Wheat (Triticum aestivum) collected in the Nawanshahr-Hoshiarpur Region (Punjab, India) showed the highest selenium concentrations ever recorded in cereal grains (29-185 microg g(-1)). There was a strong positive relationship between the selenium content in shoots and that in kernels, showing that grain selenium concentration can be predicted from that in the vegetative tissues of the plant. The identity and content of the selenocompounds in the grain samples and in wheat-based reference materials were investigated by HPLC-ICP-dynamic reaction cell-MS. Reversed-phase, cation exchange, and anion exchange HPLC were used to separate the selenium species after ultrasound-assisted enzymatic extraction with an ultrasonic probe. Selenomethionine and selenate accounted for 72-85% and 2-6% of the sum of the selenium species, respectively. The proportion of organic Se species varied with increasing Se content; namely, SeMet showed a relative reduction whereas the other organoselenium compounds increased up to 18-22% of the total chromatographed selenium. Se-methyl-selenocysteine was detected as a minor compound (0.2-0.5%) in high-Se wheat by both reversed-phase and cation exchange HPLC using retention time matching with the standard substance spiked to the sample extracts. Regular consumption of locally produced wheat-based food items may lead the population of the study area to an excessive intake of selenium. On the other hand, the large predominance of selenomethionine shows that local wheat can be a promising raw material for naturally enriched products to be used to supplement human and animal diets in low selenium areas.
The distribution and potential bioaccumulation of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss Walbaum, 1792), a major aquaculture species, was studied in relation to fish growth over a period of >3 years. Fish were reared under normal farming conditions, that is, fed a standard fish food and exposed to negligible levels of waterborne trace elements. The age-related variations in the content of each trace element in gills, kidney, liver, muscle, and skin were studied through nonparametric regression analysis. A buildup of all elements in all tissues and organs was observed, but due to dilution with growth, the concentrations did not increase, except in a few cases such as cadmium and mercury in liver and kidney. In muscle tissue, the concentrations of mercury, lead, and selenium did not alter significantly with growth, whereas cadmium increased but remained at exceedingly low levels. The concentration of arsenic in muscle tissue peaked at 14 months and then decreased in adult specimens. Arsenic speciation by high-performance liquid chromatography--inductively coupled plasma mass spectrometry revealed that arsenic in muscle was almost exclusively present in the form of nontoxic arsenobetaine. Application of a mercury mass balance model gave predicted concentrations in agreement with measured ones and showed that in farmed rainbow trout the ratio of mercury concentrations in feed and in fish is about 1:1. Therefore, rainbow trout does not approach the limits established for human consumption even when reared with feed at the maximum permitted levels. These findings highlight the low bioaccumulation potential of toxic trace elements such as cadmium, lead, and mercury in rainbow trout following dietary exposure. On the other hand, selenium concentrations in muscle (about 0.2 microg g (-1) of fresh weight) show that rainbow trout may be a good source of this essential element.
HPLC with on-line ICP-MS was used for the determination of V(IV) and V(V) in natural mineral water. Cationic and anionic tetravalent and pentavalent vanadium species were converted into V-EDTA complexes, i.e. [VO(EDTA)] 2À and [VO 2 (EDTA)] 3À , which could be effectively separated on a short anion exchange column in <6 min. Pre-column EDTA complexation also prevented species interconversion as a result of loss of CO 2 from samples and their exposure to atmospheric oxygen. A low-salt mobile phase (4 mM carbonate buffer and 5 mM EDTA-Na 2 ) compatible with ICP-MS detection was used in chromatographic separations. The method was tested on real samples spanning one order of magnitude of V concentrations and encompassing a wide range of potential interfering ions and total dissolved solids, providing accurate and reproducible results. Mass balance budgets gave a mean value of 100% (range 96-107%). Recoveries from spiking experiments were in the range 98-103%. Precision as average intra-day repeatability was 1.2% and 0.9% for V(IV) and V(V), respectively. Average inter-day repeatability was 5.5% and 1.4% for V(IV) and V(V), respectively. Limits of detections were 0.16 mg L À1 for V(IV) and 0.025 mg L À1 for V(V). The interference arising by 35 Cl 16 O was resolved chromatographically. V(V) was found to largely predominate in PET-bottled mineral water samples. Species distribution was consistent with theoretical predictions based on thermodynamic equilibria of vanadium in water. Overall, a rapid, sensitive, on-line method is provided which can be readily employed for monitoring purposes.
2À, with polynuclear species, e.g., decavanadates H x V 10 O 28 (6 À x) existing only above a critical concentration (''mononuclear wall''
Seven hundred and twenty-six samples of wheat grains from the majority of Italian agricultural areas were pooled into 141 composite samples, homogeneous with respect to geographical origin and wheat variety. The average arsenic concentration of the pooled samples was 9 ng g(-1), with a range of 2-55 ng g(-1) (dry weight basis). The spread of arsenic concentrations (coefficient of variation of 91%) was related to spatial variability associated with geochemical and environmental factors. Temporal variability was investigated by a 3-year longitudinal study on 7 wheat cultivars grown in 22 areas of central and northern Italy. Average year-to-year variation in arsenic levels was low, and the average of the coefficients of variation was 23%. These results show that mapping of phytoavailable arsenic in agricultural soils can be done by measuring arsenic concentration in representative samples of wheat grains. Arsenic speciation in the grain showed that As(III) and As(V) were the major As compounds, highlighting the importance of wheat as a source of inorganic arsenic in the diet.
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