I am not aware of any authentic research which supports this claim.
Also, it does not coincide with what creationist scientists would currently anticipate based upon our understanding of the impact of the Flood on radiocarbon.
For this reason special precautions need to be exercised when sampling materials which contain only small amounts of radiocarbon.
Reports of young radiocarbon ages for coal probably all stem from a misunderstanding of one or both of these two factors.
If this water is in contact with significant quantities of limestone, it will contain many carbon atoms from dissolved limestone.
Since limestone contains very little, if any, radiocarbon, clam shells will contain less radiocarbon than would have been the case if they had gotten their carbon atoms from the air.
This gives the clam shell an artificially old radiocarbon age.