Comparative investigation of concentrations of major and trace elements in organic and conventional Danish agricultural crops. 1. Onions (Allium cepa Hysam) and peas (Pisum sativum ping pong).

210 samples of onions (Allium cepa Hysam) from 11 conventionally and 10 organically cultivated sites and 190 samples of peas (Pisum sativum Ping Pong) from 10 conventionally and 9 organically cultivated sites in Denmark were collected and analyzed for 63 and 55 major and trace elements, respectively, by high-resolution inductively coupled plasma mass spectrometry. Sampling, sample preparation, and analysis of the samples were performed under carefully controlled contamination-free conditions. Comparative statistical tests of the element concentration mean values for each site show significantly (p < 0.05) different levels of Ca, Mg, B, Bi, Dy, Eu, Gd, Lu, Rb, Sb, Se, Sr, Ti, U, and Y between the organically and conventionally grown onions and significantly (p < 0.05) different levels of P, Gd, and Ti between the organically and conventionally grown peas. Principal component analysis (PCA) applied to the 63 elements measured in the individual onion samples from the 21 sites split up the sites into two groups according to the cultivation method when the scores of the first and third principal components were plotted against each other. Correspondingly, for peas, a PCA applied to the 55 elements measured as mean values for each site split up the 19 sites into two groups according to the cultivation method when the scores of the third and fourth principal component were plotted against each other. The methodology may be used as authenticity control for organic cultivation after further method development.