3.1 HMs concentration and their distributions
This investigation used three different types of water sampling methods: water samples from 9 gas wells, discharge water samples from 5 gas process facilities, and 5 tube-well or drinking water samples. The mean pH value of produced water was found to be 6.56 ± 0.76 in the summer and 6.91 ± 1.98 in the rainy season. The average pH value for discharge water was found to be 7.19 ± 0.84 in the summer and 7.52 ± 0.56 in the rainy season. Furthermore, the average pH value for drinking water was found to be 6.25 ± 1.2 in the dry season and 7.24 ± 0.49 in the wet season. The outcome of pH represents water’s alkalinity or acidity (Ravikumar et al., 2013), where pH (6–8.5) is considered useful (Garg et al., 2010) and low pH water is considered erosive water, which may adversely affect eyes and skins (Li et al., 2017). This study found that water pH around gas fields is suitable for human consumption or productivity (Proshad et al., 2020). The average electrical conductivity (EC) in produced water was 13300.7 ± 12635.9 and 15902.3 ± 14389.5; discharge water was 17752.22 ± 11470.7 and 10791.45 ± 12427.5 and drinking water 247.936 ± 216.1 and 249.47 ± 221.7 in summer and rainy season respectively. The EC is a common indicator of saline water, and water with an EC greater than 2250 µS/cm is considered extremely salty (Proshad et al., 2020). The observed EC indicated that the gas field produced and discharged highly saline water (Wu & Sun, 2016). The EC of discharge water during the rainy season is lower than in the summer because of water dilution with rain (Islam et al., 2019; Cheng et al., 2005). The rain has no effect on the EC of PW because PW composition varies with the reservoir's structure, not with seasonal variation (Al-Ghouti et al., 2019).
Table 1
HMs concentration with other water parameters.
Parameter | Water Type | Summer Season | Rainy Season | ECR, 1997 | MAC (a,b) |
Min-Max | Median | Mean ± St.dev. | Skewness | Min-Max | Median | Mean ± St.dev. | Skewness |
pH | P | 5.32–7.32 | 6.99 | 6.56 ± 0.76 | -0.51 | 1.82–8.14 | 7.58 | 6.91 ± 1.98 | -2.6 | N/A | N/A |
D | 5.81–7.98 | 7.37 | 7.19 ± 0.84 | -1.44 | 6.85–8.16 | 7.66 | 7.52 ± 0.56 | -0.236 | 6 to 9 |
T | 4.7–7.59 | 5.88 | 6.25 ± 1.2 | -0.06 | 6.52–7.75 | 7.42 | 7.24 ± 0.49 | -0.78 | 6.5 to 8.5 |
EC µS/cm | P | 106-29620 | 18830 | 13300.7 ± 12635.9 | 0.002 | 87.95–39800 | 13400 | 15902.3 ± 14389.5 | 0.3303 | N/A | N/A |
D | 131.1-29320 | 18640 | 17752.22 ± 11470.7 | -0.93 | 82.25–29020 | 5815 | 10791.45 ± 12427.5 | 0.9024 | 1200 |
T | 35.38–500.4 | 178.1 | 247.936 ± 216.1 | 0.389 | 39.8-501.7 | 142.7 | 249.47 ± 221.7 | 0.4954 | N/A |
As µg/L | P | 0.28–1.98 | 0.43 | 0.66 ± 0.5 | 2.137 | 0.33–5.13 | 0.65 | 1.62 ± 1.68 | 1.4002 | N/A | 10 |
D | 0.45–1.4 | 0.45 | 0.73 ± 0.42 | 1.385 | 0.43–0.9 | 0.58 | 0.64 ± 0.19 | 0.5718 | 200 |
T | 0.33–11.3 | 0.55 | 4.26 ± 5.3 | 0.748 | 0.43–10.8 | 2 | 4.49 ± 4.85 | 0.659 | 50 |
Cd µg/L | P | 0.11–1.90 | 0.22 | 0.54 ± 0.6 | 1.674 | 0.12–4.1 | 0.95 | 1.11 ± 1.27 | 1.9143 | N/A | 5 |
D | 0.32–1.18 | 0.37 | 0.58 ± 0.37 | 1.405 | 0.23–1.8 | 0.38 | 0.89 ± 0.79 | 0.5968 | 50 |
T | 0.15–0.3 | 0.25 | 0.23 ± 0.07 | -0.33 | 0.21–1.01 | 0.42 | 0.58 ± 0.40 | 0.4436 | 5 |
Co µg/L | P | 1.85–72.80 | 13.8 | 30.06 ± 28 | 0.742 | 1.5–235 | 11.4 | 54.36 ± 79.16 | 1.8669 | N/A | 4 |
D | 1.32-42 | 20.7 | 21.54 ± 16.1 | 0.048 | 2.88–13.8 | 7.54 | 8.64 ± 4.95 | 0.128 | N/A |
T | 1.02–15.1 | 9.07 | 8.46 ± 6.3 | -0.17 | 1.82-16 | 5.93 | 6.55 ± 5.67 | 1.5345 | N/A |
Cr µg/L | P | 3.53–20.40 | 6.53 | 7.83 ± 4.92 | 2.532 | 4.52–16.1 | 5.75 | 7.22 ± 3.78 | 2.0113 | N/A | 50 |
D | 5.87–536 | 7.24 | 112.65 ± 236.7 | 2.236 | 4.59–6.5 | 5.29 | 5.36 ± 0.72 | 1.0883 | 500 |
T | 3.53–6.3 | 4.82 | 4.85 ± 0.99 | 0.327 | 4.1–5.4 | 4.96 | 4.89 ± 0.56 | -0.808 | 50 |
Cu µg/L | P | 11.0–33.0 | 15 | 17.56 ± 7.54 | 1.43 | 9-225 | 17 | 45 ± 69.59 | 2.6952 | N/A | 50 |
D | 12 to 84 | 16 | 29.4 ± 30.7 | 2.188 | 9 to 20 | 12 | 13.8 ± 4.27 | 0.68 | 500 |
T | 6 to 31 | 12 | 16.6 ± 9.89 | 0.757 | 7 to 28 | 13 | 14.2 ± 8.41 | 1.4125 | 100 |
Fe µg/L | P | 1450–74400 | 2520 | 17628.8 ± 25747.2 | 1.731 | 140-26600 | 1940 | 6588 ± 8774 | 1.7656 | N/A | 300 |
D | 1180–34500 | 2330 | 8716 ± 14453.7 | 2.206 | 160–1670 | 910 | 794 ± 637.4 | 0.3286 | 2000 |
T | 20–550 | 300 | 316 ± 213.4 | -0.37 | 100–2920 | 230 | 740 ± 1220.5 | 2.2191 | 300 |
Mn µg/L | P | 49–682 | 112 | 263.22 ± 261.9 | 0.879 | 26-5685 | 150 | 774.56 ± 1845 | 2.9764 | N/A | 100 |
D | 121–614 | 496 | 379 ± 232.4 | -0.45 | 21–324 | 92 | 124 ± 119.1 | 1.6085 | 500 |
T | 10 to 44 | 27 | 24.8 ± 14.1 | 0.296 | 10–592 | 15 | 129.6 ± 258.5 | 2.2355 | 100 |
Ni µg/L | P | 4.94–276.5 | 35.74 | 68.21 ± 87 | 2.039 | 4.35–510.6 | 31.68 | 153.66 ± 201.8 | 1.1346 | N/A | 20 |
D | 7.34–206.1 | 42.49 | 72.25 ± 80.94 | 1.525 | 6.7-296.8 | 28.91 | 83.1 ± 121.6 | 2.0539 | 1000 |
T | 4-19.64 | 7.09 | 9.1 ± 6.23 | 1.743 | 1.64–14.29 | 9.56 | 7.64 ± 5.38 | -0.078 | 100 |
Pb µg/L | P | 0.72–25.2 | 1.5 | 4.06 ± 7.9 | 2.983 | 1.38–54.3 | 2.31 | 9.1 ± 17.1 | 2.9189 | N/A | 10 |
D | 1.02–13.1 | 2.62 | 4.168 ± 5.1 | 2.114 | 0.25–3.48 | 1.41 | 1.59 ± 1.24 | 0.8716 | 100 |
T | 0.24–15.4 | 0.92 | 3.84 ± 6.5 | 2.174 | 0.13–2.1 | 1.07 | 1.04 ± 0.71 | 0.336 | 50 |
Zn µg/L | P | 11.6-811.4 | 83.5 | 169.3 ± 249.2 | 2.649 | 27.3–4620 | 219.8 | 720.4 ± 1478.1 | 2.8807 | N/A | 5000 |
D | 91.6–5720 | 120.7 | 1245.68 ± 2501.51 | 2.235 | 5.1-258.4 | 85.7 | 92.64 ± 101.98 | 1.3274 | 5000 |
T | 48-395.9 | 75.1 | 132.76 ± 147.7 | 2.192 | 36.2-308.2 | 149.4 | 146.8 ± 113.4 | 0.5363 | 5000 |
N/A = not available, ECR'1997 = Environmental conservation rule (Bangladesh); MAC=maximum allowable concentration; a = Shen et al., 2019; b = WHO,2017 |
However, in this study, the average heavy metal concentration for produced water was found in ascending order as Cd < As < Pb < Cr < Cu < Co < Ni < Zn < Mn < Fe in both seasons. The concentration of Fe was found to be extremely high, and Mn and Ni also had a high concentration. Except for iron, metal accumulation in produced water was observed to be higher during the monsoon than pre-monsoon. A previous study also found similar observation as produced water is an intrusion of formation liquid into the well from the top or bottom of the petroleum reservoir. Hence, water chemistry varies from well to well based on the geological structure, age, and flow of fluid (Hedar and Budiyano, 2018). Hence, seasonal variation seems to have no effect on the toxic metal concentration in PW (Ahmadun et al., 2009).
Moreover, the average value of water parameter in discharge water found as: Cd (0.58 ± 0.37), As (0.73 ± 0.42), Co (21.54 ± 16.1), Cr (112.65 ± 236.7), Cu (29.4 ± 30.7), Fe (8716 ± 14453.7), Mn (379 ± 232.4), Ni (72.25 ± 80.94), Pb (4.168 ± 5.1), and Zn (1245.68 ± 2501.51) µg/L during summer. During rain, the TMs in discharge water observed as: As (0.64 ± 0.19), Cd (0.89 ± 0.79), Co (8.64 ± 4.95), Cr (5.36 ± 0.72), Cu (13.8 ± 4.27), Fe (794 ± 637.4), Mn (124 ± 119.1), Ni (83.1 ± 121.6), Pb (1.59 ± 1.24), and Zn (92.64 ± 101.98) µg/L. However, the average quantity of toxic metal obtained in discharge and drinking water within the national recommended limit (ECR’1997), except Fe (Table-1). Nevertheless, the mean value of Cr, Fe, Ni, Mn, and Co were substantially greater than global standards (Hossain et al., 2022; WHO, 2017). In addition, high levels of trace metals were observed during the summer than during the rainy season, which may be attributed to the diluting effects of rain (Proshad et al., 2020; Mohiuddin et al., 2012). The previous report also discovered that surface water exhibits seasonal variation and rainfall significantly decreases metal concentrations due to increased water levels (Ali et al., 2018; Ali et al., 2016). Consequently, Figs. 2 and 3 depict the spatial variation of TMs during the summer and the rainy periods. In Figs. 2, the reddish zone represents a higher concentration of the observed parameter, while the blue zone represents a lower concentration. In addition, the green zone represents lower metal content, and the red zone reflects higher metal accumulation in Figs. 3.
3.2 Pollution status based on HMEI
The HMEI is valuable for evaluating trace metal pollution scenarios (Prasanna et al., 2012). The outcome of HMEI ranging from 17.35 to 257.07, with a mean of 73.44 for produced water during the summer (Table 2). During the rainy season, HMEI ranges from 4.22 to 172.08, averaging 53.45 for produced water. In addition, the lowest, highest, and average HMEI values for discharge water were obtained as 13.29, 138.29, and 45.54 in the time of dry season and 6.51, 18.64, and 11 throughout wet season, respectively. The value of drinking water samples is comparatively low, with an average of 5.18 in the summer and 6.86 in the rainy season. The outcome reveals that most of the produced water exhibits high pollution status since the value is greater than 20 (Bodrud-Doza et al., 2016), discharge water exhibits moderate to low pollution (10 < HMEI < 20) (Biswas et al., 2017) and drinking water have low pollution level (HMEI < 10) (Prasanna et al., 2012). The pre-monsoon discharge water has a higher HMEI value than the monsoon discharge water, which may be due to the monsoonal rain's dilution and flushing effects (Shil & Singh, 2019).
Table 2
Heavy metal evaluation index
Sample ID | Summer season | Rainy season |
HMEI | Remarks | HMEI | Remarks |
Produced water | P1 | 27.97 | High | 50.29 | High |
P2 | 23.33 | High | 19.80 | Medium |
P3 | 161.76 | High | 96.69 | High |
P4 | 34.37 | High | 27.40 | High |
P5 | 72.81 | High | 33.10 | High |
P6 | 17.35 | Medium | 66.72 | High |
P7 | 257.07 | High | 4.22 | Low |
P8 | 39.57 | High | 172.08 | High |
P9 | 26.76 | High | 10.76 | High |
min | 17.35 | Medium | 4.22 | Low |
max | 257.07 | High | 172.08 | High |
Mean | 73.44 | High | 53.45 | High |
Discharge water | D1 | 27.12 | High | 18.64 | Medium |
D2 | 29.45 | High | 8.79 | Low |
D3 | 138.19 | High | 6.51 | Low |
D4 | 19.64 | Medium | 12.13 | Medium |
D5 | 13.29 | Medium | 8.93 | Low |
min | 13.29 | Medium | 6.51 | Low |
max | 138.19 | High | 18.64 | Medium |
Mean | 45.54 | High | 11.00 | Medium |
Drinking water | T1 | 5.40 | Low | 18.43 | Low |
T2 | 3.82 | Low | 7.20 | Low |
T3 | 5.21 | Low | 3.21 | Low |
T4 | 4.97 | Low | 2.55 | Low |
T5 | 6.49 | Low | 2.92 | Low |
min | 3.82 | Low | 2.55 | Low |
max | 6.49 | Low | 18.43 | Low |
Mean | 5.18 | Low | 6.86 | Low |
3.3 Environmental and ecological toxicity evaluation
Figure 4 depicts the environmental pollution index (EPI) that was calculated to investigate the environmental toxicity status of TMs presence in studied water (Islam et al., 2015).According to the results, environmental pollution ranges from low (EPI < 0.5) to moderate (0.5 < EPI < 1) to high (EPI > 1) (Kowalska et al., 2016).EPI values for DW03 (summer), PW 06 (rainy), and PW 08 (rainy) indicate a high risk. Other produced and discharge water poses a moderate risk, whereas all samples of potable water pose a lower risk. In the majority of instances, the environmental risk during the summer has a greater value than rainy season samples (Fig. 4).
However, for this study, another index known as the ecological risk index was evaluated, which is a well-known tool for assessing the ecotoxicological status of water (Ma & Han, 2020). It combines single ecological risk indicator (ERI) to assess the total possible risk (RI) of HMs presence in water (Weissmannová et al., 2019). Based on ERI and RI potential toxicity can be classified as low ( at ERI < 40 and RI < 150), medium (when 40 ≤ ERI < 80 and 150 ≤ RI < 300), considerable (at 80 ≤ ERI < 160 and 300 ≤ RI < 600), high (when 160 ≤ ERI < 320 and RI ≥ 600) and extreme (ERI ≥ 320) (Akarsu et al,2022; Ma & Han, 2020). At the time of summer and rainy periods, the average ERI of produced water found as 67.44 and 136.23, the mean ERI of discharge water was 65.11 and 44.71, and the average ERI of drinking water was 23.44 and 23.85 correspondingly (Table 3). Co and Ni demonstrated the most ERI for a single metal in three types of water during both seasons. Furthermore, for produced water, the mean index value for single metal followed as Co > Ni > Cd > Mn > Pb > Cu > As > Cr > Zn in both seasons, where for discharge and drinking water obtained as different order (Table 3). The average ERI for three types of water samples was less than 40 (except for Co (produced during the rainy season), indicating a low level of ecological risk (Howladar et al., 2021). Total ecological risk (RI) is typically less than 150 for all sample types, indicating a low possibility of ecological risk near gas fields (Acharjee et al., 2022).
Table 3
Ecological toxicity status of studied water samples.
ERI of HMs | Summer season | Rainy season |
Produced water | Discharge water | Drinking water | Produced water | Discharge water | Drinking water |
As | 0.66 | 0.73 | 4.26 | 1.62 | 0.64 | 4.49 |
Cd | 5.38 | 5.82 | 2.30 | 11.07 | 8.86 | 5.80 |
Co | 37.58 | 26.93 | 10.57 | 67.95 | 10.79 | 8.19 |
Cr | 0.31 | 4.51 | 0.19 | 0.29 | 0.21 | 0.20 |
Cu | 1.76 | 2.94 | 1.66 | 4.50 | 1.38 | 1.42 |
Fe | - | - | - | - | - | - |
Mn | 2.63 | 3.79 | 0.25 | 7.75 | 1.24 | 1.30 |
Ni | 17.05 | 18.06 | 2.26 | 38.41 | 20.77 | 1.91 |
Pb | 2.03 | 2.08 | 1.92 | 4.50 | 0.79 | 0.52 |
Zn | 0.03 | 0.25 | 0.03 | 0.14 | 0.02 | 0.03 |
RI | 67.44 | 65.11 | 23.44 | 136.23 | 44.71 | 23.85 |
3.4 Health Risk (HR) Scenario around Gas Fields Region
HR assessment in water refers to the estimation of potential health effects caused by cancer-causing or non-cancer-causing elements present in water (USEPA, 2001). It helps decision-makers understand the potential outcomes of actions, possible treatments, disposal, mitigation, and clean-up standards. The risk assessment process is made up of four main steps: (a) Hazard Identification; (b) Exposure Assessment; (c) Dose-response Toxicity Evaluation; and (d) Risk Level Computation (USEPA, 2001). The primary objective of hazard identification is to examine pollutants at a site, initial concentrations, and regional variations of pollutants (Kamunda et al., 2016). This study evaluated the initial concentration and spatial variation of toxic metals in gas field water, computed dose response exposure (EDD), and then determined the cancer and non-cancer risk. However, in recent years, along with noncarcinogenic (HI score) and carcinogenic risk (CR score), heavy metal toxicity tools (HMTL) have also been used as noncarcinogenic health risk evaluation to investigate potential human health risks from trace metals (Saha& Paul, 2019; Hossain & Patra, 2020a).
Table 4
(a). HMTL of TMs presence in gas fields water.
Trace elements | Dry Season | Wet Season | Permissible toxicity limit |
P | D | T | P | D | T |
As | 1109.884 | 1216.776 | 7143.112 | 2718.844 | 1069.288 | 7528.592 | 16760 |
Cd | 708.7911 | 767.076 | 303.14 | 1458.587 | 1167.748 | 764.44 | 3954 |
Co | 30397.4 | 21780.98 | 8549.016 | 54959.08 | 8728.974 | 6622.05 | 2022 |
Cr | 6997.151 | 100596.5 | 4329.264 | 6444.483 | 4788.266 | 4373.914 | 44650 |
Cu | 14132.22 | 23667 | 13363 | 36225 | 11109 | 11431 | 805000 |
Mn | 209788.1 | 302063 | 19765.6 | 617320.8 | 98828 | 103291.2 | 239100 |
Ni | 67728.12 | 71740.28 | 8962.818 | 152583.3 | 82504.4 | 7584.534 | 69510 |
Pb | 6215.86 | 6381.208 | 5885.164 | 13782.4 | 2428.166 | 1586.116 | 15310 |
Zn | 154570.9 | 1137306 | 121209.9 | 657694.8 | 84580.32 | 134028.4 | 4565000 |
HMTL | 281860.3 | 1363456 | 169745.4 | 1543187 | 295204.2 | 277210.2 | 5761306 |
The HTML values of studied fields are shown in Table 4(a). The average HTML values found in produced water were 281860.3 and 1543187; in discharge water, they were 1363456 and 295204.2; and in drinking water samples, they were 169745.4 and 277210.2 in the summer and rainy seasons, respectively. Previous research has shown that HTML can be used to evaluate the concentration of toxic elements in water, which may have harmful effects on public health (Proshad et al., 2020; Kumar et al.,2019). Additionally, these studies also reveal the percentages of toxic metals that must be removed from water before it is safe for human consumption (Huang et al., 2021). In this current study, the total HTML combined with all measured heavy metals was found to be below the allowable toxicity limits, indicating minimal contamination in the studied water (Ayejoto et al., 2021; Huang et al., 2021). However, in the case of individual metals, the average HTML concentration of certain elements such as Mn in (wet season produced water), Ni in (produced water in both seasons), Co present in (produced, discharged, and drinking water of both seasons) and Cr of discharge water (dry season) exceeded the permissible toxicity limits (Saha & Paul, 2019). Although the total HTML is within the permissible limit (PL), the values of Ni, Co, Mn, and Cr in some cases were above the permissible limit (PL), and they need to be removed for safe water consumption. The percentages of trace metals required to eliminate are displayed in Table 4(b) (Ayejoto et al., 2021; Saha & Paul, 2009). Respective authorities should make reasonable efforts for the necessary percentages of trace metals to be eliminated from produced and discharged water (Kumar et al., 2019).
Table 4
(b). Percentages of Heavy metals required to eliminated for safe consumption.
Trace elements | Dry Season | Wet Season |
P | D | T | P | D | T |
As | PL | PL | PL | PL | PL | PL |
Cd | PL | PL | PL | PL | PL | PL |
Co | 93.35 | 90.72 | 76.35 | 96.32 | 76.84 | 69.47 |
Cr | PL | 55.61 | PL | PL | PL | PL |
Cu | PL | PL | PL | PL | PL | PL |
Mn | PL | 20.84 | PL | 61.27 | PL | PL |
Ni | PL | 3.11 | PL | 54.44 | 15.75 | PL |
Pb | PL | PL | PL | PL | PL | PL |
Zn | PL | PL | PL | PL | PL | PL |
HMTL | PL | PL | PL | PL | PL | PL |
The mean noncarcinogenic (NCR) hazard score of TMs present in water samples is presented in Table 5 and spatial distribution map (Fig. 5). The possible non-cancerous and cancerous risks via ingestion and dermal absorption of trace metals were evaluated for children and adults (female, male). In the summer season, the mean HI of produced water was found to be 3.50E-03 for children, 3.61E-03 for males, and 3.96E-03 for females; in the case of discharge water, the average HI obtained was 5.82E-03 for children, 4.45E-03 for males, and 4.81E-03 for females, whereas for drinking water the value was 1.39E-03, 1.19E-03, and 1.29E-03 for children, adult males, and females, individually (Fig. 5). Moreover, during the rainy season, mean HI was found as 5.08E-03 (children), 5.98E-03 (male) and 6.60E-03 (female) for produced water, 1.24E-03 (Children), 1.16E-03 (male) and 1.27E-03 (female) for discharge water, whereas 1.72E-03 (children), 1.25E-03(male) and 1.34E-03 (female) for drinking water samples around the gas fields area (Fig. 5).
However, the findings from Table 5 showed that the hazard index of As, Co, Cr, Cd, Cu, Mn, Fe, Pb, Ni, and Zn were higher in children than adults and higher in females than males (Aendo et al., 2022). It was also observed that the total hazard score (HI) of all studied metals was less than 1 indicating an acceptable level of noncarcinogenic risk in studied samples (Mohammadi et al., 2019). Among all trace metals, the hazard score for Fe, Mn, and Co in PW was observed to be higher than others (Table 5). In the case of discharge water, the non-cancer risk index was found to be higher for Cr and Mn than others, whereas drinking water samples had different trends. The summertime discharge water results in higher HI values than the rainwater, in line with previous findings (Proshad et al., 2020; Ji et al., 2020). As non-cancer elements, excess amounts of TMs present in water can affect the liver, skin and pancreas, cause nausea, vomiting, hematemesis, diarrhea, abdominal pain, sickness, and dizziness, as well as asthma and chronic bronchitis, allergic reactions, heart disorders (Ogidi et al., 2021; Odangowei et al., 2020), immune imbalances, frank anemia, hypertension, intellectual disability, gastrointestinal effects, skeletal delay, hearing loss, infertility, and so on (Hossain et al., 2022). Since the combined hazard score is less than one, it can be concluded from the present study that there is no potential non-cancerous risk associated with consuming water from the studied gas fields region (Ogidi et al., 2021; Aendo et al., 2022).
Table 5
Hazard index of summer and rainy season water samples.
HMs | As | Cd | Co | Cr | Cu | Fe | Mn | Ni | Pb | Zn |
Hazard Index (Summertime) | Children | P | 1.33E-04 | 6.47E-05 | 5.20E-04 | 1.99E-04 | 2.86E-05 | 1.53E-03 | 7.13E-04 | 2.05E-04 | 6.76E-05 | 3.41E-05 |
D | 1.46E-04 | 7.00E-05 | 3.73E-04 | 2.86E-03 | 4.79E-05 | 7.59E-04 | 1.03E-03 | 2.17E-04 | 6.94E-05 | 2.51E-04 |
T | 8.54E-04 | 2.77E-05 | 1.46E-04 | 1.23E-04 | 2.70E-05 | 2.75E-05 | 6.72E-05 | 2.71E-05 | 6.40E-05 | 2.67E-05 |
Female | P | 6.26E-05 | 3.05E-05 | 2.40E-03 | 1.19E-04 | 1.36E-05 | 7.59E-04 | 4.28E-04 | 1.01E-04 | 3.15E-05 | 1.67E-05 |
D | 6.86E-05 | 3.30E-05 | 1.72E-03 | 1.72E-03 | 2.27E-05 | 3.75E-04 | 6.17E-04 | 1.07E-04 | 3.23E-05 | 1.23E-04 |
T | 4.03E-04 | 1.30E-05 | 6.74E-04 | 7.39E-05 | 1.28E-05 | 1.36E-05 | 4.04E-05 | 1.33E-05 | 2.98E-05 | 1.31E-05 |
Male | P | 6.13E-05 | 2.99E-05 | 2.10E-03 | 1.12E-04 | 1.33E-05 | 7.39E-04 | 4.08E-04 | 9.82E-05 | 3.09E-05 | 1.63E-05 |
D | 6.72E-05 | 3.23E-05 | 1.51E-03 | 1.62E-03 | 2.22E-05 | 3.65E-04 | 5.87E-04 | 1.04E-04 | 3.17E-05 | 1.20E-04 |
T | 3.95E-04 | 1.28E-05 | 5.91E-04 | 6.95E-05 | 1.26E-05 | 1.32E-05 | 3.84E-05 | 1.30E-05 | 2.93E-05 | 1.28E-05 |
Hazard Index (Rain time) | Children | P | 3.25E-04 | 1.33E-04 | 9.40E-04 | 1.83E-04 | 7.33E-05 | 5.74E-04 | 2.10E-03 | 4.62E-04 | 1.50E-04 | 1.45E-04 |
D | 1.28E-04 | 1.07E-04 | 1.49E-04 | 1.36E-04 | 2.25E-05 | 6.91E-05 | 3.36E-04 | 2.50E-04 | 2.64E-05 | 1.87E-05 |
T | 9.00E-04 | 6.98E-05 | 1.13E-04 | 1.24E-04 | 2.31E-05 | 6.44E-05 | 3.51E-04 | 2.29E-05 | 1.72E-05 | 2.96E-05 |
Female | P | 1.53E-04 | 6.27E-05 | 4.33E-03 | 1.10E-04 | 3.48E-05 | 2.84E-04 | 1.26E-03 | 2.27E-04 | 6.98E-05 | 7.13E-05 |
D | 6.03E-05 | 5.02E-05 | 6.88E-04 | 8.18E-05 | 1.07E-05 | 3.42E-05 | 2.02E-04 | 1.23E-04 | 1.23E-05 | 9.17E-06 |
T | 4.24E-04 | 3.29E-05 | 5.22E-04 | 7.47E-05 | 1.10E-05 | 3.18E-05 | 2.11E-04 | 1.13E-05 | 8.03E-06 | 1.45E-05 |
Male | P | 1.50E-04 | 6.15E-05 | 3.80E-03 | 1.03E-04 | 3.41E-05 | 2.76E-04 | 1.20E-03 | 2.21E-04 | 6.85E-05 | 6.95E-05 |
D | 5.91E-05 | 4.92E-05 | 6.03E-04 | 7.69E-05 | 1.04E-05 | 3.33E-05 | 1.92E-04 | 1.20E-04 | 1.21E-05 | 8.94E-06 |
T | 4.16E-04 | 3.22E-05 | 4.58E-04 | 7.02E-05 | 1.07E-05 | 3.10E-05 | 2.01E-04 | 1.10E-05 | 7.88E-06 | 1.42E-05 |
Furthermore, The potential cancer risk of TMs for Cd, As, Cr, Pb, and Ni was computed through the average daily dose of the cancer slope factor. Table 6 and Fig. 6 depict the outcomes. The findings reveal that the cancerous effects of Ni and Cr are comparatively higher than other metals in water of both seasons. The measured constituents for cancerous risk follow the increasing trends of Pb < As < Cd < Cr < Ni for all age groups in summer season water samples and follow the ascending order of Pb < As < Cr < Cd < Ni in rainy season water. The average CR of Ni for produced water found in children was 6.95E-03 and 1.57E-02, female 1.19E-04 and 7.40E-03, and male 3.22E-03 and 7.26E-03 in the summertime and rain time, respectively (Table 6). The mean CR value of Ni for discharge water was obtained as children: 7.37E-03 and 8.47E-03, females 1.72E-03 and 4.00E-03, males 3.41E-03 and 3.92E-03. The outcome indicated that the cancer risk score for Ni was greater than the international safe limit (1E-4) for all age groups (Hossain & Patra, 2019). The CR value of Cr also surpassed international standards. The cancer hazard score of metal (Cd) exists as a safeguard value for most of the cases of rainy season water and some cases of summer season water (Siddique et al., 2021). The cancer risk factor for arsenic (As) is also close to the threshold limit (Table 6) (Hossain et al., 2022).
Table 6
Cancer risk of trace metals.
Trace Metals | Total carcinogenic risk (summer season) | Total carcinogenic risk (rainy season) |
As | Cd | Cr | Ni | Pb | As | Cd | Cr | Ni | Pb |
Children | P | 5.97E-05 | 1.97E-04 | 2.36E-04 | 6.95E-03 | 2.08E-06 | 1.46E-04 | 4.06E-04 | 2.18E-04 | 1.57E-02 | 4.60E-06 |
D | 6.55E-05 | 2.13E-04 | 3.40E-03 | 7.37E-03 | 2.13E-06 | 5.75E-05 | 3.25E-04 | 1.62E-04 | 8.47E-03 | 8.11E-07 |
T | 3.84E-04 | 8.44E-05 | 1.46E-04 | 9.20E-04 | 1.96E-06 | 4.05E-04 | 2.13E-04 | 1.48E-04 | 7.79E-04 | 5.30E-07 |
Female | P | 6.26E-05 | 3.05E-05 | 2.40E-03 | 1.19E-04 | 1.36E-05 | 6.90E-05 | 1.91E-04 | 1.02E-04 | 7.40E-03 | 2.17E-06 |
D | 6.86E-05 | 3.30E-05 | 1.72E-03 | 1.72E-03 | 2.27E-05 | 2.71E-05 | 1.53E-04 | 7.60E-05 | 4.00E-03 | 3.82E-07 |
T | 4.03E-04 | 1.30E-05 | 6.74E-04 | 7.39E-05 | 1.28E-05 | 1.91E-04 | 1.00E-04 | 6.94E-05 | 3.68E-04 | 2.50E-07 |
Male | P | 2.76E-05 | 9.12E-05 | 1.09E-04 | 3.22E-03 | 9.59E-07 | 6.76E-05 | 1.88E-04 | 1.00E-04 | 7.26E-03 | 2.13E-06 |
D | 3.03E-05 | 9.87E-05 | 1.57E-03 | 3.41E-03 | 9.84E-07 | 2.66E-05 | 1.50E-04 | 7.45E-05 | 3.92E-03 | 3.75E-07 |
T | 1.78E-04 | 3.90E-05 | 6.74E-05 | 4.26E-04 | 9.08E-07 | 1.87E-04 | 9.83E-05 | 6.81E-05 | 3.61E-04 | 2.45E-07 |
Among the HMs, Ni is a major cancer risk-causing element that may cause human lung and nasal cancer (Son,2020), damage kidneys and lungs (Cameron et al., 2011), increase allergies and dermal infections in the child (Ahlstrom et al., 2019), causes congenital heart defects (Zhang et al., 2019). In addition, excess Ni absorption via the respiratory tract, digestive system, and skin which can harm all age groups (Aendo et al., 2022). The heavy metal Cr is responsible for lung, nose, and nasal sinuses cancer, causing losses in a fatality, birth rate, growth, and spontaneous miscarriage (Aendo et al., 2022; Peng et al., 2018), increasing congenital disabilities, perinatal jaundice, and respiratory problems (Banu et al., 2018). In addition, Cd has been linked to lung, jugular, prostate, pancreatic, and breast cancer (Djordjevic et al., 2019; Pal et al., 2017). It has also been shown to lower the intelligence quotient (IQ) of children, the ingenuity of boys (Kippler et al., 2012), and cause detrimental health effects in all age groups (Aendo et al., 2022). Arsenic (As) can cause skin, lung, and bladder cancer, as well as pigmentation and keratosis (Hossain et al., 2022; Martin & Griswold, 2009). Additionally, the carcinogenic metal Pb can cause neurological problems, kidney malfunction, renal dysfunction, anemia, arthritis, dyslexia, autism, and other birth defects (Collin et al., 2022; Martin & Griswold, 2009). However, from both categories, children are observed to be in a more susceptible state than adults according to the health risk, similar to previous studies (Hossain et al., 2022; Howladar et al., 2021; Mohammadi et al., 2019).
3.5 Status of TMs Sources according to PMF
The PMF model was used in this study to detect and quantify the possible sources of TMs in gas field water of the Sylhet region, Bangladesh. The contents of toxic metals and their associated unpredictability were used in the method. In this study, all heavy metals were classified as "strong" for the purposes of assessing model fitness and identifying the optimal solution (Kuerban et al.,2020). A unique initial seed value was employed each time the model was run (Jiang et al., 2017). The model was run 20 times with 100 seed values, with three source components for water samples from both seasons. Three variables were selected for the samples based on the minimum and steady Q values and maximum r2 values between observed and predicted HM levels (Nasiruddin et al., 2022). The anticipated trace element concentrations by the PMF method were compared to quantified metal concentrations. The correlation coefficient (r2) was used to evaluate the efficiency of the PMF technique (Supplementary materials S1 & S2). The highest r2 found as Co (0.97), Fe (0.95) in summer season (Table S1) while the highest r2 observed as Cd (0.97), Pb (0.98), Zn (0.98), Mn (0.87) during rainy season (Table S2). The heavy metals including Co, Cr, and Mn had correlation coefficients more than 0.6, whereas other trace elements had slightly lower r2 values represented the observed values good enough at the majority of sites, which had no effect on determining the optimal solution (Kuerban et al., 2020). The PMF technique results for each factor contribution are displayed in Fig. 7. The first factor was primarily weighted by Mn (87.5%) and Fe (73.4%) during the summer and Cd (85.6%) during the rainy season. Materials from the upper continental crust or parent rock materials provide the water and soil through ingestion and mineral decomposition (Siddiqui and Pandey 2019). The origins of these metals may be associated with lithogenic processes (Islam et al., 2020b). According to a previous study, Cd originated mostly from three waste sources: (1) waste gas, (2) wastewater, and (3) waste residue (Veeken and Hamelers, 2002; Li et al., 2014). The trace metals Fe and Mn are biologically necessary elements, they may accumulate in fine-grained fractions of sedimentary rock (Han et al., 2015). Thus, higher percentages of Fe and Mn in factor one may indicate a common source of origin. Factor 2 was represented in summer season samples by Co (92.7%), Ni (87.5%), Cr (31.3%), As, and Cu (30%). In addition, As (55.5%), Cd (66.5%), Cr (52.1%), Cu (61%), Pb (64.1%), and Zn (60%) were related to factor 3.
Moreover, factor 2 in rainy season water is comprised of Ni, Pb, Zn, Cu, Co, and Mn with relative contributions of 82.2%, 79.6%, 91.1%, 52.2%, 48.6%, and 49.3%. While factor 3 was dominated by factor loadings of Fe (69.9%), Mn (48.6%), Cr (48.8%), and As (44.3%). The value of Ni, Cu, and Pb in factor 2 with large factor contributions and low variability suggests a natural source of origin (Hao et al., 2022), which may be derived from similar parent materials (Lu et al., 2012). Additionally, environmental geoscientists have observed in recent years that most of the environmental difficulties caused by toxic elements such as Cr, Pb, As, and Ni are associated with the geographical setting (Proshad et al. 2021a; Siddique et al. 2021).
Since PMF approach detects the source of metal contamination in water, the outcomes may be subject to some uncertainty; however, it delivers more precise results than other factor analyses like principal component analysis (PCA) or hierarchical cluster analysis (HCA) (Jiang et al., 2017). It is essential to combine regional management because it enables the implementation of a unified set of water safety rules and strategies. Besides, pollution management techniques need macro-policy assistance. In addition, the authorities should raise residents' knowledge and conduct campaigns to prevent pollution and protect the aquatic ecosystem (Nasiruddin et al., 2022).