Environmental exposure assessment of cadmium, lead, copper and zinc in different Palestinian canned foods

Many chemical elements that present in the human diet are essential for human life at low concentrations but can be toxic at high concentrations and chronic exposure. We aimed to assess the levels of some heavy metals in canned food that are sold in the Palestinian market and compare them with the recommended international limits. A total of sixteen canned food samples were collected. The samples included four different manufactures for each of beans, chickpeas, corn and mushroom. After homogenization and samples treatment, the concentrations were determined using flame atomic absorption spectrometer IcE-3000 SERIES. The concentrations were found to be in the range of 0.089–1.17 mg/L for Pb, 0.019–0.32 mg/L for Cd, 2.05–10.6 mg/L for Zn and 0.79–3.97 mg/L for Cu. Cadmium and copper results were higher than the maximum permissible limit (0.006 and 0.9 mg/L, respectively), whereas lead (except for only one sample: marina corn) and zinc levels were within the maximum permissible limits (1 and 11 mg/L, respectively). The results necessitate continuous monitoring of Cd and Cu levels and controlling of canning process to obtain food safety. As an important environmental health concern, we recommend future human biomonitoring studies to correlate environmental exposure of these elements to biological markers.


Dedication
To my parents who made the best for me and gave me the opportunity to have this master degree.  Lead and Cadmium are from the prevalent toxic elements in food and environment that have a long half-life after absorption. In humans and animals; they can make unpleasant effects such as damage to internal organs. Cadmium accumulates in the human body and especially in the kidneys which could lead to dysfunction of the kidney with impaired reabsorption of some molecules such as: proteins, glucose, and amino acids [5] . Exposure to lead affects multiple health outcomes and physiological systems, including: hypertension, the gastrointestinal system, anemia, nephropathy, vitamin D metabolism, decreased growth, the immune system, the nervous system, behavioral/cognitive/IQ, nerve conductive effects, hearing loss, effects on reproduction and development and death from encephalopathy [6] . 2 Trace heavy metals are significant in nutrition, either for their essential nature or their toxicity. Copper and Zinc are known to be essential and may enter the food materials from soil through mineralization by crops or environmental contamination with metal-based pesticides. The adult human body contains about 1.5 to 2 ppm (parts per million) of Copper [7] and 33ppm of Zinc [8] . Excessive intake of either Copper or Zinc has been reported to be toxic [9] .
Heavy metal ions are essential micronutrients for plant metabolism but when present in excess, can become extremely toxic. Heavy metals are dangerous because they tend to bio-accumulate. Bioaccumulation means an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment [10] .
Copper and Zinc are essential micronutrients if consumed in adequate amounts, but they might become toxic when consumed excessively. In contrast, Cadmium (Cd) and Lead (Pb) are toxic metals and are harmful at low concentration and are not easily biodegradable [11] . Therefore, it is important to assess the concentrations of these metals in the human food chain as environmental exposure assessment technique in order to evaluate their actual concentrations in the environmental medium (food) and whether these concentrations perform dangerous effects on the consumers when compared to the reference permissible values.

Significance of the study
Canned food is popular food sources in Palestine because they are inexpensive and affordable. There are no studies conducted in the 3 Palestinian market regarding the determination of heavy metals Pb, Cd and trace metals Cu, Zn in canned food. This study will shed the light to any exposure levels to these elements in our diet and compare it to the permissible exposure limits. This would further suggest a preventive measures and alternatives to these food sources with the policy and decision makers at the national level.

General objective
To determine the concentrations of heavy metals (Cd, Pb) and trace elements (Cu, Zn) in the food chains in the Palestinian market. Canning is a method of preserving food by first sealing it in air-tight jars, cans or pouches, and then heating it to a temperature that destroys contaminating microorganisms that can either be of health or spoilage concern because of the danger posed by several spore-forming thermoresistant microorganisms. The process of canning is sometimes called sterilization because the heat treatment of the food eliminates all microorganisms that can spoil the food and those that are harmful to humans, including directly pathogenic bacteria and those that produce lethal toxins [12] .

Cadmium
Cadmium has been widely dispersed into the environment through the air by its mining and smelting and by other man-made routes such as: usage of phosphate fertilizers, presence in sewage sludge, and various industrial uses such as the Nickel-Cadmium (Ni-Cd) batteries, plating, pigments and plastics. Then Cadmium compounds can be associated with respirablesized airborne particles and can be carried long distances. Once on the ground, Cadmium moves easily through soil layers and is taken up into the food chain by plants' uptake such as leafy vegetables, root crops, cereals and grains [13] . 5 The total Cadmium body burden at birth is non-detectable .It gradually increases with age to about 9.5 mg to 50 mg [13] .The kidneys and liver together contain about 50% of the body's accumulation of Cadmium [35] .
The biological half-life of Cadmium in the kidney is estimated to be between 6 to 38 years; the half-life of Cadmium in the liver is between 4 and 19 years .These long half-lives reflect the hypothesis that humans do not have effective pathways for Cadmium elimination. Cadmium has no known biologic function in humans. Bioaccumulation appears to be a byproduct of increasing industrialization. Any excessive accumulation in the body should be regarded as potentially toxic. Due to slow excretion, Cadmium accumulates in the body over a lifetime and its biologic half -life may be up to 38 years [13] .
Cadmium is known to increase the oxidative stress by being a catalyst in the formation of reactive oxygen species, increasing lipid peroxidation and depleting glutathione and protein-bound sulfhydryl groups. It also can stimulate the production of inflammatory cytokines and down regulates the protective function of nitric oxide formation [13] .

Lead
Lead occurs naturally in the environment. However, most of the high levels found throughout the environment come from human activities.
Environmental levels of Lead have increased more than 1,000-fold over the past three centuries as a result of human activity. The greatest increase occurred between the years 1950 and 2000, and reflected the increasing worldwide use of Leaded gasoline. Lead can enter the environment through 6 releases from mining Lead and other metals, and from factories that make or use lead, lead alloys, or Lead compounds.
The amount of lead found in canned foods decreased 87% from 1980 to 1988 in the United States, which indicates that the chance of exposure to Lead in canned food from Lead-Soldered containers has been greatly reduced. However, Lead-Soldered cans are still used in some other nations.
The effects of Lead are the same whether it enters the body through breathing or swallowing. The main target for Lead toxicity is the nervous system, both in adults and children. Long-term exposure of adults to Lead at work has resulted in decreased performance in some tests that measure functions of the nervous system [31] . Lead exposure may also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure, particularly in middle-aged and older people.
Lead exposure may also cause anemia. At high levels of exposure, Lead can severely damage the brain and kidneys in adults or children and ultimately cause death. In pregnant women, high levels of exposure to Lead may cause miscarriage. High level exposure in men can damage the organs responsible for sperm production [14] .

Zinc
Zinc is an essential element needed by our body in small amounts. We are exposed to Zinc compounds in food.

Copper
Copper can be found in plants and animals, and at high concentrations in filter feeders such as mussels and oysters. Copper is also found in a range 8 of concentrations in many foods and beverages that we eat and drink, including drinking water [32] .
Copper is readily absorbed from the stomach and small intestine. Animal studies had also reported gastrointestinal effects (hyperplasia of forestomach mucosa) following ingestion of Copper Sulfate in the diet.
Copper is also irritating to the respiratory tract. Coughing, sneezing, runny nose, pulmonary fibrosis, and increased vascularity of the nasal mucosa have been reported in workers exposed to Copper dust [17] .
The liver is also a sensitive target of toxicity.

The Food Industry Sector in the West Bank
The food processing industry is considered one of the oldest industries in Palestine. In its early days, this industry was limited to the production of few processed foods and sweets. Currently, this industry is a major contributor to the Palestinian economy and its gross domestic product. In addition, this sector has created job opportunities in the local market [18] .
According to the Palestinian Food Industries Union, the following are the most important food processing industries in the West Bank, related to agro products targeted in the project [19] :  Canned vegetables and fruits: In Palestine, there are 18 factories specialized in the production of canned vegetables and fruits.  Pasta and vermicelli: There are 5 factories working in the production of pasta and vermicelli. samples, but also exceeds the international tolerance levels [20] .

Previous Studies
Another study conducted in Lebanese market to assess heavy metals in canned food. Lead had the highest levels in corn and fava beans. Thirty percent of vegetables and legumes and 45% of fish samples had Cd levels 12 above European Union (EU) permissible level (0.1 μg/g), The concentrations of elements in food samples are shown in Table 1 [21] .  μg/person/day respectively [22] . Table 2 shows the concentrations of Lead in canned food samples in this study. the levels of (trace metals) in canned foods were higher than the reported vegetable samples [23] .
Another important study was performed in Egypt to determine heavy metals Cd and Pb and trace elements, Cu and Zn contents in legumes, cereals, cereal products and fried potatoes purchased from the Egyptian market were carried out using atomic absorption spectrometry, the levels of Pb in broad beans, common bean, lupine, fenugreek, rice, wheat, spaghetti and pasta were found to be above the permissible levels. respectively [24] .

Sampling
A total of sixteen canned food samples including beans, chickpeas, corn and mushroom were collected from a popular supermarket in Nablus city during 2015.We have chosen randomly 4 companies of each product. The different samples were transported to the chemistry laboratory at An-Najah National University and stored in a clean dry place prior to the digestion and analysis.

Samples preparation and digestion:
Each can was opened and the contents were mixed in blender and homogenized.We weighted 5 g of each can and transferred it to 100 ml CuNO 3 salt (0.465g), and dissolved in de-ionized water to give 1000 mg/L standard solution.

Apparatus
Flame Atomic absorption spectrometer IcE-3000 SERIES, Serial number c113500021 designed in UK AA Spectrometer with a hollow cathode lamp for Cadmium ,Lead, Copper and Zinc. The wavelength, slit width and lamp current of each metal was adjusted according to the description given in the manufacturer manual for determination of Cd, Pb, Cu and Zn [25] .

Calibration
The Calibration was done by introducing water as blank to adjust reading of the instrument. Stock solution was used to prepare different concentrations 0, 2,5,10 and 20 mg/L of heavy metals Cd, Pb, Zn and Cu.
After calibration, we introduced each sample into the instrument recording the steady reading obtained, and then apparatus was washed after each introduction with water as a blank solution to check that the reading returns to its initial setting.

Introduction
The results of this study were devoted to determine heavy metals

Samples origin
As shown in

Corn results
As shown in

Chickpeas results
As shown in                 Canned Beans also has the highest concentration of Cu. In contrast canned corn has the lowest. Chickpeas has higher concentration of Cu than mushroom.

References values for the studied elements
The ATSDR stated that the chronic durational oral minimal risk level (MRL) for Cd is 0.1µg/kg/day based on its renal effect (ATSDR). If we take 60 kg person , he needs 6µg/day to reach the permissible level which is lower than our results for Cd, whereas our ranges of Cd in our study was (0-0.322)mg/L which were higher than the permissible level (0.006 mg/L) [13] . Therefore, canned food may harm human health in chronic use and this maybe one of the risk factors for kidney diseases in the society, because Cd had a very high effect on kidneys, and this is an alarm in public health for kidney diseases.
Expert Committee on Food Additives has suggested a provisional tolerable intake of 400-500µg Pb per week for man [26] . However, the Food and Drug Administration (FDA) has set an action of 0.5µg/ml for Pb in products intended for use by infants and children, and has banned the use of Lead-Soldered food cans. (FDA 1994, as cited in ATSDR 1999) [14] . The Food and Agriculture Organization (FAO) has set (1mg/kg) as maximum level of Lead in canned food [27] . In our study, the maximum level of Lead was  [20] .
In our study we assessed Pb, Cd, Cu and Zn in canned foods which include corn, chickpeas, beans and mushroom that are sold in Palestinian market at Nablus city in 2015.

Main study findings
The contents of investigated metals in canned food in this study were found to be in the range of (0.089-1.17mg/L) for Pb, (0.019-0.322mg/L) for Cd, (2.05-10.6mg/L) for Zn and (0.79-2.97mg/L) for Cu. According to these data, Zn had the highest concentrations, followed by Cu then Pb .As expected, the lowest metal in our study canned food was Cd.
Cadmium had no known biological function in humans; it almost accumulates in kidneys and liver, also it has long half-life (4-19 years) [13] .
In our study the highest concentrations of Cd were in "kaseeh"canned beans (0.322mg/L) and this result agree with Korfali, Hamadan et al.2013 [21] who reported that Cd in Fava beans level as (0.483µg/g) . On the other hand, the lowest concentration of Cd in canned beans was in "Delmonaty" 0.23 mg/L and this is higher than levels of Cd reported in Radwan et al.2005 [24] in legumes at the range of (0.01-0.178) mg/kg.
Mushroom had generally low concentrations of Cd (0 -0.065mg/L in comparison to all canned food in our study and these results almost agree with S.Abd_Al-Wahab et al. 2014 [29] [21] . The presence of (Pb) in canned food may due to use of Pb in product package materials or due to absorbed Lead by plants in limit level [29] .
In general, beans had the lowest concentrations of Pb in comparison to canned food types in this study and this agree with a study conducted in Riyadh to measure Pb levels in canned beans which was reported as 0.019 µg/g in Othman ZAA et al .2010 [22] . Our reported levels of Pb in Marina corn (1.17 mg/L) which produced in Thailand was higher than that indicated in S.Abd Al_Wahab, et al .2014 [29] for sweet corn (0.75ppm) even they are from same origin. In contrast, our reported results for Pb in mushroom (0.549 mg/L for BigSea , 0.293mg/L for Marina , 0.439mg/L for Sahten o Afia , 0.454 mg/L for Americana) were lower than levels reported in S.Abd Al-Wahab et al.2014 [29] which was (1ppm) , even they are from the same origin (China).
In a study conducted in Saudi Arabia for Z.thagafi, H.Arida et al. 2014 [20] to measure heavy metals in fresh and canned food, the highest level of Pd in canned food was 7.11mg/kg which is very high in comparison to our results, whereas the highest level of Pb in our study was 1.17mg/L in Marina corn.
Lead was determined in legumes in a study performed in Egypt for Radwan et al .2005 [24] , ranged from (0.013-0.281)mg/kg, which is lower than our results in chickpeas (0.127-0.756mg/L) but approximate to our beans results (0.089-0.35)mg/L.
Copper is known as vital and toxic for many biological systems and may enter food from soil through mineralization by crops, food processing or environmental contamination, such as Copper-based pesticides [30] .
The minimum Copper value in our study was found as 0.793mg/L for "Freshly" corn and maximum value as 3.25mg/L for "Americana" beans.
Our results for Copper were low in comparison to Tuzen, Soylak et al.2007 [23] study which reported a concentration of 4.8 µg/g in Mushroom, 3.52µg/g in corn and 7.77 µg/g in canned Beans.

38
Copper value in canned food in a study performed in Saudi Arabia for Z.thagafi, H.Arida et al. 2014 [20] reported a range level of (6.22-8.03 mg/kg) which is very high in comparison to our results (0.79-3.97mg/L).
Whereas in a study conducted in Lebanon for Kofrali, Hamdan et al .2013 [21] , Cu concentration was reported as not detected in chickpeas ,mushroom and fava beans.
Zinc is one of the most important trace metals for normal growth and development of humans. Deficiency of Zinc can result from inadequate dietary intake, impaired absorption, excessive excretion or inherited defects in Zinc metabolism [15] .
Zinc had the highest levels in the present study. The maximum level of Zn was in chickpeas with average 9.9mg/L, and lowest was in mushroom with average 3.89mg/L. These results disagree with Tuzen and Soylak et al .2007 [2] who reported that mushroom had the highest levels of Zn (21.9µg/g) followed by beans (12.8µg/g) and corn (8.5µg/g), while Zn levels in our study was 6.17mg/L for corn and 8.2mg/L for beans.
The present study reported a range of (2.05-10.6mg/L) of Zn in all food samples whereas it is almost lower than levels of Zn reported in Radwan et al. 2005 [24] with a range of (6.11-15.86mg/kg) in legumes. In contrast to the study performed in Lebanon for Kofrali, Hamdan et al .2013 [21] which reported Zn concentration as not detected in the canned food .

Conclusion:
This study has assessed the metal content (essential and toxic) in different canned food categories and brands sold in Palestinian market. For toxic metals (Pb,Cd), Lead concentrations in our study were within international permissible levels, but Cadmium results were higher than international permissible levels and this is an important issue in public health for food safety and heavy metals accumulation in the human body. For the essential metals (Zn,Cu), Zinc levels were within the permissible levels, in contrast ,Copper levels were higher than the international permissible levels. In conclusion, we didn't assess or correlate the environmental exposure levels of canned food elements with human biological biomarkers or adverse effects. Therefore, conclusions whether these levels were toxic at the biological levels should be drawn with caution as we only assess some exposure concentrations of which they might be different when reaching the human body. Recommendations: 1. Efforts should be made by the government to control processing of canning raw materials.
2. The study findings necessitate continuous monitoring of Cd and Cu levels in canned food to obtain food safety.
3. A better selection of the fresh material, including an analysis for toxic elements prior to processing, could surely improve the situation.
4. The government should control the use of fertilizers by farmers which may increase Cu levels.
5. This study suggests more investigation studies to determine the contamination of canned food with heavy metals in different canned food.
6. We recommend further future studies that assess the levels of the studied elements in human body and selecting samples from hair, nails and blood and correlate this concentrations with the individual intake of the studied food items to find out whether there will be a significant correlations or not.