Rising home loan arrears and new concerns over concentration risks in its home market have led Standard & Poor's to revise its outlook on the Bank of Queensland's credit rating.S&P said yesterday that it had lowered its outlook on BOQ's rating to negative from stable. S&P affirmed the bank's long-term credit rating of BBB+, and rating of A-2 on short-term debt.One factor cited by S&P for the revised view was "the emergence of asset-quality pressure". While not spelled out by S&P, the bank's February 2011 financial statements show a ratio of impaired assets of 1.31 per cent, up from 0.47 per cent in August 2010.While some of this surge is temporary, the result of the flooding and storms at the start of the year, most of the reduced asset quality reflects deeper problems in commercial loan quality in Queensland, including at the bank."The rating could be lowered if BoQ did not progressively improve its key asset-quality metrics to a level more consistent with similar rated peers over the next 12 to 18 months," S&P wrote.S&P also noted the bank's "meaningful appetite for acquisitions and increased focus on high-return businesses", such as the takeover of merchant finance firm CIT.