Sampling of kidneys from cattle and pigs for cadmium analysis

Cadmium accumulates in proximal tubule cells causing a gradient of cadmium through the kidney, which is important to consider when sampling kidney tissue for cadmium analysis. In this study different sampling techniques of cattle and pig kidneys have been tested. Cadmium was determined by dry ashing-FAAS (detection limit 6.0 micrograms l-1, BCR (Community Bureau of Reference) No. 186 3.1 +/- 0.17 mg kg-1 (mean +/- s), laboratory quality sample (LQS) 495 +/- 17 micrograms kg-1) and microwave digestion-graphite furnace AAS (detection limit 0.24 microgram l-1, BCR No. 186 2.7 +/- 0.16 mg kg-1, LQS 444 +/- 14 micrograms kg-1) in homogenates, slices, and in cortex, intermediate and medulla zones of bovine and porcine kidneys. The bovine kidney lobulus cortex, intermediate zone, and medulla contained 70, 28 and 2% of the total cadmium content, and the relative weights of the zones were 53, 35 and 12%, respectively. The cadmium concentration in bovine cortex, intermediate zone and medulla was 1.37 +/- 7, 0.79 +/- 0.06 and 0.10 +/- 0.06 times the calculated homogenate concentration. Pig renal cortex, intermediate zone and medulla, contained 73, 26 and 0.5% respectively of the total cadmium content, and the relative weights were 63, 36 and 2.4%, respectively. The cadmium concentration in porcine cortex, intermediate zone and medulla was 1.14 +/- 0.05, 0.78 +/- 0.09 and 0.23 +/- 0.11 times the calculated homogenate concentration. Freezing of pig kidney caused a slight redistribution of cadmium from cortex to medulla. The results show that sampling technique is of greater importance for the determination of cadmium in bovine kidney than in pig kidney. A well described method for sampling of kidney is necessary to make it possible to compare results. To detect small differences in renal Cd levels between groups, as, e.g., in the case of biological monitoring of Cd exposure, sampling of the outer cortex is suggested as an optimal method.