Introduction

All industries, including agriculture, mining, energy, transportation, construction, and consumers, generate waste. In different industrial processes, some industrial wastes are produced and released into the quantity of harmful discharge from industrial actions. There are many industries in the Ishwardi Export Processing Zone (IEPZ) producing chemicals, garment accessories, metals, plastic goods, lead-acid batteries, etc. Industrial effluent is discharged into the land, surface, and groundwater bodies either directly or indirectly due to inadequate treatment. They can increase the absorption of pollutants such as toxic metals. The heavy metal contamination of soil is a significant issue because of its ability to accumulate in the surroundings of the Ishwardi EPZ area (Rahman et al. 2012). The pollution level should be monitored for socio-environmental and human health safety claims and be claimed for maintainable development for administrative procedures (Azom et al. 2012). The heavy metal contamination of soil in this study was assessed near the Ishwardi Export Processing Zone (IEPZ) area using different parameters such as the enrichment factor (Taylor 1964) and the geo-accumulation index (Abrahim and Parker 2008), and the potential contamination index. Lack of proper waste management, lack of facilities for treating industrial effluent, and environmental problems are increasing daily. So, it is a problem for the environment and the country’s social welfare. This study focused on the present scenario arising from such activities and proposed several subsidence measures. This was done by analyzing the effects of various toxic metals on the environment of the studied area. Because of the health implications, an assessment technique investigation of heavy metal pollution in the soil is required. Ishwardi is the westernmost Upazila of Pabna District in Rajshahi Division, Bangladesh. Ishwardi Upazila has an area of 246.90 km2 and is located between 24°03′ and 24°15′ north latitudes and 89°00′ and 89°11′ east longitudes (Fig. 1). The aims of this work are: (i) to determine the present scenario of the content of heavy metals in soil, (ii) to identify the source of the studied heavy elements, and (iii) to determine the pollution level by some indices for monitoring soil quality in the surrounding IEPZ area.

Fig. 1
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Location map of the study area

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Materials and methods

Collection and preparation of samples

The soil samples were collected from the surroundings of the IEPZ area (Fig. 2) located at Sara Union of Ishwardi Upazila in February 2019 from the surface layer and were placed in airtight polythene bags and labeled. The heavy metals of Pb, Cu, Cr, Ni, Zn, Fe, and Mn of these soil samples were measured by XRF study in the laboratory of IMMM (Institute of Mining Mineralogy and Metallurgy), BCSIR (Bangladesh Council of Scientific and Industrial Research), Joypurhat. The collected soil samples were dried up in an electronic oven at 100 °C for 1 h to dry (Hasan et al. 2013). Noticeable roots and remains were removed. The dry samples have been crinkled gently by the pestle and are in powder form. Then, these powder samples were pulverized in a pulverizing machine (Rigaku by Japan). The finely ground powder (75 mm) was then placed in a porcelain crucible and dried in an oven overnight at 1000 °C to remove moisture. The powder samples were mixed up in a ring with a binder at the ratio of stearic acid to sample of 1:10 and pulverized for a few minutes. The acquired mixing powder has been spooned up an aluminum cap (30 mm). The cap was sandwiched between two tungsten carbide pellets using a manual hydraulic press at 10 tons/square inch for 2 min, and finally, the pressure was released slowly. The pellet was then ready for X-ray analysis (Hasan et al. 2020).

Fig. 2
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Soil sampling location

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Obtained value of the enrichment factor (EF)

The degree of enrichment factor was assessed by comparing the amount of metal pollution in the circumstantial area of the Ishwardi Export Processing Zone (Selvaraj et al. 2004). Metal contamination has been standardized to the relative abundance of a chemical element to the reference point values’ comparison with a convenient measure of geochemical trends in the enrichment factor (Aprile and Bouvy 2008; Salomons and Froster 1984). The enrichment factor (EF) values for metals contamination in soil have been measured by the equation followed by Aprile and Bouvy (2008):

$$\mathrm{EF}=\left[\left(\mathrm{Ms}\right)/\left(\mathrm{Fes}\right)/\left(\mathrm{Mr}\right)/\left(\mathrm{Fer}\right)\right]$$

where Ms and Fes are the concentrations of heavy elements for soil samples, whereas Mr and Fer are the concentrations in reference values; the reference concentration is Fe because this chemical element has a significant sorbent phase for trace elements and is a conservative tracer (Hasan et al. 2013). The amount of heavy metals is generally influenced by anthropogenic activity, and certain amounts might have been released from geogenic sources under aerobic conditions (Zhang et al. 2014). Iron also absorbs Mn and As from the soil. EF values for the crustal extensive quantity data have been used (Krauskopf and Bird 1995).

Obtained value of geo-accumulation index (Igeo)

The degree of the geo-accumulation index (Igeo) values for seven samples were calculated based on the content of heavy metal concentrations according to Muller (1979), Subramanian and Mohanachandran (1990), Angelidis and Aloupi (1995), Rubio et al. (2000); Muller (1979), and Abrahim and Parker (2008). The equation is as follows:

$$\mathrm{Igeo}=\mathrm{log}2\left(\left[\mathrm{Ms}\right]/{1.5}^{*}\left[\mathrm{Rs}\right]\right)$$

where Ms is the soil value, and Rs is the reference value; seven studied heavy metals of Pb, Cu, Cr, Ni, Fe, Mn, and Zn were investigated. To reduce the consequence of potential differences in the corresponding values, a factor of 1.5 has been used, which might be recognized as lithological distinctions in the soil (Al-haidarey et al. 2010). The mentioned crustal abundance data of the reference samples were Mn: 950, Cr: 100, Pb: 13, Cu: 55, Zn: 70, Ni: 75, and Fe: 50,000 mg/kg followed by Krauskopf and Bird (1995).

Obtained value of potential contamination index (Cp)

The degree of potential contamination Index (Cp) in soil was detected in the rate of heavy elements by the equation followed by Davaulter and Rognerud (2001) and Aprile and Bouvy (2008):

$$\mathrm{Cp}=\left[\mathrm{Mm}/\mathrm{MB}\right]$$

where Mm is the highest heavy metal concentration in the soil and MB is the expected value of the similar metal at a background level. The background data taken by Krauskopf and Bird (1995) is known as crustal abundance data.

Results and discussion

1Assessment of studied soil data with standard data

The heavy metal concentration in the soil of the surroundings of the IEPZ area has been related to the standard values of uncontaminated soil. Table 1 shows the obtained minimum, maximum, and mean values of trace metal concentration. The difference between the obtained values of heavy metals and the values of heavy metals mentioned in the unpolluted soils is shown in Table 2. Table 3 represents the difference between heavy metal concentrations in the soil of the studied area and the standard value according to IAEA (1990) and GESAMP (1982). The heavy metal of Pb concentration is at a higher level in 4 stations in the study area than the value of 22.8 µg/g (GESAMP 1982; IAEA, 1990), which is due to the runoff from industrial effluent polluting the soil. The toxic metals of Pb range from 142.037 to 952.48 µg/g indicating pollution by comparing with standard data, which is unusually similar to Baker and Harris (1991), and the average value is 233.412 µg/g of Pb. Cr of heavy metals near the IEPZ area is significantly higher in all the stations. The amount of maximum contamination of heavy elements could be due to waste materials discharged from industrial processes. The Cr concentration in studied samples varies from 1882.9 to 7056.78 µg/g, 47 times greater than the standard value (77.20 µg/g) of unpolluted soils (GESAMP 1982; Salomons and Froster 1984; IAEA 1989). The mean value is 3692.391 µg/g, whereas the recommended value of Cr is 77.20 µg/g (IAEA, 1990). The Cu of heavy metals is at the maximum level in all stations. The pattern of distribution of Cu of the heavy element is not regular. The metal of Ni ranges from 132.012 to 1477.287 µg/g. The metal of Ni recorded as 354.164 µg/g is more than the standard value of 56.1 µg/g (IAEA, 1990). A comparison between the affected site value and the standard value of heavy metal pollution in the selected area is shown in Fig. 3. So, it is observed that the soil samples are vastly affected by heavy metals around the IEPZ area owing to the significant effluents discharged by various industries in the IEPZ.

Table 1 Obtained heavy metal concentrations in sediments collected from the Sara Union, Export Processing Zone Area, Ishwardi, Pabna
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Table 2 Comparison between obtained values of heavy metals with recommended standard values of uncontaminated soils (values in µg/g)
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Table 3 Comparison between heavy metal concentrations of soil samples and standard value according to IAEA (1990), GESAMP (1982)
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Fig. 3
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Shows the comparison among the affected and standard value of trace elements in soil

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Correlation matrix between heavy elements

The correlation matrix observes the correlation among the heavy metals. It represents the possible source of toxic metals (Kaur et al. 2019; Chandrasekaran et al. 2015). The resulting correlation matrix of samples in the study area is shown in Table 4. A significant correlation was measured by p < 0.05 (Hasan et al. 2013). Elements of the study area correlated with the metals of Pb are Cr (q = 0.754), Ni (q = 0.683), Zn (q = 0.908), Cu (q = 0.868), Mn (q = 0.900), and Fe (q = 0.827). Lead is considerably correlated with Zn (q = 0.908), and Cr is considerably correlated with Cu (q = 0.976) and Fe (q = 0.976). The metal of Ni is also correlated with Cu (q = 0.837) and Fe (q = 0.847). Manganese was also correlated with Fe (r = 0.984), and Cu was correlated with Mn (r = 0.997). Zn is correlated with Mn (r = 0.997). The value of the correlation matrix shows that almost all the metals are highly correlated with each other. So, these values indicate the possible sources of toxic metals are almost the same in the IEPZ area, which is discharged from different industries (Hasan et al. 2020). Anthropogenic activities contaminate the natural environment, as the use of Fe compounds increases the Fe content.

Table 4 Correlation matrix results of heavy metals of soil samples
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Degree of the enrichment factor value

The classification of the enrichment factor values is given by Taylor (1964) (Table 5). The computed value of EF value (Table 6) shows that the soil samples were moderately to extremely enriched by Pb through industrial activity owing to industrial effluent. These samples are severely enriched by Cr, moderately enriched by Cu, Zn, and mildly to severely enriched by Ni and Mn. The collected samples are relatively unhealthy because of the concentration of lead metal, which is extremely enriched. The blank line in the data table indicates the average value of each studied metal. An EF value greater than 1.5 should be classified as polluted (Abrahim and Parker 2008). In the study area, the outcomes of the EF value of heavy elements have followed the hierarchy: Pb > Cr > Cu > Zn > Ni > Mn. From the above results, soils are mostly contaminated by heavy metals lead, which may cause negative effects on the environment in the surroundings of the IEPZ area.

Table 5 The degree of heavy metal pollution is based on enrichment factor value, according to Taylor (1964)
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Table 6 The obtained value of the enrichment factor of heavy metals in the studied area
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Degree of the geo-accumulation index value

The classification of geo-accumulation index (Igeo) values is given in (Table 7) by Abrahim and Parker (2008) and Muller (1979). The Igeo value is more similar to the EF value. The Igeo value of the studied metals of Pb is highly concentrated. The samples are extremely polluted by the metal Pb in station 1 (952.48 mg/kg), station 7 (338.85 mg/kg), and station 3 (200.52 mg/kg). The maximum contamination of Cr was observed at station 6 (5555.97 mg/kg). There is also high contamination of Cr all over the stations. The maximum concentration of Ni was observed in station 2 (3714.95 mg/kg). According to Abrahim and Parker (2008), the computed value of Igeo classes is shown in Table 8 and Fig. 4. The observed Igeo values have followed the hierarchy: Pb > Cr > Zn > Ni > Cu > Mn > Fe. The Igeo values of metals like Pb, Cr, and Zn range between 6 and 3, which means they are extremely to moderately contaminated. Almost all stations are unpolluted with Mn and Fe metals.

Table 7 The degree of heavy metal pollution is based on geo-accumulation value, according to Abrahim and Parker (2008)
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Table 8 The obtained value of metal pollution is based on geo-accumulation values (Abrahim and Parker 2008)
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Fig. 4
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The geo-accumulation index of 7 studied heavy metals of soil in the IEPZ area of Ishwardi Upazila, Pabna

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The degree of the potential contamination index value

The results of the potential contamination index (Cp) for heavy metals in soil are given in Table 9. The Cp values that have measured the metal of Pb at station 1 (73.26) and station 7 (26.065) indicate a very high contamination index. The metals of Cr range from 18.829 to 70.567, Ni ranges from 1.67 to 19.69, Zn ranges from 1.985 to 6.197, Cu ranges from 1.62 to 2.54, Mn ranges from 1.13 to 2.45, and Fe ranges from 1.035 to 1.584. The maximum potential contamination index is the Cr in all stations. The ranges of Ni ranged from 1.67 to 19.69, Zn ranged from 1.985 to 6.197, Cu ranged from 1.62 to 2.54, Mn ranged from 1.13 to 2.45, and Fe ranged from 1.035 to 1.584 showing moderate contamination. The metal Mn showed the lowest contamination. The outcomes of potential contamination index values are mostly contaminated with heavy elements caused by an industrial impact on soil near the IEPZ area of Ishwardi Upazila, Pabna.

Table 9 The obtained value of the potential contamination index of heavy metals near the IEPZ area of Ishwardi Upazilla, Pabna, according to Aprile and Bouvy (2008)
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Comparison of mean concentration of heavy metals in IEPZ and ship breaking industry

An attempt was made to show the comparison of the mean concentration of heavy metals in IEPZ and the ship breaking industry. From Fig. 5, it can be concluded that the mean iron, copper, and zinc concentration is higher in the ship breaking industry (Hasan et al. 2020) than in the IEPZ. The average concentration of Pb, Mn, Cr, and Ni is higher in IEPZ. These results suggest that the IEPZ area is composed of various types of industries in the study area.

Fig. 5
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Mean concentrations of different heavy metals of ship breaking industry and IEPZ

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Conclusions

The heavy metal concentration of topsoil samples collected from the Iswardi Export Processing Zone (IEPZ) and its environs was investigated. Due to industrial activity, the IEPZ’s environmental impact assessment has been negatively impacted. Therefore, heavy metal (i.e., Zn, Cu, Fe, Pb, Cr, Ni) concentrations in soil samples collected from IEPZ were analyzed by X-ray fluorescence (XRF) spectrometry. The present research work shows that the soil has higher concentrations of heavy metals, indicating that the investigated soil composition is affected by heavy metal contamination in the surrounding area of IEPZ due to industrial processes. Heavy metal soil contamination can pass these metals into the human food chain through surface water movement. If it rises further, the environment may become adversely polluted. Compared with the standard value of the affected site, it is mainly affected by Cr, Ni, Pb, Zn, and Cu, whereas the mean concentration of iron, copper, and zinc content is lower in the IEPZ than in the ship breaking industry. These metals are highly correlated with each other. The enrichment factor, the geo-accumulation index, and the potential contamination index values reveal that the soils are extremely moderately polluted near the IEPZ area. Due to these pollution indices, soil near the Ishwardi Export Processing Zone is contaminated, which is inappropriate for the environment. It can impact health and also the socio-environment.