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Impact of Deactivated Mine Waste Substrates on the Growth and Cu, As and Pb Accumulation in Tubers, Roots, Stems and Leaves of Three Solanum tuberosum L. Varieties

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  • New University of Lisbon, Faculty of Sciences and Technology

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Potato (Solanum tuberosum L.) is the world’s third most popular vegetable in terms of consumption and the fourth most produced. Potatoes can be easily cultivated in different climates and locations around the globe and often in soils contaminated by heavy metals due to industrial activities. This study assessed heavy metal accumulation in different organs of three S. tuberosum L. varieties (Agria, Désirée, and Red Lady) grown in different substrate formulations containing slag and waste from the Caveira polymetallic sulfite mine in Portugal. Results reveal that Cu, Pb, and As accumulation in the different organs of the plant depends on variety and substrate formulation, with tubers exceeding reference values from the literature. Tubers accumulated less Cu (varying between 17.3 and 32 mg/kg), Pb (varying between 5 and 27.6 mg/kg) and As (varying between 4 and 14.8 mg/kg) compared to other plant organs, and the Désirée variety exhibited high Pb (with a maximum of 27.6 mg/kg) accumulation in tubers compared to the remaining varieties. Although the phenological development of plants was not impacted, substrate formulation played a critical role in the plant’s metal uptake. The Agria variety presented a lower contamination risk in tubers, but potato cultivation in contaminated soils can present a risk to human health.
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Academic Editor: Valeria Spagnuolo
Received: 25 November 2024
Revised: 20 December 2024
Accepted: 13 January 2025
Published: 15 January 2025
Citation: Coelho, A.R.F.; Simões, M.;
Reboredo, F.H.; Almeida, J.; Cawina, J.;
Lidon, F. Impact of Deactivated Mine
Waste Substrates on the Growth and
Cu, As and Pb Accumulation in
Tubers, Roots, Stems and Leaves of
Three Solanum tuberosum L. Varieties.
Plants 2025,14, 230. https://
doi.org/10.3390/plants14020230
Copyright: © 2025 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/
licenses/by/4.0/).
Article
Impact of Deactivated Mine Waste Substrates on the Growth
and Cu, As and Pb Accumulation in Tubers, Roots, Stems and
Leaves of Three Solanum tuberosum L. Varieties
Ana R. F. Coelho 1,2 ,* , Manuela Simões 1,2 , Fernando H. Reboredo 1, 2,* , José Almeida 1,2 , Joaquim Cawina 1
and Fernando Lidon 1,2
1Earth Sciences Department, NOVA School of Sciences and Technology, Campus de Caparica,
2829-516 Caparica, Portugal; mmsr@fct.unl.pt (M.S.); ja@fct.unl.pt (J.A.); j.cawina@campus.fct.unl.pt (J.C.);
fjl@fct.unl.pt (F.L.)
2GeoBioTec Research Center, NOVA University Lisbon, 2829-516 Caparica, Portugal
*Correspondence: arf.coelho@fct.unl.pt (A.R.F.C.); fhr@fct.unl.pt (F.H.R.)
Abstract: Potato (Solanum tuberosum L.) is the world’s third most popular vegetable in
terms of consumption and the fourth most produced. Potatoes can be easily cultivated
in different climates and locations around the globe and often in soils contaminated by
heavy metals due to industrial activities. This study assessed heavy metal accumulation in
different organs of three S. tuberosum L. varieties (Agria, Désirée, and Red Lady) grown in
different substrate formulations containing slag and waste from the Caveira polymetallic
sulfite mine in Portugal. Results reveal that Cu, Pb, and As accumulation in the different
organs of the plant depends on variety and substrate formulation, with tubers exceed-
ing reference values from the literature. Tubers accumulated less Cu (varying between
17.3 and 32 mg/kg
), Pb (varying between 5 and 27.6 mg/kg) and As (varying between
4 and 14.8 mg/kg
) compared to other plant organs, and the Désirée variety exhibited high
Pb (with a maximum of 27.6 mg/kg) accumulation in tubers compared to the remaining
varieties. Although the phenological development of plants was not impacted, substrate
formulation played a critical role in the plant’s metal uptake. The Agria variety presented a
lower contamination risk in tubers, but potato cultivation in contaminated soils can present
a risk to human health.
Keywords: arsenic; Caveira mine; contaminated soils; copper; heavy metal accumulation;
lead; Solanum tuberosum L.
1. Introduction
Human health is closely related to the food people consume and, to some extent, to
the soil that produces it. Some solutions to human health problems can be probably solved
with agriculture through the production of food in a regenerative way, ensuring that human
health stems from soil health [
1
]. Soil is a complex biogeochemical system, performing
ecological, economic, social, and cultural functions that are relevant to human activity and
the survival of ecosystems [
2
]. Furthermore, soil plays a vital role in the production of
approximately 90% of human food resources and is essential, for example, for animal feed
as well [
3
], although soil coastal areas are also important to preserve for future generations,
as a buffer between land and water, although they are not used for food purposes [4].
Global demand for agricultural crops is increasing due to the increasing population [
5
],
resulting in a higher demand not only in agriculture but also in natural resources [
6
].
Plants 2025,14, 230 https://doi.org/10.3390/plants14020230
Plants 2025,14, 230 2 of 18
Consequently, there is a need to assess the accumulation of heavy metals in plants organs,
particularly in regions with higher concentrations of heavy metals in soils, which can pose
a potential risk to human health.
Several studies have been carried out in staple foods grown in soils contaminated with
heavy metals, such as rice cultivated in soil with different concentrations of Hg [
7
] and
corn, pea, goldenrod, and sunflower produced in a Pb-contaminated soil [
8
]. Additionally,
other studies have shown that plants are often contaminated by heavy metals from mining
and smelting operations. For instance, [
9
] demonstrated that untreated abandoned mines
can result in heavy metal accumulation (namely, Cu, As, and Pb) in vegetation. On the
other hand, in a study carried out by [
10
], twenty vegetables and their corresponding soils
were collected and analyzed, revealing the transfer of heavy metals from soil to vegetables,
with a decreasing tendency of Cd > Zn > Cu > Pb > Hg.
Moreover, heavy metal uptake by plant roots from contaminated soils can lead to
plant contamination and even excessive concentrations of these elements in food and feed
plants [11], potentially causing food safety issues [10].
In Portugal, one of the most well-known mines is “Mina da Caveira” or Caveira mine,
which initially operated in the open air but transitioned to underground exploration from
the 19th century onwards. The modern exploration of the Caveira mine began in 1854 with
the discovery of an iron hat (gossan), and mining consisted of the exploration of Cu, Pb,
and Zn, and, later, pyrite was explored for the manufacture of sulfuric acid. From 1936
onwards, the mine was explored to produce sulfur and sulfuric acid. However, mining
operations ceased in the 1960s [
12
]. The Caveira mine is currently known to have a huge
dump of waste rocks, tailings, and slag. Despite the area’s semi-arid climatic conditions,
the waste is considerably eroded by surface water, particularly during rain events.
Although deactivated, contaminated mining areas must be excluded for agricultural
practices, although they often occur with human health risks [
13
]. For example, Reboredo
et al. (2018) [
14
] observed the enrichment of Cu of several edible species, particularly in
the case of Ficus carica,Cucurbita pepo, and Phaseolus vulgaris, that were cultivated in the
vicinity of an important world copper deposit located in the so-called Iberian Pyrite Belt
was noted, concluding that the consumption of these species must be strongly reduced.
It is well known that soils contaminated by heavy metals such as As, Cu, or Pb
can cause metal toxicity and inhibit the growth and development of plants, promoting
cellular changes such as the distortion of chloroplast ultrastructure [
15
,
16
], promoting ionic
imbalances [
16
,
17
], inhibiting and/or reducing chlorophyll biosynthesis [
18
], or affecting
the photosynthetic apparatus by irreversibly binding the components of photosynthetic
electron transport chain [19], among other varied effects.
Potato (Solanum tuberosum L.) originated in South America and was introduced to
Europe through Spain [
20
]. Nowadays, it is the world’s third most popular vegetable in
terms of consumption and the fourth most produced [21]. As a versatile and nutritionally
rich crop, it offers a significant opportunity for controlling micronutrient malnutrition [
22
].
Furthermore, it serves as the basis for a wide range of processed food products.
A recent study carried out by Yang et al. (2020) [
23
] demonstrated that potato (S.
tuberosum L.) can be grown safely in artificially Hg-contaminated soils, suggesting that
potatoes can be considered a low-Hg-accumulating species, although yields in acidic soils
were lower than those in alkaline or neutral soils.
In the same context, it was observed that the ability of potato to uptake heavy metals
from the soil was poor, even with high levels of Cr, Ni, and As in the soils. Also, a high
As concentration in the soil could increase the content of Pb in potatoes; a lower pH was
beneficial to the accumulation of Cr and Ni in tubers [
24
], and high altitude is detrimental
to the accumulation of Zn and Cu.
Plants 2025,14, 230 3 of 18
Bedoya-Perales et al. (2023) [
25
], studying potato cultivars grown at different altitudes
in a typical mining region in Peru, concluded that potatoes grown at lower altitude ac-
cumulated more As, Cr, Ni, and Al than those grown at higher altitudes, while modern
cultivars show a higher metal content than native cultivars, in most cases.
In this framework, our research aims to assess the impact of different substrate for-
mulations using commercial soil substrata and soil nearby Caveira mine, enriched in Cu,
Hg, Pb, and As, on the vegetative development and their accumulation in the different
vegetative organs of three varieties of S. tuberosum L. (Agria, Désirée, and Red Lady) highly
produced in Portugal. The main goal is to understand the transfer of metals from soil to
plants and their potential accumulation in edible parts, particularly in potatoes.
2. Results
2.1. Mine Leachate
The leachate analysis from the Caveira mine (Table 1) revealed a chemical composition
indicative of a change in sulfides, namely a low pH value (pH = 3.03) and a high concentra-
tion of sulfate (436.80 mg/L), fluoride (145.42 mg/L), and potassium (18.97 mg/L). The
analysis also revealed the concentration of chloride (145.42 mg/L), sodium (82.96 mg/L),
calcium (38.23 mg/L), and magnesium (34.96 mg/L). The mean electrical conductivity was
1240 mS/cm.
Table 1. Physicochemical composition of the leachate sample average (n= 3) from the Caveira mine.
Parameters
Electric conductivity (mS/cm) 1240 ±0.01
pH 3.03 ±0.01
(mg/L) (mmol/L)
Sulfate 436.80 ±0.01 4.55 ±0.0001
Chloride 145.42 ±0.01 4.102 ±0.0003
Fluoride 5.64 ±0.01 0.297 ±0.0005
Potassium 18.97 ±0.09 0.485 ±0.0023
Magnesium 34.96 ±0.12 21.438 ±0.0049
Calcium 38.23 ±0.01 0.953 ±0.0002
Sodium 82.96 ±0.04 3.607 ±0.0017
2.2. Mine Waste and Substrate Formulation Characterization
The pH and electrical conductivity (EC) of the different substrate formulations were
measured before planting and after tuber harvest (Table 2). Before planting, the pH of the
different substrates varied between 6.7 and 7.3, with a tendency towards slight acidity in
the substrates with composites 1 and 2, compared to the control substrate pots, which had
an average pH of 7.0. The lowest pH value of 6.6 was obtained in pot 15 (composite 1),
while the highest pH of 7.4 was recorded in pot 5 (Cu-enriched substrate). After harvest,
there was acidification in all the substrate formulations, with pH values varying between
6.1 and 6.4 (overall for the three varieties). The lowest pH was 6.0, observed in pots 5 and 11.
The EC of the substrates varied between 44 and 152 mS/cm before planting and between
32 and 1990 mS/cm after harvest. The highest value was obtained in the control substrate,
both before planting and after harvest, as soluble salts predominate in this composition.
Plants 2025,14, 230 4 of 18
Table 2. pH and electrical conductivity (EC) (mS/cm) in the different substrate formulations, before
plantation (BP) and after tuber harvest (AH).
Plot/Substrate Formulations/Variety BP AH
pH EC pH EC
1
Control substrate
Agria 7.0
7.0 *
152
148 *
6.3
6.4 *
164
170 *
2 Désirée 7.1 148 6.6 148
3 Red Lady 6.9 145 6.5 199
4
Cu-enriched substrate
Agria 7.1
7.1 *
132
86 *
6.4
6.2 *
95
85 *
5 Désirée 7.4 65 6.0 89
6 Red Lady 6.8 62 6.3 72
7
Substrate less enriched in Cu and Pb
Agria 7.0
6.9 *
62
108 *
6.1
6.3 *
77
69 *
8 Désirée 7.0 127 6.2 74
9 Red Lady 6.7 135 6.7 56
10
Substrate enriched in Pb and Hg
Agria 7.3
7.1 *
72
85 *
6.2
6.1 *
148
100 *
11 Désirée 6.8 70 6.0 76
12 Red Lady 7.2 114 6.3 76
13
Substrate with composite 1
Agria 7.1
6.8 *
59
64 *
6.3
6.3 *
90
66 *
14 Agria 7.1 62 6.4 71
15 Désirée 6.6 59 6.4 85
16 Désirée 6.7 67 6.2 43
17 Red Lady 6.7 59 6.3 39
18 Red Lady 6.7 79 6.3 68
19
Substrate with composite 2
Agria 7.0
6.9 *
90
72 *
6.2
6.1 *
52
45 *
20 Agria 7.1 44 6.2 55
21 Désirée 6.7 63 6.3 35
22 Désirée 6.9 66 6.1 61
23 Red Lady 6.9 87 6.2 33
24 Red Lady 7.0 65 6.1 39
25
Substrate with composite 3
Agria 6.9
7.1 *
74
66 *
6.2
6.1 *
32
39 *
26 Désirée 7.1 62 6.1 44
27 Red Lady 7.3 63 6.1 42
* Average value of the different pots.
2.3. Cu, Pb, Hg, and As Content in Mine Waste and Substrate Formulations
The analysis of Cu, Pb, Hg, and As of mine waste samples from sites A, B, and C
(Table 3) revealed substantial variation in Cu concentrations. Site A exhibited higher Cu
levels (4.39 mg/kg), surpassing those of site B (0.12 g/kg) and C (0.61 g/kg) by 37-fold and
7-fold, respectively.
Upon incorporating these mine wastes into the agricultural substrate, the Cu con-
centration increased in proportion to the quantity added, as evidenced by comparation
with control samples (0.02 g/kg) (Table 3). In substrate formulations containing equal
proportions of site A mine waste, pots 4 to 6 and 25 to 27 showed 50-fold (0.99 g/kg)
and 68-fold (1.36 g/kg) increases, respectively. Moreover, pots 13 to 24 demonstrated
34-fold and 48-fold Cu increase in pots with composite 1 and 2, respectively; moderate
increases were observed in pots 10 to 12 (9-fold). In pots 7 to 9, the addition of mine waste
material with a lower initial Cu content resulted in a 2.5-fold increase, relative to the control.
Plants 2025,14, 230 5 of 18
Comparing the analysis of Cu concentrations in substrate formulations before planting and
after harvest revealed a general declining trend across most substrate formulations (except
for pots 4 to 6, which exhibited an increase in Cu concentration, and for control pots which
maintained stable concentration). The most pronounced reduction occurred in pots with
composite 2, showing an approximately 36% decrease in Cu content, and the remaining
pots displayed a decrease around 20% (specifically of 20%, 22%, 26%, and 23%).
Lead analysis (Table 3) revealed that the mine waste sample of site C contained the
highest Pb concentration (9.31 g/kg), followed by site A (4.78 g/kg) and site B (1.68 g/kg).
The incorporation of mine waste into the agricultural substrate increased Pb levels from
non-detectable concentrations by the XRF analyzer to a range of 0.69–2.39 g/kg. This
increase was greater in pots 19 to 27 (which had more mine waste added to the substrate),
and lower in pots 7 to 9. Moreover, post-harvest analysis indicated a general reduction
in Pb concentrations, which was non-detectable by the XRF analyzer in control substrate.
In pots 4 to 6, there was an increase in concentration (as occurred with Cu) and, in the
remaining pots, there was a variation in Pb decrease: 20% in pots 10 to 12 (mine waste
enriched in Pb and Hg), 27% in pots 25 to 27 (substrate with composite 3), 29% in pots 13 to
18 (substrate with composite 1), and 40% in both pots 7 to 9 (substrate with mine waste less
enriched in Cu and Pb) and pots 19 to 24 (residues with composite 2).
Arsenic analysis (Table 3) revealed high concentrations in mine waste from sites A
and C (0.90 and 0.80 g/kg, respectively), while site B exhibited lower levels (0.48 g/kg).
In the control substrate, the As concentration was below the XRF analyzer’s detection
limit. The remaining pots showed initial As concentrations (before planting) ranging
from
0.19 g/kg
to 0.49 g/kg, which decreased from 0.16 g/kg to 0.36 g/kg after harvest.
Substrates with mine waste enriched in Pb and Hg and composites 1, 2, and 3 showed
the highest concentrations of As before planting. Furthermore, As levels demonstrated a
correlation with the proportion of mine waste incorporated into the substrate. Post-harvest
analysis revealed a decrease in As content in all the pots, with the percentage of decrease
being greater in pots 13 to 18 and 19 to 24 at 47% and 40%, respectively, with the substrate
and composites 1 and 2; 26% in pots 25 to 27 (substrate with composite 3); 14% and 15% in
pots 10 to 12 and 7 to 9 (substrate with mine waste from sites C and B, respectively); and
4% in pots 4 to 6 (substrate with mine waste from site A).
Mercury analysis (Table 3) revealed quantifiable concentrations (above the detection
limit of the XRF analyzer) only in mine waste from site C (0.15 g/kg) and in substrate
formulations where this mine waste was added (pots 10 to 27). Among these pots, pots
containing composite 2 exhibited the highest Hg concentrations. Moreover, post-harvest
analysis demonstrated a reduction in Hg concentrations of 9.5% in pots 25 to 27; 17% in pots
10 to 12; 22% in pots 19 to 24; and 27% in pots 13 to 18. Thus, pots containing composite
1 achieved the greatest percentage reduction in Hg content, while those pots containing
composite 3 showed the lowest reduction in Hg content.
Table 3. Copper, Pb, Hg, and As average content (n= 4) (g/kg) in mine waste (sites A, B, and C) and
in the different substrate formulations, before plantation (BP) and after tuber harvest (AH). Letters
(A, B, and C) express significant differences between the sites for each mineral element (Cu, Pb, Hg,
and As) and letters (a, b, c, and d) express significant differences between substrate formulations for
each mineral element before plantation and after tuber harvest.
Site/Pot Substrate
Formulations Cu Pb Hg As
BP AH BP AH BP AH BP AH
Site A Cu-enriched
mine waste 4.39 ±0.02 A - 4.78 ±0.01 B - * - 0.90 ±0.02 A -
Site B Cu and Pb
less enriched
mine waste
0.12 ±0.01 C - 1.68 ±0.01 C - * -
0.48
±
0.006 C
-
Plants 2025,14, 230 6 of 18
Table 3. Cont.
Site/Pot Substrate
Formulations Cu Pb Hg As
BP AH BP AH BP AH BP AH
Site C Pb- and
Hg-enriched
mine waste
0.61 ±0.02 B - 9.31 ±0.01 A - 0.15 ±0.01 A - 0.80 ±0.03 B -
1–3 Control
substrate 0.02 ±0.005 d 0.02 ±0.005 b * * * * * *
4–6 Cu-enriched
substrate 0.99 ±0.01 ab 1.05 ±0.01 a 0.88 ±0.01 c 0.93 ±0.01 ab * * 0.22 ±0.01 a 0.21 ±0.01
7–9 Substrate less
enriched in
Cu and Pb 0.05 ±0.006 d 0.04 ±0.006 b 0.69 ±0.1 c 0.41 ±0.005 b * * 0.19 ±0.01 a 0.16 ±0.01 ab
10–12 Substrate
enriched in
Pb and Hg 0.18 ±0.03 dc 0.14 ±0.01 b 1.41 ±0.3 bc 1.12 ±0.01 ab 0.029 ±0.01 a 0.024 ±0.001 a 0.28 ±0.01 a 0.24 ±0.01 b
13–18 Substrate
with
composite 1 0.69 ±0.02 bc 0.51 ±0.01 ab 1.33 ±0.03 bc 0.94 ±0.01 ab 0.022 ±0.005 ab 0.016 ±0.001 ab 0.42 ±0.01 a 0.22 ±0.01 ab
19–24 Substrate
with
composite 2 0.96 ±0.02 ab 0.61 ±0.01 ab 2.24 ±0.03 ab 1.31 ±0.01 a 0.027 ±0.003 a 0.021 ±0.001 ab 0.44 ±0.01 a 0.26 ±0.01 ab
25–27 Substrate
with
composite 3
1.36 ±0.03 a 1.04 ±0.01 a 2.39 ±0.02 a 1.73 ±0.01 a 0.021 ±0.001 ab 0.019 ±0.001 ab 0.49 ±0.01 a 0.36 ±0.01 a
* Under the limit of detection of the XRF analyzer; “-” means not applicable. For each mineral element, different
statistical letters express significant differences between pots (a, b) or between sites (A, B).
2.4. Cu, Pb, Hg, and As Content in Solanum tuberosum L. Organs
Analysis of Cu, Pb, As, and Hg accumulation in the different post-harvest vegetative
organs revealed distinct distribution patterns (Table 4). Mercury was never detected in
both substrate formulations and plant organs. Similarly, in control substrates, both Pb and
As concentrations in the different organs were below the XRF detection limit (6 mg/kg).
Arsenic was detected (Table 4) in the leaves of all three varieties, in Red Lady stems
(6.0 mg/kg), and in Désirée tubers (4.5 mg/kg), for non-control substrate formulations.
Lead was quantified in the roots and stems of all varieties, as well as in Red Lady tubers
(5.0 mg/kg) and leaves (14.3 mg/kg) (Table 4). Notably, higher Pb and As concentra-
tions were observed in plant roots from pots 4 to 6, with lower concentrations in the
remaining organs.
Copper was quantified in all substrate formulations, varieties, and plant organs
(Table 4), exhibiting a specific accumulation pattern regarding the different plant organs.
The highest Cu concentration was found in the leaves, followed by the roots, stems, and
tubers. Among varieties, Désirée leaves showed the highest Cu accumulation, while Agria
tubers showed the lowest Cu concentration. The Cu-enriched substrate showed the highest
Cu content in the leaves of the Agria variety (109 mg/kg) and in the roots of the Red Lady
variety (109 mg/kg). The general distribution pattern showed higher Cu concentrations in
leaves and roots compared to stems and tubers.
In substrates less enriched in Cu and Pb, Cu concentrations were highest in Agria
leaves, stems, and roots and in Désirée tubers. Lead was quantified in the roots
of all three varieties, with Agria and Désirée showing similar, higher concentrations
(
50.3 and 50.4 mg/kg
, respectively). Moreover, Pb was only quantified in Désirée and
Red Lady tubers.
Considering the substrate enriched in Pb and Hg, Désirée showed the highest Cu
levels in leaves, stems, and roots. Red Lady leaves were the only ones to show quantifiable
Pb (compared to the remaining varieties), while roots across all varieties had the highest
Pb levels, particularly in Désirée. Arsenic was detected in the roots of all varieties, with
Désirée variety showing the highest concentration (44.3 mg/kg) and the lower content
being found in Red Lady (19.3 mg/kg). Tubers from the Désirée and Red Lady varieties
showed a concentration of As between 4 and 6 mg/kg.
Plants 2025,14, 230 7 of 18
Table 4. Copper, Pb, and As average content (n= 4) (mg/kg) in the different organs (tubers/potatoes, roots, stems, and leaves) of Solanum tuberosum L. from Agria
(A), Désirée (D), and Red Lady (RL) varieties, after tuber harvest, from the different substrate formulations (S).
Pot SF VTubers Roots Stems Leaves
Cu Pb As Cu Pb As Cu Pb As Cu Pb As
1
Control
substrate
A18.7 ±1.4 cd * * 34.6 ±4.0 hi * * 26.0 ±2.0 ab * * 81.3 ±6.5 bc * *
2 D 20.7 ±1.8 abcd * * 42.3 ±3.4 ghi *6±0.4 gh 54.3 ±6.3 a * * 87.0 ±2.6 bc * *
3 RL 24.7 ±0.8 abcd * * 34.0 ±3.5 hi * * 34.3 ±2.1 ab * * 65.6 ±8.0 c * *
4
Cu-enriched
substrate
A31.0 ±1.7 ab * * 101 ±6.3 bcd 50.0 ±1.0 ih 45.0 ±1.1 cd 39.6 ±8.8 ab 10.3 ±1.4 e * 109 ±4.1 abc *9.3 ±1.2 b
5 D 25.7 ±3.3 abcd *4.5 ±0.4 bc 84.0 ±1.7 cdef 50.3 ±2.8 ih 22.0 ±2.6 efg 37.0 ±3.4 ab 8.0 ±0.8 e * 74.0 ±5.5 bc * 7.0 ±0.8 c
6 RL 29.7±4.7 abc 5.0 ±0.1 e * 109 ±5.5 abc 83.6 ±2.0 hgf 44.0 ±1.4 cd 26.0 ±2.0 ab 12.0 ±1.1 e 6.0 ±0.4 a 97.0 ±6.0 abc 14.3 ±1.7 ab 14.0 ±1.1 a
7Substrate less
enriched in Cu
and Pb
A18.7 ±1.3 cd * * 29.3 ±0.8 i 50.3 ±0.8 ih 19.0 ±1.1 fg 39.5 ±7.7 ab * * 112 ±3.9 abc * *
8 D 22.3 ±0.3 abcd 5±0.4 e * 28.7 ±1.4 i 50.4 ±2.3 ih 14.6 ±2.6 gh 22.0 ±2.8 b * * 73.0 ±1.5 bc * *
9 RL 17.3 ±0.8 d 5.5 ±0.4 e * 26.3 ±3.3 i 33.7 ±1.7 ij 12.3 ±0.8 ghi 24.6 ±4.3 ab * * 74.6 ±3.4 bc * *
10 Substrate
enriched in Pb
and Hg
A22.0 ±0.02 abcd 6±0.4 e * 25.0 ±1.1 i 92.0 ±0.5 efg 35.3 ±2.0 cde 28.3 ±1.8 ab 8.50 ±0.4 e * 75.7 ±3.3 bc * *
11 D 22.6 ±0.02 abcd 19.7 ±1.2 bc 6 ±0.4 b 38.3 ±6.1 hi 117 ±2.3 def 44.3 ±1.8 cd 28.6 ±3.8 ab 19.3 ±1.2 d *76.3 ±2.4 bc * 7.6 ±0.6 c
12 RL 23.0 ±0.01 abcd 13.0 ±0.4 c 4 ±0.4 c 31.6 ±5.1 hi 79.0 ±1.1 fgh 19.3 ±0.8 fg 26.3 ±0.8 ab 11.7 ±0.8 e * 72.3 ±4.9 bc 11.0 ±0.8 b 6.5 ±0.4 c
13–14
Substrate with
composite 1
A26.8 ±0.02 abcd 6±0.4 e * 62.8 ±3.0 fgh 62.8 ±1.8 ghi 21.8 ±2.7 efg 35.3 ±5.4 ab 12.5 ±0.4 e * 106 ±5.5 abc 10.3 ±1.2 b 6.0 ±0.4 c
15–16 D 23.6 ±0.01 abcd 5±0.4 e 6±0.4 b
97.5
±
0.7 bcde
145 ±2.3 cd 47.6 ±2.1 c 44.1 ±4.7 ab 10.8 ±0.6 e * 135 ±3.1 ab * 6.0 ±0.4 c
17–18 RL 23.8 ±0.02 abcd 9 ±1.5 d *116 ±5.6 ab 193 ±1.1 b 63.6 ±1.8 b 47.5 ±3.5 ab 25.3 ±2.1 c 9.8 ±1.2 a 123 ±2.1 ab 11.0 ±1.5 b 7.5 ±0.8 c
19–20
Substrate with
composite 2
A23.3 ±0.01 abcd 9.4 ±1.0 d 4±0.4 c 69.5 ±3.5 efg 84.9 ±2.7 fgh 32.6 ±1.5 def 34.6 ±2.3 ab 18.2 ±2.8 d 11.0 ±0.8 a 88.3 ±5.1 bc * 6.5 ±0.4 c
21–22 D 30.3 ±0.02 ab 23.8 ±0.4 b 6.5 ±1.2 b 77.5 ±4.1 def 125 ±1.4 cde 34.6 ±2.1 cde 40.3 ±1.5 ab 30.5 ±1.3 b *166 ±2.8 ab 16.6 ±1.5 a *
23–24 RL 24.6 ±0.02 abcd 5.3 ±1.5 e 14.8 ±0.4 a 122 ±5.1 ab 237 ±4.3 a 82.2 ±3.9 a 52.7 ±3.0 a 40.5 ±2.7 a 10.7 ±0.8 a 192 ±4.3 a 8.5 ±0.8 c *
25
Substrate with
composite 3
A21.3 ±0.01 abcd 6.7 ±0.3 e * 86.7 ±7.4 cdef 137 ±2.3 bc 42.0 ±2.3 cd 51.3 ±2.9 ab 35.3 ±2.0 b 15.0 ±0.8 a 67.6 ±4.6 bc * *
26 D 32.0 ±0.01 a 27.6 ±0.3 a 6.3 ±0.3 b
94.3
±
2.6 bcde
141 ±3.3 cd 43.7 ±2.3 cd 42.6 ±3.3 ab 31.0 ±1.0 b *74.0 ±11 bc 8.0 ±0.8 c *
27 RL 27.3 ±0.01 abc 9.0 ±0.5 d * 131 ±3.7 a 163 ±3.7 bc 48.0 ±2.0 c 53.7 ±3.1 a 27.3 ±0.8 c 10.0 ±0.4 a 79.0 ±3.6 bc * *
* Under the limit of detection of the XRF analyzer. For each mineral element, different statistical letters express significant differences between pots.
Plants 2025,14, 230 8 of 18
The composite-1 substrate (pots 13 to 18) showed Cu accumulation in the following
pattern: leaves > roots > stems > tubers. Agria tubers had the highest Cu concentration
(26.8 mg/kg), and Pb was detected in all organs except in Désirée leaves. Arsenic was
quantified in the roots and leaves of all varieties, with Red Lady roots showing the highest
concentration (63.6 mg/kg) and Agria and Désirée leaves showing the lowest (6.0 mg/kg).
Only Désirée tubers and Red lady stems contained quantifiable As, being, respectively,
6 mg/kg and 9.8 mg/kg.
Considering composite 2, tubers and roots of all varieties grown in that substrate
formulation showed quantified levels of Cu, Pb, and As. Désirée tubers showed the
highest Cu and Pb concentrations, while Red Lady tubers had the highest As (14.8 mg/kg).
Red lady roots showed the highest Cu, Pb, and As levels. The highest Cu concentration
was obtained in Red Lady leaves (192 mg/kg), followed by Désirée leaves (166 mg/kg).
Regarding stems, Agria showed a lower Pb content, and Désirée was the only variety with
an As content under the detection limit of the XRF analyzer. Moreover, Agria showed an
As content of 6.5 mg/kg in the leaves and a Pb content under the device’s detection limit.
In composite 3 (pots 25 to 27), the Red Lady variety presented the highest Cu content in
leaves, stems, and roots, while Désirée had the highest content in tubers. Lead was detected
in the tubers, roots, and stems of all varieties, with the highest concentrations in Agria stems
(35.3 mg/kg), Red Lady roots (163 mg/kg), and Désirée tubers (27.6 mg/kg). Arsenic was
detectable in the roots of all varieties, with Red Lady showing the highest concentration
compared to the remaining varieties (48 mg/kg); was not quantified in the leaves of
the three varieties; and was quantified in Agria and Red Lady stems (
15 and 10 mg/kg
,
respectively) and in Désirée tubers (6.3 mg/kg).
Statistical analysis of element correlations between the different substrate formulations
and plant organ accumulation (tubers, roots, stems, and leaves) is present in Tables 57.
The relationship between substrates and organs’ metal concentrations was evaluated using
both Person and Spearman correlation coefficients, providing a comprehensive assessment
of metal translocation patterns.
The concordance between both Pearson and Spearman correlations indicates robust
relationships not affected or influenced by potential outliers or anomalous values.
Copper demonstrated moderate/medium to strong/high correlations between sub-
strate concentrations and accumulation in roots and tubers, while correlations with stem
and leaf concentrations were residual to zero (Table 5).
Table 5. Pearson (lower half) and Spearman (upper half) correlations between Cu concentrations
measured in soils and those in plant organs (tubers, roots, stems, and leaves) in the 27 pots.
Substrate BP Substrate AH Average of Substrates Tubers Roots Stems Leaves
Substrate BP 1 0.80 0.93 0.62 0.71 0.39 0.31
Substrate AH
0.67 1 0.95 0.57 0.81 0.48 0.19
Average of
substrates 0.93 0.90 1 0.60 0.78 0.44 0.20
Tubers 0.51 0.53 0.57 1 0.42 0.19 0.30
Roots 0.72 0.80 0.83 0.42 1 0.56 0.48
Stems 0.42 0.46 0.48 0.14 0.57 1 0.28
Leaves 0.33 0.09 0.24 0.32 0.41 0.29 1
Lead exhibited moderate/medium to strong/high correlations with stem, root, and
tuber concentrations, whereas leaf correlations remained residual or minimal (Table 6).
Plants 2025,14, 230 9 of 18
Table 6. Pearson (lower half) and Spearman (upper half) correlations between Pb concentrations
measured in soils and those in plant organs (tubers, roots, stems, and leaves) in the 27 pots.
Substrate BP Substrate AH Average of Substrates Tubers Roots Stems Leaves
Substrate BP 1 0.71 0.95 0.82 0.70 0.79 0.35
Substrate AH
0.68 1 0.87 0.63 0.82 0.89 0.36
Average of
substrates 0.95 0.88 1 0.78 0.79 0.87 0.36
Tubers 0.64 0.51 0.64 1 0.59 0.73 0.35
Roots 0.66 0.76 0.76 0.45 1 0.84 0.41
Stems 0.66 0.81 0.79 0.59 0.82 1 0.44
Leaves 0.18 0.37 0.28 0.44 0.33 0.44 1
Arsenic showed average correlations between the concentration in substrates and that
in roots, while correlations with the remaining organs were residual (Table 7).
Table 7. Pearson (lower half) and Spearman (upper half) correlation between As concentrations
measured in soils and those in plant organs (tubers, roots, stems, and leaves) in the 27 pots.
Substrate BP Substrate AH Average of Substrates Tubers Roots Stems Leaves
Substrate BP 1 0.70 0.96 0.32 0.57 0.42 0.02
Substrate AH
0.43 1 0.81 0.38 0.75 0.49 0.12
Average of
substrates 0.94 0.72 1 0.30 0.61 0.38 0.04
Tubers 0.09 0.38 0.22 1 0.33 0.10 0.16
Roots 0.33 0.69 0.52 0.38 1 0.60 0.26
Stems 0.19 0.44 0.31 0.07 0.63 1 0.02
Leaves 0.02 0.08 0.04 0.03 0.19 0.04 1
Table 8presents, for each element (Cu, Pb, and As) and variety, the quotients calculated
between the amounts of heavy metals in plant organs and those in the substrate (average
between BP and AH substrates), with maximum values highlighted in bold. Analysis of
metal-specific translocation patterns revealed distinct accumulation across plant organs
and varieties. Copper exhibited a systematic organ-specific accumulation, with greater
accumulation in leaves, followed by roots and, to a lesser extent, stems and tubers. Among
varieties, Désirée and Red Lady demonstrated enhanced Cu accumulation in both leaves
and roots compared to Agria. Lead demonstrated preferential root accumulation, with
lower translocation in the remaining organs, indicating a very differentiated accumulation.
Similarly, As displayed predominant root accumulation, with less in the remaining organs,
with minimal to negligible differences in accumulation between varieties.
Table 8. Average quotients between Cu, Pb, and As contents in plant organs (tubers, roots, stems, and
leaves) and those in substrates (average between values before planting and after harvest, carried out
with the mean value of 9 pots).
Element Variety Tubers Roots Stems Leaves
Cu
Agria 0.042 0.110 0.069 0.168
Désirée 0.043 0.134 0.075 0.190
Red Lady 0.041 0.133 0.056 0.182
Plants 2025,14, 230 10 of 18
Table 8. Cont.
Element Variety Tubers Roots Stems Leaves
Pb
Agria 0.006 0.080 0.013 0.005
Désirée 0.008 0.086 0.016 0.004
Red Lady 0.008 0.091 0.013 0.005
As
Agria 0.013 0.129 0.016 0.016
Désirée 0.013 0.131 0.018 0.016
Red Lady 0.012 0.140 0.019 0.018
3. Discussion
Among the studied elements As, Pb, and Hg are considered non-essential for human
metabolism; thus, their toxicity depends on multiple interacting factors varying from mild
to chronic or even acute toxicity and death [26].
Conversely, Cu is considered an essential element to human physiology, being found
in various foods in the daily diet, such as meats, seafood, vegetables, cereals, and nuts [
27
].
Although the incidence of Cu toxicity in the general population is lower, the excess
of Cu ions in cells is detrimental due to the appearance of free radicals and increase in
oxidative stress, while its deficiency may cause or aggravate certain diseases such as Menkes
disease, Wilson disease, neurodegenerative diseases, and cardiovascular diseases [28].
Drainage from abandoned mines impacts water in mining regions [
29
], and the ex-
traction of sulfides (mainly pyrite) from Caveira mine generates acid mine drainage with
lower pH values (1.5–3.0) and high heavy metal concentrations [
30
]. Our mine leachate
was characterized (Table 1), revealing a pH of 3, in agreement with other values reported
in acid mine drainage studies, also in Caveira mine, which exhibited pH values between
2.5 and 2.7
and between 1.1 and 2.0, in two distinct sampling points. Silva et al. (2015) [
12
]
and Smith et al. (2022) [
31
] reported values less than 3 in an acid mine drainage in a coal
mining region in South Africa.
The sulfate levels noted by Silva et al. (2015) [
12
] are in the range of 756–906 mg/L in
one sampling point, whereas those in the second one range between 9066 and 49,920 mg/L,
far from our mean value—437 mg/L (Table 1). However, it is important to consider the
season in which the samples were collected, the different sampling sites, and the methods
used in both studies.
Regarding EC, our data (Table 1) showed a higher value compared to the reference
for acid mine drainage in Caveira mine [
12
] and to another mine leachate located in
Portugal [32].
According to Cravotta (2008) [
33
], dissolved sulfate is a concern in abandoned mine
discharges, especially in low-pH solutions, posing risks to ecosystems and wildlife. Low pH
levels promote the dissolution of metals and metalloids, while high sulfate concentrations
can also intensify corrosion [
31
]. These factors together exacerbate the risks of the water
leachate and the surrounding areas, it being crucial to implement control measures/actions
and mitigate potential environmental risks.
The pH levels of all the substrate formulations (Table 2) are indicated for potato
growth—between 5.7 and 8.4 [
34
]—with the ideal pH being between 6 and 7 [
35
]. According
to our data (Table 2), there was a slight acidification tendency in the substrates with higher
concentrations of mine waste before plantation due to the soil type and an acidification in
all the substrate formulations post-harvest, likely due to mineral uptake by plants being
within the pH range (before plantation) that is adequate for plant nutrient availability [
35
].
According to our data (Table 3), relative to the three sampling sites of mine waste,
site A had the highest concentration of Cu, Pb, and As. Post-harvest data of Cu, Pb,
Plants 2025,14, 230 11 of 18
As, and Hg concentrations (Table 3) showed a general declining trend across substrate
formulations. This change can be explained by different processes like plant strategies and
mechanisms to deal with the presence of heavy metal (i.e., by cell sequestration or binding
of heavy metals in different structures) [
36
], due to absorption mechanisms—the pathway
of mineral elements (being selectively absorbed or diffused from the soil by roots) [
37
] or
metal leaching [38].
Despite it being considered an essential element for the growth and development of
crops, copper toxicity may occur due to its greater availability [
39
] as it occurs in acidic soils.
According to Kabata-Pendias (2011) [
40
], Cu in soils varies between 14 and 109 mg/kg;
thus, except for the control substrate, all the three sites and the substrate formulations
showed a higher Cu content (Table 3). Moreover, some of the values are similar to the ones
obtained in rocks (317 mg/kg) and in an old slag mine site of Caveira mine (1736 mg/kg
and >10,000 mg/kg) [30].
Except for the controls, all the substrate formulations were heavily contaminated by
Pb (Table 3). While natural levels of Pb in soil range between 50 and 400 mg/kg [
41
],
surrounding areas near mining and smelting activities have large concentrations, as in our
case, with levels ranging between 690 and 9310 mg/kg [41].
Regarding Hg, concentrations in soils can vary between 0.58 and 1.8 mg/kg, and
those in old mine areas can vary between 0.21 and 3.4 mg/kg [
40
]. In our study, only
substrates with composites and in the substrate with the mine waste from site C presented
Hg concentrations above the limit of detection (Table 3), exceeding the limit range expected
for old mine areas (>3.4 mg/kg). Nevertheless, according to Portuguese law, for agricultural
soils, Hg concentrations must not exceed 2 mg/kg [39].
Arsenic concentrations in soils above 76 mg/kg require intervention [
39
]. Moreover,
in contaminated soils, As levels can reach 2000 mg/kg [
40
]. In this context, it can be
considered that the substrates used for potato production are contaminated by As, with the
exception of the control substrate. According to Reis et al. (2012) [
30
], in 233 soil samples
from Caveira mine, the average As content was 254 mg/kg, with our data from pots 4–6,
7–9, and 10–12 being similar to that value.
Regarding the different organs of Solanum tuberosum L. plants (Table 4), it is important
to mention that there is great complexity in the mechanisms of As, Cu, Hg, and Pb uptake.
Lead is one of the heavy metals that raises the greatest concern for human health, although
only about 3% of Pb uptake was translocated to the aerial parts [
40
], after root absorption
via the apoplastic pathway or via Ca2+-permeable channels [16].
Since the edible organs are tubers, a careful evaluation must be considered when
crops grow in contaminated soils. Furthermore, the limits of the European Commission
Regulation of 2006 [
42
] were established as 0.1 mg/kg on a fresh-weight basis for peeled
potatoes, but not for non-peeled potatoes, which can contain higher levels, especially if
grown in sludge-amended soil (3.19 mg/kg dry weight [
43
]) or in mining-impacted areas,
with Pb levels in peeled slices varying between 0.9 and 4.0 mg/kg on a dry-weight basis [
44
],
excluding the levels observed in potatoes from the reference area. In the same context,
in peeled potatoes imported and sold in Tenerife (Canary Islands), Luis et al. (2014) [
45
]
observed Pb values ranging between 0.007 and 0.023 mg/kg fresh/wet weight, whereas for
local varieties, the range was between 0.06 and 0.013 mg/kg.
In our case, tubers from the three varieties grown in the substrate enriched in Pb
and Hg (those from substrates with composite 1, 2, and 3; the Red Lady variety grown in
Cu-enriched substrate; and Désirée and Red Lady grown in substrate less enriched in Cu
and Pb) showed Pb concentrations higher than 3 mg/kg (Table 4). Overall, Agria-variety
tubers seem to accumulate less Pb comparatively to the Désirée and Red Lady varieties.
Plants 2025,14, 230 12 of 18
Similarly to Pb, the concentration of total As in potatoes, swedes, and carrots was
lower in peeled products compared to unpeeled ones [
46
], and on average, 98.5% of the
total was in the inorganic, most toxic form.
The Désirée variety appears to accumulate more As than the other varieties, although
the highest concentration was observed in the Red Lady variety (14.8 mg/kg) when cul-
tivated in the substrate with composite 2. In the study by Hussain et al. (2014) [
47
], with
different varieties and different As contamination levels, it was found that both varieties
and contamination levels influenced As accumulation in tubers, with a maximum content
of 6.27 mg/kg. Additionally, it is established that for agronomic crops, the maximum allow-
able concentration for As is 0.2 mg/kg on a fresh-weight basis [
40
]. Hence, tubers from pots
5, 11, 12, 15–16, 19–20, 21–22, 22–23, and 26 are contaminated by As, with levels ranging
between 4.0 and 14.8 mg/kg, while the element was not detected in the remaining tubers.
Interestingly, different accumulation patterns were observed for Cu, Pb, and As
(Table 4). In general, in the three varieties studied, the accumulation trend for Cu is
leaves > roots > stems > tubers; that for Pb is roots > stems > leaves > tubers; and that
for As is roots > leaves > stems > tubers. Thus, tubers accumulate the least Cu, Pb, and
As among S. tuberosum L. organs. The predominant accumulation of Pb and As in roots
can be attributed to the fundamental role of roots as the primary barrier in heavy metal
uptake, being retained in the roots (root retention), blocking their transfer to the remaining
organs, especially to the aerial parts, thus reducing the possible toxic effects and acting
as a detoxification mechanism [
37
,
48
]. Furthermore, these tendencies can be observed in
Tables 57. Additionally, considering a study with twenty vegetables [
10
], the transfer
from soil to vegetables showed a tendency of Cu > Pb, which aligns with our data from
tubers (Table 4).
4. Materials and Methods
4.1. Description and Location of the Sampling Sites
The Caveira mine is an abandoned metal sulfide mine located on the northwestern
edge of the Iberian Pyrite Belt, located in the south of Portugal (Alentejo), in the municipality
of Grândola, 6 km southeast of the village of Grândola. It is the westernmost copper mine
in the Iberian Pyrite Belt and is geologically identical to the Minas de São Domingos and
Aljustrel mines. Figure 1shows a map of the location of the Caveira mine, at both the
national and regional levels.
The sampling of waste and slag (referred to as mine waste in the following texts) was
conducted on 28 April 2023, at three different locations within the former Caveira mine
(Figure 1). Previous studies identified the existence of materials with abnormally high
concentrations of Cu (site A), Pb, and Hg (site B and C). As such, soil sampling was carried
out in these specific locations (Figure 2).
4.2. Mine Leachate Characterization
Leachate samples were collected from the Caveira mine waste drainage line
(
Figure 3
), located in the middle of the three locations, sites A, B, and C (Figure 2), for
laboratory characterization.
The pH and electrical conductivity were measured using a multiparameter analyzer
(Consort C6030—Consort bvba, Turnhout, Belgium) coupled with SP21 and SK20 T electrodes.
Soluble ions, including chloride, sulfate, fluoride, sodium, calcium, magnesium,
and potassium, were determined by ion chromatography (IC) with Metrohm equipment,
model 761 Compact IC (Metrohm, Herisau, Switzerland), equipped with a Metrosep
Cation 1–2 column
(Metrohm, Herisau, Switzerland) (tartaric acid eluent, C
3
H
6
O
6
), accord-
ing to Simões (2008) [
49
], and a Dionex, model DX-120, equipped with an ASRS-Ultra
Plants 2025,14, 230 13 of 18
suppressor (Thermo Fisher Scientific, Waltham, MA, USA), IonPac As14, 4
×
250 mm, with
a pre-column and eluent consisting of a solution of sodium carbonate, Na
2
CO
3
, 48 mM,
according to the method proposed by EPA 300.0 (A) and in accordance with the method
proposed in Metrohm Application Bulletin No.257/1.
Plants2025,14,xFORPEERREVIEW12of18
mg/kg.Additionally,itisestablishedthatforagronomiccrops,themaximumallowable
concentrationforAsis0.2mg/kgonafresh-weightbasis[40].Hence,tubersfrompots5,11,
12,15–16,1920,21–22,2223,and26arecontaminatedbyAs,withlevelsrangingbetween
4.0and14.8mg/kg,whiletheelementwasnotdetectedintheremainingtubers.
Interestingly,differentaccumulationpatternswereobservedforCu,Pb,andAs(Table
4).Ingeneral,inthethreevarietiesstudied,theaccumulationtrendforCuisleaves>roots
>stems>tubers;thatforPbisroots>stems>leaves>tubers;andthatforAsisroots>leaves
>stems>tubers.Thus,tubersaccumulatetheleastCu,Pb,andAsamongS.tuberosumL.
organs.ThepredominantaccumulationofPbandAsinrootscanbeattributedtothefun-
damentalroleofrootsastheprimarybarrierinheavymetaluptake,beingretainedinthe
roots(rootretention),blockingtheirtransfertotheremainingorgans,especiallytotheaerial
parts,thusreducingthepossibletoxiceffectsandactingasadetoxificationmechanism
[37,48].Furthermore,thesetendenciescanbeobservedinTables5–7.Additionally,consid-
eringastudywithtwentyvegetables[10],thetransferfromsoiltovegetablesshoweda
tendencyofCu>Pb,whichalignswithourdatafromtubers(Table4).
4.MaterialsandMethods
4.1.DescriptionandLocationoftheSamplingSites
TheCaveiramineisanabandonedmetalsuldeminelocatedonthenorthwestern
edgeoftheIberianPyriteBelt,locatedinthesouthofPortugal(Alentejo),inthemunici-
palityofGrândola,6kmsoutheastofthevillageofGrândola.Itisthewesternmostcopper
mineintheIberianPyriteBeltandisgeologicallyidenticaltotheMinasdeoDomingos
andAljustrelmines.Figure1showsamapofthelocationoftheCaveiramine,atboththe
nationalandregionallevels.
Figure 1. National and regional location of the Caveira mine, Grandôla (Portugal).
Plants2025,14,xFORPEERREVIEW13of18
Figure1.NationalandregionallocationoftheCaveiramine,Grandôla(Portugal).
Thesamplingofwasteandslag(referredtoasminewasteinthefollowingtexts)was
conductedon28April2023,atthreedierentlocationswithintheformerCaveiramine
(Figure1).Previousstudiesidentiedtheexistenceofmaterialswithabnormallyhigh
concentrationsofCu(siteA),Pb,andHg(siteBandC).Assuch,soilsamplingwascarried
outinthesespeciclocations(Figure2).
Figure2.LocationinaerialimageonGooglemapsoflocationssitesA,B,andC,wheremining
wasteswerecollectedtoformulatetestsubstrates(GoogleEarth,2024).
4.2.MineLeachateCharacterization
LeachatesampleswerecollectedfromtheCaveiraminewastedrainageline(Figure
3),locatedinthemiddleofthethreelocations,sitesA,B,andC(Figure2),forlaboratory
characterization.
Figure3.LeachateresultingfromthedrainageofwastefromtheCaveiramine.
ThepHandelectricalconductivityweremeasuredusingamultiparameteranalyzer
(ConsortC6030—Consortbvba,Turnhout,Belgium)coupledwithSP21andSK20Telec-
trodes.
Solubleions,includingchloride,sulfate,uoride,sodium,calcium,magnesium,and
potassium,weredeterminedbyionchromatography(IC)withMetrohmequipment,
model761CompactIC(Metrohm,Herisau,Swierland),equippedwithaMetrosep
Figure 2. Location in aerial image on Google maps of locations sites A, B, and C, where mining
wastes were collected to formulate test substrates (Google Earth, 2024).
Plants 2025,14, 230 14 of 18
Plants2025,14,xFORPEERREVIEW13of18
Figure1.NationalandregionallocationoftheCaveiramine,Grandôla(Portugal).
Thesamplingofwasteandslag(referredtoasminewasteinthefollowingtexts)was
conductedon28April2023,atthreedierentlocationswithintheformerCaveiramine
(Figure1).Previousstudiesidentiedtheexistenceofmaterialswithabnormallyhigh
concentrationsofCu(siteA),Pb,andHg(siteBandC).Assuch,soilsamplingwascarried
outinthesespeciclocations(Figure2).
Figure2.LocationinaerialimageonGooglemapsoflocationssitesA,B,andC,wheremining
wasteswerecollectedtoformulatetestsubstrates(GoogleEarth,2024).
4.2.MineLeachateCharacterization
LeachatesampleswerecollectedfromtheCaveiraminewastedrainageline(Figure
3),locatedinthemiddleofthethreelocations,sitesA,B,andC(Figure2),forlaboratory
characterization.
Figure3.LeachateresultingfromthedrainageofwastefromtheCaveiramine.
ThepHandelectricalconductivityweremeasuredusingamultiparameteranalyzer
(ConsortC6030—Consortbvba,Turnhout,Belgium)coupledwithSP21andSK20Telec-
trodes.
Solubleions,includingchloride,sulfate,uoride,sodium,calcium,magnesium,and
potassium,weredeterminedbyionchromatography(IC)withMetrohmequipment,
model761CompactIC(Metrohm,Herisau,Swierland),equippedwithaMetrosep
Figure 3. Leachate resulting from the drainage of waste from the Caveira mine.
4.3. Experimental Design
Seed potatoes of three of S. tuberosum L. varieties (Agria, Désirée, and Red Lady) were
pre-germinated in a humid, dark environment for approximately four weeks, from 5 April
to 5 May 2023, prior to cultivation.
The experimental trial was carried out in 27 plastic pots, each with an approximate
capacity of 10 L (heigh = 23 cm, average radius = 12 cm). A biological agricultural substrate
from Siro Horta brand, recommended for vegetable and fruit plants, was used as the
control substrate. This substrate consisted of matured horse manure and biological organic
fertilizer of animal origin, with the following characteristics: >70% of organic matter, pH
between 5.5 and 6.5, electrical conductivity between 150 and 200 mS/cm, granulometry
< 1.5 mm, and NPK 9-3-3: 4 kg/m
3
. Soils collected from the mine, containing higher
concentrations of Cu, Hg, Pb, and other heavy metals, were sieved with a 1.5 mm sieve and
incorporated into different substrate formulations for potato plant growth (Table 9).
Table 9. Composition of the different substrates in the pots of the experimental design and respective
formulations.
Pot Variety Soil Substrate Formulations
1 Agria
Control/Control substrate 100% biological agricultural substrate from Siro Horta
(agricultural substrate)
2 Désirée
3 Red Lady
4 Agria
Cu-enriched substrate 5 L agricultural substrate + 500 mL of mine waste from site A
5 Désirée
6 Red Lady
7 Agria
Substrate less enriched in Cu and Pb 5 L agricultural substrate + 500 mL of mine waste from site C
8 Désirée
9 Red Lady
10 Agria
Substrate enriched in Pb and Hg 5 L agricultural substrate + 500 mL of mine waste from site B
11 Désirée
12 Red Lady
Plants 2025,14, 230 15 of 18
Table 9. Cont.
Pot Variety Soil Substrate Formulations
13 Agria
Substrate with composite 1 5 L agricultural substrate + 500 mL of mine waste from sites A
(166.6 mL), B (166.6 mL) and C (166.6 mL)
14 Agria
15 Désirée
16 Désirée
17 Red Lady
18 Red Lady
19 Agria
Substrate with composite 2
5 L agricultural substrate + 1000 mL of mine waste from sites A
(333.3 mL), B (333.3 mL) and C (333.3 mL)
20 Agria
21 Désirée
22 Désirée
23 Red Lady
24 Red Lady
25 Agria
Substrate with composite 3
5 L agricultural substrate + 1500 mL of mine waste from sites A
(500 mL), B (500 mL) and C (500 mL)
26 Désirée
27 Red Lady
Pot positioning is displayed in Figure 4.
Plants2025,14,xFORPEERREVIEW15of18
27RedLady
PotpositioningisdisplayedinFigure4.
Figure4.PotpositioningattheDepartmentofEarthSciencesatNOVAFCT.
Thepotswerewatereddaily,exceptforweekendsduetotheclosureofNOVAFCT,
alwaysinthelateafternoon,around6pm,with150mLofwaterfromthepublicsupply
networkoftheMunicipalWaterandWaterServicesfromAlmada(SMAS),fromthedate
ofplantinguntilthe12ofJuly(5daysbeforeharvest),toallowthetuberskintobecome
rmer.Despitethepotsbeingprotected,intenserainfalloccurredintheAlmadaregion
on22,23,and27May.Theplantingofseedpotatoestookplaceon5May2023,atthe
DepartmentofEarthSciencesatNOVAFCT(Almada,Portugal).Thepotsandplantsre-
mainedinthesameplaceduringtheproductioncycleuntilharvest,whichtookplaceon
July17and18,75daysafterplanting.
4.4.DeterminationofpHandECinSubstrates
ThepHandelectricalconductivity(EC)weremeasuredinthesoilsubstrateleachate
ofeachpotbeforeplantingandafterharvestusingamultiparameteranalyzer(Consort
C6030—Consortbvba,Turnhout,Belgium)coupledwithSP21andSK20Telectrodes.One
gramofsoilsubstrateleachatefromeachpotwassuspendedin100mLofultrapurewater,
followedbyreadings,induplicate,inthesuspendedliquid,atareferencetemperatureof
20°C.
4.5.MineralContentinTubers
ThemineralcontentsofCu,Pb,As,andHgweredeterminedinminewastefrom
sitesA,B,andC,inthecontrolsubstrate,inthedierentsubstrateformulations,andinS.
tuberosumL.organs(tubers,root,stems,andleaves).ForS.tuberosumL.organs,theanal-
ysiswasperformedafterthesamplesweredriedat60°Cuntilreachingaconstantweight
andground.AllsampleswereanalyzedusinganXRFanalyzer(VANTATMHandheld
XRFAnalyzer,Olympus,Espoo,Finland).Theanalyseswerecarriedoutinquadruplicate.
Thelimitofdetectionoftheanalyzerwas<5ppmforPb,As,Cu,andHg.
4.6.StatisticalAnalysis
StatisticalanalysiswascarriedoutwithIBMSPSSsoftware(version20)usingone-
wayANOVAtoassessthedierencesbetweenthedierentsubstrateformulationsin
eachmineralelementanalyzed,followedbyTukey’sanalysisformeancomparison.A
95%condencelevelwasadoptedforallthetests.Allthestatisticalanalyseswerecarried
outwithquadruplicatesofeachsample.Additionally,statisticalanalysiswasalsocarried
outusingtheRsoftware(version4.2.2)“RProjectforStatisticalComputing”forPearson
andSpearmancorrelations.
Figure 4. Pot positioning at the Department of Earth Sciences at NOVA FCT.
The pots were watered daily, except for weekends due to the closure of NOVA FCT,
always in the late afternoon, around 6 pm, with 150 mL of water from the public supply
network of the Municipal Water and Water Services from Almada (SMAS), from the date of
planting until the 12 of July (5 days before harvest), to allow the tuber skin to become firmer.
Despite the pots being protected, intense rainfall occurred in the Almada region on 22, 23,
and 27 May. The planting of seed potatoes took place on 5 May 2023, at the Department
of Earth Sciences at NOVA FCT (Almada, Portugal). The pots and plants remained in the
same place during the production cycle until harvest, which took place on July 17 and 18,
75 days after planting.
4.4. Determination of pH and EC in Substrates
The pH and electrical conductivity (EC) were measured in the soil substrate leachate
of each pot before planting and after harvest using a multiparameter analyzer (Consort
C6030—Consort
bvba, Turnhout, Belgium) coupled with SP21 and SK20 T electrodes.
One gram of soil substrate leachate from each pot was suspended in 100 mL of ultrapure
water, followed by readings, in duplicate, in the suspended liquid, at a reference temperature
of 20 C.
Plants 2025,14, 230 16 of 18
4.5. Mineral Content in Tubers
The mineral contents of Cu, Pb, As, and Hg were determined in mine waste from sites
A, B, and C, in the control substrate, in the different substrate formulations, and in S. tubero-
sum L. organs (tubers, root, stems, and leaves). For S. tuberosum L. organs, the analysis
was performed after the samples were dried at 60
C until reaching a constant weight and
ground. All samples were analyzed using an XRF analyzer (VANTATM Handheld XRF
Analyzer, Olympus, Espoo, Finland). The analyses were carried out in quadruplicate. The
limit of detection of the analyzer was <5 ppm for Pb, As, Cu, and Hg.
4.6. Statistical Analysis
Statistical analysis was carried out with IBM SPSS software (version 20) using one-way
ANOVA to assess the differences between the different substrate formulations in each
mineral element analyzed, followed by Tukey’s analysis for mean comparison. A 95%
confidence level was adopted for all the tests. All the statistical analyses were carried out
with quadruplicates of each sample. Additionally, statistical analysis was also carried out
using the R software (version 4.2.2) “R Project for Statistical Computing” for Pearson and
Spearman correlations.
5. Conclusions
In this study, we investigated the impact of different substrate formulations contami-
nated with Cu, Hg, Pb, and As on metal accumulation in Solanum tuberosum L. varieties
produced in Portugal. Our findings highlight the significant influence of heavy metal
contamination on the accumulation of these elements in various plant organs (tubers, roots,
stems, and leaves), with variations depending on the variety and substrate formulation.
Although the different substrates did not affect phenological development, they played a
crucial role in metal accumulation. This study found that Cu, Pb, and As levels in tubers
produced in substrates with mine waste exceeded values in the literature, and Pb accumu-
lation was notably higher in the Désirée variety. Additionally, correlations between metal
concentrations in substrates and plant organs were carried out, and different tendencies
of accumulation were observed. In the three varieties, roots accumulate more Pb and As
relative to the other plant organs. Despite maximum allowable limits, even the control
substrate showed higher concentrations of metals in tubers, particularly Désirée and Red
Lady, emphasizing the need for caution in potato consumption. In this context, it is im-
portant to monitor and assess soil quality in agricultural areas impacted by heavy metal
contamination. Moreover, selecting potato varieties that are tolerant to soil contaminants,
especially heavy metals, can further reduce risk to human health.
Author Contributions: Conceptualization, A.R.F.C., M.S., F.H.R. and J.A.; methodology, A.R.F.C.,
M.S., F.H.R., J.A. and F.L.; software, J.A.; formal analysis, A.R.F.C., M.S., J.A. and J.C.; investigation,
A.R.F.C., M.S., J.A. and J.C.; writing—original draft preparation, A.R.F.C., M.S., J.A. and J.C.; writing—
review and editing, A.R.F.C., M.S. and F.H.R.; supervision, A.R.F.C., M.S. and J.A. All authors have
read and agreed to the published version of the manuscript.
Funding: This research was funded by GeoBioTec Research Center (UIDB/04035/2020—https:
//doi.org/10.54499/UIDB/04035/2020).
Data Availability Statement: Data are contained within the article.
Acknowledgments: The authors would like to thank Casa Carvalho, located at Rua Quinta dos
Carvalhos, Sobreda, for offering the seed potatoes.
Conflicts of Interest: The authors declare no conflicts of interest.
Plants 2025,14, 230 17 of 18
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