Evaluation of Heavy Metal Concentrations in Soil and Edible Vegetables Grown in Compost from Unknown Sources in Al-Jiftlik, Palestine

The use of compost as a fertilizer has been widely used in many countries. However, compost that contains heavy metals can transfer these metals to soils and plants (vegetables). This study investigates the concentrations of metals in soil and edible vegetables that were fertilized by polluted unknown compost in Al-Jiftlik region (Palestine). The source of the compost is the autocratic dumping sites of the Israeli settlements. The compost is distributed free of charge to the Palestinian farmers. The concentrations of Ba, Cu, Pb, Th, Se, Mn, Co and As in the contaminated farms were measured. Vegetables include: Eggplant, Corn, Bell Pepper, Cucumber and Marrow. Metals availability as well as the pH, was also examined in the soil samples. Normal farms that did not use this unknown compost were used as a reference. The concentrations of Ba, Cu, Pb, Th, Se, Mn, Co and As in soil and vegetables in the polluted farms were above the WHO limits. Barium concentrations in the vegetables were ranged from 1.00 mg/kg to 0.453 mg/kg. It is high when compared to WHO limit of 0.3 mg/kg. Copper concentrations in the vegetables were ranged from 63.84 mg/kg to 50.53 mg/kg. It is high when compared to WHO limit of 40 mg/kg. Lead concentrations in the vegetables were ranged from 1.00 mg/kg to 0.453 mg/kg. Lead concentration is high when compared to WHO limit of 0.3 mg/kg. Thallium concentrations in the vegetables were ranged from 2.99 mg/kg to 1.22 mg/kg. Thallium concentration is high when compared to WHO limit of 0.3 mg/kg. Selenium concentrations in the vegetables were ranged from 0.550 mg/kg to 0.348 mg/kg. It is high when How to cite this paper: Bawwab, M., Qutob, A., Al Khatib, M., Malassa, H., Shawahna, A. and Qutob, M. (2022) Evaluation of Heavy Metal Concentrations in Soil and Edible Vegetables Grown in Compost from Unknown Sources in Al-Jiftlik, Palestine. Journal of Environmental Protection, 13, 112-125. https://doi.org/10.4236/jep.2022.131007 Received: November 4, 2021 Accepted: January 14, 2022 Published: January 17, 2022 Copyright © 2022 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Introduction
Food quality and safety are global issues [1]. Agricultural products free of chemical contaminants especially heavy metals are important for food safety [1] [2].
Consumption of food products contaminated with metals (repeated) may cause health risks to people. They are often considered to be toxic-and toxicity depends on the dose of the toxic metal, route of exposure, and the nutritional status of the exposed human being [3] [4]. The dangerous effects of heavy metals lie in the fact that it tends to be bio-accumulated in different organs or tissues.
The bioaccumulation of these compounds in living things is due to their speed of taking [5].
Compost is a decomposed organic fertilizer resulting from the fermentation and decomposition of chopped plant residues, animal waste or aerobic garbage [6]. The use of compost as a fertilizer is significant enthusiasm for the soil and for keeping up an appropriate soil structure as well as adding organic matter that is lost due to the practice of intensive agriculture [6] [7]. Among the possible negative impacts of applying compost to cropland, are the potential arrival of dangerous metals into the soil, and the exchange of these components from the soil to the food cycle [8]. In order to use compost as a fertilizer it should be free from any Plastic materials, metals and metal objects, Grease, petroleum materials and contaminated materials [8] [9].
Recently, some regions in the West Bank agricultural land have been used as random dumps and landfills for Israeli solid wastes, especially the toxic wastes [10] [11]. Most of these lands are located close to Israeli settlements and beyond the separation wall. This operation is often carried out in coordination with local contractors. The unknown waste, which is transported from the Israeli settlements, is buried in nearby agricultural lands. The dumping waste is not subjected to any waste treatment process or any supervision practice according to international standards [12] The process of environmental pollution that begins with the soil, water, unpleasant smells and bad appearance continue by distri-

Climate
The area has an arid Mediterranean climate. The mean annual rainfall is 232 mm. The average annual temperature is 22˚C, and the average annual humidity is approximately 49.2% [15].

Population
According to the Palestinian Central Bureau of Statistics (PCBS), the total population of Al Jiftlik in 2007 was 3714; of whom 1857 were male and 1857, female.
There were additionally registered to be 578 households living in 692 housing units [16].

Economy
The economy in Al Jiftlik depends on several economic sectors, mainly: the agriculture sector, which absorbs 90% of the human workforce. Samples were taken from the surface and from the depth of 0 -30 cm according to the type of vegetables. The coordination and the vegetable type are shown in Table 1. Sampling was done according to the random method [17] for each location as shown in Figure 2. The sampling method includes: 1) A sample from each location (polluted, Reference) was taken from soil, water and vegetables. Vegetables include: Eggplant, Corn, Bell Pepper, Cucumber and Marrow.
2) The representative sample was taken by the identification of circle with a radius of 6 meter ( Figure 2).
3) Five cores were sampled inside the 6-meter circle at the surface and at a depth of 0 -30 cm from all the sites ( Figure 2).
4) The five cores were mixed with each other to form a homogeneous represented sample according to each depth, site (polluted, Reference) and the type of vegetables.
5) The representative samples were analyzed in the laboratory.

Water Sampling
Samples were collected and stored in clean plastic bottles and brought to the laboratory for analysis. Water samples were collected from the wells and the pools that were used for irrigating these vegetables in this region following the reported procedure [18].

Soil Analysis
80 ml of milli-Q water were added to 20 grams of the soil sample. The soil samples were leaved for fourteen days. Then 2 ml of the leachate were taken for analysis [18]. The samples were then analysed for the following metals Ba, Cu, Pb, Th, Se, Mn, Co and As by ICP/MS (Agilent technologies 7500 series). For accurate quantitative determination of heavy metals in water samples, an internal standard method was used using Nd as internal standard and a multi-standard calibration method: Journal of Environmental Protection metals analyzed in this study, reflecting the precision the method for the analysis of these heavy metals. Calibration curves for all metals analysed were constructed by plotting the ratio of the intensity of the analyse metal to that of the internal standard (Nd) vs. concentration of the trace metal (in µg/L), and results showed that the calibration curves are linear with correlation coefficient (r 2 ) greater than 0.999 for the trace metals analysed [18].

Vegetables Analysis
The collected vegetable samples were washed with distilled water to remove dust particles. The samples were cut into small pieces. The vegetables' part was take, and dried in an oven at 50˚C. After drying, the samples were ready for acid digestion. 0.5 grams of the dried vegetable was digested with 5 ml of 65% pure nitric acid using Mars 6 digestive apparatus, until the solution has transparent color. The digested samples were filtered using CA sterile syringe filters that has a diameter of 30 mm and the pore size 0.22 µm [19]. Determination of heavy metals in the filtrate of vegetables was achieved using ICP-MS, as described above.

Water Analysis
Water samples were tested for their content by the addition of 65% pure nitric acid. 2 ml of the sample were taken for analysis. They were analyzed by the use of ICP-MS [18].

pH Soil Analysis
The pH of soil samples was measured after the soil was soaked in water for more than 24 h. pH of the filtrate was measured using a pH meter.

Field Soil Samples
The concentrations of heavy metals in soil samples are shown in Table 1 [13]. It is important to say UDC main source does not come from Animal or Agricultural sources, but it comes from other sources that contain high concentration of Barium. Barium compounds are important pigment industry and paints [21]. Barium is also used in optical glass, ceramics, glazed pottery, glassware and Motor oil detergents [22]. Barium concentrations for all soil reference field samples at 0 cm and 0 -30 cm did not exceed the limits given by [13] (Table 1).  [13]. Thallium is used in optics, high-density glasses electronics industry and radiation devices [23]. The concentration of Thallium in the clean farms at 0 cm and 0 -30 cm soil mixtures does not exceed the FAO/WHO limit of 5 mg/kg [13].  [13]. Selenium is used in photovoltaic photocells, light meters and solar, photoconductive industry and glass industry [27]. The concentrations of Selenium in the clean soil farm were below the standard limits for all samples.  [13]. Cobalt has many applications in industry [28]. The concentrations of Cobalt in the clean soil farm were below the standard limits for all samples.
Arsenic concentrations in soil samples at 0 cm were 2.384 mg/kg, 5.172 mg/ kg, 6.362 mg/kg, 3.423 mg/kg and 12.58 mg/kg respectively. Arsenic concentrations in soil from 0 -30 cm wer 3.360 mg/kg, 5.237 mg/kg, 3.264 mg/kg, 1.573 mg/kg and 8.427 mg/kg, respectively. Arsenic concentrations are higher than WHO/FAO limit of 0.2 mg/kg [13]. Arsenic is used in semiconductor and microchip industry. The concentrations of Arsenic in the clean soil farm were below the standard limits for all samples.

Heavy Metals Concentration in Vegetable Samples
The concentrations of heavy metals in vegetable samples are shown in Table 2 [13]. Barium concentrations in the vegetables that were grown in the clean farms were below the permissible limits ( Table 2). The concentrations of Thallium in the vegetables that were fertilized by the compost were 2.350 mg/kg, 1.215 mg/kg, 2.608 mg/kg, 1.608 mg/kg and 2.986 mg/kg respectively. Thallium concentrations in vegetables exceeded the WHO limit of 0.3 mg/kg [13]. Thallium concentrations in the vegetables that were grown in the clean farms were below the permissible limits.  [30]. Manganese concentrations in the vegetables that were grown in the  [32]. Cobalt concentrations in the Corn samples were below the permissible limits. Cobalt concentrations in the vegetables that were grown in the clean farms were also below the permissible limits (Table 2). Arsenic concentrations in Corn soil, Bell pepper, Eggplant, Cucumber and Marrow vegetables that were fertilized by the compost were 0.662 mg/kg, 2.677 mg/kg, 4.306 mg/kg, 1.591 mg/kg, 3.798 mg/kg, respectively. Arsenic concentrations in these vegetables exceeded the WHO limit of 0.2 mg/kg [13] [31] [32]. Arsenic concentrations in the vegetables that were grown in the clean farms were below the permissible limits ( Table 2).

Heavy Metals Concentration in Water Used for Irrigation
The concentration of lead, cobalt, copper, Arsenic, Selenium, Barium in Agri-

pH of Soil Samples
The pH of soil samples ranges between 7.15 and 8.05. There is no clear relation between compost farms and pH values. Soil pH was basic for all clean and compost soil farms.

Conclusion
From the present study, it can be concluded that heavy metals concentrations in soil and vegetables are very high when compost is applied as a fertilizer. Heavy metals concentrations are above the recommended levels of the WHO/FAO limit.
Clearly, the compost is largely composed of industrial wastes. This kind of compost should not be used as fertilizer because of its high content of heavy metals.