Potential androgenic effects of urban sewage sludge in male rats

The processing of urban sewage by waste water treatment plants produces a pasty mixture of complex organic materials (microorganisms, plants, chemical contaminants) and inorganic (minerals, metals, etc.) known as sewage sludge (SS). Facing the possibility of using this mixture for agricultural soil enrichment this study was designed to assess in vivo the potential endocrine disrupting activity of a SS sample using pubertal male Wistar rats or weanling rats in a modified Hershberger assay. Pubertal male rats (42-days old) were exposed ad libitum through adulthood (98-days old) to a diet containing 0, 2500, 5000, 10000 or 20000 ppm of SS. In another study, weanling male rats (21-days old) were treated daily for 10 d by gavage with flutamide (anti-androgenic positive control), testosterone propionate s.c. (androgenic positive control), or SS at 10000 and 20000 ppm in the diet. Despite no alterations in body and reproductive organs weights, diet consumption or sperm count, SS treatment impaired the sperm quality of pubertal rats, as indicated by a decreased proportion of sperm showing progressive movement. No evidence of SS-induced adverse effects was found in weanling rats. The treatments did not induce direct androgenic effects in both life periods studied in rats. However, the observed impaired sperm motility in the SS-treated pubertal rats raises some concern about the use of this material as soil additive, or in other applications where human and animals are potentially exposed.