Toxicity assessment of industrial wastewaters reaching dandugan oya, Sri Lanka using a plant based bioassay

Abstract

Industrial waste may contain complex chemical mixtures with potential cytotoxic and genotoxic effects. The Dandugan Oya, a water canal located in the Western Province of Sri Lanka receives industrial waste from multiple sources. In the present study potential toxicity of selected industrial wastewaters reaching the Dandugan Oya, and the downstream water was assessed using a plant based bioassay with onion (Allium cepa L. var. ascalonicum) as the test organism. Of the physico-chemical characteristics tested, temperature, pH, biochemical oxygen demand, chemical oxygen demand, cadmium and chromium levels of the wastewaters collected during three sampling occasions in the year 2012 were within the national tolerance limits specified for the discharge of industrial effluents into inland surface waters. The exposure of A. cepa bulbs to wastewater and downstream water from the Dandugan Oya resulted in the reduction of root growth (24 – 62 %) and mitosis (31 – 55 %), induction of micronuclei (up to 0.6 %), nuclear abnormalities (3 - 14 folds) and chromosomal aberrations (3 - 21 folds) in the root tip meristematic cells compared to those exposed to the control and the upstream water, indicating cytotoxic and genotoxic effects. No significant difference between the control and the upstream water was found in relation to the measured biological effects (p > 0.05). The present study revealed that the tested wastewaters contained cyto-genotoxic contaminants and, the inherent dilution/detoxification capacity of Dandugan Oya during the study period was not adequate to eliminate the toxic effects in the downstream water. In addition to the conventional physico-chemical analyses, inclusion of suitable bioassays as additional assessments in water quality monitoring programmes could alert cyto-genotoxic impacts in wastewater receiving inland surface waters.