A 30-City Survey of Selected Metals in Biosolids Generated in the Midwestern United States

The concentrations of several heavy metals (Arsenic, Cadmium, Copper, Lead, Nickel, Selenium, and Zinc) in biosolids were measured at 30 randomly selected publicly owned treatment works (POTWs) located in the Midwestern United States. Two reference laboratories using standardized and federally accepted analytical protocols provided the analyses. The sampling, transport, analysis, and reporting procedures were guided by a project review group consisting of volunteers from the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC), the Chicago-based United States Environmental Protection Agency, Region 5 (USEPA-Region 5), and other contracted professionals. The assessment of accuracy of POTW results reported to USEPA-Region 5 is based on the results of each POTW's metals analyses of their biosolids as compared with the combined USEPA- Region 5's Central Regional Laboratory (CRL) and MWRDGC Stickney, Illinois POTW Laboratory (Stickney Laboratory) analyses. None of the 11 POTW results for Selenium were within the 3 σ limit. Zinc and Lead were acceptable 21 of 25 times; Arsenic and Cadmium were acceptable 14 of 21 and 24 times, respectively; Copper and Nickel were acceptable 16 and 12 of 25 times, respectively.Using the statistical tests on grouping, only the measurement of Lead and Zinc fell into Group 1 (i.e., POTW results were within acceptance limits above 67% of the time). The measurement of Arsenic, Cadmium, Copper, and Nickel fell into Group 2 (above 33% but less than 67%), while the measurement of Selenium fell into Group 3 (below 33%). The authors recommend additional analytical methods development work for Selenium. Although few analytical shortcomings were observed, over 95% of POTWs in the Midwestern United States since 1997 have consistently met the Part 503 risk-based metals ceiling limits. The overall results indicate that the success of the industrial pretreatment program in reducing the metals content of biosolids well below levels of concern for the safe use and disposal of biosolids in the environment.