Metal concentrations of seaweed Ulva sp. and mussels Mytilus sp. from October 2022 - April 2023 from Penn Cove, WA.

Freeze-dried and ground samples were weighed (0.2-0.25 g) and digested using a closed-vessel microwave digestion system (Milestone ETHOS 1 Series) using the “Beech Leaves” protocol (USEPA, 1996) for seaweed. Samples were diluted to 50 mL with nanopure water. For ICP-MS analysis, 2.78 mL of the diluted seaweed digestate was further diluted to 10 mL to achieve acidification of 5%. Blank solutions and certified reference materials were prepared using the same methods. All samples were analyzed using ICP-MS (Agilent 7900), with an inline internal standard and five replicates per isotope (EPA method 200.8). Elemental concentration was expressed in mg element/kg tissue dry weight. A calibration curve was made with 10 standards of different concentrations, ranging from 0-1000 ppb (IV Stock 50), with blanks and spiked samples evenly distributed throughout tissue samples to quantify instrument drift. All values are presented in mg/kg DW. ND: values below detection DW: Dry Weight