How to convert casbah mongodb list to json in scala / play

I'm learning scala and mongodb at present and using the play! framework, so I'm making all sorts of mistakes as I get my head around things. Currently I have a scala object that returns a list of database objects returned from a mongodb query via casbah as follows;

object Alerts  {

   def list() : List[DBObject]= {

        val collection = MongoDatabase.collection;
        val query = MongoDBObject.empty
        val order = MongoDBObject("Issue Time:" -> -1)
        val list = collection.find(query).sort(order).toList
        list
   }

... }

Elsewhere in my code I wish to output the List of objects in Json - so I have;

  val currentAlerts = Alerts.list()

What I'd like to write is something like;

  val resultingJson = currentAlerts.toJson 

But when I do this, I understandably get the following error;

  value toJson is not a member of List[com.mongodb.casbah.Imports.DBObject]

My question is - what's the right way to convert a List of com.mongodb.casbah.Imports.DBObject into Json for output?

EDIT:

For clarity, what I really want to do is the equivalent of

val listInJson = collection.find(query).sort(order).toJson

In the same way that I CAN write

val listAsString = collection.find(query).sort(order).toString