Ecological and health risk assessment of trace metals in water collected from Haripur gas blowout area of Bangladesh

Physiochemical characteristics of water in the blowout region

The physiochemical properties of water were measured in the laboratory. The analyzed properties are shown in Table 3.

The average value of pH is 6.529 indicates water of the study area is slightly acidic in nature. The average value of CO₂ (6.5) complied with the lowering tendency of pH. The average ORP value 36 also reflecting the sign of acidic water in the study region. According to WHO standards (2011), the value of conductivity within range 0–800, Total dissolved solids less than 500 ppm, alkalinity 120 ppm, and total hardness less than 300 mg/L are allowable for drinking and domestic purpose³⁷. The average value of conductivity 76.7 µs/cm, total dissolved solids 44.2 ppm, alkalinity 109.1 concurred with the dirking water standard by WHO (2011). The average value of TH is 49 ppm points out that the properties of water are soft.

Spatial distribution of trace elements derived from water bodies around the blowout area

The primary purpose of this study is to understand the concentration level of different Trace metals in the area. In this study, Pb, Ni, Cu, Cd, and Zn were examined (Fig. 3). Besides the toxic metal spatial distribution map is constructed using the inverse distance weighting (IWD) method in Arc GIS (version 10.5). The map (Fig. 4) shows common patterns of hotspots near the Syl-1 blowout area for every metal. This scenario indicates that these metals are originated from the same source⁴⁶.The contiguous area near Syl-4 well also exhibited a similar pattern to Syl-1 for all metals except Cd. A high concentration of Cd was found closed to the Syl-1 area. The elevated concentration of toxic metals like Ni, Pb, and Cd are found in the adjacent areas of blowout points (Fig. 4). Continuous gas escaping from these abandoned wells might stimulate the trace metal accumulation, especially Pb would be more toxic when it will come to a contact with gasoline (Syl-1 and Syl-4)⁷. The non-essential toxic metals like Ni, Cd, and Pb in water can pose a serious health threat inthesite⁴⁷. In addition, these toxic elements can contribute to acute or chronic health issues like high blood pressure, kidney failure, headache, abdominal pain, cancer, nerve damage, and so on for the long-term consumption of such water⁴⁸.Standard value of Pb in water is 0.01 mg/L, Ni is 0.02 mg/L, Cu is 2 mg/L, Cd is 0.003 mg/L in water³⁷. In this analysis, the average value of Pb = 0.04, Cd = 0.05, Ni = 0.16, Cu = 0.03 mg/L, respectively. The TMs like Zn concentration is about zero or below the detection level for water samples in the study location. The values of Pb, Cd and Ni were higher than the standards level indicates that the water should not be used for any purpose⁴⁹.

Correlation coefficient (R) matrix of water quality parameter presented in the blowout area

A Correlation matrix represents the relationship among several variables. It is generated based on the correlation coefficient, which ranges from − 1 to 1. The value of correlation coefficient (1, − 1) indicates perfect correlation, (− 0.9 to − 0.7 or 0.9–0.7) shows strong correlation, (0.4–0.6 either positive or negative) represents moderate correlation, (0.1–0.3 or − 0.1 to − 0.3) displays as weak and 0 indicates no relationship between variables⁵⁰. The mathematical expressions are described in the article by MacMillan et al.⁵¹ to evaluate the correlation coefficient (r).

The correlation matrix is shown in Table 4. From the Table 4, it is clear that the pH shows a moderate to strong correlation with CO₂ (0.63) and alkalinity (0.69). Whereas, it shows a very strong positive correlation with Total Hardness (TH) and Ca²⁺ (0.88), respectively. The moderately positive correlation reflects with EC (0.41) and trace elements Ni (0.62). The rest of parameters show a negative correlation. The CO₂ exhibits a good correlation with EC (0.72), TH and Ca²⁺ (0.52). Alkalinity states a good correlation with TH and Calcium ions (0.76). EC shows a maximum correlation with TDS (1.00); maximum correlation also found in the case of TH and Ca²⁺. Turbidity has a positive correlation for all of the parameters except EC and TDS. TDS shows a strong positive correlation with all of the trace elements, in the case of Pb (0.54), Cd (0.88), Ni (0.68) and for Cu the value is 0.64. All trace elements have a strong correlation with each other. Pb represents a good correlation with Cd (0.65), Ni (0.54) and Cd (0.35). Ni has a strong correlation with Cd (0.61), Cu (0.43). Cu also implies a good correlation with Cd (0.58). In the end, it can be mentioned that a strong positive correlation can be detected among all of the trace elements and also for most of the relative parameters. CO₂ established the equilibrium state in the water with ions might be lowering the oxidation. The trace metals Cu and Cd were positively correlated with the turbidity. The washed turbid water from the blow out areas might stimulate these trace metals. The inverse association with oxidation and total hardness indicates the less vegetated areas have higher influx rate of soil materials. It implies the result of the correlation matrix indicated that all of the trace elements and also relevant ions presented in the water of blowout area resultant from the same source⁴⁶.

Factor loading of water parameters

The interrelationship within a set of variables or objects is represented by factor analysis. The factors contain all of the basic information about a wider set of variables or observed objects. It shows how the variables are strongly correlated with the determined factor. Factor analysis is also known as a multivariate approach to reducing data³³. Among different types of factor analysis, Principal component analysis account for the maximum variance of observed variables. So, it can be called variance-oriented³³. Factor loading shows how certain variables strongly correlate for a given factor. Factor loading varies from − 1 to + 1 where the value of factor loading below − 0.5 or above 0.5 suggested good correlations and value closed to − 1 or + 1, suggesting a more robust correlation³². The Table 5 represented the principal component analysis result of factor solution.

From analysis (Table 5), it can be realized that the water quality parameters such as Turbidity, TH, Ca²⁺, Cd, Ni and Cu have a stronger correlation with each other’s reflecting their source of origin might be from the same area¹⁴. Factor loading also suggested that more robust interconnection exists among CO₂, EC and TDS. In this analysis, the two-factor solution explained approximately 80.6% of the variance. The eigenvalue, total variance explained are represented in Supplementary Table S1. That percentage is high enough to accept the results. It can also be added that the red and yellow colored loading represented strong correlation with each other^46,52.

Water quality index (WQI)

The WQI is one of the best tools for monitoring the surface-groundwater contamination and can be used for water quality improvement programs. The WQI is determined from various  physicochemical parameters like pH, EC, TDS, TH, EC, and so forth. Higher estimation of WQI indicates poor water quality and lower estimation of WQI shows better water quality. During this examination, WQI esteems a range from 0.02633 to 5144.37 and are characterized into five water types shown in Table 6. The noteworthy WQI is recorded in case of (sample-1) which demonstrates an elevated level of contamination. Water sample 2, 5, 8 and 10 are grouped under class-1 which demonstrates there is a lower degree of pollution in water. In addition, WQI calculation for sample 2, 5, 8 and 10 excluded trace elements value and WQI evaluation for sample 1, 3, 4, 6, 7 and 9 included the heavy metals value in water. These results also clarify the association of heavy metals on water quality degradation of the study area.

The situation of contamination in the area

The level of contamination has been demonstrated in terms of the CFi, PLI, and also PI analysis of water samples around the blowout area. The values of CFi are indicated the degree of contamination. The intensity of CFi has been determined with some numerical values like 1, 3, and 6. The CFi value is less than 1, which implies low contamination, as the value is > 6 indicated a high degree of contamination³⁶. The Table 7 elucidates that the degree of contamination in the case of trace elements Pb, Cd, and Ni are very high for most of the locations of the research sides. Besides Cu and Zn exhibit that level contamination is low in the area. In other cases, the PLI can be evaluated by using the CFi value. The value of PLI greater than 1 symbolizes polluted and less than 1 represents the unpolluted status^36,39. The pollution load index rate of Pb, Cd, and Ni are 2.3, 2.87, and 2.56, respectively (Fig. 5).This result indicates the pollution of water bodies in the sampling sites. The other elements such as Cu and Zn are within the allowable limit are shown in Fig. 5. Moreover, the PI indicates similar results as CFi and PLI.

The state of potential ecological threat in the area

The ecological potential risk index has been appealed to detect the possible threat to the ecological system in the adjoining area. The calculated RI value provided the risk factor of water for understanding the ecological threat. When the RI value is more than 600, it is considered a polluted case^11,14,36. The computed RI value of the study for Pb, Cd, Ni, and Cu are 123.5, 2770, 235, and 0.23, respectively (Table 8). The value of Cd is high enough (RI > 600). So, the Cd values indicated that the potential threat to the ecological system. Besides, the TMs like Ni and Cu are specified medium to low ecological pollution in the area are shown in Table 8. Moreover, the spatial distribution has been presented to outlook the potential ecological threats around the blow out location of the gas field is shown in Fig. 6.

The spatial distribution map of RI also pointed out the high ecological risk closed to the blowout areas (Fig. 6). From these results, it can be implied that the use of  this water for domestic or drinking purposes, can be harmful for living beings. Moreover, it can be distressed the ecological system in the site. Hence, the use of the water from this site should be avoided by dwellers near the blowout areas of the gas field.

Assessment of noncarcinogenic health risks

Noncarcinogenic risk is one of the vital categories of human health risk assessment. It is known that a polluted environment is highly liable for causing a health risk. Toxic metal presents in water also very harmful for public health, including child and adult both. The health risks may be extended through ingestion and skin absorption of water. To know the harmful impacts of trace elements of water on the human body, noncarcinogenic risk evaluation is more important. For that, the value of CDI for ingestion and dermal absorption was evaluated at the beginning to identify such risk index (Supplementary Table S2 and S3). Then the CDI has been divided with the RfD value. From where, the HQ can be acquired separately for ingestion and dermal absorption. The summation of HQ_ingestion and HQ_dermal expressed the HQ_total. And the HQ_total entirety was used to achieve the HI are shown in Table 9.

The results elucidate that case of adult, the mean value of CDI_Total for Pb is 1.29E-03, Cd is 1.45E-03, Ni is 4.93E-03 and Cu is 4.83E-04, respectively. For the child, the mean value of CDI_Total in the case of Pb, Cd, Ni, and CU is4.7544E-03, 5.33E-03, 1.81E-03 and 1.77E-04, correspondingly. Additionally, the order of CDI_Total for adults are Ni > Cd > Pb > Cu (Supplementary Table S2) whereas, for child, it is quite different. In the case of children, the order  are Cd > Pb > Ni > Cu are presented in Supplementary Table S3.

The mean values of HQ_Total of Pb, Cd, Cu, and Ni are ranging from 4.46E−05 to 1.45E−02 for child. Besides, these values for adults are extending from 1.21E−05 to 4.66E−03. These values suggest that the trace elements in the water of the study area are quite harmful to the child than an adult. The children’s HQ_Total has been ordered as Cd > Pb > Ni > Cu and for the adult Cu < Ni < Pb < Cd using the mean values of water in the blowout area. The minimum, maximum and mean values of HI for children are 3.82E−03, 7.55E−02, and 2.41E−02, respectively. And for adults, these values are 9.15E−04, 1.84E−02, and 4.65E−03. At this point, the mean value of HQs and HI of the study are less than 1, which defines that there is no adverse health-hazardous threat due to the exposure of toxic metals⁵³. Hence from this computation, it can be concluded that noncarcinogenic risks are minor for the public health around the blowout area of Haripur Gas Field.

Carcinogenic health risk evaluation

The excess TMs in water, soil or foods are blamed for causing the risk for ecology and health. These elements can cause cancer in the case of drinking such water for a long time. In this article, the values of ILCR of TMs in the areas are shown in Table 10. It is recognized that the ILCR value less than 1 × 10^–6 can be considered as insignificant event to cause disease^11,44. At this time, the risk of cancer can be neglected. Whereas, the values of ILCR more than 1 × 10^–4 can be considered as significant to cause cancer like disease^11,14,44.

The ILCR values of the trace elements are presented in Table 10.This Table also displays the mean, maximum, and minimum ILCR values for children as well as adults. The mean values of Pb, Cd and Ni for adults are 2.20 × 10^–2, 8.87 × 10^–3, 4.06 × 10^–3, respectively. But, these values for children are 8.08 × 10^–2, 3.25 × 10^–2, and 1.82 × 10^–2, respectively. The mean ILCR values of Cd and Ni (Fig. 7) are harmful and Pb values represented more harmful for children⁴⁵. For Adults, the ILCR values of Cd and Ni are also significant and Pb is more noticeable to cause health risk (Fig. 7)^7,13,36,42. The carcinogenic risk of these elements can be ranked as Pb > Cd > Ni.

A study carried out by Xu et al.⁵⁴ where shown that the pollution status from an oil-based drill cuttings field. The result of that study revealed that the metal pollution was moderate and also noticed that the noncarcinogenic and carcinogenic risks of drilling workers were within the permissible level. The present research implied the same as that the blown-out areas were out of the health exposure except for children. Besides, another study led by Guan et al.⁵⁵ in a mining area found an uneven distribution of potential ecological risk. However, this article addressed this gap considering risk assessment indices and spatial distribution of trace metals in a comprehensive way which could be a good foundation for future study in this field.

Source: Ecology - nature.com