Int. J. Environ. Res. Public Health 2009, 6 3135 pathohistological findings of renal tissues and toxic elements in kidneys from slaughtered pigs are summarized in Figure 3. 3. Experimental Section 3.1. Sampling A total of 90 kidneys from healthy slaughtered swine from three different regions of Serbia were sampled during a six month period. The slaughtered pigs had an average weight of about 105 kg and age of about six months. Sampling in the slaughterhouses consisted of collecting one kidney per pig, from five pigs per farm. All samples were packed in plastic bags, kept in a small freezer (+4 °C) during transport, and immediately transported to the laboratory. Visible fat, connective tissue and major blood vessels were excised and the samples were then homogenized. Sub-samples (10 g approximately) were taken and frozen at –18 °C until analysis. 3.2. Digestions Kidney samples for instrumental analysis were prepared using the method of acid microwave digestion. Samples underwent digestion in a microwave digestion unit (Milestone TC) with temperature control. Heavy metal contents (Pb and Cd) were determined using GF-AAS technique, atomic absorption spectrophotometer-Varian Spectra 220, equipped with Varian-GTA 110 graphite furnace. Mercury (Hg) concentrations in samples were analyzed by hydride generation atomic absorption spectrophotometry at 253.7 nm (HG–AAS, cold vapour technique), using Varian Spectra A220-atomic absorption spectrometer equipped with a Varian VGA-77 hydride generator. Total arsenic (As) content was measured by hydride generation atomic absorption spectroscopy HG-AAS, in flame at 197.3 nm, on the same instrument configuration as mentioned above. 3.3. Quality Assurance Appropriate quality assurance procedures were carried out to ensure reliability of the results. Samples were carefully handled to avoid contamination. Glassware was properly cleaned, and the reagents were of analytical grade. Double distilled deionised water was used throughout the study. Reagents blank determinations were used to correct the instrument readings. Recoveries for all analytes ranged from 95% to 102% and the variation coefficient ranged between 4% and 9%. Quality control procedures included the analysis of a standard reference material (BCR No.186). 3.4. Microscopic Examination Kidney samples were fixed in 10% neutral buffered formalin and absolute alcohol for 5 to 7 days, processed using standard histological techniques, and stained with hematoxylin and eosin (HE) for light microscopic examination.