Citigroup Inc., the third-biggest U.S. bank by assets, said first-half costs at a unit holding some of the lender’s most toxic loans and securities multiplied by almost 10 times from a year ago on higher legal expenses, Bloomberg News reported yesterday. The Special Asset Pool’s operating expenses climbed to $1.25 billion for the first six months of the year from $129 million in the same period last year, according to figures on the New York-based bank’s website. That’s more than double the unit’s $619 million in total costs for 2012 and 2011 combined. Swelling expenses in the unit, one of three that house distressed and unwanted assets in the Citi Holdings division, point to the continuing legal costs facing Chief Executive Officer Michael Corbat.