bp_activity_new_at_mention_permalink( $link,  $item_id,  $secondary_item_id )

function bp_activity_new_at_mention_permalink( $link, $item_id, $secondary_item_id ) {

	$activity_obj = new BP_Activity_Activity( $item_id );

	if ( 'activity_comment' == $activity_obj->type ) {
		$notification = BP_Notifications_Notification::get(
			array(
				'user_id'           => bp_loggedin_user_id(),
				'item_id'           => $item_id,
				'secondary_item_id' => $secondary_item_id,
				'component_name'    => 'activity',
				'component_action'  => 'new_at_mention',
			)
		);

		if ( ! empty( $notification ) ) {
			$id   = current( $notification )->id;
			$link = add_query_arg( 'crid', (int) $id, bp_activity_get_permalink( $activity_obj->id ) );
		}

	}

	return $link;
}