The risk of nanoparticles (NPs) to organisms and the environment has become more noticeable alongside their rapid applications in many fields. The release of Cd(2+) from CdTe-based NPs (CdTe-NPs), an important class of engineered nanomaterials, is one of the possible factors responsible for the cytotoxicity of these NPs. Based on the same CdTe core, CdTe/CdS, CdTe/ZnS and CdTe/SiO(2) NPs were synthesized and their Cd(2+) release rates were carefully studied based on dialysis using inductively coupled plasma mass spectrometry (ICPMS). Results obtained indicated that the Cd(2+) release rates of the CdTe-NPs decreased in the order CdTe (8.78 ng mL(-1) mg(-1) h(-1)) > CdTe/CdS (2.63) > CdTe/SiO(2) (0.89) > CdTe/ZnS (0.72). Phaeodactylum tricornutum was used as a model diatom for evaluating the cytotoxicity of the CdTe-NPs. Results obtained from the CdTe-NPs exposure experiments together with ICPMS and fluorescence microscopy studies suggested that the cytotoxicity of the CdTe-NPs increased along with the increase in their Cd(2+) release rates. Effective coating materials such as ZnS and SiO(2) for the CdTe core significantly reduced the cytotoxicity of CdTe.

Mercury (Hg) is a toxic heavy metal with its biogeochemical cycling in the ocean depending on the type and behavior of the oceanic microalgae. The present work aimed to evaluate bioaccumulation and transformation of Hg by Phaeodactylum tricornutum, a typical unicellular diatom, when exposed to the extremely high level of Hg in order to understand the possible mechanisms of acute stress response. P. tricornutum can accumulate Hg (its bioaccumulation factor is at 10 4 level), and the 96 h EC 50 was estimated to be 145 g L -1 . The amounts of surface-bound Hg being about 1.2 to 4.8 times higher than those of intracellular Hg under exposure to HgCl 2 (from 20 to 120 g L -1 concentrations) suggested that the cell wall of P. tricornutum is an important "fence" towards Hg. After entering the P. tricornutum cell, Hg underwent transformation in its chemical form via interactions with high molecular weight sulfur-containing proteins (accounting for 68% of the intracellular Hg), and glutathione as well as the induced phytochelatins (PCs) (24% Hg) which alleviated the toxicity of HgCl 2 . In addition, the existence of organic ligands greatly influenced the uptake and transformation behavior of P. tricornutum towards HgCl 2 , especially in the case of cysteine (Cys), which increased the uptake of Hg, but alleviated the toxicity of Hg towards P. tricornutum due to the fact that Cys is an important precursor for the synthesis of PCs inside the cell. The uptake process of Hg by P. tricornutum was in agreement with the Freundlich isotherm, suggesting a typical heterogeneous sorption process. More importantly, we observed the conversion of HgCl 2 into methylmercury inside the P. tricornutum cells and its release into the culture solution using HPLC/CVG-AFS and GC-MS, although the mechanism needs to be further investigated. mercury, methylmercury, P. tricornutum, species transformation, toxicity, phytochelatin Citation:Deng G F, Zhang T W, Yang L M, et al. Studies of biouptake and transformation of mercury by a typical unicellular diatom Phaeodactylum tricornutum. Chin Sci Bull, 2013Bull, , 58: 256265, doi: 10.1007 Microorganisms are able to accumulate heavy metals via both ways of surface-bound sorption and intracellular involvement [1]. The cell walls of microorganisms contain many different functional groups such as amine, carboxyl, hydroxyl, sulfates and phosphates, which interact with heavy metals. Microorganisms can also produce proteins and/or polypeptides such as metallothioneins and other cysteine-rich peptides which complex heavy metals and thus detoxify them in the cells [2]. On the other hand, many kinds of natural and anthropogenic ligands are always present in the aquatic environment, and heavy metals may form complexes with such existing ligands resulting in various chemical species, determining significantly the modes and amounts of the heavy metals to enter into the cells of microorganisms. In addition, some heavy metals may be transformed to methylated compounds by microorganisms [3]. All these accumulation a...