National Australia Bank yesterday opted to disclose the financial impact - which will be $100 million in the financial year ending yesterday, and $60 million a year over the next five years - of hedging arrangements in relation to part of its conduit portfolio.The scale and credit risks of NAB's conduit exposure have been the subject of plenty of conjecture since the bank, at the beginning of August, took a writedown of close to $1 billion on structured finance exposure tied to US mortgage-backed securities.The impact on 2008 earnings at a time of hyper-sensitivity forced the bank to spell this out. According to the bank, "these hedge costs will be accommodated within normal levels of credit hedge spending and will therefore not affect 2009 cash earnings".The hedges in question cover $1.6 billion of synthetic collateralised debt obligations, though the bank did not spell out any more detail on the underlying investments or the credit events that could derail the asset for the bank.NAB said it entered into the hedge with a "large, highly reputable global bank counterparty".