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New arsenic species detected in carrot samples

(31.01.2008)


Background:
Arsenic contamination in water and soil is one of the biggest calamities of the world (see EVISA News on Arsenic in water) and can be attributed to the presence of natural hydrogeological backgrounds, volcanic activity, or anthropogenic sources such as pesticides or wood preservation compounds (see EVISA News on CCA-treated timber, and arsenic pesticides).

Arsenic undergoes biochemical transformations influencing its toxicity. For the assesment of risks for human health,  it is therefore essential not only to analyse total arsenic entering the food chain but also individual arsenic species. More than 25 arsenic species have been identified in various plants and animals over the last 50 years and this list continues to grow. Researchers have up-to-now mainly focused on water solubile compounds in marine organisms. Arsenolipids and arsenic speciation in terrestrial foods have not been studied as extensively because the concentrations are generally lower than in marine organisms.
However, rice has attracted a lot of attention because of the relatively high worldwide consumption especially in endemic areas such as Bangladesh, Vietnam, India and China (see EVISA News on arsenic in rice). Also carrots have been reported to have high arsenic content, especially when harvested from contaminated soil.


The new study:

The new study performed by reserachers from US FDA, US EPA and University of Cincinnati aimed at the identification of arsenic compounds in carrots. Using anion-exchange chromatography coupled to ICP-MS, the researchers performed arsenic speciation analysis in aqueous carrot extracts.

Besides of As(III), As(V) and monomethylarsonic acid (MMA(V)) two other species were observed. Using retention time matching under different chromatographic conditions and sample preparation steps, these could be identified as monomethyl- arsonous acid (MMA(III)) and the sulfur analogue of MMA(V), monomethylthioarsonic acid (MMTA). 

Total arsenic concentration in different carrot samples varied over 3 orders of magnitude, ranging from 67 to 18700 µg/kg. Highest concentrations were found in samples collected from a 1980 field study, which might have been contaminated by MMA(V)-based pesticides. MMTA was only found in those carrots samples having total arsenic concentration above 9000 µg/kg. The only arsenical common to all carrot samples is inorganic arsenic (As(III) + As(V)) ranging between 44 and 85 %. The authors also concluded from their observations that conversion of inorganic arsenic to organic arsenic is not promoted by the carrot plant.


The original study:

Santha Ketavarapu V. Yathavakilla, M. Fricke, P. A. Creed, D.T. Heitkemper, N.V. Shockey, C. Schwegel, J.A. Caruso, J.T. Creed, Arsenic Speciation and Identification of Monomethylarsonous Acid and Monomethylthioarsonic Acid in a Complex Matrix, Anal. Chem., 80/3 (2008) 775-782. doi: 10.1021/ac0714462



Related studies

Rui Zhao, Mengxia Zhao, Hui Wang, Yasuhito Taneike, Xinrong Zhang, Arsenic speciation in moso bamboo shoot - A terrestrial plant that contains organoarsenic species, Sci. Total Environ., 371/1-3 (2006) 293-303. doi:10.1016/j.scitotenv.2006.03.019

P. Tlustos, W. Goessler, J. Szakova, D. Pavliková, J. Balik, Arsenic Compounds in the leaves and Roots of Radish Grown in three Soils treated by Dimethylarsinic Acid, Plant, Soil and Environment, 50/12 (2004) 540-546.

Pavel Tlustos, Walter Goessler, Jirina Száková, Jiri Balík, Arsenic compounds in leaves and roots of radish grown in soil treated by arsenite, arsenate and dimethylarsinic acid, Appl. Organomet. Chem., 16/4 (2002) 216-220. DOI: 10.1002/aoc.282

Nohora P. Vela, Douglas T. Heitkemper, Kirsten R. Stewart, Arsenic extraction and speciation in carrots using accelerated solvent extraction, liquid chromatography and plasma mass spectrometry, Analyst (London), 126/7 (2001) 1011-1017. DOI: 10.1039/b102420p

Hans Helgesen, Erik H. Larsen, Bioavailability and speciation of arsenic in carrots grown in contaminated soil, Analyst (London), 123/5 (1998) 791-796. DOI: 10.1039/a708056e

R.A. Pyles, E.A. Woolson, Quantitation and characterization of arsenic compounds in vegetables grown in arsenic acid treated soil, J. Agri. Food Chem., 30 (1982) 866-870.



Related Resources

LC-ICP-MS - The most often used hyphenated system for speciation analysis


Related News

EVISA News on arsenic in drinking water
EVISA News on CCA-treated timber
EVISA News on arsenic pesticides
EVISA News on arsenic in rice











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