Abstract:
Assessing toxic hazards associated with polluted
riverine ecosystems is essential for the development of effective
strategies for their management. The present study explored the
combined utility of bioassay responses of the plant, Allium cepa
and surface water physico-chemical characteristics to assess
the toxic hazards of an industrial waste receiving canal system
located in the lower catchment of the Kelani River basin,
Sri Lanka. Surface water samples from seven sites, viz. Maha
Ela upstream (Site A), Manikagara Ela (Site B), Manikagara
Ela - Maha Ela confluence (Site C), Maha Ela downstream (Site
D), Maha Ela - Kelani River confluence (Site E), River downreach
(Site F) and upper-reach (Site R) were analysed on three
occasions in 2015 covering dry and wet periods. Irrespective of
the sampling periods, exposure of A. cepa bulbs to water from
the Sites B, C, D and E resulted in root growth retardation and
mitosis depression (p < 0.05) in the root meristem signifying
toxic/cytotoxic hazards. Occasional micronuclei evolution and
nuclear bud induction were also found in the root cells exposed
to Site B and C samples indicating genotoxicity. Toxic hazards
were somewhat reduced towards down-reach of the river, which
may be associated with self-depuration effects. The principal
component analysis based on surface water characteristics and
bioassay responses revealed clear separations of Sites B and C
from the other sites. The results revealed that water quality of
Manikagara Ela and Maha Ela needs improvements considering
toxic hazards to the riverine ecosystem and human health
