Regular assessment and monitoring of soil pollution in the NENA region is lacking. Researchers have often concluded that there is a need to elaborate measures to address the impact of pollution on human health and the environment, and emphasize the role of legislative and executive bodies in developing, implementing and enforcing legislation for the protection of public health and environment. In 2020, no monitoring system had been established for soil contaminants in the region, and only area-specific data exist from development or research projects. Some examples are cited below.
Trace elements and many other contaminants become attached to eroded soil particles and settle as sediments in water bodies. Floods can then mix these sediments with lowland soils. Bed sediments and adjacent flood soils of the Ibrahim River (Lebanon) show elevated levels of cadmium, chromium, copper, iron, manganese, nickel, lead and zinc, from the upstream source to the sea outlet (Korfali and Davies, 2004). Korfali and Davies (2005) studied Mediterranean soils developed from calcareous rocks to determine the fate and seasonal variation of trace elements in weathered and transported soil particles. The results showed an increase in the total iron content in Fluvisols (a soil with fluvial origin) after winter floods, but the total concentration and availability of cadmium, copper and lead decreased due to the increase in the carbonate-linked forms of the trace elements. This finding was used to postulate about river self-purification in Mediterranean karst areas. However, this conclusion can only be justified in undisturbed basins. In highly populated watersheds with diverse anthropogenic activities and pressures, eroded soil material and direct discharge in winter can bring additional contaminants into low lands such as the coastal flood plain.
Surface sediments of the Gabes Gulf, Tunisia, have shown to be a “high ecological risk” indicate the “potential negative impacts of industrial pollutants” notably zinc, cadmium, chromium, lead, copper and mercury partly derived from phosphogypsum and other industrial wastes (El Zrelli et al., 2015). The pollution load index (PLI) values ranged between 1.27 and 26.25. Compared to the classification of Tomlinson et al. (1980), these surface sediments, with their mean PLI value of 4.43, should be classified as “polluted”.
Othman, Mat Jafri and San (2010) demonstrated that satellite images could be used to detect, with a high confidence interval the concentration of particulate matter over Makkah, Saudi Arabia. This could facilitate the monitoring and control of contaminated dust transport and fall out in large cities, water reservoirs and agricultural land. The use of proximal and remote sensing tools to assess and monitor soil contamination with trace elements and petroleum hydrocarbons has several advantages. These technologies allow large areas to be monitored with high temporal and spatial resolution at a feasible cost (Gholizadeh et al., 2018).
The long-range, and sometimes transboundary, windborne migration of dust contaminated by radionuclides can impact the soil and food chain of areas of deposition. The Lebanese National Environmental Radiation Survey Program has been conducting continuous radiation monitoring since 2009. A total of 950 environmental samples (rivers, wells, marine samples, soil and food) had been collected and analysed through a radiation early warning system (El Samad et al., 2017). The levels of caesium-137 detected in samples of milk, serum and jam samples were well below the national allowable level, while the levels of other radionuclides, such as uranium-238, thorium-232, and potassium-40 were comparable to those reported in other studies conducted in elsewhere in the world.
Samples collected inside and outside Greater Cairo, Egypt, showed concentrations of rare earth elements as high as 60 mg/kg. The highest concentration of rare earth elements was found in dust samples collected in the middle of the Nile Delta, Egypt’s most important zone of agricultural production of food and feed crops for domestic use and export. The radioactivity of soils on Mount Lebanon was surveyed and mapped. The main radionuclides and their average level of radioactivity were: uranium-238 (37 Bq/kg), thorium-232 (24 Bq/kg), radium-226 (46 Bq/kg), potassium-40 (206 Bq/kg), and caesium-137 (23 Bq/kg) (El Samad, Baydoun and Abdallah, 2018). While the radiation of all elements stated was within the permissible level, radium-226 showed slightly elevated values compared to those reported worldwide. The risk of transfer of radionuclides to crops was tested in Jordan and revealed that the largest transfer of potassium-40 was to apple trees (transfer factor2 of 2.2) while the least was to wheat (transfer factor of 0.9). There was a direct correlation between the amount of rainfall and transfer of uranium-239 (Awadallah and Arafah, 2006).
The German-Arab Technical Cooperation Project No 96.2189.7 (1997-2002) assessed the status and vulnerability to contamination of soils in the plains of Ghouta (Syrian Arab Republic) and Bekaa (Lebanon).
Soil sampling in the traditional agricultural zone of Ghouta showed increased levels of certain trace elements related to point sources of pollution. The project examined the concentration and spatial distribution of trace elements in 51 soil profiles and 22 topsoil samples in an intensive agricultural area of the Damascus Ghouta (Möller et al., 2005). The main source of trace elements was attributed to emissions from transport and sewage inputs. The study considered that household and industrial sewage effluents were responsible for the increased trace elements concentrations in the soils. According to the study, the tannery industry in Zablatani caused high concentrations of chromium (up to 2 100 mg/kg). However, other trace elements (lead, copper and zinc) were below the tolerable values for agricultural land use, according to Eikmann and Kloke guidelines (Eikmann and Kloke, 1991). A hot spot was identified in the south of Jaramana that contained copper (5 670 mg/kg), zinc (3 037 mg/kg) and nickel (130 mg/kg). Despite the increased ecological risk from trace elements, the calcareous nature of local soils can limit the mobility of trace elements. Although this can reduce potential health problems, direct ingestion of soil and dust inhalation may contribute to the accumulation of trace elements in human tissue and livestock. The study concluded with the recommendation that technical measures to treat the domestic and industrial effluents and remediate the contaminated soils should be a top priority for the Syrian Arab Republic.
Soil analysis in the Lebanese studied area revealed the accumulation of chromium, nickel, lead, and arsenic in the topsoil related to point sources. The results showed a natural background concentration of nickel below the critical level, with large areas classified as tolerable level II, and a small area classified as tolerance level III, according to the classification recommended by Eikmann, Kloke and Eikmann (1993) for soil contamination with trace elements (Error! Reference source not found.). This classification makes it possible to determine the recommended land use based on soil quality, where the level I (close to natural background values) allows for multifunctional land use. The application of these criteria to the soils studied in Lebanon made it possible to recommend a controlled cropping pattern in soils with level II and advised land restoration in soils with level III. The overall assessment of soil vulnerability to trace element contamination and its tolerance to different levels of contamination in both Ghouta and Central Bekaa revealed that a large area of arable soils was moderately affected by trace elements accumulation. These areas would require policy interventions to control local land use. No risks from PAH and PCB contaminants in either Ghouta (Syrian Arab Republic) or Bekaa (Lebanon) was revealed by the surface soil sampling and analysis. The study recommended that soil contamination by pesticides and plastics should be placed on the agenda of national and regional stakeholders and decision-makers to complement the assessment on soil vulnerability and hazards and to set guidelines for well-known and emerging organic contaminants.
A comparative study on residual DDT concentrations in rural, agricultural and urban Lebanese soils showed permissible levels for agricultural soils (<1 mg/kg soil) except for urban soils where relatively high concentrations of DDT were found (Bashour et al., 2004). The ratio between DDT and DDE indicated a past use of DDT before the banning in 1982.
A study in Elhajeb-Sfax (Morocco) assessed the fate of trace elements in the soil-groundwater system and the food chain. It identified the vertical and lateral distribution of trace elements in calcisols and fluvisols that had been furrow irrigated with treated wastewater over 17 years and 4 years, respectively (Belaid et al., 2019). In fluvisols, deep vertical and lateral soil sampling revealed a translocation of chromium, zinc and copper to the subsoil at a depth of 90 cm. While in sub-alkaline calcisols, trace elements accumulated at the soil surface (0-30 cm). Thus, the nature of soil is a major factor in the mobility of trace elements and hazards.
In the Gaza Strip the DRASTIC model3 for spatial analysis was used in a study of the vulnerability of soil and groundwater to nitrate contamination that originated from different agricultural activities (Almasri et al., 2005). The outputs provided excellent material for farmers and regulators to monitor unsustainable land management practices. A similar assessment was undertaken in the Bekaa Plain, Lebanon, which represents the main agricultural area of the country. The results of multiyear seasonal monitoring the wells of 15 farms with different cropping pattern (vegetable, potato-wheat rotation, fruit trees, and grapevines), and different agricultural practices, showed the leaking of nitrates from the soil, and pointed out the high vulnerability of the soil-groundwater system to contamination with soluble contaminants (Darwish et al., 2011a). The spatial distribution of nitrate levels in groundwater, reaching 450 mg/litre (as NO3) confirmed nitrogen over-fertilization and over-irrigation, which mobilized nitrate over a large area of groundwater, and increased NO3 contamination. However, as the Lebanese standards set by the Ministry of Agriculture respect the FAO irrigation water quality thresholds, the extension service does little to raise awareness on the risks associated with nitrate contamination of the soil, water, and food chain.
Agricultural soils along the Orontos River in the Syrian Arab Republic have shown increased levels of trace elements in the topsoil due to intensive agricultural practices, agrochemical application and irrigation with untreated sewage water. The semi-arid area in the south-west of the country became densely-populated following urban and industrial expansion (Husein et al., 2019). Agricultural soils revealed acceptable lead concentrations, but areas located along and in the vicinity of the riverbanks showed high values of lead (over 95 mg/kg), exceeding Syrian standards. The soil pollution could possibly result from recurrent flooding or irrigation with contaminated water from the river into which wastewater and industrial water are often discharged without prior treatment. According to the authors, the greater variability and increase in the total concentration of zinc (760 mg/kg) and cadmium (9.8 mg/kg) required attention because of the potential impacts on human-health and livestock. Copper increased in the vicinity of a sewage plant and showed high concentrations that correlated significantly with soil organic matter content. The addition of solid waste compost for 15 years to agricultural soils in the Syrian Arab Republic contributed to the accumulation of lead, cadmium, zinc and iron in amounts exceeding 2-3 times the soil background values (Ibrahim et al., 2017). In the absence of national quality standards for the composted materials, the continuous addition of composted solid waste can pollute the soil and groundwater system. A three-year study on the application of good quality sewage sludge (up to 15 tonnes per hectare) under field crops (wheat and cotton), did not significantly change the content of lead, cadmium, nickel and chromium in the soil, which remained within the natural occurrence values (Jezdani et al., 2009). These results demonstrate the importance of quality controls for soil organic amendments.
Following the intensive use of agrochemicals and other soil amendments around the city of Benghazi, Libya, four arable soils were sampled and found to be polluted with trace elements (lead, cadmium, zinc and copper). Total earthworm mortality was observed along with a simultaneous decline in the number of cocoons (Haeba et al., 2013). The biota in other soils with moderate and low trace elements concentrations showed no negative effects.
Taghipour et al. (2013) have reported the potential pollution of arable soils resulting from the application of municipal and industrial wastewater, sludge and fertilizers in Tabriz, the fourth largest city of Iran (Islamic Republic of). Soils had the following average trace element concentrations: cadmium (1.6 mg/kg), lead (10.6 mg/kg), copper (101.3 mg/kg), chromium (87.4 mg/kg), nickel (38.7 mg/kg), and zinc (98.3 mg/kg). The reported data by Taghipour et al. (2013) exceeded the natural background values, set for the country, but did not exceed the national threshold limits for agricultural lands. With a mean value of the pollution index4, equivalent to 1.81, soils showed moderate contamination. However, some sites had to be considered severely polluted as they had concentrations of chromium (up to 1 364 mg/kg) that exceed the guideline levels.
Agricultural soils enriched with organic matter from 12 sites in Quessna district, located in the south-western Nile Delta, Egypt, presented an ecological risk due to their elevated content beyond background values of zinc, chromium and lead, with evident translocation to deep soil layers (Khalifa and Gad, 2018). The vertical and spatial distribution of trace elements was linked to soil properties and anthropogenic sources, such as dense urban expansion, industry and agricultural practices. The use of different pollution indicators (enrichment factor, geo-accumulation index, improved Nemerow pollution index, pollution load index and potential ecological risk index) (see Kowalska et al. (2018) for explanation on the different indices) allows the studied area to be classified as uncontaminated to moderately polluted. These ranges compare to those three Libyan soils with minor or no effect on biota that were mentioned above.
The assessment of the extent of soil pollution in traditional arable lands in the Nile Delta using all available trace elements accumulation and pollution indices led to a recommendation for additional research to determine the risk of trace elements to human health. However, an earlier study (Badawy et al., 2017) indicated that after four millennia of human activities, Lower Nile sediments and the Delta soils are not adversely contaminated by the trace elements nickel, zinc and arsenic. This study, based on 72 soil and sediment samples collected in the Asyut-Cairo Nile section, showed that the concentrations and distribution of these elements did not affect the quality of the transported sediments. This was despite the igneous origin of the minerals derived from rock weathering in the Ethiopian highlands indicating natural abundance. A previous study conducted by Shokr et al. (2016) on agricultural soils in El-Gharbia Governorate, Egypt, showed high levels of vanadium, nickel and chromium caused by industry and urban activities, but with no risk of accumulation of copper and zinc in the soils.
In Libya, Aishah and Elssaidi (2019) identified high levels of trace elements in soils around the industrial areas of Benghazi, Sirt, Zwara and Komes. The authors noted that the areas of Benghazi and Al-Marj potentially represented a higher pollution hazard and indicated the need to implement monitoring and control of soil quality in Libya.
In Abu-Kammash, Libya an assessment of soil contamination by trace elements, including titanium, beryllium, tungsten, phosphorus and vanadium, showed the influence on soil quality of its proximity to the discharge area of wastewater from a petrochemical complex (Banana et al., 2017). The mean concentration of trace elements on soil surface ranged from 18.5 µg/kg for vanadium to 1 120 µg/kg of zinc. Several organic contaminants, such as petrochemical compounds, were frequently identified in the studied soils. The hydrocarbon contaminants included hentriacontane (C31H64), 3-methyl-2oxopropylfuran (C8H10O2) and tertrapentacontane (C54H108Br2), which alter soil properties and lead to changes in plant species distribution. They can affect human health via transfer through the food chain (Pichtel, 2016).
Cadmium and lead resulting from various anthropogenic activities and arsenic from a nearby cement factory were identified as the main contaminants in agricultural topsoil surrounding the Urmia Lake in the north-west of Iran (Islamic Republic of). Seven percent of sites in the study had contaminant levels that exceeded the national guidelines (Mohammadi et al., 2018). Kaydan, Nazarpour and Ghanavati assessed trace element pollution originating from vehicle emissions in 20 Ahvaz parks in Iran (Islamic Republic of). Average concentrations of chromium, zinc, nickel, lead were several times higher than the “base content” level. These levels posed a significant health risk to children, the most frequent visitors who not only touch the soil particles but potentially inhale and digest them (Kaydan, Nazarpour and Ghanavati, 2019).