Distribution, Accumulation and Translocation of the Heavy Metal Cd in Various Varieties of Edible Rapeseed under Cd Stress

Abstract

To examine the safety of producing edible rapeseed in heavy-metal-contaminated farmland, field experiments were performed with 25 varieties of edible rapeseed on farmland lightly polluted with Cd in the central southern part of Hunan Province. Growing characteristics and Cd contents in rapeseed tissues were measured, and Cd uptake, translocation and removal potential were calculated. The results showed that the growth of 25 rapeseed varieties was not inhibited without withering or inconsistent changes in the shoot. The shoot and root Cd contents of rapeseed varieties ranged from 0.05 to 0.26 mg·kg⁻¹ and 0.04 to 0.26 mg·kg⁻¹, respectively. The bioaccumulation factor (BCF) showed that the shoot had a greater capacity for Cd transport than roots. The total Cd removed by rapeseed varieties ranged from 1.606 to 16.159 μg·plant⁻¹. There were significant differences in plant height, BCF of soil available Cd in the shoot, translocation factor (TCF) of Cd from root to shoot and Cd intake by rapeseed among the edible rapeseed varieties. Cluster analysis of Cd accumulation in the 25 rapeseed varieties indicated that Lvjin 1, Guanyou Qingjing and Guanyou brassica not only reduced soil pollution but also allowed for the production of safe leafy rapeseed, although Cd contents in the shoot of 25 rapeseed varieties did not exceed the national safety standards of China.

1. Introduction

Heavy metal contamination in agricultural soils threatens food safety, human health and agricultural sustainability [1]. Cadmium (Cd) is the most critical toxic heavy metal as it can accumulate in the kidney, liver and bone of humans over an entire lifetime [2]. Rapid industrialization and modernization in China have increased heavy metal contamination, resulting in about 7% of agricultural land being polluted with Cd [3]. How to promote remediation and ensure safe production has become a research hotspot, especially in China, which has limited cropland and a large human population. Phytoremediation with hyperaccumulators of heavy metals has been a more efficient and economical remediation technique for Cd pollution on farmland compared with conventional remediation methods [4]. With a low Cd concentration in the seed and high Cd accumulation in the plant, rapeseed has the characteristics of having a high nutritional value, being easy to cultivate and having a high biomass, and has been a good candidate to remediate Cd-polluted soils and secure the production of rapeseed oil [5,6,7], especially when the soil Cd content is lower than 20 mg·kg⁻¹ [2].

Edible rapeseed is an important crop in China. Heavy metal contents in edible rapeseed are strongly associated with human health [8]. However, information on the safe production of edible rapeseed in soils lightly or moderately polluted with Cd is not available. Plant species and even cultivars within the same species differ widely in their capacity to uptake, accumulate, translocate and tolerate heavy metals [9]. Thus, we raise the question of whether the safety utilization of edible rapeseed with different varieties in soils lightly polluted with Cd remains consistent and positive. Data on Cd accumulation in edible rapeseed of different varieties may give insights into phytoremediation coupled with agro-production. In this research, 25 varieties of edible rapeseed were cultivated on farmland polluted with Cd in Middle South Hunan, China. The aim of this study was to investigate the growth characteristics and Cd distribution, accumulation and translocation in varieties of edible rapeseed in soils lightly polluted by Cd. The results will be useful in the selection of edible rapeseed varieties for use to reduce Cd pollution and ensure healthy eating for humans.

2. Materials and Methods

2.1. Site Description and Experimental Design

Experiments were performed at Hengyang, Hunan Province, China. The study site is under a humid subtropical monsoon climate with an average annual temperature of 17.9 °C and an average annual rainfall of 1452 mm. The soil has moderate fertility and good drainage and irrigation conditions. Soil total Cd ranges from 0.30 to 0.60 mg·kg⁻¹ and soil available Cd is between 0.17 and 0.32 mg·kg⁻¹, mainly due to the high geochemical background in the soil. The soil pH values range from 5.0 to 5.8. According to the soil environmental quality risk control standard for soil contamination of agricultural land [10] and report on the national general survey of soil contamination in China [11], the Cd contents of soil in the study area exceed the risk screening values and the soil is lightly polluted with Cd.

Twenty−five varieties of rapeseed, widely grown in the south or north of China (

Table 1. The name of the 25 edible rapeseed varieties in the experiment.

No.	Name	No.	Name	No.	Name
1	Yanyu	10	Daye Heidatou	19	Rapeseed 905
2	Dongqing	11	Heixuanfeng	20	Rapeseed 908
3	Dongjin 1	12	Youliang Suzhou	21	Rapeseed 810
4	Dongjin 2	13	Aiji Suzhouqing	22	Guanyou Qingjing
5	Lvjin 1	14	Fenpiqing	23	Jinyang 401
6	Lvjin 2	15	Hangzhou Youdonger	24	Guanyou brassica
7	Jingyou 4	16	Lvjingang	25	Zhongji 605
8	Sujun 316	17	Huaguan Qingjingcai
9	Heishuaige	18	Wuyue Manyoucai

), were obtained from seed marketing companies. The experiment comprised 25 treatments and 75 cultivation plots for every treatment to be replicated three times. Each cultivation plot measured 3 m × 4 m (12 m²), and the 75 plots were arranged in a completely randomized block design. In each plot, the rapeseed sowing rate was 2 kg ha⁻¹, and the application rates of nitrogen, phosphorus and potassium fertilizers were 200 kg N ha⁻¹ with urea, 90 kg P₂O₅ ha⁻¹ with calcium triple superphosphate and 90 kg K₂O ha⁻¹ with potassium chloride, respectively. All fertilizers were applied once as basal dressing before seeding. Pesticide applications, weeding and other practices were performed according to local practices.

2.2. Sample Collection and Analysis

The rapeseed plants were weeded once after 42 days of growth. At harvest, one row of plants from the central area in every cultivation plot was selected to determine the yield. Three rapeseed plants were randomly collected to measure the shoot and root length and determine Cd content in the shoot or root. Rapeseed plant samples were washed with tap water and rinsed with deionized water before absorbing surface moisture with filter paper and digesting the plants with a mixture of nitric and perchloric acid (3:1, v/v) [6]. The digestion solution was filtrated before the filtrate was tested by an inductive coupling plasma spectrophotometer (ICP−OES 5110, Agilent, Palo Alto, CA, USA) [7].

After harvest, three soil cores in each cultivation plot were randomly collected from 0 to 20 cm depths using a soil auger with a 2.5 cm diameter, and were mixed thoroughly for analysis. Soil pH was measured using a pH meter with a water/soil ratio of 2.5:1. Soil available Cd content was determined by filtering the soil with DTPA after immersion for 2 h at a soil–liquid ratio of 1:2.5 (w:w) [12]. Soil total Cd content was determined by digesting the soil with a mixture of aqua regia and perchloric acid [13]. The Cd contents in the leach liquor and digestion solution were filtrated and tested by an inductive coupling plasma spectrophotometer [6].

2.3. Data Analysis

The bioaccumulation factor (BCF) and translocation factor (TCF) were calculated to evaluate the capacity of the 25 rapeseed varieties to transport or accumulate Cd [14]. The following formulas were used:

BCF = Cd content in shoot or root (mg·kg⁻¹)/Soil available Cd or soil total Cd (mg·kg⁻¹)

TCF = Cd content in shoot (mg·kg⁻¹)/Cd content in root (mg·kg⁻¹)

To evaluate the Cd removal potential of the rapeseed varieties, the Cd accumulation in all tissues of the 25 rapeseed varieties was calculated using the following formula:

The amount of Cd accumulation (mg·plant⁻¹) = DWshoot × Cdshoot + DWroot × Cdroot

where DW (kg·plant⁻¹) is the weight of the shoot or root of a rapeseed plant and Cd (mg·kg⁻¹) is the Cd content in the shoot or root of rapeseed plants.

One−way analysis of variance (ANOVA) was performed to evaluate the differences among rapeseed varieties or tissues using the statistics packages of R software 4.3.0 with “agricolae” [15]. Cluster analysis was used to group the 25 rapeseed varieties into various categories based on their ability to accumulate and translocate Cd in the shoot using the systematic clustering method in R software “vegan” [16] and “factoextra” packages. All figures were produced using the Origin 2021 software.

3. Results

3.1. Growth Characteristics of the 25 Rapeseed Varieties

The plant height of the 25 rapeseed varieties ranged from 14.0 to 28.0 cm, with a median value of 17.78 cm. There were significant differences among 25 rapeseed varieties (p < 0.05). The plant heights of Hangzhou Youdonger and Rapeseed 905 were significantly higher than those of others, whereas Yanyu was the shortest. The root length of the 25 rapeseed varieties ranged from 6.93 to 16.83 cm, with a median value of 12.35 cm. The root lengths of Zhongji 605 and Guanyou Qingjing were significantly higher than those of others, and Aiji Suzhouqing was the shortest. However, there were no significant differences among the 25 rapeseed varieties (Figure 1).

The shoot fresh weight of the 25 edible rapeseed varieties ranged from 20.91 to 101.14 g·plant⁻¹, with a median value of 48.07 g·plant⁻¹. The shoot fresh weight of Dongjin 2 was higher than those of others, and Youliang Suzhou and Fenpiqing had the lowest. The root fresh weight of the 25 rapeseed varieties ranged from 1.11 to 5.03 g·plant⁻¹, with a median value of 2.07 g·plant⁻¹. The highest root fresh weight was recorded in Guanyou Qingjing and Zhongji 605, whereas the lowest was recorded in Aiji Suzhouqing. However, no matter the fresh weight of the shoot or root, there was no significant difference among rapeseed varieties (Figure 2).

3.2. Cd Content in the Soil and Plant in Different Rapeseed Varieties

The Cd contents in the shoot of the 25 rapeseed varieties ranged from 0.05 to 0.26 mg·kg⁻¹, with a median value of 0.103 mg·kg⁻¹ (Figure 3). The average Cd contents in 25 rapeseed varieties were all less than 0.2 mg·kg⁻¹, which is the national food safety standard limit for contaminants in food in China [3]. However, in some samples of certain rapeseed varieties, such as Dongqing, Lvjin 2, Heixuanfeng, rapeseed 905, Jingyou 4, Lvjingang, Youliang Suzhouqing, Hangzhou Youdonger and Aiji Suzhouqing, the Cd contents in the shoot were above 0.2 mg·kg⁻¹. Additionally, there were no significant differences among these rapeseed varieties (p = 0.066). The Cd contents in the roots of the 25 rapeseed varieties ranged from 0.04 to 0.26 mg·kg⁻¹, with a median value of 0.102 mg·kg⁻¹ (Figure 3). Although the mean Cd contents in the root of 25 rapeseed varieties are all less than 0.2 mg·kg⁻¹, some samples of Lvjingang, Aiji Suzhouqing and Youliang Suzhouqing had Cd contents exceeding 0.2 mg·kg⁻¹. There was no significant difference in Cd content in the root among 25 rapeseed varieties (p = 0.592).

The soil available Cd content and soil total Cd content in 25 edible rapeseed varieties are shown in Figure 4. The soil available Cd content ranged from 0.17 to 0.32 mg·kg⁻¹, with a median value of 0.22 mg·kg⁻¹. Although there were no significant differences among the 25 rapeseed varieties, the soil available Cd content was highest in Lvjin 2 and lowest in Dongjin 2, Lvjin 1, Jingyou 4 and Guanyou Qingjing. The soil total Cd content ranged from 0.29 to 0.58 mg·kg⁻¹, with a median value of 0.37 mg·kg⁻¹. There were no significant differences in soil total Cd content among rapeseed varieties. Risk screening values and risk intervention values for the soil contamination of agricultural land in China [10] indicated that 97.5% of soil samples in the study had exceeded the risk screening values for Cd, but all samples were below the risk intervention values.

3.3. Cd Accumulation and Transport Characteristics in 25 Rapeseed Varieties

The BCF of soil available Cd in the shoot ranged from 0.26 to 0.99, with a median value of 0.51, and there was a significant difference among the 25 varieties (p = 0.023). Aiji Suzhouqing had the highest BCF in the shoot with 0.668, whereas Yanyu, Rapeseed 810, Guanyou Qingjing and Zhongji 605 had the lowest BCF with 0.404, 0.392, 0.387 and 0.353, respectively. The BCF of soil available Cd in roots ranged from 0.17 to 1.04, with a median value of 0.5062, and there were no significant differences in BCF in the shoot among 25 varieties (p = 0.698). The results are shown in Figure 5.

The BCF of soil total Cd concentration in the shoot or roots is shown in Figure 6. The BCF of soil total Cd concentration in shoots ranged from 0.148 to 0.657, with a median value of 0.282, and the BCF of soil total Cd concentration in roots ranged from 0.113 to 0.541, with a median value of 0.275. There were no significant differences in soil total Cd concentration among the 25 varieties in shoots or roots. However, Yanyu, Dongjin 2, Lvjin 1, Aiji Suzhouqing, Lvjingang, Rapeseed 908, Guanyou Qingjing, Jinyang 401, Guanyou brassica and Zhongji 605 had a higher BCF of total or available Cd in roots than those of other varieties in shoots.

The TCF of Cd from root to shoot ranged from 0.51 to 2.95, with a median value of 1.033. There were 16 varieties with TCF > 1, and the order was as follows: Dongqing (2.04), Rapeseed 905 (1.77), Youliang Suzhou (1.49), Lvjin 2 (1.29), Dongjin 1 (1.27), Heixuanfeng (1.24), Hangzhou Youdonger (1.15), Sujun 316 (1.08), Fenpiqing (1.07), Heishuaige (1.07), Aiji Suzhouqing (1.06), Rapeseed 810 (1.05), Daye Heidatou (1.05), Huaguan Qingjingcai (1.04), Jingyou 4 (1.03) and Wuyue Manyoucai (1.02). Additionally, there were significant differences in the TCF of Cd from root to shoot among the 25 varieties (p = 0.049). Dongqing, Rapeseed 905 and Youliang Suzhou (1.48) had a higher TCF of Cd from root to shoot than those of other varieties (Figure 7).

3.4. Cd Uptake in the 25 Rapeseed Varieties

The total Cd uptake by plants in the 25 rapeseed varieties (

Table 2. Cd uptake by plant in 25 rapeseed varieties.

Rapeseed Variety	Plant a (μg·plant−1)	Shoot b (%)	Root b (%)	Rapeseed Variety	Plant a (μg·plant−1)	Shoot b (%)	Root b (%)
Yanyu	5.22 ± 1.70	95.45 ± 0.35	4.55 ± 0.35	Fenpiqing	4.56 ± 2.48	94.48 ± 2.92	5.52 ± 2.92
Dongqing	6.02 ± 2.76	97.62 ± 0.81	2.38 ± 0.81	Hangzhou Youdonger	10.23 ± 4.83	96.20 ± 1.16	3.80 ± 1.16
Dongjin 1	6.55 ± 3.50	97.01 ± 1.74	2.99 ± 1.74	Lvjingang	7.37 ± 3.33	95.24 ± 1.47	4.76 ± 1.47
Dongjin 2	7.23 ± 3.39	95.57 ± 1.66	4.43 ± 1.66	Huaguan Qingjingcai	6.22 ± 3.32	95.11 ± 2.41	4.89 ± 2.41
Lvjin 1	5.18 ± 0.86	94.62 ± 1.51	5.38 ± 1.51	Wuyue Manyoucai	6.40 ± 0.90	96.29 ± 0.25	3.71 ± 0.25
Lvjin 2	11.14 ± 1.18	97.0 ± 0.69	3.0 ± 0.69	Rapeseed 905	9.01 ± 6.55	96.86 ± 2.54	3.14 ± 2.54
Jingyou 4	6.82 ± 4.74	95.17 ± 0.82	4.83 ± 0.82	Rapeseed 908	3.98 ± 1.58	95.58 ± 0.42	4.42 ± 0.42
Sujun 316	7.73 ± 5.52	95.56 ± 2.53	4.44 ± 2.53	Rapeseed 810	4.69 ± 1.33	95.66 ± 0.75	4.34 ± 0.75
Heishuaige	6.79 ± 4.71	94.44 ± 0.34	5.56 ± 0.34	Guanyou Qingjing	7.76 ± 0.23	92.10 ± 1.49	7.90 ± 1.49
Daye Heidatou	8.56 ± 4.82	95.0 ± 1.14	5.0 ± 1.14	Jinyang 401	3.86 ± 0.47	94.53 ± 0.14	5.47 ± 0.14
Heixuanfeng	7.26 ± 5.68	96.85 ± 1.0	3.15 ± 1.0	Guanyou brassica	4.83 ± 2.36	93.92 ± 2.30	6.08 ± 2.30
Youliang Suzhou	5.76 ± 5.64	96.77 ± 0.49	3.23 ± 0.49	Zhongji 605	4.11 ± 2.94	94.71 ± 1.64	5.29 ± 1.64
Aiji Suzhouqing	6.62 ± 5.47	92.81 ± 6.97	7.19 ± 6.97

^a The total Cd uptake by the plant; ^b the proportion of Cd uptake by the shoot or root.

) ranged from 1.606 to 16.159 μg·plant⁻¹, with a median value of 6.555 μg·plant⁻¹. Although rapeseed Lvjin 2 and Hangzhou Youdonger had a higher uptake of Cd than others, there were no significant differences among the 25 rapeseed varieties (p = 0.074). The proportion of Cd uptake by the shoot ranged from 84.77% to 98.96%, with a median value of 95.38%, and there were significant differences in ones among rapeseed varieties. Guanyou brassica, Aiji Suzhouqing and Guanyou Qingjing had a significantly lower proportion of Cd uptake than Dongqing, Dongjin 1, Lvjin 2, Rapeseed 905, Heixuanfeng, Youliang Suzhou, Wuyue Manyoucai, Hangzhou Youdonger, Rapeseed 810, Rapeseed 908, Dongjin 2, Sujun 316 and Yanyu. The proportion of Cd uptake by the root ranged from 1.04% to 15.23%, with a median value of 4.62%. There were significant differences among rapeseed varieties, and Guanyou brassica, Aiji Suzhouqing and Guanyou Qingjing had a significantly higher proportion of Cd uptake by the root than others, which was contrary to the proportion of Cd uptake by the shoot.

3.5. Cluster Analysis on Cd Accumulation in 25 Rapeseed Varieties

Based on the Cd content in the shoot, BCF from soil to shoot and TCF from root to shoot, cluster and statistical analyses grouped the 25 rapeseed varieties into three categories (Figure 8). The first category included Guanyou Qingjing, Guanyou brassica, Rapeseed 810, Zhongji 605, Rapeseed 908 and Jinyang 401, representing the lower ability to accumulate and translocate Cd in lightly Cd-contaminated soil. In this category, the Cd content in the shoot ranged from 0.077 to 0.107, with a mean value of 0.089, BCF ranged from 0.219 to 0.281, with a mean value of 0.239, and TCF ranged from 0.756 to 1.050, with a mean value of 0.907. Yanyu, Dongjin 2, Lvjin 1, Dongjin 1 and Sujun 316 were in the second category, with a slightly higher ability to accumulate and translocate Cd than the rapeseed varieties in the first category. The Cd content in the shoot ranged from 0.082 to 0.121, with a mean value of 0.099, BCF ranged from 0.230 to 0.331, with a mean value of 0.263, and TCF ranged from 0.779 to 1.269, with a mean value of 0.982. It should be noted that Rapeseed Lvjing 1 had a lower Cd content in the shoot and lower TCF. The remaining 14 rapeseed varieties belonged to the third category, with the highest ability to accumulate and translocate Cd in this study. In this category, the Cd content in the shoot ranged from 0.122 to 0.167, with a mean value of 0.142, BCF ranged from 0.306 to 0.417, with a mean value of 0.367, and TCF ranged from 0.904 to 2.040, with a mean value of 1.230. Varieties Lvjin 2 and Hangzhou Youdonger had the highest Cd content in the shoot and the highest BCF.

4. Discussion

Cd pollution in the soil can inhibit or promote the growth of rapeseed depending on soil Cd contents. Low contents of Cd promote the growth of rape, whereas a high content of Cd inhibits it [17,18,19,20,21,22,23]. However, previous studies have reported conflicting results regarding the threshold of Cd concentration for inhibiting or promoting crop growth. The biomass of rapeseed roots, stems and leaves reaches maximum values when the Cd content < 1.8 mg·kg⁻¹ and decreases when the Cd content > 1.8 mg·kg⁻¹ [17]. A Cd concentration above 5 mg·kg⁻¹ will hinder the growth of rapeseed, inhibit plant height, lose green leaves and reduce biomass [19,20,21]. In this study, the growth of 25 rapeseed varieties was not inhibited under a soil Cd concentration from 0.2 mg·kg⁻¹ to 0.8 mg·kg⁻¹ without withering or inconsistent changes in the leaf and so on. Correlation analysis showed that there was no significant correlation between plant height or fresh weight and soil Cd content. Additionally, the mean Cd contents in shoots within the 25 edible rapeseed varieties were all below 0.2 mg·kg⁻¹ in this study, indicating that edible rapeseed planted in mild Cd-contaminated soil was generally safe.

The accumulation and translocation of Cd differ among rapeseed tissues. Currently, it is widely accepted that the Cd content in the shoot of rapeseed is higher than that in the roots [17,24,25,26,27,28], indicating that Cd is more toxic to shoots than to roots [20]. However, the root is the organ in direct contact with soil Cd pollution. This observation is explained by the greater surface area of the shoot compared to that of the root [29]. Under the influence of root pressure and transpiration, Cd was transported to the shoot. The stronger the transpiration, the easier it is for Cd to migrate upward and the higher the content in the shoot [30]. In this study, there was a significant positive correlation between Cd content in the shoot and Cd in the root (r = 0.6; p = 0.001). Wang [17] reported a TCF of Cd in rapeseed above 1, indicating that more Cd is transferred from roots to shoots. Additionally, because of rhizosphere microorganisms, rhizosphere cells were protected from Cd toxicity [30]. However, some previous studies reported that the content of Cd in rapeseed tissues occurs in the order of root > stem > leaf [31]. The accumulation of Cd in the roots of rapeseed is higher than that in the stem and leaf [32,33], which means that Cd transportation in some rapeseed varieties is greatly hindered at the interface of the root and stem. In this study, the Cd content in the plant, BCF of soil available Cd and BCF of soil total Cd were not significantly different between the shoot and the root, although the values in the shoot were slightly higher than those in the root. However, the uptake of Cd by shoots was significantly higher than that of the roots due to the higher biomass in the shoots. There was a significant positive correlation between TCF and Cd contents in the shoot and BCF, and BCF was significantly correlated with the Cd content of plant. However, TCF and BCF were both not significantly correlated with plant biomass.

The bioavailability of Cd in the soil is related to soil characteristics, such as pH, Eh, OM, microorganisms, etc. [34,35]. Within the same rapeseed variety, the cumulative absorption of Cd in acidic soil was higher than that in alkaline soil, and there is a significant difference in Cd adsorption capacity among rapeseed varieties [32]. Plant species differ widely in their capacity to uptake, accumulate and tolerate heavy metals [9]. China has a large number of rapeseed germplasm resources, with some varieties or genotypes having high levels of accumulated Cd, e.g., Brassica junica [28]. Rapeseed Xikou Huazi has a remarkedly higher shoot biomass, Cd uptake and soil purification rate than Zhucang Huazi when the Cd concentration in the soil is ≤20 mg·kg⁻¹ [25].

A previous study reported that the accumulation of Cd varied among varieties. In alkaline soil, the highest concentration of Cd in the shoot was determined to be 0.68 mg·kg⁻¹ in Rapeseed Jinhua Guanqing, which was 2.13 times higher than the lowest of 0.32 mg·kg⁻¹ in Rapeseed Xiawang. In contrast, in acidic soil, 0.96 mg·kg⁻¹ was observed in the shoot of Rapeseed Jinhua Guanqing, which was 1.88 times higher than the lowest of 0.51 mg·kg⁻¹ recorded in Rapeseed Xiawang [32]. In this study, there were significant differences in plant height, BCF of soil available Cd in the shoot and TCF from root to shoot among the 25 rapeseed varieties. Based on the ability of Cd accumulation and translocation in the shoot, cluster analysis grouped the 25 rapeseed varieties into three categories. Except for Guanyou Qingjing, Guanyou brassica, Rapeseed 810, Zhongji 605, Rapeseed 908 and Jinyang 401 were placed in the first category, and Lvjin 1 also showed a lower ability to accumulate and translocate Cd, which was in the second category. Notably, to achieve win–win results in the research on safe production and soil remediation in heavy-metal−contaminated farmland, it is necessary to pay attention to the enrichment of not only the edible parts but also the non-edible parts, the former having a lower ability for Cd enrichment than the latter. Therefore, in this study, the rapeseed varieties with low enrichment in edible shoots and high enrichment in non-edible roots, such as “Lvjin 1”, “Guanyou Qingjing” and “Guanyou brassica”, should be widely applied and promoted not only to reduce soil pollution but also to allow for the production of safe leafy rapeseed. These differences may be attributed to different genotypes of different varieties of rapeseed.

This study was conducted in the field, and the experimental results are more reliable than those of experiments performed in artificially Cd-added systems. However, the applicability of the findings of this experiment is limited only to lightly polluted soils. In the future, experiments with different levels of Cd pollution should be conducted to enhance the applicability of the findings of these experiments.

This experiment studied 25 rapeseed varieties popular in southern and northern China. The accumulation and growth characteristics of different rapeseed varieties under the same pollution conditions were compared, and the varieties of rapeseed that are prone to cadmium accumulation were identified. The more suitable rapeseed varieties for planting in lightly polluted soil were identified.

5. Conclusions

This study screened 25 edible rapeseed varieties and identified those that are safe to use in soil lightly or moderately polluted with Cd. The growth of 25 rapeseed varieties was not inhibited without withering or inconsistent changes in shoots and so on. The fresh weight of the shoot or root and the root length were not significantly different among the 25 rapeseed varieties, but plant height was. The Cd contents in rapeseed shoot and roots ranged from 0.05 to 0.26 mg·kg⁻¹ and from 0.04 to 0.26 mg·kg⁻¹, respectively. Although the mean values of Cd contents of the shoots or roots of all 25 rapeseed varieties were less than 0.2 mg·kg⁻¹, samples of certain varieties had Cd contents above 0.2 mg·kg⁻¹. The BCF of soil−activated Cd in the shoot and root ranged from 0.26 to 0.99 and from 0.17 to 1.04, respectively. There was a significant difference among the 25 varieties in the BCF of soil−activated Cd in the shoot. The total Cd removed by rapeseed varieties ranged from 1.606 μg·plant⁻¹ to 16.159 μg·plant⁻¹. Although there was no significant difference among edible rapeseed varieties, Cd uptakes by the shoot were significantly higher than those of the root. Cluster analysis grouped the 25 rapeseed varieties into three categories based on Cd enrichment ability. In conclusion, although the Cd contents in the shoot of 25 rapeseed varieties did not exceed the national safety standards, planting Lvjin 1, Guanyou Qingjing and Guanyou brassica can reduce soil pollution and also allow for the production of safe edible rapeseeds.