Toxicological effects of metal-EDTA/NTA complex formation in a synthetic medium on the macroalga Gracilaria domingensis

Abstract

Algae are appropriate target organisms both for the development of toxicological assays and as bioindicators of marine degradation by inorganic and organic compounds. In recent years, the compounds ethylenediaminetetraacetic (EDTA) and nitrilotriacetic (NTA) acids have been released from household and industrial processes and have been considered to be the major emerging contaminants in aquatic environments because they form higher, stable complexes with essential and unessential cations, lowering the bioavailabilities and toxicities of these metals. In the present work, the toxicity relationships of cadmium, copper, zinc, and lead, either free or available and after complexation by EDTA and NTA ions, were evaluated because these complexes may have contributed to the modification of cations toxicity under the experimental conditions. The assay is based on the daily growth rates of the red seaweed Gracilaria domingensis (Gracilariales, Rhodophyta) in synthetic seawater during a 48-h exposure. The ratios of free ions (aqueous complex) were calculated by software minimization of the total equilibrium activity (MINTEQA2). The toxicity of uncomplexed Cd, Cu, Zn, and Cu cations decreased with increasing EDTA ion concentrations because of the formation of metal complexes. The increasing NTA agents successfully mitigated the free-metal toxicity effects with the exception of that of Cu-NTA. The results suggest that there are relationships between toxicity for algae and free ions in solution.