Undaria pinnatifida, Wakame is a popular edible seaweed in Asia (Yamanaka & Akiyama, 1993). Wakame has been recognized as a food rich in minerals, fiber and bioactive compounds such as proteins, vitamins, carotenoids such as fucoxanthin, and polyunsaturated fatty acids (Murata & Nakazoe, 2001).

U. pinnatifida was first recorded in New Zealand in Wellington Harbor in 1987. (Hay & Luckens, 1987) It was classified as an unwanted species according to the Biosecurity Act 1993 under section 164c however, when it was clear that it could not be eradicated a new policy was applied in April 2010, which allowed greater freedom to use U. pinnatifida commercially.

The primary aim for this study was to evaluate the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), calcium (Ca), mercury (Hg), magnesium (Mg), manganese (Mn), sodium (Na), nickel (Ni), phosphorus (P), potassium (K), lead (Pb), selenium (Se) and zinc (Zn) in U. pinnatifida and to compare the metal concentrations between the blade and sporophyll tissue. These data were compared with nutrient reference values for Australia and New Zealand and WHO/FAO guidelines to determine the safety and suitability of harvesting U. pinnatifida to manufacture edible wakame products.

U. pinnatifida was collected from two mussel farms, PE 327 and 106 from Port Underwood, South Island, New Zealand. Sampling of PE 327 was carried out on a monthly basis from April 2011 to October 2011. Sampling of 106 was carried on monthly basis from July 2011 to October 2011. Two additional sites on the eastern and western side of Miramar Peninsula in Wellington Harbor; Shelley Bay (site A) and Worser Bay (site B) were integrated into the study from August 2011 to November 2011.

Harvested samples were dried by oven or freeze dried method then ground to a powder using a blade mill. The dried U pinnatifida was digested with nitric acid and perchloric acid and the resulting solutions then analysed by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

In brief, the highest monthly mean concentration of metals found in New Zealand wild U. pinnatifida were Ca (16.97 g kg-1), K (48.48 g kg-1), Mg (9.47 g kg-1), Na (62.55 g kg-1), P (12.05 g kg-1), Cr (1.04 mg kg-1), Cu (3.78 mg kg-1), Mn (14.61 mg kg-1), Ni (2.78 mg kg-1), Se (0.83 mg kg-1), Zn (35.03 mg kg-1), As (46.71 mg kg-1), Cd (2.91 mg kg-1), Hg (0.042 mg kg-1) and Pb (0.31m g kg-1).

The results showed that New Zealand U. pinnatifida is a good source of the nutritionally important minerals calcium, sodium, magnesium, potassium and phosphorus. They also contained trace amounts of minerals such as chromium, copper, manganese, nickel, selenium and zinc. Contaminants such as arsenic, cadmium, mercury and lead were found at very low, safe, levels.