Geographical variations in arsenic contents in rice plants from Latin America and the Iberian Peninsula in relation to soil conditions.

Arsenic is a ubiquitous, toxic element that is efficiently accumulated by rice plants. This study assessed the spatial variability in the total As (tAs) contents and organic and inorganic forms in different types of rice, plant parts (husk, stem, leaves and phytoliths) and residues. Samples were collected in different countries in Latin America (Ecuador, Brazil and Peru) and the Iberian Peninsula (Spain and Portugal). The tAs content in commercial polished rice from the Latin American countries was similar (0.130-0.166 mg kg-1) and significantly lower than in the rice from the Iberian countries (0.191 ± 0.066 mg kg-1), and together, the tAs concentration in brown rice (236 ± 0.093 mg kg-1) was significantly higher than in polished and parboiled rice. The inorganic As (iAs) content in rice was similar in both geographical regions, and the aforementioned difference was attributed to dimethylarsinic acid (DMA). The relative abundance of organic species increased as the tAs content in rice grain increased. A meta-analysis of our and previously reported data confirmed the negative correlation between iAs/tAs and tAs. At low tAs concentrations, inorganic forms are dominant, while at higher values (tAs > 0.300 mg kg-1) the concentration of organic As increases substantially and DMA becomes the dominant form in rice grain. On the contrary, inorganic arsenic was always the dominant form, mainly as arsenate [As(V)], in leaves and stems. The presence in soils of high concentrations of amorphous Fe and Al oxides and hydroxides, which are capable of strongly adsorbing oxyanions (i.e. arsenate), was associated with low concentrations of As in rice plants. In addition, the presence of high concentrations of As(V) in stems and leaves, low concentration of As in phytoliths, and the As associated with organic matter in stems and husk, together suggest that rice plants take up more As(V) than As(III).

Method development for the control determination of mercury in seafood by solid-sampling thermal decomposition amalgamation atomic absorption spectrometry (TDA AAS).

A very simple and rapid method for the determination of total mercury in fish samples using the Direct Mercury Analyser DMA-80 was developed. In this system, a previously weighted portion of fresh fish is combusted and the released mercury is selectively trapped in a gold amalgamator. Upon heating, mercury is desorbed from the amalgamator, an atomic absorption measurement is performed and the mercury concentration is calculated. Some experimental parameters have been studied and optimised. In this study the sample mass was about 100.0 mg. The relative standard deviation was lower than 8.0% for all measurements of solid samples. Two calibration curves against aqueous standard solutions were prepared through the low linear range from 2.5 to 20.0 ng of Hg, and the high linear range from 25.0 to 200.0 ng of Hg, for which a correlation coefficient better than 0.997 was achieved, as well as a normal distribution of the residuals. Mercury reference solutions were prepared in 5.0% v/v nitric acid medium. Lyophilised fish tissues were also analysed; however, the additional procedure had no advantage over the direct analysis of the fresh fish, and additionally increased the total analytical process time. A fish tissue reference material, IAEA-407, was analysed and the mercury concentration was in agreement with the certified value, according to the t-test at a 95% confidence level. The limit of quantification (LOQ), based on a mercury-free sample, was 3.0 µg kg(-1). This LOQ is in accordance with performance criteria required by the Commission Regulation No. 333/2007. Simplicity and high efficiency, without the need for any sample preparation procedure, are some of the qualities of the proposed method.