# Contribution of chemical inputs on the trace elements concentrations of surface soils in urban allotment gardens

Sophie Joimel, Jérôme Cortet, Jean Noël Consalès, Philippe Branchu, Claire-Sophie Haudin, Jean Louis Morel, Christophe Schwartz

<figure><img src="image_1.png" /></figure>

## To cite this version:

Sophie Joimel, Jérôme Cortet, Jean Noël Consalès, Philippe Branchu, Claire-Sophie Haudin, et al. Contribution of chemical inputs on the trace elements concentrations of surface soils in urban allotment gardens. Journal of Soils and Sediments, 2021, 21 (1), pp.328-337. 10.1007/s11368-020-02784-z. hal-03119511

HAL Id: hal-03119511

https://hal.science/hal-03119511v1

Submitted on 29 Aug 2025

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Contribution of chemical inputs on the trace elements concentrations of surface soils in urban allotment gardens

Sophie Joimel<fnref n="1" /> Ⓒ • Jérôme Cortet<fnref n="2" /> • Jean Noël Consalès<fnref n="3" /> • Philippe Branchu<fnref n="4" /> • Claire-Sophie Haudin<fnref n="1" /> •
Jean Louis Morel<fnref n="5" /> • Christophe Schwartz<fnref n="5" />

**Abstract**

**Purpose** Urban soil contamination by heavy metals is one of the foremost challenges for urban soil quality, especially in the urban agriculture context. Urban gardening is a common practice in many industrialized and developing countries. How sources of soil contamination relate to inputs and influence the heavy metal content in soils, however, is not established yet.

**Materials and methods** This study aims to assess the potential of pesticide applications (such as Bordeaux mixture) on soil quality. A set of 104 allotment gardens was selected in three cities in France, and topsoil was sampled and analyzed.

**Results and discussion** The four most abundant metals in urban vegetable garden topsoils were Zn, Pb, Cu, and Cr. The past and/or present industrial and urban activities are not the only cause of the metal contamination in urban vegetable garden soils. Gardens, where pesticides such as the Bordeaux mixture are being used showed significantly higher total Cu values in soils (78 mg kg⁻<fnref n="1" /> compared with 49 mg kg⁻<fnref n="1" /> for untreated gardens).

**Conclusions** Even though the risk of metal contamination through vegetable consumption is usually considered low, we clearly identified indicators of anthropogenic Cd, Cu, Pb, and Zn pollution due to pesticides inputs. This link was particularly strong between the use of Bordeaux mixture and increases Cu levels.

**Keywords** Agrochemicals • Bordeaux mixture • Heavy metals • Urban allotment gardens • Urban soils

# 1 Introduction

Urban allotment gardens, also called community gardens, are expanding worldwide, especially in industrialized countries (Draper and Freedman 2010; Guitart et al. 2012). They have

the particularity of offering a unique combination of economic, social, and environmental functions (Bell 2016) such as leisure activities (Consalès 2004), whilst providing a wide range of ecosystem services to their users and citizens (Duchemin et al. 2009) (e.g., vegetable production). However, the value of these services is directly related to the soil quality, including fertility and presence of high concentrations of contaminants, such as metals, above the geochemical background. In some cases, higher concentrations due to pollution may impair the soil functioning and increase the risk of metal dissemination into the food chain. Metal accumulation in soil is of particular concern due to its long residence time and the associated potential risk to human health (Kabata-Pendias 2004; Liu et al. 2013) induced by consumption of contaminated vegetables, inhalation of dust suspension, or by direct contact with soil (Douay et al. 2013; McBride et al. 2014). The risk induced by metals in soils depends on their bioavailability, which is controlled by several factors (Morel 1997; van Gestel 2008). Methods to assess bioavailability of soils metals are chemical extraction, plant

<figure><img src="image_3.png" /></figure>

Sophie Joimel
sophie.boulanger-joimel@agroparistech.fr

<footnote n="1">¹ UMR ECOSYS, INRAE, AgroParisTech, Université Paris-Saclay, F-78850 Thiverval-Grignon, France</footnote>

<footnote n="2">² UMR CEFE 5175, Université de Montpellier, EPHE, Université Paul-Valéry Montpellier, F-34199 Montpellier cedex, France</footnote>

<footnote n="3">³ Aix Marseille Univ, CNRS, UMR 7303 TELEMME, Aix-en-Provence, France</footnote>

<footnote n="4">⁴ Cerema, Equipe TEAM, Direction territoriale Ile de France, F-78190 Trappes, France</footnote>

<footnote n="5">⁵ Université de Lorraine, INRAE, LSE, F-54000 Nancy, France</footnote>
tests, and isotopic dilution techniques (Morel, 1997; Echevarria et al. 1998; Gerard et al. 2000). However, there is still no universally acceptable method for assessing bioavailable soil metal concentrations (Giller et al., 2009).

Several studies have documented metal contamination in urban topsoils (Morel et al. 2005; Cheng et al. 2015; Joimel et al. 2016; Foti et al. 2017) and more specifically in allotment gardens (Morel and Schwartz 1999; Alloway 2004; Joimel et al. 2016; Burghardt and Schneider 2018). Metal concentrations in agroecosystems are either inherited from soil parent materials or input through human activities (He et al. 2005). In some cases, significant quantities of metals may be of both origins, resulting in abnormally high concentrations in soils (Jean-Soro et al. 2015). Cultivation practices for improving soil fertility and food biomass production may also induce metal contamination due to the use of fertilizers and pesticides, which contain trace metals either due to additives and impurities (Belon et al. 2012) or to amendments such as sewage sludge (Cambier et al. 2009). Metal contamination in urban agriculture could also be related to urban activities, such as industrial emissions or road traffic (Béchet et al. 2009; El Hamiani et al. 2010) due either to historical or current emissions (Douay et al. 2007). The variability of sources affects metal availability for uptake by or contamination of garden products and consequently potential human exposure (Hamiani et al. 2015; Béchet et al. 2018) and pollution risks.

Previous surveys in several countries, such as the USA or Hungary, have highlighted a wide range of metal concentrations in garden soils (Szolnoki et al. 2013; Mitchell et al. 2014; Cheng et al. 2015). Investigations revealed that all metals studied exceeded background concentrations, but that contamination was city specific and varied with local conditions (Szolnoki et al. 2013) in relation to the environmental context (e.g., geochemical background) and historical, sociopolitical (gender, age), and economic backgrounds. If several studies have been conducted in urban gardening with a social point of view (e.g., Harpet 1998; Consalès 2004), only a few studies have focused on the relationship between soil quality and gardening practices (e.g., Tresch et al. 2018). Several studies have focused these relationship on agricultural land uses in urban (Nabulo et al. 2010; Charlesworth et al. 2011) or periurban areas (Nabulo et al. 2012). However, differences may occur between gardening and market gardening due to more intensive practices in garden (e.g., pesticides inputs) unlike market gardening with profit objectives (Joimel 2015). In addition, heavy metals are generally present in agricultural soil at low levels contrary to urban garden soils (Joimel et al. 2016).

In France, soil contamination of urban vegetable garden soils has been studied at the scale of cities and their surrounding areas (Jean-Soro et al. 2015; Béchet et al. 2018), and contamination of urban soils in France was also assessed on a large number of cities (Joimel et al. 2016). Moreover, it is

important for the management of allotment gardens to assess the contamination ranges and sources, in order to improve decision support systems concerning garden soil quality.

This study aims to assess the potential influence of pesticides inputs on soil metal contamination within three cities in France (104 allotment gardens), particularly the effects of the Bordeaux mixture, a common agrochemical inputs in urban agriculture. We hypothesized that the anthropogenic contributions and the geochemical contributions to the contamination of topsoil could be studied by analyzing the enrichment factors and the reference values. In addition, we considered that the temporal dynamics of the processes leading to soil contamination could be characterized using the proxy of the age of the allotment gardens or the inputs.

# 2 Materials and methods

## 2.1 Study areas

The choice of gardens (and his gardener) was conducted on the basis a previous work (Chenot et al. 2012) which determine the current state of knowledge and how to study them on the French territory. Garden soils have been considered to be influenced by seven factors (Chenot et al. 2012): urbanization (e.g., urban, rural, periurban) (Schroeder et al. 1987), age and gender of the gardener, gardening practices (Crößman and Wüsteman 1992), socioprofessional category of the gardener, types and relative shares of productions, climate, and age of the garden (Putegnat, 2001). Among these factors, two are independent of the garden: climate and urbanization. Allotment sites were selected according to these two independent influence factors of the gardens.

Also, the study took place in 104 urban vegetable gardens from allotment sites located in three cities in France: Grand Nancy (The Greater Nancy Metropolitan Area), Nantes and Marseille (Joimel et al. 2016). To assess the variability among gardens, allotment sites were chosen from different urban contexts (residential, industrial and semi-natural) under contrasting climates (oceanic, Mediterranean, and semicontinental climates) in order to investigate the variation in age, plot size and gardeners (gender, form of employment) (Table 1).

Three French urban areas were selected: Marseille (Mediterranean climate), Grand Nancy (The Greater Nancy Metropolitan Area), (semicontinental climate) and Nantes (oceanic climate). Marseille, the 2nd largest city in France (area: 241 km², population: 850,600 inhabitants), is located in South-Eastern France, bordering the Mediterranean Sea, and is characterized by clay loam or loam soils. In Marseille, most of the allotment gardens are located in the Northern and Eastern districts. The area of Grand Nancy (The Greater Nancy Metropolitan Area), (area: 142 km², population: 434,000 inhabitants) is located in North-Eastern France. In Grand Nancy (The
<table><caption>**Table 1** Characteristics of the 26 allotment gardens studied</caption><thead><tr><th>Site no.</th><th>Age (years)</th><th>Number of gardens by site</th><th>Mean surface (m²)</th><th>Number of gardens investigated</th></tr></thead><tbody><tr><td>1</td><td>&lt;10</td><td>2</td><td>100</td><td>1</td></tr><tr><td>2</td><td>&gt;100</td><td>40</td><td>190</td><td>3</td></tr><tr><td>3</td><td>70–80</td><td>240</td><td>300</td><td>5</td></tr><tr><td>4</td><td>70–80</td><td>110</td><td>180</td><td>4</td></tr><tr><td>5</td><td>&lt;10</td><td>10</td><td>100</td><td>2</td></tr><tr><td>6</td><td>&gt;100</td><td>40</td><td>150</td><td>7</td></tr><tr><td>7</td><td>&gt;100</td><td>70</td><td>190</td><td>4</td></tr><tr><td>8</td><td>&lt;10</td><td>100</td><td>200</td><td>3</td></tr><tr><td>9</td><td>70–80</td><td>20</td><td>20</td><td>5</td></tr><tr><td>10</td><td>&gt;100</td><td>–</td><td>500</td><td>1</td></tr><tr><td>11</td><td>&lt;10</td><td>20</td><td>100</td><td>1</td></tr><tr><td>12</td><td>40–50</td><td>100</td><td>200</td><td>10</td></tr><tr><td>13</td><td>&lt;10</td><td>10</td><td>100</td><td>4</td></tr><tr><td>14</td><td>&gt;100</td><td>100</td><td>270</td><td>7</td></tr><tr><td>15</td><td>20–30</td><td>100</td><td>170</td><td>10</td></tr><tr><td>16</td><td>30–40</td><td>40</td><td>200</td><td>1</td></tr><tr><td>17</td><td>10–20</td><td>60</td><td>100</td><td>5</td></tr><tr><td>18</td><td>30–40</td><td>40</td><td>160</td><td>4</td></tr><tr><td>19</td><td>10–20</td><td>80</td><td>150</td><td>5</td></tr><tr><td>20</td><td>30–40</td><td>80</td><td>110</td><td>3</td></tr><tr><td>21</td><td>10–20</td><td>90</td><td>100</td><td>5</td></tr><tr><td>22</td><td>30–40</td><td>100</td><td>150</td><td>2</td></tr><tr><td>23</td><td>10–20</td><td>20</td><td>2</td><td>3</td></tr><tr><td>24</td><td>&lt;10</td><td>16</td><td>80</td><td>3</td></tr><tr><td>25</td><td>10–20</td><td>22</td><td>150</td><td>2</td></tr><tr><td>26</td><td>10–20</td><td>9</td><td>100</td><td>3</td></tr></tbody></table>

Greater Nancy Metropolitan Area), allotment gardens are only located in small cities, surrounding the center of Nancy and urban vegetable gardens present mostly clay and clay loam soils. Nantes, the 6th biggest city in France (area: 65 km², population: 283,000 inhabitants), is located in Western France, close to the Atlantic Ocean and its allotment gardens are located in all districts and present mostly sandy loam soils.

In total, 104 urban vegetable gardens, from 26 allotment sites, were investigated. An allotment site contained several gardens, each being managed by a single gardener with the purpose of edible plant biomass production. The oldest allotment gardens were established at the beginning of the twentieth century, while some allotment gardens are only a few years old. The urban allotment sites studied were managed by various associations of allotment gardeners and directly or indirectly by cities.

## 2.2 Soil sampling and analysis

In each urban vegetable garden, twenty subsamples of cultivated topsoil (0–20 cm mostly depending on the depth

affected by digging were collected in 2013 from the cultivated area of each garden. The elementary samples were mixed and homogenized to obtain a single representative sample for each garden. The soil samples were air dried, disaggregated, and sieved at 2 mm, following the ISO 11464 standard protocol. Soil analysis was performed by a certified laboratory (quality assurance and quality control with use of reference materials) for soil analysis (Laboratoire d'Analyses des sols-INRAE, Arras, France) as follows: total metal analysis (Cd, Co, Cr, Cu, Mo, Ni, Pb, TI, and Zn following NF EN ISO 17294-2, NF ISO 22036 standards) after HF-HCLO4 acid dissolution (INRAE Method) and metal extraction (Cd, Cr, Cu, Mo, Ni, Pb, and Zn; extraction to CaCl₂ 0,01 mol l⁻¹, INRAE method). In addition, total As was determined using a portable X-ray fluorescence tool (Niton 792) with 10% of the samples also being analyzed after acid digestion in order to calibrate the device (Béchet et al. 2018). In order to study related variables of soil physicochemical parameters, pH (NF ISO 10390) and the organic matter content of soils (SOM, NF ISO 10694) were also analyzed.
## 2.3 Survey of gardening practices

In addition to soil sampling and analysis, a questionnaire on gardeners (the gardener of each garden) and garden characteristics, including gardening practices, was conducted in the 104 urban vegetable gardens. Gardeners was selected, as far as possible, randomly but only if gardeners was volunteers. The survey was undertaken with plot holders and carried out directly in gardens. Our survey was conducted either as face-to-face interview. For this study, we focused on the information about the type of plant protection treatments used (chemical such as metaldehyde, organic compounds such as nettle manure or other practices such as plant removal) and particularly about the use of Bordeaux mixture in urban vegetable gardens. Bordeaux mixture is a mixture of copper sulfate and slaked lime, frequently used as fungicide, especially in organic practices. A previous study (Consalès et al. 2016) presents another part of this survey.

Questions concerning inputs was closed-response with possible multiple answers and paired with open-response and investigations in the garden shed in order to clarify any concerns about inputs practices. The age of the gardens was also noted.

## 2.4 Threshold of soil contamination and pollution

We assessed the enrichment factors (EF) of metals in soils (e.g., Sterckeman et al. 2006; Bourennane et al. 2010; Szolnoki et al. 2013). Enrichment factors also called contamination were calculated in order to determine the deviation of metal concentrations in comparison to the pedogeochemical background. In many cases, this approach has been used to detect the contribution of anthropogenic emissions to trace element fluxes (Bourennane et al. 2010).

$$EF_I = \frac{I_{sample}}{Ir}$$

where *I* is the concentration of the element under consideration (in mg kg⁻¹); *Ir* corresponds to the background concentration in order to detect anomalies in each reference area.

In our study, we calculated, for each metal concerned, the ratio between its total content and the local geochemical background value. The local pedogeochemical background values have been defined (“vibrisse”) by the RMQS database (Arrouays et al. 2002), which primarily consists of 2146 observations of soil properties on a 16-km regular grid across the 550,000 km² of the French metropolitan territory. An EF ratio higher than 1 indicates enrichment in metals compared with geochemical background and thus a contamination. Nevertheless, as we do not perform soils analysis by in situ depth sampling to parent material depth, the EF inform mostly on a generic reference point that may under or overestimate

thresholds relative to garden plots than conclusions on geochemical background.

EF might be not precise enough to detect diffuse contamination due to human activities. To improve the sensitivity of the EF to the anthropogenic influence, the lithologic enrichment factor (LEF) was calculated in our study in the following manner, according to Sterckeman et al. (2006):

$$LEF_I = \frac{I_{sample}/Al_{sample}}{I_{crust}/Al_{crust}}$$

where *I* is the concentration of the element under consideration (in mg kg⁻¹) in the sample or in the background concentration (crust) for detecting anomalies. Aluminum (Al) is used as reference element. Crust refers to the Earth’s crust, most often the continental or the upper continental crust.

According to Bourennane et al. (2010), the use of Al as reference element also improves the sensitivity of the LEF to the anthropogenic enrichment, particularly with the less mobile elements, which have similar geochemical behaviors to that of Al. Moreover, Al appears to be more conservative than iron (Fe), and this is the reason why we prefer to use it to calculate the LEF (Sterckeman et al. 2006). Moreover, in order to deepen the soil pollution investigation, we estimated the number of urban vegetable gardens showing higher metals contents than the soil reference values. This threshold value serves only as an “alert signal”, above which a more detailed investigation is required (Baize 1997, 2000). However, as in France, no legislation determines limit values for soil metal pollution, contrary to some other countries like Hungary (Szolnoki et al. 2013) or the USA (EPA 2003; Mitchell et al. 2014; Clarke et al. 2015). Most of time, threshold levels used in France correspond to the Decree of 8 January 1998 (Arrêté 1998-06-03 art. 1 JORF 30 June 1998), concerning limit values of agricultural soil contents for the spreading of urban sludge which is often, although wrongly, used as a surrogate for soil pollution (Cortet et al., 2011). We thus used the pollution limit value used in Hungary which present values for almost all heavy metals studied: As = 15, Cd = 1, Co = 30, Cr = 75, Cu = 75, Ni = 40, Pb = 100, and Zn = 200 mg Kg⁻¹, except for Mo and Tl.

## 2.5 Statistical analysis

As soil parameters did not match the basic assumptions of normality and homoscedasticity required for parametric statistics (Wilk–Shapiro test at rejection level of α = 0.05), we log-transformed data and used one-way ANOVA to assess differences in soil parameters between the three cities, or between factors such as gardening practices. In order to study correlations between metal contents in soils, a principal component analysis (PCA) was performed on the ten metals. Site ages, SOM content and pH were added as supplementary
quantitative variables. Differences in metal contents between cities were tested by permutational analysis of similarities (ANOSIM) (Clarke 1993). All statistics were performed using the R software version 3.2.2 (R Development Core Team, 2015) with “FactoMineR” packages (Lê et al. 2008).

# 3 Results

## 3.1 Variability of pH, SOM content, and metals distribution in urban vegetable garden topsoils

Contrary to most metal total concentrations, SOM contents and pH showed less variation in garden topsoils (Table 2), especially pH, which was mainly slightly basic with a mean of 7.6. However, extreme values ranging from markedly acid (6.2) to basic (8.2) were noted. Organic matter contents in garden soils were more variable than pH, with 4.9% of SOM on average and value distributions from 1.7 to 10.3.

The four most abundant metals in urban vegetable garden topsoils were Zn, Pb, Cu, and Cr (Table 2). In some urban vegetable gardens, Zn concentrations exceed 1 g kg⁻¹. Except for Cr, metals presented very high variation coefficients (106, 91, and 87% for respectively Cu, Zn, and Pb). Ni, As, Co, Mo, Tl, and Cd were also present at much lower concentrations, with generally low variation coefficients, the highest of which was Cd, at 186%, with total concentrations values ranging from 0.1 to 8.9 mg kg⁻¹.

The nine EFs can be grouped into three different metal distribution groups of (Table 3). The first group of metals, including Co, Ni, and Tl, always presented a ratio lower than 1. The second group of metals, including Mo, Cr, and Cd,

<table><caption>**Table 3** Distribution of metal enrichment factors (compared with Al content and crust reference) in urban vegetable garden topsoils (n = 104)</caption><thead><tr><th rowspan="2"></th><th colspan="3">Enrichment factor</th><th colspan="3">Lithologic enrichment factor</th></tr><tr><th>Minimum</th><th>Maximum</th><th>Mean</th><th>Minimum</th><th>Maximum</th><th>Mean</th></tr></thead><tbody><tr><td>As</td><td>—</td><td>—</td><td>—</td><td>0.0</td><td>22.7</td><td>8.1</td></tr><tr><td>Cd</td><td>0.0</td><td>9.6</td><td>0.6</td><td>1.9</td><td>312.4</td><td>12.7</td></tr><tr><td>Co</td><td>0.1</td><td>0.8</td><td>0.3</td><td>0.4</td><td>2.5</td><td>0.9</td></tr><tr><td>Cr</td><td>0.2</td><td>1.2</td><td>0.4</td><td>1.2</td><td>3.7</td><td>1.2</td></tr><tr><td>Cu</td><td>0.2</td><td>8.2</td><td>1.1</td><td>0.6</td><td>36.7</td><td>3.5</td></tr><tr><td>Mo</td><td>0.1</td><td>1.4</td><td>0.4</td><td>0.7</td><td>9.4</td><td>2.6</td></tr><tr><td>Ni</td><td>0.1</td><td>0.9</td><td>0.3</td><td>0.3</td><td>5.4</td><td>1.2</td></tr><tr><td>Pb</td><td>0.3</td><td>10.0</td><td>1.5</td><td>1.5</td><td>5.4</td><td>10.8</td></tr><tr><td>Tl</td><td>0.2</td><td>0.8</td><td>0.3</td><td>1.2</td><td>6.8</td><td>2.3</td></tr><tr><td>Zn</td><td>0.2</td><td>6.1</td><td>1.1</td><td>1.3</td><td>23.7</td><td>5.6</td></tr></tbody></table>

No reference available for EF<sub>As</sub>

presented between 2 to 11% of ratio values higher than one, which corresponded to a few extreme outliers (e.g., 9.6 for Cd). The third group of metals, including Cu, Pb, and Zn, presented between 29 to 51% of ratio values higher than 1.

Except for FEL<sub>Co</sub>, most of the FEL values were greater than one (Table 3). FEL<sub>Cr</sub>, FEL<sub>Mo</sub>, FEL<sub>Tl</sub> and FEL<sub>Ni</sub> were below 3, whereas the lithologic enrichment factors of the urban vegetable garden topsoils for As, Cd, Cu, Pb, and Zn were much greater than for the other trace elements.

Values of extractable metals were almost exclusively below detection levels for Cr, Ni, and Pb (Table 4). For other metals, mean extractable metal contents were less than 1% of total contents. However, some extreme values could be noted for Cd and Zn (25 and 2120 µg kg⁻¹ respectively), corresponding to 3.5% and 15.5% of total metal contents.

<table><caption>**Table 2** Distribution of pH, organic matter, total concentrations in metals, coefficient of variation (CV) in urban vegetable garden topsoils</caption><thead><tr><th></th><th></th><th>Mean</th><th>Minimum</th><th>Maximum</th><th>CV (%)</th><th>% of gardens</th></tr></thead><tbody><tr><td>pH<sub>water</sub></td><td></td><td>7.6</td><td>6.2</td><td>8.3</td><td>6</td><td></td></tr><tr><td>Organic matter (% dry mass)</td><td></td><td>4.9</td><td>1.7</td><td>10.3</td><td>40</td><td></td></tr><tr><td>Metals</td><td>Zn</td><td>199.8</td><td>43.4</td><td>1020.0</td><td>91</td><td>26</td></tr><tr><td>(mg kg<sup>-1</sup> dry mass)</td><td>Pb</td><td>98.6</td><td>19.5</td><td>566.0</td><td>87</td><td>33</td></tr><tr><td></td><td>Cu</td><td>56.8</td><td>11.9</td><td>473.0</td><td>106</td><td>19</td></tr><tr><td></td><td>Cr</td><td>55.3</td><td>21.3</td><td>136.0</td><td>50</td><td>24</td></tr><tr><td></td><td>Ni</td><td>26.5</td><td>8.1</td><td>98.5</td><td>70</td><td>12</td></tr><tr><td></td><td>As</td><td>21.1</td><td>0.2</td><td>65.2</td><td>59</td><td>67</td></tr><tr><td></td><td>Co</td><td>9.2</td><td>3.2</td><td>20.5</td><td>52</td><td>0</td></tr><tr><td></td><td>Mo</td><td>1.1</td><td>0.4</td><td>4.5</td><td>72</td><td>—</td></tr><tr><td></td><td>Tl</td><td>0.6</td><td>0.3</td><td>1.3</td><td>37</td><td>—</td></tr><tr><td></td><td>Cd</td><td>0.5</td><td>0.1</td><td>8.9</td><td>186</td><td>11</td></tr></tbody></table>

Concentrations are compared with threshold values (As = 15, Cd = 1, Co = 30, Cr = 75, Cu = 75, Ni = 40, Pb = 100, Zn = 200 mg Kg⁻¹) for pollution investigations (% of gardens exceeding values) (n = 104)
<table><caption>**Table 4** Concentrations of CaCl₂ extractable metal (10³ mg kg⁻¹) in urban vegetable garden topsoils (n = 104)</caption><thead><tr><th></th><th>Cd</th><th>Cr</th><th>Cu</th><th>Ni</th><th>Pb</th><th>Zn</th></tr></thead><tbody><tr><td>Number of values below limits of detection</td><td>52</td><td>104</td><td>0</td><td>74</td><td>103</td><td>30</td></tr><tr><td>Mean</td><td>5</td><td>—</td><td>113</td><td>28</td><td>5</td><td>149</td></tr><tr><td>% of total content</td><td>0.10</td><td>—</td><td>0.20</td><td>0.03</td><td>0.10</td><td>0.10</td></tr></tbody></table>

## 3.2 Relation between soil characteristics and gardening practices

Ninety-two percent of gardeners answered our questionnaire (96 of 104 gardeners) (Table 5). On average, gardeners were elderly (69% of gardeners were aged ≥ 61 years old), male (81%) and retired (70%). Thirty-five percent of them used Bordeaux mixture, and 62% preferred to use organic products (e.g., nettle manure, black soap) in order to fight plant diseases.

The first two axes of the PCA respectively accounted for 50% and 21% of the total variability (Fig. 1). Three groups of metals were distinguished on the PCA. A first group correlated positively to axis 1 and negatively to axis 2, including Cd, Cu, Pb, and Zn. The second group correlated positively with axes 1 and 2, and comprised Mo, Ni, Cr, and Co. The third group correlated positively with axis 2, including TI and As. There were significant positive correlations between the age of urban vegetable gardens, SOM and pH with most of the metals, especially for Cd, Cu, Pb, and Zn. Total metal concentrations significantly discriminated the three cities along axes 1 and 2 (ANOSIM, *p* = 0.01). Axis 1 opposed Marseille (positively) and Nantes (negatively), whereas Grand Nancy (The Greater Nancy Metropolitan Area), was

located in the center of the PCA, slightly positively on axis 2.

Gardens, whose gardeners used the Bordeaux mixture showed significantly higher total Cu values in soils (78 mg kg⁻¹ compared with 49 mg kg⁻¹ for untreated gardens) (Fig. 2).

Similarly, concentrations of Cd, Cu, Pb, and Zn in chemically treated garden soils (e.g., metaldehyde) were significantly greater than those with other modes of disease control (e.g., Cd: 0.63 vs 0.35 mg kg⁻¹, Cu: 78 vs 44 mg kg⁻¹) (Fig. 3). Garden soils under organic farming practices (e.g., nettle manure, ferric phosphate) also tended to show lower metal concentrations than those using synthetic chemical molecules (e.g., Pb: 109 vs 131 mg kg⁻¹, Zn: 208 vs 293 mg kg⁻¹).

## 3.3 Assessment of metal pollutions in garden topsoil

When considering the thresholds of soil pollution defined by Hungary, As anomalies appeared to be the most frequent, followed by Pb, Zn, Cr, and Cu anomalies (Table 2). The percentage of gardens requiring further investigation varied, depending on the metal considered, from 0 (Co) to 67% (As).

<table><caption>**Table 5** Characteristics of the gardeners and gardening practices (% of respondents, n = 36 for Marseille, 33 for Nantes, 26 for Grand Nancy)</caption><thead><tr><th></th><th></th><th>Marseille</th><th>Nantes</th><th>Grand Nancy</th></tr></thead><tbody><tr><td rowspan="4">Age (%)</td><td>≤40 years</td><td>0</td><td>6.0</td><td>3.7</td></tr><tr><td>41–50</td><td>13.9</td><td>15.2</td><td>22.2</td></tr><tr><td>51–60</td><td>5.6</td><td>15.2</td><td>11.1</td></tr><tr><td>≥61</td><td>80.5</td><td>63.6</td><td>63.0</td></tr><tr><td rowspan="2">Gender (%)</td><td>Female</td><td>13.9</td><td>33.3</td><td>11.1</td></tr><tr><td>Male</td><td>86.1</td><td>66.7</td><td>88.9</td></tr><tr><td rowspan="3">Employment status (%)</td><td>Employed</td><td>19.4</td><td>30.3</td><td>29.6</td></tr><tr><td>Retired/pensioner</td><td>77.8</td><td>66.7</td><td>63.0</td></tr><tr><td>Unemployed</td><td>2.8</td><td>3.0</td><td>7.4</td></tr><tr><td rowspan="2">Bordeaux mixture (%)</td><td>Yes</td><td>36.1</td><td>42.4</td><td>25.0</td></tr><tr><td>No</td><td>63.9</td><td>57.6</td><td>75.0</td></tr><tr><td rowspan="3">Treatment type</td><td>Other</td><td>22.2</td><td>24.2</td><td>25.0</td></tr><tr><td>Organic</td><td>63.8</td><td>72.7</td><td>25.0</td></tr><tr><td>Chemical</td><td>14.0</td><td>3.0</td><td>50.0</td></tr></tbody></table>
<figure><img src="image_4.png" /><figcaption>**Fig. 1** Graphic display of the first two axes of the principal component analysis on the global topsoil characterization dataset (axis 1 = 50%, axis 2 = 21%). **a** Black labels correspond to ten total metals contents (log-modified data). Blue labels correspond to quantitative supplementary</figcaption></figure>

variable (age of urban vegetable gardens, soil organic matter—OM and pH); **b** representation of observations depending on cities. A: Marseille, B: Nantes, C: Grand Nancy

# 4 Discussion

## 4.1 Multiple contamination in urban vegetables gardens

Our results indicate multiple contaminations, except for Co, Cr, and Ni, with different distribution patterns for each metal and for each city. Cadmium, Cu, Pb, and Zn concentrations tend to increase together in urban vegetable gardens, as shown in Los Angeles gardens (Clarke et al. 2015) and urban forests and lawns (Foti et al. 2017). These results agree with previous studies of soil contamination with various land uses (industrial, agriculture, urban or forest), which demonstrated contamination in increasing quantities: Cd > Cu > Pb > Zn (Thiry et al. 2002; Cambier et al. 2009). Other metals, Mo and As, present high enrichment factor values, mostly related to a few anomalies (in Nantes for As and Marseille for Mo), rather than the common situation of all urban vegetable gardens.

<figure><img src="image_5.png" /><figcaption>**Fig. 2** Total concentrations in Cu in urban vegetable garden topsoils according to the use of Bordeaux mixture (n = 63) or not (n = 34). Letters indicate significant differences (p < 0.05)</figcaption></figure>

This metal contamination in urban vegetable garden topsoils could result from multiple anthropogenic and geogenic sources.

## 4.2 Sources of the metal contamination

In Nantes gardens, following studies performed by Jean-Soro et al. (2015), we presume a link to a moderate natural geochemical anomaly, due to the local occurrence of mica schists, since the Pb values are between 30 and 60 mg kg⁻¹ (Baize 2000). Molybdenum contents are also higher in the clay soils of Grand Nancy (The Greater Nancy Metropolitan Area), due to their Jurassic bedrock (Gis Sol 2011). In the same way, Pb contents are naturally higher in some French regions, which present sedimentary bedrocks as Nantes or are located downstream of major rivers such as “La Loire” passing through the city (Gis Sol 2011).

However, the high values of lithological enrichment factors for As, Cd, Cu, Pb, and Zn and the high variability of contents indicate an obvious anthropogenic origin. Sources and inputs of anthropogenic contamination did not have the same duration and did not concern the same areas. Contamination could result from diffuse contamination, i.e., the increase in a contaminant content can be long-term over a large area (Cambier and Mench 1998), or local and occasional. The difference in rank between EF and FEL, especially in the case of Cd or Pb, could be related to a diffuse contamination, which is hardly perceptible and could occur in all soils of the area considered. The presence of a road infrastructure (e.g., traffic in vehicles running on leaded fuel, tire wear) and industrial developments (e.g., steel mills emitting Cd and As) (e.g., Councell et al. 2004; Clark et al. 2006) are sources of diffuse atmospheric contamination. In urban vegetable gardens, the construction of shelters made of salvaged materials containing Pb paints are also sources of diffuse contamination (Zhideeva et al. 2000; Clark et al. 2006). Metallic soil contamination can also originate from previous land use through frequent overlapping of
<figure><img src="image_6.png" /><figcaption>**Fig. 3** Total contents in Cd, Cu, Pb, and Zn in urban vegetable garden topsoils according to the use of organic (n = 59) or chemical treatments (n = 9) or other methods of disease control (n = 28). Letters indicate significant differences (p < 0.05)</figcaption></figure>

urban uses (Chenot et al. 2012). A large number of old gardens were created as part of a company policy, especially heavy industry in Marseille (Consalès 2004). The gardens were then set up on the factory wasteland, which were often waste disposal areas. For example, gardens with multiple contaminations (e.g., Cd, Cu, Pb, Zn) are located on former railway areas without soil treatment prior to their reuse as vegetable gardens. Gardeners also report finding artifacts in their soils (e.g., old tiles, oil from old locomotives). Some soils may also be composed of materials that have supported mining activity, thus inducing a metal charge in Hg or As (Loredo et al. 2003).

However, the past and/or present industrial and urban activities (Chenot et al. 2012) are not the only cause of the metal contamination in urban vegetable garden soils. Gardening practices acts as an important driver of soil properties and especially soil contamination.

The use of chemical pesticides increases metal concentrations in garden soils, due to their composition of Zn, Cu, and Pb (Belon et al. 2012). The use of “organic” treatments does not prevent contamination, especially in the case of frequent use of Bordeaux mixture as demonstrated in our results. Fertilizers also contain metals (Cd and Zn in pig manure) (Cambier et al. 2009). Many authors have thus shown an accumulation of metals (As, Cd, Cu, Zn) in agricultural soils, gardens, and orchards as a result of the use of plant protection products, animal manure, and/or fertilizers (Chen et al. 1997) or aerial deposits (Cortet et al. 2011).

The lower variability within each city than between cities, confirms the importance of pedoclimatic factors on the quality of urban vegetable garden topsoils. The higher contamination in Marseille and Grand Nancy (The Greater Nancy Metropolitan Area) could be related to their higher clay

contents than Nantes with sandy soil. Lamy et al. (1999) have demonstrated on topsoil samples that maximal contents are observed in clay fractions for Cd, Cu, Pb, and Zn. Another origin of differences could be related to other factors of garden soils determined by the SOJA review (Chenot et al. 2012), like the gardener's sociological type which indirectly involves differences in garden soil quality. The differentiation between cities could also relate to the historical differences of city allotments. Urban vegetable gardens in Nantes are more recent than in Marseille or Grand Nancy, which could involve degradation of soil quality with garden age. The relationship between age and metal contamination underpin this hypothesis.

## 4.3 Implications for urban vegetable garden management

According to investigation thresholds, several gardens have values requiring further investigation for Cu, Pb, and Zn. In these gardens, precautions need to be taken when gardening, especially when children are present. The risk of metal transfer could be related to (a) particles deposit on vegetables, which could be avoided by washing vegetables before consumption, or (b) the metals dissolved or likely to be released in soil solution. Indeed, the thresholds, based on total levels, do not provide information about the bioavailability of metals for plants and thus the metal transfer into the plants. Only bioavailable metals, assessed by measurement of extractable metals into the soil, will help determine any risks of transfer to plants and therefore to human health. In gardens, the majority of extractable contents are low for all metals due to (i) a basic pH, (ii) high levels of organic matter (Joimel et al. 2016), and (iii) a balanced texture. Furthermore, there is no relation
between total and extractable contents. The risks of contamination of vegetables are therefore assumed to be low. However, there are mobility peaks for Cd and Zn due to the nature of these elements, which are more mobile than other metals such as Pb (Kabata-Pendias 2004). Moreover Jean-Soro et al. (2015) have demonstrated in allotment gardens, a risk of Pb contamination of vegetables by soil solution, whereas extractible Pb contents were low depending on vegetable types (roots or leaves).

The multiple contaminations and the accumulation of metals over the years have implications for urban vegetable garden management. Because of the relation between gardening practices and soil quality, gardeners play a major role in maintaining the quality of their soil. Thus, it appears necessary to progress, towards an increase in ecologically intensive gardening practices (Griffon 2013), comprising an essential reduction in inputs. These changes in gardening practices could be favored by the evolution of generation gardens of gardeners. Until now, gardeners were mostly elderly and male because of the history of the allotment in France, which implied that gardening, which provided food for his family, was male's activity (Chenot et al. 2012; Joimel 2015). However, women and young people are starting to get more involved in gardening and are developing different gardening practices (Chenot et al. 2012; Joimel 2015). In addition, this new category of gardeners more frequently decides to join urban community garden initiatives rather than allotments gardens. It would be interesting to carry out the same type of study in others forms of urban agriculture in order to have an overview of the relationship between gardening practices and soils.

## 5 Conclusion

By performing an original investigation in order to relate pesticides inputs and the quality of garden soils, we confirmed the heterogeneity of garden soils composition and properties, the origins of pollutants, and the gardening practices implemented at national and local scales. Even though the risk of contamination by metal through vegetable consumption is usually considered low, we clearly showed anthropogenic soil pollution by Cd, Cu, Pb, and Zn. The quality of garden soils appeared to be linked first to their local geochemical background, then to the cultivation practices and the urbanization context which contribute to increase the total metal concentrations. The Bordeaux mixture, which is widely used in gardening, is a strong contributor to metal pollution, and the increase of Cu concentration on soil advocates for a reduction in inputs, even with organic gardening. Further study could be carried out on the relationship between gardening practices and organic matter inputs on soils in urban agriculture.

**Acknowledgments** The authors wish to thank the technical staff of the LSE and especially Alain Rakoto, the gardeners and all the partners involved in the JASSUR program, especially Béatrice Béchet, Liliane Jean-Soro, Thierry Lebeau, and Cécile Le Guern, for their substantial help.

**Funding** This work was supported by the French National Agency of Research (ANR) (JASSUR research project; ANR-12-VBDU-0011).

## References

* Alloway BJ (2004) Contamination of soils in domestic gardens and allotments: a brief overview. Land Contam Reclam 12:179-187

* Arrouays D, Jolivet CC, Boulonne L et al (2002) A new initiative in France: a multi-institutional soil quality monitoring network. Comptes Rendus Acad Agric Fr 88:93-105

* Baize D (1997) Teneurs totales en éléments traces métalliques dans les sols (France). Editions Quae

* Baize D (2000) Teneurs totales en " métaux lourds " dans les sols français: résultats généraux du programme ASPITET. Courr Environ

* Béchet B, Carré F, Florentin L et al (2009) Caractéristiques et fonctionnement des sols urbains. In: In Sous les pavés la terre. Cheverry et Gascuel éd. Omniscience, Montreuil, pp 45-74

* Béchet B, Joimel S, Jean-Soro L, Hursthouse A, Agboola A, Leitão TE, Costa H, do Rosário Cameira M, Le Guern C, Schwartz C, Lebeau T (2018) Spatial variability of trace elements in allotment gardens offour European cities: assessments at city, garden, and plot scale. J. Soils Sediments 18:391-406. https://doi.org/10.1007/s11368-016-

* Bell S (2016) Urban allotment gardens in Europe. Routledge, Taylor & Francis Group, London, New York

* Belon E, Boisson M, Deportes IZ, Eglin TK, Feix I, Bispo AO, Galsomies L, Leblond S, Guellier CR (2012) An inventory of trace elements inputs to French agricultural soils. Sci Total Environ 439: 87-95. https://doi.org/10.1016/j.scitotenv.2012.09.011

* Bourennane H, Douay F, Sterckeman T, Villanneau E, Ciesielski H, King D, Baize D (2010) Mapping of anthropogenic trace elements inputs in agricultural topsoil from Northern France using enrichment factors. Geoderma 157:165-174. https://doi.org/10.1016/j.geoderma.2010.04.009

* Burghardt W, Schneider T (2018) Bulk density and content, density and stock of carbon, nitrogen and heavy metals in vegetable patches and lawns of allotments gardens in the northwestern Ruhr area, Germany. J Soils Sediments 18:407-417. https://doi.org/10.1007/s11368-016-1553-8

* Cambier P, Mench M (1998) Contamination des sols par les métaux lourds et autres éléments-traces. In: Stengel P, Gelin S (eds) Sol: interface fragile. INRA, Paris, pp 161-172

* Cambier P, Schvartz C, van Oort F (2009) Contaminations métalliques des agrosystèmes et écosystèmes péri-industriels. Éditions Quæ, Versailles

* Charlesworth S, De Miguel E, Ordóñez A (2011) A review of the distribution of particulate trace elements in urban terrestrial environments and its application to considerations of risk. Environ Geochem Health 33:103-123. https://doi.org/10.1007/s10653-010-9325-7

* Chen TB, Wong JWC, Zhou HY, Wong MH (1997) Assessment of trace metal distribution and contamination in surface soils of Hong Kong. Environ Pollut 96:61-68. https://doi.org/10.1016/S0269-7491(97)00003-1

* Chenot E-D, Douay F, Dumat C et al (2012) Jardins potagers : terres inconnues ? EDP Sciences, Les Ulis
Clark HF, Brabander DJ, Erdil RM (2006) Sources, sinks, and exposure pathways of lead in urban garden soil. J Environ Qual 35:2066-2074

Clarke KR (1993) Non-parametric multivariate analyses of changes in community structure. Aust J Ecol 18:117-143. https://doi.org/10.1111/j.1442-9993.1993.tb00438.x

Clarke LW, Jenerette GD, Bain DJ (2015) Urban legacies and soil management affect the concentration and speciation of trace metals in Los Angeles community garden soils. Environ Pollut 197:1-12. https://doi.org/10.1016/j.envpol.2014.11.015

Consalès JN (2004) Les jardins familiaux à Marseille, Gênes et Barcelone : laboratoires territoriaux de l'agriculture urbaine dans l'Arc Méditerranéen Aix Marseille 1

Consalès JN, Joimel S, Cordier F, et al (2016) De l'argument à l'action : la biodiversité au service des jardins familiaux. **Proj Paysage**

Councell TB, Duckenfield KU, Landa ER, Callender E (2004) Tire-wear particles as a source of Zn to the environment. Environ Sci Technol 38:4206-4214

Crößman G, Wüsteman M (1992) Belastungen in Haus- und Kleingärten durch anorganische und organische Stoffe mit Schadstoffpotential

Douay F, Pelfrène A, Planque J, Fourrier H, Richard A, Roussel H, Girondelot B (2013) Assessment of potential health risk for inhabitants living near a former lead smelter. Part 1: metal concentrations in soils, agricultural crops, and homegrown vegetables. Environ Monit Assess 185:3665-3680. https://doi.org/10.1007/s10661-012-2818-3

Douay F, Roussel H, Fourrier H, Heyman C, Chateau G (2007) Investigation of heavy metal concentrations on urban soils, dust and vegetables nearby a former smelter site in Mortagne du Nord, Northern France. J Soils Sediments 7:143-146

Duchemin E, Wegmuller F, Legault A-M (2009) Urban agriculture: multi-dimensional tools for social development in poor neighbourhoods. Field Actions Sci Rep J Field Actions

El Hamiani O, Khalil HE, Lounate K et al (2010) Toxicity assessment of garden soils in the vicinity of mining areas in Southern Morocco. J Hazard Mater 177:755-761. https://doi.org/10.1016/j.jhazmat.2009.12.096

EPA (2003) Superfund lead-contaminated residential sites handbook. United States Environmental Protection Agency, Office of Emergency and Remedial Response

Foti L, Dubs F, Gignoux J, Lata JC, Lerch TZ, Mathieu J, Nold F, Nunan N, Raynaud X, Abbadie L, Barot S (2017) Trace element concentrations along a gradient of urban pressure in forest and lawn soils of the Paris region (France). Sci Total Environ 598:938-948. https://doi.org/10.1016/j.scitotenv.2017.04.111

Gis Sol (2011) Synthèse sur l'état des sols de France. GIS Sol, Paris

Griffon M (2013) Qu'est ce que l'agriculture écologiquement intensive? Quae éditions, Versailles

Hamiani OE, Khalil HE, Sirguey C et al (2015) Metal concentrations in plants from mining areas in South Morocco: health risks assessment of consumption of edible and aromatic plants. CLEAN - Soil Air Water 43:399-407. https://doi.org/10.1002/clen.201300318

Harpet C (1998) Etats des lieux sur les pratiques des jardiniers amateurs: Modes de stockage, utilisation et élimination des produits phytopharmaceutiques et de leurs emballages. Essai de propositions pour une collecte sélective. Rapport de mission, UPJ

He ZL, Yang XE, Stoffella PJ (2005) Trace elements in agroecosystems and impacts on the environment. J Trace Elem Med Biol 19:125-140. https://doi.org/10.1016/j.jtemb.2005.02.010

Jean-Soro L, Guern CL, Bechet B et al (2015) Origin of trace elements in an urban garden in Nantes. France J Soils Sediments 15:1802-1812. https://doi.org/10.1007/s11368-014-0952-y

Joimel S (2015) Biodiversité et caractéristiques physico-chimiques des sols de jardins associatifs urbains français. Université de Lorraine

Joimel S, Cortet J, Jolivet CC, Saby NPA, Chenot ED, Branchu P, Consalès JN, Lefort C, Morel JL, Schwartz C (2016) Physico-

chemical characteristics of topsoil for contrasted forest, agricultural, urban and industrial land uses in France. Sci Total Environ 545-546: 40-47. https://doi.org/10.1016/j.scitotenv.2015.12.035

Kabata-Pendias A (2004) Soil-plant transfer of trace elements in environmental issue. Geoderma 122:143-149

Lamy I, Latrille C, Ducaroir J (1999) Apport des fractionnements physiques dans l'étude de la dynamique des éléments traces dans les sols. In: Spéciation des métaux dans le sol. Cahiers des Clubs CRIN, Paris, pp 56-72

Lê S, Rennes A, Josse J, et al (2008) FactoMineR: an R package for multivariate analysis. J Stat Softw 1-18

Liu X, Song Q, Tang Y, Li W, Xu J, Wu J, Wang F, Brookes PC (2013) Human health risk assessment of heavy metals in soil-vegetable system: a multi-medium analysis. Sci Total Environ 463-464:530-540. https://doi.org/10.1016/j.scitotenv.2013.06.064

McBride MB, Shayler HA, Spliethoff HM et al (2014) Concentrations of lead, cadmium and barium in urban garden-grown vegetables: the impact of soil variables. Environ Pollut 194:254-261. https://doi.org/10.1016/j.envpol.2014.07.036

Mitchell RG, Spliethoff HM, Ribaudo LN, Lopp DM, Shayler HA, Marquez-Bravo LG, Lambert VT, Ferenz GS, Russell-Anelli JM, Stone EB, McBride MB (2014) Lead (Pb) and other metals in New York City community garden soils: factors influencing contaminant distributions. Environ Pollut 187:162-169. https://doi.org/10.1016/j.envpol.2014.01.007

Morel JL, Schwartz C (1999) Qualité et gestion des sols de jardins familiaux. Comptes-Rendus L'académie D'Agriculture 85:103-114

Morel JL, Schwartz C, Florentin L (2005) Urban soils. Encycl Soils Environ 335:202-208

Nabulo G, Black CR, Craigon J, Young SD (2012) Does consumption of leafy vegetables grown in peri-urban agriculture pose a risk to human health? Environ Pollut 162:389-398. https://doi.org/10.1016/j.envpol.2011.11.040

Nabulo G, Young SD, Black CR (2010) Assessing risk to human health from tropical leafy vegetables grown on contaminated urban soils. Sci Total Environ 408:5338-5351. https://doi.org/10.1016/j.scitotenv.2010.06.034

Schroeder WH, Dobson M, Kane DM, Johnson ND (1987) Toxic trace elements associated with airborne particulate matter: a review. J Air Pollut Control Assoc 37:1267-1285

Sterckman T, Douay F, Baize D, Fourrier H, Proix N, Schvartz C (2006) Trace elements in soils developed in sedimentary materials from Northern France. Geoderma 136:912-929. https://doi.org/10.1016/j.geoderma.2006.06.010

Szolnoki Z, Farsang A, Puskás I (2013) Cumulative impacts of human activities on urban garden soils: origin and accumulation of metals. Environ Pollut Barking Essex 1987 177:106-115. https://doi.org/10.1016/j.envpol.2013.02.007

Thiry M, Huet-Taillantier S, Schmitt J-M (2002) The industrial waste land of Mortagne-du-Nord (59) - I - Assesment, composition of the slags, hydrochemistry, hydrology and estimate of the outfluxes. Société Géologique Fr 4:

Tresch S, Moretti M, Le Bayon R-C, et al (2018) A Gardener's influence on urban soil quality. Front Environ Sci 6: https://doi.org/10.3389/fenvs.2018.00025

van Gestel CAM (2008) Physico-chemical and biological parameters determine metal bioavailability in soils. Sci Total Environ 406: 385-395. https://doi.org/10.1016/j.scitotenv.2008.05.050

Zhideeva VA, Vasenev II, Shcherbakov AP, Vaseneva EG (2000) Contamination of chernozemic allotment soils by heavy metals in the affected zone of the lead-nickel-cadmium plant. Eurasian Soil Sci 33:196-206