Assessment of potentially toxic elements in water and sediments in the drainage network of Lake Mariout, Egypt

The present work investigated the distribution and assessment of potentially toxic elements (PTEs) in the water and surface sediments of both Qalaa and Umum Drains. The water samples were taken from eighteen sampling sites covering the downstream part of the two drains before reaching Lake Mariout Main Basin (LMMB) and Lake Mariout Fishery Basin (LMFB) during the summer period. The samples collected were analyzed for Cu, Cd, Zn, Co, Ni, Mn, Fe and Al. Pollution loading index (PLI), enrichment factor (EF), contamination factor (CF), Geo accumulation index (Igeo) and sediment quality guidelines (SQGs) were calculated as a criterion of possible contamination. Qalaa Drain is characterized by a low pH value of 6.93 compared to the other waters in the studied areas. The lowest Cl was always recorded in the water of Qalaa Drain with an average of 0.65 g Cl/L. The water of Umum Drain, LMMB and LMFB are continually aerated with O2 concentration, compared to the Qalaa drain, which constantly carries H2S. The outcomes revealed that the concentrations of the dissolved metals are at suitable levels according to U.S. Environmental Protection Agency (USEPA). Fe and Al are the two abundant metals in the sediment of the four studied areas. The order of abundance of the metals in the sediments of the present study areas was Fe > Al > Zn > Mn > Cu > Ni > Co > Cd. For the sediments, only cadmium and zinc concentrations in all sites during the study period exceeded the average shale rock concentration. According to the examined indices, the level of contamination in Qalaa Drain ranges from considerable to extremely high. Additionally, the four examined regions have higher Cu and Zn contents than SQGs. Base line of the PTEs pollution for the Lake Mariout drainage network. Pollution indices analysis of water and sediment of Lake Mariout. Ecotoxilogical and background concentrations of PTEs in sediments. Base line of the PTEs pollution for the Lake Mariout drainage network. Pollution indices analysis of water and sediment of Lake Mariout. Ecotoxilogical and background concentrations of PTEs in sediments.


Introduction
PTEs are considered a major anthropogenic contaminant in coastal and marine environments worldwide [1]. They pose a serious threat to human health, living organisms and natural ecosystems because of their toxicity, persistence and bioaccumulation characteristics [2]. Many PTEs are known to be toxic or carcinogenic to humans [3]. PTEs can contribute to the degradation of marine ecosystems by reducing species diversity and abundance and accumulating metals in living organisms and food chains [4]. Anthropogenically, PTEs can be introduced to coastal and marine environments through various sources, including industries, wastewaters and domestic effluents [3]. PTEs in marine sediments originate from geogenic (physical and chemical weathering of parent rocks) and anthropogenic sources [5]. With rapid industrialization, urbanization, and associated activities like agriculture, domestic and mining waste disposal constitute the major anthropogenic inputs. These unusual activities affect the natural environment and ecosystem i.e. water, sediment, and organisms [6]. Pollutants and their relationship with anthropogenic activities are used in understanding pollution status in marine systems for example: study the trace metals and nutrients in bottom sediments of the Southport Broad water [7], in surficial sediments of the northwest coast of Baja California, Mexico [8], Lake Mariout Drainage System [9,10], pesticides pollution and treatment techniques [11], and study the ecological conditions of Mariout Lake and relation to their suitability for fish living [12].
Previous studies have proven the presence of pollution in places close to drainage sites on the Mediterranean Sea [13,14]. Several studies have looked at the distribution and concentration of Cu, Cd, Zn, Co, Ni, Pb, Mn, and Fe in Qalaa and Umum Drains utilizing the Chelex-100 resin for particulate and dissolved metals detection [9,10,12]. These drains led the introduction of several PTEs to the Mediterranean coast of Egypt [15,16]. This work aimed to assess the existing levels of concentrations of Cu, Cd, Zn, Co, Ni, Mn, Fe and Al in water and surface sediment of four studied areas at Qalaa and Umum Drains, LMFB and S-LMMB in Alexandria city, Egypt. The structure of the article is as follows. The materials and experimental techniques employed in this work are presented in Sect. 2. The results and discussion for the heavy metals in the water and sediment gathered from the study region are detailed in Sect. 3. We conclude the work and give the results in Sect. 4.

Study area
The agricultural drainage waters from the watershed agricultural fields of Alexandria and El-Bohaira Provinces enter Mariout Lake via two major drains, the Qalaa and Umum Drains, respectively (Fig. 1). The heavily contaminated Qalaa Drain on the southeast edge of the Lake Mariout Main Basin (LMMB), where its dirty water enters the LMMB. However, Umum Drain borders LMMB on its extreme west side, and a large portion of its water feeds this basin via frequent unlawful breaches caused by fishers on its east bank, particularly in the region adjacent to LMMB's southwest corner [9][10][11]. Prior to the building of the East wastewater treatment plant (EWTP) in 1993, Qalaa Drain was filled with a significant amount of oxygen-consuming debris, which caused the water to be perpetually anoxic and emit poisonous and malodorous odours (mostly H 2 S) [10]. As this drain is the primary supply of water for the LMMB, and its water still contains H 2 S, the majority of the LMMB, particularly its eastern half, has deteriorated. The unsuitability of LMMB water for live aerobic organisms, including fish, has an effect on the fish harvest [10]. According to the Egyptian Environmental Affair Agency [12], the water quality of this drain contains H 2 S and a number of elements in quantities that exceed the recommended maximums. However, the dumping of agricultural and industrial waste into the seas along the Egyptian coasts causes numerous marine pollution issues [12].

Sampling and analysis
The present study is concerned with collecting surface water, and sediment samples in the lower reach of both Qalaa and Umum Drains besides LMFB and the southern side of LMMB (Fig. 1). Eighteen sampling sites were selected, covering the downstream part of the two drains before reaching the south part of Lake Mariout besides the southern part of the LMMB and LMFB during the summer of 2007. Three of these seven sampling sites [Sites (I), (II), and (VI)] were flowing waters from three key subsidiary pumping stations (PSs) called Dishudi, Haris, and Abis, respectively, in the Umum Drain course. The other four sites were located in the Umum Drain's main stem downstream section.
In Qalaa drain, eight sampling sites were sampled starting from Qalaa PS (mixture between wastewater effluent from EWTP and the agriculture drainage water from east Alexandria city). In contrast, the others were | https://doi.org/10.1007/s42452-022-05123- 8 Research Article distributed along the drain course downstream before joining Lake Mariout (at its southeast part). Further, two sites were located at LMMB. One (station VIII) was in the SW-LMMB near Umum Drain inlet, while the other (Station IX) faced Qalaa Drain inlet to the SE-LMMB. The last station was in the center of the LMFB. A 5-L plastic sampling bottle was used to collect the water samples, with at least 4 L of each water sample being used for metals analysis. Sub-water sample was used for the measurement of water temperature and pH. Each temperature, Secchi disc transparency depth STD and the water column total depth were in situ measured. Water samples for dissolved oxygen (DO) or hydrogen sulphide (H 2 S) measurements were independently collected using an APHA-DO Sample and analyzed according to APHA [17] and Grasshoff and Kremling [18]. Millipore 0.45 m filter membrane was used to filter the water samples before the metal analysis. The filtrate was pre-concentrated by passing it through Chelex-100 resin in ammonia form, and the eluted metals were collected. Particulate metals were also identified by digesting the TSM left on the filters [19]. The metals in the acid extract were examined using an Atomic Absorption Spectrophotometry Perkins-Elemer 2380 equipment, including dissolved and particulate metals. The concentrations of metals after passing through columns containing Chelex-100 were determined after solutions with known various metal concentrations were passed through them. The efficiency for the tested metals was computed after the findings were compared to the actual standard values, and it was within (97 ± 0.5%). Only ten sampling sites were sampled for sediments using the Van-Veen Grab sampler. Four were from Umum Drain, two from LMMB, three from Qalaa Drain, and the last sample was from LMFB. The sediment samples were kept in self-sealed plastic bags and stored in an icebox. The sediment samples after dryness in an oven at 60 °C were used to determine some of their physical and chemical properties (such as grain size, OC and ON) in addition to the contents of the metal (Cu, Cd, Zn, Co, Ni, Mn, Fe and Al). The Grain size were determined using the sieve and pipette analysis methods [20]. The organic carbon (OC) content in the sediment was determined according to the method described by Gaudette et al. [21]. Known portion of the sediment samples was grinded and passed through a 63 μm screen; 0.2 g of the dry grinded sediment sample was oxidized using 10 mL of 1 N dichromate solution in a 500 mL conical flask. Then 20 mL of concentrated H 2 SO 4 acid was carefully added and mixed gently for about one minute. After 30 min, the contents were diluted with distilled water to 200 mL, then 10 mL orthophosphoric acid and 1 mL diphenylamine indicator were added. (0.4 N) ferrous ammonium sulphate was used to titrate the sample (FAS). The identical procedure was followed for the blank determination but without the sediment sample.
The micro Kjeldahl technique determined the Organic nitrogen (ON) in the sediment according to Moore and Gorsline [22]. Where 0.2 g of dried sediment sample was placed in a Kjeldahl flask and 3 ml of conc. H 2 SO 4 was added. The mixture was heated gently initially, then over a strong flame for a total 15 min. After slightly cooling, a few drops of 30% hydrogen peroxide were added and the heating was continued for 10 min. The cooled sample solutions were washed into a stream distilling unit of the Kjeldahl type and mixed with 40% NaOH. The two solutions were mixed, and the resulting ammonia was distilled over the acid trap by stream drive. The evolved gas is carefully passed through 10 mL of 0.01 N HCl for ten min. The acid solution is boiling and back titrated with 0.01 N NaOH to clear the pale orange endpoint using a few drops of methyl red indicator.
The studied PTEs were determined using the method described by Oregioni & Aston [23]. 0.3 g of the dried and grounded sediment sample was treaded with 3 mL conc. HNO 3 , 2 ml conc. HClO 4 and 1 mL conc. HF in a Teflon beaker and left for 24 h as a pre-digestion step and then heated on the hot plate at 180 °C for near dryness. Then 1 mL conc. HCl was added and repeats heating again and cooling to room temperature. The sample is transferred and completed to 25 mL by 1% HNO 3 in a measuring flask [23,24]. The analysis was performed using the AAS. The metal concentrations were expressed as μg/g.

Water
The measured physical and chemical parameters are listed in Table 1. Both air and water temperature distributions in the investigated areas have a common pattern, the highest air temperature (33.14 °C) and the lowest (30.69 °C). While, the highest water temperature (30.08 °C) and the lowest one (27.6 °C). Transparency was measured in all areas except in Qalaa Drain because the water of Qalaa Drain is always dark in color because its water contains H 2 S and is mostly loaded with black iron sulphide (FeS) [9,10]. The waters of both S-LMMB and LMFB show transparency values that ranged between 40 and 55 cm, and for deep wastewater, it ranged from 35 to 70 cm with an average of 50.71 cm. The drainage water of Qalaa Drain has the lowest value of TSM (5.2 mg/L) due to its water containing over 70% of wastewater from EWTP, and the rest is agriculture drainage water.
On the other hand, Umum Drain has a low TSM at sites I and III compared to LMMB, due to its great depth. Low pH values characterize the water of Qalaa Drain, ranging from 6.84 to 7.7, with an average of 6.93 compared to the other waters of the studied areas. However, the presence of H 2 S appears to be the main reason for this slightly acidic pH. The lowest Clv was always recorded in the water of Qalaa Drain, ranging from 0.53 to 0.72 g Clv/L with an average of 0.65 g Clv/L. The water of Umum Drain has a higher Clv values ranging from 0.72 to 1.98 g Clv/L, with an average of 1.22 g Clv/L, whereas the highest value of Clv is located in LMFB, where it reached 2.88 g Clv/L, and this may be attributed to the fact that the water in this region stays for a long time, and thus exposed more to the process of evaporation, in addition to the fact that the region does not receive fresh water from any other sources. The waters of Umum Drain, LMMB and LMFB are always aerated with O 2 concentration of 7.04, 4.4 and 4.68 mg O 2 /L, respectively, compared to the Qalaa drain, which constantly carries hydrogen sulfide, reflecting the increased oxygen consumption in the Qalaa drain water that exceeds the amount of dissolved oxygen available in the Qalaa drain, resulting in an euxinic state in this drain.

PTEs in water
The results for the measured PTEs are listed in Tables 2  and 3

Sediment
The obtained results for the sediment analysis are listed in (Table 4). The main important feature of the sediments collected from Umum Drain is mostly muddy sand (mud > 78% of the total sediment), while those of Qalaa Drain are of mud content < 58%. In Umum Drain, the

PTEs in sediments
The range and mean concentrations of the studied PTEs are shown in Table 4. A comparison between the levels of these metals in the sediments of the present areas with those recorded in the standard rocks and in other world wide areas are shown in Tables 5 and 6, respectively. The concentration of Cu in the Umum Drain ranged from 41.0 µg/g at station IV to 94.8 µg/g at station II with an average of 66.5 µg/g. The high concentration level of Cu is also noticed at station I, about 78 µg/g. In LMMB, at station VI (near Qalaa Drain inlet) the Cu concentration is 59.7 µg/g, while at station V (near Umum Drain outlet) the Cu concentration is 49.4 µg/g. The sediment of LMFB has almost the same concentration level (57.5 µg/g), which is closer to that of Umum Drain. The Qalaa Drain sediments are remarkably enriched with Cu compared to those of Umum Drain, which ranged from 136.3 µg/g at station IQ to 72.1 at station IIIQ with mean of 100.6 µg/g. This high concentration level may be attributed to the contamination from the primary treated sewage discharged into the drain from EWTP, which lead to the privilege of euxinic condition that encourages the precipitation of Cu as insoluble CuS. The level of Cu in the oxic sediments of Umum Drain and LMFB are more or less at the same level as that in the crust but are higher than that in shale rock. Obviously, the level in the sapropetic sediments of the Qalaa Drain is the highest. The Cd concentrations in Umum Drain sediments fluctuated between 2.50 µg/g at station I and 12.1 µg/g at station III, with a mean of 5.9 µg/g. In Qalaa Drain, it ranged between 1.9  and 3.9 µg/g with an average of 3.0 µg/g, which is slightly higher than that of Umum Drain. In LMMB, the Cd concentrations were 7.05 µg/g at station V (oxic sediment) and 8.53 µg/g at station VI (anoxic sediment). These levels are higher than that in either LMFB (4.08 µg/g) or Umum Drain. The level of Cd in the sediments of the present study areas are extremely higher compared to those in the standard sediments (Table 5); but they are still lower than   (Table 6). In Umum Drain, the concentrations of Zn varied from 625 µg/g at station II to 875 µg/g at station I, with a mean of 781 µg/g. In Qalaa Drain sediment the concentration values of Zn are higher than those found in Umum Drain at station V near to those in LMMB, it ranged between 366 µg/g at station IIQ and 1116 µg/g at station (IQ) with a mean value of 803 µg/g. In LMFB, the Zn concentration is generally more or less at the same level as in the oxic sediments of Umum Drain. From Table 5; it is easy to see that the level of Zn concentrations in the sediments of the four present areas is at least six times that in shale rocks, reflecting contamination of these sediments with this metal. In Umum Drain, the Co concentrations in the sediment ranged from 18.3 µg/g at station III to 42.2 µg/g at station II with an average of 27 0.0 µg/g. In Qalaa Drain sediments, the concentrations of Co is fluctuated between 13.3 µg/g at station IIQ and 33.1 at station IIIQ with a mean of 22.5 µg/g, which is slightly lower than Umum Drain. In LMMB, Co concentrations fluctuate between 31.8 µg/g at station V and 16.9 µg/g at station VI. Usually, the main source of nickel comes from the metallurgical industries, burning of fossil fuels, municipal wastewater, and geological weathering [25,26]. In Umum Drain sediments, the concentration of Ni varied from 23.0 µg/g at station III to 90.1 µg/g at station I, with mean of 57.3 µg/g. The high value of Ni in the sediment is related to the high load of suspended matter from the pump stations along the coarse of Umum drain as mentioned by Nriagu and Pacyna [26]. In LMMB, 82.8 µg/g is in the anoxic sediments at station VI, while the lowest was 80.5 µg/g in the oxic sediments at station V. Both values in LMMB are generally higher than in LMFB (64.3 µg/g). In Qalaa Drain sediments, Ni ranged from 45.41 µg/g at station IIQ to 79.9 µg/g at station IIIQ, with a mean of 67.7 µg/g. From Table 5, the concentration level of Ni in the sediments is quite close to that in shale rocks; as suggested by Nriagu and Pacyna [26], The main sources of Ni in are: metallurgical industries, burning of fossil fuels, municipal wastewater, and geological weathering in our study the municipal wastewater in Qalaa drain may be the reason for high Ni Concentrations. Manganese is usually found in the form of carbonates, oxides, silicates, and sulphides in minerals [27]. Mn concentrations in Umum Drain sediments ranged from 59 µg/g at station I to 1330 µg/g at station III, with a mean of 462 µg/g.
In Qalaa Drain, the values of Mn ranged between 121 µg/g at station IIIQ and 389 µg/g at station IQ, with a mean of 297 µg/g. This means the concentration is considerably less than that in Umum Drain. This could be attributed to the anoxic condition, which is always prevailing in Qalaa Drain led to the solublization of Mn oxyhydroxides to the more soluble Mn(II). The concentration values in LMFB sediment are surprisingly low about 99 µg/g. In south LMMB, Mn value is the highest with a value of 1579 µg/g in the oxic sediment at station V, which is neighboring to the inlet from Umum Drain, compared to station VI (87 µg/g), near the inlet of Qalaa discharge. The low value 87 µg/g is mostly attributed to the reducing condition. From Table 5, the level of Mn in the sediments of the present study areas is lower than that in the shale rocks. The Fe concentrations in Umum Drain fluctuated between 35,598 µg/g at station IV, and 47,759 µg/g at station I, with an average of 41,351 µg/g. In Qalaa Drain, the concentration values of Fe ranged between 25,025 µg/g at station II and 42,910 µg/g at station IQ, with a mean of 35,284 µg/g, which is lower than that recorded at Umum Drain. In south LMMB, the concentrations of Fe are low, about 41,594 µg/g at station VI and about 50,821 µg/g at the oxic sediment at station V. The last is about two times more than that found in LMFB 24,891 µg/g. Aluminum (Al) is the second most abundant metal after Fe in the sediment of the four studied areas. As mentioned before, for Mn, both Fe and Al also show concentration levels lower than those found in standard rocks, including shale. This reflects the dilution of these sediments with other sediments of lesser content of these dominant metals (Mn, Fe and Al).
The values that were obtained for the PTEs in this investigation were compared with their corresponding values in various aquatic sediments from different areas across the world ( Table 6). The levels of copper, cadmium, and zinc are all more here than what was discovered in the Rhine Estuary in Germany [32]. Copper levels in the Qalaa and Umum Drains, as well as in the LMMB and LMFB, were found to be significantly greater than those found in Lake Edku and Lake Borollus ( Table 6) [33][34][35]. When compared to the levels that were documented in Lake Manzalah [34,35], the concentration of copper in Umum Drain is significantly lower. The concentration of manganese in the four regions that were investigated was found to be greater than what was found in Lake Edku by Abdel-Moati and El-Sammak [29], but it was found to be less than what Samir and Shaker [35] found in the same lake. Abdalah [36] recorded a higher concentration of Co at El-Mex Bay and in the Eastern Harbor of Alexandria, but this value for the concentration of Co is lower. The order of abundance of the metals in the sediments of the present study areas was Fe > Al > Zn > Mn > Cu > Ni > Co > Cd. While in shale the order is Al > Fe > > Mn > > Zn > Ni > Cu > > Co > > Cd.

Enrichment factor (EF)
EF values were interpreted as suggested by Birth [51] for the metals studied with respect to the shale average [28].
where x/Al is the ratio of the PTEs to Al. for all analyzed metals in this study are listed in Table 7; the descriptive statics of all metals were also calculated and represented in Table 8 and Fig. 2.

Geoaccumulation index (I geo )
The geo-accumulation index (I geo ) can be calculated via Eq. (2): where C n is the measured concentration of the examined metal (n) in the sediment or TSM μg/g, 1.5 is the factor used for lithologic variation of trace metals, and B n is the background value of the same metals according to concentration in shale rocks. Based on the I geo data suggested by Förstner et al. [54], and Müller & Suess [55], the geoaccumulation index, with respect to each metal in the sediment of the studying area is ranked in Table 9. In Umum Drain, among the whole 8 studied metals, the I geo of Cd was ranked from moderate to strong contamination at station III (I geo class = 3-4), I geo value of Cd in LMMB, Qalaa Drain and LMFB was ranked between moderate and moderate to strong. I geo of Zn in Umum, Qalaa Drains, LMMB and LMFB was ranked between moderate to moderate to strong (I geo class = 2-3) ( Table 9). On the other hand, the rest of the metals (Cu, Co, Ni, Mn, Fe and Al) in Umum and Qalaa Drains, LMMB and LMFB were ranked from practically uncontaminated to moderate (I geo class = 0-1). These results might indicate that the study area has a heavy accumulation of Cd and Zn, which apparently comes from sewer and from the primary treated discharge of WTP in (2) I geo = ln C n 1.5B n

Contamination factor (CF) and contamination degree (CD)
Hakanson [56] has suggested a contamination factor ( C i F ) and the degree of contamination (C D ) to describe the contamination of given toxic substance by Eqs. (3) and (4): where C i F is the mean content of the substance; and C i n is the reference value of the substance ( Table 10).
The contamination factor (C i F ) and contamination degree (C D ) of the sediment sample are given in Table 10. In Umum Drain both Stations II and III indicate a very high degree of contamination, the value of C D > 28. While stations I and IV indicated a considerable degree of contamination with the value of 14 < C D > 28. Both stations V and VI in LMMB indicate a very high degree of contamination, the value of C d > 28. On LMFB station show a considerable degree of contamination, the value of C D = 26.06. In Qalaa Drain, the stations IIIQ and IIQ indicated a considerable degree of contamination, with values of C D = 21.91 and 21.64 respectively, while station IQ shows a very high degree of contamination value of C D > 28.

Ecotoxilogical sense of PTEs contamination
The ecotoxilogical sense of PTEs contamination was determined using sediment quality guidelines (SQGs) developed for marine and estuarine ecosystems [57,58]. Sediments were classified as non-polluted, moderately polluted and heavily polluted, based on SQG of USEPA [59] as shown in Table 11. The toxicity unit values shown in Table 11

Pollution loading index (PLI)
Tomlinson et al. [60] and Satyanarayana et al. [61] applied a simple method using the pollution loading index (PLI) to study the extent of pollution load in sediments, which can be calculated using Eq. (5).
The calculated PLI value for the studied locations was reported in Table 12. The PLI value of < 1 is non-polluted whereas PLI value of > 1 is polluted. The values of the PLI at all sites in the studying area are > 1, which indicated that all studied locations have high pollution loading. The highest PLI value was recorded at station V in LMMB with a value of 2.367, while the lowest PLI value was found at station IV in Umum Drain with a value of 1.2, which indicated that both were the highest and lowest value are > 1.

Conclusion
The results of the Physicochemical parameters revealed that the water of Qalaa Drain is characterized by low pH values ranging from 6.84 to 7.7 with average of 6.93 compared to the other waters of the studied areas. However, the presence of H 2 S appears to be the main reason for this slightly acidic pH. The lowest Clv was always recorded in the water of Qalaa Drain ranging from 0.53 to 0.72 g Cl/L with an average of 0.65 g Cl/L.   (I)  1  2  3  0  0  0  0  0  (II)  1  3  2  1  0  0  0  0  III  0  4  2  0  0  1  0  0  IV  0  2  2  0  0  0  0  0  Mean  0  3  2  0  0  0  0  0  LMMB  V  0  3  1  1  0  1  0  0  VI  0  3  3    Data availability All data is available to the reasonable request.
Code availability Not applicable.

Conflict of interest
The authors declare no competing interests.
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