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 recomm ended as cheap supplement in animal feed. It has been incorporated into cat tle and poultry feed. It is well known that sewage of purely domestic origi n is also contaminated with heavy metals, pesticides, and other organic pol lutants. A study was undertaken to determine the toxic effects of heavy met al-contaminated domestic sewage sludge on young male Wistar rats by supplem enting 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 (ca dmium) mg/g of dry sludge, by analysis by atomic absorption spectroscopy. T he 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 succina te dehydrogenase (SDH) were significantly low in all the sludge-supplemente d diet-fed (SSDF) rats. Similarly, serum lactate dehydrogenase (LDH) and mu scle SDH activity were also significantly reduced in the SSDF rats. On the other hand, liver and muscle LDH, serum and liver aspartate aminotransferas e, and serum and muscle alkaline phosphatase activities were significantly higher in all the SSDF animals. Brain and muscle acetylcholinesterase activ ity was significantly high in all the SSDF groups. This study indicates tha t even though the sludge is a rich source of nitrogenous matter, its supple mentation in poultry and animals feed should be done with caution. Otherwis e, the contaminants found in the sludge will biomagnify in the food chain a nd lead to various toxicological hazards. (C) 1999 Academic Press.