The more velocity and turbulent mixing, the quicker the dispersion.  If the stream has large pools relative to flow rate, longitudinal transfer is much slower and dilution greater.    Lateral mixing can be slow, but generally after several meander bends, sediment plumes from one tributary are not as pronounced to several more meanders, concentration differences eventually not evident.  The Rosgen (www.wildlandhydrology.com) channel type as well as flow conditions for that stream are factors in how quickly pollutants move, are dispersed or in some instances delayed and stored.  Pollutants that adhere to sediments will probably have a strong relationship with how sediments move.  Interesting, complex subject that likely one size does not fit all, ie depends on circumstances.

Respected Sir, as per my knowledge about contaminated sediments, contaminants are adsorbed in sediments rather being absorbed, does not the meander currents try to break the adsorption bond?

Yes my fault, adsorbed is correct if attached to particle surface, and both adsorbed and absorbed is probably  more appropriate for soils.  But in sediments, possibly both too may exist, depending on the pollutant, as some do not adsorb well and if detained in sediment, just being held in solution, not held stronly as adsorbed or absorbed.  Some pollutants adsorb more stronly than others to sediment particles, some extra fine sediment particles stay in suspension and do not settle, while other sediments tend to settle in point bars, on flood plains if flood or in stream coarse substrates and pools.  I do not know what to tell you about meander currents and the breaking or not breaking of the pollutant bond forces.  If i had to guess, I would say it depends on the strength of the bond relative to the stream velovity and substrate friction forces as the particle moves or tumbles along..  My first answer was aimed more specifically at dissolved pollutants or what might be suspended pollutants, than pollutants transported by sediment, but definately that is another type to consider.  The instream velocities and circulation pattern is complex as outside of bends erode and inside deposit.  I found some good papers a while back on shear forces on the internet.  One was a flume study and I will try to find and send when I am in my computer.

Thanks a lot sir for your reply.