# Atomic Spectroscopy-Based Analysis of Heavy Metals in Seaweed Species
## 2 Atomic Spectroscopy-Based Heavy Metal Analysis Methods for Seaweed
### Atomic Emission Spectroscopy
#### 2.3.1 Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES)
The cleaned seaweed samples were dried, ground, and ashed at 350 \({}^{\circ}\)C. The resulting ash was dissolved in 50% HCl on a hotplate and subjected to ICP-OES analysis for the determination of concentrations of Cd, Cu, Pb, and Zn. The metal concentrations followed the pattern: Zn \(>\) Cu \(>\) Pb \(>\) Cd. Although the metal concentrations of some species at the first two sites were much higher than background levels, the third site showed metal levels close to the clean sites, suggesting that the metal pollution caused by the Cu/Zn mine did not extend to outside the estuary area. Besides proposing future monitoring of seaweed diversity and tissue chemistry in this area, the authors also brought up the possibility of utilizing seaweeds to remediate metal pollution. In a comprehensive study by [PERSON] et al., 295 dried seaweed samples (142 red seaweeds and 153 brown seaweeds) were collected at four sites in Zhejiang, China, and analyzed for concentrations of As, Cd, Cr, Cu, Hg, Ni, Mn, Pb, and Se to address food safety concerns [38]. Quantities of 0.5-2 g of each sample were digested in 6 mL HNO\({}_{3}\) at 180 \({}^{\circ}\)C for 30 min in a microwave digestion system. The digested solutions were evaporated to 0.5 mL, further diluted to 5 or 10 mL with DI water, and then analyzed for metal concentrations with ICP-OES. Two CRMs (GBW 10023 and GBW 08517) were used as quality controls, and the authors deemed the analysis results acceptable, since the mean recoveries for CRMs were between 82.6 and 99.4%. Considering all seaweed samples, the metal concentrations were ordered in this way: Mn > As > Cu > Cr > Ni > Cd > Se > Pb > Hg, though red seaweeds and brown seaweeds showed significant concentration differences for some of the metal elements. When comparing the four geographical origins, Hg and Pb showed significant differences. Pairwise association was examined, and only a weak correlation was found between the following pairs: Ni-Cr, Mn-Cu, and Mn-Pb. Food safety was assessed with targeted hazard quotients (THQs) and hazard indices (HIs), which both indicated low risk to human health, assuming 5.2 g/capita/day consumption in China. The authors also pointed out the uncertainty of health risk assessments due to potential interactive effects among multiple metals as well as possible loss of elements caused by the food preparation process. Five species of green seaweeds were collected along the Southeast Coast of India and analyzed to assess their nutritional values [76]. A quantity of 0.5 g of dried sample was digested in two microwave cycles: in 2 mL H\({}_{2}\)O\({}_{2}\), 8 mL purified concentrated HNO\({}_{3}\), and 2.0 mL HF for the first cycle; then 2.0 mL purified concentrated HNO\({}_{3}\) and 2.0 mL HClO\({}_{4}\) were added before the second cycle. The selection of microwave power and time was optimized to ensure complete dissolution of the different types of tissues [77]. The resulting digests were evaporated and dissolved in 2.5 mL of concentrated HNO\({}_{3}\) and diluted to volume with double-distilled water (DDW). The samples were then measured via ICP-OES for metal concentrations (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). The results showed that the metal concentrations varied in different species. The possibility of utilizing concentration profiles of some major and trace elements to characterize edible seaweed harvested from Northwestern Spain was studied by [PERSON] et al. [6]. Thirty-five edible seaweed samples were supplied by a local manufacturer. For the dry seaweed samples, 100 g were oven-dried, cut by hand, pulverized, and sieved, while canned seaweed in brine was lyophilized then pulverized. Dried powder samples were further subjected to a microwave-assisted acid digestion method: 8 mL of concentrated HNO\({}_{3}\) and 2 mL concentrated H\({}_{2}\)O\({}_{2}\) were added to 0.2 g of powdered seaweed samples, followed by a timed program of microwave irradiation.