Major and trace element distributions in compost feedstocks. Figure 2a illustrates the geochemical variation in calcium and silica, the major element constituents in these matrices. Each source stream has a unique major element signature. Figure 2b shows that Pb and Zn are correlated within these source streams with the biosolid matrix displaying a unique and characteristically higher Zn signature. (Note, samples marked with asterisks are Boston biosolid data points from this study while the rest of the biosolid data is from Northeast EPA TNSSS data (2009). DOI: https://doi.org/10.1525/elementa.238.f2