Friday, 15 March 2013

Heavy metal veggies: ICP-MS worth a nickel

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Heavy metal veggies: ICP-MS worth a nickel


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Nickel and chromium


The presence of heavy metal ions of nickel and chromium in vegetables, including potatoes, carrots and onions, irrigated with polluted water is revealed using X-series inductively coupled plasma mass spectrometry.
Sotiris Stasinos and Ioannis Zabetakis of the Food Chemistry Laboratory, at the University of Athens, Greece, explain how heavy metals ions, in general, can migrate from polluted soil and/or irrigation water to tuberous plants and root vegetables. The implications of such migration being that these toxic agents can enter the food chain leading to long-term, chronic consumption and the many putative health problems such exposure can cause. This not only includes the direct toxic effects of such metals but the depletion of essential trace elements in the body. Part of the issue is that unlike certain organic residues metal ions persist, they cannot be degraded or otherwise broken down into less harmful constituents by virtue of being elements rather than compounds. They point out that other researchers have highlighted various sources of contamination by human sources including: mining, industrial and domestic wastewater and sewage sludge, as well as atmospheric deposition.

Cross contamination

"The cross-contamination of food by heavy metals is an emerging nutritional hazard as there is a proven link between environmental pollution and the food chain," the researchers explain, with certain crop plants being as susceptible to contamination as any other but because of their role as basic components of our diets representing more of a problem in terms of human health. Among those crops are carrots (Daucus carrota), onions (Allium cepa) and potatoes (Solanum tuberosum). The research team has investigated the uptake of chromium and nickel ions by these three species in greenhouse experiment. The growing conditions were designed to simulate open-field irrigation used in major agricultural regions of Greece, the Asopos River in Viotia and Messapia in Evia. The water table is contaminated in these regions, the team points out.
The vegetables were grown over a period of about four months in and non-controls were irrigated with water containing specific levels of toxic and carcinogenic Cr(VI) and toxic Ni(II) ranging from 0 (control) to 250 micrograms per litre. The controls would represent crops grown on land uncontaminated by heavy metals whereas the 250 level represents realistic concentrations determined in the most contaminated parts of the two agricultural regions.
"Both Cr and Ni are toxic, this is the reason that they are both regulated in drinking water legislation," Zabetakis told SpectroscopyNOW. "However, there are no legal limits for Ni and Cr in food (EC 1881/2006), there is clear legal gap there...and these two metals are emerging chemical hazards in the food chain."

Agricultural solution

The team used a microwave oven digester to prepare samples of plants and soils on which X-series ICP-MS could then be carried out to determine how much nickel and chromium had been taken up by the three vegetable crops. Subsequent statistical analysis unearthed the relevant details showing uptake in onions and potatoes although carrots seemed not to be susceptible to uptake of either Cr(VI) nor Ni(II) ions. The team suggests that farmers using irrigation water contaminated with Cr(VI) and Ni(II) polluted water should be supplied with clean irrigation water so as to minimize the heavy metal cross-contamination of the food chain. It is possible that processing might be a more straightforward solution to removing such contamination given the huge volumes of water needed for agricultural irrigation.
"The next step is to study the effect of heavy metals on plant physiology and next to study the uptake of heavy metals from other plants that are not part of the food chain," Zabetakis adds.

Related Links

Ecotoxicol Environ Safety 2013, online: "The uptake of nickel and chromium from irrigation water by potatoes, carrots and onions"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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