The brown seaweed Sargassum cymosum: changes in metabolism and cellular organization after long-term exposure to cadmium.

Sargassum cymosum was exposed to cadmium (Cd) to determine any physiological and ultrastructural effects. To accomplish this, S. cymosum samples were cultivated under photosynthetic active radiation (PAR) and Cd (0, 0.1, 0.2, 0.4 and 0.8 mg L-1) during 7 and 14 days in laboratory-controlled conditions (0 mg L-1 Cd at both exposure times as control). Seaweeds had high retention capacity (over 90 %) for both exposure times. Growth rates showed significant increases by 14 days, especially for 0.1 and 0.4 mg L-1 Cd. Photosynthetic parameters were unaffected by Cd treatments. Chlorophyll contents were present in higher concentrations for all Cd treatments compared to respective control. Carotenoid profile showed significant differences in total composition and proportion of fucoxanthin and ß-carotene, and no lutein was detected at 14 days. Phenolic and flavonoid compounds showed major accumulation at 14 days. Transmission electron microscopy (TEM) analyses presented major alterations in Cd-treated samples, when compared with respective control, in particular disorganization of cell wall fibrils. When compared to respective control samples, multivariate analyses showed disparate and complex interactions among metabolites in Cd-exposed seaweeds, giving evidence of physiological defence response. Thus, it can be concluded that Cd is a stressor for S. cymosum, resulting in physiological and structural alterations related to defence mechanisms against oxidative stress and toxicological effects resulting from long-term metal exposure. However, in the present paper, some observed changes also appear to result from acclimation mechanisms under lower concentration of Cd relative to the tolerance of S. cymosum to experimental conditions.

Influence of the drying conditions of Sargassum sp. alga on the bioadsorption of hexavalent chromium.

Industrial wastes containing synthetic organic compounds and heavy metals are among the most dangerous residues, whose growth has followed the increase in industrial activity. Heavy metals are readily assimilated into the food chain and therefore easily accumulated in the ecosystem. To remove heavy metals from aqueous solutions, marine algae may be used as adsorbents either in their natural form or after treatments by a cross-linking process to improve their mechanical resistance. Drying of biosorbents, such as marine algae, is mentioned in many previous works as a step preceding the adsorption/dessorption cycle. Concerning algae, drying of its fresh biomass allows for proper storage and enhances performance in the sorption of heavy metals. In this work, physical and morphological analyses of fresh and dried Sargassum sp. marine algae, harvested offshore São Sebastião, São Paulo state, Brazil, were performed in order to assess the influence of drying conditions on the biosorption process. Chromium concentrations were also determined in different parts of the algal structure before and after the biosorption process. The drying promoted structural changes in the algae, like shrinkage and porosity reduction. It was also observed that the chromium retention was dependent on the structural arrangement of the alga parts, in which the leaf was the major biosorbent.