Translocation and dissipation of seven indicator polychlorinated biphenyls from contrast soils cultivated with different root vegetables

doi:10.21203/rs.3.rs-4835190/v1

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Translocation and dissipation of seven indicator polychlorinated biphenyls from contrast soils cultivated with different root vegetables

https://doi.org/10.21203/rs.3.rs-4835190/v1

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The behaviour of 7 polychlorinated biphenyls (PCBs) in agricultural Chernozem and Fluvisol soils from the Czech Republic planted with radishes, onions and carrots was studied. Only the total biomass carrot yield was significantly (P < 0.05) reduced when compared to the control biomass yield. All tested PCBs, especially congener PCB 28, were able to accumulate in slightly higher amounts in the radish surface than in the onion one. The highest PCB content was observed in the surface layer of carrots, which could be related to the agrochemical properties of the soil, vegetation period and more intensive contact of carrot roots with PCBs in a bulk soil. The translocation factors of PCBs were lower than 1, indicating a poor ability for PCB uptake from soil. The highest relative PCB removal from soil was observed in acidic Fluvisol, accounting for 27.2%, with a maximum of 2% plant contribution to soil PCB dissipation. Non-significant (P < 0.05) PCB removal from vegetable-planted soils indicated that root vegetables were not able to enhance the autochthonous soil microorganisms to degrade PCBs by releasing exudates in the rhizosphere of vegetables. Bioaccumulation PCB factors derived from the cultivation of examined root vegetables in Chernozem and Fluvisol soils contaminated with PCBs at nearly 1500 µg/kg dw can be considered as low and negligible.

PCBs

contamination

pollutant uptake

removal

food quality

Polychlorinated biphenyls (PCBs) belong to the group of persistent organic pollutants, which are considered hazardous organochlorine pollutants that threaten human health and the whole environment due to chemical and biological degradation, toxic and carcinogenic properties (Valizadeh et al., 2021). PCBs are widespread in the environment with up to 209 artificially made PCB congeners, which consist of two benzene chlorinated rings of the general formula C₁₂H_10 − xCl_x (Starr et al., 2020). They were produced worldwide on a large scale for many sectors of industry due to their unique industrial properties, such as thermal stability, non-flammability and dielectric behaviour, and for many applications, e.g., heat exchange fluids, insulating agents in electric transformers, capacitors, and plasticisers in the building and printing industry (Stella et al., 2017). Because of their industrial utilisation, PCBs are released into the environment and accumulate in each environmental matrix but mostly in river sediments and wastewater sewage sludges (Dvořák et al., 2017; Košnář et al., 2023), soils, plants (Kacálková and Tlustoš, 2011) and humans (Asamoah et al., 2018).

Due to the ageing process, PCBs persist mainly in soil, and their bioaccessibility decreases in soil over time. The increment of soil organic matter diminishes their bioavailability for strengthened adsorption, while the increased particle size and soil moisture elevates it due to the less adsorption of soil particles, thereby increasing the PCB concentration in the soil solution. This could be related to their undesirable uptake by plants (Ti et al., 2018). There is a threat of PCBs entering the food chain via direct plant consumption by humans and livestock. The ingestion of PCB-contaminated soils or indoor dust are also possible pathways of human exposure (Shen et al., 2019).

Although PCBs were heavily restricted and regulated by the Stockholm Convention in the Czech Republic in 2004, Czech soils and other related environmental media still suffer from huge contamination by aged PCB congeners (Vácha et al., 2016). According to our unpublished results of screening PCBs in garden/field soils impacted by heavy industry, these soils contain almost 10 times more PCBs than the limit, 1000 µg/kg dry weight (dw), for Czech soils of 7 PCB congeners suggested by the United States Environmental Protection Agency (USEPA) (Public notice No. 153, 2016). In recent decades, several bioremediation strategies for PCB-contaminated soils using plants in relationship with soil microorganisms have been intensively studied (Maurya et al., 2023). These contaminants originated from different sources, such as heavy industry. Moreover, in recent decades, the utilisation of sewage sludge as an organic fertiliser has become economically feasible together with positive effects on plant yield and as an input of organic matter into the agricultural soil. In the long term, the contamination of agricultural soils by PCBs not far from heavy industry sources could also be increased. There is a lack of studies focused on the behaviour of PCBs in different agricultural soil types originating from the Czech Republic that are suitable for vegetable planting. Therefore, model vegetation experiments with common vegetables planted on PCB-contaminated soils need to be investigated, as the uptake of PCBs by vegetables is a critical pathway for human exposure (Vácha et al., 2011; Vašíčková et al., 2013; Han et al., 2023).

This study assumes that the removal of 7 PCB congeners from soil and their plant uptake is directly related to the soil type and cultivation of common vegetable species, which could enhance the soil autochthonous microorganisms. The main aims of this study were 1) to investigate the dissipation of 7 USEPA PCBs in contrasting agricultural soils from the Czech Republic, 2) to determine the contribution of root vegetables to the dissipation of 7 PCBs from the soil, and 3) to evaluate the uptake and translocation of PCBs by vegetables.

2.1 Experimental soils and PCB spikes

Two contrasting agricultural soils suitable for vegetable planting, neutral Chernozem and acidic Fluvisol, were collected from a garden/field in the Czech Republic from an arable layer of 0–30 cm. The basic agrochemical characteristics of these experimental soils are given in Table 1. Individual parameters were measured using the methods described by Javorská et al. (2009). The collected soils were air-dried, thoroughly homogenised and sieved (4 mm) to remove stones and debris. Prior to the establishment of the experiment, the soils were spiked with 7 USEPA PCB (Table 2) standard solutions obtained from Chromservis Ltd. (Czech Republic) to obtain approximately 200 µg/kg dw of each PCB congener in the soil. Thin layers of Chernozem and Fluvisol were spiked with PCB solutions in cyclohexane and left to evaporate the solvent. Fresh PCB-spiked soils were aged in the dark for one month and mixed regularly to homogenise PCB contamination. The initial content of 7 indicator USEPA PCBs (PCB 28, 52, 101, 118, 138, 153 and 180) in experimental soils is shown in Table 2. The respective compound name, CAS number, and molecular and structural formula of the 7 USEPA PCBs are listed in Table S1.

Table 1

Basic properties of the experimental soils used in the vegetation experiment.
Characteristics	Chernozem	Fluvisol
Clay (%)	34	11
Loam (%)	29	6.0
Sand (%)	38	83
¹CEC (mmol⁽⁺⁾/kg)	235	76
\(\:{\:\text{p}\text{H}}_{{\text{C}\text{a}\text{C}\text{l}}_{2}}\)	7.3	5.2
Soil organic matter (%)	2.9	1.1
PCBs (µg/kg dw)	²<MLOD	<MLOD
¹CEC – cation exchange capacity, ²<MLOD – PCB congeners were lower than the method limit of detection (lower than 1.0 µg/kg dw).

Table 2

Initial content of individual PCBs (µg/kg dw) in the experimental soils used in the vegetation experiment.
	Chernozem	Fluvisol
PCB 28	210.2 ± 18	198.6 ± 4
PCB 52	196.6 ± 19	195.0 ± 5
PCB 101	200.5 ± 14	197.8 ± 13
PCB 118	203.1 ± 13	201.8 ± 14
PCB 138	178.0 ± 5	170.7 ± 7
PCB 153	164.5 ± 3	169.7 ± 4
PCB 180	160.0 ± 14	176.4 ± 7
Total of 7 PCBs	1301 ± 38	1278 ± 42

2.2 Pot experiment

The experiment was conducted in 6 L plastic pots with 5 kg dw of PCB-contaminated soils during the vegetation period in a growing weather-controlled outdoor vegetation hall. As experimental root vegetables, radishes (Raphanus sativus L., Cartago F1 hybrid), carrots (Daucus carota L. var. Nantes), and onions (Allium cepa L., Bratko F1 hybrid) obtained from Reprosam s.r.o (Czech Republic) were used. The pot experiment was conducted with eight treatments and four replications. The soil treatments were as follows: 1) non-PCB-contaminated (control) soil without plants, 2) planted non-PCB-contaminated (control) soil, 3) PCB-contaminated soil without plants, and 4) planted PCB-contaminated soil.

Prior to sowing, each pot received the same dose of fertiliser with 0.5 g N, 0.16 g P and 0.4 g K as a water solution. Approximately 20 − 30 seeds were sown in each pot to a depth of 1–2 cm and slightly watered. After germination, the plants in each pot were thinned to 10 plants per pot. Plants were manually watered daily with demineralised water to obtain 60–70% of the maximum soil water-holding capacity. Possible weeds were removed during cultivation. Radishes were harvested after 30 days, onions after 60 days and carrots after 90 days. All plants were carefully washed with demineralised water to remove the remaining soil particles. Harvested vegetables were separated into roots and shoots. Carrot roots, radishes and onion bulbs were further divided into the surface (1–3 mm) and inner part of the respective roots. Separated plant samples were cut into small pieces, air-dried, milled to an analytical fine powder and stored in a freezer prior to the analyses.

2.3 PCB extraction and GC/MS analysis

Soil (5 g dw) and plant (2 g dw) samples were weighed in rounded glass-capped flasks and extracted with 30 mL of cyclohexane/acetone mixture (1:1, v/v) according to the procedure described by Javorská et al. (2007). All solvents used for the preparation of extracts were analytical GC/MS grade (Chromservis, Czech Republic). Prior to the extraction, the surrogate standard of p-terphenyl-d₁₄ obtained from Merck, Czech Republic (Table S2) was added at 100 ng/mL to obtain extraction method recovery. The reaction mixture was shaken on an orbital shaker for 60 min and ultrasonicated for an additional 30 min. To remove chlorophyll, 5 mL of 96% H₂SO₄ (Chromservis, Czech Republic) was added and rigorously shaken for 10 min and left for 15 min in the dark to settle the solid sample particles.

The extraction mixture was further transferred to a conical open glass and evaporated to near dryness using a rotatory evaporator. The evaporated extract was then dissolved with 2 mL hexane and cleaned using 6 mL Florisil 500 mg with 60 Å mesh solid-phase extraction (SPE) cartridges. The SPE columns were conditioned with 10 mL of dichloromethane and equilibrated with 10 mL hexane. After sample loading, the SPE was washed with 10 mL of 5% (v/v) dichloromethane-hexane and eluted with 10 mL dichloromethane-hexane (1:1, v:v). The eluted phase was then evaporated to near dryness and dissolved to a 2 mL final volume with hexane in a vial, including 50 µL PCB 116-d₅ (Table S3) at 200 ng/mL as an internal standard (Merck, Czech Republic).

Soil and plant samples were analysed for PCBs using gas chromatography with a mass spectrometry detector (6890N GC/5975 MS, Agilent Technologies, USA). Separation of analytes was performed on an HP5-MS column with a 30 m length, 0.25 mm inner diameter and 0.25 µm film thickness (J&W Scientific, USA). Detailed GC/MS analytical conditions were used the same as those previously described by Javorská et al. (2007). Sample extracts of 1 µL were injected into the splitless regime of the GC inlet. The selected ion monitoring (SIM) mode with two characteristic ions was used for the acquisition of the respective PCBs. The characteristic SIM ions of the target compounds and their retention times on the column are shown in Table S4. Fresh calibration standards (1.0–1000 ng/mL), including the surrogate standard and 7 PCBs, obtained from Neochema, Germany, were analysed at the beginning of each run. The conducted calibration curve of the tested compounds was always linear, with an R > 0.995. The method limit of detection, mean values of spike blank recoveries, spike soil recoveries and spike plant recoveries of the extraction method are shown in Table S5. The average recovery of p-terphenyl-d₁₄ done during each sample extraction was 97%.

2.4 Data evaluation

One-way analysis of variance at P < 0.05 (Statistica 12.0, StatSoft, Oklahoma, USA) was used to evaluate significant differences between the treatments. Microsoft Excel 2010 (Microsoft Corporation, Washington, USA) was used to prepare the figures. The percentage removal of PCBs from soil, their uptake by plants, bioaccumulation and translocation factors were calculated using equations described in a previous study by Košnář and Tlustoš (2018).

3.1 Yield of vegetables grown on PCB-contaminated soils

The influence of PCB contamination in different soils, neutral Chernozem and acidic Fluvisol, on vegetable cultivation was estimated from the biomass yield of plants, as shown in Table 3. The investigated level of spiked PCB contamination reflected the contemporary contamination in US residential soils in the range from 20 to 1700 µg/kg dw (Martinez et al., 2022). In this study, the total amount of dry radish biomass (16.2 g dw/pot) harvested from Chernozem was not statistically different (P < 0.05) from the dry weight of radishes planted on non-PCB-contaminated control Chernozem. The dryness of the respective harvested morphological parts of bulbs (surface layer and inner part) and shoots of contaminated Chernozem and the control treatment were comparable. Similar results for dry amounts of radishes cultivated on Fluvisol were obtained, as shown in Table 3. The same trends were also observed in the case of onion cultivation in these soils, where the total dry biomass ranged from 44.0 to 64.7 g dw/pot. The influence of the tested concentration of 7 PCBs (~ 1300 µg/kg dw), which was above the limit of PCBs (20 µg/kg dw) for Czech soils, had no adverse effect on radish or onion yield in Chernozem and Fluvisol treatments. This could be caused by the fact that radishes and onions usually grow mostly on the soil surface; therefore, contact with PCB compounds could be very limited. The negative effect of PCB contamination on the yield of carrot roots, shoots and total biomass (Table 3) was evident in the case of carrot cultivation on both tested soils in comparison to control soils. The yield of all carrot parts from PCB-contaminated Chernozem and Fluvisol treatments were statistically decreased (P < 0.05) compared to the respective control treatments. This could be because carrot roots usually grow deeper into the bulk soil, and contact with PCBs in the soil is longer during the vegetation period than in the case of radishes or onions. A similar reduction in plant growth and yield was observed by Javorská et al. (2011), who planted parsley and red beet on different soil types contaminated by PCBs with concentrations higher than 2100 µg/kg dw.

Table 3

Biomass dry weight (g dw/pot) of vegetables cultivated in PCB-contaminated soils.
Vegetable	Biomass (g dw/pot)	Chernozem		Fluvisol
Vegetable	Biomass (g dw/pot)	Control soil	PCB soil	Control soil	PCB soil
Radish	Shoots	9.1 ± 1.8a	8.3 ± 1.7a	7.7 ± 1.7a	7.0 ± 1.4a
	Bulbs – surface layer	5.1 ± 2.9a	3.9 ± 2.1a	4.2 ± 2.2a	3.3 ± 1.6a
	Bulbs – inner part	5.0 ± 1.3a	4.0 ± 1.1a	4.1 ± 1.0a	3.3 ± 0.8a
	Total biomass	19.3 ± 5.9a	16.2 ± 4.8a	16.1 ± 4.5a	13.6 ± 3.7a
Onion	Shoots	21.5 ± 4.2a	17.7 ± 2.9a	17.3 ± 2.3a	15.6 ± 2.2a
	Bulbs – surface layer	13.2 ± 4.5a	10.6 ± 3.4a	11.3 ± 3.5a	8.8 ± 2.6a
	Bulbs – inner part	30.0 ± 5.5a	24.1 ± 4.1a	24.8 ± 5.2a	19.6 ± 5.0a
	Total biomass	64.7 ± 13.9a	52.4 ± 9.4a	53.4 ± 10.6a	44.0 ± 8.9a
Carrot	Shoots	12.8 ± 3.2a	9.4 ± 2.1ab	10.3 ± 1.6ab	9.3 ± 1.5b
	Roots – surface layer	15.8 ± 3.8a	12.5 ± 2.5ab	12.3 ± 2.0ab	9.6 ± 1.0b
	Roots – inner part	65.9 ± 6.3a	50.7 ± 5.0ab	57.4 ± 2.4b	44.9 ± 3.0c
	Total biomass	94.5 ± 12.7a	72.7 ± 7.4bc	80.0 ± 5.5ab	63.8 ± 4.9c
All values represent the mean of four replications. Different lowercase letters within the same row indicate significant differences among the treatments (Tukey test; P < 0.05).

3.2 Accumulation of PCBs in vegetables cultivated on PCB-contaminated soils

The surface layer, inner part of roots, and shoots were carefully evaluated for the content of 7 PCB congeners, and their sum was calculated, as shown in Fig. 1, which excluded the control treatments where PCBs were lower than the detection limit (< 1 µg/kg dw). All 7 tested indicator PCB congeners were found in all analysed morphological parts. From the obtained results, it was evident that higher PCB contents were found in the surface layer of the experimental vegetables (500–1400 µg/kg dw). The lowest content of the sum of 7 PCBs was found in the surface layer of onions (P < 0.05), but there was no significant difference (P < 0.05) between Chernozem and Fulvisol treatments. A slightly higher PCB content was found in the surface layer of radishes than in onions, and the highest PCB content was observed in the surface layer of carrots. Our results correspond to the findings of Javorská et al. (2011), who found a higher PCB concentration in peels than in the cortex of parsley or red beet cultivated Fluvisol and Chernozem. This could be related to the deeper growth in the bulk soil, longer contact with PCBs in soil during cultivation and the fact that carrot roots are known for higher lipid and carotene contents than onion or radish, where these lipophilic compounds, such as PCBs, are accumulated (Collins et al., 2006). In our study, PCB 28 was prone to accumulate in the highest amount compared to all individual PCBs. Other PCB congeners accumulated in vegetables with a similar level, and their content was not higher than 200 µg/kg dw. This could be explained by the octanol-water partition coefficient (K_ow), which is used to predict the interaction between pollutants and cultivated plants. A higher uptake of PCB 28 than other congeners could be expected, as this congener had the lowest log K_ow of all investigated PCBs (Whitfield Åslund et al., 2007).

From the results of PCBs in the total biomass, it was obvious that radishes and carrots planted on Fluvisol had a higher ability to accumulate individual PCBs than from Chernozem. This is in concordance with a study by Javorská et al. (2011), who investigated the fate of 7 PCB congeners in Fluvisol from different localities in the Czech Republic planted with parsley or red beet. This could be related to the agrochemical properties of the experimental soils (Table 1). Our Fluvisol contained 83% sand and 1.1% soil organic matter, which is a much lower amount of organic matter than that in Chernozem (2.9%). Therefore, it could be expected that highly chlorinated PCB congeners (PCB 118, PCB 138, PCB 153 and PCB 180) have a greater affinity for soil organic matter and are more persistent in the environment than the lower ones, which are also considered to be more degradable (Backe et al., 2004). Due to this fact, selected PCBs were probably not firmly adsorbed on soil organic matter of Fluvisol, and they were able to be obtained in the soil solution, being more bioavailable than in the Chernozem soil.

A much lower PCB content was found in the inner part of the vegetables in comparison to the respective vegetable peels (Table 3). Tested PCBs were also found in the shoots of vegetables, but their content was on the edge of the detection limits of PCBs (Table S5). Low amounts of PCBs found in the inner parts of roots indicated that the possible uptake of PCBs by aboveground biomass is very limited. This could be supported by the calculated translocation factors shown in Table 4. All translocation factors were lower than 1, indicating a poor ability to take up PCBs from contaminated soil. Kacálková and Tlustoš (2011) also found only low chlorinated PCB 28, PCB 52 and PCB 101 in shoots of maize, sunflower and poplars (45 − 135 µg/kg dw) in a field experiment with very low bioaccumulation factors (0.03 − 0.09). Nevertheless, the bioaccumulation factors of carrots in this study were close to 1, indicating the potential to accumulate PCBs in higher amounts. Similar PCB distributions to our study have been found in crops (turnip, sweet potato and broccoli) grown around the waste-dismantling area in China (Liu et al., 2020).

Table 4

Bioaccumulation and translocation factors of total PCBs in vegetables cultivated on PCB-contaminated soils.
Vegetable	Factor	Chernozem		Fluvisol
Vegetable	Factor	Control soil	PCB soil	Control soil	PCB soil
Radish	Bioaccumulation	–	0.49 ± 0.01a	–	0.69 ± 0.01b
Radish	Translocation	–	0.01 ± 0.00a	–	0.03 ± 0.01b
Onion	Bioaccumulation	–	0.46 ± 0.02a	–	0.46 ± 0.03a
Onion	Translocation	–	0.01 ± 0.00a	–	0.01 ± 0.00a
Carrot	Bioaccumulation	–	0.87 ± 0.04a	–	0.95 ± 0.02b
Carrot	Translocation	–	0.02 ± 0.01a	–	0.03 ± 0.00b
All values represent the mean of four replications. – not estimated, as the content of PCBs in biomass was below the limit of detection. Different lowercase letters within the same row indicate significant differences between treatments (Tukey test; P < 0.05)

Unfortunately, from the data obtained in the current experiment, it is not clear whether some PCB degradation can occur in plants. The low PCB accumulation in the inner part of the vegetables indicated that the PCBs were only adsorbed on the root surface. This means that individual PCBs are not able to enter the epidermal plant cells of roots, thereby suppressing symplast/apoplast transfer of PCBs in plant roots. Furthermore, from the obtained results, the possible translocation of PCBs from plant roots to their shoots was not evident. Therefore, the contamination of shoots by PCBs could be caused by the volatilisation of PCBs directly from contaminated soil during the vegetation period of vegetables, as suggested by Salihoglu and Tasdemir (2009). This is supported by the results of Wang et al. (2023), who used clover in their phytoremediation of PCB-contaminated soil and detected no PCBs in either the roots or the aboveground parts of the clover. The low PCB concentrations in the soil suggest that the removal of PCBs was mainly due to rhizosphere microorganisms. In general, root exudates can induce the desorption of soil residual PCBs and secondary metabolites of root exudates induce the biphenyl catabolic pathway to degrade PCBs in soil.

3.2 Dissipation of PCBs from non-planted and vegetable-cultivated soils

The relative removal of individual PCB congeners and their sum in soils and the contribution of plants to the total dissipation of PCBs from experimental soils are shown in Fig. 2. The highest relative removal of PCBs from soil was observed in PCB-contaminated Fluvisol with carrots, accounting for 27.2%. This removal of the total sum of PCBs was significantly (P < 0.05) higher than in other realised treatments in the range from 12 to 17%. As mentioned above, this observation could be related to the soil type and the physical and chemical properties of the experimental soil. The total sum of PCBs (Fig. 2) also indicated that PCBs could be removed and taken up by selected plants more easily from acidic soil with a low pH reaction, especially together with a low amount of soil organic matter (Table 1).

From the individual PCBs, the removal of PCB 28 was higher than that of other PCB congeners with a higher molecular weight. This could be linked to a higher bioavailability of PCB 28 in tested soils due to the ability to be dissolved in solution in a higher portion, which is further consumed by roots. The removal of PCB 28 from soil planted with carrots was nearly 7%, and there was no significant difference between the removal from Chernozem and Fluvisol. The remaining PCB congeners were less removed < 5% with no differences at P < 0.05.

As indicated from the relative dissipation of PCBs in soils (Fig. 2), there were no significant differences (P < 0.05) between tested treatments, including the control soil. This means that the root vegetables of the planted treatments were not able to enhance the ability of soil microorganisms to degrade these compounds in comparison to the soil without plants. Nevertheless, the total soil PCB removal was in the range of 11.5–14.6%, which could not be considered negligible. This relatively high removal could be caused by the higher activity of soil autochthonous microorganisms involved in PCB degradation, which was probably enhanced by fertilisation prior to the establishment of the experiment. Similar behaviour of PCBs in soil to the current study has been reported by Javorská et al. (2009), who found that the depletion of PCBs in the fertilised rhizosphere of rape was significantly (P < 0.05) higher in the Fluvisol by 32 − 38% with lower organic matter content than in Chernozem. Nevertheless, the remaining PCB content in soil was still high and could be hazardous for the whole biota in the environment, as reported by Xu et al. (2019a). Soil microorganisms can be boosted for the reduction of PCBs in the soil by biochar amendment, as it could be used as the medium of PCB adsorption to reduce plant uptake and PCB accumulation in soil microorganisms (Valizadeh et al., 2021; Silvani et al., 2019). Dissipation of PCBs in soil can also be accelerated by the addition of organic matter, such as sludge from wastewater treatment plants (Xu et al., 2019b). The abundance and potentially the most successful PCB-degrading bacterial genera (Bacillus, Streptomyces, Ramlibacter and Paenibacillus) in different soil types was reported by Xu et al. (2020c). The most promising strategies for degrading PCBs in soil are graphene oxide-assisted bacterial agent amendment (Li et al., 2023) and pyrophosphate-chelated Fenton-like reaction (Sun et al., 2020) for soil remediation.

The overall contribution of plant uptake to the relative removal of total PCBs from soil is shown in Fig. 2. The best results were obtained in soils planted with carrots compared to radishes, onions and bare soils. The contribution of plants to the total removal of PCBs was 2% at maximum, which was achieved in treatments where carrots were cultivated. Only PCB 28 removal of 3.6% was slightly higher from Fluvisol than in the case of Chernozem. The removal of the remaining individual PCBs from neutral and acidic soils was almost the same. The soil organic matter together with the time of PCB ageing and other soil physicochemical properties diminish the bioaccessibility for strengthened adsorption; therefore, less accommodation of PCBs in soil pore water can be expected (Ti et al., 2018; Shen et al., 2019). Based on the data obtained from the conducted experiment, the root vegetables are not able to accumulate PCBs in a relatively high amount. Therefore, according to Public Notice No. 53 (2012) about the chemical requirements of foodstuff and other materials for health protection in the Czech Republic, the cultivation of root vegetables at a contamination level of nearly 1500 µg/kg dw in Chernozem and Fluvisol soils can be considered safe.

This study focused on the behaviour of 7 USEPA-evaluated PCBs in different Czech agricultural soils planted with common vegetables. The influence of PCB contamination in neutral Chernozem and acidic Fluvisol was estimated from the biomass yield of planted radishes, onions and carrots. Only carrot biomass was significantly (P < 0.05) decreased in comparison to the biomass yield from control soils. In general, a slightly higher PCB content was found in the surface layer of radishes compared to onions, and the highest PCB content was observed in the surface layer of carrots. Carrots planted had a higher ability to accumulate individual, especially low chlorinated, PCBs in Fluvisol soil than in Chernozem soil, which could be related to the agrochemical properties of the soil, vegetation period and more intensive contact of roots with PCBs in a bulk soil. All translocation factors of PCBs were lower than 1, indicating a poor ability to uptake PCBs from soil. The highest relative removal of PCBs from soil was observed in acidic Fluvisol, accounting for 27.2% with a maximum of 2% plant contribution to the total soil PCB dissipation. Removal of PCBs in vegetable-planted Chernozem soil was not significant (P < 0.05) compared to the PCB-contaminated soil without plants. This suggests that the root vegetables of planted treatments were not able to enhance the ability of soil microorganisms to degrade PCBs in the vegetable rhizosphere of Chernozem. Nevertheless, the poor bioaccumulation factors of PCBs in both experimental soils of Chernozem and Fluvisol indicate that the cultivation of root vegetables at a contamination level of nearly 1500 µg/kg dw can be considered safe.

Ethics approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Competing interests

The authors declare no competing interests.

Funding

This study was supported by the European Regional Development Fund (project NUTRISK no. CZ.02.1.01/0.0/0.0/16_019/0000845).

Author Contribution

Zdeněk Košnář: methodology, investigation, datacuration, writing—original draft; Pavel Tlustoš: writing—reviewing and editing, supervision, funding acquisition.

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You are reading this latest preprint version

Translocation and dissipation of seven indicator polychlorinated biphenyls from contrast soils cultivated with different root vegetables

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material and methods

2.1 Experimental soils and PCB spikes

2.2 Pot experiment

2.3 PCB extraction and GC/MS analysis

2.4 Data evaluation

3. Results and discussion

3.1 Yield of vegetables grown on PCB-contaminated soils

3.2 Accumulation of PCBs in vegetables cultivated on PCB-contaminated soils

3.2 Dissipation of PCBs from non-planted and vegetable-cultivated soils

4. Conclusion

Declarations

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Consent for publication
Not applicable.

Competing interests

Funding

Author Contribution

References

Additional Declarations

Supplementary Files

Status:

Version 1

Translocation and dissipation of seven indicator polychlorinated biphenyls from contrast soils cultivated with different root vegetables

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material and methods

2.1 Experimental soils and PCB spikes

2.2 Pot experiment

2.3 PCB extraction and GC/MS analysis

2.4 Data evaluation

3. Results and discussion

3.1 Yield of vegetables grown on PCB-contaminated soils

3.2 Accumulation of PCBs in vegetables cultivated on PCB-contaminated soils

3.2 Dissipation of PCBs from non-planted and vegetable-cultivated soils

4. Conclusion

Declarations

Ethics approval and consent to participate Not applicable.

Consent for publication Not applicable.

Competing interests

Funding

Author Contribution

References

Additional Declarations

Supplementary Files

Status:

Version 1

Ethics approval and consent to participate
Not applicable.

Consent for publication
Not applicable.