Cytogenotoxicity screening of untreated hospital wastewaters using the Allium cepa test

Abstract

Cytogenetoxicity of University Teaching Hospital (UTH) wastewaters was investigated using the Allium cepa assay. Heterogeneous samples of untreated wastewaters from four sections of the hospital comprising the laboratories, mortuary, laundry and the kitchen were collected twice daily for six months and designated as complex mixtures. Physico-chemical parameters of the wastewaters were determined in accordance with standard methods. Onions root growth inhibition test was used to assess the toxic status of the wastewaters, while cytogenotoxicity was measured by microscopic investigation of the chromosomal aberrations. Onion bulbs were exposed to 1%, 5%, 10% 25% and 50% concentrations of the effluent samples in the dark for 72 hours before measuring the root lengths of the onion bulbs. Results of BOD, COD, TSS and pH showed levels above the maximum permissible limits for discharge of hospital effluent into the environment. There was inhibition of root growth of A. cepa in a concentration dependent pattern compared to control. An effective concentration EC₅₀ of 8.20% and 9.1% was deduced for the 1^st and 2^nd samples respectively. Various morphological defects of the onions roots were also observed. Cytological analysis of root tips after 48 hrs exposure to the different concentrations showed reduction in frequency of mitosis in the meristematic zones of the root tips. Various types of structural chromosomal aberrations and micronucleus were induced in the treated cells. The University Teaching Hospital wastewaters samples are believed to contain potent toxic substances that provoked the cytogenotoxic responses herein and should be treated before discharge into the environment.

Keywords: Cytogenotoxicity screening, hospital wastewaters, Allium test