Toxicologic studies with swine fed corn grown on municipal sewage sludge-amended soil [Heavy metals]

Over a 3-yr period 336 MT/ha of dried sewage sludge, from a municipal waste treatment plant, was applied in liquid form to land subsequently used to grow corn. The sludge contained 115 mg Cd, 4,200 mg Zn and 538 mg Ni/kg dry matter and comprised the solids remaining after treatment of the waste waters of approximately 260 industries as well as domestic users. Corn grain harvested from the plot amended with sewage sludge (SA corn) or corn grown on a plot without sludge addition (control corn) was fed to a total of 56 pigs to determine the effect on growth performance and parameters indicative of toxicity. Each treatment consisted of seven pens of four pigs each with an average initial weight of 17.6 kg. The growth trial was terminated when pigs weighed approximately 90 kg. No differences were observed between treatment groups for average daily gain, feed: gain ratio or daily feed intake. Higher (P less than .01) concentrations of Cd, Ni and Zn were found in SA corn compared with the control corn. This resulted in higher (P less than .01) concentrations of Cd in kidney and liver and Ni in kidney of pigs fed SA corn as compared with pigs fed control corn. No significant differences were observed in Cd or Ni concentrations in muscle or in hepatic microsomal mixed-function oxidase (MFO) activity and liver:body weight ratios, which is indicative of the absence or low levels of organic toxicants in SA corn. In addition, no significant treatment effects were observed when corn, feces and urine samples were evaluated for the presence of mutagenic substances. Histopathologic analysis of various tissues for lesions demonstrated that pigs fed SA corn were not adversely affected.