Growth and metal uptake of microalgae produced using salt groundwaters from the Bay of Bourgneuf

International audienceThe Bay of Bourgneuf, France, is a main site of shellfish production. In the marshes along the bay, oyster intensive rearing and fattening need the mass production of microalgae. Salt groundwaters, available in this region, support a large part of this production for aquaculture. Studies carried out by local authorities have brought to the fore the accumulation of lead (Pb) in several samples of algal pastes derived from cultures using salt groundwater. The aim of this study was to compare growth, nutritional value and metal (Cd, Cu, Pb and Zn) uptake of four microalgae grown in two salt groundwaters or in enriched coastal seawater. Cultures of microalgae used in aquaculture (Haslea ostrearia, Phaeodactylum tricornutum, Skeletonema costatum and Tetraselmis suecica) were realised at the laboratory under controlled experimental conditions. Results indicated that salt groundwaters provided cultures with, at least, an equal biomass and a nutritional value similar to cultures grown in enriched seawater. There was no difference regarding metal accumulation whatever the culture medium, except when S. costatum was grown in one of the salt groundwater in which case its cadmium levels were higher and could be above the French guideline level. These observations questioned on the bioavailability of metals in salt groundwaters. It also underlines the specificity of metal uptake and accumulation by microalgae

Les métaux (Cd, Cu, Pb et Zn) dans la production des microalgues sur différents milieux de culture (biodisponibilité, bioaccumulation et impact physiologique)

La qualité et la production d une culture de microalgues sont dépendantes de différents facteurs physico-chimiques: salinité, pH, concentration en nutriments majeurs et en oligo-éléments dont les métaux traces dans le milieu de culture. Dans ce travail de doctorat, la biodisponibilité de quatre métaux pour des microalgues est étudiée dans les eaux marine côtière et souterraine salée. La biodisponibilité d un métal est dépendante de sa concentration totale et de celle des ligands présents dans le milieu ainsi que de l affinité respective de ces ligands pour le métal. Suite à l étude comparative de la qualité des algues produites, les capacités de complexation des eaux souterraines salées et l eau de mer côtière ont été étudiées afin de mieux comprendre les variations de bioaccumulation des métaux par les microalgues. Une approche expérimentale sur le milieu artificiel DAM élaboré dans ce travail a permis de formuler des hypothèses sur les variations interspécifiques de la bioaccumulation des métaux.The quality and the productivity of microalgal cultures depend on different physico-chemical factors like salinity, pH, nutrient and trace element (including trace metals) concentration in the culture medium. During this doctoral study, the bioavailability of four metals for microalgae was tested in coastal seawater and several salt groundwaters. The bioavailability of a metal depends on its own total concentration as well as that of ligands in the medium, and on the relative affinity of each ligand towards the given metal. After a comparative study of the quality of algae grown in coastal seawater and salt groundwaters, the complexation capacities of these media were studied to allow a better understanding of the observed variations of metal bioaccumualtion in the produced microalgae. An experimental study with a new artificial medium (DAM) developed during our work allowed to put forward some hypotheses regarding the interspecific variations of metal bioaccumulation.NANTES-BU Sciences (441092104) / SudocSudocFranceF

STUDIES OF INTERACTION BETWEEN DISSOLVED METALS AND THEIR SPECIATION AND PHYTOPLANKTON IN A CONTINUOUS FLOW PHOTOBIOREACTOR

particiapantHalf of the world primary productivity is due to marine phytoplankton. Factors that affect the physiology of these organisms are therefore very important to understand plankton dynamics in the global ocean coastal and pelagic settings. Depending on local conditions, metallic micronutrients can be limiting (e.g., Fe in HNLC areas) and affect plankton population structure. While iron is a pivotal micronutrient that impacts global primary productivity, interactions of other metals with phytoplankton have also gained attention. Among these interactions are the potential effects of increased trace metals on plankton dynamics and vice versa. In order to examine the impact of other trace metals upon selected phytoplankton species, we furthered the development of an already existing continuous flow photobioreactor to make it compatible with trace-metal-clean conditions and neutral with respect reduced sulfur gases which were examined. The effect on reduced sulfur dynamics has global relevance because a fraction of this pool (dimethylsulfide) is gaseous and after fluxing into the atmosphere, it is active in Earth's solar radiation balance. Experimenting with mono-specific continuous cultures, we examined the effects of environmentally relevant, dissolved Ag and Cd concentration and speciation on the growth of Isochrysis isogalbana and Phaeodactylum tricornutum. Results acquired so far suggest that while increased Ag and Cd levels have little effect on the growth of these phytoplankton species, they have one reduced sulfur release. Effects of pCO2 on culture growth and metal speciation were also investigated. Preliminary results of the photobioreactor and this suite of experiments will be presented