Seaweeds along KwaZulu-Natal Coast of South Africa—3: Elemental Uptake by Ulva lactuca (Sea Lettuce)

Abstract

The elemental uptake by Ulva lactuca (Sea lettuce), a marine macro-algae (chlorophyta, green alga) grown richly along KwaZulu-Natal coastline. The total elemental concentrations of seven important elements, namely manganese, iron, arsenic, boron, titanium, zinc and mercury, selected based on their abundance in U. lactuca were investigated for one year cycle (June 2002 to May 2003). The four selected sampling sites, Zinkwasi, Ballito, Treasure Beach and Park Ryrie are spread over 150 km wide along the KwaZulu-Natal coastline from North to South. The Ulva lectuca possess good manganese and arsenic accumulating ability and an excellent bio-indicator for most of the metals studied. A typical U. lectuca sample at Zinkwasi (in winter) recorded Mn (25.3 ± 1.16 ppm), Fe (21.0 ± 0.85 ppm), As (6.2 ± 0.30 ppm), B (935 ± 14 ppb), Ti (863 ± 34 ppb), Zn (421 ± 21 ppb), and Hg (61.3 ± 1.2 ppb). The general trend found at all sites was high elemental concentrations in winter and a decrease in concentrations from winter to spring and summer. Iron uptake was lowest in summer and autumn at all sites. Ulva lactuca recorded highest mercury levels (>400 ppb) during the spring season at the Treasure Beach site near Durban.