Concentrations of Poorly Studied Technology-Critical Elements Ge, Zr, Mo, Sn, Sb, Hf, Ta, W and Ti in the Sediments of Three Northern Egyptian Lakes

Thirty five Sediment samples were collected from three Northern Egyptian Lakes namely El Burullus, El Manzala and El Bardawil to evaluate for the first time the concentrations of poorly studied technology-critical elements, namely Ge, Zr, Mo, Sn, Sb, Hf, Ta, W and Ti, and how that may be linked to local water quality parameters and other geochemical factors. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to determine element’s concentration. The results were compared with Upper Continental Crust (UCC) and Nile sediment (ANS). Lake sediments generally have relatively low contents of most elements. The average concentration of Zr, Hf, Ta and W are lower than UCC and ANS in three Lakes. El Bardawil Lake attained the lowest average concentration for all elements except Mo. Correlation analysis revealed that water quality and geochemical properties did not play any important role affecting the metal distribution and the studied metals are generally not affected by the complex lacustrine system of these lakes and their spatial distribution still not affected by the different anthropogenic activates.


Introduction
The Egyptian Mediterranean coast, which is considered to be between arid and hyper-arid, has five coastal lakes, namely Mariut, Idku, El-Burullus, El-Manzala and El-Bardawil. These lakes constitute about 25% of the total Mediterranean wet lands. All of them are directly connected to the Sea except Lake Mariut. More than 20% of Egypt's total population lives along the northern coastal zone of the country, with more than 40% of its economic activities including industry, agriculture, tourism, petroleum and mining activities, and urban development concentrated along the coast [1] [2]. Unfortunately, many factors exist in Egypt which directly or indirectly threaten the Egyptian coastal lakes ecological system. The degradation of these coastline habitats due to the rapid development and urbanization lead to imbalance of the ecosystems and generate polluting elements that affect the quality of these frail and precious areas mainly due to the discharge of large quantities of agricultural, industrial, and municipal wastes through several drains and from factories around them [3]- [7]. Although the Egyptian Northern Lakes are productive ecosystems that provide a good quantity of fish, they are usually under pressure from industrial activities and potentially polluting activities developed around them. Therefore close monitoring are required to develop feasible approaches to mitigate fish contamination and the associated human health risks. The Egyptian government recently launched a program and established a strong policy framework to mitigate these lakes' pollution and prioritized minimizing the release of harmful contaminants within these lakes [6] [8] [9].
Among all the pollutants, heavy metals have received a paramount attention to environmental chemists [10] [11] [12] [13]. Because of their persistence and their tendency to be bio accumulated by the aquatic organisms, they are considered very harmful for the aquatic environment. The deleterious effects of some of the trace elements on living organisms were well documented in the Egyptian ecosystems [14]- [24]. Metal's concentrations in the aquatic environment were regulated by Egyptian Environmental Affairs Agency (EEAA) protocols and directives that determine their appropriate environmental concentrations according to Law No. 4 of 1994 Promoting the Law on the Environment and its Executive Regulation, Egypt (EEAA, 2005) [25].
Metal pollutants occur mainly from two sources in the aquatic environment; 1) natural sources such as volcanic eruptions, and soil erosion. 2) Some anthropogenic behavior. These two factors are the primary cause of disruption to the natural ecosystem and eventually to humans via the food chain [6] [26]- [32]. However, a significant number of trace elements in these studies are excluded. This is due to: 1) their low ambient concentrations, in general, the detection limits of the analytical procedures used and 2) the lack of any significant industrial role in the past has no apparent environmental consequences [33]. This situation is presently changing, since some of these non-regulated trace elements such as Tellurium (Te), Germanium (Ge), gallium (Ga), Indium (In), Niobium (Nb), Tantalum (Ta) etc. are now key of the development of new technologies, such as semiconductors, electronic displays, energy-related technologies or telecommunications technology. The extent of the environmental impact of the increasing anthropogenic use of these elements needs therefore to be further assessed including knowledge of their concentrations in the environment along with better understanding of the chemical processes underlying its environmental behavior. A major reason for this scarcity in environmental studies relies in the fact that their analytical determination is still challenging [34] [35].
Sediments are the primary habitat and source of food for benthic organisms. Sediment pollution is directly or indirectly detrimental to aquatic organisms, and may even have further adverse impacts on terrestrial organisms and human beings as a result of bioaccumulation. The main objectives of this study are to analyze the concentrations, better understand the occurrence and the distribution patterns of poorly studied metals, namely Germanium (Ge), Zirconium (Zr), Molybdenium (Mo), Tin (Sn), Antimony (Sb), Hafnium (Hf), Tantalium (Ta), Tungsten (W) and Titanium (Ti), in the sediments of three Northern Egyptian Lakes. Based on this study, an evaluation of the current gaps in our knowledge of these elements in sediments of three Egyptian lakes will be provided to indicate directions for future research. This study was the first study to determine the concentrations of these elements in the sediments of the three lakes, and thus it provides base-line information that is the beginning of a database that can be used in assessing human-induced changes. Therefore, this study offers a valuable data for better monitoring of technology critical elements in three northern Egyptian lakes which will be helpful for environmental managers and policymakers.

Study Area, Site Selection and Sampling
The northern lakes play an important role in the Egypt's economy, not only because of producing more than 40% of the nation's fish catch but also for being resting areas for migrating birds [8] [9]. More than 75% of the harvest of Egyptian lake production is from them. Moreover, they have an ecological importance due to a variety of biodiversity inhabiting the lakes and their hydrologic attributes. Changes in environmental conditions along with other human-induced stresses and interferences have played an important role in the degradation of the lake and the consistency of the water and increase all the biological productivity along the lakes causing less diverse system. Sediment samples were collected from different locations ( Table 1 & Figure 1) by using a van-veen grab sampler. In addition to sediment samples, water samples were collected by completely submersing the sample bottle, opening the lid and filling the bottle, and then recapping the bottle underwater. In addition, the reproducibility of the sampling procedure was verified through collection of 3 replicate samples. Water quality parameters such as water temperature, salinity, pH, dissolved oxygen (DO), biological oxygen demand (BOD) and chemical oxygen demand (COD) were measured on each aqueous sample immediately after collection. Journal of Environmental Protection

Field Procedures and Analysis
Measurements of temperature (T), salinity (S), and pH were performed in situ during sampling. A salinometer (Thermo Fisher Eutech Salt, USA) was used to measure the salinity of water, and a pH meter (Thermo Fisher Orion Star A221, USA) was used for the pH measurement. The contents of dissolved oxygen/hydrogen sulfide (DO/H 2 S); biological oxygen demand (BOD) and chemical oxygen demand (COD) were determined according to APHA [36]. In the sediment samples, granulometric analysis was based on determination of sandy and muddy fraction by separating the coarser (both sand and gravel) fractions above 4Φ (0.063 mm), from finer (mud) fraction below (0.063 mm) involving the sieving of raw sediments on a standard sieve (4Φ) mounted on an electric shaker machine (Labor-technique) and 10 minutes was applied as a standard time of sieving according to Folk [37]. The dry sediments were used for determination of the total organic carbon (TOC) according to Schumacher [38], and water contents were determined by drying at 105˚C for constant weight. Total phosphorus and inorganic phosphorus as well as total nitrogen were determined according to Aspila et al. [39].

Method Validation and Quality Control Studies
In order to guarantee the accuracy of the results, adequate quality assurance/ quality control (QA/QC) was adopted in all aspects of the study. Quality control (QC) and quality assurance (QA) for quantitative ICP-MS included triplicate analyses, dilution checks, reference solutions, analysis spikes, an interference check, and calibration checks were applied. Triplicate field sediment samples were taken at each site and an average of the resulting element concentrations was used to represent that site. Precision was determined by three replicate analyses of one sample and expressed as a coefficient of variation (CV). The results of the precision were agreed within 10%. The accuracy of the method was tested by five replicates of a standard reference material (GBWO7301) stream sediment, China. In general, quantitative recoveries for Ge, Zr, Mo, Sn, Sb, Hf, Ta, W and Ti using ICP-MS 810/820-USA fall within ±20%.

Water Quality of the Three Egyptian Northern Lakes
The water quality of the three Egyptian Northern Lakes has become a focus of various studies due to the influence of the severe anthropogenic activities result- Lake > El-Burullus Lake > El-Manzala Lake. The salinity level varies regionally within a wide range, from Mediterranean shelf water in El-Bardawil Lake waters to brackish water in El-Burullus Lake and El-Manzala Lake which is mainly attributed to the huge amounts of agricultural and sewage wastewaters effluents.
The pH values fluctuated between 7.56 at El-Manzala Lake to 9.44 at El-Burullus Lake. On the meantime, the relatively low pH value in El-Manzala Lake waters was most probably due to the oxidation (decomposition) of organic matter, exhausted DO and liberation of H 2 S. Unlike salinity, the spatial variations in pH were not obvious. Journal of Environmental Protection at El-Burullus Lake. It was noticeable that the waters of the three northern lakes were well aerated i.e. they were in oxic condition ( Table 2). It is worth to mention that the observed DO mean concentration (>7 mg·l −1 ) in the three northern lakes was more than that optimum DO concentration level (exceed 3 mg·l −1 ) for good growth and the suitability of water for aquaculture purposes [41]. The range of DO concentrations was comparable to that in other Egyptian lakes. The BOD values ranged between 1.46 mg O 2 /l at El-Bardawil Lake and 126.83 mg O 2 /l at El-Manzala Lake in which the order of abundance of BOD values was: El-Manzala Lake > El-Burullus Lake > El-Bardawil Lake. The COD levels varied between 9.41 mg O 2 /l at El-Bardawil Lake and 705 mg O 2 /l at El-Manzala Lake.
The measured high COD concentrations at El-Manzala Lake were mainly due to the autochthonous source from endogenous phytoplankton and algae [42]. The increased industrialization, urbanization and man's greed to over exploit nature has led high differences in the northern lakes water chemistry which is reflected in differences in hydrology, amount of water discharges into these lakes, rate of water exchange between these lakes and the Mediterranean Sea etc. [

Geochemical Characteristics of the Three Egyptian Northern Lakes
The grain size is one of the main factors that govern heavy metal contamination in the particulate fraction. In general, small particles are more likely to bear heavy metals because of the rise in particular surface area and because of the presence of clay minerals, organic matter, and Fe/Mn/Al oxides associated forming fine-sized aggregates [48].
The results of the total mean levels of different geochemical parameters in surface sediments of northern lakes (Table 3) revealed that the sandy size showed the highest value in El-Bardawil Lake 88.25%, while the lowest value was observed in El-Burullus Lake (11.72%). The sandy size in the lake sediments can be arranged as follows: El-Bardawil Lake (67.47%) > El-Manzala Lake (39.15%) > El-Burullus Lake (29.80%) depending on the availability of different sizes in source sediments, and the transport operations affected by sediments. The mean of silt (%) in sediments of the northern lakes cleared out that the highest value was observed at El-Burullus Lake (85.95%); while the lowest ones (14.22%) was measured in the sediments of El-Bardawil Lake ( Table 3). The mean of silt (%) of the lake sediments can be arranged as follows: El-Burullus Lake (69.14%) > El-Manzala Lake (59.47%) > El-Bardawil Lake (31.09%).
The organic matter is made of low density materials. It is widely regarded as a vital component of a healthy soil. It is a major part of physical, chemical and biological fertility of the soil. The deposition of the organic matter is closely related to the precipitation of the fine volumes as they follow the same behavior.
Both of them are deposited in the calm sediment media, and the organic matter affects the ecosystem significantly [49]. By studying the organic carbon, it was found that Al-Manzala Lake contains the highest value (4.90), while El-Bardawil Lake attained the lowest value (0.40%). The organic carbon in the lake sediments can be arranged as follows: El-Manzala Lake (3.92%) > Al-Burullus Lake (2.16%) > Al-Bardawil Lake (1.34%).
Comparing the mean sulfide concentrations in sediments of the three northern Lakes revealed the highest value of 419 mg·g −1 at El-Burullus Lake, while the lowest value of 0.89 mg·g −1 was measured in sediments of El-Bardawil Lake. The descending order was as follows: El Burullus Lake (168.7 mg·g −1 ) > El Bardawil Lake (86.3 mg·g −1 ) > El Manzala Lake (58.7 mg·g −1 ) for Lakes sediments (Table   3). The water contents of sediments is one of the most important factors affecting chemical, physical and biological processes that affect sediments in the ecosystem [50]. The water contents results of the surface sediments in the three northern lakes revealed the lowest value of 22% in the sediments of El-Bardawil Lake, while the highest value was measured at El-Manzala Lake (74%). The water contents in the lake sediments can be arranged as follows: El-Manzala Lake (64%) > El-Burullus Lake (54%) > El-Bardawil Lake (37%).
By studying different phosphorus forms, it was also found that El Burullus Lake had the highest values of total and inorganic phosphorus (972 and 780 µg·g −1 ), while the organic phosphorus exhibited the highest value of 210 µg·g −1 in El-Manzala Lake. On contrast, El-Bardawil Lake showed the lowest values (274, 203 and 88 µg·g −1 ). Lakes sediments can be arranged according to the ratio of inorganic phosphorus and total phosphorus as follows: El Burullus Lake > El Manzala Lake > El Bardawil Lake. While the descending order according to the contents of organic phosphorus and total nitrogen was as follows: El Manzala Lake > El Burullus Lake > El Bardawil Lake for the Lakes sediments. El-Manzala Lake showed the highest percentage of organic phosphorus (210 µg·g −1 ) and total nitrogen (2.08%), while El-Bardawil Lake attained the lowest values (88 µg·g −1 and 0.95%, respectively) which is mostly related to the high contents of organic carbon (Table 3).

Distributions of Different Metals of the Three Egyptian Northern Lakes
Concentrations of nine rare earth elements in sediments from three lakes along the Mediterranean Sea are given in Table 4 with the corresponding values for Upper Continental Crust (UCC) [51], North America Shale Composite (NASC) [52], Average world suspended sediment (AWSS) [53], as well as average Nile sediment (ANS) as previously reported by Arafa et al. [54]. The present study indicated that lakes sediments generally have relatively low contents of most elements. Germanium is an important element used in electronics devices, flat-panel display screens, light-emitting diodes, night vision devices, optical fiber, optical lens systems, and solar power arrays. Concentrations of Ge, in sediments of the three lakes were ranged between 0.76 -3.10; 1.14 -23.84 mg·kg -1 ; and 0.17 -1.98 mg·kg -1 ; for El-Burullus lake, El-Manzala Lake, and El-Bardawil Lake. The descending order was as follows: El Manzala Lake (3.75 mg·kg -1 ) > El Burullus Lake (2.05 mg·kg -1 ) > El Bardawil Lake (0.77 mg·kg -1 ). These reported concentrations in El Manzala Lake and El-Burullus Lake are higher than abundance of Ge in UCC. Ge is sorbed by clay minerals, co-precipitates with Fe-oxides and has a strong tendency to bind to organic matter [55] [56] [57].
Zirconium and Hafnium are likely not essential for human health and generally are considered elements of low toxicity to humans [58]. The results of the present study ( Because of the low solubility of zirconium and hafnium and their resistant to weathering, ecological health concerns in the aquatic environment are minimal. The lethal concentration for 50 percent (LC) in controlled laboratory tests was estimated to be greater than 1000 µg·kg -1 for both zirconium and hafnium [59].
Average concentration of Zr was close to that reported in Nylandssjon Lake lo- The average content and geometric mean were 1.9 mg·kg -1 and 0.7 mg·kg -1 , respectively [63]. The concentration of molybdenum found in the northern lakes of Egypt is much lower than that found in Qaroun Lake (6.77 mg·kg -1 ) and its drains (6.27 mg·kg -1 ) sediments [64], but it is within the range that recorded in sediments  [61]. Table 4 shows that average concentration of Mo is lower than UCC.
The mean value of Tin in the northern Egyptian lakes was 2.63 mg·kg -1 (ND -12.23) for El-Burrlus Lake; while it was 1.07 mg·kg -1 (ND-5.9) for El-Manzala Lake. There was a tendency to much lower Sn concentrations in El-Bardawil Lake (0.26 -0.70; av. 0.43 mg·kg -1 ) ( Table 4). The concentration of Sn found in the northern lakes of Egypt is lower than that found in Qaroun Lake (3.27 mg·kg -1 ) and drains (3.07 mg·kg -1 ) sediments [65]. Moreover, the median value of Sn was found to be 2.52 mg·kg -1 (0. 76 -3.37) in surface sediments of Lake Qaroun, Egypt [64]. Lower concentrations were reported in sediments of the far south-east coast of New South Wales, Australia where Sn concentrations were found to be <0.01 -2 mg·kg -1 [66]. On contrast, much higher concentrations of  [71]. A notable feature of the Ta distribution in the three lakes sediments is its very low concentrations in El-Bardawil Lake compared to the other two northern Egyptian lakes.
Generally, average Ta concentration is lower than UCC, NASC, WASS and ANS and that observed in sediments from the Egyptian central Nile Valley (0.9 mg·kg -1 ) [61]. Tantalum is absorbed only minimally by the human body; and nearly all the tantalum that enters the human body is eliminated within a relatively short period of time.
Tungsten which is widely used resource in industrial and manufacturing applications due to its high density and tensile strength showed varied concentrations in sediments of the three Egyptian Lakes. It is largely used in high-tech and military industries and has been identified as an emerging contaminant by the Environmental Protection Agency (EPA) [72] [73] [74] [75]. It potentially represents a significant threat to both human and environmental health, which merits further research over the coming years in order to fill the present knowledge gaps [76]. The concentrations of W in lake sediments were in the ranges of (0.03 -0.64 mg·kg -1 ), (0.16 -0.76 mg·kg -1 ), and (ND-0.76 mg·kg -1 ) for El-Burullus lake, El-Manzala lake and El-Bardawil Lake; respectively, revealing an increase tendency in the order: El-Burullus Lake (0.40 mg·kg -1 ) > El-Manzala Lake (0.35 mg·kg -1 ) > El-Bardawil Lake (0.14 mg·kg -1 ). The W concentrations recorded in Lakes sediments are lower than UCC (1.9 mg·kg -1 ). Increasing use of tungsten (W)-based products opened new pathways for W into environmental systems and may be introduced into the food chain [77].
The average concentrations of Titanium in sediments were 5.72 g·kg −1 , 3.77 g·kg −1 and 2.18 mg·kg −1 in El-Burullus, El-Manzala and El-Bardawil respectively (Table 4) revealing an increase tendency in the order: El-Burullus Lake > El-Manzala Lake > El-Bardawil Lake. This indicated that the geochemistry of un- Chica de San Pedro lake in Chile [80] and in Nylandssjon Lake located in the Nordingrå peninsula (northern Sweden) (2.3 mg·kg -1 ) [60]. Data are in line with previous studies on soils which concluded that Ti in the humic layer was due to mixing from underlying mineral soils. This is also in line with the sediment survey, which concluded that Ti in sediment was dominated by geological sources [81].

Correlation Analysis
In a complex lacustrine system, variations of any environmental factors is not independent. But it is interdependent with other environmental parameters, which can be analyzed by correlation method. Correlation analysis can estimate the strength and direction of linear relationships between pairs of continuous variables. The correlation between water quality parameters and the geochemical parameters in the three lakes showed limited relationships (Table 5). For example, sand was negatively correlated with Wc s (−0.76) in El-Burullus Lake. While,   (Table 5). This suggests that the studied metals are generally not affected by the complex situation of these lakes and their spatial distribution still not affected by the different anthropogenic inputs such as municipal wastewater, manufacturing industries, and agricultural activities discharged inside the three lakes. Moreover, the high correlations among these metals are a further evidence of the absence of any anthropogenic source of contamination by these metals in the three lakes. Journal of Environmental Protection

Conclusion
Egypt has undergone a rapid industrial revolution and urbanization which is largely responsible for the release of a large amount of pollutants among them heavy metals into the northern Egyptian lake. This rapid industrialization and urbanization have led to a serious environmental pollution problem that cannot be ignored. One easily can conclude that the concentrations of the examined nine rare earth elements were relatively low in sediments of the three lakes. The present study cleared out also that water quality and geochemical properties did not play any important role affecting the metal distribution suggesting that these heavy metal concentrations as well as their distribution were not influenced by the different human factors. Since it was the first study for these metals in the Egyptian ecosystems, it is therefore challenging to get a general overview for better understanding of their concentration, distribution, and accumulation in different water compartments, especially the food chains across the entire Egypt.

Data Availability
All the data that support the findings of this study are displayed in this manuscript.

Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.