Multi-element bioconcentration kinetics in Dictyota spiralis for active biomonitoring of coastal marine ecosystems

Environmental alterations of chemical element abundances may affect marine ecosystems either directly, due to toxicity, persistence and biomagnification, or indirectly by altering ecosystem dynamics. In this context, investigating element accumulation in organisms lay the foundation for their use in biomonitoring and bioremediation applications. In the present research, the bioconcentration kinetics of 15 elements were investigated in a brown seaweed, Dictyota spiralis Montagne, recently described as an effective passive biomonitor, using both devitalized (by boiling in a 35% NaCl solution) and non-devitalized samples, washed in a 100 µM EDTA solution to reduce the initial element concentrations. The alga, collected in a marine protected area, was characterized for lipid (1.0±0.4 % d.w.), glucose (6.7±1.7 mg/g d.w.), fructose (3.9±1.4 mg/g d.w.), galactose (3.3±1.3 mg/g d.w.), starch (20.1±2.2 mg/g d.w.) and polyphenol (0.04±0.02 mg GAE/g d.w.) concentrations before processing and exposure. Algae were placed in 2 mm mesh polyethylene/polypropylene bags and exposed in 4 sites characterized by different anthropogenic pressures. Bags were collected in triplicate at 2, 4, 8, 16 and 24 days, and analyzed for element concentrations. In terms of preprocessing, Student paired t-tests and ANOVAs demonstrated the uselessness of, respectively, EDTA treatment in reducing the initial concentrations and devitalization in affecting element bioconcentrations (apart from S showing reduced concentrations). Kinetics had either peaked responses, with the reaching of the highest concentrations in a few days (on average 4 days for As, Cd, Mg, Ni, P and S), or monotonic increases in concentration (Co, Cr, Cu, Fe, Mn, Pb, Si, V and Zn), suggesting that saturation may occur after the 24 days of exposure - an important finding in active biomonitoring applications.