Abstract:
Buriganga, Sitalakhya and Turag are some of the polluted rivers around Dhaka city.
Encroachment, disposal of untreated domestic and industrial wastewater and dumping
of solid wastes have degraded the overall quality of the rivers. The present study
investigated the extent of pollution of sediments of these rivers.
Sediment samples have been collected from five locations of Sitalakhya river and
available data from previous studies on ten locations of Buriganga and Turag river
have been used for sediment analysis. Samples were collected in April 2011 from
Sitalakhya river and analyzed for the concentrations of Cr, Pb, Zn, Cu and Cd using
atomic absorption spectrophotometer (AAS). Aqua regia digestion has been
performed for the dissolution of the sediment samples prior to the determination of
heavy metals.
The metal ion concentrations in the sediment samples have been compared with
USEPA sediment quality guidelines. Based on this comparison, the sediment samples
have been characterized as “heavily polluted”, “moderately polluted” and “not
polluted”. The sediments of Buriganga river assessed in this study have been found to
be highly polluted with respect to Cu, Pb and Zn; not polluted to moderately polluted
with respect to Cd; moderately to highly polluted with respect to Cr. The sediments of
Sitalakhya river assessed in this study have been found to be unpolluted to moderately
polluted with respect to Cr; moderately to heavily polluted with respect to Cu; not
polluted to moderately polluted with respect to Zn; not polluted to heavily polluted
with respect to Pb; not polluted with respect to Cd. The sediments of Turag river
assessed in this study have been found to be moderately to highly polluted with
respect to Cr, Cu and Zn; not polluted with respect to Pb and Cd.
Toxicity characteristics leaching procedure (TCLP) test for sediment samples have
been performed for the heavy metals Pb, Cd, Cr, Cu and Zn. The metal concentrations
in the TCLP samples have been found to be well below the regulated level as per
USEPA. Therefore, the sediments are not likely to readily leach these metals in the
water.
A major objective of this study was to assess suitability of different methods for
assessment of sediment quality. The methods assessed included metal pollution index,
marine sediment pollution index, toxic unit, geo-accumulation index, PIN index,
potential ecological risk index, contamination factor, degree of contamination,
pollution load index, mean sediment quality guideline quotient, Pearson’s correlation,
principal component analysis and cluster analysis. The methods differ in a number of
ways, especially with respect to data requirement. The suitability of different methods
in the context of Bangladesh has been assessed utilizing the sediment quality data
used in this study.