Characterization of alloying components in galvanic anodes as potential environmental tracers for heavy metal emissions from offshore wind structures
AbstractThe impact of offshore constructions on the marine environment is unknown in many aspects. The application of Al- and Zn-based galvanic anodes as corrosion protection results in the continuous emission of inorganic matter (e.g. >80 kg Al-anode material per monopile foundation and year) into the marine environment. To identify tracers for emissions from offshore wind structures, anode materials (Al-based and Zn-based) were characterized for their elemental and isotopic composition. An acid digestion and analysis method for Al and Zn alloys was adapted and validated using the alloy CRMs ERM®-EB317 (AlZn6CuMgZr) and ERM®-EB602 (ZnAl4Cu1). Digests were measured for their elemental composition by ICP-MS/MS and for their Pb isotope ratios by MC ICP-MS. Ga and In were identified as potential tracers. Moreover, a combined tracer approach of the elements Al, Zn, Ga, Cd, In and Pb together with Pb isotope ratios is suggested for a reliable identification of offshore-wind-farm-induced emissions. In the Al anodes, the mass fractions were found to be >94.4% of Al, >26200 mg kg−1 of Zn, >78.5 mg kg−1 of Ga, >0.255 mg kg−1 of Cd, >143 mg kg−1 of In and >6.7 mg kg−1 of Pb. The Zn anodes showed mass fractions of >2160 mg kg−1 of Al, >94.5% of Zn, >1.31 mg kg−1 of Ga, >254 mg kg−1 of Cd, >0.019 mg kg−1 of In and >14.1 mg kg−1 of Pb. The n(208Pb)/n(206Pb) isotope ratios in Al anodes range from 2.0619 to 2.0723, whereas Zn anodes feature n(208Pb)/n(206Pb) isotope ratios ranging from 2.0927 to 2.1263.