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Explora: Environment
and Resource Trace elements in Mediterranean mussels

well-documented. 14,15 Therefore, a deep understanding in these organisms. Although with different profiles,
of the factors and dynamics underlying the seasonal and fluctuations in trace element levels affect different tissues
annual fluctuations of trace element bioaccumulation in and organs, such as the gills and digestive glands. These
the tissues of aquatic organisms is essential for a correct observations suggest that seasonal fluctuations in the
interpretation of the results derived from monitoring bioaccumulation rates of trace elements in mussels depend
plans. New knowledge continues to emerge through the not only on environmental factors, such as temperature,
application of these monitoring plans, although often on a pH, salinity, dissolved oxygen, and nutrients but also on
limited geographical or temporal scale. the biological cycle of the organisms themselves, which
The aim of the present review is to summarize the determines distinct phases of organ and tissue development
current knowledge regarding the bioaccumulation of throughout the year. 14,15
trace elements in mussels as bioindicator organisms of Since then, several authors have investigated the nature
environmental contamination in the Mediterranean. The of seasonal fluctuations of trace elements in mussels in the
review seeks to establish a framework for understanding Mediterranean area, providing reference databases of the
the presence and impact of this class of environmental normal concentration ranges found in the tissues of these
pollutants while also focusing on the natural factors and organisms. Table 1 summarizes the ranges obtained from
dynamics affecting seasonal and annual variations in various areas of the Mediterranean over the past 25 years,
bioavailability and bioaccumulation levels. Specifically, the including additional data from the Marmara Sea and the
most relevant literature from the past 25 years has been Black Sea. 4,18-28
discussed, identified through Scopus (Elsevier, 2025), and To understand seasonal trends in trace elements,
organized to first describe natural phenomena altering the researchers often employ the condition index (CI). This
bioavailability of trace elements and then examine the key parameter is calculated by dividing a seasonally variable
contamination hotspots in the Mediterranean Sea.
physiological characteristic, like the total soft tissue weight
2. Species and investigations of the mollusks, by a more stable variable, such as shell
weight or size. An increase in CI typically indicates growth
The present review explored the most relevant literature in tissue weight, often linked to the expansion of digestive
related to the use of bioindicator mussels in the or gonadal tissues. 4,14,15,23,28,29
Mediterranean Sea. The most common species in this
region is Mytilus galloprovincialis (Lamarck, 1819), which Most trace elements, with a few exceptions, preferentially
is widely used in bioaccumulation and bioavailability accumulate in digestive tissues, while gonads are less prone
investigations. In contrast, Mytilus edulis (Linnaeus, 1758), to accumulation due to their higher lipid content. 4,14,15
primarily distributed in the Atlantic Ocean and Northern Consequently, element concentrations often peak during
Seas, is only occasionally included in Mediterranean phytoplankton blooms, when digestive tissues grow, as
monitoring plans. However, the two species are closely reflected by the CI trend. On the contrary, gonad growth,
related, and given almost all the available data on trace which occurs before gamete release, can dilute element
element bioaccumulation in the Mediterranean refer concentrations, leading to lower bioaccumulation despite
to M. galloprovincialis, the species are not discussed increasing the CI. Therefore, a direct statistical correlation
separately here. To maintain a clear framework, the between CI and trace element levels is often observed only
natural phenomena influencing the basal levels of trace during specific periods, such as phytoplankton blooms or
4,14,15
elements in mussel tissues – essential for understanding gametogenesis.
bioaccumulation in altered environmental conditions – An exception is arsenic, which is generally accumulated
are discussed first, followed by an exploration of the main in the form of organic compounds that show an affinity
contamination hotspots in the Mediterranean. to lipid-rich tissues. As a result, arsenic can be distributed
uniformly across all tissues of mollusks, showing a direct
2.1. Basal levels and natural fluctuation of trace relationship with the trend of the CI. Therefore, the seasonal
4
elements in Mediterranean mussels trend of CI and trace elements, including arsenic, offers
Even at the end of the last century, some authors observed important insights into understanding and identifying
significant seasonal variations in the levels of trace elements phenomena of increased bioavailability or contamination
in the tissues of sentinel bivalve organisms. 14-17 Regoli & in mussel populations, both in pristine areas and those
Orlando verified that these seasonal variations occur subjected to environmental impacts. The availability of
15
both in reference mussels from pristine, uncontaminated extensive databases, such as those summarized in Table 1,
areas and in populations sampled from polluted sites, also offers the opportunity to understand geographic and
complicating the interpretation of bioaccumulation levels environmental variations in these phenomena.

Volume 2 Issue 2 (2025) 3 doi: 10.36922/eer.8078