Potential biomonitoring of the environmental contamination using snails as sentinel organism: A case study from the Manzala Lagoon, Egypt

3.1 Fieldwork

The current bottom sediment samples in the Manzala Lagoon were amassed seasonally from 17 selected stations along with profiles chosen including the entire area (Fig. 1a). The sampling began in the winter of 2018 to the spring, summer, and autumn of 2019. The bottom sediments were obtained from the lagoon using a grab sample (Ekman type) immersed to a depth ranging from 85 to 180 cm. The hydrogen ion concentrations (pH) of the selected samples were measured immediately (Table 3) using a movable pH sensor (HANNA model, HI 9125). While the mercury thermometer was used for measuring the bottom water temperature which should be lower than 5 °C. Table 2 displays the rainfall, organic matter, and sediment types in the Manzala Lagoon for the four seasons.

Table 2 Bottom sediment types, organic matter %, and statistical analysis of monthly rainfall over Manzala Lagoon.

Table 3 Bottom sediment samples depth and hydrogen ion (pH) in different seasons of the Manzala Lagoon.

3.2 Determination of sediment organic carbon content

The organic carbon content was assessed using the acid/dichromate titration approach designated by Gaudette et al. (1974). The results of the analysis were obtained using the equation: $$\mathit{Organic}Carbon\%=10\left(1-T/S\right)\left[1.0N\left(0.003\right)\left(100/W\right)\right]$$

In the equation, T is the sample titration (ml ferrous solution), and S is the standardization blank titration (ml ferrous solution). The T/S factor cancels out the effect of the ferrous solution normality; the value 0.003 refers to the milliequivalent weight of carbon, 1.0 N is the normality of K₂Cr₂O₇, and 10 is the volume of K₂Cr₂O₇ in ml. W is the weight of the sediment sample in grams. The organic carbon is converted to organic matter by multiplying the organic carbon values by the factor of 1.8.

3.3 Snail study

The snails were diagnosed using morphological markers (i.e., shells with short spires, periostracum ornamented with spiral sculptures, and ureter with two distant flexures; Pointier 2008). The snail species of Pseudosuccinea columella were mostly gathered only at four stations (14, 15, 16, and 17) in front of the most important drains of Faraskur El-Serw and Gamalya, which have poured into the Manzala Lagoon for the duration of the four seasons (winter of 2018 and spring, summer, and autumn of 2019) (Fig. 1a). The snail samples have been gathered through handpicking. The freshwater gastropods of Pseudosuccinea columella are recorded as mid-way hosts for Fasciola hepatica. The acquired soft sediments were then analyzed to count the living and dead faunas. Then, approximately 100 g of individual sample was dehydrated in an oven at 80–100 °C for 12  h and finally, soaked in a 10 %–15 % hydrogen peroxide solution for 24  h. The analyzed samples were sieved using a 2- to 125-mm screen mash and then dehydrated again. Mollusks identification was carried out through binocular microscopic (Fig. 1b) and counting them for each station (Table 4).

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Fig. 1b

Snail shell samples were examined by the binocular microscope.

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Table 4 Dead and alive numbers of Pseudosuccinea columella and the total relative densities of snail species found in 100 g in the different seasons of the Manzala Lagoon.

3.4 The heavy metals analysis of water samples

Water sampling (200 ml) was processed by 5 ml of a diacid mixture (HNO₃:HCLO₄, 9:4 ratio) on a hot plate and sorted through the Whatman No. 42 papers. Double distilled water was then added to increase the volume to 50 ml. The heavy metals in the water samples were analyzed following the method given by the Association of Official Analytical Chemistry (Association of Official Analytical Chemistry (AOAC), 1995) using an atomic absorption spectrophotometer (SolarM600531 v1.27).

3.5 Analysis of heavy metals in sediment samples

Portions of 1 g from the dehydrated sample were weighed and moved into a hot block digester. Further, they were treated with HNO₃ solution (Analar grade, BDH 69 %) in two steps; low temperature (40 °C) for 1  h and high temperature (140 °C) for 3 h. Then, diluted with purified deionized water. Finally, the values of Mn, Fe, Cu, Pb, and Zn have been counted through the AASs (Pb through the furnace AAS Model 67OG and Cu and Zn by the flame AAS Model 67OG). Relevant data were illustrated in parts per million (Table 5).

Table 5 Chemical parameters of bottom sediments in Manzala Lagoon (different seasons).

3.6 Analysis of heavy metals in snail tissues

Live Pseudosuccinea columella snails have been acquired to identify the bioconcentrations of trace metals in their soft tissues in every station (Tables 6-9). The soft tissues of Pseudosuccinea columella snails have been carefully unglued from their shells and rinsed with distilled water and methanol to minimize contamination in mantle fluids and remove any sediment particles. About 0.01 g of the soft tissues of each snail sample was dehydrated at 50 °C, weighed, and then dissolved through 1 ml of concentrated HNO₃ at 70 °C for 2  h. In the end, these samples were diluted in 5 ml of ultrapure deionized water to evaluate their heavy metal contents (Federici et al., 2007).

Table 6 Shows the tissue/sediment (BSAF) and tissue/water (BCF) during the winter season of the Manzala Lagoon (parts per million, ppm).

Table 7 Shows the tissue/sediment (BSAF) and tissue/water (BCF) during the spring season of the Manzala Lagoon (parts per million, ppm).

Table 8 Shows the tissue/sediment (BSAF) and tissue/water (BCF) during the summer season of the Manzala Lagoon (parts per million, ppm).

Table 9 Shows the tissue/sediment (BSAF) and tissue/water (BCF) during the autumn season of the Manzala Lagoon (parts per million, ppm).

The concentrations of chemical substances in aquatic organisms may be calculated using two different factors: the bioconcentration factor (BCF) and the bioaccumulation factor (BAF). BCF refers to concentration levels of chemical substances in organisms only due to uptake from the surrounding water, whereas BAF additionally includes uptake from food. In this regard, the bioaccumulation sediment factor was calculated as an organism’s average metal-to-average sediment concentration ratio at a given time (Zhao et al., 2012) to evaluate the performance of metal bioaccumulation in organisms. The BCF of Gobas and Morrison (2000) (Tables 6-9) was calculated as follows: $$\mathit{BCF}=\mathit{Concentration}ofbiota/\mathit{Concentration}ofwater$$

The biota sediment accumulation factor (BSAF) was estimated for designated metals in the snails through the following relationship to estimate the proportion of metals in the organism to the associated sediments (Szefer et al., 1999): $$\mathit{BSAF}=\mathit{Cx}/\mathit{Cs}$$ where Cx and Cs are the concentrations of the designated metals in the snail tissues and the accompanying sediments, respectively. The tissues of snails were categorized as macroconcentrators (BSAF > 2), microconcentrators (1 < BSAF < 2), or deconcentrators (BSAF < 1), following Dallinger (1993). The deposition of mollusk shells has been illustrated in Fig. 1b.

4.1 Life and dead snails

Table 4 displays a comparison between the density of living mollusks and dead fauna (Table 4). This reveals the quantity of living Pseudosuccinea columella snails found only in the four samples from the west and northwest regions (Samples 14–17). The quantity of living Pseudosuccinea columella snails from the surface bottom deposits indicates the ecological explanations and inspection of relations amongst species and physicochemical environmental variables. In Egypt, Pseudosuccinea columella became one of the most widely distributed freshwater snail species. It is also an efficient midway host of Fasciola hepatica (Coelho and Lima, 2003). This could increase the risk of the emergence of fascioliasis in another area and its occurrence in endemic areas due to the presence of greater numbers of susceptible hosts.

4.2 Trace metals in water samples

The Cu, Pb, Fe, Mn, and Zn (ppm) concentrations in the various samples of water in all seasons vary between 4.10–8.45, 5.21–7.67, 4.30–7.54, 3.97–5.98, and 0.28–0.34, respectively. The maximum trace metal levels were recorded in front of the El-Serw drain, where the values of trace metals in both freshwater and sediment samples enhanced significantly through the high effluent discharge level into this drain from the industrial region of Damietta.

4.3 Trace metals in bottom sediments

The percentages of all heavy metals were higher in the bottom sediment than in the water. This revealed that the metals precipitated in the sediment instead of dissolving in water (Table 5), where sediments are important sinks for numerous pollutants such as pesticides and heavy metals. Also, sediments play an extensive function in remobilizing contaminants in aquatic systems under favorable situations and in water–sediment interactions (Hyun et al., 2007).

Iron: In summer, the minimum average concentration value of iron at the four stations was 4.80 mg/g. It increased slowly in winter (4.83 mg/g) and reached 5.03 mg/g in spring and 5.42 mg/g in autumn. The maximum annual average concentration values of iron (6.21 mg/g) were recorded at Station 16 during autumn. Zinc: The maximum average concentration value of zinc was recorded (36.3 μg/g) in autumn. It decreased gradually in winter and summer (33.75 and 33 μg/g, respectively) and reached its minimum average value in spring (23 μg/g). The maximum annual average concentration values of zinc (60 μg/g) were recorded at Station 16 in autumn. Copper: The highest concentration value for copper was monitored in summer (96 μg/g). In contrast, the lowest value was recorded in spring (76.3 μg/g). It decreased gradually in autumn and winter (86.8 and 84 μg/g, respectively). The maximum annual average values were recorded at Station 17 (163 μg/g) in summer. The most concentrated trace metal recorded were Fe and Zn, whereas the least was Cu. These findings agree with the previous observations of Abd El-Azim et al. (2018) in Lake Timsah.

Manganese: The highest average concentration value of manganese (35.1 μg/g) was reported in winter while the lowest was in summer (13.75 μg/g). It decreased slowly in autumn and spring (25.08 and 21.0 μg/g, respectively) till reached the minimum in summer (13.75 μg/g). The extreme annual average concentration value of manganese was recorded at Station 14 (58.0 μg/g), and the lowest value was 18.5 μg/g at Station 17 in summer. Lead: The highest average concentration values of lead were recorded in winter and summer and reached 15.5 and 14.8 μg/g, respectively. These gradually decreased in autumn and spring (6.3 and 4.3 μg/g, respectively). The lowest average value reached 4.3 μg/g in spring. The maximum annual average concentration value of lead was recorded at Station 17 (39 μg/g). Lead is a toxic metal originating from natural processes and anthropocentric activities (coal power plants, mining, waste gas fuel, leather whipping, paint, and battery factories). It is detrimental to the environment and human health.

4.4 Bsaf

The BSAF in winter, spring, summer, and autumn in the area under investigation revealed that all the soft tissues of the Pseudosuccinea columella snails were macroconcentrators (BSAF > 2) (Tables 6–9) except for Mn (where they were deconcentrators in summer and autumn; BSAF < 1) and Fe (where they were deconcentrators in autumn; BSAF < 1). These show that selective tissues are thus good biomonitors of pollution rates. The minimum BSAF values for Cu in the soft tissues varied from 3.1 to 4.55 in winter. These increased to 3.30–4.55 in spring. The maximum values for Cu were recorded in summer (7.60–9.62). The minimal BSAF values for Zn in the soft tissues varied from 2.20 to 3.90 in autumn. These increased to maximum values during summer (4.11–5.72). The maximum BSAF values for Pb in the soft tissues ranged from 3.11 to 4.41 in spring, whereas the minimum values (2.10–3.30) were recorded in autumn.

The minimum BSAF values for Fe in the soft tissues ranged from 1.80 to 3.00 in autumn. The maximum values ranged from 4.28 to 7.13 in summer. The minimum BSAF values for Mn in the soft tissues ranged from 1.70 to 2.40 in summer. The maximum values ranged from 3.12 to 4.28 in winter. Laszczyca et al. (2004) illustrated that enzymatic activities are responses to environmental stress. Thus, they can be used to estimate pollution at population and ecosystem levels. Meanwhile, El-Khayat et al. (2015) used physiological and biochemical parameters as indicators of histopathological changes. These parameters have also been widely used as biomarkers in the health evaluation of animals.

4.5 Bcf

The BCF confirmed that the highest concentrations (ppm) of Cu ranged from 13.21 to 32.56 in autumn. Those of Fe ranged from 119.78 to 895.12 in summer, and those of Mn ranged from 10.22 to 62.16 in autumn. The highest concentrations of Zn ranged from 21.22 to 85.21 in autumn, and those of Pb ranged from 1.16 to 3.86 in summer (Tables 6-9). The BCF values obtained for Cu and Pb were>1.00, indicating that both were highly bioaccumulated and biomagnified in the tissues of Pseudosuccinea columella snails (Cu has higher BCF than that of Pb). Copper is essential in some enzymes for organisms (Yap et al. 2016) and serves as a micronutrient for cellular metabolism (Ismarti et al. 2017). The cuproprotein hemocyanin (Cheung and Wong, 1992) functions similarly to Fe in the metabolism of molecular oxygen in snails because the oxygen-carrying pigment in mollusks’ blood is not hemoglobin. This study confirmed the high variations in BCF limits depending on the metal type (Tables 6-9). This is due to the tolerance effect of snails to the persistent toxic chemicals and can be considered effective biomonitors (Rehman et al., 2016). The concentration factors (BCF) exceeding 1 indicated that the freshwater snail Pseudosuccinea columella may be used to clean up the trace metal contamination caused by human activity.

5.1 Ecological factors affecting the abundance of P. Columella

5.2 Factors controlling the distribution of trace elements