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.