Substrate Station Pre-monsoon Monsoon Post-monsoon Overall year River water-High tides S1 BDL BDL BDL BDL S2 BDL BDL BDL BDL S3 0.002 ± 0.001b BDL BDL 0.001 ± 0.001a S4 0.004 ± 0.000aA 0.004 ± 0.001aA 0.011 ± 0.002aB 0.006 ± 0.005b River water-Ebb tides S1 BDL BDL BDL BDL S2 BDL BDL BDL BDL S3 0.001 ± 0.000aA 0.002 ± 0.001aA BDL 0.001± 0.001a S4 0.001 ± 0.000aA 0.004 ± 0.001aB 0.014 ± 0.001aC 0.006 ± 0.006b River water (Pooled) S1 BDL BDL BDL BDL S2 BDL BDL BDL BDL S3 0.002 ± 0.001aA 0.001± 0.001aA BDL 0.001 ± 0.001a S4 0.002 ± 0.001aA 0.004 ± 0.003bA 0.012 ± 0.004bB 0.006 ± 0.005b River sediment S1 0.057 ± 0.005bA 0.026 ± 0.007cB 0.011 ± 0.002aC 0.031± 0.02ab S2 0.040 ± 0.005bA 0.011 ± 0.005cB 0.010 ± 0.001abB 0.02 ± 0.01a S3 0.083 ± 0.010aA 0.156 ± 0.021bB 0.007 ± 0.001bC 0.08 ± 0.06bc S4 0.085 ± 0.005aA 0.260 ± 0.014aB 0.002 ± 0.000cC 0.11 ± 0.11c

Table 2: Mean concentrations of total mercury (THg) in river water (μg ml-1) and river sediment (μg g-1) at Bidyadhari estuarine stretches. Kulti-Ghushighata (S1); Malancha (S2); Kanmari (S3); Dhamakhali (S4); BDL- Below Detection Level Superscripts like a, b, c in same columns were significantly different (P<0.01) in Tukey’s HSD mean separation test Superscripts like A, B, C in same rows were significantly different (P<0.01) in Tukey’s HSD mean separation test.