Bioaccessibility and transformation of cadmium in different tissues of Zhikong scallops (Chlamys farreri) during in vitro gastrointestinal digestion.

Scallop is well known for its high accumulation of cadmium. The bioaccessibility and speciation of cadmium in different tissues of scallops during gastrointestinal digestion could influence the evaluation of its biological effects and consumption safety in humans. The bioaccessibility of total Cd ranged from 44.0 % (kidney) to 90.2 % (gonad) for different tissues of scallop Chlamys farreri. Steaming decreased the total Cd bioaccessibility in the mantle, gill, gonad, digestive gland and the muscle. During in vitro digestion, the reactive inorganic Cd2+ could be detected in the digestive juice of five tissues except for the muscle. Steaming process increased the bioaccessible Cd2+ content for the digestive gland, gill and gonad tissues. Based on the bioaccessible total Cd and Cd2+ content, the muscle, gonad, and mantle of the steamed scallops are the safe tissues for human consumption according to the scenarios of Cd intake established by WHO and EFSA.

Hyperaccumulation of cadmium by scallop Chlamys farreri revealed by comparative transcriptome analysis.

Cadmium (Cd) is a hazardous environmental contaminant, which has a serious effect on the ecosystem, food safety and human health. Scallop could accumulate high concentration of Cd from the environment and has been regarded as a Cd hyper-accumulator. In this work, we investigated the antioxidative defense, detoxification and transport of Cd in the kidneys of scallops by transcriptome analysis. A total of 598 differentially expressed genes including 387 up-regulated and 211 down-regulated ones were obtained during Cd exposure, and 46 up-regulated and 260 down-regulated ones were obtained during depuration. Cadmium exposure could cause oxidative stress in the kidneys, which was particularly shown in the pathways involved in proteasome and oxidative phosphorylation. The mRNA expression of 5 metallothionein (MT) genes were overexpressed under Cd exposure and significantly decreased during Cd depuration, which played a vital role in Cd chelation and detoxification. The expression of divalent metal transporter (DMT) genes were down-regulated insignificantly during accumulation and depuration of Cd, which suggested that the DMT played little roles in Cd transport in scallops. A positive relationship in the expression of the zinc transporter (ZIP6 and ZIP1) genes with Cd exposure and depuration was observed, which confirmed its important role for Cd uptake in the kidneys of scallops. 26S proteasome activities and MT expression were Cd-dependent. This study supplied the important reference on the hyperaccumulation of Cd by scallops and identified some effective bioindicators for the environmental risk assessment.

Subcellular distribution and chemical forms of cadmium in the edible seaweed, Porphyra yezoensis.

The subcellular distribution and chemical forms of Cd were investigated in the edible seaweed, Porphyra yezoensis. The seaweed was exposed to different Cd concentrations (0.01, 0.05, 0.1, 0.5, 1.0 and 5.0mgl(-1)) for up to 96h. In both the controls (no Cd added) and treatment groups, 41.2-79.2% of Cd was localised in the cell wall, and the proportion of Cd in the cell wall increased with increasing concentrations of Cd and exposure time. In the control groups, 74.8% of Cd was extracted by 1M NaCl, followed by 2% acetic acid, HAC (18.9%). In the treatment groups, most Cd was extracted by 2% HAC. The proportion of Cd extracted by 2% HAC increased with exposure to increasing concentrations of Cd and over time. Cell wall deposition and forming of precipitates with phosphate may be a key strategy to reduce Cd toxicity in P. yezoensis.