Download Accumulation of heavy metals in food plants and

Agriculture, Ecosystems and Environment 78 (2000) 85–91
Short communication
Accumulation of heavy metals in food plants and grasshoppers
from the Taigetos Mountains, Greece
B. Devkota a , G.H. Schmidt b,∗
a
b
Department of Ecology, Faculty-5, University of Osnabrueck, Barbarastr. 11, D-49076 Osnabrueck, Germany
Department of Zoology–Entomology, University of Hanover, Herrenhaeuserstr. 2, D-30419 Hanover, Germany
Received 11 November 1998; received in revised form 18 June 1999; accepted 9 September 1999
Abstract
Geogenic, as well as anthropogenic heavy metals from distant sources, gradually increase the level of toxic metals in
natural environments and these will be increasingly taken up by the plants and transferred further up the food chain. The
level of different heavy metals (Hg, Cd, Pb) was studied in the producers (food plants) and consumers [four species of acridid
grasshoppers: Calliptamus italicus (L.), Oedipoda caerulesens (L.), O. germanica (Latr.) and Chorthippus(Glyptobothrus)
crassiceps(Ramme, 1926)] of a grassland located 1200 m above the sea level in the Taigetos Mountains, Peloponnesus,
Greece. The concentrations of heavy metals in the food plants and grasshoppers were in the order Pb > Cd > Hg and the
mean concentration of Pb was about 55 and 20 times the concentrations of Hg and Cd, respectively. The solely herbivorous
C.(G.) crassiceps had a significantly higher Hg-concentration than in the food plants, but it did not exceed that of Cd and Pb.
Cd-concentration in the grasshoppers was significantly higher than in food plants, and female grasshoppers had higher Cd
accumulation than males. Lead accumulation in grasshoppers was always lower than in their food plants. The accumulation
factors of these elements in the grasshoppers were found in the order Cd > Hg > Pb, thus showing greater affinity to Cd
accumulation. Significantly higher concentration of Hg in both sexes of C.(G.) crassiceps than in other three grasshoppers
proved this species to be a comparatively better bioindicator of Hg pollution. Elevated concentrations of Cd in both, females
and males of all four grasshopper species suggested that any grasshopper, irrespective of the sex, could equally play the role
of bioindicator. Studies on the bioaccumulation and biotransfer of different heavy metals showed that the organisms of such
distantly located ecosystems were also exposed to measurable amounts of toxic heavy metals. ©2000 Elsevier Science B.V.
All rights reserved.
Keywords: Heavy metals; Hg; Cd; Pb; Accumulation; Bioaccumulation factors; Grasshoppers
1. Introduction
The occurrence of toxic heavy metals in the soil is of
geogenic or anthropogenic origins. The natural content
∗ Corresponding author. Tel.: +49-511-7625548;
fax: +49-511-7625381.
of heavy metals in the soil is dependent on geochemical and geophysical processes. Heavy metals from the
point and other sources of emission can be transported
to distant environments (Steinnes, 1980). Transport of
heavy metals from the atmosphere to the soil and vegetation takes place by dust fall, bulk precipitation and
gas or aerosol adsorption processes (Andersen et al.,
0167-8809/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 8 8 0 9 ( 9 9 ) 0 0 1 1 0 - 3
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B. Devkota, G.H. Schmidt / Agriculture, Ecosystems and Environment 78 (2000) 85–91
1978). The bulk of the elements is naturally bound
as insoluble compounds in rock and sediments, and
a multitude of ions can be released from sediments
by redox changes (Lieth and Markert, 1990). The input of anthropogenic toxic metals in distantly located
mountain ecosystems is generally lower than in valleys and settlement areas, but due to different natural
(geophysical and geochemical) processes, the amount
of pedogenic and lithogenic metals is also gradually
increasing and is capable of interacting with biota.
Some elements, such as mercury (Hg), zinc (Zn), cadmium (Cd), lead (Pb), and arsenic (As), may be increasingly taken up by the crop and transferred further
to the food chain (Beijer and Jernelöv, 1986).
About 20–30% of the total arthropod biomass during summer in a grassland ecosystem is due to acridid grasshoppers (Schmidt, 1986). Being herbivorous
(primary consumer) and being preyed upon by other
insectivorous vertebrates and arthropods, they play a
significant role in accumulating and further transferring toxic metals to higher trophic levels. The studies
on the transfer of heavy metals in an aquatic ecosystem by Jamil and Hussain (1992), and in a copper
(Cu) and Cd contaminated grassland by Hunter et al.
(1987) showed that the accumulation and biotransfer
of anthropogenic heavy metals can be very high.
Organisms, like grasshoppers, occurring in such environments are also exposed to gradually increasing
toxic metals and contribute to the accumulation and
biotransfer of heavy metals. Hunter et al. (1987) studied the influence of toxic heavy metals on the acridids Chorthippus(Glyptobothrus) brunneus (Thunbg.)
from a Cd and Cu contaminated grassland. Higher accumulation of Hg in males than in females of Eyprepocnemis plorans (Charp.), but more Hg in females
than in males of Aiolopus thalassinus (Fabr.), and
no clear difference in Cd and Pb concentrations between the two sexes of A. thalassinus exposed to contaminated food under laboratory conditions showed
that different grasshoppers accumulate different heavy
metals in various concentrations and the accumulation of toxic metals might be sex dependent (Devkota, 1992). This study was undertaken to evaluate
the dynamics of toxic heavy metals in a relatively
less polluted grassland ecosystem and to determine
whether some species are more suitable bioindicators
and whether there is any sex-specific metal accumulation in the grasshoppers of such grasslands.
2. Materials and methods
Using insect nets, males and females, ten each,
of four species of acridid grasshoppers Calliptamus
italicus (L.), Oedipoda caerulcesens (L.), O. germanica (Latr.) and Chorthippus (Glyptobothrus) crassiceps (Ramme, 1926) were collected from a grassland
(1200 m above the sea level) in the Taigetos Mountains, Peloponnesus, Greece, during the summer of
1991. A mixture of food plants (grass) from the same
grassland was also collected. During transportation
to the Department of Zoology–Entomology, University of Hanover (Germany), the grasshoppers were fed
the same grass. The grass samples were washed with
deionised water to remove the heavy metals attached
on the surface and were freeze-dried. Five samples
each of both, males and females, and two grasshoppers in each sample, of all four grasshopper species
were ground in a vibrating mill (Retsch, Germany) to
a homogenous powder. For the food plants, only one
sample was ground.
2.1. Determination of elements
Cadmium (Cd) and lead (Pb) were determined with
a Zeemann AAS SM30 (Gruen Optiker, Wetzlar, Germany) equipped with graphite furnace and suitable for
element determinations in solid samples (Steubing et
al., 1980; Grobecker and Kurfürst, 1990; Devkota and
Schmidt, 1992). About 40–60 ␮g of a homogenous
sample weighed in a graphite boat was introduced into
graphite tube furnace using special tweezers. After
stepwise heating and ashing, the samples were atomised at 2000◦ C (for Cd) and 2300◦ C (for Pb) in an argon atmosphere. Atomic absorption was measured at
wavelengths of 228.3 nm during Cd and 283.3 nm during Pb determination using respective hollow cathode
lamps. BCR reference materials CRM 060 (Aquatic
plant) and CRM 061(Aquatic plant) for plant samples and CRM 185 (Bovine liver) and CRM 186 (Pig
kidney) for insect samples were used for calibration.
Along with the samples, the solid reference materials
were also determined for Cd and Pb concentrations.
The obtained data were within the range of certified
values.
Mercury (Hg) in the samples was determined according to the flameless cold-vapour technique (Welz,
B. Devkota, G.H. Schmidt / Agriculture, Ecosystems and Environment 78 (2000) 85–91
1985) using a Perkin–Elmer AAS 1100 equipped
with a mercury hydride system (MHS 10). About
200 mg of finely ground sample was wet digested in
3 ml aqua regia (conc. H2 SO4 and conc. HNO3 in
2 : 1 V/V of spectroscopic grade (Riedel-de Haen)
at 140–150◦ C for 4 h; one digestion per sample of
grasshoppers and three digestions of the grass sample
were carried in parallel. Sample aliquots were diluted
to 20 ml with deionised water. From diluted sample
solution, 10 ml was pipetted for each determination
and reduced by 3% NaHBO4 and 1% NaOH in the
presence of KMnO4 . The atomic absorption of the
elemental mercury was measured at 253.6 nm using a
hollow cathode mercury lamp. Nitrogen (extra pure)
was used as carrier gas and Fixanal mercury standard
solution (manufacturer: Riedel-de Haen, Germany)
was used for calibration. The Hg concentration in the
blank sample was also determined and this value was
subtracted from sample values to avoid any unwanted
contamination during sample preparation.
2.2. Analysis and presentation of data
Mean and standard deviation of five determinations
(one measurement per sample of five separate samples
87
in case of grasshoppers, but five measurements of one
grass sample) of each heavy metal was calculated and
the data are given in ␮g g−1 dry weight of the sample.
Differences between the mean concentrations in food
plants and in grasshoppers were calculated using Student’s t-test (Wardlaw, 1985). The data were subjected
to analysis of variance to calculate the F-ratio of intergroups variance (variations in metal concentrations
between species means) to intragroups variance (variations of individual concentrations within each species)
of heavy metal concentrations in grasshoppers.
3. Results
As shown in Fig. 1, heavy metals (Hg, Cd, Pb)
were found in remarkably high concentrations in the
grass samples from the Taigetos Mountains, where
the concentrations of these heavy metals were in the
order Pb > Cd > Hg. The mean concentration of Pb was
about 55 and 20 times the concentrations of Hg and
Cd, respectively.
Concentrations in grass vs. grasshoppers showed
that these toxic metals have been differently accumulated in different trophic levels in this ecosystem. The
Fig. 1. Concentrations (mean ± SD in ␮g/g dry weight) of heavy metals (Hg, Cd, Pb) in food plants and in females (F) and males (M) of
four species of grasshoppers from the Taigetos Mountains. Each bar represents the mean of five measurements and the differences in the
mean concentrations between food plants and grasshoppers are indicated by ***p < 0.001, **p < 0.01, *p < 0.05 and ns — not significant
differences.
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B. Devkota, G.H. Schmidt / Agriculture, Ecosystems and Environment 78 (2000) 85–91
Table 1
Accumulation factors (concentration in grasshoppers/concentration in food plants) of three heavy metals (Hg, Cd, Pb) in females (F) and
males (M) of four grasshopper species, where the factor >1 means higher concentration in grasshoppers than in food plants
Metal
Hg
Cd
Pb
C. italicus
O. caerulescens
O. germanica
C.(G.) crassiceps
Remarks
F
F
F
M
F
M
concentration in acridids
0.70
4.35
0.57
∼
=0.71
>2.15
<0.62
2.00
3.27
0.47
∼
=2.04
>2.72
>0.39
either ∼
= or > or > in food plants
always > in food plants
always < in food plants
0.84
4.19
0.53
M
<0.99
>3.09
>0.32
1.30
2.97
0.42
M
>0.62
>2.16
<0.47
concentration of Hg in these grasshoppers showed no
sex-specific difference in bioaccumulation. The solely
herbivorous C.(G.) crassiceps had Hg-concentration
significantly higher than in food plants and both sexes
of this grasshopper had the same level of accumulation (accumulation factor 2.00 in female and 2.04 in
male) (Table 1).
All four species of grasshoppers had significantly higher Cd concentration than the food plants.
Cadmium accumulation in female grasshoppers was
always higher (accumulation factors 2.97–4.35) than
in males (accumulation factors 2.15–3.09) and it was
remarkably high in O. germanica and C. italicus.
In the case of Pb, the accumulation in grasshoppers
(herbivores) never exceeded that of food plants (producers). In all grasshoppers, the concentration of Pb
was higher than Hg and Cd. Though O. germanica
was found to accumulate the highest amount of Pb,
the accumulation factor was still <1. Like Hg, accumulation behaviour towards Pb in these grasshoppers
was also quite different, and neither the females nor
the males were found to have higher concentrations
of Pb than food plants. In C.(G.) crassiceps, the accumulation behaviour of Hg and Cd was different (significantly higher) than of Pb (significantly low), but in
other grasshoppers such differences between different
heavy metals could not be observed within the same
species. The accumulation factors of these elements
in the grasshoppers were in the order Cd > Hg > Pb,
with Cd bioaccumulation being significantly higher in
all grasshoppers.
Mercury in females of O. caerulescens was found
in significantly higher concentrations than in males,
but in other grasshoppers there was no intraspecific
difference between the females and the males (Table
2). Though both sexes of all grasshoppers accumulated significantly high amounts of Cd, the difference
in Cd concentration between females and males was
significantly high only in O. germanica, where females had higher concentration than males. Significantly lower concentrations of Pb in O. caerulescens
and C.(G.) crassiceps than in food plants could not
deliver any intraspecific difference in Pb accumulation between the females and the males of these
species.
The variations in Hg concentration between different species (inter-group variations) was greater than
the variations within each species (intra-group variations), which could be verified with the very large F
value (F = 25.453, significant at p = 1% level). In case
Table 2
Differences in the mean concentrations of Hg, Cd and Pb in grasshoppers (Ci: C. italicus; Oc: O. caerulescens; Og: O. germanica; Ch:
C.(G.) crassiceps) between females and males of the same species and F-ratio of intergroup (four different species) and intragroup (males
and females of all four species of grasshoppers) variances in metal concentrations
Difference in metal concentrations between females
and males of the same species of grasshoppers
Hg
Cd
Pb
∗
a
Ci
Oc
nsa
∗
ns
ns
ns
ns
ANOVA table for metal concentrations of four
species of grasshoppers (n = 40, k = 4)
Og
Ch
intergroup
intragroup
F-ratio
ns
*
ns
ns
ns
ns
0.2815
1.2148
16.266
0.011
0.731
10.992
25.453 (**)
1.728 (ns)
1.479 (ns)
Levels of significance are indicated as: **p < 0.01, *p < 0.05.
Not significant differences.
B. Devkota, G.H. Schmidt / Agriculture, Ecosystems and Environment 78 (2000) 85–91
of Cd and Pb, such inter- and intragroup variations
did not vary significantly and the variations between
different species and within the species were same.
4. Discussion
The concentration of heavy metals in the food plants
and grasshoppers from the Taigetos mountains was
proportional in the order Pb > Cd > Hg, with the same
pattern of occurrence, both in producers and in herbivores. The concentrations of Cd, Cu, Pb and Zn in the
larvae of four ephemeroptera species from a polluted
stream were also proportional to the concentrations in
water and sediment in the order Cd < Pb < Cu < Zn
(Jop, 1991). Plants have a key function in the biotransformation of chemical elements from soil, water and air (Ernst, 1990), but green plants are unable to take up much mercury from contaminated soil
(Lodenius, 1990). Rauter (1976) found only 4.6 ␮g
Hg kg−1 in grasses of an industrially contaminated
area and its concentration in grasses of distantly located grassland of the Taigetos Mountains was still
lower (0.284 ␮g g−1 ). In grasshoppers, the accumulation factor was in the order Cd > Hg > Pb, where Cd
was in significantly higher concentrations than Hg and
Pb. This might indicate that different metals have different affinities leading to bioaccumulation in different organisms. Among these three elements, the concentration of Pb in grass was high (about 55 and 20
times higher than Hg and Cd, respectively), but it was
comparatively low (10–49 times of Hg and only 2–6
times of Cd) in the grasshoppers.
The higher bioaccumulation of Cd could be responsible for its higher toxicity, whereas the poor accumulation of Pb in the organisms could be one cause
to its less toxicity. The difference in the accumulation
behaviour towards Cd and Pb may be due to the opposite solubility properties and to the chemical similarities between Cd and the essential Zn (Roth-Holzapfel,
1990). Cadmium can replace the Zn in the enzyme carbonic anhydrase (Hopkin, 1989), changing the properties and activity of this enzyme.
Jamil and Hussain (1992) studied the transfer of
heavy metals through water — aquatic plants —
aquatic insect system using the plant Eichhornia
crassipes Solms. and its specific feeder Neochetina
eichhorniae. The study showed the biotransfer of
89
metals by a simple food chain model representing the
transfer of metals from polluted waters to insects via
aquatic plants. Clark (1992) measured the concentrations of organochlorine compounds and heavy metals
in the 17-year cicada to determine the possible food
chain hazards to birds. This homopteran contained
metal concentrations similar to or less than other
local invertebrates. Roth-Holzapfel (1990) could not
find an enrichment of elements, except Cd and Ni,
with increasing trophic level. Also during the present
study, Cd was found to be enriched in the grasshoppers, but the concentration of Hg in all four species
of grasshoppers was lower than Cd. Mukherjee and
Nuorteva (1994) likewise reported lower concentrations of Hg than Cd in bark beetles and ants from a
forest surrounding the steel works in northern Finland. In the beetles and ants, the concentrations of
these metals were near background levels. Copper
and Zn, being essential for insect metabolism, are accumulated and Cd, due its chemical property related
to Zn, is also accumulated (Roth-Holzapfel, 1990).
Devkota and Schmidt (1992) after feeding Hg-, Cdand Pb-contaminated food to adult Aiolopus thalassinus (Fabr.) found very high concentrations of Cd in
midgut, malpighian tubules, muscles, fat bodies and
gonads of these grasshoppers, but concentration of Hg
was high only in midgut and malpighian tubules (sites
of absorption and excretion, respectively), and Pb was
very low in these organs. With the growth of muscle
tissues and fat bodies during post-embryonic development (nymph — adult) the concentration of Cd was
found to be steadily increasing (Devkota, 1992).
Herbivorous animals, like most short-horned
grasshoppers, can magnify heavy metals in their bodies and may transfer them to higher trophic levels
(Roberts et al., 1979). During the present study, it was
found to be true only in the case of Cd. Being herbivorous (primary consumers), acridid grasshoppers
accumulate heavy metals from food plants (producers) and also directly from the soil through the eggs
laid there. Due to feeding and oviposition behaviour,
the acridid grasshoppers are thus simultaneously exposed to toxic substances through different paths. The
transport of Cd through the trophic level via acridid
grasshoppers seemed to be more efficient than that of
the other two heavy metals, Hg and Pb. According
to Hunter et al. (1987), Cd and Cu are highly mobile
in the invertebrate food web. Heliovaara (1990) also
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B. Devkota, G.H. Schmidt / Agriculture, Ecosystems and Environment 78 (2000) 85–91
found a higher accumulation of Cd in the European
pine sawfly Neodiprion sertifer (Hymenoptera; Diprionidae) than in pine needles, whereas the levels of
Cu, Ni and Fe were higher in pine needles than in
the insects. Because N. sertifer might be one of the
most abundant forest insects, this might be an important pathway for these metals to higher trophic levels.
Likewise, grasshoppers constitute significantly large
amounts of the arthropod biomass of the grassland
(Schmidt, 1986) and. thus, the biotransfer of geogenic
heavy metals, especially Cd, via the grasshoppers to
higher trophic levels may be very important.
Insignificant differences in the metal concentrations
between the females and the males of the same species
of grasshoppers showed that both sexes could equally
accumulate the heavy metals in their bodies and, for
the purpose of biomonitoring, the preference to one
sex of grasshopper might not be necessary. Significantly higher concentrations of Hg in both sexes of
C.(G.) crassiceps than in those of other three grasshoppers showed that this species might serve better as
test animal for the evaluation of Hg pollution. Significantly higher concentrations of Cd in both females
and males of all four grasshopper species would suggest that any grasshopper irrespective of the sex could
equally play the role of a bioindicator. Although the
degrees of bioaccumulations and biotransfers were different for different elements, the grasshoppers of this
mountain grassland can be regarded as the bioindicators of heavy metal pollution.
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