Spatial and temporal variations of the contamination in the Mediterranean Sea food webs (CONTAMPUMP ANR project)

The contamination of the marine environment by toxic, persistent, and biologically active substances and trace elements, of natural and anthropogenic origins, is a major problem worldwide, owing to its effects on the biodiversity and functioning of ecosystems, and its impact on the exploitation of marine resources, socio-economic activities and human health.

The CONTAMPUMP project (Plankton: biological PUMP of CONTAMinants in marine ecosystems, ANR-19-CE34-0001) concerned the study of the chemical contamination at the basis of marine food webs (plankton and both pelagic and benthic planktivores). Target contaminants have been selected among the priority substances of the Water Framework Directive (WFD) and MSFD lists: trace metals (ETMs), Hg, MMHg, PAHs, PCBs and pesticides. The main aim of this project was to determine the plankton exposome and to provide concepts and models of trophic transfer of contaminants from plankton to higher trophic levels.

During this project two campaigns (MERITE-HIPPOCAMPE from North to South of the Mediterranean Sea in April-Mai 2019, and CONTAMPUMP in Marseille Bay from February 2020 to November 2021) allowed to investigate the spatial and monthly variations of the contaminant concentrations in marine plankton food webs according to environmental factors. A total of 55 million liters of seawater were filtered. Different size classes of phytoplankton (0.7-2.7, 2.7-20, 20-60 µm) and zooplankton (60-200, 200-300, 300-500, 500-1000, 1000-2000 and > 2000 µm) were sampled during both campaigns. The biomass and composition of all plankton size classes were determined along with trophic markers (δ¹³C and δ¹⁵N). Additionally, mysids, mussels, fish and sediments were sampled in the Bay of Marseille.

Picoplankton and nanoplankton, which dominated the Mediterranean plankton biomass, represented the main sources of ETMs, Hg, MMHg and PAHs contamination in food webs. In contrast, PCBs and pesticides were particularly concentrated in microplankton and coastal areas (e.g Marseille Bay). The size of zooplanktonic organisms influenced the contamination level in different ways according to the type of contaminants (bioaccumulation for MMHg or biodilution for PAHs and most ETMs). The influence of the length of plankton food webs, short or long depending on nutrients and primary production, was highlighted, along with the importance of organisms’ trophic level (biomagnification for MMHg, PCBs and pesticides, and bioreduction for Hg, PAHs and most ETMs).

Plankton is more exposed to contaminants in human impacted sites. Terrestrial inputs and the resuspension of sediments highly influenced the monthly variations of contaminants in plankton in Marseille Bay. Mussels and fish presented particularly high PCBs values and a bioaccumulation with increasing size. Eventually, it was evidenced that food selection influenced contaminant concentrations in planktivorous species. Thus, according to the contaminants considered, trophic transfers from plankton to fishery resources resulted in bioreduction for some contaminants (e.g. most ETMs) or biomagnification (e.g. MMHg, PCBs).

 

Keywords: plankton exposome, trophic transfer, contaminants, spatial and temporal variations