After 24 hrs, the shaker was stopped and the tubes and their contents were centrifuged at 3000 rpm for ten min-utes. The resulting clear supernatant in each tube was transferred into another labeled clean centrifuge tube. All the labeled centrifuge tubes with their liquid contents were sent to PACE Analytical Services, Inc for lead ana- lysis using EPA Method 6010. Note that PACE Analyti-cal Services, Inc. is a commercial environmental labora- tory that is accredited in accordance to the National En- vironmental Laboratory Accreditation Conference (NE- LAC).