Heavy metals and arsenic in macrophytes, sediments and seawater from the coastal area of Northern and Central Vietnam

In the past decade, there has been a boost in the industry development in Vietnam, which is the cause of increased heavy metal release in the environment. The study presents the results of voltammetric analysis of heavy metals (Cu, Zn, Cd, Pb) and arsenic in water, sediments and 38 macrophyte species from the coastal area of Northern and Central Vietnam. The effects of sampling station location, depth, and algal divisions/species on elemental concentrations in the macrophytes were tested. Among the macrophyte species, the highest elemental concentrations were found in the red alga Laurencia sp. (As – 72 mg·kg⁻¹) and brown algae Padina australis (Cd – 3.8 mg·kg⁻¹), Spatoglossum vietnamense (Pb – 14.8 mg·kg⁻¹), Dictyota dichotoma (Cu – 102 mg·kg⁻¹), and Sargassum sp. (Zn – 32.5 mg·kg⁻¹). The red and brown algae were the strongest trace element accumulators, while the green algae showed modest accumulation abilities. A significant decrease in the elemental concentrations in the seaweeds was observed with increasing depth, but As in the brown and red algae and Cd and Pb in the green algae were most accumulated at intermediate depths (5–8 m). The maximum arsenic and the minimum zinc concentrations in sediments were noted at the southern exit of the gulf. The bioaccumulation factors followed skewed, long-tailed distributions, with their maxima ranging from near zero (Cu) to several hundred (Cd). The study highlights spatial regularities of heavy metal accumulation and applicability of brown algal species as non-selective bioindicators of heavy metal pollution in the coastal area of Vietnam.