Control blanks were also digested. Final extract pH ranged from 4.79 to 6.16. Extracts were digested and acidified below pH 2.0 with nitric acid for sample preservation. Samples were stored at 4 C until analysis. Samples were analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES, iCAP 6000 Thermo Scientific).