Cd Peru

Science of the Total Environment 605–606 (2017) 792–800
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Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv
Heavy metal accumulation in leaves and beans of cacao (Theobroma
cacao L.) in major cacao growing regions in Peru
Enrique Arévalo-Gardini a,⁎, Cesar O. Arévalo-Hernández a, Virupax C. Baligar b, Zhenli L. He c
a
b
c
Instituto de Cultivos Tropicales (ICT), Tarapoto, Peru
U.S. Department of Agriculture/Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, MD 20705, USA
Department of Soil and Water Sciences, Indian River Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Fort Pierce, FL 34945, USA
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• From 2019, the European Community
will begin to limit levels of cadmium
for chocolate affecting the Cocoa economy of Peru
• N 60% of the cacao beans studied had Cd
content bellow the critical level
• Concentration of Cd, Cr, Cu, Mn, Ni and
Zn in leaves were correlated with the
accumulation in cocoa beans
• The accumulation of heavy metal in
leaves and beans of cacao, are different
by genotypes composition in the plantations
• bCd and Pb accumulation in leaves and
cacao beans were in plantations with
more clones and with natives genotypes
a r t i c l e
i n f o
Article history:
Received 4 April 2017
Received in revised form 14 June 2017
Accepted 15 June 2017
Available online xxxx
Editor: D. Barcelo
Keywords:
Cadmium
Lead
Zinc
Cacao beans
Food quality
Trace elements
a b s t r a c t
Peru is one of the leading exporters of organic cacao beans in the world. However, the accumulation of heavy
metals in cacao beans represents a problem for cocoa bean export and chocolate quality. The aim of this study
was to investigate the distribution and accumulation of heavy metals in cacao leaves and cocoa beans in three
major cacao growing regions of Peru. The study was conducted in cacao plantations of 10 to 15 years old in
three regions of Peru: North (Regions of Tumbes, Piura, Cajamarca, and Amazonas); Center (Regions of Huánuco
and San Martin) and South (Junin and Cuzco). Samples of leaf and cacao beans were collected from 70 cacao plantations, and the nature of cacao clone or genotype sampled was recorded. The concentrations of heavy metals
such as Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in leaves and beans were determined using atomic absorption spectrophotometer. Overall, concentrations of heavy metals were below the critical limits; however, the presence of high
levels of Cd in cacao grown in Amazonas, Piura, and Tumbes regions is of primary concern. Plantations of cacao
with different cacao clones show differences in Cd accumulation both in leaves and cocoa beans. Therefore, it
is promising to screen low Cd accumulator cacao genotypes for safe production of cacao on lightly to moderately
Cd contaminated soils. Also, synergism between Zn and Cd present both in plant and soil suggests that Zn has a
direct effect on Cd accumulation in cacao.
© 2016 Elsevier B.V. All rights reserved.
⁎ Corresponding author.
E-mail addresses: e.arevalo@ict-peru.org (E. Arévalo-Gardini), v.c.baligar@ars.usda.gov (V.C. Baligar).
http://dx.doi.org/10.1016/j.scitotenv.2017.06.122
0048-9697/© 2016 Elsevier B.V. All rights reserved.
E. Arévalo-Gardini et al. / Science of the Total Environment 605–606 (2017) 792–800
1. Introduction
In 2014, the European Union announced, by Regulation (EU) No
488/2014, plans to implement regulations governing chocolate and
cocoa products containing excessive levels of Cd, which will be in effect
on January 1, 2019 (EU, 2014). Currently, the Codex Alimentarius Commission of the Joint FAO/WHO Food Standards Programme is in the process of soliciting comments on the proposed draft maximum levels for
Cd in chocolate and cocoa derived products (EU, 2014). Noncompliance with the Regulations will bear significant economic and social consequences for cocoa producing countries from 2019. Cadmium
has received attention in the last decade due to its importance in food
quality and security, and human health, since consumption of food
with high Cd content could produce renal tubular dysfunction, formation of kidney stones, disturbance of calcium metabolism and skeletal,
endocrine, reproductive and respiratory defects (Järup and Åkesson,
2009; Tripathi et al., 2007; Salem et al., 2000; WHO, 2010).
In general, Latin America possess higher levels of heavy metals in
cacao beans, especially Cd and Pb (Bertoldi et al., 2016), as compared
with other producers in the world (West Africa) (Takrama et al., 2015).
The presence of heavy metals in cocoa beans poses a threat to cacao producers, since high contents of heavy metals could affect the exportation of
cocoa beans. This crop is in high demand for manufacturing cacao liquor,
cacao butter, and chocolate, etc. Chocolate has been attributed to attainment of optimal human health and development due to its high content
of flavonoids that are crucial in reducing the risk or delaying the development of cardiovascular disease, cancer and other age-related diseases
(Cooper et al., 2008; Afoakwa, 2008). Heavy metals are defined as elements with a density exceeding 5 g cm−3 (Ali et al., 2013). Copper, Fe,
Mn and Zn at low concentrations are essential for biochemical and physiological processes in plants, while As, Cd, and Pb have no known role in
plants (Benavides et al., 2005). Accumulation of heavy metals in plants
is affected by several factors such as pH, organic matter content and texture of soil, plant genotype and heavy metal content in growth medium
(Businelli et al., 2009; Alloway, 2013). Heavy metal accumulation in
plants varies between elements and plant species (Vaculík et al., 2012;
Jan and Parray, 2016). Cadmium is one of the most mobile elements
with a bioconcentration factor in plants greater than some essential nutrients, and mostly accumulates in shoots while Pb mainly accumulates in
roots (Kabata-Pendias, 2011; Li et al., 2014). Elemental interactions influence heavy metal accumulation in shoots and fruits, and plants with adequate levels of essential nutrients usually contain less heavy metal such as
Cd (Sarwar et al., 2010). Nevertheless, interactions among these elements
could lead to a higher accumulation of heavy metals in plants (Nan et al.,
2002); Zinc and Cd interactions are controversial, both synergism and antagonism being reported, while P and As interactions were shown to be
antagonistic (Kabata-Pendias, 2011; Alloway, 2013).
Since high concentration of heavy metals in cacao beans threatens
food security and economic development, there is a great need for information regarding concentrations of heavy metals in this crop. In Peru,
cacao plantations have increased considerably; and the cultivated area
currently has reached N107,000 ha with a total cocoa bean production
of 82,000 mt/year (MINAGRI, 2016), the export of cocoa beans is vital
to its international trade. With the impending implementation of
these Regulations (EC Regulation No 1881/2006) on Maximum Permissible levels for Cd, it is crucial that all cocoa producing countries undertake this type of research as shown in this study, which was aimed to
investigate the accumulation of heavy metals in leaves and cocoa
beans in the major cacao production regions of Peru.
2. Material and methods
2.1. Location and cacao plants
In Peru, cacao is mainly propagated by seeds (for rootstock) and afterwards, grafted with the desired clone, most of cacao plantations in
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Peru are dominated by CCN-51.The study was conducted in 70 cacao
plantations between 10 and 15 years of age, located in North (Amazonas, Cajamarca, Piura and Tumbes Regions); Center (Huánuco, San Martin and Junin Regions) and South (Cuzco Region), the main cacao
growing regions of Peru (Fig. 1). In each sampled plantation, the genetic
material of planted cacao was characterized. The Table 1, shows the genotypes and genotypes associations identified in each region.
2.2. Sampling of soil
Soil samples were collected at the depth (0–20 cm), where the roots
of cacao have more intense activity of nutrients absorption (Wood and
Lass, 1985), in the cacao plantations selected in each region between
February and April of 2014. The collected soils were air dried and sieved
prior to analysis. The results of soil analysis and content of heavy metals
in each selected region were reported earlier by Arévalo-Gardini et al.
(2016).
2.3. Sampling of leaves and fruits
Samples of leaves and fruits were collected between February and
April of 2014, the samples were collected from the central part of the
trees located near soil sampling sites described by Arévalo-Gardini
et al. (2016). For each plantation, three plots were randomly selected
for sampling. Within each plot, 10 cacao trees were selected, and one
middle-aged leave was sampled in each cardinal point of the tree.
Fruits were sampled according to its availability in each tree (at
least one). After collection, leaves and fruits samples were properly
labeled and transported to Instituto de Cultivos Tropicales (ICT) Laboratory in Tarapoto-Peru, where they were thoroughly rinsed with
distilled water. Beans were extracted from each fruit and mixed for
a composite sample. Separately, leaves and beans were oven dried
at 60 °C, mixed and milled (20 mesh) and stored in plastic bag
prior to analysis.
2.4. Determination of heavy metals in leaves and beans
Oven dried leaf or bean samples were weighed (500 mg each) and
digested with 10 ml of a mixture of HNO3 (65%) and HClO4 (98%)
from Merck® in 4:1 ratio respectively (Nogueira et al., 2005). The digestion was conducted on a block at 120 °C for 3 h and then at 200 °C for 2 h
(Güldaş, 2008). The digested solution was filtered through a Whatman
N°42 filter paper, and diluted prior to analysis. Concentrations of Cd, Cu,
Cr, Fe, Mn, Ni, Pb and Zn in the filtrate were determined using atomic
absorption spectrophotometer (SAA; Varian model “Spectra 55B”
Made in Australia). In order to achieve analytical quality, three repetitions were carried for each sample and the means were used for statistical analysis.
2.5. Statistical analysis
All the statistical analyses were performed in R, ver 3.2 (R Core Team,
2014). Concentrations of Cd, Cu, Cr, Fe, Mn, Ni, Pb, and Zn in leaves and
beans were submitted to analysis of variance (ANOVA) for each studied
region; the same analysis was conducted for genotype from each region
sampled to assess genotypic differences in heavy metal accumulation.
Region wide means were compared by the DGC (Di Rienzo et al.,
2014) test (P ≤ 0.05). A Pearson's correlation was carried out between
concentrations of Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn in leaves and beans
in cacao. Finally, soil attributes were correlated with concentrations of
the metals in beans, and a cluster analysis was performed using
ClustofVar R package (Chavent et al., 2010).
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E. Arévalo-Gardini et al. / Science of the Total Environment 605–606 (2017) 792–800
Fig. 1. Location of cacao plantations sampled for heavy metal analysis in Peru. (Google earth*). The plantation stretched from the northeast point (3.10°S; 77.83°W) to the southeast point
(12.41°S; 72.52°W).
3. Results and discussion
3.1. Regional variation in metal concentrations of cacao leaves and beans
Mean concentrations of Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn in leaves of
cacao, per region studied is presented in Fig. 2. Significant differences
(P ≤ 0.05) for Cu, Cr, Fe, Mn, and Zn were observed, except for Cd, Ni
and Pb (P N 0.05)(Table S1).
Concentrations of Cd in leaves ranged from 0.23 ± 0.62 μg g−1 in
Cuzco to 2.50 ± 0.62 μg g− 1 in Tumbes; Cr of 1.0 ± 0.73 μg g−1 in
Huanuco to 2.86 ± 0.31 μg g−1 in Amazonas; Cu showed a range of
7.17 ± 0.62 μg g−1 in Piura to 10.25 ± 1.08 μg g− 1 in Tumbes; Fe of
50.5 ± 24.75 μg g−1in Junin to 275.77 ± 13.73 μg g−1 in Piura; Mn of
Table 1
Cacao genotypes sampled for determinations of heavy metals in leaf and cacao beans in
each region of Peru.
Region
Department
Cacao genotypes
North
Tumbes
Piura
Cajamarca
Amazonas
San Martín
Huánuco
Junín
Cuzco
CCN51, Spontaneous hybrids
Blanco Piurano, Spontaneous hybrids
CCN51, Native from Marañon
CCN51/ICS95
CCN51, CCN51/ICS95, CCN51/ICS95/ICS39
CCN51
CCN51, CCN51/ICS95/ICS39, Native from Satipo
CCN51/ICS95/ICS39, Chuncho
Center
South
88.20 ± 58.05 μg g−1 in Cajamarca to 347.38 ± 36.00 μg g− 1 in San
Martin; Ni from 2.25 ± 3.28 μg g− 1 Cajamarca and 12.20 ± 2.94 in
Cuzco; Pb of 1.20 ± 0.32 μg g−1 in Cajamarca to 2.50 ± 0.36 μg g−1 in
Junin; Zn of 43.80 ± 12.17 μg g−1 in Cuzco to 103.95 ± 4.36 μg g−1 in
Amazonas. In leaves, the highest mean values of these elements were
observed in Tumbes (Cd, Cu), Amazonas (Cr, Zn), San Martin (Mn),
Piura (Fe), Junin (Pb), and Cuzco (Ni).
In Peru, Huamani-Yupanqui et al. (2012) reported elemental concentration values in cacao leaves, which were within the concentration
ranges reported in this study, except that the means of Cd, Mn, Pb and
Zn were lower. This could be explained by the higher concentrations
of these elements in the north region; for the same locations mean
values were similar. In cacao leaves, Aikpokpodion (2010), in Nigeria,
reported higher elemental concentration for Fe and lower for Mn and
Zn, even though soil pH values of the soils assessed was N6.5, indicating
that probably these types of soils had higher background levels of these
heavy metals. Sodré et al. (2001) in Bahía, Brazil reported higher values
of Cu and Zn concentrations in cacao leaves while lower for Fe and Mn.
In Trinidad and Tobago, Ramtahal et al. (2016) reported higher concentration values for Cd in leaves. In Bolivia, Gramlich et al. (2017) observed, in general, lower values for Cd, higher for Fe, and within the
range of this study for Zn.
In cacao beans, the mean concentration of Cd, Cu, Cr, Fe, Mn, Ni, Pb
and Zn in cacao beans per region studied are presented in Fig. 2. Significant differences (P ≤ 0.05) in concentrations of Cu, Cr, Mn, Pb and Zn
were observed, while insignificant differences (P N 0.05) were noted
for Cd, Fe and Ni (Table S1).
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Fig. 2. Mean concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in cacao leaves and beans per region in Peru, i.e. Tumbes (TUM), Piura (PIU), Cajamarca (CAJ), Amazonas (AMA), San Martín
(SMA), Huánuco (HUA), Junin (JUN), Cuzco (CUZ).
Mean concentrations of Cd in beans ranged from 0.17 ± 0.41 μg g−1 in
Cuzco to 1.78 ± 0.35 μg g−1 in Tumbes. Concentration of Cu of 18.75 ±
3.91 μg g−1 in Cuzco to 30.41 ± 1.41 μg g−1 in Amazonas. Chromium
concentration ranged from 1.00 ± 0.87 μg g−1 in San Martin to 4.83 ±
0.71 μg g− 1 in Amazonas. Concentrations of Fe were from 34.00 ±
5.95 μg g− 1 in Cuzco to 53.55 ± 3.59 μg g− 1 in Piura. Concentration
of Mn ranged from 13.33 ± 3.76 μg g−1 in Junin to 28.5 ± 3.25 μg g−1
in Huanuco. Nickel concentration values ranged from 3.5 ± 2.00 μg g−1
in Tumbes to 9.25 ± 2.00 μg g−1 in Huanuco. Concentrations of Pb
were between 1.00 ± 0.67 μg g−1 in Cajamarca and Cuzco to 3.78 ±
0.39 μg g−1 in Piura. Zinc varied from 37.25 ± 2.70 μg g−1 in Huanuco
to 59.17 ± 1.56 μg g−1 in Piura. Nearly 57% of all collected samples
exceeded this critical limit (0.8 μg g−1 for Cd), indicating that it is necessary to execute a national plan in Peru to prevent Cd contamination in
cacao production systems.
Lee and Low (1985), in Malaysia, reported concentration within
the range observed in this study for Cu and Cd while it was higher
for Pb. In Nigeria, Aikpokpodion (2010) reported higher concentrations of Fe, Mn and Zn in cacao beans. Afoakwa et al. (2013), in
Ghana, reported lower cacao bean concentrations of Cu, Fe and Zn
in comparison with our study. In Brazil, Loureiro (2014) reported
lower concentration values in cacao beans for Cu, Zn and Cd, higher
for Fe and similar for Mn as compared with the results from this
study. Chavez et al. (2015), studied Cd in soils and plants of
Ecuador, and Ramtahal et al. (2016), in Trinidad and Tobago, reported higher concentration values of Cd in comparison to our research,
however our values were within the ranges reported in those studies. In Bolivia, Gramlich et al. (2017), observed, in general, lower
values for Cd and Fe and similar values for Zn.
3.2. Concentrations of metals in leaves and beans of different cacao
accessions
Mean concentrations (±SE) of Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn from
cacao leaves and beans of genotypes in various regions of Peru, are presented in Fig. 3. In this study significant differences (P ≤ 0.05) in leaf and
bean concentrations were found for Cd, Cr, Cu, Fe and Zn. Concentrations of Cd, Cr, Cu, Fe, Mn, Pb and Zn in cacao beans were statistically significant among the different genotypes (P ≤ 0.05) (Table S2).
Mean concentrations of Cd in leaves was in the range of 0.10 ± 0.9
μg g−1 (Native from Marañon) to 2.6 ± 0.7 μg g−1 (Spontaneous Hybrids). Chromium had a low concentration of 0.7 ± 0.8 μg g−1
(Chuncho) with maximum value of 4.4 ± 0.3 μg g−1 (CCN51/ICS95/
ICS39). Mean Cu concentration ranged from low of 7.00 ± 0.6 μg g−1
(Blanco Piurano) to high of 11.3 ± 0.5 μg g− 1 (CCN51/ICS95/ICS39).
Mean Fe concentrations ranged from 76.3 ± 29.9 μg g−1 (Chuncho) to
243 ± 16.4 μg g−1 (Blanco Piurano). Manganese concentrations were
in the range of 72.3 ± 75.5 μg g−1 (Spontaneous Hybrids) to 230.0 ±
38.0 μg g−1 (CCN51). Mean concentrations of Ni ranged from 3.0 ±
4.7 μg g− 1 (Native from Marañon) to 15.0 ± 3.8 μg g− 1 (Chuncho).
Lead had a low concentration of 0.94 ± 0.3 μg g− 1 (CCN51/ICS95/
ICS39) to 3.0 ± 1.0 μg g−1 (Native from Satipo). Mean concentrations
of Zn ranged from low of 44.7 ± 18.4 μg g− 1 (Chuncho) to 105.0 ±
31.8 μg g−1 (Native from Satipo).
Similar trends occurred to metal concentrations in beans of different
cacao genotypes. Mean concentration of Cd in cacao beans ranged from
0.15 ± 0.8 μg g−1 (Native from Satipo) to 1.8 ± 0.4 μg g−1 (Spontaneous Hybrids). Chromium mean concentrations in Chuncho and Native
from Satipo were below the limit of detection, also low values were
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E. Arévalo-Gardini et al. / Science of the Total Environment 605–606 (2017) 792–800
Fig. 3. Mean concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb y Zn in cacao leaves and beans per genotype found in the regions studied in Peru.
found from 0.2 ± 0.4 μg g − 1 (CCN51/ICS95) to 5.1 ± 0.5 μg g− 1
(CCN51/ICS95/ICS39). Mean concentrations for Cu ranged from
19.7 ± 4.3 μg g−1 (Chuncho) to 38.1 ± 2.0 μg g−1 (CCN51/ICS95/ICS39).
Concentrations of Fe were from 34.0 ± 6.5 μg g−1 (Chuncho) and
63.0 ± 8.0 μg g−1 (Native from Marañon). Concentrations of Mn were
from 14.5 ± 4.3 μg g−1 (Spontaneous hybrids) to 32.0 ± 8.5 μg g−1 (Native from Satipo). Concentrations of Ni were from 3.3 ± 2.1 μg g− 1
(Spontaneous hybrids) to 10.0 ± 4.2 μg g−1 (Native from Satipo). Concentrations of Pb were from 0.67 ± 0.7 μg g−1 (Chuncho) to 3.0 ± 1.3
μg g−1 (Native from Satipo). Concentrations of Zn were from 34.7 ±
3.4 μg g−1 (Chuncho) to 59.0 ± 1.8 μg g−1 (Blanco Piurano). Highest
mean values of heavy metal concentrations in cacao beans were recorded in genotypes Blanco Piurano (Zn); CCN51/ICS95/ICS39 (Cr, Cu);
Spontaneous hybrids (Cd); Native from Marañon (Fe) and Native from
Satipo (Mn, Ni, Pb).
Plants have differential responses to soil contamination with heavy
metals (Kabata-Pendias, 2011). Some plant species or genotypes can
tolerate high concentration of heavy metals in soil by excluding these
elements from entering into root or by volatilization through stomata
(Peer et al., 2005; He et al., 2015). For perennial plants, Zacchini et al.
(2009) reported differential accumulation patterns of Cd in Poplar
clones; while Willow clones showed higher tolerance to Cd toxicity.
For cacao, literature that describes the accumulation of heavy metals
by different genotypes is limited. However, Castro et al. (2015) and
Reis et al. (2015), in Bahia-Brazil, worked with cacao seedlings from a
self-fertilization of Catongo and a cross of CCN51 × SCA6, and assessed
the effects of Cd and Pb, respectively. They reported that the progeny
of the cross of CCN51 × SCA6 was more tolerant to high Cd and Pb stress,
as compared with the progeny of Catongo, indicating that there is differential response of the plant species/genotypes to heavy metal stress.
Also, associated to genotype differences, production systems and soil
management could have an important effect on heavy metal absorption
in cacao; Gramlich et al. (2017), studied cacao cropping systems associated to organic and conventional management in agroforestry or monoculture; the authors report that even though no significant differences
were found for Cd and Zn in leaves and beans, TSH 565 absorbed
more Cd in relation to ICS 1 in monoculture. Nevertheless, Fe in leaves
was more accumulated in the conventional system in relation to the organic system and TSH 565 absorbed more Fe in relation to ICS 1, no significant differences were reported for beans. These results indicate that
the genetic factor could be an important strategy in agriculture systems
with excess heavy metals in plants.
3.3. Critical limits of heavy metals in cacao leaves and cacao beans
Since there is no consensus in critical limits for Cd concentration
levels in cacao leaves and beans, we used optimal values and critical
limits for cacao leaves established by Sodré et al. (2001); Broadley
et al. (2012) and Kabata-Pendias (2011) to evaluate the data from the
present study. For bean Cd concentration, the critical value of 0.8
μg g−1, established by the European community and becoming effective
on the first of January of 2019, as maximum permissible for chocolate
containing ≥50% of cacao beans solids will be used for assessment. For
the other elements, the ranges established by Kabata-Pendias (2011)
will be employed as a reference. For optimal limits in cacao beans, the
values established by Araujo et al. (2014) were adopted for comparison.
In cacao leaves, all the elements studied, in general, presented concentrations below the maximum limits regardless of regions assessed.
However, for Cd, the values per region were above the normal concentration (0.2 μg g−1) for most plants (Kabata-Pendias, 2011). The mean
E. Arévalo-Gardini et al. / Science of the Total Environment 605–606 (2017) 792–800
Ni concentration in Cuzco was higher that the tolerable crop value
(10 μg g− 1 ) established by Kabata-Pendias (2011). Pb concentrations in leaves at all regions were below the value of b 4.3 μg g− 1 suggested by Araujo et al. (2014).
For beans, concentrations of Cr, Cu, Fe, Mn, Ni, Pb, and Zn per region
were in general, higher than the optimal values established by Araujo
et al. (2014), but below the values reported as tolerable in agronomic
crops by Kabata-Pendias (2011) of 2 μg g− 1; 50 μg g−1; 300 μg g− 1;
50 μg g−1; 300 μg g−1for Cr, Cu, Mn, Ni and Zn, respectively. Bean Cd
concentrations in Amazonas, Piura and Tumbes exceed the maximum
permissible limit of 0.80 μg g−1. Cuzco reported bean Cd concentration
above the normal value of 0.20 μg g−1 (Araujo et al., 2014). Cuzco was
the only region that presented normal values for this element, indicating that Cd contamination of cacao beans may be a problem to other regions. Further studies are needed to confirm the potential risk of Cd
contamination in these regions including Amazonas, Piura and Tumbes.
Overall, concentrations of heavy metals in leaves of various genotypes (Fig. 3) were below the critical limits established for agronomic
crops (Kabata-Pendias, 2011). However, in cacao plantations with genotypes CCN51 and ICS95, Cd exceeded the tolerable value (3.0 μg g−1)
proposed for agronomic crops Kabata-Pendias (2011), indicating a
higher accumulation of Cd in these plantations probably due to grafting
combination, where the plants from spontaneous hybrids were used as
rootstock, since CCN51 clone alone had a leaf Cd concentration 50%
lower than that of the combination of clones (CCN51/ICS95). Furthermore, the combination in the plantation of clones CCN51/ICS95/ICS39,
where the plants from spontaneous hybrids were used as a rootstock accumulated less Cd in relation to the combination of CCN51/ICS95 and
CCN51 itself. This implies that the combination of more clones may reduce Cd concentration in leaves and the rootstock could be an efficient
alternative for preventing Cd accumulation in shoots. Further studies
are needed to assess the genotypic differences for Cd uptake efficiency
in soils from various cacao growing regions.
The assessed genotypes had Cd concentrations in beans (Fig. 3)
mostly between the normal levels (Araujo et al., 2014) and critical limits
proposed by Kabata-Pendias (2011). However, the clones and combinations of Blanco Piurano, CCN51, CCN51/ICS95 and spontaneous hybrids
had bean Cd concentrations exceeding the critical limit of 0.80 μg g−1
established by Commission of Regulation (EU) (EU, 2014), implying
that the use of these combinations should be used with caution in the
strategies of diminishing Cd accumulation in cacao beans, especially in
regions with soil Cd enrichment. On the other hand, the combination
of clones CCN51/ICS95/ICS39 could lead to low Cd concentration in
beans and merit attention for future strategy in diminishing Cd accumulation. Chuncho and Native Marañon should be considered high in soil
Cd. However more controlled research is needed to confirm their traits
related to Cd uptake and accumulation in beans. Effects of rootstocks
and scion on the accumulation and translocation of heavy metals have
been reported by Arao et al. (2008) working with Solanum melongena
for Cd and Rouphael et al. (2008) in Cucumis sativus for Cu. This approach needs to be considered in the assessment of various cacao clones
for their uptake and translocation efficiency for Cd either as single clone
or as grafted material, since genetic differences and their interaction
could be an efficient strategy in Cd absorption in cacao cropping
systems.
3.4. Relationship between concentrations of heavy elements in cacao leaves
and beans
Complex interactions between heavy metals occur in plants that
could affect their absorption, levels of toxicity and regulatory mechanisms. The interactions can be additive, synergistic or antagonistic depending on environmental conditions and plant species (Siedlecka,
1995; Kabata-Pendias, 2011). These relationships could give an overall
idea of the possible practices that can lead to efficient management of
heavy metals in cacao production regions.
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The correlation matrix of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn concentrations in cacao beans and leaves are presented in the Table 2. Significant
(P ≤ 0.05) correlations were observed for concentrations of Cd, Cr, Cu,
Mn, Ni, and Zn while non-significant correlations occurred for Fe and Pb.
Cadmium in cacao beans had a significant (P ≤ 0.05) positive correlation (0.21) with Zn in leaves which is contradictory to some previous reports that Zn is antagonistic with Cd uptake (Kabata-Pendias, 2011;
Alloway, 2013). Cadmium toxicity may, in part, result from its interactions with mineral nutrients such as Zn, Fe, Ca, K, Mn, Cu and Mg
(Wang et al., 2007; Nedjimi and Daoud, 2009). Metals that can increase
or decrease uptake of other elements are readily absorbed and
translocated to plant shoots, and these processes are competitive between elements, especially between Cd and Zn (Mengal et al., 2001).
However, Zn and Cd could be simultaneously absorbed due to their
ionic similarities; therefore, Cd is mainly absorbed by the same carriers
as Ca+2, Fe+2, Mg+2, Cu+2 and Zn+2 (Papoyan et al., 2007); principally
in sites where Zn has a crucial catalytic or structural function (Tang
et al., 2014). Other reports indicated that Zn favored Cd absorption
(Synergistic effect) in tobacco (Nicotiana tabacum) (Tkalec et al.,
2014); maize (Zea mays) (Nan et al., 2002); barley (Hordeum vulgare)
(Nan et al., 2002) and spring wheat (Triticum spp.) (Piotrowoska et al.,
1994).
The concentrations of Ni in beans had significant (P ≤ 0.05) correlations with Mn (0.31) and Ni (0.68) in leaves. Chen et al., 2009 reported
inhibitory effects of high concentrations of Ni on Mn uptake in Oryza
sativa. Cataldo et al. (1978) reported inhibitory effects of Ni on Mn in
soybean (Glycine max) seedlings; Heale and Ormrod (1982) reported
the same results in Acer rubrum, Cornus stolonifer, Lonicera tatarica and
Pinus resinosa. This behavior can be explained by the similar characteristics of Ni in relation to Mn, resulting in competition for uptake. However since concentrations of Ni in cacao leaves were mostly below the
tolerable levels for agronomical crops (50 μg g− 1) (Kabata-Pendias,
2011), and thus, competition in uptake between these metals may not
occur in cacao.
Bean Zn concentration had significant (P ≤ 0.05) correlations with
concentration of Zn (0.26), Mn (−0.33), Fe (0.50), Ni (−0.30) and Cd
(0.21) in leaves. Zinc has a significant role in the translocation of Fe
from roots to aerial parts; therefore, plants with higher contents of Zn
have a tendency to accumulate higher concentrations of Fe (Rengel
and Graham, 1995; Rengel et al., 1998). Imtiaz et al. (2003) reported
negative effects of Mn concentrations in soil solution on Zn nutrition
in wheat plants; without application of Zn, the Mn concentration in
plants was high. Due to similar characteristics of Zn and Ni, competition
of these sites is expected (Cataldo et al., 1978; Heale and Ormrod, 1982).
The positive correlation between Zn concentration in beans and Cd concentration in leaves confirms the synergism of these elements in cacao
plants sampled, indicating that interactions with other metals should
be considered in an efficient management plan for Cd absorption in
cacao plants.
Table 2
Correlation matrix of Cd, Cu, Cr, Fe, Mn, Ni, Pb y Zn in leaves and beans of cacao plants sampled in different regions of Peru.
Elements in Elements in cacao leaves (n = 72)
cacao beans
Cu
Zn
Mn
Fe
Pb
(n = 72)
Cu
Zn
Mn
Fe
Pb
Ni
Cd
Cr
Ni
Cd
Cr
0.51⁎
0.20 −0.12
0.03 −0.07 −0.19
0.12
0.05
0.02
0.26 −0.33
0.50 −0.14 −0.30
0.21
0.05
−0.01 −0.03
0.58 −0.11
0.05
0.19
0.04
0.00
−0.04
0.12 −0.09
0.12 −0.19 −0.06
0.06
0.14
−0.06 −0.13
0.05
0.10
0.12 −0.02 −0.15 −0.01
0.00
0.19
0.31
0.00 −0.05
0.68
0.16 −0.16
0.07
0.21 −0.05
0.21 −0.08 −0.09
0.74
0.07
0.03
0.04 −0.12 −0.06
0.21
0.07 −0.15 −0.10
⁎ Values in bold are significant at P ≤ 0.05.
798
E. Arévalo-Gardini et al. / Science of the Total Environment 605–606 (2017) 792–800
Fig. 4. Dendrogram with soil attributes and concentration of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in cacao beans for all the studied areas. The mean concentrations for these elements are
represented by BCd, BCr, BCu, BFe, BMn, BNi, BPb and BZn, respectively.
3.5. Soil attributes and heavy metals in cacao beans
4. Conclusions
The relationships of soil attributes and concentration of heavy
metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in cacao beans are represented
in Fig. 4. These results confirmed the observed correlations between
beans and leaves of cacao, where synergy of these elements and their
joint absorption occurred. The ratio of Cd over Fe or Zn in beans was
synergistic, this may be due to the use of the same transporters for
their entry into the cells (Broadley et al., 2012). Nan et al. (2002) reported significant positive correlations between total Cd in soil and Cd in the
plant of wheat. Chavez et al. (2015) reported highly significant correlations between the concentrations of extractable Cd in the soil (Melich-3
and HCl) and the Cd content in cacao beans, indicating that the methodologies used in the study are appropriate for the prediction of available
content of Cd on the soil. Ramtahal et al. (2016) indicated that the
concentration of Cd is mainly distributed in leaves and in a lower concentration in grains and soil; these authors reported significant correlations
(P ≤ 0.05) between the concentration of Cd in soil, leaves and cacao beans.
These results confirm the hypothesis proposed by Nan et al. (2002) that,
in general, significant correlations between Cd and Zn are observed in the
field, while the opposite occurred under nursery conditions.
Concentration of Pb in beans was related to the presence of silt,
sand, Fe, Zn and Cu in the soil. This can be attributed to the interactions of Fe, Zn and Cu with Pb in competing for absorption by the
plant (Alloway, 2013). Nan et al. (2002) reported positive correlations between Pb concentration in beans and Zn concentration in
the soil. The concentration of Ni in beans was related to the availability of Cr, Ni, S and P in the soil.
On the other hand, the concentration of Cu in beans was mainly related to the concentrations of Pb and Mn in the soil. Manganese concentration in beans was related to pH, since it is the main soil factor that
determines Mn availability (Alloway, 2013). Finally, the concentration
of Cr in beans was related to available K, B, Mg and electrical conductivity of the soil (CE).
The European Union has announced that the addition to Regulation
1881 of 2006 begins to be mandatory from January 2019, as this may affect the Cocoa economy of Peru. From 2019, the European Community
will begin to demand maximum levels of Cd for cocoa and its derivatives. The European Union notified the Committee on Sanitary and
Phytosanitary Measures of the World Trade Organization (EC) No
1881/2006. Three major cacao-producing regions (North, Center and
South) of Peru were selected for assessing the uptake and accumulation
of heavy metals in cacao leaves and beans. The results indicated that
concentrations of Cu, Fe, Mn, and Zn in cacao leaves were adequate
and beans concentrations of Cr, Cu, Fe, Mn, Ni, Pb, and Zn were below
the critical limits. However high levels of Cd occurred in cacao beans
in Piura and Tumbes, of Peru. This may pose a threat to cacao production
in these regions. There were genotypic differences in Cd uptake and accumulation in cacao leaves and beans. Some clones or combinations accumulated less Cd in leaves and beans under the same soil Cd
conditions, indicating that this may represent an opportunity to
exploiting low Cd accumulators for future breeding and production of
cacao in the high Cd background regions. Cadmium and Zn interactions
were found in both plant and soil, indicating that Zn may have direct implications in Cd accumulation in cocoa beans.
Conflict of interest
The authors declare that they have no conflicted of interest.
Acknowledgments
We are grateful to “Programa Nacional de Innovación para la
Competitividad y Productividad (Innóvate Perú)”, for financial support,
Contract No 167-FINCyT-IB-2013. Special deference to Velia Maruxie
Yufra Picardo and Carmen Rosa Maza Córdova for opportune advisor
E. Arévalo-Gardini et al. / Science of the Total Environment 605–606 (2017) 792–800
to develop this work. To United State Department of Agriculture – Agricultural Research Service (USDA-ARS) for technical and financial support. To Indian River Research and Education Center (IRREC),
University of Florida, USA for technical support (Cooperative Agreement
ICT-IRREC/UF). To US Embassy in Lima-Perú for partial financial support
to this study. To “Instituto de Cultivos Tropicales – ICT” for facilities of
infrastructure and laboratories. To all Cacao Organizations of Peru for facilities of samples obtained. We thank Marshall Elson for review of the
manuscript.
Appendix A. Supplementary data
Supplementary data associated with this article can be found in the
online version, at doi: http://dx.doi.org/10.1016/j.scitotenv.2017.06.
122. These data include the Google map of the most important areas described in this article.
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