Seasonal variation of nickel and cobalt in the macroalga Cystoseyra abies-marina (Phaeophyta) from the Canary Islands determined by high speed voltammetry

Abstract

This article presents an analytical procedure for a fast and reliable determination of Ni and Co in algae and its application to monitoring the seasonal evolution of these metals on Cystoseyra abies-marina. The method incorporates a digestion and an electrochemical step. Several quick mineralization methods were tested. The best results were obtained employing a HNO3/KClO4 (2:1) combination and periods of 5 min of maximum microwaves irradiation for 0.2 g of sample. The procedure to measure Ni and Co after the digestionwas optimized using high speed cathodic stripping voltammetry in presence of oxygen. These techniques have achieved a remarkable reduction of the total analysis time. The method was applied to establish the annual variability of Ni and Co contents on Cystoseyra abies-marina at two different locations on the island of Tenerife, Tacoronte and Guimar (Canary Islands, Spain). Tacoronte is an unpolluted and open coast located at the north of the Island while Guimar is a sheltered southern station where the influence of waste waters can be important. Annual variation of Ni and Co contents in C. abiesmarina is related to its annual growth cycle: low metallic contents are followed by periods of high growth rates. Brown seaweeds have frequently been used as bio-indicators for metal pollution in seawater because of their high accumulation capacity. However, an extensive knowledge of the natural variations of the metal concentrations on the algae is required in order to interpret correctly the measurements. The results from this paper show natural oscillations along the annual cycle.