Subchronic Toxicity Evaluation of a Treated Urban Sewage Sludge

Abstract

Disposal of tons of sludge produced daily by sewage treatment plants in large cities is a serious problem. Because recycling and application in agriculture have been proposed, the Brazilian National Environmental Council (CONAMA, 2006) issued a legal norm that regulates the use of the sewage sludge (SS) in crops. Due to the complex chemical nature of such products, characterization by analytical methods for health and environmental risk assessment has severe limitations. To overcome such limitations, it is necessary to (1) assess the toxicological potential of SS and (2) identify possible adverse effects in vivo in order to provide critical information for future environmental regulations. The present study was conducted to determine the potential toxicity of SS obtained from a representative urban treatment plant located in the São Paulo State, Brazil. Male and female Wistar rats were fed ad libitum a pelleted diet containing varying amounts of SS. No relevant clinical, hematological, urinary, or gross organ morphological alterations were observed in both genders of rats orally exposed to SS at up to 3.8 g/kg/d for 90 d. Sewage slude produced increased incidence of centrilobular hepatocyte hyperplasia at the high dose and significantly increased aspartate aminotransferease (AST) activities at all doses in both genders. Although the present data indicate some liver involvement, these alterations were considered adaptative and not toxicologically relevant, as the responses were relatively mild, not dose dependent, and no other parameters were markedly affected. The present results may contribute to the establishment of protocols for potential usage in SS agricultural soil application.

This study was granted by the State of São Paulo Agency for Support of Research (FAPESP), the Center for the Evaluation of the Environmental Impact of Human Health (TOXICAM), at the State University of São Paulo (UNESP), and by the National Council for Technological and Scientific Development (CNPq), Brazil. The authors also thank Paula Regina Pereira Silva for biomedical technical help and CETESB (Companhia de Tecnologia de Saneamento Ambiental) for providing the samples and related data of the sewage sludge samples tested in this study, as well as information about the sewage treatment process. This article does not necessarily reflect the views of CETESB and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.