INTRODUCTION:

They are the sites of intense human activity and/or hydraulic developments leading to discharges of various types of pollutants that disturb the natural functioning of these ecosystems¹. This is the case of the Bouregreg estuary on the Moroccan Atlantic coast of the Rabat/Salé region, known for its important ecological diversity². The Bouregreg estuary has been subjected to many anthropogenic effects. After the construction of the Sidi Mohammed Ben Abdellah dam in 1974, the flow became almost nil³. The estuary is bordered by two cities, Rabat and Salé, in which the processes of urbanization, hospitality, and industrialization have continued to increase. Estuary waters are used for recreational activities like fishing, but at the same time, they receive water that collects domestic and industrial wastewater⁴. Waste from old landfills was not treated and discharged into river water⁵. Human activities are responsible for many pollutants released into the environment, including heavy metals⁶.

The objective of this study is to evaluate the physico-chemical quality, in particular the accumulation of these six heavy metals (Cu, Fe, Zn, Cr, Cd, and Pb) in the water and sediments of the Bouregreg estuary, and to predict their impact on the global state of the environment and the state of marine ecosystems in particular. This allows us to perceive their impact on the health of consumers.

Figure 1: Map of Morocco

Figure 2: Location of stations along the Rabat/Salé estuary (Bouregreg)

MATERIALS AND METHODS:

Materials:

The Bouregreg estuary forms the boundary between the city of Rabat (the capital of Morocco) and that of Salé.Salé at 34° north and 6°50' west⁷. The estuary extends 24km from the mouth and receives a high organic and mineral load generated by domestic and industrial discharges⁸. Five stations were selected along the estuary.

Sampling sites:

Station 1 (S1):Located about 700m from the mouth, this station is characterized by the restructuring of the Oudaya and fishing activities, but more than that, it is a place for flocks of birds.

Station 2 (S2): Located about 1.3km from the mouth, it is a place of great human activity throughout the day and almost throughout the year (crossing the boat between Rabat and Salty, collecting clams and knives, recreational activities of the two nautical clubs of Rabat and Salé). Recently, a change in estuary morphology was recognized by the project development of the Marina Salé and the tourist area (cafés, terraces, restaurants, etc.) on both sides of the river.

Station 3 (S3): Located about 4 km from the mouth, between the two bridges Moulay Youssef and Al Fida, downstream of the terrace Oulja. It is subject to the potters of Salé, those of domestic sewage from the locality of Hay Moulay Ismail, and the construction activities of the great theater and the Mohammed VI Tower.

Station 4(S4): Located in an agricultural area 14.4km from the mouth, it is the most continental station and relatively far from urban centers. It is characterized by its location upstream of the islets, which are rocky dikes that represent a physical obstacle limiting the rise of the tide. It is subject to discharges from the Technopolis industrial zone and the Sala Eljadida habitable zone.

Station 5(S5): Located 16.2km from the mouth, this station is the closest to the confluence of the Akrech wadi, which brings, among other things, ONEP drinking water treatment discharges, Akrech landfill discharges and leachates, and Ain Aouda discharges. This station is only completely submerged during the high tide of whitewater; it is of very shallow depth to the point that it is crossing at a ford during the low sea.

METHODOLOGY:

Sediment:

Approximately 1kg of wet sediment was collected in vacuum-sealed polyethylene bags and transported to the laboratory at 4°C⁹. The sediments are dried at 105°C for 48 hours to remove moisture. After drying, the sediments were ventilated and sifted¹⁰. A fraction less than 63um was used for digestion with nitric acid¹¹. For the determination of total heavy metals. A gram of sediment is placed for 48 hours at room temperature in a beaker with 20ml of nitric acid (HNO₃ 65%)¹¹. The solution is then heated to 100°C for 2hours¹². An HNO₃-HFHClO₄ mixture was then added to a Teflon container on a hot plate¹³. The liquid samples were then evaporated to an almost dry state on the hot plate¹⁴. Finally, the samples were fitted into a suitable centrifuge tube with double demineralized water and filtered with a membrane (0.45μm)¹⁵. The samples were then analyzed using an inductively coupled Emission Spectroscopy Atomic Plasma (ICP-AES) type ULTIMA2 at UATRS in the Molecular and Elementary Chemistry Laboratory at the National Centre for Scientific and Technical Research in Rabat, Morocco.

Water:

Water samples were collected from the same sites, such as sediments, using 1-litre polyethylene bottles washed with acid¹⁶. The samples collected were filtered through a 0.45µm¹⁷ membrane filter, acidified with 2ml of concentrated HNO₃, and stored at a temperature of 4°C until the date of analysis¹⁸. For the determination of the physicochemical parameters, before sampling, the bottles were first rinsed with distilled water, followed by the samples to be studied¹⁹. Sediment is stored in plastic bags at 4°C²⁰. To avoid contamination by the environment or sampling equipment, the sampling procedures were carried out by the precautions described in the Aminot manual²¹.

Figure 3: Visual appearance of water sample

Figure 4: Visual appearance of the Bouregreg oued estuary

Statistical Analysis:

The variability of metal contents is studied by a one-factor variance analysis (station) performed by the ANOVA procedure, abbreviated in English as "Analyse of Variance" in Microsoft Office Excel 2016.

RESULTS AND DISCUSSION:

The results of the parameters measured in Bouregreg estuary waters are presented by location in Figures 5 and 6.

Variation of heavy metals in water and sediment:

Variation in water :

The highest concentrations of trace metal elements studied are recorded in the downstream part of the estuary of Bouregreg: Fe (7.45mg/kg), followed by Cu (8.06mg/kg), and Zn (2.94mg/kg). Stations S4 and S5 show the highest levels.This can be linked to the nearby Oum-Azza landfill and thus to anthropogenic activities in S4 by discharges from the Technopolis industrial area and domestic sewage from the locality of Sala Eljadida. This may also be related to the concentration of anthropogenic activities, especially during the summer. Fe is a metal element characteristic of urban pollution. Concentrations at the mouth of this estuary, especially during the summer: fishing, swimming, restaurants, and cafes However, low levels of chromium (0.0064mg/kg) and cadmium (0.0mg/g) were recorded during this study period.

Figure 5: Spatial evolution of trace metal elements in the waters of the Bouregreg estuary

Sediment variation:

However, 99% of heavy metals are considered to be stored in sediments²²; they cause serious environmental problems (at high concentrations) with ecological, health, and certainly economic consequences²³. The highest mean concentrations are Fe (1694mg/kg)> Zn (60.5 mg/kg)> Pb(44.07mg/kg)> Cr (27.12mg/kg)> Cu (26.55mg/kg)> Cd (0.061mg/kg).The highest chromium level was recorded at stations 4 and 3, with a value of Cr = 27.12mg/kg, while station 1 recognized the lowest concentration. This reduction may be related to tidal dynamics in the estuary. Indeed, the rise of highly mineralized marine waters leads to the remobilization and leaching of metals, particularly chromium, from sediments²⁴. For iron, this is an element that has a maximum value mainly in station 4(1694mg/kg). The maximum value of Fe may be linked to the natural geology of the region (iron-rich earth)²⁵; however, these elements (Zn, Cd, and Pb) have a rate in water that is greater than oneand have significant sedimentary concentrations.This demonstrates how crucial the sedimentary compartment is to the accumulation of these marine components in estuarine ecosystems²⁶. Based on a comparison between this level's heavy metal values and the norms (F.C., 2012)²⁷, cadmium does not exceed the standard, which is 0.2mg/kg, and also for Cu, which is below the value of 30mg/kg according to R.O. (1995)²⁸, chromium, meets the standards (F.C., 2012)²⁹, which is 52.3mg/kg.µ.The comparison of our results is consistent with a study conducted by Tahiri in 2005³⁰, before estuary development, that showed that stations s1 and s2 had low metal levels when compared to those measured at other stations.

Moreover, the comparison of our results with another study carried out by EL AMRAOUI³¹ in the first years of the development project shows a significant decrease in heavy metal concentrations, where the mean values for chromium (25.16 to 82.14mg/kg) and cadmium (0.005 to 0.35mg/kg) were significantly elevated relative to the concentrations recorded in this study.This can be primarily connected to the function of the new dam. On the other hand, if we contrast our findings with those of other research³² on the Lower Loukkos River, which had a higher concentration of heavy metals than the Bouregreg estuary, such as chromium (75.03 mg/g) and Pb (102.90 mg/g), our findings would be in contrast.

Figure 6: Spatial evolution of trace metal elements in the sediments of the Bouregreg estuary

CONCLUSION:

The Bouregreg estuary's quality can be determined by comparing the toxicity levels of heavy metals in the water and sediments. Before and after the implementation of development projects, all the results of the analyses carried out have shown that the decrease in metal load was mainly in the water, while in the sediments, metal contamination was mainly by heavy metals (Cr, Cu, Cd, Zn, Pb, and Fe).These high levels are probably due to significant anthropogenic activities in the area characterized by permanent pollution in Hay Moulay Ismail and the industrial area of Oulja (S3), the population of Sala Eljadida and the Technopolis industrial area (S4), as well as development projects such as the development of the Marina and the Grand Theatre (S2 and S3), which raise toxicological problems that could harm public health.The statistical approach confirms a significant variation between metal elements with remarkable amounts of iron and zinc. The downstream site S5 has a high content compared to the other sampling sites and can be found at the approach to the domestic landfill site Oum-Azza. This study on the biotope (water and sediment) will provide metallic data on all compartments of the Bouregreg estuary ecosystem, opening up a new avenue for research on the accumulation of heavy metals in the biological indicator.

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Received on 28.05.2023 Modified on 24.08.2023

Research J. Pharm. and Tech 2023; 16(12):5637-5642.

DOI: 10.52711/0974-360X.2023.00911