Archives of Environmental Contamination and Toxicology (2022) 82:481-492 
background threshold values, often the Median +2 median 
absolute deviation (M2MAD) or the Tukey inner fence (TIF) 
method are used. The M2MAD method usually results in 
lower, thus more conservative, threshold values compared 
to the TIF method, whereas the TIF method provides very 
robust threshold values against possible outliers within the 
used datasets (Reimann et al. 2018). 
Particularly in marine environmental analysis, sediment 
analysis is used to investigate possible trends in complex 
systems such as rivers, estuaries, or coastal regions (Ack- 
ermann et al. 1983; Deng et al. 2021; Leschber et al. 1985; 
Logemann et al. 2022; Reese et al. 2019). For this reason, 
sediment analysis is often used for the long-term assessment 
of contaminants of aquatic systems like the North Sea. How- 
ever, in order to obtain comparable and standardized mass 
fractions of the individual elements, different normalization 
approaches are commonly applied. Isolation of the fine frac- 
tion by sieving (commonly either <20 um or <63 um) is 
regarded as a physical normalization reducing differences 
in the granulometric composition. Coarser particles, which 
usually do not bind anthropogenic contaminants and would 
therefore dilute their mass fractions, are removed from the 
sample. Subsequently, natural geochemical differences in 
sediment composition may be further corrected by the use 
of cofactors like the Al content (Ackermann et al. 1983; 
Federal Maritime and Hydrographic Agency (BSH) 2009; 
Federal Maritime and Hydrographic Agency (BSH) 2016; 
OSPAR/CEMP 2002). The North Sea is considered an area 
with high anthropogenic pressures such as shipping, offshore 
Dil and gas production, offshore wind energy production, as 
well as inputs from its fluvial tributaries (e.g., Rhine, Elbe, 
Glomma, Weser, Ems) (Deng et al. 2021; Federal Ministry 
for the Environment Nature Conservation Nuclear Safety 
and Consumer Protection (BMUV) 2018; German Environ- 
ment Agency (UBA) 2018; Reese et al. 2020; Reese et al. 
2019). Today the environmental status of the North Sea is 
constantly monitored by national agencies with the aim of 
achieving a good environmental status in accordance with 
the EU Maritime Strategy Framework Directive. However, 
up to now some metals like Pb, Hg, and Zn are still above 
the defined threshold values, indicating possible anthro- 
pogenic pollution (Federal Maritime and Hydrographic 
Agency (BSH) 2016; Federal Ministry for the Environment 
Nature Conservation Nuclear Safety and Consumer Protec- 
tion (BMUV) 2018). Even though elevated inputs of TCEs 
are considered possible, data on the TCE load of North Sea 
sediments are very scarce. Potential TCE input sources in 
this context are offshore industries and fluvial tributaries 
such as the Elbe, Weser, Ems, or Rhine (Deng et al. 2021; 
Kirchgeorg et al. 2018; Reese et al. 2020, 2019). 
In this work, a time series of sediment samples of two 
different locations within the German North Sea were ana- 
lyzed for their TCE mass fractions within the grain size 
483 
fraction <20 um to determine the occurrence and temporal 
varlation of TCEs in the North Sea. Furthermore, this study 
aims to define preliminary reference values for TCEs in these 
particular areas using the M2MAD and TIF approaches. 
Material and Methods 
Reagents and Standards 
Preparatory laboratory work was conducted in class 10,000 
or class 1,000 clean rooms. Only type I reagent grade water 
>18.2 MQ cm), obtained from an ultrapure water system 
consisting of an Elix 3 module (Merck Millipore, Darm- 
ztadt, Germany), a Milli-Q element module (Merck Milli- 
yore, Darmstadt, Germany), and a Q-POD element (Merck 
Millipore, Darmstadt, Germany), was used. Used acids 
were either further purified by double sub-boiling in per- 
fluoralkoxy polymer (PFA)-sub-boiling stills (DST-4000 & 
DST-1000, Savillex, Minnesota, USA) from analytical grade 
acids (HNO; (65% w/w, Fisher Scientific GmbH, Schwerte, 
Germany), HC1 (30% w/w, Carl Roth GmbH + Co. KG, 
Karlsruhe, Germany)) or were obtained in ultrapure quality 
‘HBF, (38% w/w, Chem-Lab, Zedelgem, Belgium)). 
Single element standards (Carl Roth GmbH, Karlsruhe, 
Germany or Sigma-Aldrich, Missouri, USA) and custom- 
made multielement standards (all traceable to NIST stand- 
ards) of different compositions (Inorganic Ventures, Chris- 
tiansburg, USA) were used for the preparation of diluted 
standard solutions. 
The reference marine sediment GBW 07313 (National 
Research Centre for Certified Reference Materials, Beijing, 
China), the reference stream sediment GBW 07311 (National 
Research Centre for Certified Reference Materials), and 
Jasalt reference material BCR-2 (United States Geological 
Survey Certificate of Analysis, Denver, USA) were used for 
method development and validation. 
Sampling 
In the course of several sampling campaigns between 2010 
and 2020, a total of 50 sediment samples were obtained. 
For each campaign, the sampling was performed by either 
the Bundesamt für Seeschifffahrt und Hydrographie (Federal 
Maritime and Hydrographic Agency (BSH)), the Helmholtz- 
Zentrum Hereon (Hereon) or in cooperation of both. Table 1 
lists all sampling campaigns along with the sampling time, 
‘he respective research vessel, and the campaign code. All 
surface sediment samples were collected with a box corer. 
The top layer (approx. 2-3 cm) of one or more individual 
samples (depending on sediment type) were collected, 
pooled, and deep-frozen. For this study, a subset of seven 
sediment samples from each campaign was used. Samples 
2 Springer