Heavy Metals Concentration in Sediments of South Brittany Waters, France: An Ecological Risk Assessment Approach

Distribution patterns of selected heavy metals content in sediments from the Bay of Quiberon and Gulf of Morbihan were studied to understand the current heavy metals contamination due to urbanization and mariculture activities in the coastal area. Therefore, a survey was conducted and 196 sediments collected were characterized for heavy metals content using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) after mix acid digestion process. The distribution maps of the concentrations of the heavy metals studied were produced as an isopleth map based on data interpolation by the ArcGIS software application. The association with the adverse effects on aquatic organisms was determined by the classification of the sediment according to the sediment quality guidelines. Therefore, two approaches were employed namely: direct comparison with Sediment Quality Guidelines (SQGs) by USEPA (United States Environmental Protection Agency) and comparison with other numerical SQGs, threshold effect level/probable effect level, and effect range low/effect range medium. In order to estimate the effect of multiple contaminations of heavy metals, the mean-ERM-quotient was calculated at each sampling point. How to cite this paper: Ong, M.C., Pan, H.-J., Shazili, N.A.M., Menier, D., Dupont, V., Révillon, S. and Connell, A. (2021) Heavy Metals Concentration in Sediments of South Brittany Waters, France: An Ecological Risk Assessment Approach. Open Journal of Marine Science, 11, 55-68. https://doi.org/10.4236/ojms.2021.111004 Received: October 27, 2020 Accepted: January 18, 2021 Published: January 21, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Human pressures on the ocean are thought to be rising globally in diverse and profound ways [1] [2]. The demand for marine space and resources is expanding as the population grows and migrates toward coastal areas, resulting in new challenges and risks for marine ecosystems [3] [4]. Nowadays, estuary and coastal environments are contaminated through activities such as tourism, and areas such as harbors and industrials sites. These release elevated concentrations of heavy metals, nutrients, organic pollutants, and radionuclides into the marine environment [5]. The pollution of coastal zones near metropolitan areas, caused by this anthropogenic waste is due to the large human population and the enormous amount of sewage discharged into coastal waters [6]. The addition of waste products into rivers and estuaries, particularly those in industrial and populated centres, has led to a significant increase in contamination caused by heavy metals [7].
Heavy metals, such as copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb), have a great affinity for sediment in the aquatic environment. These pollutants are persistent contaminants that bioaccumulate throughout the food chain with potential toxicity for aquatic organisms and humans [8] [9]. It is difficult to remove the toxic heavy metals once they enter the body of organisms [10] [11].
Furthermore, heavy metals are enriched at consecutive trophic levels of food chains resulting in biomagnification of these chemicals in the food web [12] [ 13]. Top predators, such as marine mammals and humans, may be at a greater risk from heavy metals due to their top position in trophic chains, resulting in adverse health effects [14].
For example, lead can penetrate the body and cell membranes easily, and is associated with nervous system disorders and lead encephalopathy [15]. Long-term exposure or intake of food with a high concentration of Cd may cause itai-itai disease and kidney damage [16]. It occurred in numerous residents of the Jinzu River basin in Toyama Prefecture, Japan, a region extremely polluted with Cd that originated from a zinc mine located upstream [17]. Moreover, green-colored oysters as a result of Cu contamination have been found in several estuaries and harbors around the world, including the USA [18], Spain [19], Chinese mainland [20] [21], and Taiwan area [22]. Chronic Cu toxicity can cause liver disease and critical neurological damage [23]. Zn has been considered to be relatively nontoxic; however, taking high levels of Zn-contaminated food can damage the pancreas and disturb protein metabolism, causing health problems, such as stomach cramps, bloody urine, liver failure, nausea, and anemia [24] [25]. As a Open Journal of Marine Science consequence, a systematic assessment of heavy metal pollutants is critical, especially for the coastal area.
Coastal areas are sensitive to both climate changes and human impacts, which make these areas ideal for studying environmental changes and the sequence of coastal sediments, and have become attractive targets for documenting paleoenvironmental changes. The Bay of Quiberon and Gulf of Morbihan on the south coast of Brittany Region, France, are an excellent example of the coastal sea with high terrestrial influence, a semi-enclosed bay, surrounded by densely populated areas and mariculture activities. Such an investigation is required if the environmental impacts of the region are to be understood quantitatively and qualitatively.
Accumulation of heavy metals in surface sediments from industrial effluents and urban discharged into the river without proper cleaning is easily identified by heavy metals spatial variations in sediments [26]. In this exploration, surficial spatial distributions of selected heavy metals; Cu, Zn, Cd, Pb (identified as priority contaminants in aquatic systems by the European Community (EC) Water Framework Directive 2000/60/EC) [27] were characterized in the surficial sediments which reflects the recent input to evaluate the contamination level resulting from anthropogenic inputs. This EC work recommends the monitoring of fluvial loads of heavy metals as a tool for sustainable management in the aquatic ecosystem [28].
Information on contamination background is required for managers and policymakers to make strategic regulations, guidelines, and monitor progress towards management objectives. In order to establish such a knowledge, the present study investigates the spatial distribution of four heavy metals (Cu, Cd,   The tide is semi-diurnal with a mean spring tidal range of 4.5 m. The tidal were stronger in the vicinity of the coast and especially in the passage between the Quiberon peninsula and neighboring Houat and Hoedic islands, and are amplified in shallower water depths [31] [32]. Due to this water physical characteristic, the outer bay was much influenced by the strong water current and tidal wave compared to the inner bay.

Study Area
The Gulf of Morbihan ("Morbihan" = "little sea" in Breton) is a natural harbor located in the South Brittany, northwest France ( Figure 1). It is a close sea body (11,500 ha) and a shoreline of 250 km [33]. It is a shallow basin with a maximum depth of 30 m and is connected to the sea by a 900 m wide and 30 m deep tidal inlet at Port Novalo [34]. Institut Géographique National recorded that there are 37 islands located in the gulf where the two largest islands are Moine and Arz Islands. The gulf is sheltered from the Atlantic Ocean (Biscay bay) by the peninsula of Quiberon, Houat, Hoëdic, and Belle Islands.
Across the gulf entrance, strong tidal currents affect the basin with water speeds that can reach 2.2 m/s during ebb tides and 1.8 m/s during flood tide.
This gulf has a semidiurnal tidal regime with freshwater input from Auray, La Open Journal of Marine Science Marle and Noyalo rivers [33]. The further from the entrance, the lower tidal range; 3 m at the eastern part and 5 m at the gulf entrance. Hence, tides are hypersynchronous, a characteristic feature of tidal dominated environments [35].
Many areas along the coast are used by the public as recreation areas. A number of shipping ports for recreational purposes and fishing activities are located in this region. In addition, the surrounding coast is successfully used for commercial shellfish (oyster and mussel) mariculture activities with a significant market around the region.

Laboratory Analysis
Sediment samples were digested and analyses for total heavy metals following

Results and Discussion
All the analyzed data were visualized using ArcGIS software and presented in the form of a concentration isopleth map to identify the sediment concentration hotspot as shown in Figure 2. Visualization by overlaying maps using a geographical information system makes this presentation even easier and more successful [40]. Generally, all studied metals' concentrations were higher in the  Tomlison et al. [41] elaborated that the application of the pollution load index (PLI) provides a simple way to assess the quality of estuarine and coastal sediment. This assessment is a quick tool for comparing the status of pollution at different locations [42]. PLI represents the number of times the concentration of heavy metals in the sediment exceeds the background concentration and provides a summary indication of the overall level of heavy metal toxicity in a particular sample or location [43]. The PLI can provide the public in the surrounding area with some understanding of the quality of the components in their environment, indicating the trend both spatially and temporarily [44]. In addition, it provides valuable information to decision-makers towards better management of pollution levels in the Bay of Quiberon and Gulf of Morbihan regions.

PLI is obtained as contamination factors (CF). This CF is the quotient ob-
where, n is the number of metals (4 in the present study) and CF is the contamination factor. The CF can be calculated from:

Element concentartion in the sediment Contamination Factor CF
Background value of the element = (2) Open Journal of Marine Science The PLI value > 1 is categorized as polluted, while <1 indicates no pollution at the sampling point [45] [46].
PLI values of the analyzed surficial sediments were visualized by ArcGIS software and shown in Figure 3, which confirms that either Bay of Quiberon or Gulf of Morbihan is not seriously polluted with the heavy metals studied. PLI was found to be generally low (<1) in all the studied locations in the Bay of Quiberon, apart from Trinité-sur-Mer area. The eastern zone and rivers (Auray, Marle and Noyalo) zones also have a PLI value above 1; therefore these areas can be classified as moderate contamination factors [46].
Two approaches were used to assess sediment toxicity and ecological risk to benthic organisms for heavy metals studied in Bay of Quiberon and Gulf of Morbihan surficial sediments. The first approach was to compare the concentrations of heavy metals to the Sediment Quality Guidelines (SQGs) promulgated by the United States Environmental Protection Agency (USEPA) which were reviewed by Giesy et al. [47]. This approach was used only to screen contaminants of concern in aquatic ecosystems. On the other hand, the second approach was to apply two sets of SQGs developed for marine and estuarine ecosystems [48] to the assessment the ecotoxicology of the concentration of heavy metals in sediments, namely, 1) the effect range low (ERL)/effect range median (ERM) and 2) the threshold effect level (TEL)/probable effect level (PEL).
Based on the SQGs proposed by USEPA from Giesy et al. [47], sediment contamination is defined as three classes, non-polluted, moderately polluted and heavily polluted (Table 1). This classification of SQGs does consider the natural background or multiple elements [49].  were moderately enriched with these metals. However, no surficial sediments from both sampling areas were classified as heavily polluted with the heavy metals studied according to SQGs classification.  [27], Long et al. [48] and Larrose et al. [51] as follows:  ERM for element (i) and n is the number of elements, e.g. four heavy metals in this study.
Long et al. [48] have defined several classes of toxicity probability for biota organisms in their study from US coast based on amphipod survival test: m-ERM-Q < 0.1 has a 9% probability of toxicity); 0.1 < m-ERM-Q < 0.5 has a 21% probability of being toxic; 0.5 < m-ERM-Q < 1.5 has a 49% of being toxic; and m-ERM-Q > 1.5 has a 76% probability of toxicity. Using the concentrations of the heavy metals studied, the m-ERM-Q value was calculated, and the obtained distribution visualized by ArcGIS software in Bay of Quiberon and Gulf of Morbihan is shown in Figure 4. The m-ERM-Q distribution pattern in the Bay of Quiberon surficial sediments showed that the inner bay zone had values below 0.1, which indicated a 9% probability of being toxic to the benthic organisms in that area. In the outer bay, the m-ERM-Q values slightly exceed 0.1, but not more than 0.2 indicate that this zone is between 9% and 21% probability to be toxic to benthic organisms. However, in Trinité-sur-Mer area, m-ERM-Q ranged from 0.2 and 0.3; therefore, this area can be categorized as 21% probability of toxicity to the benthic organisms according to Long et al. [48] classification.
Meanwhile, in the gulf of Morbihan sediments, the m-ERM-Q values at the western zone of the gulf were lower than 0.1m, and therefore this zone can be categorized as 9% probability of being toxic to the benthic organisms. Towards the inner gulf of eastern zone, the values of m-ERM-Q were increased but do not exceed the 21% probability of toxicity to the benthic organisms, 0.2. Generally, some sampling locations located at the rivers zone (Auray, Marle and Noyalo) had the m-ERM-Q value higher than 0.3, which meant a 21% probability of toxicity to the benthic organisms. The impact of contaminated sediment probably on aquatic ecosystems is likely to be due to re-suspension and remobilization processes [52] [53].

Conclusion
In comparison with the sediment quality guidelines for the ecological risk assessment, generally, all metals studied were not exceeding the ERL and PEL classification. Hence, these metals were considered not toxic to the marine organisms. The multiple contamination evaluation by mean-ERM-quotient shows that the sediments do not have more than 21% probability of being toxic to the aquatic organism. However, it is suggested that continuous monitoring including other pollutants such as hydrocarbons, microplastics, nutrient and pharmaceutical wastes should be implemented as the site is important for the recreation area, fishing and oysters mariculture activities.