A. Zonderman et al.

3.2.3.4. Pb. Mass fractions of Pb in mussel tissue were measured with a
nean of 0.89 mg kg”! + 0.56 mg kg”* (1 SD). Mass fractions of Pb are
generally lowest in the southwest of the study area, in area N-2 and the
westernmost OWF of area N-3. Area N-5 and OWF B in area N-3
exhibited higher Pb mass fractions, with both the mean of 1.37 mg kg*
in area N-5 and 1.41 mg kg”! in OWF B being higher than the ICES BAC
of 1.3 mg kg *; 24 individuals (12 % of the dataset) were found to have
mass fractions over the BAC (ICES, 2021). In fact, mass fractions in this
study are on average lower than geographically comparable data:
Aelmholz et al. (2015) reported a mean Pb mass fraction of 2.8 mg kg*
for mussels placed in coastal waters in the Elbe Estuary in Cuxhaven
(nearshore) and 1.4 mg kg”! for the island of Heligoland (offshore), and
monitoring efforts report similar ranges (Fryer, 2022, UWPB). In the
case of Pb, a second sampling period would be of use, as Pb shows
seasonal variation in the North Sea in both the water column and
M. edulis (BSH, 2016; Knopf et al., 2020).
Reese et al. (2020) report Pb mass fractions in Al anodes between
6.70 mg kg-! and 9.48 mg kg7! and propose the metal as a tracer.
Moreover, exposure of OWF-colonizing organisms to Pb may also occur
due to remobilization of Pb from sediments resulting from increased
offshore activity and construction (Layglon et al., 2024). Concentrations
n the North Sea seawater are reported in the low ng L* range (1.45 ng
171 + 0.08 ng L7! to 39 ng L7* + 27 ng L7') (BSH, 2016) with no
ıoticeable increase in approximation of OWFs in recent seawater samples
 (BSH and Hereon, 2022, Ebeling et al., 2025). These concentrations
are well below experimental concentrations of 45 pg L7'_63 pg L7*
reported to cause negative effects in M. edulis embryos (Nadella et al.,
2013).

3.3. Additional analyses

Overall, absence of larger coastal input sources appears to have a
positive impact on the mass fractions of monitored contaminants in the
analyzed mussels. Findings indicate that offshore sources including
OWFSs contribute to the uptake of these metals by M. edulis at a much
'ower magnitude than other anthropogenic sources, for example the
#lbe River. Other commonly used anthropogenic tracers (Gd) and
cluster analysis were used to explore their applicability to differentiating
sources of contaminants in mussel datasets. These results can be found in
Appendix A (data tables and description and discussion).
3.4. Implications

This study is one of the first to present a large dataset of mussels
originating from large-scale industrial offshore wind structures in the
North Sea and presents first information about the burden of metals in
mussels grown within OWF boundaries. Due to the complexity of the
marine system and the lack of applicable reference datasets, the specific
source of the metals found in mussel tissues cannot be determined at this
>oint and may originate from various sources including OWF corrosion
protection, geographical differences, or other anthropogenic inputs such
as shipping. Furthermore, we did not identify a correlation between the
applied corrosion protection systems (GACP or ICCP) and the metal
»urden of mussels collected from the OWFs. Our dataset provides
daseline values for future assessments in the North Sea and other areas
‘hat are affected by the intensive expansion of OWF. Besides typical
monitoring and toxicologically relevant metals a broad set of metals
including OWF-specific tracers like In and Ga were analyzed.
Currently, no significant accumulation of OWF tracer elements in
mussels could be related to offshore structures, and mussels do not seem
:o be a sink for OWF-induced metals. Furthermore, in comparison to
‚nternational standards and recent literature, levels of the investigated
metals in the dissolved fraction and in tissue are not expected to cause
negative effects in M. edulis at the current stage. However, monitoring
efforts are recommended as e.g. larval stages are more sensitive to
elevated metal concentrations and emissions may vary over the lifetime

Marine Pollution Bulletin 218 (2025) 118216
9f offshore wind structures or increase with further installations in the
related areas. The sampling and analysis of mussels growing on turbines
for contaminants could be completed on a regular schedule by operators
and/or regulatory bodies to ensure that any increased emissions and
metal accumulation are detected. Analytes should be chosen based on
toxicity, relevance to OWF corrosion protection, and analytical capabilities.
 This is especially relevant for future multi-use scenarios in
zeveral regions that plan on using the space in OWFSs for aquaculture
‘Buck et al., 2017; Di Tullio et al., 2018; Lagerveld et al., 2014; van den
3urg et al., 2017). However, especially when considering the planned
increases in OWF development, it is advisable to take steps to minimize
metal emissions from corrosion protection by using ICCP anodes. This
:ould be complemented by long-term strategic monitoring of OWFimpacted
 areas for known OWF tracers and chemicals of concern to
better understand the impacts of OWFs on the marine environment.
Dverall, results indicate that mussels located within OWFSs exhibit on
average lower metal mass fractions than those of local coastal monitoring
 programs. This result is presumed to be caused by the distance of
IWF-based mussels to large coastal contaminant inputs like rivers. As
with other studies related to the assessment of the impact of anode
dissolution on the concentrations of metals in the natural environment,
(he dataset highlights the challenges of attributing metal emissions to
different sources. Further investigations, including time series, increased
sampling density within OWFs, and sampling at multiple times of the
year, are recommended to better understand the interactions between
mussels and metal emissions in OWFs as well as to mitigate risks for
future multi-use scenarios. Additionally, the flexible and adaptable
study design ensures that the findings are generalizable to various lozations.
 This approach not only informs broader expectations and study
ldesigns but also provides valuable insights into the global distribution of
»ffshore wind farms (OWFSs) with bivalve fouling communities.

CRediT authorship contribution statement

Alexa Zonderman: Writing — original draft, Visualization, Investization,
 Formal analysis. Dominik Wippermann: Supervision, Investization.
 Anna Ebeling: Writing —- review & editing, Methodology. Ole
Klein: Formal analysis. Hans-Burkhard Erbslöh: Methodology, Investigation.
 Tristan Zimmermann: Writing - review & editing, Conceptualization.
 Lars Hildebrandt: Writing - review & editing. Simone
Aasenbein: Conceptualization. Ingo Weinberg: Writing — review &
aditing, Conceptualization. Torben Kirchgeorg: Writing — review &
aditing. Daniel Pröfrock: Supervision, Funding acquisition,
Zonceptualization.

Declaration of competing interest

The authors declare the following financial interests/personal relationships
 which may be considered as potential competing interests:
Alexa Zonderman reports financial support was provided by Interrreg.
Dominik Wippermann reports financial support was provided by European
 Partnership on Metrology. Anna Ebeling reports financial support
was provided by Federal Ministry of Education and Research. Lars Hildebrandt
 reports financial support was provided by Helmholtz Association
 of German Research Centres. Ole Klein reports financial support
was provided by Helmholtz Association of German Research Centres. If
there are other authors, they declare that they have no known
:ompeting financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgements

We would like to thank the IfAÖ - Institut für Angewandte
Ökosystemforschung GmbH for collecting the mussel samples and all
wind farm operators for their cooperation. Thank you to Elena Hengstmann
 (BSH), Wiebke Pape (BSH) and Anna Plaß (BSH) for their valuable