URI::QueryParam doesn't use anything for query parameters, it just passes it's data on to URI, which lets you choose how they are delimited...

use URI;
my $u = URI->new( "http://www.example.com/" );
$u->query_form( { foo => 1, bar => 2 }, ';' );
print "$u\n";
[download]

And if you just want the query string, you can get it from $u->query.