Though the reasons 13 U.S. banks failed in April varied, New York-based Trepp LLC said lending in the commercial real estate arena represented the largest source of nonperforming loans on those financial institutions’ balance sheets. National Real Estate Investor reported that three of the bank failures took place in the Midwest – one each in Illinois, Michigan and Minnesota. Among the 13 failed banks last month, commercial real estate loans accounted for $599 million, or 79 percent, of the $759 million in nonperforming loans. Construction and land loans made up $346 million, or 46 percent, of the nonperforming loans. Trepp said the failures represented the highest monthly total since July 2010.