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Arsenic Speciation in
environmental Samples and Food Products
GALAB Laboratories determines arsenic species on a routine basis
However, arsenic speciation has not yet routine status in contract laboratories, whereas an increased demand for the determination of arsenic species, particularly in food industry, is already foreseeable. At GALAB Laboratories a robust method for arsenic speciation has been developed and integrated in the routine testing scheme to analyse all kind of environmental samples and food products. For each sample type, a particular extraction procedure is applied. The measurement of the sample extracts is carried out by HPLC-ICPMS, a technique which combines powerful separation with a detector at trace level.
With our method up to 17 different arsenic species were detected so far in a single chromatographic run. An overview of the most common arsenic species and their chemical structures is presented in Fig. 1. In Fig. 2 three chromatograms are shown in which the chromatographic performance as well as the different arsenic distribution patterns of arsenic in different organisms are elucidated. In fish, arsenobetaine is the main arsenic compound, in algae samples arsenosugar compounds and arsenate are dominant and rice shows elevated levels of arsenite next to DMA and arsenate. GALAB Laboratories is accredited according to DIN EN ISO 17025 for this method. In addition, we regularly participate in international interlaboratory comparisons and certification studies for reference materials for arsenic species.
Chemical structures of arsenic compounds
Chromatograms of fish (A), algae (B) and rice (C)
Arsenic - Poisonous or not ?
Famous cases of arsenic poisoning refer to arsenic in the form of arsenic trioxide. But arsenic occurs in many chemical forms and not all of these compounds are that toxic. Inorganic arsenic, like oxides, acids and salts occur in the trivalent or pentavalent state, and all these are highly toxic and belong to the carcinogenic substances, with the trivalent forms being particularly poisonous. Inorganic arsenic is the main compound of arsenic in water, soil and sediment. In living organisms, inorganic arsenic is methylated.
In contrast to tin and mercury compounds, where the methylated species are much more toxic than the inorganic compounds, arsenic methylation can be regarded as detoxification mechanism. For instance, compounds like monomethylarsonic acid or dimethylarsinic acid are assigned an intermediate toxicity whereas arsenobetaine and arsenocholine are considered non-toxic.
Sources and sinks of arsenic
Arsenic is introduced into the environment from natural sources (volcanoes, weathering of minerals) as well as from anthropogenic activities like ore smelting or the use of pesticides in agriculture or industrial effluents. Due to its mobility, arsenic is therefore found in soil and sediment, groundwater and seawater. Depending on the region, the arsenic levels of ground water can differ significantly, which poses a severe problem in some countries for the processing of drinking water.
In living organisms, arsenic is taken up, bioaccumulated and biotransformed, so that arsenic levels often are much higher in such organisms than in their surrounding environment. As a result, arsenic is present in a lot of food products like fish, shellfish, algae, mushrooms, wine and rice and indirectly also in chicken that are fed on fish meal based food according to the food chain. Some measures to reduce the anthropogenic introduction of arsenic in the environment have already been taken, like the ban of using arsenic containing pesticides in Germany.
Limit values for total arsenic have been established for water, the most important part of our nourishment. According to the German "Trinkwasserverordnung", the limit value is 0.010 mg/L arsenic for drinking water. For mineral water, a limit value of 0.050 mg/L has been established. No common limit values exist for food products within the EU, though. As there are many sources of arsenic in our food with very different toxicity, it is important to differentiate between the species in order to evaluate the impact of arsenic on our health. The necessity of arsenic speciation is already reflected in some limit values: The "Joint Expert Committee on Food Additives and Contaminants" suggested a PTWI-value (provisional tolerable weekly intake) of 15 µg inorganic arsenic / kg body weight.
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