Major and trace elements in organically or conventionally produced milk John E Hermansen 1 *, Jens H Badsberg 2 , Troels Kristensen 1 and Vagn Gundersen 3 1 Danish Institute of Agricultural Science, Department of Agroecology, PO Box 50, 8830 Tjele, Denmark 2 Danish Institute of Agricultural Science, Department of Animal Breeding & Genetics, PO Box 50, 8830 Tjele, Denmark 3 Risø National Laboratory, P.O. Box 49, 4000 Roskilde, Denmark Received 14 October 2004 and accepted for publication 23 December 2004 A total of 480 samples of milk from 10 organically and 10 conventionally producing dairy farms in Denmark and covering 8 sampling periods over 1 year (triplicate samplings) were analysed for 45 trace elements and 6 major elements by high-resolution inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry. Sampling, sample preparation, and analysis of the samples were performed under carefully controlled contamination- free conditions. The dairy cattle breeds were Danish-Holstein or Jersey. Sources of variance were quantified, and differences between production systems and breeds were tested. The major source of variation for most elements was week of sampling. Concentrations of Al, Cu, Fe, Mo, Rb, Se, and Zn were within published ranges. Concentrations of As, Cd, Cr, Mn and Pb were lower, and concentrations of Co and Sr were higher than published ranges. Compared with Holsteins, Jerseys produced milk with higher concentrations of Ba, Ca, Cu, Fe, Mg, Mn, Mo, P, Rh, and Zn and with a lower concentration of Bi. The organically produced milk, compared with conventionally produced milk, contained a significantly higher concentration of Mo (48 v. 37 ng/g) and a lower concentration of Ba (43 v. 62 ng/g), Eu (4 v. 7 ng/g), Mn (16 v. 20 ng/g) and Zn (4400 v. 5150 ng/g respectively). The investigation yielded typical concentrations for the following trace elements in milk, for which no or very few data are available: Ba, Bi, Ce, Cs, Eu, Ga, Gd, In, La, Nb, Nd, Pd, Pr, Rh, Sb, Sm, Tb, Te, Th, Ti, Tl, U, V, Y, and Zr. Keywords : Trace elements, cow milk, organic production. The importance of microelements in food, including el- ements occurring in ultra low concentrations, in relation to positive as well as negative health aspects, is increasingly acknowledged. However, owing to difficulties in measur- ing elements with ultra low concentrations, only limited information exists on the content of and sources of vari- ation of microelements in food, including milk. New ana- lytical methods have been developed and this gives us an opportunity to study such relations in more detail. Recent reviews of minerals and trace elements in milk (Jenness, 1988; Flynn, 1992) include 20 and 14 trace ele- ments, respectively. More recent investigations (Coni et al. 1994; Garcia et al. 1999) only included a few more trace elements in their analyses. The potential number of trace elements in milk is much higher. Recently, Gundersen et al. (2000) successfully quantified 54 trace elements in onions using a high-resolution inductively coupled plasma mass spectrometry (ICP-AES). ICP-AES has also been evaluated for use in milk and dairy products (Coni et al. 1994) and was recently used as a reference method in evaluating new analytical techni- ques in relation to dairy products (Tokusoglu et al. 2004). Apart from the analytical challenge as such, a common problem in the study of trace elements is the risk of measur- ing an elevated concentration due to contamination es- pecially by sampling and sample preparation procedures. The purpose of this study was to determine the content of a large range of trace elements in raw milk produced under different conditions, including organic v. conven- tional farms. Materials and Methods Farms and milk sampling Samples were collected from 20 farms in the period July 1997–June 1998 balanced among organic and conventional farms and balanced according to breeds (Danish-Holstein *For correspondence ; e-mail : John.hermansen@agrsci.dk Journal of Dairy Research (2005) 72 362–368. f Proprietors of Journal of Dairy Research 2005 362 doi:10.1017/S0022029905000968 Printed in the United Kingdom