Cadmium in organic and conventional pig production

The main sources of cadmium (Cd) input to soils have been phosphate fertili zers and deposition from air. In organic farming, phosphate fertilizers are not used, which may in the long term result in lower Cd levels. In the pre sent study, feed, kidney, liver, and manure from growing/finishing pigs rai sed conventionally and organically on the same farm were microwave-digested and analyzed for Cd by graphite furnace atomic absorption spectrometry. Cd was also analyzed in soil and water. A quality control program was include d. The organic pigs (n = 40) were raised outdoors and fed an organic feed; the conventional pigs (n = 40) were raised indoors and given a conventional feed. The Cd levels in organic and conventional feed were 39.9 mug/kg and 51.8 mug/kg, respectively. Organic feed contained 2% potato protein, which contributed 17% of the Cd content. Conventional feed contained 5% beet fibe r, which contributed 38% of total Cd content. Both feeds contained vitamin- mineral mixtures with high levels of Cd: 991 mug/kg in organic and 589 mug/ kg in conventional feed. There was a significant negative linear relationsh ip between Cd concentration in kidney and kidney weight. There was no signi ficant difference in liver Cd levels between organic and conventional pigs and the mean +/- SD was 15.4 +/- 3.0. In spite of the lower level of Cd in the organic feed, the organic pigs had significantly higher levels in kidne ys than the conventional pigs, 96.1 +/- 19.5 mug/kg wet weight (mean +/- SD ; n = 37) and 84.0 +/- 17.6 mug/kg wet weight (n = 40), respectively. Organ ic pigs had higher Cd levels in manure, indicating a higher Cd exposure fro m the environment, such as ingestion of soil. Differences in feed compositi ons and bioavailability of Cd from the feed components may also explain the different kidney levels of Cd.