor role in transferring fluoranthene to mussels tissues in comparison with waterborne and foodborne exposures. After depuration, a higher fluoranthene concentration was detected in mussels exposed to micro-PS and fluoranthene, as compared to mussels exposed to fluoranthene alone. This may be related to direct effect of micro-PS on detoxification mechanisms, as suggested by a down regulation of a P-glycoprotein involved in pollutant excretion, but other factors such as an impairment of the filtration activity or presence of remaining beads in the gut cannot be excluded. Micro-PS alone led to an increase in hemocyte mortality and triggered substantial modulation of cellular oxidative balance: increase in reactive oxygen species production in hemocytes and enhancement of anti-oxidant and glutathione-related enzymes in mussel tissues. Highest histopathological damages and levels of anti-oxidant markers were observed in mussels exposed to micro-PS together with fluoranthene. Overall these results suggest that under the experimental conditions of our study micro-PS led to direct toxic effects at tissue, cellular and molecular levels, and modulated fluoranthene kinetics and toxicity in marine mussels.
This study evaluates the nutritional value of several species of freeze-dried microalgae used to feed the seed of Ruditapes decussatus. These microalgae were: Isochrysis galbana, clone T-ISO; Tetraselmis suecica; and Phaeodactylum tricornutum. The addition of antibiotics, kaolin and fresh microalgae to the freeze-dried diet was also evaluated, and a study was made of the nutritional value of one species of microalga in each of the four stages of preparation of the freeze-dried diet: culture; concentration; freezing and freeze-drying. Both physiological and biochemical criteria were used to evaluate the different diets: availability; acceptability; digestibility; and biochemical composition.The highest seed growth rate were achieved with a diet of Isochrysis, followed by Tetraselmis, whilst the growth rates achieved with a dried diet of Phaeodactylum were much lower. The differences observed between diets of Isochrysis and Tetraselmis were due to a greater ingestion of the cells of Isochrysis. The minimal nutritional value of Phaeodactylum appears to be related to the low digestibility of its cell wall. The growth rates of seed fed on a diet of dried microalgae were significantly lower than those achieved with fresh diets (Albentosa et al., 1996b) for each of the species of microalgae that were tested, and this appears to be related to the lower digestibility of the microalgae after they have been freeze-dried. The addition of antibiotic or kaolin to the freeze-dried diet did not result in a major increase of seed growth rates. The substitution of a small proportion of freeze-dried microalgae with fresh microalgae produced a significant increase in seed growth rates, although these were still lower than those obtained with a completely fresh diet. The loss of nutritional value of microalgae when they are freeze-dried may be due to some kind of process which occurs during freezedrying, altering the digestibility of the microalgae.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.