I assume you are making a tomato topping for bruchetta ;. In this case you can use dried basil.Take boar_d_laze's advise and start with a little and adjust the taste as you go along. Too much of any dried herb can taste very nasty and I don't want you to waste any tomatoes.
It is my understanding that the harvesters purge the clams at the same location of harvest in the same seawater they were grown in. I wish I could tell you more about how they actually do it.
Does anyone know ?