Ecotoxicology and Environmental Safety 101 (2014) 233–239
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Ecotoxicology and Environmental Safety
journal homepage: www.elsevier.com/locate/ecoenv
Orchards for edible cities: Cadmium and lead content in nuts, berries,
pome and stone fruits harvested within the inner city neighbourhoods
in Berlin, Germany
Laura Pauline von Hoffen, Ina Säumel n
Department of Ecology, Technische Universität Berlin, Ernst Reuter Platz 1 (BH 9-1), D-10587 Berlin, Germany
art ic l e i nf o
a b s t r a c t
Article history:
Received 28 August 2013
Received in revised form
21 November 2013
Accepted 22 November 2013
Available online 25 January 2014
Today's urban gardening focuses mainly on vegetable production and rarely includes fruit trees. Health
effects of consuming urban crops are questioned due to high local pollution loads. Here, we determined
cadmium and lead content in the edible parts of nuts, berries, pome, and stone fruits harvested from fruit
trees and shrubs within inner city neighbourhoods of Berlin, Germany. We analysed how local settings at
sampling sites shaped the trace metal content. We revealed significant differences in trace metal content
depending on species, fruit type, local traffic, and parameters related to barriers between the sampling
site and neighbouring roads. Higher overall traffic burden and proximity to roads increased whereas
buildings or vegetation as barriers reduced trace metal content in the edible biomass. We demonstrate,
that the consumption of non-vegetable fruits growing in inner city sites in Berlin does not pose a risk on
human health as long as the fruits are thoroughly washed and it is provided that site pollutions and
impacts are considered in garden concepts and guidelines.
& 2013 Elsevier Inc. All rights reserved.
Keywords:
Urban horticulture
Agroforestry
Fruit trees
Trace metals
Traffic burden
1. Introduction
Urban gardening is booming worldwide and enhances food
security, particularly in developing countries (FAO (Food and
Agriculture Organisation of the United Nations), 2007). The interest of city dwellers for producing their own fresh food is also rising
in developed countries (Leake et al., 2009) and food production for
low-income citizens is supported by self-organisation and local
authorities (Hancock, 2001).
Beyond local food production, urban gardening provides a
broad range of ecosystem services and is recognised as a key
instrument in environmental education (Krasny and Bonney,
2005), for community building (Bendt et al., 2013; Glover et al.,
2005), and for enhancing urban biodiversity (Galluzzi et al., 2010).
Fruit tree species have been used for ornamental purposes as a
reminiscence of rural landscapes (Lenné, 1825) and fruit trees
along urban roads or in parks have been leased to get financial
support for street or park maintenance in the 19th century
(Schmidlin, 1852). Currently, fruit trees remain unused although
abundant in public urban green spaces (see Fig. 1A for Berlin) and
the urban gardeners focus mainly on vegetable production (Bendt
et al., 2013; Hough et al., 2004).
n
Corresponding author. Fax: þ 49 30 314 29022.
E-mail address: [email protected] (I. Säumel).
0147-6513/$ - see front matter & 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.ecoenv.2013.11.023
The effect on human health caused by the consumption of
urban gardening products is discussed controversially, mainly due
to the high pollution loads in urban areas (Alloway, 2004; Finster
et al., 2004; Hough et al., 2004; Leake et al., 2009). Studies of
vegetables demonstrated, that the uptake and accumulation of
trace metals differed among crop type, species, and among plant
parts (Alexander et al., 2006; Finster et al., 2004; Säumel et al.,
2012). Few studies investigated the relation between trace metal
content in the edible parts of vegetables and local traffic burden
(Kloke et al., 1984; Säumel et al., 2012). Planting and building
structures (i.e. hedges, shrubs, lead free painted houses or walls)
can function as barrier between planting site and road, decreasing
trace metal content in the crops (Säumel et al., 2012).
Yet, there are only few studies analysing trace metal content in
fruit tree products growing in urban environments (Li et al., 2006;
Rossini Oliva and Valdés, 2003; Rossini Oliva et al., 2008; SamsøePetersen et al., 2002). Consequently, the aim of this study was to
analyse the cadmium (Cd) and lead (Pb) content in the edible parts
of different non-vegetable fruit types and fruit tree species. We
determined the influence of traffic burden (i.e. traffic burden of the
nearest and the nearest main arterial road, distances from the
planting site to nearest and nearest main arterial road, overall
traffic burden at sampling site) on trace metal content in the
fruits. We evaluated whether characteristics of the planting site
(i.e. sampling height, presence or absence of barriers between
planting site and roads, barrier width or height, degree of
enclosure of the sampling site by barriers) influence the trace
234
L. Pauline Hensel, I. Säumel / Ecotoxicology and Environmental Safety 101 (2014) 233–239
Fig. 1. (A) Number of fruit trees and shrubs in public green spaces in Berlin, Germany including pome and stone fruit trees (i.e. apple, apricot, cheery, mirabelle, pear, plum,
quince, sloe), berries (i.e. blackberry, blueberry, currant, elder, juniper berry, mulberry, raspberry, sea buckthorn), and nuts (i.e. chestnut, hazel, walnut) according to
Mundraub (2013) added by own survey data. Internet domains such as www.mundraub.org document fruit trees for a public use. (B) Sample sites per species in the inner
city of Berlin, Germany (pome and stone fruits indicated by squares; berries indicated by circles and nuts indicated by diamonds). (C) Examples of different local conditions of
the sample sites (black points: sampling sites with different distances to the nearest street or to the nearest arterial street and different traffic burden (red, orange or green
line indicate high, medium or low traffic burden); open circles are sampling sites with a barrier between street and sampling site). Photos for typical sites are given (i.e., 1:
sampling site along small street with low traffic burden; 2: sampling site along street with medium traffic burden; 3: sampling site along street with high traffic burden and
4 sampling site within a courtyard with a barrier between streets and sampling site; Photos taken by von Hoffen). (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
metal content. Furthermore, we compared the trace metal content
of the urban non-vegetable fruits with supermarket products to
assess health risks by consuming these urban fruits.
2. Materials and methods
We collected nuts, berries, pome and stone fruits of nine different species at
172 randomly chosen sites of the inner city of Berlin, Germany (Fig. 1B). The
sampling sites represented different urban conditions (Fig. 1C) and were characterised by the following parameters: distance to nearest road (d1) and to nearest
main arterial road (d2) in meters, traffic burden on the nearest road (tb1) and on
the nearest main arterial road (tb2) according to the number of vehicles per day
(1 r 5000; 2 ¼5001–10000; 3¼ 10001–15.000; 4 ¼15001–20000; 5¼20001–
30000; 6¼ 30001–40000; 7¼ Z 40001; Berlin Department for Urban Development, 2009), presence and absence of barriers between planting sites and nearest
roads (b); height of barrier (bh) and width of barrier (bw) in meters; the degree of
enclosure of the sampling site by barriers (eb), and sampling height in meters (sh).
Furthermore, we classified the overall traffic burden (otb) within a radius of 250 m
around the planting sites (low: low traffic burden, existing barriers or high distance
between planting site and nearest street; medium: low to medium traffic burden
and lacking barriers between planting sites and streets, lower distance to the
nearest street; high: high traffic burden and lacking barriers, small distance
between planting site and nearest street).
All fruits were collected in 2012 at the usual harvest time of each fruit species.
We classified fruit types as follows: ‘nuts' (dry fruits with a hard woody shell
including almond nuts); ‘berries’ (fleshy fruits including aggregate fruits such as
blackberries or strawberries); ‘stone fruits’ (drupes with an outer edible fleshy part
surrounding a seed containing shell); and ‘pome fruits’ (fruits with an outer edible
fleshy part surrounding cores). In total, we sampled nuts: walnut (Jugland regia,
N¼ 18), hazel (Corylus avellana, N ¼ 13), ginkgo (Ginkgo biloba, N ¼ 3); berries:
blackberry (Rubus fruticosus agg, N ¼ 16), seabuckthorn (Hippophae rhamnoides,
N¼ 12), elder (Sambucus nigra, N ¼ 27); and pome and stone fruits: apple (Malus
domestica, N ¼29), mirabelle (Prunus domestica subsp. syriaca N ¼28), plum (Prunus
domestica subsp. domestica, N ¼ 26). For each fruit species, we collected mixed
samples of common supermarket fruits (N¼ 3) except for ginkgo, elder, and
seabuckthorn. Elder and seabuckthorn were not available in supermarkets; therefore we harvested samples from rural sites far away from potential pollution
sources. In gingko, no trace metals were detected. We used these samples to
compare the potential dietary exposure to trace metals of someone consuming
urban horticulture products versus supermarket products.
Directly after the harvest, the edible parts of the berries, pome and stone fruits
were thoroughly washed and afterwards frozen similar to the supermarket
samples. The nuts were stored dry in their nutshells. Edible parts of all fruits were
dried at a temperature of 60 1C for 72 h to 14 d depending on sample size and fruit
species. After drying, the samples were ground ( o 100 mm) and stored in a
dehydrator. Then the samples were dried at a temperature of 105 1C for 48 h.
Approximately 500 mg dry fruit powder and creamy nut powder was digested in
10 ml HNO3 (69 percent) in a drying chamber at a temperature of 185 1C. After the
digestion, the samples were filled up to a volume of 40 ml with ultrapure water.
The determination of the trace metal content in the biomass was made with an
atomic absorption spectroscopy using the Atomic Absorption Spectrometer AA880Z
(Varian, Australia). The used wave lengths/ detection limits of the elements were
228.8/2.0 mg/l for Cd and 217.0/3.0 mg/l for Pb. We used a melon powder (IPE 950)
as standard to assess the quality of our measurement (reference/measured values
in mg/kg DW for N ¼20: Cd: 1.03/1.34; N ¼ 28: Pb: 3.50/3.55).
We used analysis of variance (ANOVA) for data analysis. Cd or Pb content in the
dried biomass is the response variables and species, fruit type, and the parameters
characterising local settings at sampling site (overall traffic burden, distance to the
nearest road and number of vehicles of the nearest road, distance to the nearest
arterial road and the number of vehicles per day of the nearest arterial road,
presence and absence of a barrier and type, height, width and degree of enclosure
L. Pauline Hensel, I. Säumel / Ecotoxicology and Environmental Safety 101 (2014) 233–239
of the sampling site by barriers, sampling height) were taken as explanatory
variables. Homogeneity of data (Brown–Forsythe's test) and normal distribution of
data (Shapiro–Wilk test) were tested before applying the ANOVA. Log transformations were applied if necessary to comply with the assumptions of the residual
normality and variance homogeneity needed for the analysis. We used the Tukey
test for the comparison of means. Effects were considered significant at p o 0.05
level. The statistical analysis was done by using R version 2.15.2 (R Foundation for
Statistical Computing, Vienna, Austria).
3. Results
The trace metal contents differed significantly among species
and fruit types (Table 1) and depended on traffic related and on
barrier related parameters (Table 2).
235
Cd content of blackberry and seabuckthorn berries were up to 26
times higher compared to nuts, pome and stone fruits, and elder
berries (Fig. 2A). Compared to the inner city fruit samples, the Cd
content in control samples was higher in hazel (39 times), blackberry (2 times) and mirabelle (3 times), similar in walnut, elder,
plum and apple—and lower in seabuckthorn (2 times; Table 1).
Pb content of pome and stone fruits was 8 times higher and up
to 17 times higher in berries than in nuts (Table 1, Fig. 2B).
Compared to the inner city fruit samples, Pb content in control
samples was higher in apple (2 times), mirabelle (4 times) and
plum (16 times) and was in the same range in seabuckthorn and
elder (Table 1).
The sampling height of the fruits affected the trace metal
contents significantly (Table 2). A decreasing sampling height
Table 1
Content of Cd and Pb in nuts, berries and pome and stone fruits grown in the city of Berlin in mg/kg biomass dry weight (DW): median (Med), minimum (Min), maximum
(Max); values for N samples and the control value (C) refers to the median concentrations from supermarket products (N¼ 3) are given. nd ¼ not determined. In 28 percent of
the samples the content of Cd was below the detection limit of 10 ppm. In 17 percent of the samples the Pb content were below the detection limit of 10 ppm. European
standards for Pb: 0.20 mg/kg FW for berries and small fruits and 0.10 mg/kg FW for other fruits and for Cd: 0.05 mg/kg FW for fruits).
Content of trace metals [mg/kg DW]
Element
Nuts
Berries
Pome and stone fruits
Cd
Pb
Species
N
Min
Med
Max
C
Min
Med
Max
C
Jugland regia
Corylus avellana
Ginkgo biloba
Rubus fruticosus agg
Sambucus nigra
Hippophae rhamnoides
Malus domestica
Prunus domestica subsp. Syriaca
Prunus domestica subsp. Domestica
18
13
3
16
27
12
29
28
26
0.0
0.0
0.0
4.5
0.0
1.2
0.0
0.0
0.0
0.0
0.5
0.0
8.1
0.0
12.9
1.1
0.9
1.2
0.7
5.7
0.0
180.4
9.2
37.6
3.7
9.3
13.3
0.0
19.7
nd
16.7
0.0
8.3
1.1
2.7
1.4
0.0
0.0
0.0
4.5
19.1
21.6
0.0
5.7
8.1
0.0
6.5
0.0
59.5
51.9
57.4
29.3
23.1
23.2
5.7
15.2
0.0
1438.1
149.4
100.4
170.3
567.8
143.4
0.0
6.7
nd
12.8
55.2
50.2
60.1
87.2
290.1
Table 2
ANOVA results of the species, fruit type (i.e. nuts, berries and pome and stone fruits) and site effects as well as the interactions between species and site effects on content of
Cd and lead [in mg/kg biomass dry weight (DW)]. Minimum adequate linear models were chosen using a step-by-step reduction of the maximum model to find the minimum
value of Akaike's information criterion (AIC). The maximum model considered Cd or Pb content of biomass [mg/kg DW] in relation to species (sp), fruit type (ft), overall traffic
burden (otb), number of vehicles per day on the nearest road (tb1), distance (m) to the nearest road (d1), number of vehicles per day on the nearest main arterial road (tb2),
distance (m) to the nearest main arterial road (d2), Presence or absence of barrier (b; i.e. no barriers, buildings, plantings or buildings and plantings) and the degree of
enclosures by barriers (de) between fruit tree or shrub and streets and relevant interactions between parameters. The models with the lowest AIC value were Cd
content spnshnd1ntb2notbnbnbhnbwnde and Pb content spnshnd1ntb1notbnbnbhnde. F and p values of the ANOVA are given (ns, not significant). F value is the ratio between
the variance of the group means and the mean of the within group variances.
Element
Content of trace metals in mg/kg DW
Cd
Pb
Parameter
F
p
F
p
Species (sp)
Fruit type (ft)
Sampling height (sh)
Overall traffic burden (otb)
Distance (m) to nearest road (d1)
Number of vehicles per day on the nearest road (tb1)
Distance (m) to the nearest main arterial road (d2)
Number of vehicles per day on the nearest main arterial road (tb2)
Presence/absence of barrier (b)
Height (m) of barrier (bh)
Width (m) of barrier (bw)
Degree of enclosure by barriers (de)
Relevant interactions between parameters:
sp sh
sp tb1
sp otb
sp b
sp d1
d1 b
d1 bh
Residuals
df
MS
105.1
7.1
15.2
5.9
213
ns
ns
90.7
16.5
55.9
56.8
53.3
o 0.001
0.001
0.001
0.030
o 0.001
22.1
4.6
19.7
20.6
8.3
ns
ns
ns
11.1
9.6
ns
29.0
o 0.001
0.011
o 0.001
o 0.001
0.009
18.2
ns
ns
8.1
234.7
11.5
185.7
o 0.001
28.8
14.5
11.8
29.8
7.2
10.3
52.1
o 0.001
o 0.001
o 0.001
o 0.001
o 0.001
o 0.001
o 0.001
39
57356
o 0.001
o 0.001
o 0.001
o 0.001
o 0.001
o 0.001
o 0.001
0.001
o 0.001
22
40009
o 0.001
0.005
o 0.001
236
L. Pauline Hensel, I. Säumel / Ecotoxicology and Environmental Safety 101 (2014) 233–239
Pb content, than fruits at sampling sites without a barrier between
planting sites and roads (Fig. 3M, Q, and V).
Cd content µg/kg DW
50
b
40
4. Discussion
30
b
20
a
a
a
10
a
a
a
Jr
Ca
Gb
a
0
Rf
Sn
Hr
Md
Pd
Ps
Pb content in µg/kg DW
300
b
250
ab
200
ab
b
150
b
ab
100
50
a
a
a
Jr
Ca
Gb
0
Nuts
Rf
Sn Hr Md Pd Ps
Species
Berries
Pome & Stone fruits
Fig. 2. Content of Cd and Pb in the nuts, berries and, pome and stone fruit biomass
in mg/kg biomass dry weight (DW). The boxplots indicate the 25th and 75th
percentiles and means of the distribution. Different lower case letters associated
with the boxplots indicate significant interspecific differences and identical lower
case letter indicate groups not significantly different from each other. The sampled
vegetable types are walnut (Jr), hazel (Ca), gingko (Gb), blackberry (Rf), elder (Sn),
seabuckthorn (Hr), apple (Md), plum (Pd), mirabelle (Ps). The significance level is
p o0.05. For ANOVA results see Table 2. Red lines indicate the control value
(i.e. median concentrations from supermarket products or samples from rural sites
far away from potential pollution sources). Only one sample of 172 different fruit
samples exceeds European limits for lead in fruits. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
increased Pb and Cd content of blackberries (pcd ¼0.01; ppb ¼
0.001).
Some traffic related parameters of sampling sites (i.e. overall
traffic burden, distance to the nearest road, the number of vehicles
per day on the nearest main arterial road) affected the trace metal
contents of the fruits (Table 2). Cd content in apple, plum, blackberry and seabuckthorn increased significantly with increasing
overall traffic burden at the sampling site (Fig. 3A, B, E–F). Pb
content of fruits increased with increasing overall traffic burden at
sampling sites for plum, mirabelle, and blackberry (Fig. 3H–L).
Trace metal contents of other fruits varied largely among different
overall traffic burdens and were not related to different traffic
burdens (Fig. 3C, D and G).
The presence or absence of a barrier, the height of a barrier, and
the degree of site enclosure by barriers influenced the Cd and Pb
contents of fruits (Table 2). Apples growing behind a barrier had
significantly lower Cd content and blackberries had lower Cd and
Our study highlighted that (1) urban non-vegetable fruits in
Berlin accumulated considerably less Cd or Pb in the edible tissues
compared to urban vegetables and partially to supermarket
products (i.e. hazel, mirabelle, apple, plum) and did not exceed
European standards for trace metals; (2) accumulation of health
relevant trace metals differed among fruit types (i.e. nuts opome
and stone fruits oberries); and (3) beyond general urban pollution
load, site-specific parameters (i.e. traffic burden, characteristics of
barriers between sampling site and road, sampling height)
affected the trace metal contents of fruits.
Previous studies on trace metal contents in edible fruits focused
mainly on rural sites with diverse pollution sources such as spill
contamination (Madejón et al., 2006), sewage irrigation (Batarseh
et al., 2010; Menti et al., 2006a, 2006b), usage of compost and
fertilisers (Merino et al., 2006; Pinamonti et al., 1997) or vicinity of
contaminating industries (Arik and Yaldiz, 2010).
In general, Cd and Pb content of non-vegetable fruits from
Berlin's inner city were similar or lower compared to fruits from
uncontaminated rural sites (Ademoroti, 1986; Bi et al., 2010;
Yaman et al., 2000) and significantly lower compared to fruits
irrigated with sewage water or sludge (Batarseh et al., 2010; Menti
et al., 2006a, 2006b). Cd and Pb content of stone fruits from Berlin
were lower compared to unwashed mango fruits growing on rural
sites that were classified as uncontaminated (Bi et al., 2010). Cd
and Pb content of orange fruits growing in the inner city of Seville
and Palermo were higher or similar to our berry samples (Rossini
Oliva and Valdés, 2003). Fruits from Copenhagen, Denmark, had
higher trace metal contents compared to our samples (SamsøePetersen et al., 2002).
A previous study on trace metal contents of vegetables grown
in Berlin's inner city demonstrated that urban crops are not
automatically ‘healthy' or ‘safe' compared to supermarket products
(Säumel et al., 2012). In the present study, trace metal contents of
urban non-vegetable fruits were in the range of supermarket and
control samples (Table 1). Moreover, supermarket samples of some
non-vegetable fruits exhibited higher levels of Pb or Cd than inner
city samples (Table 1).
Almost all urban fruits analysed in this study had significantly
lower Cd and Pb content compared to vegetables harvested in the
same study area (Säumel et al., 2012). Similar differences between
non-vegetable fruits and vegetables have been reported for medium contaminated urban sites (Samsøe-Petersen et al., 2002).
None of our samples exceeded the EU standards for Cd in fruits
(0.05 mg/kg FW) and only one sample of the 172 samples
exceeded the EU standards for Pb (0.20 mg/kg FW for berries
and small fruits and 0.10 mg/kg FW for other fruits; European
Commission, 2006). The WHO dietary intake limits for adults are
0.060 mg for Cd and 0.214 mg for Pb per day (FAO/WHO Joint
Expert Committee on Food Additives, 1999). The recommended
daily vegetable and fruit consumption is 400 g for adults. Thus, an
adult consuming an average of 200 g of non-vegetable urban fruits
would be ingesting less than 0.3 percent and 2 percent of the
accepted daily intake of Cd and Pb, respectively. Thus, we did not
prove a human health risk by consuming fruits from inner city
areas. In contrast to our results, Cd content of the edible fruits
from orchards in a large Chinese metropolis markedly exceeded
Chinese and EU standards (Li et al., 2006).
A further important finding of our study is, that accumulation
of health relevant trace metals differed between non-vegetable
fruit types. Similar to our samples, carambola berries had generally
L. Pauline Hensel, I. Säumel / Ecotoxicology and Environmental Safety 101 (2014) 233–239
237
Fig. 3. Content of Cd (above) and Pb (below) in the edible fruit parts in mg/kg dry weight (DW) in relation to the overall traffic burden at sampling site (green: low; orange:
medium and red: high traffic burden; (A–L) and in relation to the absence and presence of a barrier between sampling site and nearest road (M–V). Lower case letters
associated with the boxplots indicate significant interspecific differences. The significance level is p o 0.05. Significant differences are indicated (**p o0.01; *p o 0.05; ns, not
significant). The boxplots indicate the 25th and 75th percentiles of the distribution. For ANOVA results see Table 2. (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
higher Cd content compared to pome and stone fruits (i.e. wampee
and longan fruits; Li et al., 2006). Menti et al. (2006a, 2006b)
reported higher Cd contents in lemons than in almonds. Adapting
the concept of low and high accumulators from vegetable crops to
address species-specific differences in the capacity for uptake,
accumulation, and tolerance of trace metals (e.g. Alexander et al.,
2006; Finster et al., 2004), our results provide evidence that nonvegetable fruits can be addressed as low accumulators for both
trace metals. Nuts with a compact protecting shell accumulate
almost no Pb or Cd. Pome and stone fruits accumulate more Pb
compared to nuts. Blackberry and seabuckthorn accumulate more
Cd compared to the other fruit types whereas elder berries did not
(Fig. 2). Our data provide evidence, that the higher sampling
height of the elder berries compared to the other berries reduced
trace metal contents (Table 2). Shielding properties of nut and fruit
shells isolate the edible parts during growth from the environment
and reduce airborne pollution (Wyttenbach and Tobler, 1998;
Rodushkina et al., 2008). In contrast to our results, nuts from
Copenhagen, Denmark, had higher Pb contents compared to
berries and stone fruits (Samsøe-Petersen et al., 2002). However,
more research is needed to highlight the mechanisms beyond
these patterns.
The high variability of our data seen in Table 1 might be due to
the heterogeneity of urban soil. Contaminated sites in urban
environments can increase trace metal contents in fruits growing
in a low overall traffic burden (Alloway, 2004). However, trace
metal contents of urban fruits and vegetables were not always
correlated with different degrees of soil contaminations (SamsøePetersen et al., 2002). Pb uptake from soils is generally passive and Pb
is not directly translocated to the edible parts of a fruit tree (Ward and
Savage, 1994). The atmospheric deposition of trace metals on the fruit
surfaces apparently has a stronger effect than uptake from the soils
(Madejón et al., 2006; Samsøe-Petersen et al., 2002) and more traffic
related Pb was deposited on rough surfaces such as tree bark
compared to rather smoth fruit skins (Ademoroti, 1986). Consequently, unwashed olive fruits growing in spill-affected soils compared to non-affected soils showed no significant differences with
regard to Cd and Pb contents (Madejón et al., 2006).
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L. Pauline Hensel, I. Säumel / Ecotoxicology and Environmental Safety 101 (2014) 233–239
Traffic related pollutants are strongly enhanced along roads
compared to background values. Pollutants deposited in the soil
remain there for a long time and acting as a source of further
pollution in urban environments (Hjortenkrans et al., 2008; Querol
et al., 2007). We revealed that a high traffic burden and proximity
to the nearest road significantly increased the Cd and Pb contents
in non-vegetable fruits (Table 2, Fig.3). The accumulation of Pb and
Cd in the soils decreased with increasing distance from the road
(Hjortenkrans et al., 2008). Cd and Pb contents in apple and grape
fruits did not decrease with increasing distances to roads but with
decreasing traffic densities (Bakirdere and Yaman, 2008). Pb
deposits on unwashed fruit skin varied according to traffic volume
in Benin City, Nigeria (Ademoroti, 1986).
Furthermore, our study revealed that barriers between planting
site and road reduced Pb and Cd in the edible parts of fruit trees
(Fig. 3M, Q, and V). As particles washed off of painted houses and
walls doubled Pb contents in the topsoil (Alloway, 2004), closeness
of buildings and walls can also increase trace metal contents in the
topsoil. Our data showed that the increasing height and width of a
barrier decrease the trace metal contents in the edible part of
fruits. Traffic related particles could be immobilised on plant
surfaces of vegetation barriers such as hedges and thus reduce
the deposition of traffic related pollution on the fruits (Hodel and
Chang, 2004). Studies from the 1970s already demonstrated, that
hedges or trees near roads efficiently reduced traffic related Pb
emissions (Keller, 1974). However, the function of barriers was
discussed controversially and it was assumed that the windbreak
effect and the related higher deposition rates inside the hedges
might be more important than the filtration effects of hedges
(Keller, 1974; Bouvet et al., 2007).
The integration of productive fruit trees in urban gardening can
support long-term establishment of local production and thus
urban sustainability efforts (Deelstra and Girardet, 2000) and
strengthen the environmental benefit of gardens for city-dwellers,
urban flora, and fauna. Horticultural studies on rural landscapes
have demonstrated benefits derived from an integration of productive fruit trees in gardens: shading and cooling effects of fruit
trees between vegetables patches increased the crop yields (Huang
et al., 1990), reduced soil erosion and functioning of leaf litter as
organic fertiliser (Marten, 1986), enhanced agrobiodiversity
(Altieri, 1999) as fruit trees attract a wide range of insect and bird
species (e.g. Davies et al., 2009). In addition to these benefits,
urban trees improve air quality (Akbari et al., 2001).
Finally, our study provides evidence for the development of
planting concepts for urban gardens. Hedges or walls minimise
contamination effects, especially within high traffic areas. Nut
trees can form the outer and pome and stone fruits the medium
boundary of urban garden areas, whereas berries and vegetables
should preferably be cultivated in the central area of urban
gardens.
5. Conclusion
Our study demonstrated that the Cd and Pb contents in fruits
harvested from trees growing within inner city neighbourhoods
were below the EU standards for fruits (European Commission,
2006), partially below values found in fruit samples from supermarkets and were considerably lower in urban non-vegetable
fruits than in urban vegetables (Samsøe-Petersen et al., 2002;
Säumel et al., 2012). However, more research is needed to identify
harmless and risky fruit species for urban gardening. Based on our
data, the consumption of urban fruits is not harmful to human
health and fruit trees and shrubs can be considered more suitable
for urban gardening in highly polluted areas compared to
vegetables.
Overall, our study gives evidence that the consumption of nonvegetable fruits growing on inner city sites in Berlin does not pose
a risk on human health, as long as the fruits are thoroughly
washed and it is provided that site pollutions are considered in
garden concepts and guidelines (e.g. minimum distance to roads,
usage of barriers, planting concepts).
Capsule
Urban non-vegetable fruits accumulated less cadmium or lead
in the edible tissues compared to urban vegetables and to some
supermarket products and did not exceed European limits for
trace metals in fruits.
Acknowledgments
This study was funded by Peter Dornier Stiftung Lindenau and
by the Freunde der TU Berlin e.V. Special thanks go to Christa
Müller and the Stiftungsgemeinschaft Anstiftung & Ertomis for
supporting our research. We want to thank Claudia Kuntz, Iris
Pieper, and Kotan Yildiz for technical assistance.
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