# Atomic Spectroscopy-Based Analysis of Heavy Metals in Seaweed Species
## 2 Atomic Spectroscopy-Based Heavy Metal Analysis Methods for Seaweed
### Atomic Mass Spectrometry
Quantities of 0.5 g of homogenized and powdered samples were mineralized with the standard microwave-assisted acid digestion method with 6 mL HNO\({}_{3}\) and 2 mL H\({}_{2}\)O\({}_{2}\). Single isotopes were selected for all the elements, except for Pb, where, in order to improve sensitivity, the signals from three isotopes were summed. Among these trace elements, As, Co, Cr, Cu, Fe, Mn, Ni, Se, V, and Zn were analyzed in DRC (dynamic reaction cell) mode. Methane gas was used as a reaction gas for Se, and ammonia gas was used as a reaction gas for the other elements analyzed in DRC mode. Calibration was carried out with the standard addition approach, and five addition levels were selected per element to ensure linearity. Method validation was performed with a CRM, while for elements without certified values, spike recovery was determined with the addition of standard monoelement solutions. The authors found that the trace element profiles of the samples mainly depended on taxonomic species and, to a lesser extent, on geological origin as well. Comparisons of the measured values and tolerable levels of some toxic elements were made, and, alarmingly, 26% of the samples were found to be non-compliant with respect to Cd. In addition, pairwise correlation of the trace elements was also looked into with statistical analysis; a strong correlation was observed between Sn-Fe and Cr-Ni. However, comparisons with existing data could not be made due to the lack of such studies. In a study by [PERSON] et al., seaweed samples were collected at three sites along the coast of the Northwestern Mediterranean Sea [4]. The three sites varied in their shipping traffic, industrial activity, and population densities. Quantities of 1.0-1.5 g of samples were digested in a mixture of 7 mL HNO\({}_{3}\) and 1.5 mL H\({}_{2}\)O\({}_{2}\). After microwave-assisted acid digestion of the samples, the ICP-MS method was used to measure multiple trace metal contents (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se, Sn, TI, V, and Zn), while Hg contents were measured using a direct mercury analyzer. Calibration was performed with an external multi-element standard solution, with rhodium and germanium as internal standards. The samples were run in CCD mode (H\({}_{2}\) as reaction gas) and KED mode (He as collision gas). The results showed significant intersite differences between most of the trace metals, suggesting that growth site conditions play an important role in the degree of trace metal accumulation in seaweed. The authors also compared the trace metal levels with the maximum levels allowed for animal feed and human nutrition. While the toxic elements As and Cd were below the set limit, Hg concentrations were close to the maximum limit in some samples of brown and red alga, and Pb exceeded the maximum limit in most species from site 1. However, the authors concluded that seaweeds could be safe as animal feed since they are usually diluted with other feed sources. On the other hand, some seaweed species from these sampling sites could pose potential risks for human consumption since they contain considerable amount of some trace elements, such as Fe and Pb. In addition, comparisons were made with other Mediterranean areas. While most data were comparable to those from other studies, not surprisingly, seaweed samples from site 1, which had the highest shipping traffic and industrial activity, contained higher contents of the trace metals Pb, Cr, Fe, and Zn. To assess risk and provide regulatory guidelines for seaweed consumption in Europe, where seaweed is growing in popularity as a healthy and sustainable food source, seven species of seaweed were cultivated and harvested in Denmark [3]. ICP-MS was used to analyze the levels of As, Cd, Hg, and Pb. In particular, inorganic As was separated from total As using HPLC prior to ICP-MS analysis, though these data were not available at the time of publication.