Concentrations, source apportionment and potential health risk of toxic metals in foodstuffs of Bangladesh

Abstract Toxic metal contamination in foodstuff is a major concern for public health and human beings are continuously exposed to toxic metals through consumption of cereals, pulses, vegetables, fruits, and other crops grown in the metals contaminated soil. The present study was conducted to investigate the concentrations of chromium (Cr), nickel (Ni), copper (Cu), arsenic (As), cadmium (Cd), and lead (Pb) in foodstuffs and their possible human health risks in Jhenaidah and Kushtia districts, Bangladesh. The range of Cr, Ni, Cu, As, Cd, and Pb in the studied foodstuffs were 1.57–12.52, 1.71–37.78, 1.97–16.67, 0.36–3.72, 0.00–4.02, and 1.04–10.88 mg/kg dw, respectively. Multivariate principal component analysis revealed significant anthropogenic contributions of Cr, Cu, As, and Pb in the studied foodstuffs. The estimated daily intake (EDI) values of all the metals except Cu were higher than the maximum tolerable daily intake (MTDI). The target hazard quotients (THQs) of the studied metals, excluding Cr, from all foodstuffs were higher than 1, indicating that if people consume these types of foods in their diet, they might pose risk to these metals. The estimated target carcinogenic risk of As was higher than USEPA standard (10−4), indicating increased risk of cancer for adults and children in the study area.


Introduction
Food is absolutely the most essential commodity to the survival of life. Availability and access to safe and fresh food is a basic need and is one of the most important contributors of public health. Because of the increasing rate of metal pollution in the environment, the food safety issue has become a major public health concern worldwide (Shaheen et al. 2016a). The increasing demand of food safety has attracted attention to the scientists recently regarding the risk associated with metals contaminated food consumption (Mansour et al. 2009, Saha andZaman 2013). The risks associated with metal pollution in foods are of great concern, particularly in agricultural crops such as rice, cereals, vegetables, and fruits. Consumption of metal contaminated foods pose serious health problems that range from shortness of breath to several types of cancers Shah 2013, Islam et al. 2017). Therefore, the environmental safety of foods against metals pollution is exclusively crucial to human health.
Agricultural crops are the most important dietary source of nutrients as it contains protein, carbohydrates, vitamin, fibers, minerals, essential metals etc. and also contain antioxidants (Garg et al. 2014, Islam et al. 2018a. But it becomes harmful to human as it accumulates heavy metals in their tissue when grown in the contaminated soil. Both natural and anthropogenic interventions have been considered for the release of heavy metals into the environment that can pollute soil, water, and plants including other compartments of the ecosystem and eventually affect human health and well-being (Bundschuh et al. 2012, Ahmed et al. 2015. The activities such as rapid industrialization, vehicular exhaustion, wastewater irrigation, sludge application, and the use of large quantities of agrochemicals such as metal-based pesticides and fertilizers are the sources of toxic metals contamination in agricultural crops and other foodstuffs (Loutfy et al. 2012, Pourang andNoori 2012). Therefore, the presence of toxic metals in agricultural crops and other foods are of great concern due to their non-biodegradable nature, long half-lives and toxicity to humans and other organisms (Cherfi et al. 2014. In Asian countries like Bangladesh, India, Thailand, China, and Vietnam, rice and vegetables are the two main foodstuffs commonly consumed by the population on a daily basis (Islam et al. 2018b). However, agricultural crops other than rice and vegetables, e.g. pulses, fruits, cereals, and so on, are also being consumed at a significant amount in those countries (Khoury et al. 2016). Toxic metals contamination of agricultural crops and subsequent accumulation in humans via food-chain interaction, even in low concentrations throughout the lifetime, can possibly result in a number of carcinogenic and non-carcinogenic health problems including neurological, immunological, cardiovascular, renal, and reproductive disorders (Anyanwu et al. 2018, Mohammadi et al. 2019. Usually metals are accumulated in vital organs in the human body such as the kidneys, bones and liver through dietary intake of contaminated foods; resulting in depletion of some essential nutrients in the body and causing serious health problems (Duruibe et al. 2007, Zhuang et al. 2009. For instance, toxic metals such as Pb and As have shown carcinogenic effects (Khan et al. 2012), whereas high concentrations of Cu, Cd, and Pb in rice, pulse, vegetables, fruits, and other foods are related to high prevalence of upper gastrointestinal cancer (T€ urkdo gan et al. 2003). Therefore, a serious health issue has attracted notable attention in Asian region, especially in developing countries, owing to increasing levels of toxic metals in agricultural soils and their transfer to agricultural products including rice, pulses, vegetables, fruits, and other food crops (Williams et al. 2006).
The assessment of daily dietary intake of toxic metals and health risk based on the regular food consumption studies is essential for both the children and adult in Bangladesh (Williams et al. 2006. Numerous studies have been focused on the concentration of toxic metals in rice, vegetables and fruits of Bangladesh and some other countries (Bo et al. 2009, Hu et al. 2013. However, to the best of the authors' knowledge, no detailed study on the concentration of toxic metals in cereal crops, pulses, vegetables, fruits, and other crops in the study areas of Bangladesh has been conducted so far. Therefore, the objectives of this study were to measure the concentrations of Cr, Ni, Cu, As, Cd, and Pb in commonly consumed foodstuffs (cereals crops, pulse crops, vegetables, and fruits) in Jhenaidah and Kushtia districts of Bangladesh along with identification of possible sources of the studied toxic metals in the foodstuffs. In addition, a detailed human health risk assessment was performed to assess the carcinogenic and non-carcinogenic health hazards of toxic metals through the consumption of commonly consumed but contaminated foodstuffs on daily basis.

Study area and sample collection
The studied samples were collected from industrial areas of Jhenaidah and Kushtia districts, Bangladesh ( Figure 1). Jhenaidah and Kushtia are densely populated (900 and 1,200/km 2 ) districts of the country having an area of 1965 and 1609 km 2 , respectively (BBS 2011). There are several types of industrial units including tobacco industries, garments, tannery industries, packaging industry, dyeing, brick kiln, metal workshops, battery manufacturing industries, textile industries, pesticide, and fertilizer industries, different food processing industries, and other industrial areas produce huge volumes of effluents that contain trace metals (Kormoker et al. 2019). The untreated wastes and effluents from these industries are discharged randomly to river and canals. Then that wastes are mixed with soils and the soil is continuously polluted by heavy metals.
Crop samples were collected near industrial vicinity and at each sampling station, same species of cereals, pulses, vegetables, and fruits were collected as subsamples and were thoroughly mixed to form a composite sample. Two hundred and seventy samples of twenty five different agricultural crops i.e., rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), mung bean (Phaseolus radiate), lentil (Lens culinaris), black gram (Vigna mungo), bottle gourd (Lagenaria siceraria), chili (Capcicum frutescens), potato (Solanum tuberosum), cucumber (Cucumis sativus), danta shak (Amaranthus lividus), red amaranth (Amaranthus albus), drumstick leaf (Moringa oleifera), okra (Abelmuschus esculentus), Indian spinach (Basella alba), bean (Phaseolus vulgaris), papaya (Carica papaya), brinjal (Solanum melongena), carrot (Daucus carota), banana (Musa paradisiaca), mango (Mangifera indica), guava (Psidium guajava), jackfruit (Artocarpus heterophyllus), tobacco (Nicotiana tabacum), and betel leaf (Piper betle) were collected by hand from the selected agricultural fields during March-April, 2017. The samples were kept in polythene zip-bags with definite marking and tagging and brought to the laboratory on the day of sampling for chemical analysis. Crop samples were washed with distilled water and cut into small pieces by stainless steel knife and was kept in oven at 70-80 C to attain constant weight (Tiwari et al. 2011). The fresh and dry weights were recorded to calculate moisture contents. The processed samples were brought to Yokohama National University, Japan for chemical analysis.

Toxic metal analysis
All chemicals were analytical grade reagents; Milli-Q water (Elix UV5 and MilliQ, Millipore, Boston, MA, USA) was used for the preparation of solutions. The Teflon vessel and polypropylene containers were cleaned, soaked in 5% HNO 3 for more than 24 h, then rinsed with Milli-Q water and dried. For metal analysis, 0.3-0.5 g of the crop sample was treated with 6 mL 69% HNO 3 (Kanto Chemical Co, Tokyo, Japan) and 2 mL 30% H 2 O 2 (Wako Chemical Co, Tokyo, Japan) in a closed Teflon vessel and was digested in a Microwave Digestion System (Berghof speedwave1, Eningen, Germany). The digested samples were then transferred to a Teflon beaker, and the total volume was increased up to 50 mL with Milli-Q water. The digested solution was then filtered by using syringe filter (DISMIC1-25HP PTFE, pore size ¼ 0.45 mm; Toyo Roshi Kaisha, Ltd., Tokyo, Japan) and stored in 50 mL polypropylene tubes (Nalgene, New York, NY, USA). After that the digestion tubes were then cleaned using blank digestion procedure following same procedure of samples. For toxic metals, samples were analyzed using an inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7700 series, Santa Clara, CA, USA). Instrument operating conditions and parameters for metal analysis are done. The detection limits of ICP-MS for the studied metals were 0.7, 0.6, 0.8, 0.4, 0.06, and 0.09 mg/L for Cr, Ni, Cu, As, Cd, and Pb, respectively. Multi-element Standard XSTC-13 (Spex CertiPrep V R , Metuchen, NJ, USA) solutions were used to prepare the calibration curves. Internal calibration standard solutions containing 1.0 mg/L of indium, yttrium, beryllium, tellurium, cobalt, and thallium were purchased from Spex Certi Prep V R (Metuchen, NJ, USA). During the procedure, 10 mg/L internal standard solution was prepared from the primary standard and added to the digested samples. Multi-element solution (purchased from Agilent Technologies, Japan) was used as the tuning solution covering a wide range of masses of elements. All test batches were evaluated using an internal quality approach and validated to see if they satisfied the defined Internal Quality Controls (IQCs). Before starting the analysis sequence, the relative standard deviation (RSD, <5%) was checked by using tuning solution purchased from Agilent Technologies. The certified reference materials INCT-CF-3 (corn flour) bought from the National Research Council (Canada), were analyzed to confirm analytical performance and good precision (relative standard deviation bellow 20%) of the applied method.

Estimated daily intakes (EDIs)
Estimated daily intakes (EDIs) of toxic metals (mg/day) were calculated using their respective average concentration of toxic metals in crops by the weight of foodstuff consumed by an individual (FAO 2006), which was obtained from the household income and expenditure survey (HIES 2011, Shaheen et al. 2016b. They are calculated by the following formula: where, FIR is the food ingestion rate (g/person/day), C is the metal concentration in food samples (mg/kg), and BW is the body weight assuming 60 kg and 15 kg for adult and children in the present study.  (USEPA 1989), which is "the ratio of a single substance exposure level over a specified time period (e.g. sub-chronic) to a reference dose (RfD) for that substance derived from a similar exposure period". The equation used for estimating the target hazard quotient is as follows (USEPA 2000, FAO/ WHO 2011): where, THQ is the target hazard quotient, EFr is the exposure frequency (365 days/year), ED is the exposure duration (70 years for adult and 6 years for children), FIR is the food ingestion rate (g/day), C is the metal concentration in foods (mg/kg fw), RfD is the oral reference dose (mg/kg/day), and AT is the averaging time for non-carcinogens (365 days/year Â number of exposure years). The oral reference doses were based on 1.5, 0.02, 0.04, 0.0003, 0.0005, and 0.0035 mg/kg/ day for Cr, Ni, Cu, As, Cd, and Pb, respectively (JECFA 1993, USEPA 2007. If the THQ value is less than one then population experience obvious adverse effects due to exposure of heavy metals. Again, if THQ value is higher than one, there is a potential health risk (Wang et al. 2005, Proshad et al. 2017, and related interventions and protective measurements are needed to be taken.

Hazard Index (HI).
In order to assess the overall potential for non-carcinogenic effects from more than one heavy metal, a hazard index (HI) has been formulated based on the guidelines for health risk assessment of chemical mixtures of USEPA (USEPA 1999). The hazard index (HI) from THQs is expressed as the sum of the hazard quotients (USEPA 2010). The equation used for estimating the hazard index is as follows:

Carcinogenic risks
The target carcinogenic risks derived from the intake of As and Pb were calculated using the equation provided in USEPA Region III Risk-Based Concentration Table ( USEPA 1999USEPA , 2006. where, TR represents the target cancer risk or the risk of cancer over a lifetime; AT is the averaging time for carcinogens (365 d/year Â ED). CSFo is the oral carcinogenic slope factor from the Integrated Risk Information System (USEPA 2010) database were 1.5 and 8.5 Â 10 À3 (mg/kg/day) À1 for As and Pb, respectively.

Statistical analysis
The data were statistically analyzed using the statistical package SPSS 20.0 (International Business Machines Corporation [IBM] Armonk, NY, USA). The means and standard deviations of the metal concentrations in food samples were calculated. Multivariate methods in terms of principal component analysis (PCA) were used to interpret the potential sources of hazardous element in foodstuffs. The extraction method was performed to find out the principal components (PC) in PCA analysis that was Eigen values. For dividing the crop species into several groups, cluster analysis (CA) with dendrogram using Ward's method was adopted by using the overall heavy metals concentration in samples. Cluster analysis (CA) was used to obtain the detailed information of the dataset and gain insight into the distribution of trace metals by detecting similarities or differences in samples. Microsoft Excel 2013 was used for other calculations.

Heavy metal concentration in foodstuffs
The concentrations of toxic metals (Cr, Ni, Cu, As, Cd, and Pb) found in different kinds of cereal crops, pulses, vegetables, fruits, and other crops are summarized in Table 1. The average concentration of toxic metals in the studied food samples were in the decreasing order of Ni > Cu > Cr > Pb > As > Cd. For the investigated foodstuffs, a great variability was observed in concentration of toxic metals, even within the same group of crop which could be due to climatic conditions of the study areas, growth period and stages of food, variation in species, and variable capabilities of absorption and accumulation of toxic metals (Pandey andPandey 2009, Proshad et al. 2019). The studied metal concentrations in the studied foodstuffs were compared to the standard value set for food samples given by FAO/WHO (USEPA 2010) ( Table 1). The concentrations of Cr were ranged from 3.18 (wheat) to 10.2 mg/kg (maize) for cereal crops, 1.87 (lentil) to 2.53 mg/kg (mung bean) for pulses, 1.57 (red amaranth) to 12.52 mg/kg (bean) for vegetables, and 2.32 (jackfruit) to 8.2 mg/kg (mango) for fruits. The average concentration of Cr in foodstuffs followed the descending order of cereals > vegetables > fruits > other crops (tobacco and betal leaf) > pulses. The observed elevated levels of Cr in the cereals and vegetables samples might be due to the use of untreated or poorly treated wastewater from industrial establishments for irrigation, application of chemical fertilizers and pesticides, and throwing industrial wastes in open environment which contain a very high level of Cr . Chromium concentrations in all the foodstuffs (80% samples) exceeded the FAO and WHO standard value, indicating severe Cr contamination in the foodstuffs. The Cr concentrations of the present study were compared with other study conducted in Bangladesh and other countries. However, the results of Cr content in cereals crops, pulses, vegetables, fruits, and other crops obtained in this study were higher than those obtained by other scientists (Ahmad and Goni 2010, Li et al. 2012, Rahman et al. 2013, Islam et al. 2016, Proshad et al. 2017, Proshad et al. 2019) and lower than those obtained by other researchers   (Table  2). Chronic exposure to Cr can cause ulceration and dermatitis of the skin (Nawab et al. 2018), while longterm exposure can cause serious problems such as weakened immune systems, lung cancer, alteration of genetics, respiratory problems, and nerve tissue damages (Pandey et al. 2010).
Nickel concentrations in the studied food samples were ranged from 4.47 (rice) to 10.3 mg/kg (maize) for cereal crops, 1.71 (mung bean) to 2.98 mg/kg (black gram) for pulses, 1.76 (okra) to 22.03 mg/kg (bean) for vegetables, 7.85 (jackfruit) to 37.78 mg/kg (banana) for Copper is an important heavy metal for normal biological activities of aminoxide and tryosinase enzymes but excessive intake may cause hepatotoxic hemolysis and nephrotoxic effects (Hashmi et al. 2005, Ratul et al. 2018. Considering of cereals and pulses, the highest Cu concentrations were found in wheat (9.04 mg/kg) and mung bean (2.26 mg/kg) and the lowest concentrations were found in rice (4.31 mg/kg) and black gram (1.97 mg/kg). In the vegetables and fruits samples, the highest concentrations were found in chili (16.67 mg/kg) and mango (10.48 mg/kg) and the lowest concentrations were found in Indian spinach (3.56 mg/kg) and banana (5.51 mg/kg). The mean concentration of Cu in foodstuffs followed the descending order of vegetables > fruits > cereals > other crops (tobacco and betel leaf) > pulses. Copper concentrations in all food samples were below the FAO and WHO standard value, indicating less Cu contamination in the foodstuffs (FAO/WHO 2011). In the present study, it was found that Cu concentrations in the studied food samples were higher than some of the other studies conducted in Bangladesh and other countries by Islam et al. 2014 (mean: 2.5  Arsenic is a metalloid which is called "slow poison" or death metal because it kills people slowly whenever it enters into the human body. The main organs which are affected by As are kidneys, blood, digestive tract,  (Kachenko and Singh 2006) skin, and nervous systems (Nawab et al. 2018). In this study, the concentrations of As were ranged from 2.04 (wheat) to 3.27 mg/kg (rice) for cereal crops, 1.13 (mung bean) to 1.74 mg/kg (lentil) for pulses, 1.02 (red amaranth) to 3.72 mg/kg (potato) for vegetables, and 1.24 (banana) to 1.81 mg/kg (mango) for fruits. The average concentration of As in foodstuffs followed the descending order of cereals > vegetables > fruits > pulses > other crops (tobacco and betel leaf). Arsenic concentrations in all the food stuffs exceed the FAO and WHO standard value, indicating severe As contamination in the foodstuffs and might pose risk to the consumers. The observed elevated levels of As in foodstuffs could be due to the effect from different sources, such as use of As containing ground water for irrigation, application of As enriched fertilizers and pesticides for crop production (Neumann et al. 2010, Polizzotto et al. 2013. Arsenic concentrations of the present study were compared with other study conducted in Bangladesh and other countries. However, the results of As content in foodstuffs obtained in this study were higher than those obtained by other scientists (Rahman et al. 2013, Islam et al. 2016, Proshad et al. 2017) ( Table 2). Cadmium is a highly toxic trace element and present in the environment at low levels. Rather than air or water, food, represents the major source of cadmium exposure (Rahman et al. 2013. Cadmium may accumulate in the human body and may give rise to renal, pulmonary, hepatic, skeletal, and reproductive effects and cancer (Shaheen et al. 2016a). In this study, the concentrations of Cd were ranged from 0.75 (rice) to 1.35 mg/kg (wheat) for cereal crops, 0.21 (Mung bean) to 0.89 mg/kg (Black gram) for pulses, 0.11 (Indian spinach) to 2.28 mg/kg (papaya) for vegetables, and 3.02 (mango) to 4.02 mg/ kg (guava) for fruits. The mean concentration of Cd in foodstuffs followed the descending order of fruits > vegetables > cereals > pulses > other crops (tobacco and betel leaf). Cadmium concentrations in all the foodstuffs exceeded the FAO and WHO standard value, indicating severe Cd contamination in the foodstuffs and might pose risk to the consumers. The transfer of elevated concentration of Cd from soil to food samples might be due to small scale industries such as electroplating, dyeing, fabrics printing, batteries and paints, which discharge their effluents directly into the surface water body and used for irrigation purposes (Khan et al. 2015). In the present study, it was found that Cd concentrations in the studied foodstuffs were higher than some of the other studies conducted in Bangladesh and other countries by Islam et al. 2014 (mean: 0.12  Lead is a non-essentials toxic metal that enters into the human body through air, water and foods and cannot be removed by washing and cooking of foods and it is well familiar that Pb can cause nephrotoxicity, neurotoxicity, and many other adverse health effects (Sharma et al. 2007, Shaheen et al. 2016b). The highest concentration of Pb was observed in Bottle gourd (10.88 mg/kg) and the lowest was found in Indian spinach (1.04 mg/kg). The average concentration of Pb in foodstuffs followed the descending order of cereals > vegetables > fruits > other crops (tobacco and betel leaf) > pulses. According to the FAO and WHO standard, Pb concentrations in all the foodstuffs exceeded the standard value, indicating severe Pb contamination in the foodstuffs and might pose risk to the consumers. The higher concentration of Pb in food samples could probably due to the lead smelting, emission from vehicles, and other industrial activity in the study area . The Pb concentrations of the present study were compared with other study conducted in Bangladesh and other countries. However, the results of Pb content in cereals crops, pulses, vegetables, fruits, and other crops obtained in this study were higher than those obtained by other scientists (Kachenko and Singh 2006, Sharma et al. 2007, Ahmad and Goni 2010, Rahman et al. 2013, Islam et al. 2016) and lower than those obtained by other researchers (Proshad et al. 2017).

Source apportionment of toxic metals in foodstuffs
In order to elucidate the inter-relationships among the studied metals in food samples and to identify the significant factors involved in controlling the transport and distribution of metal contaminants, a correlation coefficient analysis was performed (Chen et al. 2012). Inter-metal interactions may illustrate the sources and pathways of the metals present in food samples. Pearson's correlation coefficients for the investigated metals are presented in Table 3. A clear pattern of significant positive correlation was observed like Cu with Cr (r ¼ 0.595 ÃÃ ), Pb with Cr (r ¼ 0.396 Ã ), Cd with Ni (r ¼ 0.646 ÃÃ ), As with Cu (r ¼ 0.516 ÃÃ ), Pb with Cu (r ¼ 0.691 ÃÃ ), and Pb with As (r ¼ 0.523 ÃÃ ). The higher positive significant correlations among metal-metal pair may be an indication of common sources of these metals or similarly or nearly identical metal accumulation properties of food samples (Abbasi et al. 2013, Xu et al. 2013.
The principal component analysis (PCA) has been considered to be an effective tool for investigating metal sources, anthropogenic activities, or soil parent materials (Bai et al. 2011, Cai et al. 2012. The PCA was performed on the tabular and standardized forms of data set and is presented in Table 4 and Supplementary Figure S1. Multivariate PCA of heavy metals in food samples explaining about 90.64% cumulative variance. In PCA analysis, two principal components (PC) were computed and the variance explained by them was 71.45% and 19.17% for food samples (Supplementary Figure S1). Overall, PCA revealed two major groups (PC1 and PC2) of the studied six metals, whereas one group comprised of Cr, Cu, As, and Pb, while another group consisted of Ni and Cd. Generally, toxic metals can be introduced to the agricultural soils from a wide range of anthropogenic activities such as excessive and frequent application chemical fertilizers and pesticides (Atafar et al. 2010), irrigation with wastewater and contaminated groundwater/surface water (Polizzotto et al. 2013), unregulated discharge of untreated industrial wastewater (Tusher et al. 2017), industrial and vehicular emissions derived atmospheric deposition (Sharma et al. 2008), mining and smelting (Xu et al. 2013). However, intensive agricultural practices and industrial discharge are the most dominant anthropogenic activities actively operating in the study area. As a result, the PC1 (Cr, Cu, As, and Pb) seemed to be attributed to the discharge of untreated industrial wastewater and irrigation of agricultural lands by contaminated water sources Shaheen 2007, Islam et al. 2015), while the PC2 (Ni and Cd) seemed to be related to the lithogenic sources and/or also by anthropogenic activities including repeated use of inorganic phosphate fertilizers and industrial discharge and emissions (Atafar et al. 2010, Iqbal and Shah 2011. The PCA analysis revealed that the apportionment of the same kind of toxic metals in food samples were not similar, which might be due to the release of heavy metals from source to the environment and subsequent accumulation by the agricultural crops. Furthermore, using the overall toxic metal concentration in foodstuffs, cluster analysis (CA) with dendrogram using Ward's Method was adopted to divide the food samples into several groups as shown in Supplementary Figure S2. Several cluster shapes were found between the several food samples and the food samples which were in same cluster result for similar resemblance in nature. Largely, the food samples were grouped into three major clusters. Moreover, on the basis of toxic metal concentrations in food samples showed strong significant correlations by forming primary groups/clusters with each other. The primary clusters such as red amaranth, Indian spinach, tobacco,

Health risk assessment
3.3.1. Estimated daily intake (EDI) of heavy metals The dietary exposure approach of vegetables consumption is a reliable tool for investigating a population's diet in terms of nutrients, bioactive compounds and contaminants intake, providing important information about the potential nutritional deficiencies or exposure to food contaminants (WHO 1985). The EDI of Cr, Ni, Cu, As, Cd, and Pb were assessed for both adult and children according to the mean concentration of each metal in each crop species and the respective consumption rate for each species (Santos et al. 2004). The respective daily intake of heavy metals for adults and children are shown in Table 5. There are several routes of toxic metals exposure to human like oral, dermal and nasal. Out of them oral is the main route of metals exposure (ATSDR 2012). Bangladeshi people usually consume cereals, pulses, vegetables, and fruits in their daily meal. This type of foods may contribute a great portion of total diet for Bangladeshi population and daily intake of heavy metals estimation due to consumption of these types of food is a significant method to evaluate health risks (Alam et al. 2003). In cereals, pulses, vegetables and fruit samples, mean values of EDI decreased in the following order of Ni > Cu > Cr > Pb > As > Cd. Total daily intake of chromium, nickel, copper, arsenic, cadmium, and lead for adult were 13. 711, 19.446, 18.068, 5.691, 3.2021, and 11.796 mg/kg, respectively (Table 5) due to consumption of the studied foods. The total EDIs of Cr, Ni, As, Cd, and Pb for adult were 68, 65, 45, 70, and 56 times higher than the maximum tolerable daily intake (MTDI). Total daily intake of chromium, nickel, copper, arsenic, cadmium, and lead for children were 8.446, 11.738, 11.016, 3.409, 1.929, and 7.542 mg/kg, respectively ( Table 5). The total EDIs of Cr, Ni, Cd, As, and Pb for children were 42, 30, 27, 41, and 36 times higher than the maximum tolerable daily intake (MTDI) ( Table 5), indicated that these metals had the major contribution to the potential health risk via food consumption in the study area. Based on these data, we conclude that Cr, Ni, As, Cd, and Pb were the major components contributing to the potential health risk via consumption of the studied foods around the industrial areas of Jhenaidah and Kushtia districts in Bangladesh.

Non-carcinogenic and carcinogenic risk
The target hazard quotient (THQ) for non-carcinogenic risk and target carcinogenic risk (TR) of the six studied metals from consuming foodstuff for adults and children inhabitants are presented in Tables 6 and 7. The health risks from consumption of contaminated foodstuffs by adult populations were calculated based on THQ, which is the ratio of determined dose of a pollutant to a reference dose level. If THQ > 1, the exposed population will likely to experience a detrimental effect (Wang et al. 2005). The methodology for estimation of THQs does not provide a quantitative estimate on the probability of an exposed population experiencing a reverse health effect, but it offers an indication of the risk level due to contaminant exposure. Among the studied metals, the THQ values of Ni, Cu, As, Cd, and Pb exceeded the threshold value of 1 (THQ > 1) (Table 6), consequently, the consumption of studied foodstuff was considered to be unsafe and therefore, the consumers are at high risk with respect to Ni, Cu, As, Cd, and Pb which can cause non-carcinogenic risks to the consumers hence studied foodstuff was considered to be unsafe and their consumption on regular basis was not recommended; while, Cr will not cause any non-carcinogenic risks. The hazard index (HI) value expresses the combined non carcinogenic effects of multiple elements (Supplementary Figure S3). Among the selected crop species, the highest total THQ was observed for rice (75) followed by chili (59) in adult. In the studied foods, the highest total THQ was observed for rice (110) followed by bottle gourd (91.1) in children indicating potential non-carcinogenic risks. The total metal THQ value [(sum of individual metal THQ (HI)] due to consumption of the studied foodstuffs were 416.16 (>1) for adult and 818.97 (>1) for children. Potential health risks from exposure of the studied foodstuffs are therefore great concern. The analysis of non-carcinogenic health hazards resulting from exposure to metals through studied foods intake indicated that the investigated foods were not safe for human consumption.
The carcinogenic risks of As and Pb were assessed based on the target carcinogenic risk (TR) from consumption of foodstuffs by the adults and children were listed in Table 7. The TR values for As in the studied food samples were 4.97E þ 00 and 1.71E þ 02 for adult and children. The TR values for Pb in the studied samples were 1.66E-01 and 3.43E þ 00 for adult and children, respectively ( Table 7). The total carcinogenic risk of As from the foodstuffs were higher than USEPA standard (10 À4 ) indicating cancer risk to the both adult and children in the study area (USEPA 1989(USEPA , 2010(USEPA , 2015. Therefore, the potential carcinogenic risks for the urban residents through food ingestion should not be overlooked. However, estimation of potential human health risks based on total toxic metal concentrations may not be bring the real scenario since bioaccessible forms of toxic metals are considered as the basis of occurring adverse health effects through dietary intake of contaminated foods (Praveena and Omar 2017), which somehow indicates the limitation of this study in terms of potential human heal risk assessment. Nevertheless, the present study revealed that consumption of studied food items would definitely pose both carcinogenic and non-carcinogenic health risks to its consumers through the combined effects of toxic metals.

Conclusions
This study revealed that the studied food samples were heavily contaminated with various toxic metals which were found in the decreasing order of Ni > Cu > Cr > Pb > As > Cd. Most importantly, the concentrations of toxic metals including Cr, As, Cd, and Pb in foodstuffs were higher than the permissible limits recommended by WHO and FAO. Multivariate analysis showed that these major toxic metals in foodstuffs were predominantly contributed by anthropogenic activities which result in continuous accumulation of toxic metals in agricultural soils. The total estimated daily intake values of all the metals, excluding Cu, were higher than the maximum tolerable daily intake; indicating potential risk to the consumers. On the other hand, the THQ values of Ni, Cu, As, Cd, and Pb exceeded the threshold value of 1.0 which also indicated that the consumers would possibly experience serious health risks if they being exposed to the toxic metals via consumption of the studied foodstuffs. The study also showed that As in foodstuffs might exert lifetime carcinogenic health risk to the consumers. Therefore, this study recommended to review the national environmental standards and to formulate policy for safeguarding the environment from being contaminated by toxic metals. In addition, continuous monitoring of toxic metals in environmental components as well as commonly cultivated and consumed foodstuffs to alleviate their associated health risks in Bangladesh.