A Study of Toxic Effects of Heavy Metal Contaminants from Sludge-Supplemented Diets on Male Wistar Rats

Activated sludge is a rich source of nitrogenous matter and has been recommended as cheap supplement in animal feed. It has been incorporated into cattle and poultry feed. It is well known that sewage of purely domestic origin is also contaminated with heavy metals, pesticides, and other organic pollutants. A study was undertaken to determine the toxic effects of heavy metal-contaminated domestic sewage sludge on young male Wistar rats by supplementing dehydrated activated sludge in their diet at concentrations of 5, 10, 15 and 20%. The sludge was found to be contaminated with 1.820 (zinc), 0.273 (nickel), 0.017 (lead), 0.053 (copper), 0.006 (chromium), and 0.005 (cadmium)mg/g of dry sludge, by analysis by atomic absorption spectroscopy. The toxic effects of sludge-supplemented diets on individual groups of rats were assessed by assaying various enzyme activities in serum, liver, muscle, and brain. Levels of serum and liver alanine aminotransferase and succinate dehydrogenase (SDH) were significantly low in all the sludge-supplemented diet-fed (SSDF) rats. Similarly, serum lactate dehydrogenase (LDH) and muscle SDH activity were also significantly reduced in the SSDF rats. On the other hand, liver and muscle LDH, serum and liver aspartate aminotransferase, and serum and muscle alkaline phosphatase activities were significantly higher in all the SSDF animals. Brain and muscle acetylcholinesterase activity was significantly high in all the SSDF groups. This study indicates that even though the sludge is a rich source of nitrogenous matter, its supplementation in poultry and animals feed should be done with caution. Otherwise, the contaminants found in the sludge will biomagnify in the food chain and lead to various toxicological hazards.