Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-3625-3
RESEARCH ARTICLE
Metal content in edible crops and agricultural soils due to intensive use of fertilizers and pesticides in Terras da Costa de Caparica (Portugal) Fernando Reboredo 1 & Manuela Simões 1 & Celeste Jorge 2 & Malva Mancuso 3 & Jorge Martinez 4 & Mauro Guerra 5 & José C. Ramalho 1,6 & Maria Fernanda Pessoa 1 & Fernando Lidon 1 Received: 4 July 2018 / Accepted: 29 October 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract Soils and different vegetable species in Costa de Caparica (Portugal) are subject to the intensive use of inorganic fertilizers and pesticides. Thus, the concentrations of As, Cu, Fe, Mn, Pb, and Zn were evaluated. Lettuce, spinach, and potatoes collected in station 9 cause reason for concern due to their high Pb concentrations close to 20 μg g−1 which is probably related to an intensive use of copper and iron sulphate fertilizers. Additionally, the consumption of Portulaca oleracea collected in stations 3 and 4 must be avoided due to the high concentrations of Zn, and even Cu. The derived estimated daily intake (EDI) dose of Zn will be a risk to human consumption if P. oleracea was the single basis of a soup, although the addition of other ingredients might lower the tolerable upper intake (TUI) value of 39 mg/day of P. oleracea, to admissible levels, i.e., not exceeding 25 mg/day. Pumpkin collected in station 1 contained 44.1 μg g−1 Cu and a TUI value of 9.8 mg/day, when the recommendation must not exceed 5.0 mg/day. In this context, it is strongly advised to not include this vegetable in household menus. Keywords Agricultural soils . Edible vegetables . Food analysis . Food composition . Heavy metals . Risk assessment
Introduction Soils have been used intensively all over the word to fulfill several key roles, crop production being perhaps the most
important use. The increase in crop yields has been achieved with the improvement of agricultural techniques and farming practices, adequate choice of the cultivars, and above all with the intensive use of fertilizers containing heavy metals
Responsible editor: Elena Maestri * Fernando Reboredo
[email protected] Manuela Simões
[email protected] Celeste Jorge
[email protected] Malva Mancuso
[email protected] Jorge Martinez
[email protected]
Fernando Lidon
[email protected] 1
GeoBioTec, Departamento de Ciências da Terra, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
2
Laboratório Nacional de Engenharia Civil, Lisbon, Portugal
3
Universidade Federal de Santa Maria, Santa Maria, Rio Grande do Sul, Brazil
4
Queensland University of Technology, Brisbane, Australia
5
LIBPHYS, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
6
Plant-Environment Interactions & Biodiversity Lab. (PlantStress & Biodiversity), Linking Landscape, Environment, Agriculture and Food, (LEAF), Dept. Recursos Naturais, Ambiente e Território (DRAT), Instituto Superior de Agronomia (ISA), Universidade de Lisboa (ULisboa), Quinta do Marquês, 2784-505 Oeiras, Portugal
Mauro Guerra
[email protected] José C. Ramalho
[email protected];
[email protected] Maria Fernanda Pessoa
[email protected]
Environ Sci Pollut Res
although the content of heavy metals varied significantly in different fertilizers depending on the N:P:K ratio and fertilizer origin (Milinović et al. 2008). Agricultural management practices also use pesticides (herbicides, fungicides, and insecticides) containing metals. When studying the concentrations of Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn in different inorganic fertilizers (urea, calcium superphosphate, iron sulphate, and copper sulphate) and in pesticides (two herbicides and one fungicide) Gimeno-García et al. (1996) showed that superphosphate is the fertilizer that contains the highest concentrations of Cd, Co, Cu, and Zn as impurities. Copper sulphate and iron sulphate have the most significant concentrations of Pb, and are the only fertilizers in which Ni was detected. The three pesticides analyzed show similar Cd contents and the highest levels of Fe, Mn, Zn, Pb, and Ni are found in the herbicides. In regard to the binding of heavy metals into the substrata and the relationship with plant uptake, huge variations are evident, according to the plant species and their intrinsic characteristics, soil characteristics, the type of metals, and their speciation (Reboredo 2012). As the inputs of heavy metals to soils are mostly accumulated in the topsoil (Hou et al. 2014), large screenings (LUCAS Topsoil Survey) have been undertaken to evaluate if European agricultural land can be considered safe for food production (Tóth et al. 2013). In this context, several studies were performed in the topsoil where food crops reside, and the root system mainly develops. Understanding the transport and fate of heavy metals in the biota is important to evaluate the risk assessment which is particularly acute, regarding agricultural practices, to farm families and local and regional consumers. Moreover, the chronic accumulation of heavy metals in the kidney and liver of humans leads to cardiovascular, nervous, kidney, and bone diseases (Järup 2003), while in plants, the accumulation may lead to biochemical pathway disorders mostly related with photosynthesis (Reboredo 2001). In this framework, it is important to study the accumulation of heavy metals in common edible vegetables, especially when being grown in intensive exploited agricultural soils such as those of Terras da Costa, a flat portion of land between the Atlantic Ocean in the west and the fossil sea cliff in the east. This area has sand deposits, front dunes, and hinterland dunes with ground elevation between 2 and 11 m above the average sea level. The soils subject to agricultural practices in the region are classified as sandy soils according to the Food and Agriculture Organization (FAO) of the United Nations (FAO/UNESCO 1987). The land along the shoreline of Costa de Caparica (socalled Terras da Costa) has been subject to continuous agricultural practices in small production farms, which
supply the vegetable markets of Lisbon with cabbage, cauliflower, white cabbage, broccoli, potatoes, onion, garlic, capsicum, pumpkins, lettuce, and others, in three to four cultures per year. The high productivity under such intensive agricultural management has been achieved through the regular and continuous applications of fertilizers and pesticides in addition to the availability of shallow groundwater for irrigation (Simões et al. 2012) beyond the favorable climate conditions. The aim of the present study is to evaluate heavy metal concentrations in soils and edible crops collected at Terras da Costa and evaluate the risk assessment for human health, which was addressed through the determination of the estimated daily intake dose and the tolerable upper intake (TUI).
Material and methods Soil and vegetal sampling Soil samples were hand-collected in August 2010 from nine sampling points located in Terras da Costa (Fig. 1) for physical and chemical analysis, i.e., pH, oxidation-reduction potential, electrical conductivity, organic matter, water content, and metal load—As, Cu, Fe, Mn, Pb, and Zn. A reference area (dune-deposit inside a protected area, with no indication of historical agricultural activities in proximity) was also considered for analytical purposes. Three soil samples from each sampling point, at two depths (0–10 cm; 10–20 cm) were collected. Overall, 60 soil samples were used for analytical purposes. The soil samples from two different depth intervals were stored in black plastic bags, transported to the laboratory, airdried at room temperature, and sieved at 2-mm nylon sieve to remove plant debris and large particles prior to use. Thereafter, each sample was powdered in an agate mortar before X-Ray Fluorescence (XRF) analysis. Plant samples were hand-collected in different sampling points, especially the edible portions of the plants, such as the leaves of Brassica oleracea L. (cabbage— stations 5, 6, 7, and 8), Spinacia oleracea L. (spinach— station 9), Lactuca sativa L. (lettuce—station 9), the leaf/stem of Portulaca oleracea L. (common purslane— stations 3 and 4), the bulb of Allium cepa L. (common onion—station 7), the edible tuber of Solanum tuberosum L. (potato—station 9), the turnip root of Brassica rapa L. (station 2), and pumpkin fruit of Cucurbita maxima Duchesne (station 1). Plant samples were always collected in triplicate, in the total amount of 36 specimens. After sampling, plants were carefully rinsed with deionized water to remove fine particles and dried at 70 °C until constant weight. The peel was
Environ Sci Pollut Res Fig. 1 Terras da Costa de Caparica (Almada, Portugal). Location of soil and vegetable sampling points—stations 1 to 9 and reference area (Ref)
removed from pumpkin while in the case of the onion bulb the dry outer layers were peel off. Thereafter, a powder of each sample was obtained in a mortar, and the samples processed according Santos et al. (2014). For analysis, the powder was pressed into pellets 2.0 cm in diameter, and a minimum of three pellets for each sample were made to reduce the error analysis. Each pellet weighing approximately 0.3 mg was glued on the Mylar Film and put on a sample holder directly on the X-ray beam for elemental determination. The acquisition time was 1000 s.
Soil and vegetal analysis The soil samples were analyzed in the Environment Geotechnical Laboratory (LGamb) of the Geotechnical Department at the National Engineering Laboratory (LNEC) in Lisbon. The XRF Niton XL3t 900 GOLDD analyzer was used to analyze As, Cu, Fe, Mn, Pb, and Zn in representative fractions of the soil samples in accordance with EPA method 6200 (EPA 1988). Detection limits using the optimum “mining” mode for a period of 120 s under high purity helium (He)
Environ Sci Pollut Res
were As = 5 mg kg−1; Cu = 12 mg kg−1; Fe = 25 mg kg−1; Mn = 30 mg kg−1; Pb = 4 mg kg−1; Zn = 6 mg kg−1. Soil reference materials (NRCan Till-1) were run before the beginning of analyses and after every five samples; the recovery values ranged between 90% for Pb and 98% for Cu. The Portuguese technical guideline (NP84 1965) was used to determine soil moisture (W); the organic matter (OM) was quantified by the MAB-Peroxide method (Bortolin and Cassol 2010); pH, EC, and Eh were measured according to the E203 method (LNEC 1967). For the analysis of plant samples, a benchtop energydispersive X-ray fluorescence spectrometer (EDXRF), equipped with a commercial X-ray tube (PW1140, 100 kV, 80 mA) with a tungsten anode in a triaxial geometry, was used. Detection limits, similar to those referred by Santos et al. (2014) were the following: As = 3 mg kg−1; Cu = 3 mg kg−1; Fe = 6 mg kg−1; Mn = 9 mg kg−1; Pb = 8 mg kg−1; and Zn = 3 mg kg−1. Plant reference materials were used for data validation: orchard leaves (NBS 1571) and poplar leaves (GBW 07604); the recovery values ranged between 97 and 99%.
Determination of the estimated daily intake, tolerable upper intake, bioaccumulation factor, pollution load index, and contamination factor The estimated daily Intake dose (EDI) was calculated as follows: EDI = Ci × IR/BW, where Ci is the concentration of a certain element (mg kg−1) in edible portions, IR is the average daily consumption of vegetables (g per day), and BW the body weight (kg). We consider 65 kg as an average weight of an adult male. In Europe, the average consumption of fruit and vegetables is only 220 g per person per day for adults instead of the 400 g minimum recommended by the World Health Organization (excluding potatoes and starchy tubers, such as cassava) http://www.eufic.org/article/en/expid/Fruitvegetable-consumption-Europe/. The tolerable upper intake (TUI) was calculated as follows: TUI = EDI × BW, where EDI is expressed in mg kg−1/ day and BW in kg, assuming the value of 65 kg as indicated above. According the European Food Safety Authority (EFSA), the TUI values of Cu and Zn for adults are 5 and 25 mg/day, respectively (https://www.efsa.europa.eu/sites/ default/files/assets/UL_Summary_tables.pdf), while for Fe 45 mg/day Fe (https://ods.od.nih.gov/factsheets/IronHealthProfessional/). In the case of Mn, we assume a TUI level for an adult body weight of 70 kg, of 11 mg Mn/day based on a NOAEL for Western diets (https://www.ncbi. nlm.nih.gov/books/NBK222332/). The bioaccumulation factor (BAF) determines the ability of a plant to uptake a metal from soils was calculated with the following equations: BAF edible part = C edible part /C soil ; BAF leaf = C leaf /C soil ; where C edible part , C leaf , and C soil
represent the metal concentrations in the edible part, leaves, and soil, respectively. The pollution load index (PLI) was calculated according to the formula expressed by Tomlinson et al. (1980)— PLI = (CF 1 × CF 2 × CF 3 × CF 4 ……….) 1/n where CF 1 × CF2 × CF3 × CF4 are the contamination factor values of each metal and n is the number of metals. The PLI represents the number of times by which the metal content in soils exceeds the reference concentration and gives an indication of the overall toxicity risk in a particular sample. The PLI value of > 1 is polluted, whereas < 1 indicates no pollution. The contamination factor (CF) is the ratio obtained from heavy metal concentrations in polluted and reference sites (CF = Cpollut/ Creference).
Statistical analysis and control assurance Statistical analysis of the data was performed with the SPSS Statistics 18 program, through an analysis of variance (ANOVA) and the F test. A value of P ≤ 0.05 was considered to be significant. All analyses were made in triplicate. Analytical accuracy was verified using replicate determinations and Standard Reference Materials with percentages of recovery ranging between 90 and 99%.
Results Physical and chemical properties of the soil samples In the most of the soil samples, pH values ranged from neutral to alkaline; the lowest pH value was 7.4 in sampling point n° 5 (Table 1). Also, an oxidant environment in all soils samples was indicated by Eh values that range between 134 and 268 mV (Table 1). The organic matter content in soil samples from the reference area and station 9 was less than 10 g/kg. A maximum value of 41 g/kg was detected in station 6 (Table 1), in a soil ready for planting. Regarding the other sampling points, a large variation pattern was observed with cases where the organic matter content is similar in both layers of the soil (stations 1, 7, and 8), while in stations 2, 3, and 4, the second layer almost double the organic matter content of the first layer. Regarding electrical conductivity, considerable variation was observed. In the reference area and in stations 4, 7, and 9, the EC values were low (< 100 μS/cm) ranging between 36 and 39 μS/cm, 57–95 μS/cm, 102–134 μS/cm, and 132– 133 μS/cm, respectively. In station 5, the EC values were particularly high, ranging between 1861 and 2000 μS/cm, while in the other sampling points, the EC values were within the range of 200–1000 μS/cm (Table 1).
Environ Sci Pollut Res Table 1 Physical and chemical parameters of soil samples
Soil sample ID-depth (cm)
W (%)
OM (g/kg)
pH
EC μS/cm
Eh (mV)
Grain size < 0.074 mm (%)
Ref (0–10) Ref (10–20)
0.2 0.0
9 4
8.9 9.0
39 36
134.5 134.3
0 0
1 (0–10) 1 (10–20)
27.0 23.0
29 29
7.8 7.6
605 979
243.4 205.5
60 60
2 (0–10) 2 (10–20)
7.0 23
16 29
8.6 8.4
329 275
194.4 160.4
17 19
3 (0–10)
5.0
10
8.4
204
157.6
19
3 (10–20)
5.0
18
8.2
348
189.7
20
4 (0–10) 4 (10–20)
0.1 25.0
21 39
8.4 8.7
95 57
238.7 148.7
7 4
5 (0–10)
22.0
20
7.4
2000
184.1
35
5 (10–20) 6 (0–10)
22.0 14.0
26 41
7.6 8.4
1861 490
205.7 170.4
35 20
6 (10–20) 7 (0–10) 7 (10–20)
12.0 8.0 9.0
18 14 16
8.3 8.5 8.2
442 102 134
261.1 193.6 203.7
19 31 7
8 (0–10) 8 (10–20)
2.0 3.0
19 21
8.0 8.1
446 437
200.8 195.6
6 11
9 (0–10) 9 (10–20)
1.0 1.0
7 3
8.6 8.7
133 132
195.1 150.6
6 7
Ref reference area
Metal concentrations in soils
Metal concentrations in plants
In general, the reference samples showed the lowest concentration of these metals (Table 2). Some metals presented the highest concentrations in the top layer of the soil which is the case of Mn, while As and Zn are mainly accumulated in the second layer, i.e., 10–20 cm depth, although in 90% of the cases, the mean values were not significantly different at the 0.05 significance level. The remaining elements show an intermediate behavior, although in most cases, the differences between the concentrations observed in the layers were also not significantly different at the 0.05 significance level (Table 2). Regarding sampling points (stations), it can be observed that the highest As, Cu, Fe, Mn, Pb, and Zn levels were detected in stations 6, 9, 8, 4, 5, and 9, respectively. It is clear that the first three sampling points, as well as station 7, do not present a metal pollution load of particular concern. This conclusion is in agreement with the PLI values which indicate a moderate pollution degree with PLI values close to 2.5 (station 1 = 2.2; station 2 = 2.7; station 3 = 2.4; station 7 = 2.5). Conversely, stations 4, 6, 8, and 9 presented PLI values ranging between 3.6 and 4.1, while at station 5, a value of 3.1 was observed. Values of PLI < 1 suggest the absence of pollution, while higher values indicate a more polluted area.
Table 3 shows us the BAF values, i.e., the transfer of heavy metals from soil to edible plant parts. The trends in the BAF were clearly higher in station 1 with an elevated BAF value for copper (3.0) and zinc (1.3) in C. maxima and a 2.6 value for zinc in stations 3 and 4, for P. oleracea. The remaining values were < 1 regardless of the plants analyzed, although BAF values for Pb range between 0.77 and 0.88 (station 9), whereas BAF values for Zn range between 0.85 and 0.87 for onion bulb and cabbage leaf, respectively (station 7). According to Kabata-Pendias (2011), the copper critical concentration in plants (CCP) range between 15 and 20 μg g−1. In our case, the Cu levels detected in C. maxima collected in station 1 are approximately twice the maximum value—Cu levels range between 5.2 and 44.1 μg g−1, for B. rapa and C. maxima, respectively (Table 3). Zinc CCP values are within the range of 150–200 μg g−1, which is clearly above the levels observed in all the edible plants analyzed, although P. oleracea from station 3 exhibits an intermediate value of 177 μg g−1—the minimum value of 18.3 μg g−1 was observed in potatoes (Table 3). Iron concentrations range between 20.1 and 236 μg g−1, for A. cepa and C. maxima, respectively, thus indicating for the whole metals and plants a large variation pattern. With the exception of lettuce and potatoes, the levels of manganese exhibited a narrow range between 13.8 and 21.6 μg g −1, for cabbage and spinach,
CF
F
CF
CF
19.7 ± 3.2a 14.4 ± 3.0a 17.0
1.6 ± 0.07a* 9.3 ± 1.6b 5.4
226 ± 19.7a 158 ± 18.9b 192
0.60 ± 0.06a 0.42 ± 0.05b 0.51
9.0 ± 3.5a 2.0 ± 0.1b* 5.5
14.2 ± 2.7a 14.6 ± 2.7a 14.4 1.3 1.5 1.4 15.5 ± 5.6a 13.3 ± 5.5a 14.4 1.7 6.6 4.1 1.20 ± 0.08a 1.20 ± 0.08a 1.20 2.0 2.8 2.4 138 ± 18.1a 128 ± 18.1a 133 0.6 0.8 0.7 9.4 ± 2.9a 7.2 ± 2.9a 8.3 5.8 0.8 3.3 58.2 ± 4.2a 60.9 ± 4.3a 59.6 2.9 4.2 3.6 2.2
11.7 ± 2.6a 12.2 ± 2.6a 12.0 1.1 1.2 1.2 18.1 ± 5.6a 20.7 ± 5.7a 19.4 2.0 10.3 6.1 0.82 ± 0.07a 0.89 ± 0.07a 0.86 1.4 2.1 1.8 148 ± 18.2a 148 ± 18.2a 148 0.6 0.9 0.8 26.2 ± 3.2a 29.8 ± 3.3a 28.0 16.3 3.2 9.7 66.0 ± 4.4a 75.7 ± 4.5a 70.8 3.3 5.2 4.2 2.7
13.6 ± 2.7a 12.3 ± 2.6a 13.0 1.2 1.2 1.2 20.1 ± 5.7a 17.0 ± 5.6a 18.6 2.2 8.5 5.3 1.15 ± 0.08a 1.22 ± 0.08a 1.18 1.9 2.9 2.4 177 ± 19.1a 137 ± 18.1b 157 0.8 0.9 0.9 10.5 ± 2.9a 6.9 ± 2.8a 8.7 6.5 0.7 3.6 66.2 ± 4.4a 69.0 ± 4.4a 67.6 3.4 4.8 4.1 2.4
14.8 ± 2.7a 14.3 ± 2.7a 14.6 1.3 1.5 1.4 41.1 ± 6.0a 30.8 ± 5.9a 36.0 4.5 15.4 9.9 1.17 ± 0.08b 1.37 ± 0.10a 1.27 2.0 3.3 2.6 353 ± 24.2b 454 ± 27.5a 403.5 1.6 2.9 2.2 15.9 ± 3.0a 12.3 ± 3.0a 14.1 9.9 1.3 5.6 92.1 ± 5.1a 69.3 ± 4.4b 80.7 4.6 4.8 4.7 3.6
4
*
Values obtained by AAS with graphite furnace
PLI pollution load index, CF contamination factor
Means not followed by a common letter are significantly different at the 0.05 significance level
PLI
Zn
Pb
Mn
CF
Fe (%)
Cu
CF
11.0 ± 2.6a 9.7 ± 2.6a 10.3
3 10.3 ± 2.6a 10.7 ± 2.6a 10.5 0.93 1.1 1.0 23.6 ± 5.9a 24.3 ± 5.9a 24.0 2.6 12.1 7.3 0.91 ± 0.07a 0.92 ± 0.07a 0.92 1.5 2.2 1.8 137 ± 18.1a 124 ± 18.1a 130.5 0.6 0.8 0.7 38.6 ± 3.5a 40.0 ± 3.5a 39.3 24.1 4.3 14.2 111 ± 5.3a 115 ± 5.3a 113 5.6 8.0 6.8 3.1
5 35.2 ± 2.8a 38.5 ± 2.8a 36.8 3.2 3.9 3.6 18.3 ± 5.6a 23.1 ± 5.9a 20.7 2.0 11.5 6.7 2.59 ± 0.13a 2.67 ± 0.13a 2.63 4.3 6.4 5.3 240 ± 21.0a 248 ± 21.1a 244 1.1 1.6 1.4 9.6 ± 2.9a 12.1 ± 3.0a 10.8 6.0 1.3 3.6 95.0 ± 5.1a 102 ± 5.2a 98.5 4.8 7.0 5.9 4.0
6 11.0 ± 2.6a 11.7 ± 2.6a 11.3 1.0 1.2 1.1 13.5 ± 5.5a 20.8 ± 5.7a 17.1 1.5 10.4 5.9 0.98 ± 0.08a 0.96 ± 0.08a 0.97 1.6 2.3 2.0 162 ± 18.9a 176 ± 19.2a 169 0.7 1.1 0.9 18.2 ± 3.3a 15.9 ± 3.0a 17.0 11.3 1.7 6.5 57.9 ± 4.2a 60.6 ± 4.3a 59.2 2.9 4.2 3.6 2.5
7 20.5 ± 2.7a 20.6 ± 2.7a 20.6 1.8 2.1 2.0 36.4 ± 5.9a 38.5 ± 5.9a 37.4 4.0 19.2 11.6 1.57 ± 0.09a 1.56 ± 0.09a 1.56 2.6 3.7 3.2 244 ± 20.9a 233 ± 20.8a 238.5 1.1 1.5 1.3 13.7 ± 3.0a 14.1 ± 3.0a 13.9 8.5 1.5 5.0 115 ± 5.3a 117 ± 5.3a 116 5.8 8.1 7.0 3.8
8 19.6 ± 2.7a 17.0 ± 2.7a 18.3 1.8 1.7 1.8 71.6 ± 6.7a 37.5 ± 6.0b 54.6 7.9 18.7 13.3 1.19 ± 0.08a 1.07 ± 0.08a 1.13 2.0 2.5 2.2 255 ± 21.4a 205 ± 19.8b 230 1.1 1.3 1.2 28.2 ± 3.2a 18.0 ± 3.3b 23.1 17.6 1.9 9.7 187 ± 6.4a 85.7 ± 5.0b 137 9.4 6.0 7.7 4.1
9
89.2
18.1
206
1.30
26.9
16.8
Average stations 1–9
0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average 0–10 cm 10–20 cm Average
2
As
1
Depth
Metals
REF
Concentration of metals in soil samples (μg g−1 ± standard deviation) or in % (Fe); contamination factors (CF) are shown in different sampling points—stations 1 to 9; (n = 3)
Table 2
Environ Sci Pollut Res
Environ Sci Pollut Res Table 3 Copper, iron, zinc, lead, and manganese concentrations (μg g−1 ± standard deviation) in vegetables collected in different sampling points and the bioaccumulation factor (BAF); (n = 3)
Edible part
Cu
Fe
Zn
Pb
Cucurbita maxima
44.1 ± 5.1
BAF Brassica rapa
3.0 5.2 ± 0.1
BAF Portulaca oleracea BAF
236 ± 14
77.1 ± 3.6
0.019 68.9 ± 10
1.3 50.4 ± 2.8
0.27 16.2 ± 5.5
0.008 91.3 ± 13
0.71 177 ± 5.4
0.87
0.008
2.6
Portulaca oleracea
28.5 ± 5.4
689 ± 20
206 ± 5.6
BAF Brassica oleracea
0.79 13 ± 6.3
0.054 122 ± 10
2.6 54.3 ± 3.1
BAF Brassica oleracea
0.54 9.3 ± 2.2
0.013 98 ± 16
0.48 74.1 ± 10
BAF
0.45
0.004
0.75
Allium cepa BAF
10.8 ± 1.1 0.63
20.1 ± 1.9 0.002
50.3 ± 4.0 0.85
–
14.2 ± 0.9 0.084
7
Brassica oleracea BAF Brassica oleracea
6.3 ± 0.1 0.37 7.2 ± 0.3
57.7 ± 7.7 0.006 51.2 ± 4.8
51.4 ± 4.9 0.87 33.5 ± 2.7
–
7
–
16 ± 0.9 0.094 17.8 ± 1.4
BAF Solanum tuberosum
0.19 11.4 ± 2.1
0.003 35.3 ± 1.4
0.29 18.3 ± 3.0
17.9 ± 1.3
0.074 8.8 ± 0.9
9
BAF Spinacia oleracea
0.21 11.2 ± 3.8
0.003 166 ± 23
0.13 78.6 ± 9.6
0.77 19.9 ± 2.4
0.038 21.6 ± 1.8
9
BAF Lactuca sativa
0.20 8.7 ± 1.8
0.014 160 ± 19
0.57 49.4 ± 7.9
0.86 20.3 ± 1.6
0.094 57.7 ± 3.3
9
BAF
0.16
0.014
0.36
0.88
0.25
respectively (Table 3). Arsenic was never found in plant samples while Pb was detected in 25% of the samples, only (Table 3), with concentrations ranging from 17.9 μg g−1 in potatoes to 21.6 μg g−1 in lettuce which is probably related with the detection limits of the EDXRF apparatus, which are 3.0 μg g−1 for As and 8.0 μg g−1 for Pb. In this context, knowledge on diet composition and the metal contamination of foodstuff is of particular interest as well as the analysis of the EDI. Our EDI values (Table 4) are
Table 4 Estimated daily intake dose (EDI), in μg g−1 day−1, and tolerable upper intake levels (TUI) in mg day, of copper, iron, and zinc and manganese
Mn
Stations
–
14.9 ± 1.6
1
–
0.11 13.9 ± 1.1
2
–
0.094 19.5 ± 1.2
3
0.12 –
21.4 ± 2.0
4
–
0.053 15.4 ± 1.5
5
–
0.12 13.8 ± 1.3
6
0.056
8
calculated assuming an average European value of 220 g/day vegetables in the diet. In general, our EDI values are low, indicating that the TUI values derived (mg/day) are within the recommended levels. However, the TUI values for Cu and Fe for C. maxima from station 1, and the Zn TUI value for P. oleracea from station 3 are far above the recommended limits, thus indicating that those edible parts must be used with great caution (Table 4). Moreover, when we analyzed
Edible part
Cu
Cucurbita maxima
EDI 0.15
TUI 9.8
EDI 0.80
TUI 52
EDI 0.26
TUI 17
EDI 0.047
TUI 3.3
1
0.018 0.055 0.044 0.036 0.029 0.038 3.4
1.1 3.6 2.9 2.3 1.9 2.5
0.23 0.31 0.41 0.068 0.54 0.56 24
15 20 27 4.4 35 36
0.17 0.60 0.18 0.17 0.17 0.27 17
11 39 12 11 11 18
0.044 0.061 0.048 0.044 0.18 0.068 4.9
3.0 4.3 3.4 3.1 12.7 4.8
2 3 5 7 9 9
Brassica rapa Portulaca oleracea Brassica oleracea Allium cepa Lactuca sativa Spinacia oleracea TUI average—stations 1, 2, 3, 5, 7, 9 TUI recommended levels
5
Fe
45
Zn
25
Mn
11
Stations
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the metal load of P. oleracea collected in station 4, the results are even worse. This indicates that the TUI values will be higher than those reported for station 3. The accumulation of Mn by L. sativa (station 9) is a reason for concern because the TUI level is above the recommended level (Table 4). Thus, when the different plants and sampling points are taken into account, the TUI averages of Cu, Fe, Mn, and Zn are 3.4, 24, 4.9, and 17, respectively (Table 4). These values are below the recommended ones although the TUI Cu average was close to the limit, i.e., 3.4 versus 5.0.
Discussion Physical and chemical properties of the soil samples The very high EC values in station 5 indicates an excess of N based fertilizer or a high level of exchangeable sodium due to soil salinization (https://www.agriculturesolutions.com/ resources/92-the-why-and-how-to-testing-the-electricalconductivity-of-soils), although both situations might well coexist, i.e., salinization and excess of N. Furthermore, several empty sacs from different brands of ammonium sulphate were observed in the area, but without quantification of its use. At European level (EU-27), the use of N is expected to increase approximately 3.4% in the next 10 years. According to the last forecast, Portugal, Spain, and Italy are the countries where the increase in the consumption will be higher (https://www.fertilizerseurope.com/fileadmin/user_ upload/publications/agriculture_publications/Forecast_2012final.pdf). At national level, the Agricultural Statistics from 2017 point out to a consumption of 33 kg of N per hectare of utilized agricultural area with a net nitrogen balance in the soil of 117 thousand tons (INE 2018). Differences in the soil moisture are related with the fine particle size in the soil matrix and the organic matter content, as well as, the conditions of the soils at the time of the sampling events (irrigation, set aside, ready for planting). This is in agreement with the organic matter values (41 g/kg) detected in station 6—a land area ready for planting which probably indicates the previous addition of organic matter. The irrigation of the different parcels has its origin in the wells, which in turn also receive the contamination resultant of the agricultural practices. For example, the brand insecticide CLORFOS 48 is commonly used in the area and contain chlorpyrifos, an active substance under the surveillance of Portuguese authorities in waters for domestic use, in the Peninsula of Setúbal, i.e., in the area where our sampling points are included (http://www.ersar.pt/pt/site-comunicacao/ site-noticias/Paginas/lista-de-pesticidas-a-pesquisar-na-aguapara-consumo-humano-no-ano-2018.aspx). Other brands observed in the soil, as empty containers include the
insecticide FASTAC and the fungicide Mancozebe Selectis. All these small parcels have a clandestine nature; thus, the risk to the public health cannot be ignored by the authorities.
Metal concentration in soils The agricultural soils have been enriched with metals, such as Zn, Cu, As, Pb, and Fe by comparison with the reference area which is relatively free of these metals. Overall, there were no clear differences of metal concentrations between the studied layers. Bai et al. (2016) showed that Hg, Pb, Zn, and Cu were present in significantly higher concentrations in the topsoil than in deep soil layers, although the migration of metals to deeper horizons and the possible contamination of aquifers or water column is often ignored (Reboredo and Ribeiro 1984; Carrondo et al. 1984; Guerra et al. 2015). In some cases, our mean values are clearly above similar values found in agricultural soils in a Mediterranean area of Spain. In fact, Micó et al. (2006) observed that the mean values of Cu and Zn were 21.6 and 57.8 μg g−1, respectively. This somewhat contrasts with our results of 26.9 and 89.2 μg g−1 respectively. Conversely, Pb levels were similar in both agricultural areas—19.6 μg g−1 (Alicante, Spain) vs. 18.1 μg g−1 (Terras da Costa, Portugal). Also, Nunes et al. (2014), observed an average of 19.1 μg g−1 Pb in soils from Caia Irrigation Perimeter (Southern Portugal) albeit near the Portuguese-Spanish border. The same authors, however, found 16.7 μg g−1 Cu and 29.6 μg g−1 Zn, far below our results. Furthermore, the threshold and guideline values for metals in soils according to the Finnish standard values (MEF 2007) are As (5 μg g−1), Cu (100 μg g−1), Pb (60 μg g−1) and Zn (200 μg g−1), which are far above the concentrations observed in our soil with respect to Cu, Pb, and Zn and far below in the case of As. In the latter case, we had an average value of 16.8 μg g−1 As considering all the sampling points. Even our reference value (10.3 μg g−1 As) is higher than the Finnish standard value. This finding may well be related with the geological background or a possible atmospheric deposition as noticed by Nicholson et al. (2010) in England and Wales, since the reference area has no indication of historical agricultural activities in the present.
Metal concentration in plants Overall, a large variation pattern was observed in the metal accumulation by the different plant species, a conclusion also derived from the work of Pan et al. (2016). Regarding the BAF determination, our highest values were found in nonleafy vegetables (common purslane and pumpkin) and not in leaf vegetables as observed by Zhuang et al. (2009). It is well-known that soil pH is the most important factor controlling the mobility of heavy metals in soils. Zhao et al. (2012) when studying an area near Dabaoshan mine in China
Environ Sci Pollut Res Table 5 Heavy metal concentration in edible crops from other world areas, expressed in μg g−1 fresh weight (Refs. 1, 2, 3) or dry weight (Refs. 4, 5, 6, 7) Plant species
Cu
Allium cepa (urban)1
2.1–3.5 1.1–5.2 0.6–0.8 0.5–0.7 0.8–1.1 0.8–1.1 0.6 0.45 0.31
Allium cepa (rural)1 Cucurbita pepo (urban)1 Cucurbita pepo (rural)1 Brassica oleracea (urban)1 Brassica oleracea (rural)1 Brassica oleracea2 Brassica oleracea2 Brassica oleracea2 Brassica oleracea2 Allium cepa3 Allium cepa3 Brassica oleracea3 Brassica oleracea3 Allium cepa4 Allium cepa4 Spinacia oleracea4 Brassica rapa (tuber)4 Lactuca sativa cv gigante4 Cucurbita maxima4 cv coroa Spinacia oleracea5 Cucurbita pepo (urban)6 Lactuca sativa (urban)6 Allium cepa (urban)6 Cucurbita pepo (rural)6 Lactuca sativa (rural)6 Allium cepa (rural)6 Brassica rapa (tuber)7 Spinacia oleracea7 Cucurbita maxima7 Brassica oleracea7 Allium cepa7 Portulaca oleracea7 Lactuca sativa7 1
Roba et al. (2016)
2
Zhuang et al. (2009)
3
Harmanescu et al. (2011)
4
Furlani et al. (1978)
5
Gallardo et al. (2016)
6
Demirezen and Aksoy (2006)
7
Current work
Fe
0.53 0.43 1.37 1.36 2.77 12.2 8.8 13.6 8.0 9.4 7.3 17 43.1 59.9 53.8 32.1 45.4 37.5 5.2 11.2 44.1 13 10.8 16.2 8.7
15.26 4.65 60.11 31.53 74 69 248 64 925 75 174
68.9 166 236 22 20.1 91.3 160
Pb
Zn
0.5–6.4 0.6–1.7 0.2–0.4 0.2–0.3 0.6–1.0 0.6–0.9 0.23 0.10 0.01
7.7–56.1 7.3–27.3 3.2–8.7 2.2–4.0 4.2–5.7 4.2–5.2 8.96 13.8 7.38
0.16 0.50 0.13 0.90 0.25
7.2 9.7 8.7 4.3 4.4 6.0
4.99 10.91 2.01 16.30 8.51 50 56 37 42 116 30 103 13.8 39.5 21.3 117 218 116
19.9 – – – – 20.3
50.4 78.6 77.1 54.3 50.3 177 49.4
and the watershed basins of the Hengshi, Tielong, and Chuandu rivers observed that the areas with the highest human health risk do not directly coincide with the areas of highest heavy metal concentrations, but do coincide with the areas of lower soil pH.
At our neutral to alkaline pH values and under an oxidizing environment, the solubility of heavy metals in the soil solution tends to decrease with an increasing pH, thus reducing the plant uptake, particularly micronutrients. Nevertheless, even with these constraints, the common purslane and pumpkin are able to accumulate high mean concentrations of Fe (177 μg g−1) and Cu (44.1 μg g−1). When comparing our mean values with metal data in edible plant parts collected worldwide (Table 5), it seems that our results fall out of the intervals or averages defined by Zhuang et al. (2009), Harmanescu et al. (2011), and Roba et al. (2016), although their data was obtained on a fresh weight basis, while ours was based on a dry weight basis. In particular cases, our results are in good agreement with those reported by Gallardo et al. (2016) for spinach or onion cultivars—except for Fe (Furlani et al. 1978) or even pumpkin (Demirezen and Aksoy 2006). Nevertheless, there are major differences between the concentrations of certain elements and plants, according to their origin (urban or rural) and varieties used. For example, the Cu levels observed by Demirezen and Aksoy (2006), in C. pepo, L. sativa, and A. cepa were higher in rural areas than urban areas with values ranging from 32.1 to 59.9 μg g−1 in the whole plant, while the data from Furlani et al. (1978), Gallardo et al. (2016), and our own data indicate that the concentrations of Cu were in general < 17 μg g−1, except for the high value (44.1 μg g−1) observed in pumpkin (Table 5). Two particular cases present a reason for concern—the copper content of C. maxima and the zinc content of leaf/stem of P. oleracea. The leaves of B. oleracea, the edible tuber of B. rapa, and the bulb of A. cepa do not constitute a risk regarding metal load. The levels of Pb found in potatoes, spinach, and lettuce in station 9 must be monitored in the future and farmers should be warned of the health risk. This finding is probably related with an intensive use of copper and iron sulphates with high Pb concentrations as reported by GimenoGarcía et al. (1996), since we never detected Pb in other vegetables collected in the remaining sampling points. Regarding the determination of EDI values (mg kg−1 day−1), in particular cases, the EDI of a certain element may well be high than the recommended dose, although when the diet is diverse, this value is obviously diluted, unless centered in a quasi-single type of food, as it happens in Southeast Asia where the dependence of rice consumption drastically increases the risk of human disease due to the ingestion of arsenic (Hojsak et al. 2015). Thus, in the case of a diet rich in vegetables, it would be important to verify the contamination of different edible plants, especially if growing in heavy metal contaminated areas or in soils with low pH, and with high rates of fertilization. When comparing our EDI values expressed in μg g−1 day−1 with the oral reference doses (RfD) for Cu Fe, Mn, and Zn ( U S E PA 2 0 1 1 ) w h i c h a r e 0 . 0 4 μ g g − 1 d a y − 1 , 0.70 μg g−1 day−1, 0.14 μg g−1 day−1, and 0.3 μg g−1 day−1,
Environ Sci Pollut Res
respectively, it can be concluded that in the case of Cu our EDI values were in 42.8% of the cases higher than 0.04 μg g−1 day−1, being close in 28.6% of the cases. Regarding the RfD values for Fe, Mn, and Zn were in 85.7% of the cases higher than our EDI values, thus emphasizing the need of continuous surveillance of heavy metals, particularly copper. The EDI values were fundamental to the evaluation of TUI values (stations 1, 2, 3, 5, 7, and 9) considering a vegetable basket list that may well be included in the Portuguese diet. For expediency reasons, we left out some stations where the vegetables collected are already represented in other sampling points. S. tuberosum was not included in the basket list because the EDI calculus excludes starchy tubers such as cassava and potatoes. Our results (Table 4) indicate that in the case of C. maxima (pumpkin), the TUI value for Cu is of particular concern because is above the recommended value of 5 mg/day which agrees with the findings of Reboredo et al. (2018) who observed values ranging between 4.7 and 5.5 mg/day for C. pepo collected close to an area of intense mining activity. The same authors (Reboredo op. cit.) observed that all the Zn TUI values, for the different plant species (C. pepo, Phaseolus vulgaris, Lycopersicon esculentum, and Ficus carica and Citrus x sinensis fruits) are below the recommended value of 25 mg/day, whereas in the current work a noticeable high value was observed in P. oleracea (common purslane). Thus, both pumpkin and common purslane must be banned from soups or other type of dishes containing these vegetables due to the high concentrations of Cu (pumpkin) and Zn (common purslane), although other ingredients of the soup might lower the TUI levels to admissible levels, i.e., which do not exceed 5 and 25 mg/day, respectively.
Conclusions The soil samples collected at Terras da Costa, exhibit an enrichment by As, Cu, Fe, Mn, Pb, and Zn as a result of the continued use of fertilizers and pesticides for crop production. Pumpkin (Cucurbita maxima) collected in station 1 contained 44.1 μg g−1 Cu, a concentration well above the critical concentration in plants which range between 15 and 20 μg g−1, and an EDI dose of 0.15 mg kg−1 per day which corresponds to a TUI value of 9.8 mg/day, when the recommendation must not exceed 5.0 mg day. Similarly, Portulaca oleracea (common purslane) collected in station 3 contained 177 μg g−1 Zn, which corresponds to a TUI value of 39 mg/ day, when the recommendation must not exceed 25.0 mg day, which emphasizes the importance of diverse plant products in household menus. The farmers must be aware of the risk to the public health, due to the production of vegetables without the
best and safe agricultural practices, since these vegetables are commonly sold in local and regional markets. Acknowledgements The authors are grateful to anonymous reviewers for their constructive and helpful comments. Funding information This work was supported by national funds from Fundacão para a Ciência e a Tecnologia (FCT) through the research units UID/GEO/04035/2013 (GeoBioTec), UID/AGR/04129/2013 (LEAF), and UID/FIS/04559/2013 (LIBPhys), as well as through the grant SFRH/BPD/92455/2013 (Mauro Guerra).
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