Assessment of Cultivated Soil Contamination by Potentially Toxic Metals as a Result of a Galvanizing Plant Failure

Abstract

Zinc is one of the more mobile metals in the soil and thus involves the risk of entering the food chain. Zinc compounds are used in the galvanization process, which is assumed to be safe for the environment. However, random events or failures such as unsealing bathtubs with liquid zinc or hydrochloric acid, as well as violent fires in industrial halls, may pose a real threat to the environment, including human health. Therefore, this research was carried out to determine the content of zinc and selected potentially toxic metals in arable soils after a failure in a galvanizing plant located in the village of Dębska Wola (southeastern Poland). In addition, the potential risk associated with excessive accumulation of identified pollutants in the environment was assessed. In order to determine the level of contamination, soil samples were taken, and basic physical and chemical properties were analysed. The concentrations of Zn, Pb, and Cd in the soil were determined using the atomic emission spectrometry technique with inductively coupled plasma (ICP-OES), and pH measurements were performed using the potentiometric method after prior wet mineralisation of the research samples. The analysed samples had a varied pH of the organic–mineral horizon from pH_H2O 4.66 to pH_H2O 5.33 and from pH_KCl 3.89 to pH_KCl 5.06. As a result of a failure, toxic metal fumes were released into the atmosphere, causing concentrations of Zn in the soil samples from 0–5 cm in the range of 1201–2007 mg∙kg⁻¹, as well as Pb (109–509 mg∙kg⁻¹) and Cd (4.6–17 mg∙kg⁻¹). High contents of zinc and lead found in several soil samples are of anthropogenic nature and require detailed monitoring in order to eliminate the risk associated with their accumulation. The study area should be re-analysed to determine the rate of reclamation of degraded soils.

1. Introduction

Activities in the field of environmental protection and sustainable development at the European level have their references to local problems. Unfortunately, the use of natural resources continues to contribute to environmental degradation, as evidenced by the consumption footprint and material footprint reported by the European Environment Agency (EEA) and the United Nations Economic Commission for Europe (UNECE) [1,2]. The studied trends show no signs of reduction; on the contrary, they signal an increase in the global use of raw materials, including energy and water. Continuous technological progress and innovation have led to greater prosperity and have also caused extensive damage to nature.

In many parts of the world, pollution and climate change are disrupting nature’s natural capacity to provide essential services such as food, soil, and water.

Heavy metals (potentially toxic) are a commonly used indicator of environmental pollution [3,4,5,6,7]. Cultivated plants rooted in the soil surface horizon are extremely sensitive to the excess of potentially toxic metals, causing an imbalance in their metabolism and degrading changes [8,9]. Of particular importance in this aspect are catastrophic events of natural origins (volcanic eruptions, forest fires) and anthropogenic events resulting from technical infrastructure failures (leaks of oil derivatives, toxic or radioactive substances) with a diverse range of impacts on the natural environment, including on human health [10]. As a result of faulty operation of industrial equipment, a significant amount of hazardous substances, including metals, may enter the soil, water, or air in an uncontrolled manner [11,12,13]. Zinc is one of the potentially toxic metals, although commonly found in the Earth’s crust. Its average content in soils ranges from 30 to 125 mg·kg⁻¹ [14]. A high content of zinc in the soil negatively affects its properties. When the zinc content is higher than 100 mg·kg⁻¹ DM in the soil, nitrification processes are limited, and if its amount exceeds 1000 mg·kg⁻¹ DM in the soil, it negatively affects most microbiological processes [15,16]. Nevertheless, according to research made by other authors, e.g., Alloway BJ. [17], the toxic effect of zinc on plants appears at contents of 100–500 mg·kg⁻¹ DM, depending on the plant species and soil properties.

Zinc is one of the more mobile metals in soil. It occurs in compounds with good solubility, which increases its assimilation by plants [18]. This feature of zinc causes a real increase in the metal’s chances to enter the food chain. It is known that the bioavailability of zinc increases with the acidity of the soil. It is also leached more easily in the light soils [19]. Zinc, although it belongs to potentially toxic metals, is not as dangerous for plants as, for example, lead, chromium, or mercury [20]. Nevertheless, the way Zn enters the food chain makes the topic of zinc mobility in the natural environment still relevant [21].

Galvanizing plants are industrial establishments which emit mainly ZnCl₂, ZnO, as well as zinc ash and dust. Their presence, especially in agricultural areas, is usually associated with the protests of residents fearing contamination of arable lands, water, and air. Although the risk of these threats, especially with the use of appropriate measures, is not high, it becomes real during extreme events, such as failures or fires.

The galvanizing plant in Dębska Wola, like many other plants of this type, uses a hot-dip galvanizing process. This process consists of a series of technological baths of properly prepared steel elements, the so-called raw material batch. The cycle consists of acid degreasing in a 12% HCl solution; rinsing, etching, and fluxing in a solution of ZnCl₂ and NH₄Cl at 45 °C; drying of elements intended for galvanization; and their final bath in molten zinc at a temperature of approx. 445 °C. The galvanizing plant in Dębska Wola is a modern production plant, but in 2019, it suffered an accident involving the unsealing of a galvanic tank with liquid zinc and damage to several tanks containing the HCl solution. The leaking metal caused the elements of the technological installation to ignite. There was a huge fire that destroyed the production hall. The fire was brought under control, but some toxic substances leaked into the environment.

After the failure and fire in the galvanizing plant in Dębska Wola, research was undertaken aimed at:

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Assessing the condition of soils in terms of physical and chemical properties, with particular emphasis on the contents of Zn, Pb, Cd;

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Determining the level of changes in relation to the geochemical background of the tested soils;

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Determining the extent (range) of changes in the soils;

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Determining environmental risks;

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Organizing follow-up monitoring activities.

The occurring dangerous event posed some questions: Did the emission and immission of harmful substances burden the natural environment? How did it affect the condition of the soil cover? Does the accumulation of potentially toxic metals qualify the tested soils for reclamation treatments?

2. Materials and Methods

2.1. Study Area

According to the physical and geographical division of Poland [22,23], the study area is located in the macroregion of the Kielce Upland, covering the southern area of the Świętokrzyskie Mountains mesoregion in the southeastern part of Poland (Figure 1). In the study area, there are brown earth soils made of Pleistocene light clays and sandy and occasionally loamy sands [24,25].

2.2. Data Collection and Analysis

Soil samples were collected on 2–5 October 2019 from the horizons of 0–5 cm (TOP) and 5–20 cm (BOTTOM). Each sample came from a plot of 2 m × 2 m and weighed about 1 kg, which corresponded to min. 5–8 punctures made with an Egner’s stick. The structure of the soil profile (Figure 2b) is typical for brown soils [26] and is as follows: for agricultural areas (points 1–6, 9–15): Ap-Bbr-Cca (typical brown soils, cultivated); for forest areas (points 7–8 on the map): O-A-Bbr-Cca (typical brown soils) [27].

Before sampling, unhumidified organic matter was removed. The soil was dried at a constant room temperature not exceeding 40 °C, ground in an agate mill, and sieved through a two-millimetre sieve. Each soil sample was thoroughly mixed. While doing the tests, the following determinations were made: grain-size distribution via the areometric-sieve method according to PN-R-04032:1998 [28] and soil reaction (pH in 1 M KCl) via the potentiometric method according to PN-EN 15933:2013-02E [29], using a pH-meter made by Elmetron (Zabrze, Poland), with pH-EPS-1 electrode. In order to determine the total content of selected potentially toxic metals (Zn, Pb, Cd—concentrations referring to dry matter, DM), before making measurements, the soil was mineralized in a CEM Mars 6 microwave mineralizer (Matthews, NC, USA) in specially prepared cups. For mineralization, 1 g of soil was weighed, and 15 cm³ of hydrochloric acid pa grade and 5 cm³ of nitric acid pa grade (in a ratio of 1:3, aqua regia) were added. The mixture was digested at 120 °C for 1–2 h. After cooling, the solution was diluted to 30 mL with deionized water and filtered with filter paper. The content of selected heavy metals in the soil was determined by inductively coupled plasma atomic emission spectrometry (ICP-OES) using an Agilent Technologies model 5100 SVDV emission spectrometer (Santa Clara, CA, USA). Laboratory tests were carried out in the laboratory belonging to Przedsiębiorstwo Geologiczne Sp. z o.o. in Kielce. A certified reference material—Loamy Sand 4, CROM0 36-050 (Manchester, NH, USA)—was used to validate the analytical method. The measured and certified values of elemental concentrations were compared (

Table 1. Comparison the results with certified materials Loamy Sand 4, CRM036-050.

Metals	Measured Value (mg∙kg−1) ± SD	Certified Value (mg∙kg−1) ± SD	Relative Difference (%)
Cd	0.90 ± 0.20	1.0 ± 0.15	99.0
Pb	10.60 ± 0.90	9.90 ± 0.40	115.0
Zn	42.23 ± 0.70	40.41 ± 0.30	98.0

). All results obtained for this reference material were statistically close to the certified values (p < 0.05). All relative standard deviations of measured replicates were within ±5%.

The research results were developed using Statistica ver. 13 (Tibco Software Inc., Palo Alto, CA, USA). The direction of the air mass flow was visualized with the NOAA Hysplit model (Air Resources Laboratory, NOAA’s Office of Atmospheric Research, National Oceanic and Atmospheric Administration). Concentration maps of the individual properties of the analysed soil were plotted in Surfer ver. 16 (Golden Software, LLC, Golden, CO, USA). To assess the degree of soil contamination with metals, the following indicators were calculated: the index of geoaccumulation (I_geo) and the ecological risk factor (E_rⁱ). Calculated I_geo [30] in relation to the geochemical background for Poland [31] allowed the classification of the analysed samples into particular classes. The degree of soil contamination was determined on a 7-level scale [30,32,33]: practically uncontaminated (I_geo ≤ 0), uncontaminated to moderately contaminated (0 < I_geo ≤ 2), moderately to heavily contaminated (2 < I_geo ≤ 3), heavily contaminated (3 < I_geo ≤ 4), heavily to extremely contaminated (I_geo > 5). Geoaccumulation index (I_geo) was calculated using the equation:

$$Igeo={\log }_2\frac{Ci}{1.5Bi}$$

where Ci—content of a given heavy metal in the soil; Bi—geochemical background for a given heavy metal; 1.5—natural variations in the content of a particular heavy metal in the environment resulting from differences in the geological structure. The Ecological Risk Factor, Eri, was calculated in accordance with the methodology for assessing the toxicity of heavy metals in water, soil, and air [34,35,36,37,38,39]:

Eri = T_i × C_Fi,

where C_Fi—contamination factor of an individual heavy metal; T_i—metal toxic response factor for an individual substance, T_Cd = 10, T_Pb = 5, T_Zn = 1. Explanation for Eri: Eri < 40, low potential ecological risk; 40 ≤ Eri < 80, moderate potential ecological risk; 80 ≤ Eri < 160, considerable potential ecological risk; 160 ≤ Eri < 320, high potential ecological risk; Eri ≥ 320, very high ecological risk.

3. Results

The failure in the galvanizing plant took place on 6 May 2019, and the fire it caused and the firefighting operation lasted until the next day. The average daily air temperature was 8.3 °C, and relative humidity was 48%. The next day, it was 8.3 °C and 51.3%, respectively. Meteorological conditions (Figure 3) enabled the movement of polluted air masses from above the plant towards the south and east, at a speed of approx. 14.6 km∙h⁻¹ (6.05) and 16.8 (7.05) km∙h⁻¹ (data from the Kielce-Suków station of the Institute of Meteorology and Water Management).

Figure 3. Meteorological conditions in May 2019; (a) Temperature, precipitation, wind direction and speed—data from the Kielce-Suków station; (b) visualization of the direction of air mass movement above the plant—NOAA Hysplit model from 7 to 6 May 2019 (24 h); (c) frequency trajectories from 6 May 2019 (48 h). The results of the physical and chemical properties obtained in the study area are presented in Table 2.

Figure 3. Meteorological conditions in May 2019; (a) Temperature, precipitation, wind direction and speed—data from the Kielce-Suków station; (b) visualization of the direction of air mass movement above the plant—NOAA Hysplit model from 7 to 6 May 2019 (24 h); (c) frequency trajectories from 6 May 2019 (48 h). The results of the physical and chemical properties obtained in the study area are presented in Table 2.

Table 2. Tested soil’s physical and chemical properties.

Sample No.	pHH2O		pHKCl		% Fraction Content (in mm) Bottom			Zn (mg·kg−1)		Pb (mg·kg−1)		Cd (mg·kg−1)
	Top	Bottom	Top	Bottom	2–0.05	0.05–0.02	<0.002	Top	Bottom	Top	Bottom	Top	Bottom
1	4.21	4.00	4.02	3.89	75	15	10	1761.08	909.45	509.70	290.67	17.11	10.90
2	4.19	4.04	4.00	3.88	68	16	16	2007.34	701.09	420.89	210.56	13.55	11.60
3	4.53	4.12	4.20	3.98	72	42	14	1093.66	400.64	307.56	230.87	14.88	7.90
4	4.06	4.00	3.89	3.87	82	32	14	1117.23	260.66	196.78	130.67	15.77	6.90
5	4.24	4.06	4.01	4.00	78	34	12	766.90	198.76	147.80	100.33	12.66	7.09
6	4.32	4.10	4.12	4.01	71	46	17	630.11	120.78	140.89	98.78	12.09	8.11
7	4.57	4.23	4.43	4.01	60	58	18	456.89	82.89	110.87	70.09	9.87	5.11
8	4.21	4.09	4.01	3.78	58	59	17	400.09	70.79	120.77	67.98	7.99	4.68
9	4.90	4.30	4.26	4.12	61	20	19	222.19	67.55	110.98	79.89	7.09	6.78
10	5.20	5.00	5.00	4.98	77	34	11	190.80	56.90	130.89	120.33	8.01	7.12
11	5.10	5.00	4.98	4.89	80	29	9	201.56	69.78	113.90	90.67	7.33	3.45
12	4.90	4.76	4.72	4.53	82	26	8	305.05	45.89	109.07	50.80	4.56	3.78
13	5.20	4.87	5.03	4.74	72	62	17	170.89	56.04	111.77	55.89	5.71	3.04
14	5.33	5.12	5.06	4.99	76	41	17	129.89	47.90	122.55	60.45	4.71	2.89
15	5.19	5.04	5.00	5.00	59	59	18	120.99	42.33	110.73	40.97	4.90	1.02
Mean	4.68	4.45	4.45	4.31	71.40	38.20	14.47	638.31	208.76	184.34	113.26	9.75	6.02
Min	4.06	4.00	3.89	3.78	58	15	8	120.99	42.33	109.07	40.97	4.56	1.02
Max	5.33	5.12	5.06	5.00	82	62	19	2007.34	909.45	509.70	290.67	17.11	11.60
SD	0.46	0.45	0.46	0.48	8.42	15.98	3.62	603.42	264.75	126.26	73.80	4.28	2.98

Table 2. Tested soil’s physical and chemical properties.

Sample No.	pHH2O		pHKCl		% Fraction Content (in mm) Bottom			Zn (mg·kg−1)		Pb (mg·kg−1)		Cd (mg·kg−1)
	Top	Bottom	Top	Bottom	2–0.05	0.05–0.02	<0.002	Top	Bottom	Top	Bottom	Top	Bottom
1	4.21	4.00	4.02	3.89	75	15	10	1761.08	909.45	509.70	290.67	17.11	10.90
2	4.19	4.04	4.00	3.88	68	16	16	2007.34	701.09	420.89	210.56	13.55	11.60
3	4.53	4.12	4.20	3.98	72	42	14	1093.66	400.64	307.56	230.87	14.88	7.90
4	4.06	4.00	3.89	3.87	82	32	14	1117.23	260.66	196.78	130.67	15.77	6.90
5	4.24	4.06	4.01	4.00	78	34	12	766.90	198.76	147.80	100.33	12.66	7.09
6	4.32	4.10	4.12	4.01	71	46	17	630.11	120.78	140.89	98.78	12.09	8.11
7	4.57	4.23	4.43	4.01	60	58	18	456.89	82.89	110.87	70.09	9.87	5.11
8	4.21	4.09	4.01	3.78	58	59	17	400.09	70.79	120.77	67.98	7.99	4.68
9	4.90	4.30	4.26	4.12	61	20	19	222.19	67.55	110.98	79.89	7.09	6.78
10	5.20	5.00	5.00	4.98	77	34	11	190.80	56.90	130.89	120.33	8.01	7.12
11	5.10	5.00	4.98	4.89	80	29	9	201.56	69.78	113.90	90.67	7.33	3.45
12	4.90	4.76	4.72	4.53	82	26	8	305.05	45.89	109.07	50.80	4.56	3.78
13	5.20	4.87	5.03	4.74	72	62	17	170.89	56.04	111.77	55.89	5.71	3.04
14	5.33	5.12	5.06	4.99	76	41	17	129.89	47.90	122.55	60.45	4.71	2.89
15	5.19	5.04	5.00	5.00	59	59	18	120.99	42.33	110.73	40.97	4.90	1.02
Mean	4.68	4.45	4.45	4.31	71.40	38.20	14.47	638.31	208.76	184.34	113.26	9.75	6.02
Min	4.06	4.00	3.89	3.78	58	15	8	120.99	42.33	109.07	40.97	4.56	1.02
Max	5.33	5.12	5.06	5.00	82	62	19	2007.34	909.45	509.70	290.67	17.11	11.60
SD	0.46	0.45	0.46	0.48	8.42	15.98	3.62	603.42	264.75	126.26	73.80	4.28	2.98

The average soil pH value of the 0–5 cm organic–mineral horizon (T) was pH_H2O = 4.68 and pH_KCl = 4.45. In turn, in the soil samples taken from the 0–20 cm mineral horizon (B) have average values of pH_H2O = 4.45 and pH_KCl = 4.31. The grain-size distribution is dominated by sand fractions constituting from 58% to 82% (on average, approx. 71.4%). On average, dusts account for 38.2%, and the amount of clay parts is 8–19%. The average content of zinc in the soil samples collected from the organic–mineral horizon (T) was 638.3 mg∙kg⁻¹ and ranged from 121 mg∙kg⁻¹ in the eastern part of the study area to 2007 mg∙kg⁻¹ in the vicinity of the plant. The highest concentrations of zinc from the mineral horizon (B) were recorded in sample no. 1 (909.5 mg∙kg⁻¹) and the lowest ones in sample no. 15 (42.3 mg∙kg⁻¹). In both tested diagnostic horizons, lead concentrations were the highest in the samples collected at plot no. 1 (T—509.7 mg∙kg⁻¹; B—290.7 mg∙kg⁻¹), with mean values of 184.3 mg∙kg⁻¹ (T) and 114.3 mg∙kg⁻¹ (B). Minimal lead values were recorded in samples no. 12 (T—109 mg∙kg⁻¹) and 15 (B—41 mg∙kg⁻¹). The average content of cadmium in the analysed samples was 9.8 mg∙kg⁻¹ for the 0–5 cm horizon and 6 mg∙kg⁻¹ for the 5–20 cm horizon. The highest contents of cadmium, as in the case of other metals, were found in the samples located in the immediate vicinity of the plant (plot no. 1—17.1 mg∙kg⁻¹ T; plot no. 2—11.6 mg∙kg⁻¹ B), with mean values of 9.8 mg∙kg⁻¹ (T) and 6 mg∙kg⁻¹ (B). The lowest cadmium contents of 4.6 mg∙kg⁻¹ (T) and 1 mg∙kg⁻¹ (B) were recorded in the plots no. 12 and 15, respectively (Figure 4, Figure 5 and Figure 6).

The study area covered an area similar in shape to a rectangle, having dimensions of 1400 m by 700 m. In the spatial distribution of the analysed metals, a concentric increase in the concentration of pollutants around the galvanizing plant, with a significant latitudinal extension towards the east, is noticeable. Also noticeable is that along with the increase in the distance from the emission source, the concentration values were becoming lower (Figure 5).

In the case of zinc, values above 300 mg∙kg⁻¹ occurred in the samples located 500 m (T) and 150 m (B) from the plant. In the case of lead, concentrations above 100 mg∙kg⁻¹ were recorded in all samples from the 0–5 cm horizon and at a distance of 365 m from the emission source for the samples from the 5–20 cm horizon. A higher content of cadmium was recorded in all samples, with concentrations above 6 mg∙kg⁻¹ (a mean value for the samples from the 5–20 cm horizon) being recorded in the samples located up to 600 m from the plant.

4. Discussion

In southern Poland, the leading role in the economy has been played by the mining and smelting of zinc–lead ores since the 19th century, which is reflected in its increased content in the soils of, for example, Upper Silesia [40]. In most Polish soils, definitely, the content of Zn lays within the acceptable values, i.e., in the range of 15–240 mg∙kg⁻¹ DM. The standards are often exceeded point-by-point many times in the soils of cities [41], allotment gardens [42], and lands surrounding long-time operating galvanizing plants [43]. Zinc is an important element in human nutrition, which, for example, reduces the activity of viruses and inflammation in infections, lowers cholesterol, and often requires supplementation [44]. Excessive consumption of zinc, in turn, interferes with the basic biological functions of cells, e.g., by blocking thiol groups (-SH), inhibiting copper ions, lowering the immune response, and favouring anaemia [45,46].

In the environment, zinc is classified as an active migrant; hence, there is a danger of its easy penetration into food chains, causing biomagnification in living organisms.

Effective methods for removing the toxic content of zinc from the soil include bioremediation, using such bacteria as Bacillus sp., Staphylococcus sp., Streptococcus sp., Escherichia coli, Pseudomonas sp., Klebsiella sp., and Enterobacter sp., among others [47].

The soil tests carried out after the uncontrolled emission of heavy metals into the natural environment in the area of the industrial plant’s failure showed a serious disturbance in the elemental balance in the agriculturally cultivated horizon. The event caused a significant increase in the concentration of metals (Zn, Pb, Cd) considered particularly dangerous, posing a risk of migration of toxins into the human trophic chain [48]. Soil analysis carried out in the Municipality of Morawica in 2010 and 2014 [49,50] and as part of the monitoring of the District Chemical and Agricultural Station in Kielce (2015) showed the following mean concentrations: Zn in the range from 40.20 to 81.20 mg∙kg⁻¹ throughout the soil profile depth; Pb in the range from 40.40 to 85.20 mg∙kg⁻¹; and Cd in the range from 0.33 to 5.2 mg∙kg⁻¹. These are relatively low contents, which qualify these soils as uncontaminated. The determined contents of Zn, Pb, and Cd in the soil samples taken after the fire in the galvanizing plant in the village of Dębska Wola (2019) exceed the values from 2010–2015, especially in the organic–mineral level of 0–5 cm (10 times for zinc, 2.9 for times lead, and 3.5 times for cadmium). The obtained test results were compared to the reference values of metal content in soils [51] and the permissible content of substances in soils causing a risk of particular importance for the protection of Earth’s surface according to national legal regulations [52] (

Table 3. Trace element concentrations in soils by World Reference Values and Polish Soil Value References with indicators.

	World Reference Values [51]	Polish Soil Value References 0–25 cm [52]	Sample 0–5 cm Mean (Min–Max)	Sample 5–20 cm Mean (Min–Max)	Igeo Mean (Top/Bottom)	Igeo Max (Top/Bottom)	Eri (Top/Bottom)
pH	-	-	4.68 (4.06–5.33)	4.45 (4–5.12)
Cd (mg∙kg−1)	1.1	2	9.75 (4.56–17.11)	6.02 (1.02–11.6)	5.24/4.54	6.05/5.49	97.5/60.2
Pb (mg∙kg−1)	25	100	184.34 (109.07–509.7)	113.26 (40.97–290.67)	2.71/2.01	4.18/3.37	921.7/566.3
Zn (mg∙kg−1)	62	300	638.31 (120.99–2007.34)	208.76 (42.33–909.45)	5.24/4.54	5.84/4.70	638.3/208.8

). According to the Regulation of the Minister of the Environment of 1 September 2016 on the method of assessing soil contamination [52], the concentrations of the analysed metals for light mineral soils at the 0–25 cm horizon, with fraction Ø < 0.02 mm in the range of 10–20% and a pH_KCl value less than or equal to 6.5, should not exceed 300 mg∙kg⁻¹ (Zn), 100 mg∙kg⁻¹ (Pb), and 2 mg∙kg⁻¹ (Cd). The permissible concentrations were exceeded in all samples in terms of cadmium concentrations and in the vicinity of the galvanizing plant in the case of zinc and lead. Much more restrictive limits of the World Reference Values (WRV) [51] (Zn—62 mg∙kg⁻¹; Pb—mg∙kg⁻¹; Cd—1.1 mg∙kg⁻¹) made it possible to qualify metal markings as complying with acceptable standards only in four cases in the zinc concentration results. All lead determinations in the samples significantly exceeded the reference values (WRV). Only one sample (no. 15) remained below 1.1 mg∙kg⁻¹ for Cd. According to the guidelines of the Institute of Soil Science Cultivation in Puławy [53,54], the soils in Dębska Wola contaminated with heavy metals as a result of a failure of an industrial plant were classified as class VI on a six-point scale (very heavily polluted soils). The calculated I_geo values for Cd and Zn were shown to be heavily to extremely contaminated. The lowest value of geoaccumulation was calculated for the average concentrations of Pb (moderately to heavily contaminated). The ecological risk factor Eri was similarly high: significantly high for Cd and very high for Pb and Zn (TOP).

In the soil exposed to long-term pressure from the metallurgical plant in the town of Stalowa Wola, Poland [55], significantly lower average contents of lead of 20.23 mg∙kg⁻¹ (max. 23.3 mg∙kg⁻¹) and cadmium of 0.58 mg∙kg⁻¹ (max 0.8 mg∙kg⁻¹) were reported. In the area of a galvanizing plant near the town of Trzcianka [56], 19 samples of the top soil layer (0–10 cm) and 19 samples of the aboveground parts of plants were collected for further analysis. In addition, the zinc content was determined in the samples of bottom sediments (18 samples) taken from Lake Sarcze near the galvanizing plant and in the muscle tissue of fish (4 samples). The geochemical background content of zinc in soils exposed to the potential impact of the galvanizing plant amounted to approximately 53.7 mg·kg⁻¹. Similarly, in other regions of the world, where soils were tested for agricultural use, metal concentrations subjected to multidirectional pressures generally did not exceed WRV [57,58,59,60]. Higher concentrations of metals went along with the results of soil tests in the zones of long-term impact of plants with strong metallic emissions (mines and smelters). In the soils analysed around the Apiai smelter, Brazil [61], the concentrations of Zn, Pb, and Cd were extremely high and amounted to 14,062 mg∙kg⁻¹, 37,781 mg∙kg⁻¹, and 144 mg∙kg⁻¹, respectively. On the other hand, in the zone of influence of the zinc and lead mine in the Sidi village, China [62], the average soil concentrations of Zn and PB were found to be 1190 mg∙kg⁻¹ and Pb 1852 mg∙kg⁻¹, respectively. Studies conducted in industrial areas of environmental contamination confirm an increased risk of adverse health effects in the case of consumption of plants such as wheat, rice, and spices—dicots–grown on lands contaminated with Zn, Cd, and Pb [63]. In the event of the failure of the galvanizing plant in Dębska Wola, the maximum range of the negative impact of metal deposition did not exceed 1500 m (Figure 2a, Figure 5 and Figure 6). The nearest village is located 1600 m to the southwest; therefore, on the day of the failure, the local population was not exposed to the direct effects of harmful fumes moving eastwards.

5. Conclusions and Recommendations

Plants dealing with the thermal treatment of molten metals pose a real threat to the environment in the event of failure. Their location should be carefully thought out so as to minimize the effects of a possible leak.

The course and effects of accidents should be monitored during the event (fire) and in the long term (e.g., with the use of bioindicators). All elements of the environment degraded as a result of the failure should be subject to analysis.

The failure in the galvanizing plant and the fire resulting from it were of decisive importance for changes in the physical and chemical properties, as well as chemical composition of the soil in the study area. In the analysed samples, the permissible concentrations of Zn, Pb, and Cd were exceeded several times. Meteorological conditions at the time of the failure and one day after it affected the spread of pollutants in the atmosphere and the place of their deposition in the prevailing wind direction in the nearby agricultural fields. A small typological and species diversity, and especially the similar content of floatable parts and dust fractions, created good conditions for the accumulation and movement of potentially harmful metals. Soils with a degree of contamination found in the vicinity of the plant in Dębska Wola should be subjected to monitoring tests and, if high enrichment parameters of Zn, Pb, and Cd are maintained, excluded from agricultural production and subjected to reclamation treatments.