INDIANAPOLIS (AP) _ A handful of Indiana and Michigan residents concerned about Lake Michigan's water quality are calling on Indiana regulators to require BP PLC to cut its mercury discharges into the lake.
 
  Four residents from northern Indiana and adjacent southwestern Michigan visited the Indiana Statehouse on Thursday to deliver a petition to Gov. Mike Pence's office signed by about 450 people calling for tougher mercury limits on BP's Whiting, Ind., refinery. They were joined by two Indiana members of the Sierra Club.
 
  The petition calls on Indiana and federal regulators to “act aggressively to protect our nationally treasured Lake Michigan'' by requiring BP to reduce its mercury emissions.
 
  The oil giant received Indiana's permission in 2011 to discharge mercury levels into the lake nearly 20 times the federal Great Lakes standard.