Recently, there has been a worldwide concern regarding soil contamination by heavy metals and organic compounds, especially in the developing countries including Lebanon that has suffered from solid waste mismanagement for decades. Deir Kanoun Ras El Ain is a village in southern Lebanon that possesses one of the country’s worst dumps, and its leachates influx into a running canal that irrigates surrounding agricultural lands. The aim of this study was to determine the levels of some toxic heavy metals and organic compounds in different soil samples collected from the dump and along the canal during winter and summer seasons. Six research sites (four from the dump and two along the canal) were selected, and the soil samples for analysis were collected from a depth of around 10 cm. Heavy metals (lead, cadmium, arsenic, and mercury) and organic compounds (phthalates, bisphenol A, and polyaromatic hydrocarbons) content were determined using atomic absorption and high pressure liquid chromatography, respectively. The conducted research confirmed high levels of contamination in the collected soil samples by both heavy metals and organic compounds. The present study provided evidence that different sampling sites accumulated heavy metals at concentrations that exceeded the average maximum permissible levels for sewage sludge and agricultural land. These findings suggest the need for mitigation measures by the Lebanese authorities and new waste management programs to resolve the problems associated with uncontrolled dumping of solid wastes in Lebanon.
Recently, environmental contamination by high levels of heavy metals and organic compounds has raised the global public health concerns especially in the developing countries [
In addition, soil contamination by heavy metals and organic compounds may affect water resources and agricultural areas where the soil-crop system plays a chief role in the exposure of humans to contaminants [
Lebanon has suffered from solid waste mismanagement for decades [
Samples were collected in triplicate during winter and summer seasons of 2017. Sampling sites included two along the canal and four surrounding the dump as presented in Table
Sampling sites from Deir Kanoun dump and canal.
Site | Location details |
---|---|
C1 | (i) Deir Kanoun canal |
(ii) | |
C2 | (i) Klayleh |
(ii) | |
D1 | (i) Dump contact with C1 |
(ii) | |
D2 | (i) Dump ∼ 90o to C1 |
(ii) | |
D3 | (i) Dump ∼ 180o to C1 |
(ii) | |
D4 | (i) Dump ∼ 220o to C1 |
(ii) |
The concentrations of heavy metals such as lead, cadmium, arsenic, and mercury (Pb, Cd, As, and Hg) were assessed in soil samples using atomic absorption spectrophotometer (Bioteckno, Model: GF95Z, UK). Analysis was performed at the Lebanese Agricultural Research Institute (LARI) in Lebanon. Details of the analysis procedure are available in Supplemental Materials.
The methods for phthalates and bisphenol A extraction and fractionation were carried out according to those described by Fromme et al. [
The concentrations of heavy metals assessed in soil samples collected during summer season are presented in Table
Average concentrations (
Heavy metal | Sample site | |||||
---|---|---|---|---|---|---|
D1 | D2 | D3 | D4 | C1 | C2 | |
Pb | 504.3 ± 73.02 | 622.1 ± 82.98 | 1206.1 ± 80.35 | 1306.1 ± 12.62 | 1365 ± 31.5 | 728.4 ± 83.68 |
Cd | 131.1 ± 32.21 | 118.7 ± 15.03 | 117 ± 24.44 | 77 ± 27.22 | 78 ± 9.46 | 104.4 ± 5.5 |
As | 51 ± 15.54 | 471.97 ± 77.42 | 521.7 ± 74.68 | 95.87 ± 15.75 | 603.3 ± 91.08 | 281.6 ± 86.81 |
Hg | 3.587 ± 1.27 | 0.459 ± 0.156 | 2.39 ± 0.416 | 0.16 ± 0.044 | 6.48 ± 0.761 | 0.38 ± 0.073 |
Guidelines for the maximum permissible limit (MPL) values of selected heavy metals in sewage sludge used as agricultural fertilizer.
Heavy metal | US EPAa mg/kg | CCMEb mg/kg | EECc mg/kg | Franced mg/kg | Average |
---|---|---|---|---|---|
Pb | 840 | 600 | 750–1200 | 800 | 804 |
Cd | 85 | 22 | 20–40 | 20 | 39.25 |
As | 75 | 40–75 | - | - | 66.25 |
Hg | 17 | 24 | 16–25 | 10 | 17.88 |
aUnited States Environmental Protection Agency [
Guidelines for the maximum permissible limit (MPL) values of selected heavy metals in agricultural soil.
Metal | FAO/WHOa mg/kg | ECbmg/kg | UScmg/kg | Franced mg/kg | Germanyd mg/kg | Austriad mg/kg | SEPA China (Grade III) mg/kg | Arab-German Coop Projectfmg/kg | Average |
---|---|---|---|---|---|---|---|---|---|
Pb | 90–400 | 50–300 | 50–300 | 70–150 | 100 | 100 | 500 | 100 | 166.25 |
Cd | 1–3 | 1.6 | 1–3 | 1.5–3 | 5 | 1 | 1 | 2.12 | |
As | - | 20 | 14 | 30 | 50 | 50 | - | - | 32.8 |
Hg | 1 | 1 | 0.5 | 1 | 2 | 5 | 1.5 | - | 1.71 |
aFood and Agriculture Organization of the United Nations and the World Health Organization [
Distribution of heavy metals among different sampling sites.
Pb, Cd, As, and Hg were abundant in all of the collected samples from dump and canal, where their concentrations ranged 504.3–1365 mg/kg, 77–131.1 mg/kg, 51–603.3 mg/kg, and 0.16–6.48 mg/kg, respectively. Pb, As, and Hg concentrations were the highest in soil samples collected from C1 site. Concerning samples collected around the dump, D4 site contained the highest concentrations of Pb (1306.07 mg/kg), while Cd and Hg were at the highest levels at D1 site (131.1 mg/kg and 3.58 mg/kg, resp.). As was highly abundant in soil samples collected from D2 (471.97 mg/kg) and D3 (521.7 mg/kg) sites.
While absolute values of heavy metal contamination are important, especially during remediation efforts, these values do not take into account the relative toxicity of the individual metals present at each site. These relative toxicities are considered in the determination of the maximum permission limits (MPL) set by various governmental regulatory agencies. The maximal permissible levels for Pb, Cd, As, and Hg in sewage sludge are shown in Table
(a, b) The study area showing the dump and canal sites (D1, D2, D3, D4, C1, and C2). (c) Map of Lebanon showing Deir Kanoun Ras El Ain village.
Comparison of the levels of heavy metals to the sewage sludge MPLs promulgated by several countries showed that Pb levels at D3, D4, and C1 sites surpassed the quality standards of EEC, France, US EPA, and CCME. In addition, the levels of Cd at all sites except D4 and C1 surpassed the sewage sludge MPLs of EEC, France, US EPA, and CCME. The D4 and C1 sites had Cd levels that fell below the MPLs promulgated by the US EPA; however, these Cd levels exceeded the Cd MPLS set by the European Union, Canada, and France. The levels of As at all sites except D1 highly exceeded the US EPA and CCME sewage sludge standards. Only three EU member states (Bulgaria, Czech Republic, and Denmark) currently regulate As in sewage sludge, with an MPL of 25–30 mg/kg [
An average MPL value for each metal was calculated (Table
Relative toxic effects of heavy metals at different sampling sites, expressed as fold above average permissible level in sewage sludge.
Soil samples collected were also from surrounding agricultural lands apart the sludge soil. Thus, we compared the levels of the heavy metals analyzed in these samples to the maximum permissible limits of agricultural soil, as set by the guidelines shown in Table
To provide a clearer indication of which of the metals may pose the greatest risks to residents who may consume food grown in the agricultural land surrounding the studied dump area, the fold above the agricultural MPL for each metal at each site was also calculated and presented in Figure
The distribution of fold above average permissible level of different heavy metals for agricultural soil among different sample sites.
The levels of organic compounds expected at dumpsites (plastic residues and products of incomplete combustion) were also assessed in soil samples collected from the dump and canal sites during two seasons. These data are presented in Table
Average concentrations (
Organic compound | Sample site | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
D1 | D2 | D3 | D4 | C1 | C2 | ||||||
W | S | W | S | W | S | W | S | S | W | S | |
Di-n-butyl phthalate | 6.25 ± 0.002 | 8.24 ± 0.003 | — | 1.27 ± 0.0003 | 2.13 ± 0.001 | 2.42 ± 0.001 | — | — | 1.23 ± 0.002 | — | 1.79 ± 0.003 |
Bis(2-ethylhexyl) phthalate | 12.59 ± 0.003 | 15.56 ± 0.004 | 8.96 ± 0.004 | 11.13 ± 0.002 | 3.3 ± 0.002 | 4.055 ± 0.003 | — | 1.84 ± 0.001 | 3.16 ± 0.002 | — | 5.04 ± 0.004 |
Bisphenol A | 1.454 ± 0.0002 | 2.027 ± 0.001 | 0.888 ± 0.0002 | 1.23 ± 0.002 | 0.032 ± 0.0003 | 0.049 ± 0.0001 | — | 0.024 ± 0.0002 | 0.064 ± 0.0001 | — | 0.354 ± 0.0001 |
Benzo | — | — | — | — | 0.022 ± 0.0002 | — | 0.012 ± 0.0005 | — | — | 0.075 ± 0.0003 | — |
(—) means not detectable.
As seen in Table
The lack of waste management policies in Lebanon has led to uncontrolled dumping of both household and hazardous solid wastes [
Regarding heavy metals, our findings indicate that Pb, Cd, and As were the most serious metal pollutants in soil samples collected from Deir Kanoun dump and canal. Upon comparing our data to previously published research studies, it was noted that our findings are similar to those obtained by Tang et al. [
Additionally, the levels of Pb, Cd, and As exceeded the sewage sludge maximum permissible limits (MPL) of several quality standards. Fold above average MPL for each metal at each site showed that As levels had the highest fold above average MPL followed by Cd and Pb. Comparing our results to the MPL of heavy metals in agricultural soil set by different guidelines showed that the concentrations of Pb, Cd, and As in all soil samples greatly surpassed the quality standards of several agencies. It should be noted that the dump area in Deir Kanoun Ras El Ain is surrounded by agricultural lands, and the canal from which samples were collected irrigates these lands. The fact that Cd and As greatly exceed the MPLs for both sewage sludge and agricultural soil indicates that these two metals may pose a risk to residents who live near the dumpsite and consume crops grown in contaminated agricultural lands. In fact, high levels of Pb, Cd, and As have been shown to exert damaging effects and serious disorders in living organisms [
Moreover, the findings reported herein are of serious concern since Cd has been widely associated with decreased bone mineral density which subsequently leads to increased risk of bone fracture in both experimental models and populations-based studies [
In addition to heavy metals, we were also able to detect the presence of phthalates (DBP and DEHP), bisphenol A, and benzo(
Besides phthalates, bishenol A (BPA) is an important organic compound that acts as an endocrine disruptor, mainly as an estrogen, and it is widely used in the industrial manufacture of plastics [
Regarding PAHs, our study focused on benzo(
Finally, it is crucial to provide a brief comparison of pollution between the different sites of soil collection. Among all the studied sites, sites C1, D4, and D3 were the most heavily contaminated with heavy metals, while site D1 had the highest levels of organic compounds. There are several factors that lead to the different levels and distribution of heavy metals and organic compounds, such as the type of dumped waste at each site, soil properties, soil organic matter (SOM), distance to the sources of contamination, use of lands, type of grown crops, and dry or wet depositions which may explain why our summer collections had higher levels of organic compounds than winter collections [
It should be taken into consideration that the toxicological effects of such compounds depend on their bioavailability, metabolism, and excretion into organisms and humans. Thus, the current results suggest further investigation of the levels of heavy metals and organic compounds in crops grown in agricultural lands near the dump and irrigated from the canal. Furthermore, serious actions and mitigation measures must be taken by the Lebanese authorities to solve the current environmental disaster as well as other similar dumps. Additionally, it is hoped that these findings lead to a greater awareness of the hazardous consequences of unregulated waste dumping.
The results of the current study show that soil samples collected from Deir Kanoun Ras El Ein dump and canal were heavily contaminated with heavy metals. The presence of organic compounds including phthalates, bisphenol, and PAHs was also noted. The concentrations of heavy metals highly exceeded the permissible limits recommended by different agencies. The presence of heavy metals and organic compounds in the irrigation canal may also affect agricultural lands that are irrigated by canal's water and, ultimately, the health of inhabitants who consume the crops grown in these contaminated soils. More studies are clearly needed to determine the extent of heavy metal contamination at various distances from the dump’s site and in the crops grown in fields both adjacent to and more distant from this dump. Since both the heavy metals and organic pollutants are a result of the uncontrolled dumping of solid waste at this site, stricter environmental policies regarding waste management should be implemented by the Lebanese authorities and guidance should be given to local inhabitants about healthy management practices regarding information pertinent to their health status.
All data in this study are included in the figures, tables, and supplementary data.
The authors declare that they have no conflicts of interest.
This work was financially supported by the U.S National Academy of Science PEER Cycle 5 Program for Grant no. 5-56 and Grant Award Number AID-OAA-A-11-00012.
It includes detailed methods to determine the heavy metals and organic compounds and our calculation of average minimum permissible levels of heavy metals and their relationships to levels in the soils analyzed in this study, as well as graphic of organic contaminant levels at test sites during winter and summer.