Pollution of Flooded Arable Soils with Heavy Metals and Polycyclic Aromatic Hydrocarbons (PAHs)
Soils that are exposed to floodwaters because of shallow groundwater and periodical wetlands are, to a large extent, exposed to contamination by organic and inorganic compounds. These are mainly compounds that have drifted along with the inflow of heavily laden floodwater and are produced within the soil profile by the anaerobic transformation of organic matter. Heavy metals and polycyclic aromatic hydrocarbon (PAH) compounds are absorbed by the soil of the floodwaters, and moving in the soil profile, they pose a threat to groundwater. What is more, after a flood, they may be absorbed by the crops. This paper focuses on the effects of Odra River (Poland) floods, heavy metals, and PAHs on soil and the possibilities of the migration of these pollutants into the soil profile. In the tested sludge samples of floodwater and soil, there were no abnormal concentrations of heavy metals, but the flooding time positively affected the amount listed in the test samples. Concentrations of PAHs increased, but they also exceeded the standards for arable soils in the case of single compounds.
KeywordsSoil Flood Heavy metals PAHs
Severe and prolonged rainfall leads to water levels rising in rivers not only in mountainous regions but also in the lowlands. River surge, resulting in permeating or flooding, causes long-term negative effects to the environment. Sustained flooded soil, even for a short time, leads to the displacement of air from the soil pores and the creation of anaerobic conditions in the profile. The saturation stage during flooding includes all levels of genetic soil, resulting in marginal amounts of oxygen being absorbed in the soil profile. This entails the death of plants that are usually not suited for prolonged submergence underwater; it also destroys soil fauna as well as influences the chemical composition of the soil. The organic compounds in the soil of the incoming water are absorbed by the sorption complex, contributing in particular to the pollution of the humus level (Maliszewska-Kodyrbach et al. 2008). The composition of the soil has a huge impact on the amount of the substance being absorbed. If it has been previously contaminated with organic compounds of anthropogenic origin, such as tar or soot, the sorption of pollutants may increase (Motelay-Massei 2004). In addition, the dying roots of submerged plants are subjected to microbial decomposition with the evolution of hydrogen sulfide, methane, and other compounds including polycyclic hydrocarbons. Anaerobic conditions can significantly cause the decomposition of biomass—up to a sixfold increase in the amount of compounds from the group of polycyclic aromatic hydrocarbons (PAHs) in relation to the amount present in the soil before flooding (Oleszczuk et al. 2007). Absorbed with floodwater or produced in the process of microbial degradation PAHs compounds because of the occurrence in the floodwaters, hydrophilic compounds act as solvents and migrate through the soil profile along with the moving water. This is especially dangerous in the case of direct contact with the groundwater aquifers, which are used as sources of drinking water. The bioavailable fraction of PAHs can be absorbed by plants that will grow in the area covered by floodwater recession.
Floodwater includes not only significant loads of suspensions and nutrients but also large amounts of organic compounds, often harmful or toxic (Czerniawska-Kusza et al. 2006; Witt and Siegel 2000). This contamination by the floodwaters is washed away from roads, exercise yards, warehouses and petrol stations, places where solvents and pesticides are disposed, and landfills and domestic septic tanks that collect household sewage (Poluszyńska 2012). Pollution carried by floodwater can be divided into two major groups: the first group includes primarily inorganic substances that contain heavy metals and nutrients, which are retained by physical or chemical sorption during the process of migration into the soil profile and finally enrich the flooded soil (Maliszewska-Kodyrbach et al. 2012). The other group consists of the organic compounds present in the form of the predecomposed remains of plant and animal tissues derived from municipal waste and organic matter contained in compost, manure, slurry tanks, and septic tanks as well as organic compounds that may have toxic properties (e.g., omitted refining lubricants or substances with irritant properties, such as, alcohols and hydrocarbons, including aliphatic and monoaromatic hydrocarbons) (Kluska 2004; Laskowski et al. 2005). In addition, these waters contain compounds belonging to the so-called persistent organic pollutants (POPs), such as PAHs, polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and polychlorinated terphenyls (PCTs) (Witt and Siegel 2000). In between flooding, the soil is exposed, although to a much lesser extent, to the contamination of POPs (including PAHs), resulting in the precipitation of dry deposition. Many sources of these compounds, in combination with the significant dispersion, result in PAHs that are listed in all areas of the environment (Carlstrom and Tuovinen 2003; Chen et al. 2004; Wilcke et al. 2004). This may be natural (e.g., volcanoes, forest fires, and the distribution of biomass) or anthropogenic (e.g., fuel combustion) (Thiele and Brummer 2002). This group includes more than 200 compounds; however, 16 of them with particularly toxic (including carcinogenic) properties were chosen for monitoring. Not only the floodwaters but also the crops’ organic fertilization and sedimentation to the soil surface dust can add significant amounts of metals and POPs (Wilcke et al. 2004; Laskowski et al. 2005). In addition, organic fertilization with manure or compost, especially sewage sludge, also acts as a soil enrichment process, among others, in polycyclic hydrocarbons (Brandli et al. 2005; Oleszczuk 2006; Weber et al. 2007). Content of listed PAH compounds in soils accelerate anaerobic conditions (as a result of organic matter fermentation in the soil), often occurring with high groundwater levels, especially during a flood, when the waters cover the soil for a long time (Włodarczyk-Makuła and Janosz-Rajczyk 2004). Entering the soil, allochthonous metal ions and PAHs are adsorbed mainly in the humus layer (Kluska 2004). Organic matter present in amounts greater than 0.1 % is largely responsible for the sorption of pollutants (Yang et al. 2008). However, the compounds of PAHs, despite the relatively low solubility in water, accompanied by substances (e.g., humic acids) may migrate along the direction of water flow into the profile and then be taken up by the plants or enter aquifers, causing contamination, especially in the case of light soils (Ciesielczuk et al. 2006a, b; Wilcke et al. 1999). The article focuses on the presence of heavy metals and PAHs in soils subjected to short and long processes of complete inundation by floodwater as a factor that could eliminate the soil from cultivation crops intended for direct consumption.
2 Material and Methods
2.1 Research Area
Sampling site characteristics of area M1
Sampling site characteristics of area M2
In soil samples, the following parameters were determined: pH, electrolytic conductivity (EC), and the content of organic matter (methodology according to Polish standards). The contents of calcium, sodium, potassium, and lithium were determined in wet mineralizates through the flame emission spectrometry (FES) method using the BWB-XP apparatus. The contents of the other analyzed metals (zinc, copper, chromium, nickel, lead, cadmium, and manganese) were determined using the Thermo Scientific iCE 3500 Atomic Absorption Spectrometer after the microwave-assisted wet mineralization in aqua regia using the MARS-X device. Mercury content was determined in solid samples through atomic absorption spectrometry with the AMA-254 apparatus. Analytical procedure quality was checked with “LRM soil 1”—certified reference material (Gdańsk University of Technology, Poland).
A PAH analysis was carried out in a few steps. First of all, fresh samples were dried at room temperature using anhydrous sodium sulfate (POCH) (Ciesielczuk et al. 2006a, b). Extraction was carried out through a DCM/hexane (gas chromatography grade) mixture in a ratio of 1:9 (v/v) in the extraction device fexIKA (Laskowski et al. 2005; Kluska 2004). Before GC analysis, the extracts were purified by aluminum oxide (Aldrich) on glass tubes (Wilcke et al. 1999). Inspissated eluates were analyzed through the gas chromatography–mass spectrometry (GC-MS) method (Shimadzu GC 17A with MS-QP5000) on the capillary column VF-5ms (30 m, 0.25 mm i.d., and 0.25 μm). The temperature of the chromatograph injector was 300 °C while that of the detector was 320 °C. The oven temperature program involved the following: 80 °C at 8 min, heating 10 °C/min to 270 °C and heating 2 °C/min to 300 °C. The detector current was at 1.2–1.4 kV. In each sample, 16 single compounds, which are recommended for monitoring by U.S. Environmental Protection Agency (U.S. EPA), were determined: naphthalene (Naf), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Flt), pyrene (Pyr), benzo[a]anthracene (B[a]ant), chrysene (Chr), benzo[b,k]fluoranthene (B[b,k]flt), benzo[a]pyrene (B[a]p), dibenzo[a,h]anthracene (D[a,h]ant), indeno[1,2,3-c,d]pyrene (Indp), and benzo[g,h,i]perylene (B[ghi]per). The flow of a carrier gas (He) was adjusted to 1 cm3/min. Certified PAH standards (US-106 N 2,000 μg/cm3 of each compound, Ultra Scientific, USA) were used in order to determine the calibration curve. Recovery levels for this procedure were low for naphthalene (57–66 %) and higher (73–92 %) for the rest of the individual PAHs. The recovery procedure was based on dry samples of PAH reference materials: “ERM-CC013a” (BAM, Berlin, Germany) and “LRM soil 1” (University of Technology, Gdańsk, Poland). The detection limits ranged between 0.05 and 0.1 μg/kg (dry weight) for particular PAHs. The uncertainty of the results was calculated as a standard deviation value. In order to single out the petrogenic compounds, the PAH contents of ANT/(ANT + PHE), BaA/(BaA + CHR), and FLA/(FLA + PYR) in liquid and solid fuel combustion were calculated.
3 Results and Discussion
3.1 Granulometric Characteristics of Investigated Samples
Granulometric composition of samples from the areas M1 and M2 (%)
Share of fractions (mm)
Group and subgroup
Main parameters of samples from the areas M1 and M2
Electrolytic conductivity (μS/cm)
Organic matter (%)
Organic carbon (%)
CaO (mg/kg [dry matter])
Na2O (mg/kg [dry matter])
K2O (mg/kg [dry matter])
During flood phenomenon, concentrations of nutrients rise in floodwater. In particular, high concentrations of P-PO4 were noted (Fenske et al. 2001). In case of long contact with soil, phosphates can be absorbed in the top (organic) layer of soil, which finally leads to higher values of phosphorus noted in samples Z and R2. Also, the contents of potassium and calcium compounds correspond well with organic matter content. Globally, the highest values were noted in sample Z flooded for a long time. The sampling site where sample Z was taken had no outflow because of riverbanks. So most likely, a lot of water transpired, and concentrations of all components rose. Remaining water migrated through a soil profile, and a lot of compounds were stopped in a mechanical or chemical manner. A similar situation was noted in the case of sample Ż2g. The highest values of pH were also noted in both samples as a result of concentrations of alkaline metals.
3.2 Law Regulations
Compounds from the PAH group for monitoring soil samples (Soil Quality Polish Regulation)
3.3 Chemical Composition
Contents of heavy metals in investigated samples from the areas M1 and M1 (mg/kg [dry matter])
In the samples from the case of M2, recorded amounts of heavy metals were high and similar to those observed in the case of M1. None of the samples analyzed contained abnormal amounts of these elements. The highest value was recorded in sample Ż2g (379.4 mg/kg [dry matter]) and sample R2 (495.0 mg/kg [dry matter]), while the lowest amounts of metals were recorded in sample Ż1z (only 54.4 mg/kg [dry matter]) These observations correspond well with other data about low risk from metals after phenomenal floods on arable soil areas (Maliszewska-Kodyrbach et al. 2012; Vácha et al. 2003). Other data were obtained on this area by other authors (Helios et al. 2005), where high concentrations of lead, cadmium, copper, and zinc in soil cores were found, but the highest values were found in deep layers (over 100 cm) of ground. Globally, the distributions of metals in all analyzed samples were similar (correlation coefficient of 0.97–0.99). Floodwater contained a lot of suspended organic and mineral matter (high turbidity), which led to the remobilizing of heavy metals (Fenske et al. 2001). However, the obtained results of metal concentrations were not as high as expected, but the long stagnation of floodwater is a risk from the rise of heavy metal content in soil because of water evaporation and metal sorption processes.
Sum of the 16 PAH compounds in soils
Sampling site characteristics
Sum of 16 PAH (μg/kg [dry matter])
Industrial area (Motelay-Massei et al. 2004)
Bangkok City, Thailand (mean value n = 30) (Wilcke et al. 1999)
Hydromorphic (0–5 cm)
University of Bonn experimental field (Atanassova and Brummer 2004)
Hydromorphic (0–5 cm)
University of Bonn experimental field (Thiele and Brummer 2002)
Hydromorphic (0–5 cm)
Agriculture field, 10 m from road (Laskowski et al. 2005)
Arable soil (0–20 cm)
Hangzhou City, China (Chen et al. 2004)
Urban soil (0–5 cm)
Nonpolluted arable soil (Mazur et al. 2006)
Arable soil (0–25 cm)
Nonpolluted arable soil (Oleszczuk et al. 2007)
Brazilian savanna (Wilcke et al. 2004)
Floodplain terrace of Moselle River (Yang et al. 2008)
The creation of PAHs in the process of biomass decomposition can occur in all soils, but prolonged flooding intensifies this process. This is demonstrated by a model experiment, where after-sewage and distilled water were used in the process of flooding (Oleszczuk et al. 2007). When the water was poured, the changes in the prevalence of PAHs in the soil were investigated. In both cases, the observed increases in the PAH content of the experiment up to the 28th day were 28 and 38 % for distilled water and after-sewage water, respectively. After this time, there was a decrease in the content of the tested compounds. However, the behavior of individual groups of compounds varied. The strongest concentration growth was recorded for 5 and 6-ring PAHs. In the case of the “flood” made with distilled water, the final content of PAH (56 days) was less than 11–35 % compared with the beginning of the experiment. However, in the case of the “flood” made with after-sewage water, the final concentrations of the test compounds were higher than the initial, from 11 to 130 %. This points out the negative impact of flooding any soil with contaminated water (e.g., flood) by introducing substances that can increase the solubility and therefore the bioavailability of PAHs. Similar concentration dynamics (initial increase and then decrease) were recorded during the anaerobic incubation of sewage sludge (Włodarczyk-Makuła et al. 2003).
Model studies were also carried out by incubating the argillaceous soil under anaerobic conditions during the period of 730 days (Thiele and Brummer 2002). The increase in concentration was varied and ranged from 139 % for benzo(b)fluoranthene to 238 % for benzo(a)anthracene. In the case of lighter compounds, the increase in concentration was smaller, and even in the case of phenanthrene, there was a decline in its concentration levels. Pure plant material was incubated in a similar way, reaching a maximum rate of increase in concentration, which recorded 674 % for chrysene. This experiment shows that the decomposition of plant residues with oxygen deficiency leads to increased levels of PAHs by several times. A similar phenomenon was observed in glial soils with high groundwater level (Atanassova and Brummer 2004). Extremely reductive conditions at levels less than 175 cm result in generating benzo(g,h,i)perylene and dibenz(a,h)anthracene, as long as there are humic acids and biodegradable organic matter. PAHs also arise with smaller amounts of rings, such as naphthalene, acenaphthene, and phenanthrene. A huge impact on the amount of absorbed organic pollutants of floodwater has an original composition and pollution of the soil. If the soil is contaminated by the products of anthropogenic origin (e.g., tar, soot, ash), the amount of absorbed impurities and, among them, the compounds belonging to PAH will be higher (Oleszczuk et al. 2007; Yang et al. 2008). In the case the organic matter content in analyzed soil samples was low, microbial anoxic decomposition resulted in a higher PAH concentration, which was not observed and what was mentioned above.
The flooding deposits and arable soils from the M1 (Opole) and M2 (Krapkowice) objects that were tested were characterized by relatively low heavy metal content, not exceeding permissible limits in any of the analyzed samples in this study. The reason for this was the low organic matter content and a significantly high content of coarse fractions resulting in a limited absorptive surface. Therefore, it seems that there is no ecotoxic impact from the analyzed elements. However, in several cases (samples Z, U, R1Z, R2, and Ż2g), pollution caused by the compounds from the PAH group was recorded. High amounts were reported particularly for chrysene, benzo(a)pyrene, and benzo(g,h,i)perylene, which can result in large amounts of these compounds to be detected in plants that will be grown in the area covered by the flood. A high content of PAH compounds in nonflooded arable soil (sample U) shows that both flood and organic fertilizers are comparable sources of soils’ PAHs.
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