The Content of Cd and Pb in Herbs and Single-Component Spices Used in Polish Cuisine

Spices and herbs play an important role in the human diet, mostly due to the presence of essential oils and high antioxidant activity. Therefore, the toxicity of metals raises concerns about the safety of consumption of spices and herbs. This paper examines the content of Cd and Pb in fresh and dried herbs and single-component spices that are the most popular in Polish cuisine: 100 samples of nine kinds of dried herbs, 184 samples of 15 kinds of fresh herbs and 148 samples of 14 kinds of loose single-component spices. The level of Cd and Pb was determined using the GF AAS method. The safety of herbs and spices for consumption was estimated based on the percentage intake of Cd and Pb compared with the tolerable intake (% TWI, % BMDL), chronic daily intake (CDI), target hazard quotient (THQ), hazard index (HI) and comparisons of the results of chemical analyses with the maximum admissible levels of Cd and Pb in Poland and in the European Union. Calculated per fresh weight of the product, dried herbs on average contained 0.134 ± 0.168 mg of Cd and 0.548 ± 0.161 mg of Pb per kg−1, fresh herbs on average contained 0.004 ± 0.007 mg of Cd and 0.039 ± 0.033 mg of Pb per kg−1, and the mean content of Cd in spices was 0.017 ± 0.019 mg per kg−1 and 0.064 ± 0.050 mg of Pb. The % TWI, % BMDL, CDI, THQ and HI (Cd + Pb) for all the analysed products were lower than 1. The results do not imply a risk due to the supply of Cd and Pb with the diet to the human body, primarily due to the small intake of these products. However, it should be highlighted that the content of Cd in dried coriander and estragon and that of Pb in watercress, jiaogulan, celery, basil and dill exceeded the acceptable limit. Thus, their consumption for people from particularly sensitive groups such as babies, pregnant and breastfeeding women and people should be carefully limited.


Introduction
Spices play an important role in the human diet, mostly due to the presence of essential oils and high antioxidant activity [1][2][3]. They improve the taste of food, which allows reducing the use of table salt [4,5] as its intake is excessive in many countries and is one of the main reasons for the development of cardiovascular diseases. In addition, spices contribute to increasing the intake of vegetables and the preference for low-fat food [6]. Added to fat and stodgy food, they stimulate digestion through boosting gastric juice secretion [7]. They can also alleviate discomfort related to digesting such foods, e.g., passing gas due to fermentation processes or reflux [2,8]. Some active ingredients of raw spices feature functional qualities such as essential oils that protect the liver and reduce gases, which is most likely connected with their ability to inhibit the activity of 5-lipooxygenase and block α2 adrenergic receptors [9][10][11]. The bactericidal and bacteriostatic effects of essential oils present in herbs and spices suppress the development of Helicobacter pylori, one of the most significant etiological factors behind peptic ulcers and inflammatory states of the gastric mucosa [11][12][13]. At present, the role of herbs and spices and their active ingredients in stimulating metabolic processes is emphasised [14]. The stimulating effect of spices on the gastrointestinal tract is most likely based on two mechanisms: (1) stimulating the 1 3 liver to secrete bile rich in bile acids necessary for digesting and absorbing fat, and (2) stimulating the activity of digestive enzymes [7].
The fact that how we perceive the taste of food is closely linked to its smell is related to the presence of essential oils. During a short time when food stays in the mouth, olfactory and gustatory para information is transmitted to higher cortical centres of the brain as nervous impulses [15]. These impulses are produced by receptors present in the nasopharynx that receive the para signals, process them and transmit them to higher cortical centres. Studies conducted in Poland show that the most popular cooking herbs are marjoram, oregano and basil [16,17]. In addition, they reveal that Polish women prefer single-component spices and Polish men like hotter spices with a clearer taste [17].
Unfortunately, herbs and spices, similar to other foodstuffs, can be a source of toxic metals to humans, which is primarily an effect of environmental pollution (air, water and soil), but also of using pesticides and fertilisers for plant growing [18,19]. Cadmium (Cd) and lead (Pb) are the most common toxic metals in the environment. They have harmful prooxidative, mutagenic, carcinogenic, teratogenic and genotoxic effects [20,21]. The scale of disorders they cause in the human body is largely dependent on the intake level of such metals. Chronic exposure to Cd and Pb supply is particularly hazardous, as it leads to long-term latent impact on health, while in acute poisoning, an adverse impact is revealed very soon [22,23]. These metals have a long halflife-from 5 to 30 years for Cd and from 30 days (in soft tissue) to 10 years (in bones) for Pb [24,25], so their regular supply is dangerous, even in small amounts. Therefore, the consequences of the regular consumption of products containing even small amounts of these metals on human health can be manifested after many years [20]. In 2012, the European Food Safety Authority (EFSA) reduced the tolerable intake level for Cd and Pb. The TWI (tolerable weekly intake) for Cd was determined at the level of 2.5 μg kg −1 of body weight per week (0.36 μg kg −1 of body weight per day) [26], whereas the BMDL (benchmark dose lower confidence limit) for Pb was: BMDL01 in children-0.5 μg kg −1 of body weight per day and BMDL01 in adults-1.5 μg kg −1 of body weight per day and BMDL10 in adults-0.63 μg kg −1 of body weight per day [27]. No effective methods for reducing the concentration of Cd and Pb in food exist; therefore, humans are constantly exposed to the intake of these metals. Consequently, their content in food should be continually monitored.
Currently, in Poland, there is a tendency to resume a broader outlook on and use herbs and spices as MAPs (medicinal aromatic plants). Spices are officially recommended as an alternative to salt by public health organisations in Poland [28]. People consume spices and herbs for various reasons, the most important of them being a healthy lifestyle. The content of toxic metals in spices depends on multiple factors, including growing and environmental condition, and the species of plants [18,29,30]. They can be contaminated with heavy metals during processes associated with their storage and processing [18]. To ensure they are safe to the consumers' health and lives, agricultural raw materials and products should be strictly monitored for the presence of heavy metals. Therefore, the toxicity of metals raises concerns about the safety of consumption of spices and herbs. This work aimed to examine the content of Cd and Pb in fresh and dried herbs and in single-component spices used in Polish cuisine. It forms part of a project evaluating the intake of toxic and essential minerals by the population in Poland.

Preparation of Samples for Analyses
Fresh herbs were dried at 65 °C over 24 h [20,32], and then ground in a grinder fitted with plastic blades and placed in plastic, tightly sealed containers for up to 5 days. All dried products (dried herbs and spices) were ground in a grinder fitted with plastic blades [29]. The ground samples were placed in plastic, tightly sealed containers for up to 5 days until chemical analyses.

Analytical Figure of Merits
The material was mixed manually immediately prior to weighing the samples. Samples of ca. 3 g were weighed into China crucibles in two replications per sample. The samples were ash-dried in a muffle furnace at 450 °C for 12 h using H 2 O 2 as an oxidant. The process was repeated several times until white ash was produced that was later dissolved in 10 ml of 1 M HNO 3 . The methods were described in detail elsewhere [20,32]. The content of Cd and Pb was determined by GF AAS (graphite furnace atomic absorption spectroscopy) in a Varian Spectr AA 880 apparatus (

Chemical Reagents
Hydrogen peroxide H 2 O 2 and nitric acid HNO 3 were bought from POCH S.A. (Poland). Standard solutions of Cd and Pb

Calculations and Statistical Analysis
Safety of herbs and spices for consumers was estimated based on several indicators: (1) Calculation of the percentage of Cd and Pb intake compared with the acceptable levels proposed by EFSA, that is, tolerable weekly intake (TWI), and benchmark dose lower confidence limit (BMDL) calculated from the following formulas [33]: The estimated weekly intake (EWI) and the estimated daily intake (EDI) of Cd and of Pb was calculated using the following formulas [33]: %TWI = estimated weekly intake of Cd × 100 TWI %BMDL = estimated weekly intake of Pb × 100 BMDL EWI = mean weekly consumption of herbs or spices × Cd or Pb level body weight The TWI is 2.5 μg of Cd per kg −1 of body weight per week [26], BMDL01 is 10.5 μg of Pb per kg −1 of body weight per week, and BMDL10 is 4.4 μg of Pb per kg −1 of body weight per week [27]. The mean daily intake of herbs in Poland is 0.7 g [18], the mean daily intake of spices in Poland is 0.7 g [18], and the average body weight of adult Poles is 70 kg [33]. Since information on the intake of fresh herbs in Poland is not available, the percentage of TWI and of BMDL and other safety indicators were not calculated for them.
(2) Exposure to the harmful effects of Cd and Pb consumed with herbs and spices was estimated based on the Chronic Daily Intake (CDI), Target Hazard Quotient (THQ) and the Hazard Index (HI) calculated as below [33][34][35][36]  EFr means days of exposure-365 days in a year; ED tot is the duration of exposure-56 years; AT is the mean time of exposure-365 days in a year, MPI (maximum permissible intake) for Cd is 1 µg per kg −1 of body weight per day, while for Pb 3.5 µg per kg −1 of body weight per day [37]. If THQ > 1, it is likely that potentially harmful effects for human health will occur due to chronic exposure to Cd and Pb [37]. The mean values were calculated taking into account three replications for each determination in every sample.
Normality of data distribution was tested with Shapiro-Wilk tests. The significance of differences between the mean content of Cd and of Pb in respective kinds of herbs and spices was determined through one-factor analysis of variance (ANOVA) using Duncan's test. P < 0.05 was assumed as a statistically significant level.

Content of Cd and Pb in Herbs and Spices
Calculated per dry weight of the product, the highest (P < 0.05) content of Cd was found in dried herbs. No statistically significant differences in the content of Cd in fresh herbs and spices were identified (Fig. 1a). By contrast, HI = THQCd + THQPb calculated per fresh weight of the product, dried herbs on average contained 0.134 ± 0.168 mg of Cd per kg −1 (25th percentile 0.047 mg kg −1 , n = 100), fresh herbs on average contained 0.004 ± 0.007 mg of Cd per kg −1 (25th percentile 0.002 mg kg −1 , n = 184), and the mean content of Cd in spices was 0.017 ± 0.019 mg per kg −1 (25th percentile 0.012 mg kg −1 , n = 148) ( Table 3). Depending on the content of Cd, dried herbs can be ordered as follows: coriander = estragon > thyme = lovage > savory > marjoram > oregano = basil > rosemary (Fig. 2a). The order of fresh herbs based on the level of Cd is: watercress > celery > jiaogulan > mint > dill = basil > parsley > sage > oregano > coriander = thyme = marjoram > lemon balm = lovage = rosemary (Fig. 3a). The content of Cd in spices can be represented in the following order: cumin > lemon pepper > black pepper > cinnamon > ginger > rose pepper = cayenne pepper > sweet paprika = bay leaf > allspice = coriander > turmeric = white pepper = cloves (Fig. 4a). Calculated per dry weight of the product, the highest (P < 0.05) content of Pb was measured in dried herbs, followed by fresh herbs and spices (Fig. 1b). Calculated per fresh weight of the product, dried herbs contained 0.548 ± 0.161 mg of Pb per kg −1 (25th percentile 0.55 mg kg −1 , n = 100), fresh herbs 0.039 ± 0.033 mg of Pb per kg −1 (25th percentile 0.028 mg kg −1 , n = 184), and spices on average contained 0.064 ± 0.050 mg of Pb per kg −1 (25th percentile 0.044 mg kg −1 , n = 148) ( Table 3). In terms of the content of Pb, dried herbs can be ordered as follows: basil = marjoram > oregano = estragon > lovage = coriander > thyme = rosemary > savory (Fig. 2b), while the order of fresh herbs is: watercress > jiaogulan = celer y > basil > dill > mint > parsley > sage = oregano > lovage = coriander = marjoram > thyme > rosemary = lemon balm (Fig. 3b). In fresh watercress, jiaogulan, celery, basil and dill, the content of lead was above the MPL, that is, 0.3 mg per kg −1 [38]. The order of spices in terms of Pb content is as follows: allspice > cayenne pepper > pink peppercorn > ginger > black pepper > turmeric > sweet paprika > coriander = cumin > white pepper = lemon Fig. 1 Comparison of Cd (a) and Pb (b) levels in dried herbs, fresh herbs and spices, mg kg −1 dry matter a,b,c Means with different superscripts differ significantly at P < 0.05 by Duncan's test pepper = cinnamon = cloves > bay leaf (Fig. 4b). The level of Pb in the examined spices was below the MPL.

Safety of Herbs and Spices for Consumers
Taking into account the mean daily intake of herbs and spices, that is, 0.7 g [18] for the body weight of 70 kg, it was estimated that for dried herbs, the EWI is 6.75E-04 µg of Cd, which corresponds to 3.75E-04% of TWI (Table 4). An intake of 0.7 g of spices is equivalent to 8.33E-05 µg of Cd, that is, 4.76E-05% of TWI. The CDI and THQ for all the analysed products were lower than 1 and amounted to: 9.92E-05 for dried herbs, 3.70E-04 for fresh herbs and 1.26E-05 for spices, respectively (Table 4).
An intake of 0.7 g of dried herbs a day [17] will lead to a weekly intake of 2.69E-03 µg of Pb, which corresponds to 3.65E-04% of BMDL01 and 8.72E-04% of BMDL10 (Table 4). Spices containing a single species of herbs will supply 3.14E-04 µg of Pb weekly, which constitutes 4.27E-05% of BMDL01 and 1.02E-04% of BMDL10. The CDI and THQ for all the analysed products were lower than 1 and amounted to: 4.06E-04 and 1.16E-04 for dried herbs, 2.00E-04 and 5.71E-05 for fresh herbs and 4.74E-05 and 1.35e-05 for spices. In all the analysed cases, HI (Cd + Pb) was lower than 1 and amounted to 2.15E-04 for dried herbs, 6.08E-05 for fresh herbs and 2.61E-05 for single-component spices.
Comparing these results against applicable limits, the level of Cd was found to be excessive only for dried herbs: coriander (mean 0.419 mg kg −1 ) and estragon (mean 0.427 mg kg −1 ), (Fig. 2a). An above-limit level was recorded in two samples of coriander (20%) and in two samples of estragon (30%). The level of Pb was too high compared with the acceptable limit [38,40] for some fresh herbs only. These included watercress, jiaogulan, celery, basil and dill.

Discussion
Currently, in Poland, there is a tendency to resume a broader outlook on and use of herbs and spices as medicinal aromatic plants and develop the market for such products. Spices are officially recommended as an alternative to salt by Polish organisations dealing with public health [28]. On the market of spices in Poland and in many other countries, dried spices-accounting for the biggest percentage of turnoverare being replaced with their fresh equivalents [28]. Spices and herbs are consumed for various reasons, particularly as a part of a healthy lifestyle. Therefore, the presence of toxic metals raises concerns about the safety of consumption of spices and herbs.
Polish legislation established separate limits of acceptable content of Cd and Pb for fresh herbs and spices. Thus, fresh herbs can contain a maximum of 0.3 mg of Pb and 0.05 mg of Cd per 1 kg, whereas spices containing more than 50% of herbs-2.0 mg of Pb and 0.3 mg of Cd per 1 kg [38,40]. The level of cadmium in fresh herbs is also regulated by the legislation of the European Union according to which fresh herbs can contain maximum 0.2 mg of Cd per 1 kg [56].

Content of Cd and Pb in Herbs and Spices
The concentration of toxic metals in plants depends, among other factors, on their content and bio-availability in soil as well as the species of plant, its morphological part and the length of its vegetation period [29,30]. The content of heavy metals in the roots of plants was higher than in their aboveground parts [22]. By contrast, the bio-availability of toxic metals in soil, apart from their concentration, is affected by the pH and the oxidation-reduction potential of soil, soil structure and presence of organic matter and endophytes participating in metal translocation to plants [29]. Some plants, including therapeutic ones, show a high phytoremediation potential and have a phytostabilisation and phytoextraction ability [39,57]. These are normally small slow-growing plants. Tests on therapeutic plants demonstrated that most Cd and Pb accumulates in roots and leaves [58]. It was found that dicotyledons absorb metals much more easily than monocotyledons [59,60]. Respective parts of plants contain the biggest amount of metals in the following order: root > leaves > stem > flowers > seeds [53,60]. In the ready raw material, the source of contamination can be technological processes. Contaminants can also derive from auxiliary agents used in the production of food, apparatus, vessels and packaging.
In the presented own study, calculated per dry weight of the product, the content of Cd and Pb was higher (P < 0.05) in dried than in fresh herbs. In this study, fresh herbs were annual plants purchased in pots, while dried herbs can include perennial plants. Some researchers demonstrated that the accumulation of heavy metals in plants increases with their age [61], which stems from the capacity of metals to accumulate in living tissue and their long half-life [62]. Furthermore, Cd introduced into soil becomes a part of humus and takes forms that are easily assimilated by plants.
In their studies conducted in Poland, Fischer et al. [41] found that commercial samples of herbs contained more Cd than those grown at home. This can be attributed to the fact that chemicals and natural agents used in intensive farming alter soil properties (e.g., reduce its pH) and increase the bioavailability of metals, including toxic metals. Another source of contamination of soil with Cd is phosphorus fertilisers [18,41] that can be used for industrial and intensive growing of herbs. The growing procedure and data concerning agents used for fertilising and protecting commercial herbs are not publicly available. In the presented studies, dried coriander and estragon contained more Cd than the acceptable limit (0.3 mg kg −1 ) [38], whereas in spices, this limit did not exceed 0.06 mg kg −1 . Studies by Gajewska et al. [43] revealed that herbs and spices (n = 120; garlic, onion, dill, parsley, basil, oregano, estragon, thyme, curry, turmeric, chilli, nutmeg) available on the retail market in Poland, the mean content of Cd was from 0.011 mg to 0.88 mg kg −1 ( Table 5). The highest level was measured in Cd. Staniek and Krejpcio [63] found that the level of Cd in the samples of paprika and black pepper available in Poland was 0.015 -0.017 mg kg −1 , whereas Fischer et al. [41] observed that the concentration of Cd in herbs grown in Poland ranged from 0.02 to 1.94 mg kg −1 and was higher than the maximum limit of Cd in therapeutic plants. Kowalska [18] found that Polish dried herbs and spices (n = 224, 12 species of herbs and 11 species of spices) contained from < 0.02 mg to 2.17 mg of Cd per kg −1 . In the above-mentioned study, the level of Cd in spices was considerably lower than that in herbs. In none of the analysed samples did the level of Cd exceed acceptable limits; the highest mean concentration of Cd was noted in samples of black pepper and cumin seeds-about 0.08 mg per kg −1 . Reinholds et al. [64] analysed the content of Cd in dried herbs and spices. These authors demonstrated that the level of Cd was the highest in the samples of common thyme (0.4 mg kg −1 ) and basil (0.12 mg kg −1 ), while the lowest Table 4 Safety of culinary herbs and spices for consumption (the results are shown in fresh weight) 1 EWI, estimated weekly intake calculated on the basis of the mean weekly consumption of culinary herbs and spices and mean level of Cd and Pb; 2 CDI, chronic daily intake calculated on the basis of the mean weekly consumption of culinary herbs and spices, mean level of Cd and Pb and exposure duration; 3 THQ, target hazard quotient calculated on the basis of the chronic daily intake of Cd or Pb; 4 HI, hazard index is the sum of THQ for Cd and Pb; A Mean body weight was assumed as 70 kg; B TWI, 2.5 μg Cd per kg of body weight per week [26]; C BMDL01, 10 [55] levels of this element were recorded in the samples of black pepper (0.01 mg kg −1 ) and marjoram (0.02 mg kg −1 ). Studies conducted in Iran and Iraq showed that samples of herbs and spices contained from 0.012 to 1.64 mg of Cd per kg −1 [53,65,66]. Turkish researchers observed that the content of Cd in certain herbs was excessive compared with its standard limits, although the evaluation of consumer exposure does not imply a hazard [46]. In turn, studies in Malaysia revealed that the level of Cd in herbs and spices was from 0.23 to 8.07 mg kg −1 [67], and those conducted in India found that therapeutic herbs contained from 0.01 to 2.1 mg of Cd per kg −1 [68]. Fresh and dried herbs available in the United Arab Emirates (n = 81; parsley, sage, basil, oregano, mint, thyme and chamomile) contained from 0.1 to 1.11 mg of Cd per 1 kg [45]. Abualhasan et al. [69] observed that the level of Cd exceeded acceptable limits in all the analysed herbs (Hibiscus, anise, chamomile, hawthorn and ginger). By contrast, Baig et al. [55] found that the concentration of Cd in spices (26 species; allspice, areca nut, asafetida, bay leaf, black cardamom, black cumin seed, black pepper, carom seed, cinnamon, cloves, coriander seed, cumin seed, dried fenugreek leaf, dry ginger, fenugreek seed, green, mace, mustard seed, Nigella seed, nutmeg, pomegranate seed, red chilli, star anise, tamarind and turmeric) ranged from 0.010 mg to 4.70 mg kg −1 . The highest concentration of Cd was observed in allspice (3.3-4.7 mg kg −1 ), while the lowest in coriander seeds (0.01-0.02 mg kg −1 ). The examined spices and herbs can be considered safe for consumers in terms of the content of Pb that did not exceed the acceptable limit. Gajewska and Czajkowska-Mysłek [42] demonstrated that culinary herbs and spices (garlic, onion, dill, parsley, basil, oregano, estragon, thyme, curry, turmeric, chilli and nutmeg) contained from 0.02 to 0.84 mg of Pb per 1 kg; the highest content of Pb was found in nutmeg and thyme. In the study by Kowalska [18], herbs and spices (n = 224) contained from < 0.02 to 5.67 mg of Pb per kg; also, Özden and Özden [46] and Tefera and Teklewoold [54] found that the level of Pb in herbs and spices was consumer-safe. In Malaysian studies, the level of Pb in herbs and spices ranged from 1.54 mg to 8.94 mg kg −1 [67], while in Romania, it was on average 0.21 mg of Pb per kg −1 , whereas the limit was exceeded for one sample which showed 1.42 mg kg −1 [48]. Fresh and dried herbs available in the United Arab Emirates (n = 81) contained from 1.0 to 23.5 mg of Pb per 1 kg [45]. Studies conducted in Saudi Arabia showed the consumer-safe levels of Pb in spices (turmeric, cloves, black pepper, red pepper, cumin, legume, cinnamon, abazir, white pepper, ginger and coriander) [44]. Harangozo et al. [49] examined the level of Pb in four spices: black pepper, paprika, basil and marjoram available in Slovak shops. The above-named authors found that the spices contained up to ca. 5.6 mg of Pb per kg −1 ; its level was the highest in dried basil-above the acceptable limit.
It was observed that herbs purchased from the supermarket contained more Pb than those grown organically [43]. In their studies, herbs from the supermarket contained from 0.03 to 0.96 mg of Pb per 1 kg, and organic herbs from 0.02 to 0.89 mg kg −1 . Ericson et al. [70] demonstrated that single species of spices and spice blends (n = 29; 11 species) available in Georgia showed high concentrations of Pb. The Pb concentration median in six spices exceeded the acceptable limit from 2.4 to 4 times. Studies in Libya showed that among four of the examined spices (chilli, black pepper, turmeric, HRARAT blends containing lesser galangal, ginger and cinnamon), the highest Pb levels were measured in turmeric and chilli-> 1.06 (mean 1.00) mg and 1.02 (mean 0.96) mg per 1 kg, respectively [50]. In studies conducted by Ciotea et al. [71], dried mint (n = 4), basil (n = 7) and rosemary (n = 3) contained from 0.06 to 0.64 mg, from 0.06 to 0.14 mg and from 0.21 to 0.49 mg of Pb per kg −1 , respectively. Also, Shim et al. [47] observed that herbs and spices (n = 359; cinnamon, parsley, basil, oregano, coriander seed, nutmeg, cumin, bay leaf, fenugreek, rosemary, thyme, fennel, sage, clove, marjoram, tarragon, caraway, dill seed, pepper and turmeric) were safe in terms of Pb content, as the level of this metal ranged from 0.039 to 0.972 mg kg −1 . Makanjuola et al. [51], analysing five kinds of species (onion, nutmeg, garlic, ginger and pepper) found the presence of 0.001 mg of Pb per 1 kg. These values were below the standard limits established by FAO/WHO, so they were considered safe for consumers. The level of Pb amounting to ca. 1 mg per kg −1 was measured in cubeb, nutmeg, cinnamon and black pepper consumed in Jordan, irrespective of the origin of imports [72]. In turn, studies conducted in Tanzania (Zanzibar) showed that the level of Pb and that of other heavy metals in cloves is a potential threat to public health; the level of Pb ranged from 0.35 to 1.18 ppm [52]. Ibrahim et al. [53] found that the concentration of heavy metals differed depending on the part of the plant (rhizomes, seeds, leaves and fruits). The above-mentioned authors examined the level of Pb in 12 herbs and spices: black seed, cinnamon, mint, fenugreek, black pepper, ginger, turmeric, dried lime, coriander, sumac fruit, cumin and cardamom. The analysed products contained from 1.25 to 14.6 mg of Pb per 1 kg of dry weight of the product. The highest content was found in fenugreek and cinnamon. These values exceeded standard limits approved by WHO, although the estimation of risk did not show any hazard for consumers when consuming 10 g of spices a day. The level of Pb and other heavy metals in turmeric available in Bangladesh was 12.3 mg kg −1 , which was higher than acceptable limits. In addition, the concentration of heavy metals was found to be lower in loose packed samples compared with loose unpacked samples [73]. This can imply secondary contamination of the spices as a result of environmental exposure. Studies in Nigeria also revealed that the level of Pb in local spices was too high compared with standard limits and ranged from 2.61 to 8.97 mg kg −1 [74]. By contrast, in Pakistan, among 26 analysed kinds of spices, the level of Pb was too high in relation to standard limits in black cumin seeds, areca nuts, carom seeds, green cardamom and pomegranate seeds [55]. In the above-mentioned study, the highest level of Pb (47.3-52.7 mg kg −1 ) was observed in black cumin seeds, and the lowest concentration was measured in ginger (0.265-0.4 mg kg −1 ). Chinese researchers found that among 1773 therapeutic herbs 5.75% exceeded the acceptable content of Pb [29]. It was demonstrated that in therapeutic herbs, the level of Pb is the highest in roots and leaves, and is considerably lower in stems and flowers [75]. About 0.005% of Pb in soil is bioavailable to plants. They take up very easily dissolved forms of Pb 2+ accumulated in roots, and are then transported to the aboveground parts [75]. This is corroborated by the studies of Shim et al. [47] that showed a significantly higher content of Pb in leaf spices than in the fruits and seeds of herbs.
The level of Pb in the presented own studies was exceeded in fresh watercress, jiaogulan, celery, basil and dill, while for dried herbs, the level of Pb was not exceeded; however, the highest (P < 0.05) levels of Pb were measured in marjoram and basil. In studies by Kowalska [18], out of 61 samples of dried spices, basil contained the highest amount of Pb. In turn, Dghaim et al. [45] found that basil contained the highest level of Cd (1.11 mg kg −1 ) out of the seven analysed species of herbs (parsley, sage, basil, oregano, mint, thyme and chamomile), similar to the studies by Harangozo et al. [49] where the mean content of Cd in basil exceeded the limit more than two times. In contrast, results obtained by Fischer et al. [41] showed that among the examined species of spices (basil, rosemary, estragon and lovage), basil had the lowest content of Cd (0.2 mg kg −1 ). Studies by Gajewska and Czajkowska-Mysłek [42], on the content of Cd in spices, also demonstrated that the samples of basil contained less Cd than other analysed species of spices. Compared with other herbs, basil is rich in minerals (Fe, Zn and Cu) [76], which can reduce the accumulation of Cd and Pb by this plant.

Safety of Herbs and Spices for Consumers
Spices and herbs are usually consumed in small amounts in combination with other foodstuffs and do not constitute basic food components. However, depending on the amount consumed, they can be a source of Cd and Pb in the diet. No amount of Cd and Pb exists that can be deemed safe for humans, as these metals are capable of accumulating in tissues and feature a long half-life [24,25].
In the presented own studies, all the analysed indicators estimating the safety of herbs in terms of the content of Cd and Pb (% TWI, % BMDL, CDI, THQ, and HI) showed very low values, well below 1. Thus, these products can be considered consumer-safe as regards the content of Cd and Pb. Also, Gajewska and Czajkowska-Mysłek [42] demonstrated that culinary herbs are consumer-safe; 3 g of herbs a day will result in an intake of Cd corresponding to ca. 1% of PTWI and that of Pb-to ca. 4% of PTMI. However, it should be highlighted that the above-mentioned authors presumed that the consumption of herbs with the diet was four times higher than in our presented studies that were based on data provided by Kowalska [18], according to which Poles on average consume 0.7 g of herbs and 0.7 g of spices a day. Kowalska [18] found that consumption of herbs and spices increases the risk of THQ for Pb more than for Cd; while, higher values were noted for herbs than for spices. However, it should be underlined that in the above-mentioned studies, these values were lower than 1, which means they are safe for consumers. In Malaysia, the mean consumption of herbs and spices is estimated as 5 g a day, so the exposure to Cd and Pb supplied with these products is 1.11 µg kg −1 and 3.21 µg kg −1 , respectively, corresponding to 15.9% and 12.8% of PTWI [67]. The above-mentioned authors deemed those values to be high, since toxic metals are also consumed with other foodstuffs. Some researches considered spices and herbs unsafe for consumers, as the level of toxic metals present in such products exceeded standard limits [51][52][53]69]. In turn, studies conducted in Nigeria identified a risk associated with the consumption of local African spices: Prosopis africana, Xylopia aethiopica, Piper guineense, Monodora myristica and Capsicum frutescens [74]. The above-mentioned authors demonstrated that THQ was lower than 1 (0.06-0.5) and EDI was lower than the tolerable daily intake (TDI); however, the level of Pb exceeded the maximum acceptable concentration about eight to 30 times compared with the standard limit of WHO/FAO, that is, 0.3 mg kg −1 . In the studies of Baig et al. [55], the content of Cd and Pb in 26 kinds of Pakistan spices was the highest in coriander seed, allspice, Nigella seed and black cumin seed, but the estimated consumption of these ingredients fell within WHO's tolerable weekly intake. Also, the HI was lower than 1, so there was no risk for consumers.

Conclusions
The presented results of studies concerning the safety of culinary herbs and spices for consumers in Poland do not imply a risk stemming from the supply of Cd and Pb with the diet to the human body, primarily due to the small intake of these products. However, it should be highlighted that the mean content of Cd in dried coriander and estragon and that of Pb in watercress, jiaogulan, celery, basil and dill exceeded the acceptable limit. Thus, their consumption should be limited for people from particularly sensitive groups such as babies, pregnant and breastfeeding women and people with a weakened immune system. A certain limitation of this study is that people consume different amounts of herbs and spices in their diets. The results obtained represent the actual Cd and Pb content in the products but only estimate the safety of their consumption.