Monitoring of the changes in potential environmental risk of some heavy metals in water and sediments of Burullus Lake, Egypt

Abstract

Background

Burullus Lake has received a great attention because of its environmental and economic importance for connecting with the Mediterranean Sea through El Boughaz opening. Some of the chemical analyses were performed to study the potential environmental risk of Burullus Lake. The present study explores the potentiality of environmental risk of Fe, Mn, Co, Ni, Cr, Cd, Pb, Zn, and Cu for detecting most vulnerable areas to water and sediment pollution at Burullus Lake during different three periods: 2010, 2012, and 2015. The concentrations of DO, BOD, COD, and TDS during three periods 2010, 2012, and 2015 were higher than the WHO limits for the protection of fish and other aquatic life in Burullus lakes.

Results

The mean concentrations of heavy metals in Burullus bottom sediments in 2010 were arranged in descending order as follows: Fe > Mn > Cr > Zn > Ni > Cu > Pb > Cd, while the descending order in 2012 is Fe > Mn > Zn > Cr > Cu > Ni > Pb > Cd, as well as the descending order in 2015 is Fe > Mn > Zn > Cr > Ni > Pb > Cu > Cd. The Fe is the highest concentration in all years.

Conclusions

The potential ecological risk index (RI) 2010 is S4 > S11 > S7 > S6 > S9 > S5 > S1 > S10 > S8 > S2 > S12 > S3, where RI 2012, S4 > S9 > S6 > S10 > S5 > S8 > S2 > S12 > S3 > S11 > S7 > S1 as well as RI 2015, S4 > S11 > S7 > S6 > S9 > S1 > S2 > S10 > S12 > S8 > S3 > S5.

Background

Burullus Lake has received a great attention because of its environmental and economic importance for connecting with the Mediterranean Sea through El Boughaz opening. The investigation of distribution and pollution degree of heavy metals in Burullus Lake has attracted more public concerns recently because of their potential toxic effects and ability to bioaccumulation in aquatic ecosystems (Christophoridis et al. 2009; Yang et al. 2012; El-Moselhy et al., 2016; Darwish et al. 2018).

Heavy metal refers to any metallic chemical elements that has a relatively high density and is highly poisonous at low concentrations (Harris and Santos 2002). All metals are toxic at higher concentrations (Chronopoulos et al. 1997), and excessive levels can be damaging to the living organism (Fergusson 1990). Their multiple industrial, agricultural, domestic, and new technological applications have led to their wide distribution in the lakes, raising concerns over their potential effects on marine organisms and human health. Metal ions have been distributed to interact with cell components causing DNA damage and conformational changes that may lead to cell cycle modulation and carcinogenesis (Chang et al., 1996; Wang and Shi 2001; Beyersmann and Hartwig 2008).

Heavy metals from incoming drains, tidal, fresh water sources, and weathering of rock substrates are rapidly deposited onto the sediments of lakes. However, metals of anthropogenic origin are more loosely bound in sediments and thus are more readily available to organisms (Schropp and Windrom 1988).

Heavy metals such as Fe, Co, Ni, Cr, Cd, Pb, Zn, Mn, and Cu are regarded as serious pollutants of aquatic ecosystems because of their environmental persistence, toxicity, and ability to be incorporated into food chains (Forstner and Wittman, 1993).

The long axis of Burullus Lake, about 65 km long, runs parallel to the adjacent Mediterranean shore; its width is between 6 and 16 km, with the average being 11 km (Radwan and Lotfy 2002). The deepest part lies in the western sector, which also has the lowest salinity, while the eastern sector, which contains its outlet as a 250 m long canal connecting the lake to the sea (Bughaz), is shallow and saline (Doumont and El-Shabrawy 2007). Lake Burullus attracts attention of many authors because of its economic and scientifically importance. Industrial, agricultural and domestic wastes discharges have increased the levels of heavy metals in Lake Burullus. In facts, the studies dealing with the accumulation of heavy metals through different years are still scarce expect few studies.

The present study explores the potentiality of environmental risk of some heavy metals (i.e., Fe, Mn, Co, Ni, Cr, Cd, Pb, Zn, and Cu) for detecting most vulnerable areas to water and sediment pollution at Burullus Lake during different three periods: 2010, 2012, and 2015.

Study area

Burullus Lake is considered as one of the four coastal shallow lakes at Egypt Nile Delta, namely, Edku, Maryout, Burullus, and Manzala Lakes. Burullus is a coastal lagoon situated along the Mediterranean Sea, between the western Rosetta and the eastern Damietta branches of the River Nile with an average depth ranging from 0.5 to 2.1 m. It is the second northern lake in size (Fig. 1). El-Burullus lagoon brackish water (31° 22′ − 31° 26′ N and 30° 33′ − 31° 07′ E), on the northern Egyptian coast, is one of the most important Egyptian northern lakes from an economical point of view. The Lake serves as a reservoir for drainage waters, discharged from agricultural areas in addition to freshwater from Brimbal Canal, situated in the western part of the lake (Samaan et al. 1989).

Fig. 1

A Landsat image of the Nile Delta showing the location of Lake Burullus. a By using free satellite imagery data sources. b The study area of El-Burullus lagoon brackish water (31° 22′ − 31° 26′ N and 30° 33′ − 31° 07′ E)

Methods

Water and sediment samples were collected from 12 sites along Lake Burullus during the periods (2010, 2012, and 2015). The location of the sampling sites along Lake Burullus is shown in Table 1 and Fig. 2.

Table 1 Description of the collected sediments from lagoon Burullus

Fig. 2

Lake Burullus and position of 12 sites. a Water and sediments samples were collected from 12 sites along Lake Burullus. b Location of the sampling sites along Lake Burullus

Water samples were collected using NASEN bottles at 1–2 m depth. The collected water samples were filtered using pre-acid-cleaned Millipore membrane filters (0.45 mm pore size; 47 mm diameter). The filtrates were acidified to pH 2, with HNO₃ of supra pure grade; they were stored, in acid-cleaned high-density polyethylene bottles, in plastic bags. Then, these samples were filtered using 0.45-um membrane filters. All the standard precautions recommended by Kremling (1983) to reduce risks of sample contamination were followed during collection and treatment of samples. Solvent extraction was utilized using ammonium pyrrolidinedi-thiocarbamate (APDC) and methyl isobutyl ketone (MIBK). Water samples were pre-concentrated with APDC-MIBK extraction procedure according to the standard methods (APHA 1989). Heavy metals in the obtained solution were measured using the Flame Atomic Absorption Spectrophotometer (AAS; Perkin Elmer Analyst 100).

Sediment samples were collected using a Van-Veen grab coated with polyethylene. The samples were kept in self-sealed acid pre-cleaned plastic bags, rinsed with metal-free water. The samples were deep-frozen until analysis. The samples were dried in the oven at 70 °C and sieved using 0.75-mm plastic sieve and digested for about 2 h in a mixture of 3:2:1 HNO₃, HCLO₄, and HF acids, respectively, as described by Oregioni and Aston (1984).

Determination of physical parameters (pH, Eh, DO, TDS, conductivity, and temperature) in water samples was carried out according to UNEPA/APHA. pH, Eh, and temperature (°C) were measured using pH electrode meter while dissolved oxygen was measured with Jenway Model 9070 waterproof DO meter.

Determination of chemical oxygen (COD) demand was carried out according to the method described by the Standing Committee of Analysts (1986).

Dissolved oxygen (DO) meter was also calibrated prior to measurement with the appropriate traceable calibration solution of 5% HCl. The BOD₅ was computed by subtracting the DO after 5 days of incubation from the DO measured on collection of samples at point in milligram per liter.

Geostatistical analysis

• Geoaccumulation index (Igeo) is calculated by the following equation:

$$ \mathrm{Igeo}={\mathrm{Log}}_2\ \left[{\mathrm{C}}_{\mathrm{n}}/(1.5)\ {\mathrm{B}}_{\mathrm{n}}\right] $$

which was introduced by Müller (1979) and the numerical factor (1.5) artificially introduced by Covelli and Fontolan (1997).

where C_n is the measured concentration of the studied metal “n” in the sediment and B_n is the geochemical background concentration of the metal “n” values in argillaceous sediment. The factor 1.5 is used because of possible variations of the background values for a given metal in the environment, as well as very small anthropogenic influences. Müller (1979) presented seven classes of geoaccumulation index (Table 2).

• The degree of contamination (Dc) is defined as the sum of all contamination factors for a given site (Hökanson 1980):

Table 2 Geoaccumulation index (I_geo) classification [EU 1998]

$$ \mathrm{Dc}=\sum \limits_1^n CF $$

where CF is the single contamination factor and n is the count of the elements present. Dc values less than n would indicate low degree of contamination; n ≤ Dc < 2n, moderate degree of contamination; 2n ≤ Dc < 4n, considerable degree of contamination; and Dc > 4n, very high degree of contamination (Caeiro et al. 2005; Pekey et al. 2004).

For the description of the degree of contamination in the study area, the terminologies used are as follows: Dc < 8 denotes low degree of contamination, 8 < Dc < 16 moderate degree of contamination, 16 ≤ Dc < 32 considerable degree of contamination, and Dc > 32 very high degree of contamination, where n = 8 = the count of the studied heavy metals.

• Modified degree of contamination (mDc)

Abrahim, 2005, Abrahim and Parker, 2008) presented a modified and generalized form of the Hakanson (1980) equation for the calculation of the overall degree of contamination at a given sampling site. The modified equation for a generalized approach to calculating the degree of contamination is given below:

$$ \mathrm{mDc}=\left(\sum \limits_{i=1}^{i=n} Dc\right)/n $$

where n is the number of analyzed elements, i is the i_th element (or pollutant), and CF is the contamination factor. Using this generalized formula to calculate the mDc allows the incorporation of many metals as the study may analyze with no upper limit. For the classification and description of the modified degree of contamination (mDc), the following gradations have been given below (Table 3).

• An ecological risk factor (Er_i) to quantitatively express the potential ecological risk of a given contaminant is also suggested by Hakanson (1980)

Table 3 Grading of modified degree of contaminations

$$ \mathrm{Er}=\mathrm{Tr}\times \mathrm{CF} $$

where Tr is the toxic-response factor for a given substance, and CF is the contamination factor. The Tr values of heavy metals suggested by Hakanson (1980). The Tr values of Pb, Cu, Co, Cd, Cr, Ni, and Zn are 5, 5, 5, 30, 2, 3, and 1, respectively. The terminologies used to describe the risk factor are as follows: Er < 40, low potential ecological risk; 40 ≤ Er < 80, moderate potential ecological risk; 80 ≤ Er < 160, considerable potential ecological risk; 160 ≤ Er < 320, high potential ecological risk; and Er ≥ 320, very high ecological risk.

• The potential ecological risk (RI) of the heavy metals is quantitatively evaluated by the potential ecological risk index (Er) (Håkanson 1980; Zhu et al. 2008), which takes into account both contamination factor (CF) and the “toxic-response” factor.

The potential ecological risk values obtained were compared with categories grade of Er and RI of metal pollution risk on the environment suggested by Hakanson (1980) and Shi et al. (2010). The potential ecological risk index (RI) was in the same manner as the degree of contamination defined as the sum of the risk factors.

$$ \mathrm{RI}={\sum}_1^n\mathrm{Er} $$

where Er is the single index of ecological risk factor, and n is the count of the heavy metal species. The terminology used for the potential ecological risk index was as follows: RI < 150, low ecological risk; 150 ≤ RI < 300, moderate ecological risk; 300 ≤ RI < 600, considerable ecological risk; and RI > 600, very high ecological risk (Håkanson 1980; Shi et al. 2010). Er and RI denote the potential ecological risk factor of individual and multiple metals, respectively.

Results

The hydrogen ion concentration is a reflection of many biological and chemical processes occurring in the aquatic environment, photosynthetic activity of the aquatic plants, respiration of aquatic organisms, and decomposition matter. The pH of the Lake Burullus in the representative area is slightly alkaline (8.12–9.21) and varies within narrow.

During 2010 (Table 4), the concentrations of COD for the 12 sampling sites ranged between 69.3 and 220.3 mg/l. BOD ranged between 5.36 and 29.5 mg/l; DO ranged from 8.4 to 13.6 mg/l. The percentage of TDS in the water samples ranged from 1.3 to 36.5 g/l. During 2012 (Table 5), the concentrations of COD ranged from 30.3 to 66.6 mg/l and BOD ranged from 5.3 to 30.5 mg/l; DO ranged from 0.8 to 13.5 mg/l. TDS ranged from 0.6 to 10.8 g/l. During 2015 (Table 6), COD ranged from 22.3 to 102.3 mg/l, BOD ranged from 5.60 to 11.5 mg/l, and DO from 5.6 to 12.9 mg/l. TDS ranged from 1.5 to 10.2 g/l. Reduced DO levels in water during 2015 may be attributed that Burullus lake was warm due to high contamination pushes the oxygen molecules out of the spaces between the moving water molecules. COD values in all studied periods, 2010–2015 are always higher than the BOD values because COD includes both biodegradable and non-biodegradable substances whereas BOD contains only biodegradable. The concentrations of DO, BOD, COD, and TDS were higher than the WHO limits for the protection of fish and other aquatic life in Burullus lakes. The distribution of heavy metal concentrations for the 12 sites of the investigated area were reported in Table 7. Metal concentrations in Burullus water were found in Table 8, and distribution of heavy metals in Burullus lagoon are given in Table 10 while modified degree of contaminations (mDc) were listed in Tables 11, 12, and 13 and Fig. 4, and in addition, the potential ecological risk index (RI) were given in Tables 14, 15, and 16 and Fig. 5.

Table 4 Physicochemical parameters in surface water (during 2010)

Table 5 Physicochemical parameters in surface water (During 2012)

Table 6 Physicochemical parameters in surface water (during 2015)

Table 7 Distribution of Fe, Mn, Zn, Cu, Ni, Cr, Pb, and Cd (μg/L) in water samples during 2012–2015

Table 8 Statistical analysis of heavy metals during 2010, 2012, and 2015

Discussion

The dissolved cadmium concentration in water ranged between 1.6 and 8.5 μg/l during 2010, 0.3 and 7.7 μg/l during 2012, and 1.1 and 2.5 μg/l during 2015 (Table 7). The average concentration of Cd in the 12 stations under investigation was decreased in the order of 2010 > 2012 > 2015, with the total annual average of 1 μg/l which exceed the natural concentration of seawater (0.1 μg/l) according to Fifield and Haines (2000).

The concentration of dissolved lead in the investigated area ranged from 12 μg/l at S3 to 68 μg/l at S8 during 2010, from 31.2 μg/l at S1 to 91.5 μg/l at S8 during 2012, and from 22 μg/l at S3 to 78 μg/l at S8 during 2015.The average concentration of dissolved lead ranges from 41 μg/l to 46 μg/l recorded during 2012 and 2015, respectively. Based on the annual average concentration of lead, it is higher than that of natural sea water concentration (0.03 μg/l) according to Fifield and Haines (2000) but is still lower than acceptable limits (100 μg/l) according to the WHO guideline value of heavy metals.

Iron is one of the essential elements in human nutrition, and high concentration of iron in humans has been found to bring about vomiting and cardiovascular collapse, while iron deficiency may lead to failure of blood clotting. The highest concentration value of Fe (430 μg/l) in the water samples was detected at S11 (Tables 7 and 8), while the least value of 96 μg/l was observed at point S6 during 2012, according to the WHO guideline value and maximum contaminant levels of 300 μg/l (water).

Copper compounds can be added to fertilizers and animal feeds as a nutrient to support plant and animal growth. The levels of Cu in the water samples fluctuate between 7.2 and 188 μg/l. S11 during 2012 shows the highest value, while the least values was observed at S2 during 2012. The copper concentrations in the water samples in sites (S1, S4, S11, and S12) of Lake Burullus during 2012 were found to be higher than the permissible limit of 50 μg/l set by WHO (2004).

Mn concentration in water samples was observed to be higher at S4 and S11 (99 μg/L), while S8 shows the least value of 13 μg/l. Manganese compounds are used in fertilizers and as livestock feeding supplements. Manganese can be bioaccumulated in lower organisms (e.g., phytoplankton, algae, mollusks, and some fish) but not in higher organisms; biomagnifications in food chains are not expected to be very significant (Abbasi et al. 1998). The concentrations of Mn during 2010 within the sites (S1, S4, S6, S10, S11, and S12) from this portion of the lake exceeded the permissible limit of 50 μg/l (water) by WHO (2004).

Metal concentrations in Burullus water were found in Table 8 in the following order: Fe > Zn > Mn > Cu > Pb > Cr > Ni > Cd.

Nickel concentrations in the water samples ranged between 1 and 14.5 μg/l. The concentration of Ni in the water Lake S4 (10.2 μg/l), S7 (14.5 μg/l), and S8 (10.2 μg/l) exceeded the permissible limit of 10 μg/l set by WHO (2004). The high concentration of Ni in the water samples from this portion of the lake could be from agricultural runoff, which may carry higher concentrations of this metal, which arise from anthropogenic activities such as use of chemical fertilizers and pesticides in agriculture land. The concentrations of Cr in water samples from this portion of the lake were lower than the permissible limits of 100 μg/l set by WHO (2004).

The average concentration of zinc in lake ranged between 48 and 552 μg/l (Table 8). The annual average concentrations were 80, 108, and 252 μg/l which is lower than the European permissible limits (EU 1998) (30–2000 μg/l). The lowest average concentration of Zn was S2 (27.7 μg/l) during 2012 while the highest value was recorded at S11 during 2010 (552 μg/l). The low levels recorded during summer 2012 are probably attributed to high precipitation process of zinc salt from water column to sediment due the high temperature in summer season. The relatively high concentrations of Zn were reported by the low adsorption of Zn in winter with temperature decreasing (Warren and Zimmerman 1994).

Mn concentration in water samples from the 12 sites was observed to be higher at S11 during 2010 (99 μg/l), while S8 during 2015 shows the least value of 13 μg/l (Table 7). The concentrations of Mn within the six sites (S1, S4, S6, S10, S11, and S12) from this portion of Lake Burullus (Tables 7 and 8) exceeded the permissible limit of 50 μg/l (water) and 30 μg/g (USEPA 2002; WHO 2004). It is attributed that the source of manganese compounds as wastes in lake from fertilizers, varnish, and fungicides and as livestock feeding supplements. It can also bioaccumulation in lower organisms (phytoplankton, algae, mollusks, and some fish) but not in higher organisms; biomagnifications in food chains are not expected to be very significant (Abbasi et al. 1998).

The chemical properties are completely different in the 12 sites represented by P, N, H₂S, and OM during the periods 2010–2015 (Table 9). Changing values in all studied sites are attributed to the difference in the nature and the environmental conditions of the 12 locations.

Table 9 Bottom sediments with P, N, H2S, and OM in EL-Burullus Lagoon 2010–2015

Phosphorus and nitrogen are the nutrients that ultimately determine productivity in lakes. The highest concentration of phosphorous was observed at sites (S7, S1, S4, and S11, respectively) while site S2 shows the least concentration which ranges from 795 to 895 μg/g. Nitrogen and phosphorus in Burullus Lake support the growth of algae and aquatic plants, which provide food and habitat for fish, shellfish, and smaller organisms that live in water. Phosphorus indicates high concentrations from the periods of 2010 to 2015 which is attributed to the increase of human activity and to be a major cause of excessive algae growth and degraded lake water quality (Table 9). Some algal blooms are harmful to fishes because they produce elevated toxins and bacterial growth. Phosphorus remains in the sediments of the lake as it is generally not available for use by algae; however, various chemical and biological processes can allow sediment phosphorus to be released back into the water.

The concentration of H₂S ranges from 65 to 290 μg/g during 2010, ranges from 55 to 290 μg/g during 2012 and ranges between 12.2 and 250 μg/g. The highest concentrations in three periods were in S7 and S11 indicating that H₂S is an extremely active chemical and biochemical participant in biogeochemical transformations. Its presence and reactions rank with photosynthesis, algal respiration, and the iron in the aquatic environment (Bass Becking et al. 1960). Organic matter (OM) constitutes a minor in Burullus Lake but important in lake sediment which provides information that is important to interpretations of both natural and human-induced changes in ecosystem. The decomposition process of organic matter in sediments occurred in the absence of oxygen (Berner 1963).

Distribution of heavy metals in Burullus lagoon are given in Tables 10. The highest concentration of Fe (28560 μg/g) in the sediment samples was detected at site S7 during 2012, while the least value was observed at site S10 during 2012.

Table 10 The concentration of heavy metals of EL-Burullus Lagoon during periods of 2010, 2012, and 2015

The mean concentrations of heavy metals in Burullus bottom sediments of 2010 were arranged in a descending order as follows: Fe > Mn > Cr > Zn > Ni > Cu > Pb > Cd. The descending order of 2012 is Fe > Mn > Zn > Cr > Cu > Ni > Pb > Cd and in the descending order is Fe > Mn > Zn > Cr > Ni > Pb > Cu > Cd in 2015.

Comparison between the mean concentrations of each heavy metal in bottom sediments of Burullus lagoon in 3 years (2010, 2012, 2015) as Fe, 2010 < 2012 >2015; Mn, 2010 > 2012 < 2015; Zn, 2010 < 2012 > 2015; Cu, 2010 > 2012 > 2015; Ni, 2010 > 2012 < 2015; Cr, 2010 > 2012 < 2015; Pb, 2010 < 2012 < 2015; Cd, 2010 < 2012 < 2015 (Table 10 and Fig. 3).

Fig. 3

Means of heavy metals in different stations. a Means of heavy metals of EL-Burullus Lagoon during periods of 2010, 2012 and 2015. b Results show the comparison between the mean concentrations of each heavy metal in bottom sediments through different 3 years

The contamination factor (CF) for sediments are listed in Tables 11, 12, and 13 during the periods 2010, 2012, and 2015, respectively. The degree of contamination (Dc) and modified degree of contamination (mDc) were calculated and listed in these tables.

Table 11 Contamination factor 2010

Table 12 Contamination factor, degree contamination, and modified degree contamination for 2012

Table 13 Contamination factor, degree contamination, and modified degree contamination for 2015 samples

Modified degree of contaminations (mDc) were studied for 3 years (2010, 2012, and 2015) (Tables 11, 12, and 13 and Fig. 4), where the mDc vary in the stations as well as in different years as follows:

Fig. 4

Modified degree of contaminations (mDc) variations in 3 years. a Using this generalized formula to calculate the degree of contamination: mDc = (∑Dc)/n. b Results show the degree of contamination in bottom sediments through different 3 years

mDc in 2010 are in the following descending order in different stations S4 > S11 > S7 > S1 > S6 > S9 > S8 > S5 > S10 > S12 > S2 > S3 where mDc in 2012 S11 > S12 > S4> S5 > S1 > S6 > S9 > S7 >S8>S2 > S3 > S10, as well as mDc in 2015 S4 > S11> S7 > S1 > S6 > S9 > S8 > S10 > S5 > S12 > S2 > S3 (Fig. 4).

Ecological risk factor (EC) and potential ecological risk index (RI) were listed in Tables 14, 15, and 16 and Fig. 5.

Table 14 Ecological risk factor 2010

Table 15 Ecological risk factor 2012

Table 16 Ecological risk factor (2015)

Fig. 5

RI variation in 3 years. a The potential ecological risk index (RI) was defined as the sum of the risk actors: RI = ∑Er. B. b The results through different 3 years the degree of contamination in bottom sediments

The potential ecological risk index (RI) was studied for each station in the study area (Tables 14, 15, and 16 and Fig. 5), where they showing the following:

During 2010, 2012, and 2015, the highest value of RI was found for S4 in the middle sector, and the lowest degree of contamination were found for S3 during 2010, for S1 in the eastern sector during 2012, and in middle sector for S5 during 2015 of the Lake Burullus. They were arranged in a descending order as follows: S4 > S11 > S7 > S6 > S9 > S5 > S1 > S10 > S8 > S2 > S12 > S3. During 2012, RI 2012 is S4 > S9 > S6 > S10 > S5 > S8 > S2 > S12 > S3 > S11 > S7 > S1 as well as RI 2015; S4 > S11 > S7 > S6 > S9 > S1 > S2 > S10 > S12 > S8 > S3 > S5 (Fig. 5). This study has explored the potential ecological risk index of some selected heavy metals for detecting most vulnerable areas to water and sediment pollution at Burullus Lake in all studied sectors during different three periods: 2010, 2012, and 2015.

Conclusions

This study explores the potentiality of environmental risk of some heavy metals (i.e., Fe, Mn, Co, Ni, Cr, Cd, Pb, Zn, and Cu) for detecting most vulnerable areas to water and sediment pollution at Burullus Lake during different three periods: 2010, 2012, and 2015. Comparison between the mean concentrations of each heavy metal in bottom sediments through different 3 years were in the following order Fe, 2010 < 2012 > 2015; Mn, 2010 > 2012 < 2015; Zn, 2010 < 2012 > 2015; Cu, 2010 > 2012 > 2015; Ni, 2010 > 2012 < 2015; Cr, 2010 > 2012 < 2015; Pb, 2010 < 2012 < 2015; Cd, 2010 < 2012 < 2015.

The concentrations of DO, BOD, COD, and TDS during three periods 2010, 2012, and 2015 were higher than the WHO limits.

The highest degree of contamination (mDc) was found for (S4) in middle sector, and the lowest degree of contamination was found for (S3) in eastern sector of the Lake Burullus. mDc during 2010 are in the following descending order in different stations S4 < S11 < S7 < S1 < S6 < S9 < S8 < S5 < S10 < S12 < S2 < S3. During 2012, the highest mDc was found in S11 (south of western sector) and the lowest degree of contamination was in S10 (north of the western sector). They were arranged in a descending order as follows: S11 < S12 < S4 < S5 < S1 < S6 < S9 < S7 > S8 > S2 > S3 > S10. mDc during 2015 were S4 > S11 > S7 > S1 > S6 > S9 > S8 > S10 > S5 > S12 > S2 > S3.

Recommendations

This study tried to introduce some solutions and recommendations for improvement and future management of Burullus Lake like the regular evaluation and monitoring of water and sediment quality. Spatial assessment of water and sediment quality in Burullus Lake are needed to protect the biodiversity in Burullus Lake.