(Portland, OR)  --  Officials say two Portland public-school students who were found to have elevated levels of lead in their blood contracted the toxin from household sources, rather than at school.  The Multnomah County Health Department says the two students were the only ones found to have elevated lead levels among the 519 children and adults who were tested last month at Creston and Rose City Park schools.  The department says the source of the lead exposure was found to have come from the children's homes.  PPS officials reiterate that all schools will dispense bottled water through the 2016-17 school year.