Yuxiu Zhai

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.

Arsenic and cadmium in the marine macroalgae (Porphyra yezoensis and Laminaria Japonica) — forms and concentrations

Abstract Total arsenic, inorganic arsenic (iAs), total cadmium concentrations and chemical forms of cadmium were analysed in Porphyra yezoensis collected monthly from January to April in 2011 and in Laminaria Japonica collected monthly from March to July in 2010. Results showed that total As concentrations in P. yezoensis were much lower than those in L. Japonica. The iAs concentrations in both macroalgae were all below the maximum limit according to the legislation in China, while total Cd concentrations in all samples of P. yezoensis exceeded the maximum limit. The percentage of iAs to total As decreased in both macroalgae with the time. The results provide important information showing that both macroalgae are able to metabolise inorganic arsenic to organic forms. Thus both macroalgae have evolved arsenic resistance which is linked to the capability of metabolising toxic inorganic arsenic. In addition, the results suggest that the transformation rate of arsenate to organic arsenic in both algae increases with the growth and metabolic rate that increase with elevated environmental temperature. Temperatures rise from January to April in Jiangsu province and from March to July in Liaoning Province. Most Cd was associated with pectates and protein (extractable by 1 M NaCl) in both algae, and only a small percentage of the Cd was inorganic (extractable by 80% ethanol). The Cd chemical forms have no obvious relationship with the time in both algae.

Arsenic Species in Edible Seaweeds Using In Vitro Biomimetic Digestion Determined by High-Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectrometry

Arsenite [As (III)], arsenate [As (V)], methylarsonate (MMA), and dimethylarsinate (DMA) in five edible seaweeds (the brown algae Laminaria japonica, red algae Porphyra yezoensis, brown algae Undaria pinnatifida, brown algae Hizikia fusiformis, and green algae Enteromorpha prolifera) were analyzed using in vitro digestion method determined by high-performance liquid chromatography inductively coupled plasma mass spectrometry. The results showed that DMA was found in the water extracts of all samples; As (III) were detected in L. japonica and U. pinnatifida and about 23.0 and 0.15 mg/kg of As (V) were found in H. fusiformis and E. prolifera respectively. However, after the gastrointestinal digestion, As (V) was not detected in any of the five seaweeds. About 0.19 and 1.47 mg/kg of As (III) was detected in the gastric extracts of L. japonica and H. fusiformis, respectively, and about 0.31 and 0.10 mg/kg of As (III) were extracted from the intestinal extracts of Porphyra yezoensis and U. pinnatifida, respectively. The present results successfully reveal the differences of As species and levels in the water and biomimetic extracts of five edible seaweeds. The risk assessment of the inorganic arsenic in the five edible seaweeds based on present data showed almost no hazards to human health.

Direct Determination of Lead in Foods by Solid Sampling Electrothermal Vaporization Atomic Fluorescence Spectrometry

A solid sampling method for the determination of lead in foods (including grains, vegetables and seafoods) using electrothermal vaporization atomic fluorescence spectrometry was established. The method introduced samples using electrothermal vaporization by quartz furnace and used on-line ashing and vaporization to remove matrix interferences for the specific trap of lead. It was proven by the certified reference material (CRM) and the recovery rate of the standards that the electrothermal vaporization was stable and there was no effect for sampling difference. The best operating program and parameters for the new method included ashing (850°C, 160 s), vaporization and trap (1050°C, 80 s; 800°C, 10 s), release (800°C, 10 s), and mixed Ar + H2 (85:15%, v/v) as carrier gas with flow rate of 500 mL/min. The relative standard deviations of repeated Pb measurements in CRMs were all below 5.0%, and the recovery rate ranged from 90.0 - 110.0%. The limit of detection (LOD) for the new method was 3.0 pg and the limit of quantification (LOQ) was 10.0 pg. The total time of analysis was less than 6 min. No significant differences existed between the results measured by the new method and microwave ICP-MS.

Arsenic content and speciation analysis of several economic shellfishes in China

The arsenic speciation and the content of four toxic arsenic(including As3+,As5+,MMA and DMA)in several main economic shellfishes in our country were analyzed using HPLC-ICP-MS combined with in vitro digestion method.Results showed that S.strictus had the highest total arsenic content(5.68 mg/kg),the second was in S.Subcrenata(4.83 mg/kg),the total arsenic content in C.Farreri,C.Ostreae and H.discus hannai were much lower(2.26-2.70 mg/kg)and three of them had no significant difference.The lowest content was in R.Philippinarum and M.edulis.AsB was the main arsenic speciation in both water extraction and gastrointestinal extraction for all samples,and especially for Scapharca subcrenata,AsB was the only arsenic speciation.About 0.025,0.008 and 0.300 mg/kg As3+ were separated in the water extraction of C.farreri,R.philippinarum and S.strictus respectively.In addition,0.115 mg/kg As5+ was also detected in the water extraction of S.strictus.Different concentration of DMA was found in the water extraction of all samples except for S.subcrenata and M.edulis,with the highest content of 0.674 mg/kg in S.strictus.However,except in S.strictus,DMA was detected in the intestinal extraction,none of four toxic arsenic speciations were found in the gastrointestinal extraction of other shellfishes.Present experiments proved that the arsenic speciation in the water extraction which could reflect the real content in shellfishes and in gastrointestinal extraction which could reflect the real content under the gastrointestinal digestion was different,especially for four toxic arsenic speciation.

Subcellular Distribution and Mechanism of Detoxifying Arsenic in Porphyra Yezoensis

In order to disclose the compartmentation of arsenic and the mechanism of detoxifying arsenic in Porphyra yezoensis,the transformation of different arsenic speciation and the subcellular distribution of arsenic in P. yezoensis were conducted. The seaweed was exposed to different concentrations( 0. 05,0. 1,0. 5 and1. 0 mg / L) of arsenite( As(Ⅲ)) and arsenate( As(Ⅴ)) for 6 days. Samples were randomly collected every day.The arsenic speciation in P. yezoensis was analyzed using HPLC-ICP-MS and the subcellular distribution of arsenic was conducted using differential centrifugation. Results showed that the arsenic accumulated in the seaweed increased with the exposed concentration and exposure time increasing. A clear dose-response was proved to exist in both As(Ⅲ) and As(Ⅴ) exposure,and the correlation coefficient was 0. 9996( p 0. 01) and0. 9844( p 0. 01) for As(Ⅲ) and As(Ⅴ) respectively. In addition,the accumulation rate of As(Ⅲ) was higher than that of As(Ⅴ),and the accumulation coefficient of arsenic was 4719 and 4112 respectively for the seaweed exposed to 0. 1mg / L As(Ⅲ)and As(Ⅴ) after 6ds exposure. The results also proved that there was a great difference in the different subcellular distribution and the compartmentation of arsenic in P. yezoensis. The sequcence of different subcellular distribution was cyplasmic supernatant( 80%) cell wall( 15%) cell organelles( 5%). Cyplasmic supernatant was the main localization for arsenic and played an important role in the compartmentation of As. At the same time,the research of the arsenic transformation during accumulation showed that the absorbed As(Ⅴ) in P. yezoensis would be quickly methylated and then be transformed to arsenic sugar( AsX1); the absorbed As(Ⅴ) in P. yezoensis would be firstly reduced to As(Ⅲ),which was then be methylated and transformed to arsenic sugar( AsX1). The ability of the compartmention and the transformation of different arsenic speciation in P. yezoensis may play a key role in detoxifying arsenic.

Speciation analysis of cadmium in laver by size exclusion chromatography-high performance liquid chromatography-inductively, coupled plasma mass spectrometry

High content of cadmium in laver has seriously affected the edible safety,export and industry development of seaweed in our country.However,only total cadmium content was detected by present method used worldwide and the total cadmium was used to evaluate the food safety of the laver which may over-estimate the toxicity of the cadmium in laver.Because there are different cadmium forms in laver which have different biological toxicities,the speciation analysis of cadmium in the laver is very urgent.However,studies on the cadmium speciation analysis in seaweed are very scarce at present.In present experiment,we first analyzed the different cadmium forms in laver(Porphyra haitanensis and Porphyra yezoensis)which have high Cd accumulation capability by using size exclusion chromatography-high performance liquid chromatography-inductively coupled plasma mass spectrometry(SEC-HPLC-ICP-MS).The result showed that three Cd species including Phytochelatins(PC)3-Cd,glutathione(GSH)-Cd and one small molecule Cd species were detected in the deionized water extraction of the laver.In vitro whole-bionic digestion model was used to determine the main cadmium forms in laver under the action of saliva,the acidity of stomach and intestine with inorganic and organic components and digestion enzymes.Two unknown Cd species with small molecule were detected in whole-bionic digestion of gastric extracts,and the retention time of main species was 24.2min.Two Cd species was detected in whole-bionic digestion of intestine extracts,and the main species was(PC)3-Cd.However,further study is needed to study the metabolic characteristic of(PC)3-Cd in the biology.Present study further proved the main organic cadmium species in seaweed and this has provided important basis for food safety evaluation of the laver.