Crops Collect More Cadmium As Carbon Dioxide Builds

Environ. Sci. Technol.

Amassing Metal: Two graduate students study rice growing under high carbon dioxide on soil spiked with contaminants.

As human activity sends ever more carbon dioxide into the air, plants may grow faster and pull more nutrients from the soil. Now a study in food crops finds that as levels of CO₂ increase, rice and wheat also take up more of the toxic metal cadmium (Environ. Sci. Technol., DOI: 10.1021/es2001584).

In a 29-month study, researchers led by Hongyan Guo, from Nanjing University, and Jianguo Zhu, of the Chinese Academy of Science's Institute of Soil Science in Nanjing, increased CO₂ levels by 200 ppm in air over rice and wheat, to model the crops under atmospheric concentrations some scientists have predicted for the year 2050. The team spiked the soils with varying levels of cadmium, a toxic metal that is prevalent in China's soils, both from natural sources and industrial contamination.

After two growing seasons, wheat from the most contaminated soils, with 2 mg of cadmium per kilogram of soil, ended up with a cadmium concentration of 1.2 mg/kg, surpassing the 0.1 mg/kg wheat flour limit set by the European Food Safety Authority. Such high concentrations in food could lead to kidney problems in people who eat it, the researchers say. By contrast, wheat grown in the same soil but without added CO₂ had a concentration of about 1 mg/kg, which the authors say is still elevated but significantly lower.

The study suggests that crop contamination under changing climate conditions "might be a much bigger issue than people realize in certain parts of the world," comments Ben Duval of University of Illinois, Urbana-Champaign. In a similar experimental setup in Florida, he and colleagues recently found that trees also take up greater amounts of some metals as carbon dioxide builds (Environ. Sci. Technol., DOI: 10.1021/es102250u).

Chemical & Engineering News

ISSN 0009-2347

Copyright © 2011 American Chemical Society