# Atomic Spectroscopy-Based Analysis of Heavy Metals in Seaweed Species
## 2 Atomic Spectroscopy-Based Heavy Metal Analysis Methods for Seaweed
### Atomic Absorption Spectrometry (AAS) Techniques
#### 2.2.1 Flame Atomic Absorption Spectrometry
The study suggested that the daily consumption of the studied seaweed should be in the range of 38-52 g daily value (DV). [PERSON] et al. digested seaweed samples from the Bay of Bengal using aqua regia (0.5 g in 5 mL) gently heated and diluted to 50 mL with deionized water (DI) [43]. In the reported investigation, the heavy metal accumulation of seaweeds was in the following order Mn > Pb > Cd in the six studied seaweed species. Zn was observed only in free-floating brown seaweed _S. swartzi_, whereas Cu and Cr were not detected in any of the samples. The study concluded that the variability of metal accumulation could be the result of competition between the metals to bind with polysaccharides to different extents and also depended on the color of the seaweed. In another reported study, selected brown (_Sargassum_ sp.) and green (_Ulva_ sp.) seaweeds from coastal areas of Rameshwaram, Tamil Nadu, India, were digested using various concentration of acids: a 5:1 mixture of HNO\({}_{3}\): HClO\({}_{4}\), a 3:1 mixture of HNO\({}_{3}\): HClO\({}_{4}\), and a mixture of 5:1:0.5 of HNO\({}_{3}\): HClO\({}_{4}\): H\({}_{2}\)SO\({}_{4}\)[22]. In the two studied seaweed types, metal content sequences were observed to follow the trend Fe > Zn > Cu > Cd, and Pb was not detected. This study found that some local seaweeds may be used as potential biomonitors as well as absorbents of cadmium from industrial effluent. In the investigation by [PERSON] et al., eleven seaweed species from the coastline of Hormuzgan Province in Iran were analyzed using a flame atomic absorption spectrometer with a deuterium background corrector [18]. The accuracy of the analysis was certified by the inclusion of DORM-3 (Fish protein) (National Research Council of Canada) reference material. In this study, the concentrations of heavy metals in eleven seaweed species from thirteen locations decreased in the following order: Fe > Zn > Pb > Ni > Cu > Cd. The researchers showed that variation in the accumulation of metals in seaweeds depends on the type of polysaccharides present in the cell walls as well as the different electronegativities of the elements. They observed more uptake of the metals with higher electronegativity values (e.g., Fe, Ni, and Cu) compared to the other metals with lower values (e.g., Cd). The study validated the use of seaweed for biomonitoring of polluted marine environments. Red seaweeds belonging to twenty-six genera from coastal areas of Karachi, Arabian Sea, were collected over a period of three years by [PERSON] et al. [60]. Quantities of 1 g of each sample were digested in a mixture of HNO\({}_{3}\) (4 mL) and HClO\({}_{4}\) (2 mL) in Teflon vessels at 80 \({}^{\circ}\)C on a hot plate. After digestion and evaporation of the acids, the samples were redissolved in 100 mL of DI. The accumulation of heavy metals in the 40 studied seaweed species showed great variation with respect to the sampling sites, seasons, and types of species. The study elucidated that the studied seaweeds had the ability to uptake Fe, Mn, Ni, Cu, Cr, and Pb more than the other metals and did not accumulate Co and Cd to a great extent.