S. Acksen et al.
showed lower plastic shares.
The other important determinant of debris and mesoplastic abun-
dances on Sao Vicente is the level of beach use. It determined the
amount of debris from land-sources. Tourists and beachgoers leave
debris behind and this behavior presumably determined the loads that
we encountered in Salamansa, Baia das Gatas, and Sao Pedro, which
showed high levels of beach use (Table 1). This assumption is supported
>»y the composition of the debris at these beaches. In Baia das Gatas, for
.nstance, metal bottle caps and wooden skewers were found that are
presumably leftovers of weekend barbeques. In contrast to this, in Praia
Norte, fishing nets, ropes, and plastic foil were common, which could
stem from fishing boats and were presumably lost at sea. So, debris on
che beaches of Säo Vicente can either stem from land-based or from
oceanic sources, while the relevance of these sources for local pollution
levels depends mainly on the orientation and level of beach use of the
each.
We assume that the majority of mesoplastic particles found origi-
nated from fragmentation of larger plastic items. This is supported by
‘he strong positive correlation between the abundances of macroplastic
ıtems and mesoplastic particles found in our study (Pearson's r = 0.98, p
< 0.001). Similar findings were reported from beaches in South Korea
(Lee et al., 2013) and Bangladesh (Fatema et al., 2023). In our study
macro- and mesoplastics showed similarities with regard to their poly-
ner composition: Mesoplastic particles consisted of PE (69%) or PP
(30%), which are the polymers that are typically used for packaging
products (van Emmerik and Schwarz, 2019). Packaging products were
very abundant in the beach debris of Säo Vicente. The majority of
mesoplastic particles were fragment-shaped (65%). This supports the
notion that on beaches, presumably worldwide, large debris items
rommonly get fragmented and turn into mesoplastics on site (Gregory
ınd Andrady, 2003). Hence, a large share of the mesoplastic particles
hat can be found in beach sediments might not have been imported
(rom the sea in this size range, but are autochthonic.
The composition of the debris items found on Säo Vicente can give
further hints from where the items originate. Light items made from
plastic or paper as well as wood can float what makes it possible for them
‘Oo travel far distances across the ocean. Heavy objects such as pottery
fragments or metal items have a much higher mass, making long-
distance oceanic transport unlikely. Therefore, they most likely origi-
naate from land-based sources or harbour-related activities. The differ-
ence in litter composition between two beaches can, in turn, be
explained by the fact that two locations receive debris from different
sources (e.g., harbour and land-sources in Lazareto; ocean input in Praia
Norte).
4.5. Origin of ocean-based plastic debris
The pathways for plastic debris transport that we identified using the
Lagrangian ocean model PARCELS match with those that had been
suggested by Cardoso and Caldeira (2021). The authors did three
dimensional backward simulations of the transport of particles that were
‚eleased within a set scheme around the ten Cabo Verdean islands over
the course of 36 months. By this, they also identified transport pathways
from the West African coast towards the Cabo Verde archipelago. This
supports the notion that the West African coast is a significant source for
Duoyant debris reaching Cabo Verde. Furthermore, Cardoso and Cal-
deira (2021) also analyzed debris transport pathways towards the Ca-
nary Islands and showed that they are influenced by other ocean
currents than Cabo Verde. The Canaries receive water masses from the
open North Atlantic, including the North Atlantic garbage patch, by the
Dortugal Current, while Cabo Verde is influenced by the Cape Verde
Arontal Zone that transports surface-near water from the West African
coast towards the archipelago. This could explain why mesoplastic and
macrodebris densities, which were reported from the Canary Islands, are
higher than on Säo Vicente.
The direct oceanic transport pathway from Western Africa towards
Marine Pollution Bulletin 228 (2026) 119525
Sabo Verde makes the archipelago a recipient area for marine debris
from African land- and sea-based sources. The latter are mostly related
to fishing, since the West African coast is an upwelling area with
therefore productive fishing grounds (Fütterer, 1983). As fishing vessels
lose or discard material and gear (Watson et al., 2022), the ropes and
heavy-duty plastic bags that we found can come from this source.
The West African coast is also an important source for land-based
debris (Cardoso and Caldeira, 2021), which enters the sea mainly
through rivers that transport mismanaged litter. The Gambia River has
its mouth at 13.4° N and waters from the Casamance enter the ocean at
12.56° N. These are the same latitudes at which the majority of particles
that were released near Sao Vicente ended up in the backward simula-
tion. Hence, debris that is transported by these rivers presumably rea-
:hes Cabo Verde.
4.6. Limitations of this study
This study used a set of different methods highlighting the overall
pollution level on Säo Vicente. Nevertheless, all data were collected
between May and June 2023 and therefore represent only a snapshot of
pollution conditions at a single point in time. It is plausible to assume
that debris accumulation rates and mesoplastic abundances vary be-
tween seasons, as was confirmed by other studies in other locations
‚Burlat and Thorsteinsson, 2022). This is due to weather-related fluc-
tuations in beach-use as well as due to changes in the direction and
strength of the prevailing winds and currents. For the beaches of Säo
Vicente there are so far no data that would allow to assess the annual
variability in debris accumulation. The effect of seasons is expected to be
less significant than in West Iceland for example (Burlat and Thor-
;teinsson, 2022) as there are only small annual temperature changes on
Säo Vicente. Smith and Markic (2013) could show that estimates of
debris accumulation rates on beaches substantially depends on the
temporal scales of sampling. Thus, our sampling frequency of four days
lid not allow to quantify how much debris landed on a beach and was
removed again by wind, waves or beach cleaning activities before our
documentation and could therefore underestimate the daily accumula-
tion of debris.
The mesoplastic particle abundances showed high spatial variability,
aven on the same beach and within the same beach section. To better
understand mesoplastic accumulation patterns across the full beach
width, increasing the number of replicates within each beach section
would strengthen the statistical analysis and provide a clearer repre-
sentation of variability.
The Lagrangian model approach used by PARCELS can only give a
rough estimate about particle trajectories as this model considers only
main prevailing ocean currents and omits meso- and microscale water
movements, wave action and winds (Van Sebille et al., 2020). Especially
for plastic debris, which often floats on the ocean surface (Guo and
Wang, 2019) these additional processes can play an important role in
determining their transport. A further weakness of this model is that
particles are not allowed to move onto land cells. This poses a challenge
because we aimed to study both, where particles originate on land and
how they become stranded on the beaches of Säo Vicente. Longer sim-
ulations with PARCELS thus just lead to a recirculation of particles in the
antire ocean basin without showing their true origin. The direct pathway
between the West African Coast and the Cabo Verde Islands due to the
Cape Verde Frontal Zone current (Pena-Izquierdo et al., 2012) is none-
theless an important contributor to particle transport in that region. This
direct pathway could be further validated by incorporating observa-
tional data from floating GPS trackers in future studies to support the
model-based results.
5. Conclusion
This study conducted a comprehensive assessment of accumulation
rates and composition of macrodebris, abundance and characteristics of
