Effects of Three Soil Amendments on Cr (III) Bioavailability in
Cr (III)-contaminated Soil
Pengzhan Lu
1,2,*
, Youyuan Chen
1
, Bingbing Dong
1
and Ping Sun
1
1
Departments of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China
2
No. 92609 Unit of PLA, Beijing 100077, China
Keywords:
Soil Amendments, Bioavailability, Cr (III)-Contaminated Soil.
Abstract:
The effect of soil amendments on the bioavailability of heavy metals has been progressively examined both
in the field and under laboratory conditions. To evaluate the effect of three soil amendments, i.e., chicken
manure (CM), peat (PE) and vermiculite (VE) on Cr bioavailability, we planted Lolium perenne (L.
perenne) and Pharbitis purpurea (P. purpurea) in soils contaminated with 1000 mg•kg-1 Cr (III) in the
laboratory. The results showed that all three amendments decreased the bioavailability of Cr (III). Cr (III)
accumulation in L. perenne was most significantly reduced by CM, leading to a Cr (III) concentration that
was only 54.1% of that of the control. CM alleviated Cr (III) stress on the plants, most obviously. Therefore,
CM have the potential to serve as efficient soil amendments for Cr-contaminated soil.
1 INTRODUCTION
Chromium (Cr) contamination in soil is a global
problem that can enter plants and animals through
the food chain and ultimately affect human health
(Gangwar 2011). Therefore, it is urgent to study the
treatment of Cr-contaminated soil. Cr has several
valence states, but Cr (III) is the most abundant
valence state of Cr in soil (Ashraf 2011). Therefore,
studying Cr (III)-contaminated soil is of
significance.
The use of soil amendments to treat heavy
metal-contaminated soils is currently a popular and
environmentally friendly method (Huang 2018,
Liang 2014). Among them, natural soil conditioners
with cheap price and wide sources have greater
prospect and potential (Abd 2015, Habashy 2011).
In previous studies, various natural amendments
such as red mud, lime, and compost were used to
treat heavy metal-contaminated soils (Reijonen
2016, Zhou 2017). Additionally, natural
amendments can greatly affect Cr (III) concentration
and Cr (III) bioavailability in soil (Ke 2012,
Taghipour 2016). The heavy metals bioavailability is
better controlled by organic amendments in soil.
Diverse types of organic materials, such as compost
from the food industry, municipal waste solids, and
manure and agriculture residues, can be used to
remediate the soils contaminated with metals (Qi
2018). It has been reported that organic materials
can decrease the metal availability by improving the
soil pH and via the complexation of the reactive
groups in organic materials (Abbas 2017). In
addition, the functional groups of organic
amendments provide excellent adsorption sites for
binding metals. Therefore, it is necessary to study
the effect of different organic and inorganic
amendments in Cr-contaminated soil.
Extracting Cr from the soil via roots and
translocating plants is complex. The uptake of Cr by
plants and its bioavailability in the soil can be
influenced by several factors, including the plant
type, its concentration in the soil, the soil organic
matter, the pH and the cation exchange capacity
(CEC)
(Khan 2018). Different types of plants have
differing bioaccumulation capacities with respect to
Cr.
The purpose of this study is to (1) study the
effects of the three soil amendments on the
bioavailability of Cr (III) in soil; (2) explore the
differences in uptake, transport and accumulation of
Cr (III) in plants with the three soil amendments.
374
Lu, P., Chen, Y., Dong, B. and Sun, P.
Effects of Three Soil Amendments on Cr (III) Bioavailability in Cr (III)-contaminated Soil.
DOI: 10.5220/0011210000003443
In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 374-378
ISBN: 978-989-758-595-1
Copyright
c
2022 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
2 MATERIALS AND METHODS
2.1 Soil and Amendments
Soil samples were collected from the 0-20 cm
interval of Chromium Salt Factory in Upper
Loushan River, Licang District, Qingdao, China
(36.21°N, 120.39°E). To homogenize the samples,
each sample was completely mixed; then, each
sample was air dried and passed through a 2-mm
sieve. The three soil amendments examined included
chicken manure (CM), peat (PE) and vermiculite
(VE) in this study. Before addition to the soil, the
amendments were ground and passed through a
2-mm mesh. The basic chemical properties of the
experimental soil and amendments are presented in
Tables 1 and 2.
Table 1. The basic chemical properties of the soils.
Pro-
ject
pH
value
Organic
matter
content
/g·kg
-1
CEC
/cmol·kg
-1
Cr(III)
/mg·kg
-1
Cr(T)
/mg·kg
-1
Soil 7.32 10.47 16.48 9.06 9.58
Table 2. The basic chemical properties of the three
amendments.
Amen-
dments
pH
value
Organic
matter
content
/g·kg
-1
total
nitrogen
/%
Cr(T)
/mg·kg
-1
CM 7.87 45.3 20.4 -
PE 6.10 62.4 15.8 -
VE 7.40 - - -
-: indicates not detected.
2.2 Pot Experiment
The experiments in this study were conducted by
potting Lolium perenne (L. perenne) and Pharbitis
purpurea (P. purpurea) with CM and PE(organic
amendments), and an inorganic amendment (VE) in
Cr (III)-contaminated soils. L. perenne and P.
purpurea are more tolerant to Cr when exposed to
Cr (III) levels no greater than 1000 mg·kg
-1
(Chen
2017). Therefore, the concentrations of Cr (III) in
the soil samples were set at 1000 mg·kg
-1
in this
study. Cr was added uniformly in the form of a
CrCl
3
·6H
2
O solution and then equilibrated at 25
for one week in the laboratory.
The three amendments were added to the soil at a
20 mg·kg
-1
application concentration and thoroughly
mixed. Choose plastic pots of suitable size, each
containing 1 kg soil (dry weight, dw). Each
treatment and one control (no treatment) were
prepared in triplicate. Two copies were prepared for
the treatment group, one for L. perenne and another
one for P. purpurea. Irrigated deionized water was
added to the pots equally when needed.
Seeds of L. perenne and P. purpurea were
obtained from Shangpin Landscaping Engineering
Company, Hefei. The seeds were washed with H
2
O
2
and then with deionized water. Then, the seeds were
sown in the selected pots. The pots were kept in a
greenhouse with a controlled environment. After
germination, there were equal numbers of uniform
and healthy seedlings in each pot. All pots were
adjusted daily to a water content of 75% and a field
capacity (FC) of 100% by weight.
2.3 Analysis
Ten grams of treated soil was sampled after 7, 21,
and 35 days; then, the soil was air dried, gently
homogenized with a mortar and analyzed to
determine its chemical parameters.Ten grams soil
samples were taken after one week, three weeks and
five weeks, then air-dried. After gently homogenized
with a mortar, it was used for the analysis of its
physical and chemical properties. The plants were
harvested after 30 days of growth. After rinsing,
plant roots and shoots were dried and ground.
Flame atomic absorption spectrometry was used
to digest and analyze total Cr and Cr (III) in the soil
samples (with detection limits of 5 mg/kg and 2
mg/kg). Determination of Cr concentration after
digestion with 0.5 g powder sample using
H
2
SO
4
-H
2
O
2
according to a literature method
(Parkinson 1975).
The chemical fraction of Cr in the soil was
assessed according to the BCR protocol, which is a
sequential extraction program involving four
steps(Sahuquillo 1999).
2.4 Bioconcentration Factor and
Translocation Factor
The bioconcentration factor (BCF) and translocation
factor (TF) are key indexs used to assess the ability
of a plant species to remediate metal-contaminated
soil. The BCF and TF for Cr in the studied plants
were determined according to a literature
method(Sidhu 2016). The BCF and TF of the plants
were calculated using equations (1) and (2):
SP
CCBCF = (1)
where
S
C is the Cr(III) concentration in soil
(mg·kg
-1
) and is the concentration in plants
(mg·kg
-1
), and
P
C
Effects of Three Soil Amendments on Cr (III) Bioavailability in Cr (III)-contaminated Soil
375
rs
CCTF =
(2)
where
r
C and
s
C are the Cr(III) concentrations in
roots and shoots of the plants (mg·kg
-1
).
2.5 Statistical Analysis
The Statistical Product and Service Solutions
software package was used in the statistical analysis.
One-way analysis of variance (ANOVA) using
Duncan's multiple range test (P = 0.05) was
conducted to determine the statistical significance of
the differences among samples. The correlations
were analyzed by Pearson’s test (two tailed) using
SPSS 20.0 (P < 0.05).
3 RESULTS AND DISCUSSION
3.1 Cr Fraction in Soil
Although the heavy metals concentration is an
important indicator to express the degree of soil
pollution, the toxicity of heavy metals is associated
with their chemical fraction and bioavailability
(Meng 2017). According to the difficulty of
extracting the different Cr chemical fractions, the
harm and degree of toxicity of Cr to the environment
are expressed as acid-soluble > reducible >
oxidizable > residual fractions. Namely B1 > B2 >
B3 > B4. The sum of B1, B2 and B3 represents the
bioavailability content, which poses a potential
threat to organisms (Qiao 2003). Figure 1 shows the
proportion changes of the Cr (III) fractions after
application of the amendments in Cr-contaminated
soil. In each group, B4 was dominant in the initial
stage (7 days) of the incubation experiment, with the
proportions in the Cr (III) fraction ranging from
79.3% to 71.6%. The three soil amendments had
little effect on the fraction of Cr (III), which changed
slowly over time. Only CM reduced the proportions
of B1 + B2 to 66.7% of that of CK in the later stage
(35 days). The contents of Cr (III) in the soil were
influenced by the organic matter contents of CM and
PE. VE played a similar role in soil containing Cr
(III) but showed less of an effect than CM and PE.
The organic matter content in the amendments plays
a certain role in reducing the bioavailability of heavy
metals in soil.
Figure 1: Effect of amendments on the fraction of Cr(III)
in the soil.
Figure
2:Effect of amendments on Cr(III) accumulation in
two plants.
3.2 Cr Accumulation in Plants
The accumulation of Cr (III) in the shoots and roots
of L. perenne and P. purpurea is shown in Figure 2.
In the plant shoots, CM had the most significant
reduction of Cr (III) in the shoots of L. perenne and
P. purpurea, with values of only 55.6% and 68.0%
of those of CK, respectively (Figure 2a). There was
no significant change in Cr (III) accumulation in the
two plants between the PE and CK groups.
The effect of the amendments on the Cr (III)
accumulation in the roots of the two plants is shown
in Figure 2b. The rank order of the three
amendments in terms of reduced Cr (III)
accumulation in the roots of the two plants was CM
> VE > CK > PE. The decrease in the Cr(III)
concentration upon CM treatment was the most
significant and was less than 60% of that of CK (P <
0.05). PE treatments promoted the accumulation of
Cr(III) in the plant roots; the Cr(III) accumulation in
the roots of L. perenne and P. purpurea was 1.2 and
1.1 times higher than that of CK.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
376
3.3 Cr Uptake and Transport in Plants
Under Cr (III) stress, the effects of the three
amendments on the uptake and transport in L.
perenne and P. purpurea are shown in Table 3. The
transport of Cr (III) to the plant shoots was reduced.
PE had the best inhibitory effect on Cr (III) with P.
purpurea, and the TF decreased by 47.1%. The
application of the amendments did not significantly
enhance the BCF of the shoots of the two plants. In
contrast, PE had a significantly positive effect on
Cr(III) enrichment in the roots of L. perenne and P.
purpurea, and the BCF of Cr (III) reached 1.2 and
1.7 times higher than that of CK, respectively.
Table 3. Effects of amendments on Cr (III) TF and BCF
for two plants under Cr (III) stress.
amendments
P. purpurea
TF
BCF
of shoots
BCF
of roots
C
K
0.32 0.06 0.20
CM 0.37 0.04 0.11
PE 0.17 0.06 0.34
VE 0.31 0.05 0.18
amendments
L. perenne
TF
BCF
of shoots
BCF
of roots
CK 0.07 0.03 0.37
CM 0.07 0.02 0.21
PE 0.06 0.03 0.43
VE 0.07 0.02 0.31
3.4 Pearson Correlation Analysis of Cr
in Soil and Plants
As described in the above data, the amendments
significantly reduced the B1 and B3 proportions of
Cr (III) in the soil but had little effect on the B2
proportion. To explore the correlation between the
change in the Cr (III) proportion in the soil and the
Cr (III) accumulation in the plants after application
of the three amendments, Pearsons correlation
analysis of the Cr proportion and Cr (III)
accumulation was performed, and the results are
shown in Table 4. As seen from the table, the
single-factor results showed Cr (III) accumulation in
the plants in the order of B1 > B3 > B2. Usually,
B1+B2+B3 represents the bioavailable heavy metals
in soil(Wang 1997), but in this study, B1+B3 had a
similar or even greater effect than B1+B2+B3. In
addition, the role of B2 was minimal.
Table 4. Pearson correlation analysis for soil Cr forms and
plant Cr contents.
Cr fraction
L. perenne
Cr content
in shoots
Cr content
in roots
Cr content
in plant
B1 0.722
*
0.704 0.715
*
B2 0.218 0.377 0.320
B3 0.518 0.512 0.517
B1+B2 0.693 0.705 0.705
B1+B3 0.933
**
0.914
**
0.926
**
B2+B3 0.594 0.629 0.620
B1+B2+B3 0.924
**
0.931
**
0.934
**
Cr fraction
P. purpurea
Cr content
in shoots
Cr content
in roots
Cr content
in plant
B1 0.750
*
0.440 0.569
B2 0.205 0.240 0.235
B3 0.492 0.755
*
0.682
B1+B2 0.717
*
0.442 0.558
B1+B3 0.940
**
0.848
**
0.909
**
B2+B3 0.563 0.804
*
0.768
*
B1+B2+B3 0.929
**
0.847
**
0.905
**
The results showed that the amount of available
heavy metals in the soil directly reflected the
absorption of heavy metals by the plants. The
decrease in Cr (III) accumulation in the plants was
the most obvious in the CM group, followed by the
VE group; meanwhile, the PE group promoted the
accumulation of Cr in the plant roots and had the
same level as that in the shoots of the plants in the
CK group. Therefore, the amendments can reduce
the Cr content in the plants by changing the soil Cr
proportion, and the rank order was CM > VE > PE.
In the Cr-contaminated soil, we found that the
content of organic matter in the soil is not the most
important factor affecting the heavy metal
bioavailability, which is slightly different from the
study of(Xiao 2017). This difference may be
because CM and VE can increase the soil pH, which
enhances the chelating ability of the soil to heavy
metal(Reijonen 2016). The bioavailability of heavy
metals can be reduced by stabilization processes,
including surface complexation, cation exchange,
precipitation, and physical adsorption (Li 2017).
4 CONCLUSIONS
In this study, we found that the three amendments
has the improvement for the Cr (III)-contaminated
soil. In this complicated experimental system, The
positive correlation between the chemically
extractable Cr and the Cr taken up by the plants
Effects of Three Soil Amendments on Cr (III) Bioavailability in Cr (III)-contaminated Soil
377
indicates that chemical extractability is a reliable
indicator to predict the bioavailability of Cr in
amended soil. Among the three amendments, CM
has the strongest effect on reducing the
bioavailability of Cr (III).
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