Dravidian influence on Sanskrit

[Samar Abbas]

Dear List Members,

  I read somewhere that "the composition of Sanskrit vocabulary is
(Classical Sanskrit)

   - 70 % non-Aryan, of which
     > 40 % Dravidian
     > 30 % Prakrit and only
   - 30 % Vedic "

 Unfortunately, no reference was given. Could anybody provide some
references supporting or opposing the fractions given above?

Thanks.
Samar