Abstract:
Textile industry effluents that are discharged in high volumes into inland waters may contain
complex mixtures of toxic substances that could pose health impacts to biota inhabiting
receiving waters. Conventional effluent quality assessments such as physico-chemical
characterization may not be adequate to evaluate their biological effects. In the present study,
potential toxicity of selected textile industry effluents discharged into Kelani River were
assessed by a plant based bioassay using Allium cepa (onion) as the test organism. Effluents
were collected from the discharging points of two textile industries in three sampling
occasions covering mostly dry periods. Onion bulbs were exposed to the effluents under
undiluted and diluted (1:8) conditions using aged tap water as the dilution media. Toxicity
endpoints were root growth, mitotic index, occurrence of chromosomal aberrations and
nuclear abnormalities. A. cepa root tip cells exposed to undiluted effluents from both
industries caused significant (p<0.05) root growth inhibition, mitotic depression compared to
that of the controls along with a significant (p<0.05) induction in the occurrence of
condensed nuclei at each sampling occasion indicating cytotoxic effects. Moreover, undiluted
effluents significantly (p<0.05) induced chromosomal abnormalities with further induction in
micronuclei in the root tip cells indicating genotoxicity. Exposure of onion bulbs to the 1:8
diluted effluents also showed significant alterations of toxicity end points depending on the
effluent type and sampling occasion. The results revealed that 1:8 dilution was not adequate
to eliminate the cytotoxicity/genotoxicity induced by the effluents completely. Physicochemical
characterization of the effluents showed that heavy metal levels generally comply
with the national tolerance limits for effluent discharge into surface waters. However, color
measurements and chemical oxygen demand levels did not comply with the tolerance limits
in most of the cases indicating that highly oxidizable organics including textile dyes might
have contributed to the observed toxicity. Present study showed the necessity of
incorporating bioassays into effluent monitoring programs for more realistic effluent quality
assessments, considering ecosystem and public health. This study was funded by the National
Research Council research grant 11-11 and National Science Foundation equipment grant
RG/2011/EQ/16.
