Journal of Analytical & Bioanalytical Techniques
Open Access

The design requirements of ceramic crockeries are occasionally mandated for the use of decorative borosilicate enamels. However, these contain some essential and non-essential heavy metals, which may leach out from the crockeries to foodstuff and/or beverages. Moreover, it is quite difficult to eliminate the metals from the pigments used for decoration; a number of metals leached out should not surpass a certain level to avoid health threat. Toxic metals e.g., Lead and Cadmium along with those of barium, zinc, cobalt, and iron, etc. are widely contained in glazing and coloring materials. These are widely used in a variety of products, especially in ceramics, due to various aesthetic attributes. In order to have permissible levels of these metals, decorators, thirdparty laboratories and other related authorities should follow extremely accurate testing protocols to estimate the minute levels of leaching metals in parts-per-million (ppm). In this connection, national institute of hygiene and the ceramic standard in Poland recommends the limit of Cd and Pb in mg/dm3 measured by extraction and subsequent atomic absorption spectrometry [1,2]. Furthermore, according to Food and Drug Administration (FDA), the limit for Pb and Cd leachable from ceramic is 7 mg/kg and 0.5 mg/kg, respectively [3]. However, any glazed ceramic crockeries can become poisonous if it is not fired properly. Moreover, intense exposure to the heavy metals prompts sickness, anorexia, spewing, gastrointestinal irregularities and dermatitis problems [4-7]. Heavy metals are risky in light of the fact that they tend to accumulate in the living systems. This bioaccumulation implies an increase in the deposition of a chemical compound in a natural living being, which tend to have potentially failed organs as the time passes on. Basically, heavy metals refer to chemical elements with relatively high densities or with a specific gravity that is at least 5 times higher than the specific gravity of water such as As, Cd, Fe, Pb and Hg [4,8]. Therefore, the elements that are of concern in this study include Pb, Cd, Zn, Fe, Cu, Cr, Mn, and Ba.

Ceramic crockeries are widely used in many countries around the world for foodstuff. The literature survey has suggested that little attempt has been made to determine the leach out of heavy metals from glazed food and drinking products daily used not only in a specific Arab country but all over the world. Moreover, the survey demonstrated that no study has yet been carried out in Qatar to determine the leachability of different heavy metals from ceramic crockeries. Therefore, in this work, the leaching of essential and non-essential heavy metals into 4% acetic acid solution at different temperatures according to ASTM standard method (ASTM 738.81) was studied. This further enabled a simultaneous determination of Pb, Cd, Zn, Fe, Cu, Cr, Mn, and Ba by using inductively coupled plasma mass spectrometry (ICP-MS). The ceramic crockeries collected from local Qatari market were imported from China (C_china), Spain (S_spain) and India (I_india).

Fancy ceramic crockeries including bowls, teacups, saucers and dinner plates imported from China, Spain, and India, were collected from local market in Qatar. Samples from each country have been selected randomly and washed with detergent, rinsed with deionized water and conditioned at room temperature. Leachable heavy metals were collected by dipping each sample into 4% acetic acid solution at different temperatures. In a typical procedure, 2 set of samples from each country were dipped into the acid solution. After 24 hours, acid solution was decanted, and aliquots were taken for analysis. Heavy metals were analyzed according to FDA by Inductively Coupled Plasma Mass Spectrometry ICP-MS (Perkin Elmer NexION 300D). Figure 1 shows a schematic diagram of the experimental procedure.

Figure 1: Schematic diagram of the experimental procedure adopted in this study.

Inductively Coupled Plasma Mass Spectrometry (ICPMS) technique was used for elemental determinations. Inductively Coupled Plasma Mass Spectrometry is a very powerful instrument for the qualitative/qualitative analysis of heavy metals. It is a type of mass spectrometry which is capable of detecting metals at concentrations as low as one part in 10¹⁵ (part per quadrillion, ppq).

Mainly this technique was commercially introduced in 1983 and has become popular in many types of analytical laboratories due to the higher throughput and detection limits compared to other conventional spectroscopy techniques. In this connection, the detection limits of the ICP-MS, Perkin Elmer NexION 300D, instrument used for multielements analysis are given in Table 1.

Table 1: Perkin Elmer NexION 300a (ICP-MS) Minimum detection limit for multielement analysis for metals of interest in the leaching studies (ppb, μg/l).

In recent centuries, the industrial use of Pb has been considerably reduced from paints and ceramic products [9]. Despite the reduction of Pb from the paints and ceramics, human exposure to Pb remains a serious health problem [10]. Lead is the most systemic toxicant that seriously affects the kidneys, liver, central nervous system, hematopoietic system, endocrine system, and reproductive system [10]. Results of the acetic acid leaching analysis at 35°C, 45°C and 65°C are given in Tables 2-4, respectively.

Table 2: Metal released into 4% acetic acid leachate solution in ppb (μg/l) from modern DOHA ceramic samples after a contact period of 24 hours at 35°C ND means “Not Detected”.

Table 3: Metal released into 4% acetic acid leachate solution in ppb (μg/l) from modern DOHA ceramic samples after a contact period of 24 hours at 45°C ND means “Not Detected”.

Table 4: Metal released into 4% acetic acid leachate solution in ppb (μg/l) from modern DOHA ceramic samples after a contact period of 24 hours at 65°C ND means “Not Detected”.

As can be seen in Tables 2-4, Pb and Cd are not detected in Spanish imported crockeries at 35°C, 45°C, and 65°C. However, Pb which is one of the most poisonous metals, and was detected in both Chinese and Indian imported crockeries. Moreover, the amount of Pb is at a higher level for the Chinese sample (i.e., C₁ and C₂) compared to the Indian samples (i.e., I₁ and I₂) at 35°C and 45°C. However, the amount is not high enough to cause any adverse effect on human health. Interestingly, Pb was not detected from the Chinese sample (i.e., C₁ and C₂) at 65°C. In general, the higher the temperature, the higher the leaching of lead and other heavy metals as in most cases of diffusion-controlled and ion-exchange processes. However, the results as shown on comparing the general results of Tables 3 and 4, shows that the leaching at a temperature of 65°C was less than that at 45°C. This might be attributed to the formation of complexed compounds of heavy metals oxides and hydrides, which possess a lower solubility and hence not decanted with the aliquot to be analyzed. The work of Norita et al. has shown a similar trend for leaching of lead in 4% acetic acid, at which the leaching of lead has a minimum at temperature over the range of 50-70°C, with a general trend of increased leaching of lead over the range of 30-10°C [11-13].

Cd is a heavy metal of considerable ecological and industrial concern. It is extensively available in the earth's crust. Cd is frequently used in the production of alloys, pigments, and ceramics. The possible exposure to Cd is via ingestion of contaminated food and smoking, smoking being a major contributor. Extensive exposure to Cd seriously affects the blood vessels, pulmonary function and chest radiographs that are consistent with emphysema [5,6]. The analysis shows that Cd was no released from all the samples at 35°C, 45°C and 65°C, respectively.

It is noteworthy to mention that some of the heavy metals (i.e., Fe, Cu, and Zn) are essential for living beings [14-16]. These essential heavy metals are an integral part of several enzymes and also participate in redox reactions in living cells. However, all these essential heavy metals are toxic at high concentrations and can be damaging to the organism.

The amounts of essential heavy metals (i.e., Zn, Fe and Cu) are significantly higher compared to the level of Pb leached from all the samples at 35°, 45° and 65°C, respectively. Chromium (Cr) belongs to the transition element with oxidation states ranging from chromium (II) to chromium (VI) [Cr(III)]. Cr is considered an essential nutrient that plays a role in glucose, fat and protein metabolism by potentiating the action of insulin. On the other hand, chromium (VI) is mainly toxic to organism and well-known to cause numerous health effects; especially it can modify genetic materials and cause cancer. The results show that Cr was released only from Chines samples (i.e., C₁ and C₂) in the range of 11 ̴ 30 μg/l at 35°C while significantly high level of Cr was leached from all the samples at 45° and 65°C. On the other hand, Mn was found to be leached slightly even not detected from C₁ and Sp₁ samples at 35°C. The concentration of Mn leached from Indian and Spanish samples were ranges 100 ̴ 300 μg/l at 45° and 65°C, respectively. In case of Barium, the amount leached in all the samples at 35°C. Moreover, as temperature increased, the amount of Ba leaching increased, with overall range of 10-300 μg/l.

From the leaching potential, conducted with various crockeries available in Qatar market, it was fond that all the ceramic crockeries contain both leachable essential and non-essential heavy metals. However, the concentrations of these heavy metals are not potentially high to cause any adverse effect on human health. But it is concluded that the relevant regulatory agencies in the countries should come forward to enact necessary regulations to minimize the exposure of public to toxic heavy metals leaching into the foodstuff from crockeries.