Bacterial and chemical pollution level of the river Turag, Gazipur, Bangladesh

Abstract

The river Turag is the upper tributary of the river Buriganga in Bangladesh.
Aerobic heterotrophic bacterial count of the river in nutrient agar (NA) and
peptone yeast extract glucose (PYG) agar media ranged from 2.91 × 105 to 27.5 ×
105 cfu/ml and from 1.09 × 105 to 19.3 × 105 cfu/ml, respectively. Enteric and
related bacterial count on MacConkey agar was between 0.88 × 103 and 20.8 × 103
cfu/ml. Out of 91 isolated bacterial isolates, 30 were selected based on their
distinctive colony morphology for detailed study. Among these, 16 were Grampositive
(53%) and 14 were Gram‐negative (47%). Bacillus was dominant among
the Gram‐positive isolates (69%). The remaining were Brochothrix thermosphacta
(6%), Caryophanon sp. (19%) and Renibacterium salmoninarum (6%). Fourteen
Gram‐negative, enteric and related isolates were identified as Plesiomonas
shigelloides (43%), Alcaligenes denitrificans (22%), E. coli (14%), Proteus (14%) and
Citrobacter freundii (7%). Biological oxygen demand (BOD) and chemical oxygen
demand (COD) values were about 9 and 5‐fold higher than standard values
whereas dissolved oxygen (DO) of the river was found to be six times less than
the standard value. The maximum average TDS, conductivity and turbidity was
recorded during the summer season as 441.75 ± 15.52 mg/l, 858.25 ± 19.57 μS/cm
and 79.53 ± 6.49 NTU, respectively. Chemical contents viz. sulphate, chloride and
fluoride were found to be satisfactory from pollution point of view. Both BOD
and COD values along with the abundance of different heterotrophic and enteric
bacteria clearly indicated that the river Turag was polluted with organic,
chemical and bacterial pollutants.