A. Zonderman et al. 
concerning corrosion protection in each OWF is chosen to be kept 
anonymized as the information is not publicly available, however was 
disclosed confidentially to the authors and is considered in the discus- 
sion. The investigated areas are labeled according to the site develop- 
ment plan for the German North Sea and Baltic Sea (BSH, 2023). Mussels 
were delivered deep-frozen to the laboratory and stored at -80 °C. Metal- 
free tools were used throughout the preparation of mussel shells and 
‘issue. From each turbine and depth combination, nine mussels were 
subjected to analysis. The condition index (CI) based on the ratio of dry 
soft tissue weight to shell cavity capacity was determined per mussel 
1sing the method outlined by Crosby and Gale (1990). The age of each 
digested mussel was approximated by counting the number of rings 
formed in the shell under a microscope. The age-determination process 
was repeated three times per shell on separate days to ensure 
‚eproducibility. 
The soft tissue of each individual mussel was homogenized, freeze 
dried (Christ Gamma 1-16 LSCplus / Christ Beta 1-8 LSCplus; Christ 
Zefriertrocknungsanlagen, Osterode, Germany), and pulverized (Bead 
Ruptor; Omni International Inc., Kennesaw, USA). The homogenized 
nussel tissue was subjected to microwave assisted acid digestion in 
riplicates of 100 mg in 55 mL PFA vessels (Mars 6 / MarsXpress, CEM, 
<Xamp-Lintfort, Germany) using 1 mL H,O», 2 mL HCl, and 5 mL HNOs at 
200 °C for one hour. More detailed information about the digestion 
orocedure can be found elsewhere (Wippermann et al. 2023). 
2.3. Measurement 
Multi-elemental analysis was performed using an inductively 
coupled plasma tandem mass spectrometer (ICP-MS/MS) instrument 
(Agilent 8800; Agilent Technologies, Tokyo, Japan) coupled to an 
autosampler (ESI SC 4 DX FAST; Elemental Scientific, Omaha, USA). 
Prior to each measurement, a full optimization of the system with a tune 
solution containing Li, Co, Y, Ce, and Tl was conducted to maintain 
optimal sensitivity and stability. For quantification, an external cali- 
ration was applied, covering a concentration range from 0.1 ug L7! to 
100 pg L7!, Further details of the calibration and QC procedures, 
analyzed isotopes, gas modes and typical tuning parameters can be 
found elsewhere (Klein et al., 2022). 
2.4. Data processing 
Processing and evaluation of the multi-element raw data were con- 
ducted using MassHunter version 4.4 (Agilent Technologies, Tokyo, 
Japan) in combination with a custom-written Excel© spreadsheet. The 
limits of detection (LODs) (3 x SD), as well as the limits of quantifica- 
ion, (LOQs) (10 x SD) of the method were calculated based on proce- 
dural blanks (n = 16). Expanded uncertainties (U(k = 2)) for each 
sample and CRM were calculated using a simplified Kragten (1994) 
approach following Reese et al. (2019). The significant number of digits 
of mass fractions is given according to GUM and EURACHEM guidelines 
(Ellison et al., 2012; Magnusson et al., 2015). 
All distribution and survey maps were created using Esri's Arc- 
GIS®software. ArcGIS® and ArcMap'M are the intellectual property of 
Esri and were used here under license. 
3. Results and discussion 
3.1. Age and condition index 
The number of growth rings varied between 3 and 8, with a median 
of 6 for all analyzed mussels. A summary of the data for each area is 
shown in Table 1. The number of rings for each analyzed mussel indi- 
viduum can be found in Table A1 in Appendix A. Extra-annual growth 
pauses are common in M. edulis individuals (Millstein and O'Clair, 2001; 
Seed and Suchanek, 1992). Therefore, annual rings are best used as an 
estimate of a comparative metric between individuals, not an absolute 
Marine Pollution Bulletin 218 (2025) 118216 
Cable 1 
Ssummarized number of growth rings and CIs for each OWF area across all 
lepths. Areas are labeled in accordance with the site development plan for the 
German North Sea and Baltic Sea (BSH, 2023). 
Sampled Analyzed Growth Rings Condition Index 
Wind Mussels 7 7 
. median range median range 
Turbines [A] 
a +SD +SD 
5+1 3-8 236 + 35 146-450 
3 
Area 
N 
6 
79 
6+1 4-8 254 + 57 107-508 
Area 
7 
2 
18 
6+1 4—7 213 +35 142-289 
age. The results shown in Table 1 indicate that mussel larvae settled 
rapidly after placement of offshore structures; sampled OWFs were 
zonstructed between 2015 and 2018, i.e. 4 to 7 years prior to sampling. 
"his is in accordance with other studies (De Mesel et al., 2015) that 
describe the formation of a visible belt of blue mussels in the low 
intertidal to shallow subtidal zone in the year following installation of 
JWF turbine structures. 
The CI varies on an individual basis from 107 to 450, with an overall 
nedian of 238. The CI for each analyzed mussel can be found in Table A1 
'n Appendix A. A summary of the CIs for each area is shown in Table 1. 
Results indicate that the mussels are healthy when compared to previous 
astimations of CIs, which show values between approximately 50 and 
200 in the North Sea using the same method (Helmholz et al., 2015; 
Telmholz et al., 2016). It is however important to note that the high CIs 
may also relate to the time of collection (October/November 2021), as 
mussels have maximum energy storage in the autumn for preparing for 
both winter and gametogenesis (Kreeger and Langdon, 1993). 
3.2. Metal mass fractions 
In order to evaluate both the overall metal load and uptake of specific 
coxic metals in colonizing M. edulis, the mass fractions of 46 metal(loid)s 
were analyzed. The following sections present and discuss the deter- 
mined metal mass fractions in the analyzed mussel tissue in the context 
>f (a) OWF-specific tracer metals (section 3.2.2), (b) toxicologically 
relevant and traditionally monitored metals (section 3.23.) and (c) REEs 
(Appendix A). Presentation of the mussel tissue mass fractions in this 
publication is focused on the one-meter dataset unless otherwise stated 
as samples were available for all sampled wind turbines. The complete 
dataset, including additional five and ten meter samples, can be found in 
Table A1 in Appendix A. 
3.2.1. Comparison values 
In order to put the measured metal mass fractions of the OWF mus- 
sels into context, data were compared to a data set from Heligoland and 
Cuxhaven (Helmholz et al., 2016) and a set of monitoring data from the 
DSPAR 2022 CEMP (Fryer, 2022). M. edulis CEMP data were narrowed 
lown to those from the OSPAR Subregion: Southern North Sea, and 
“urther to the German and Danish North Sea coast and islands, from 
2017 to 2020. 
3.2.2. OWF-specific tracer metals 
In order to trace potential inorganic emissions of galvanic anodes 
Reese et al. (2020) proposed monitoring offshore-specific tracer metals 
(Al, Zn, Ga, Cd, In and Pb). Within this context In and Ga are promising 
due to their high mass fractions in Al anodes, low environmental 
background concentrations and the absence of other significant 
anthropogenic sources in or to the marine environment. Al and Zn, as the 
main components of Al anodes, are the starting point of theNo full text available for this image