Hg, Cd, Pb, As, Ni, Cu, Zn, Mn, Cr, Co and V were evaluated in paddy (Oryza sativa) and foreign rice collected from thirteen local government areas of Kaduna State, Nigeria. Concentration of Cu was below WHO/FAO and NAFDAC (40.00 mg/kg) regulatory limit. Concentration of Zn was within the WHO/FAO limit, Ni (0.03 mg/kg) was above the WHO/FAO threshold limit in samples Le3, Kc1, Ik2, TO and KG. Pb was detected in all samples except inKa2. Co, Fe, Pb, Cd, Mn and Cr were below WHO/FAO and NAFDAC regulatory limits in all samples. Guidance value was not available for V. Associated health risks of these metals show the daily intake of metals (EDIM)for Cd (0.0000935 mg/kg), Cr (0.001105 to 0.002125 mg/kg), Mn (0.00034 to 0.00765 mg/kg). EDIM of As was below the daily limit Target hazard quotient measured for Ni, Pb, Cd, Cr, Mn and Co in all samples were < 1, except for As. There exists cancer risk at a lower limit of 64 chances in 1000 lifetime exposure and an upper limit of 14 chances in 100 lifetime exposure for any combination of two or more of Ni, Pb, Cd, As and Cr available for consumption. Statistical analysis reveals no significant differences (p < 0.05) in the concentrations of Cu, Cr, Mn, Pb, As and V but revealed significant difference in the concentrations of Zn, Ni, Cd, Fe and Co. Hg was not detected in all samples.
Article
Toxic Metals Contamination of Paddy (Oryza Sativa) and Imported Rice Sold in Kaduna and Its Human Health Risk Assessment
https://doi.org/10.21203/rs.3.rs-1953036/v1
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Daily Intake
Health Risk
Human Health Risk
Toxic Elements
Toxic metals such as lead (Pb), cadmium (Cd), manganese (Mn), and metalloids such as arsenic (As) and antimony (Sb) are found naturally in the earth. However, this has been amplified by various human activities, especially by trial processes [1],finding entry into plants, then subsequently in human diets via groundwater and soils. The chemical form of these metals influences its solubility, mobility, and toxicity, which largely depends on the source of the metal in the environment [2].
Rice has been implicated as the main source of toxic metal exposure for inhabitants of China and Japan as its consumption has been closely associated some health challenges, especially human renal dysfunction is [13]. There is clear evidence that linked to contamination of rice with Cd in China and Japan.
O. sativa grains cultivated in paddy fields in locations close to mines and within urbanized areas in Tanzania showed that the levels of Cadmium, Chromium, Copper, Lead, Zinc and total Mercury in brown rice are generally within the acceptable levels for human food. However, higher concentration of Hg was found in the husks, suggesting the significance of atmospheric dispersal of Hg in the basin [14], while Rogan [15] evaluated very high concentrations of As, Cd, Cu, Pb and Zn in the paddy rice (0.53, 0.31, 5.8, 0.5 and 67 μg g−1) from the western part of Kočani Field (eastern Macedonia), close to the Zletovska River.
Rice is a staple food in most Nigerian household; cutting across all socio-economic classes. Its demand is evidently promoted by the increasing population index of citizens. Akande and Aupokodje [16], reported Nigeria to be the second largest importer of rice in the world and ranked also as highest producer/consumer in West Africa [17].
Rice cultivation is widespread across states in Nigeria (Enugu, Cross River, Ebonyi Benue, Kaduna, Niger, Kebbi and Taraba) [18]. Kaduna State (from 2000 to 2003) has been the largest producer of rice, accounting for about 22% of the country’s annual rice production [19].
Contamination of agricultural soil and crops by potential toxic elements is a general concern to food safety and a potential health risk to humans [3-5]. Chidimma [6] reported Pb, Cr, As, Zn, Cd, Cu, Hg and Ni as the most common toxic metals found in Nigerian agricultural soils. Other authors have reported health complications arising from toxic contamination of food [7-9]. Ihedioha [10] opined that the consumption of rice cultivated on soil contaminated with heavy metals could result to adverse health risks especially by Pb and Cd exposure.
To emphasize the bioavailability of toxic metals in rice samples as a local, national and international concern, reports by related research works have shown varying degrees of metal contaminations, and in some cases beyond the threshold value for human consumption. Ogbodo [11], investigated toxic metal levels in Paddy soils and Rice (Oryza Sativa (L) at Ikwo, in Ebonyi State, South-East of Nigeria. Metals studied were Hg, Cu, As, Pb, Cr, Fe, Cd, Zn, Mn, and Ni. Results revealed these metals in polished rice were generally within the acceptable levels for human food (< 0.01). However, the concentration of Hg found in the polished grains of Landrace, FARO44, FARO52 and Fadama rice varieties were beyond the WHO permissible concentration. Results of study [10], for the metals Cd, Cr, Pb, Mn, Zn and Ni in 40 Paddy soils and rice samples from Adani Rice Field, in Enugu, disclosed that Pb, Cd, and Cr concentrations in the samples were above the WHO maximum acceptable limit. The estimated daily intake of Pb and Cd were above the WHO and JECFA safety levels.
The concentration of toxic metals in locally produced rice from the South-East and South-South geopolitical zones of Nigeria was examined by Otitoju [12]. They discovered that Cr and Pb concentrations ranged from 0.019-0.282mg/kg and 0.000-1.722mg/kg respectively. The average mean for chromium (Cr) and lead (Pb) concentrations were 0.060 and 0.777mg/kg respectively. Mercury, cadmium and arsenic were below detectable concentration of <0.001mg/kg.
Soils, and agro-chemicals as part of rice cultivation environment are most often contaminated by toxic metals, various studies have revealed. Mindful of the significance attached to food safety, and armed with information on the various sources of metal contamination of rice through various anthropogenic sources; this study was therefore aimed at evaluating quantitatively the concentrations of of Hg, Cu, Zn, Ni, Pb, Cd, Cr, Mn, As, Fe, V and Co in rice grains cultivated in 13 local government areas of Kaduna State and five most widely purchased brands of imported rice sold at Samaru market, Zaria.. Following this, human health risks (potential cancer and non-cancer) possed to consumers from consumption of rice will be evaluated in order to determ their toxicity status. The study outcome could serve as a bases for the formulation and implementation of policies relating to food safety by policy makers. This is a justification for this study
2.1 Study Area
The study was conducted in Kaduna state, Nigeria, situated at longitude 7.429504 and Latitude 10.609319, GPS Coordinates are 100 36’ 33.5484’’ N and 70 25’ 46.2144’’ E.
2.2 Sample Collection
Thirteen (13) local government areas were identified as major rice farming zones; namely Kachia, Kubau, Soba, Kauru, Ikara, Giwa, Kudan, Sabon Gari, Kajuru, Chikun, Lere, Makarfi, and Sanga. Sampling points are shown in Fig. 1. A 250 g composite sample was collected from four points in each zone, and then compounded to give a composite of 1 kg, these was collected for each zone. Thirty nine (39) samples of local rice cultivars was collected directly from farmers and used for this study; additionally, 250 g of imported rice samples were also collected for each of: OR, KI, TO, MR and AM brands from Samaru market, Zaria and similarly evaluated. Total samples tested was 43.
2.3 Sample preparation
Samples were prepared as programmed by the equipment: Two hundred milligram (200 mg) of samples were weighed and transferred into 90 mL microwave digestion vessels. Ten milliliters mixture of 15.9 M trace metal grade Nitric acid, hydrogen peroxide (30 % w/w) and perchloric acid (11.7 M) (7:2:1) was added to each vessel. After standing for one hour (1h), the samples were processed by microwave digestion system as follows: ramp temperature from ambient to 200 0C over 20 min, then hold at 200 0C for 20 min, after digesting, samples were cooled to at least 50 0C or lower before handling. The digestate was transferred to a 50 mL volumetric flask; the solution diluted to mark with deionized water and filtered for instrumental analysis.
2.4 Elemental Investigation
All measurements were performed using Agilent 4210 MP-AES. The sample introduction system consisted of PVC peristatic pump tubing (white/white and blue/blue), a single pass cyclonic spray chamber and the oneNeb nebulizer. The Agilent MP Expert software was used to automatically subtract the background signal from the analytical signal, following this, the blank solution’s background spectrum was recorded, this was automatically deducted from each of the standards and sample solutions investigated. The software was also applied to improve both the nebulization pressure and viewing position for each of the designated wavelength in order to maximize sensitivity. Owing to this optimization, and also in view of all determinations were carried out successively, each analyte was determined under enhanced settings. A standard reference solution was employed to quickly and easily optimize the considerations. This was carried out following the instrument manufacturers’ instruction.
2.5 Toxic Studies
This was carried out following Human Health Risk Assessment criteria as proposed by the United States environmental protection (U.S. EPA, 1991), described in the Risk Assessment Information System (RAIS), 2007, supported by the Toxicological profiles developed by the USEPA Integrated Risk Information System (IRIS) and by the US Agency for Toxic Substances and Disease Registry – Toxicological profiles (ATSDR) (http://www.atsdr.cdc.gov/toxfaq.htmL). Non-cancer and cancer risks where computed as described below.
2.5.1 Estimated Daily Intake of Toxic metals
The estimated daily intake (EDIM, mg/kg/day) is a parameter used to quantify the oral exposure dosage during a specific period, expressed as a daily dose per unit body weight. The daily toxic metal intake dose depends on the toxic metal concentration and the amount of any respective food consumed. It is usually calculated using the following formula:
C is the mean toxic metal dose (mg/kg), IR is ingestion rate (mg/day), ED is exposure duration for adults(70 years), EF is exposure frequency in days/year, BW, and AT is the average time [20-22], exposure duration, exposure frequency, reference body weight, and average time, respectively. The IR was estimated to be 100 for adults, according to the average daily rice intake of adults; the BW of 50 kg was taken from data in related studies [23; 24]; the ED was days; the EF was 180 (based on age); and the AT was 25,550 (the product of 365 days and an age of 70 years).
2.5.2 Health Risk Assessment
Health risk effect posed to the Nigerian population from the consumption of rice contaminated with toxic metals was conducted following standard models for integrated metal risk assessment presented in referenced literatures consulted [25; 21] The non-carcinogenic health risk was evaluated using Hazard quotient (HQ) and total hazard index (THI). The hazard quotient characterizes the health risk of non-carcinogenic adverse effects due to exposure to toxicants:
The hazard quotient (HQ), a ratio of the EDIM to the RfD, represents the health risk of noncarcinogenic adverse effects due to exposure to toxicants:
HQs<1 can be assumed to reflect safety, whereas HQs>1 are assumed to indicate potential noncarcinogenic effects [26].
To determine the potential risk of adverse health effects from a mixture of chemical elements in brown rice, the hazard index (HI), arising from the sum of Target Hazard Quotient (THQs), was calculated:
HIs < 1 indicate that chronic risks are unlikely, whereas HIs > 1 indicate that noncancerous risks are likely to occur.
Carcinogenic health risk was assessed by using the equation below:
CR is the risk of cancer over a lifetime, AT is averaging time for carcinogens (365 day/year × ED),C is potential toxic element concentration in rice (mg/kg), IR is rice ingestion rate (g/person/day), ED is exposure duration (70 years), Efr is the exposure frequency (350 days/year), RfD is the oral reference dose (mg/kg/day), BW is the average body weight (50 kg) and AT is the average time for non-carcinogens (365 day/year × ED). The oral reference doses for the metals in mg/kg/day were Zn = 0.3, Pb = 0.004, Cd = 0.001, Mn = 0.14, Cu = 0.04, Fe = 0.7, Ni = 0.02 and Cr (III) = 1.5, Hg = 0.0001[25].
2.6 Statistical Analysis
software Excel 2013 and SPSS 16.0 were applied in data treatment, this was achieved using one-way ANOVA, at 95% confidence interval (CI) difference then validated by the Pearson Correlation at 0.001 level for a two tailed test, and at 0.05 level (two tailed) level of significance. Sampling locations were selected as group and the corresponding toxic metal concentration as the corresponding variable.
Table 1. Recorded Concentrations of Toxic Metal in Evaluated Samples
|
LGA |
Sample Identity |
Mean concentration (mg/Kg) |
||||||||||||
|
Hg |
Cu |
Zn |
Ni |
Pb |
Cd |
Cr |
Mn |
As |
Fe |
V |
Co |
|||
|
Kubau |
kb1 |
ND |
0.04±0.00 |
0.15±0.01 |
0.01±0.00 |
0.01±0.00 |
0.010±0.001 |
0.21±0.00 |
0.09±0.00 |
0.68±0.03 |
1.42±0.03 |
0.05±0.01 |
0.03±0.00 |
|
|
kb2 |
ND |
0.03±0.00 |
0.21±0.00 |
-0.01±0.00 |
0.02±0.00 |
0.011±0.002 |
0.23±0.00 |
0.13±0.00 |
0.77±0.04 |
0.97±0.02 |
0.04±0.00 |
0.03±0.00 |
||
|
kb3 |
ND |
0.03±0.00 |
0.17±0.01 |
0.01±0.00 |
0.01±0.00 |
0.010±0.001 |
0.23±0.00 |
0.11±0.00 |
0.74±0.05 |
0.82±0.04 |
0.07±0.01 |
0.02±0.00 |
||
|
Soba |
So1 |
ND |
0.03±0.00 |
0.29±0.01 |
ND |
0.01±0.00 |
0.009±0.001 |
0.20±0.00 |
0.18±0.00 |
0.69±0.03 |
0.83±0.03 |
0.07±0.00 |
0.03±0.00 |
|
|
So2 |
ND |
0.06±0.00 |
0.21±0.00 |
0.03±0.01 |
0.01±0.00 |
0.009±0.001 |
0.13±0.00 |
0.05±0.00 |
0.74±0.05 |
0.42±0.01 |
0.00±0.00 |
0.03±0.00 |
||
|
So3 |
ND |
0.11±0.00 |
0.38±0.01 |
ND |
0.01±0.00 |
0.009±0.001 |
0.25±0.00 |
0.90±0.00 |
0.77±0.04 |
1.70±0.04 |
0.25±0.00 |
0.03±0.00 |
||
|
Giwa |
Gw1 |
ND |
0.06±0.00 |
0.26±0.01 |
ND |
0.01±0.00 |
0.010±0.001 |
0.21±0.00 |
0.16±0.00 |
0.73±0.02 |
1.26±0.03 |
0.07±0.00 |
0.030.00 |
|
|
Gw2 |
ND |
0.09±0.00 |
0.22±0.01 |
ND |
0.01±0.00 |
0.009±0.001 |
0.21±0.00 |
0.26±0.00 |
0.69±0.02 |
1.72±0.03 |
0.12±0.00 |
0.03±0.00 |
||
|
Gw3 |
ND |
0.06±0.00 |
0.22±0.01 |
ND |
0.01±0.00 |
0.009±0.001 |
0.22±0.00 |
0.19±0.00 |
0.75±0.04 |
1.08±0.01 |
0.06±0.00 |
0.03±0.00 |
||
|
Makarfi |
Mk1 |
ND |
0.03±0.00 |
0.14±0.00 |
0.01±0.00 |
0.04±0.00 |
0.010±0.001 |
0.25±0.00 |
0.08±0.00 |
0.77±0.02 |
0.94±0.03 |
0.03±0.00 |
0.030.00 |
|
|
Mk2 |
ND |
0.12±0.00 |
0.26±0.00 |
0.01±0.00 |
0.02±0.00 |
0.01±0.001 |
0.17±0.00 |
0.17±0.00 |
0.72±0.04 |
0.63±0.03 |
0.04±0.00 |
0.03±0.00 |
||
|
Mk3 |
ND |
0.13±0.00 |
0.17±0.00 |
0.02±0.00 |
0.02±0.00 |
0.003±0.001 |
0.23±0.00 |
0.13±0.00 |
0.56±0.05 |
1.01±0.00 |
0.05±0.01 |
0.01±0.00 |
||
|
Kauru |
Ka1 |
ND |
0.02±0.00 |
0.16±0.00 |
0.00±0.00 |
0.01±0.00 |
0.010±0.002 |
0.19±0.00 |
0.10±0.00 |
0.68±0.05 |
0.70±0.02 |
0.03±0.01 |
0.03±0.00 |
|
|
Ka2 |
ND |
0.03±0.00 |
0.17±0.00 |
0.01±0.00 |
ND |
0.010±0.001 |
0.17±0.00 |
0.08±0.00 |
0.71±0.06 |
0.56±0.02 |
0.04±0.00 |
ND |
||
|
Ka3 |
ND |
0.06±0.00 |
0.33±0.03 |
ND |
0.02±0.00 |
0.011±0.002 |
0.20±0.00 |
0.21±0.00 |
0.71±0.05 |
1.92±0.03 |
0.07±0.01 |
0.03±0.00 |
||
Table 1(cont.).
|
LGA |
Sample Identity |
Mean concentration (mg/Kg) |
|||||||||||||
|
Hg |
Cu |
Zn |
Ni |
Pb |
Cd |
Cr |
Mn |
As |
Fe |
V |
Co |
|
|||
|
Kudan |
Kd1 |
ND |
0.030.00 |
0.13±0.00 |
0.02±0.00 |
0.01±0.00 |
0.009±0.00 |
0.24±0.00 |
0.05±0.00 |
0.78±0.04 |
0.63±0.01 |
0.05±0.00 |
0.02±0.00 |
|
|
|
Kd2 |
ND |
0.02±0.00 |
0.14±0.00 |
0.01±0.00 |
0.06±0.00 |
0.009±0.001 |
0.23±0.00 |
0.09±0.00 |
0.74±0.05 |
0.63±0.03 |
0.04±0.00 |
0.03±0.00 |
|
||
|
Kd3 |
ND |
0.02±0.00 |
0.12±0.00 |
0.01±0.00 |
0.02±0.00 |
0.009±0.00 |
0.19±0.00 |
0.07±0.00 |
0.71±0.03 |
0.49±0.02 |
0.05±0.00 |
0.03±0.00 |
|
||
|
Ikara |
Ik1 |
ND |
0.16±0.00 |
0.20±0.01 |
0.02±0.00 |
0.00±0.00 |
0.007±0.00 |
0.16±0.00 |
0.12±0.00 |
0.68±0.07 |
0.76±0.02 |
0.020.00 |
0.03±0.00 |
|
|
|
Ik2 |
ND |
0.10±0.00 |
0.17±0.00 |
0.03±0.00 |
0.01±0.00 |
0.004±0.001 |
0.15±0.00 |
0.09±0.00 |
0.72±0.04 |
0.66±0.05 |
0.02±0.00 |
0.02±0.00 |
|
||
|
Ik3 |
ND |
0.04±0.00 |
0.22±0.01 |
ND |
0.02±0.00 |
0.010±0.001 |
0.20±0.00 |
0.17±0.00 |
0.71±0.04 |
1.14±0.02 |
0.05±0.01 |
0.03±0.00 |
|
||
|
Kajuru |
Kj1 |
ND |
0.11±0.00 |
0.20±0.00 |
0.03±0.00 |
0.01±0.00 |
0.005±0.00 |
0.23±0.00 |
0.09±0.00 |
0.70±0.06 |
1.15±0.04 |
0.02±0.00 |
0.02±0.00 |
|
|
|
Kj2 |
ND |
0.06±0.00 |
0.27±0.00 |
ND |
0.16±0.00 |
0.011±0.001 |
0.24±0.00 |
0.13±0.00 |
0.70±0.05 |
1.13±0.04 |
0.05±0.00 |
0.03±0.00 |
|
||
|
Kj3 |
ND |
0.15±0.00 |
0.2±0.00 |
0.01±0.00 |
ND |
0.001±0.001 |
0.18±0.01 |
0.09±0.00 |
0.33±0.05 |
0.95±0.02 |
0.03±0.00 |
0.01±0.00 |
|
||
|
Sanga |
Sa1 |
ND |
0.11±0.00 |
0.15±0.00 |
0.02±0.00 |
0.00±0.00 |
0.001±0.002 |
0.17±0.00 |
0.06±0.00 |
0.45±0.05 |
0.57±0.02 |
0.04±0.00 |
0.02±0.00 |
|
|
|
Sa2 |
ND |
0.04±0.00 |
0.20±0.00 |
0.00±0.01 |
0.02±0.00 |
0.010±0.001 |
0.24±0.00 |
0.23±0.00 |
0.75±0.06 |
1.22±0.02 |
0.11±0.00 |
0.02±0.00 |
|
||
|
Sa3 |
ND |
0.18±0.01 |
0.17±0.00 |
0.03±0.00 |
0.00±0.00 |
0.006±0.001 |
0.18±0.00 |
0.11±0.00 |
0.71±0.07 |
0.53±0.03 |
0.02±0.00 |
0.03±0.00 |
|
||
|
Lere |
Le1 |
ND |
0.07±0.00 |
0.31±0.01 |
ND |
0.01±0.00 |
0.010±0.001 |
0.21±0.00 |
0.28±0.00 |
0.71±0.05 |
0.92±0.03 |
0.09±0.00 |
0.03±0.00 |
|
|
|
Le2 |
ND |
0.08±0.00 |
0.18±0.00 |
0.02±0.00 |
ND |
0.009±0.001 |
0.17±0.00 |
0.10±0.00 |
0.75±0.04 |
0.73±0.02 |
ND |
0.03±0.00 |
|
||
|
Le3 |
ND |
0.06±0.00 |
0.24±0.00 |
0.03±0.00 |
0.03±0.00 |
0.009±0.001 |
0.14±0.00 |
0.08±0.00 |
0.72±0.07 |
0.54±0.02 |
0.01±0.01 |
0.03±0.00 |
|
||
Table 1 (cont.).
|
LGA |
Sample Identity |
Mean concentration (mg/Kg) |
|||||||||||
|
Hg |
Cu |
Zn |
Ni |
Pb |
Cd |
Cr |
Mn |
As |
Fe |
V |
Co |
||
|
Chikun |
Ch1 |
ND |
0.04±0.00 |
0.26±0.00 |
0.00±0.00 |
0.01±0.00 |
0.010±0.001 |
0.23±0.00 |
0.20±0.00 |
0.78±0.03 |
1.06±0.05 |
0.07±0.01 |
0.03±0.00 |
|
Ch2 |
ND |
0.04±0.00 |
0.17±0.00 |
0.00±0.00 |
0.02±0.00 |
0.010±0.00 |
0.22±0.00 |
0.15±0.00 |
0.72±0.02 |
0.91±0.04 |
0.06±0.00 |
0.03±0.00 |
|
|
Ch3 |
ND |
0.05±0.00 |
0.15±0.00 |
0.00±0.00 |
0.01±0.00 |
0.011±0.001 |
0.23±0.00 |
0.13±0.00 |
0.75±0.04 |
1.57±0.06 |
0.05±0.00 |
0.03±0.00 |
|
|
Kachia |
Kc1 |
ND |
0.05±0.00 |
0.17±0.00 |
0.03±0.00 |
0.01±0.00 |
0.009±0.001 |
0.20±0.00 |
0.10±0.00 |
0.72±0.06 |
0.79±0.03 |
0.02±0.00 |
0.03±0.00 |
|
Kc2 |
ND |
0.05±0.00 |
0.16±0.00 |
0.02±0.00 |
0.00±0.00 |
0.010±0.001 |
0.13±0.00 |
0.06±0.00 |
0.73±0.03 |
0.34±0.02 |
0.01±0.00 |
0.03±0.00 |
|
|
Kc3 |
ND |
0.05±0.00 |
0.16±0.00 |
0.02±0.00 |
0.03±0.00 |
0.008±0.00 |
0.13±0.00 |
0.07±0.00 |
0.68±0.04 |
0.77±0.02 |
0.01±0.01 |
0.03±0.00 |
|
|
Sabon Gari |
Sb1 |
ND |
0.11±0.00 |
0.19±0.00 |
-0.020.00 |
0.01±0.00 |
0.009±0.001 |
0.22±0.00 |
0.21±0.00 |
0.73±0.05 |
3.66±0.02 |
0.11±0.00 |
0.02±0.00 |
|
Sb2 |
ND |
0.09±0.00 |
0.24±0.00 |
-0.02±0.00 |
0.02±0.00 |
0.0080.001 |
0.23±0.01 |
0.280.00 |
0.71±0.03 |
2.47±0.07 |
0.08±0.01 |
0.03±0.00 |
|
|
Sb3 |
ND |
0.06±0.00 |
0.210.00 |
-0.01±0.00 |
0.02±0.00 |
0.010±0.001 |
0.24±0.00 |
0.19±0.00 |
0.74±0.06 |
1.80±0.03 |
0.09±0.00 |
0.02±0.00 |
|
Key: ND= Not Detected,kb1 = Pambegua, kb2 = Anchau, kb3 = Zuntu, So1 = Damari, So2 = Maigana, So3 = Tashan Ice, Gw1 = Yakawada, Gw2 = Kaya, Gw3 = Gangara, Mk1 = Meyere, Mk2 = Makarfi Town, Mk3 = Gubuci, Ka1 = Chawai Kafin-Fadama, Ka2 = Anguwan-juri, Ka3 = Fadamam Badarin kasa, Kd1 = Hunkuyi, Kd2 = Zabi, Kd3 = Kudan Town, Ik1 = Sabon Gari, Ik2 = Saya Saya, Ik3 = Jamfalan, Kj1 = Kasuwan Magani, Kj2 = Maraba, Kj3 = Kufana, Sa1 = Gwantu, Sa2 = Fadan Karshi, Sa3 = Aboro, Le1 = YarKasuwa, Le2 = Lahadi, Le3= Mariri, Ch1 = Kujama, Ch2 = Mahuta, Ch3 = Maraban-Rido, Kc1 = Gummel, Kc2 = Katari, Kc3= Kurmin Musa, Sb1 = Likoro, Sb2 = Saka-Dadi, Sb3 = Jama’a, OR = Oriba, KI = King, TO = Tomato, MR = Mr. Rice, AM = Amaria.
Table 2. Regulatory Limits for Toxic Metal Concentration in Grains and Cereals
|
Elements |
Toxicological guidance value (mg/kg) |
|
|
WHO/FAO |
NAFDAC |
|
|
Hg |
0.004 |
NA |
|
Cu |
0.073 |
0.04 |
|
Zn |
0.1 |
0.05 |
|
Ni |
0.067 |
0.027 |
|
Pb |
0.0003 |
0.002 |
|
Cd |
0.0001 |
0.0002 |
|
Cr |
0.0023 |
0.002 |
|
Mn |
500 |
NA |
|
As |
0.35 |
NA |
|
Fe |
48.00 |
NA |
|
V |
NA |
NA |
|
Co |
50 |
NA |
Key: NA= Not Available;
Table 3. Carcinogenic Grading of Investigated Metals
|
Element |
Cancer Classification by IARC/EPA |
ORfD (mg/(kg/day) |
OCSF (mg/(kg/day) |
Minimal Risk Level (MRL) Oral (mg/m3,day) |
|
Cd |
B1 |
1.00E-3 |
3.80E-2 |
0.0001 |
|
As |
A |
3.00E-4 |
1.50E+00 |
0.0003 |
|
Pb |
B2 |
4.00E-03 |
8.50E-03 |
- |
|
Mn |
B2 |
2.00E-02 |
|
- |
|
Co |
- |
- |
- |
- |
|
Hg |
D |
1.00E-4 |
0 |
0.0002 |
|
Cr |
A(Cr VI), D(Cr III) |
1.50E-1 |
5.00E-01 |
0.005 |
|
Fe |
|
|
|
- |
|
Cu |
D |
4.00E-2 |
|
0.01 |
|
Ni |
B2 |
2.00E-2 |
1.70E+1 |
- |
|
V |
|
|
|
- |
|
Zn |
|
3.00E-1 |
|
- |
*MRL: estimates of the daily human exposure to a hazardous substance that is likely to be without an appreciable risk of adverse non-cancer health effects over specified routes and durations of exposure.
*Cancer classification: A-Human carcinogen, B1- probable human carcinogen, B2- probable human, C- possible human carcinogen, D-not classifiable as to human carcinogenicity [27].
3.1 Non Cancer Risk Index
Table 4. Estimated Daily Intake of Metals (EDIM)
|
Metals |
Kb1 |
kb2 |
kb3 |
So1 |
So2 |
So3 |
Gw1 |
Gw2 |
Gw3 |
|
Ni |
0.000085 |
-8.5E-05 |
0.000085 |
0 |
0.000255 |
0 |
0 |
0 |
0 |
|
Pb |
0.000085 |
0.00017 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
|
Cd |
0.000085 |
9.35E-05 |
0.000085 |
7.65E-05 |
7.65E-05 |
7.65E-05 |
0.000085 |
7.65E-05 |
7.65E-05 |
|
Cr |
0.001785 |
0.001955 |
0.001955 |
0.0017 |
0.001105 |
0.002125 |
0.001785 |
0.001785 |
0.00187 |
|
Mn |
0.000765 |
0.001105 |
0.000935 |
0.00153 |
0.000425 |
0.00765 |
0.00136 |
0.00221 |
0.001615 |
|
As |
0.00578 |
0.006545 |
0.00629 |
0.005865 |
0.00629 |
0.006545 |
0.006205 |
0.005865 |
0.006375 |
|
Co |
0.000255 |
0.000255 |
0.00017 |
0.000255 |
0.000255 |
0.000255 |
0.000255 |
0.000255 |
0.000255 |
|
|
Mk1 |
Mk2 |
Mk3 |
Ka1 |
Ka2 |
Ka3 |
Kd1 |
Kd2 |
Kd3 |
|
Ni |
0.000085 |
0.000085 |
0.00017 |
0 |
0.000085 |
0 |
0.00017 |
0.000085 |
0.000085 |
|
Pb |
0.00034 |
0.00017 |
0.00017 |
0.000085 |
0 |
0.00017 |
0.000085 |
0.00051 |
0.00017 |
|
Cd |
0.000085 |
0.000085 |
2.55E-05 |
0.00085 |
0.000085 |
9.35E-05 |
7.65E-05 |
7.65E-05 |
7.65E-05 |
|
Cr |
0.002125 |
0.001445 |
0.001955 |
0.001615 |
0.001445 |
0.0017 |
0.00204 |
0.001955 |
0.001615 |
|
Mn |
0.00068 |
0.001445 |
0.001105 |
0.00085 |
0.00068 |
0.001785 |
0.000425 |
0.000765 |
0.000595 |
|
As |
0.006545 |
0.00612 |
0.00476 |
0.00578 |
0.006035 |
0.006035 |
0.00663 |
0.00629 |
0.006035 |
|
Co |
0.000255 |
0.000255 |
0.000085 |
0.000255 |
0 |
0.000255 |
0.00017 |
0.000255 |
0.000255 |
|
|
Ik1 |
Ik2 |
Ik3 |
Kj1 |
Kj2 |
Kj3 |
Sa1 |
Sa2 |
Sa3 |
|
Ni |
0.00017 |
0.000255 |
-8.5E-05 |
0.000255 |
0 |
0.000085 |
0.00017 |
0 |
0.000255 |
|
Pb |
0 |
0.000085 |
0.00017 |
0.000085 |
0.00136 |
0 |
0 |
0.00017 |
0 |
|
Cd |
0.0000595 |
0.000034 |
0.000085 |
4.25E-05 |
9.35E-05 |
8.5E-06 |
8.5E-06 |
0.000085 |
0.000051 |
|
Cr |
0.00136 |
0.001275 |
0.0017 |
0.001955 |
0.00204 |
0.00153 |
0.001445 |
0.00204 |
0.00153 |
|
Mn |
0.00102 |
0.000765 |
0.001445 |
0.000765 |
0.001105 |
0.000765 |
0.00051 |
0.001955 |
0.000935 |
|
As |
0.00578 |
0.00612 |
0.006035 |
0.00595 |
0.00595 |
0.002805 |
0.003825 |
0.006375 |
0.006035 |
|
Co |
0.000255 |
0.00017 |
0.000255 |
0.00017 |
0.000255 |
0.000085 |
0.00017 |
0.00017 |
0.000255 |
|
Metals |
Kb1 |
kb2 |
kb3 |
So1 |
So2 |
So3 |
Gw1 |
Gw2 |
Gw3 |
|
Ni |
0.000085 |
-8.5E-05 |
0.000085 |
0 |
0.000255 |
0 |
0 |
0 |
0 |
|
Pb |
0.000085 |
0.00017 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
0.000085 |
|
Cd |
0.000085 |
9.35E-05 |
0.000085 |
7.65E-05 |
7.65E-05 |
7.65E-05 |
0.000085 |
7.65E-05 |
7.65E-05 |
|
Cr |
0.001785 |
0.001955 |
0.001955 |
0.0017 |
0.001105 |
0.002125 |
0.001785 |
0.001785 |
0.00187 |
|
Mn |
0.000765 |
0.001105 |
0.000935 |
0.00153 |
0.000425 |
0.00765 |
0.00136 |
0.00221 |
0.001615 |
|
As |
0.00578 |
0.006545 |
0.00629 |
0.005865 |
0.00629 |
0.006545 |
0.006205 |
0.005865 |
0.006375 |
|
Co |
0.000255 |
0.000255 |
0.00017 |
0.000255 |
0.000255 |
0.000255 |
0.000255 |
0.000255 |
0.000255 |
3.2 Cancer Risk Index
Table 5. Incremental lifetime cancer risk in adult from consumption of rice (CR)
|
Metals |
Kb1 |
kb2 |
kb3 |
So1 |
So2 |
So3 |
Gw1 |
Gw2 |
Gw3 |
|
|||||||||
|
Ni |
0.001445 |
-0.00145 |
0.001445 |
0 |
0.004335 |
0 |
0 |
0 |
0 |
|
|||||||||
|
Pb |
7.225E-07 |
1.45E-06 |
7.23E-07 |
7.23E-07 |
7.23E-07 |
7.23E-07 |
7.23E-07 |
7.23E-07 |
7.23E-07 |
|
|||||||||
|
Cd |
0.00000323 |
3.55E-06 |
3.23E-06 |
2.91E-06 |
2.91E-06 |
2.91E-06 |
3.23E-06 |
2.91E-06 |
2.91E-06 |
|
|||||||||
|
Cr |
0.0008925 |
0.000978 |
0.000978 |
0.00085 |
0.000553 |
0.001063 |
0.000893 |
0.000893 |
0.000935 |
|
|||||||||
|
As |
0.00867 |
0.009818 |
0.009435 |
0.008798 |
0.009435 |
0.009818 |
0.009308 |
0.008798 |
0.009563 |
|
|||||||||
|
Metals |
Mk1 |
Mk2 |
Mk3 |
Ka1 |
Ka2 |
Ka3 |
Kd1 |
Kd2 |
Kd3 |
|
|||||||||
|
Ni |
0.001445 |
0.001445 |
0.00289 |
0 |
0.001445 |
0 |
0.00289 |
0.001445 |
0.001445 |
|
|||||||||
|
Pb |
0.00000289 |
1.45E-06 |
1.45E-06 |
7.23E-07 |
0 |
1.45E-06 |
7.23E-07 |
4.34E-06 |
1.45E-06 |
|
|||||||||
|
Cd |
0.00000323 |
3.23E-06 |
9.69E-07 |
3.23E-05 |
3.23E-06 |
3.55E-06 |
2.91E-06 |
2.91E-06 |
2.91E-06 |
|
|||||||||
|
Cr |
0.0010625 |
0.000723 |
0.000978 |
0.000808 |
0.000723 |
0.00085 |
0.00102 |
0.000978 |
0.000808 |
|
|||||||||
|
As |
0.0098175 |
0.00918 |
0.00714 |
0.00867 |
0.009053 |
0.009053 |
0.009945 |
0.009435 |
0.009053 |
|
|||||||||
|
Metals |
Ik1 |
Ik2 |
Ik3 |
Kj1 |
Kj2 |
Kj3 |
Sa1 |
Sa2 |
Sa3 |
|
|||||||||
|
Ni |
0.00289 |
0.004335 |
-0.00145 |
0.004335 |
0 |
0.001445 |
0.00289 |
0 |
0.004335 |
|
|||||||||
|
Pb |
0E+00 |
7.23E-07 |
1.45E-06 |
7.23E-07 |
1.16E-05 |
0 |
0 |
1.45E-06 |
0 |
|
|||||||||
|
Cd |
0.000002261 |
1.29E-06 |
3.23E-06 |
1.62E-06 |
3.55E-06 |
3.23E-07 |
3.23E-07 |
3.23E-06 |
1.94E-06 |
|
|||||||||
|
Cr |
0.00068 |
0.000638 |
0.00085 |
0.000978 |
0.00102 |
0.000765 |
0.000723 |
0.00102 |
0.000765 |
|
|||||||||
|
Metals |
Le1 |
Le2 |
Le3 |
Ch1 |
Ch2 |
Ch3 |
Kc1 |
Kc2 |
Kc3 |
||||||||||
|
Ni |
0 |
0.00289 |
0.004335 |
0 |
0 |
0 |
0.004335 |
0.00289 |
0.00289 |
||||||||||
|
Pb |
7.225E-07 |
0 |
2.17E-06 |
7.23E-07 |
1.45E-06 |
7.23E-07 |
7.23E-07 |
0 |
2.17E-06 |
||||||||||
|
Cd |
0.00000323 |
2.91E-06 |
2.91E-06 |
3.23E-06 |
3.23E-06 |
3.55E-06 |
2.91E-06 |
3.23E-06 |
2.58E-06 |
||||||||||
|
Cr |
0.0008925 |
0.000723 |
0.000595 |
0.000978 |
0.000935 |
0.000978 |
0.00085 |
0.000553 |
0.000553 |
||||||||||
|
As |
0.0090525 |
0.009563 |
0.00918 |
0.009945 |
0.00918 |
0.009563 |
0.00918 |
0.009308 |
0.00867 |
||||||||||
|
Metals |
Sb1 |
Sb2 |
Sb3 |
MR |
OR |
AM |
TO |
KG |
|||||||||||
|
Ni |
-0.00289 |
-0.00289 |
-0.00145 |
0.00289 |
0.00289 |
0.00289 |
0.004335 |
0.004335 |
|||||||||||
|
Pb |
7.225E-07 |
1.45E-06 |
1.45E-06 |
0 |
2.89E-06 |
7.23E-07 |
0 |
7.23E-07 |
|||||||||||
|
Cd |
0.000002907 |
2.58E-06 |
3.23E-06 |
1.29E-06 |
1.29E-06 |
9.69E-07 |
6.46E-07 |
1.94E-06 |
|||||||||||
|
Cr |
0.000935 |
0.000978 |
0.00102 |
0.000893 |
0.000978 |
0.000638 |
0.000723 |
0.000765 |
|||||||||||
|
As |
0.0093075 |
0.009053 |
0.009435 |
0.008288 |
0.00918 |
0.00714 |
0.006248 |
0.009053 |
|||||||||||
Table 6. Cumulative Cancer Risk for Individual Local Governments (∑CRt)
|
Kubau LGA |
Soba LGA |
Giwa LGA |
||||||
|
Kb1 |
kb2 |
kb3 |
So1 |
So2 |
So3 |
Gw1 |
Gw2 |
Gw3 |
|
1.10E-02 |
9.35E-03 |
1.19E-02 |
9.65E-03 |
1.43E-02 |
1.09E-02 |
1.02E-02 |
9.69E-03 |
1.05E-02 |
|
Makarfi LGA |
Kauru LGA |
Kudan LGA |
||||||
|
Mk1 |
Mk2 |
Mk3 |
Ka1 |
Ka2 |
Ka3 |
Kd1 |
Kd2 |
Kd3 |
|
0.012331 |
0.011353 |
0.01101 |
0.009511 |
0.011224 |
0.009908 |
0.013859 |
0.011865 |
0.01131 |
|
Ikara LGA |
Kajuru |
Sanga LGA |
||||||
|
Ik1 |
Ik2 |
Ik3 |
Kj1 |
Kj2 |
Kj3 |
Sa1 |
Sa2 |
Sa3 |
|
1.22E-02 |
1.42E-02 |
8.46E-03 |
1.42E-02 |
9.96E-03 |
6.42E-03 |
9.35E-03 |
1.06E-02 |
1.42E-02 |
|
Lere LGA |
Chikun LGA |
Kachia LGA |
||||||
|
Le1 |
Le2 |
Le3 |
Ch1 |
Ch2 |
Ch3 |
Kc1 |
Kc2 |
Kc3 |
|
9.95E-03 |
1.32E-02 |
1.41E-02 |
1.09E-02 |
1.01E-02 |
1.05E-02 |
1.44E-02 |
1.28E-02 |
1.21E-02 |
|
Sabon Gari LGA |
Samaru Market |
|||||||
|
Sb1 |
Sb2 |
Sb3 |
MR |
OR |
AM |
TO |
KG |
|
|
7.36E-03 |
7.15E-03 |
9.01E-03 |
1.21E-02 |
1.31E-02 |
1.07E-02 |
1.13E-02 |
1.42E-02 |
|
3.3 Toxic Metals Analysis
In Table 1 are presented results for toxic metals (Hg, Cu, Zn, Ni, Pb, Cd, Mn, As, Fe, V and Co) evaluated in 43 samples from 13 local governments in Kaduna State, while Table 2 presents regulatory limits (WHO/FAO and NAFDAC) for metals in grains and cereals.
Hg was not detected in any of the samples studied. The level of Cu in the rice samples was found to range between 0.02 - 0.18 mg/kg. Highest concentration of Cu (0.18 mg/kg) was observed in sample Sa3 from Sanga LGA, this was above the FAO/WHO and NAFDAC tolerable limits of 0.073 and 0.04 mg/kg. The lowest value (0.02 mg/kg) from Kudan (Kd2 and Kd3) and Kauru (Ka1) local government areas were below the regulatory limits. Copper, an essential element is usually incorporated into a number of metallo-enzymes. Exposure to excessive levels of copper can result in a number of adverse health effects including liver and kidney damage, anemia, immunotoxicity, and developmental toxicity [29].
Zinc (Zn) was found to be highest (0.38 mg/kg) in sample So3 (Soba LGA).This value was found to exceed the PTDI-WHO/FAO and NAFDAC permissible limits of 0.1 and 0.05 mg/kg. Clinical studies revealed up to 600 mg of zinc sulfate (equivalent to 200 mg elemental zinc) has been administered daily in divided doses for a period of several months, without any reported adverse effects, including effects on blood counts and serum biochemistry. There is a wide margin between nutritionally required amounts of zinc and toxic levels [28].
In the present study, the highest concentration reported for nickel (Ni) is 0.03 mg/kg, this value is below the threshold limit (0.067 mg/kg) by given WHO/FAO but just above that of NAFDAC (0.027 mg/kg), as evaluated in samples Le3 (Lere LGA), Kc1 (Kachia LGA), Ik2 (Ikara LGA), and also the imported rice TO and KG. . Samples Kb2, Ik3, and Sb3 did not record any concentration for Ni. Ni’s lithogenic availability is in abundance on earth. Studies have shown that it is an essential trace element for animals. However, the essentiality of nickel in humans has not been established [29]. Exposure to excess levels of nickel may cause neurotoxicity, hepatotoxicity, nephrotoxicity, gene toxicity, reproductive toxicity, and increased risk of cancer [30].
The comparative study of the distribution of Pb in all rice samples revealed the maximum level to be 0.16 mg/kg; this value is well beyond the stipulated limits of 0.0003 mg/kg and 0.002 mg/kg (WHO/FAO and NAFDAC). Lead is a non-essential element; excess exposure can result in neurological problems, hematological effects, renal failure, hypertension and cancer [31].
All values recorded for Cd in this study were above the WHO/FAO and NAFDAC regulatory limits of 0.0001and 0.0002 mg/kg. Cd is highly toxic to humans and excessive exposure to Cd is associated with renal, pulmonary, hepatic, skeletal, reproductive effects and cancer [32; 33]. The contamination of rice with Cd and its toxicity in large populations has been documented in countries which includes China and Thailand [34].
Chromium concentration ranged between 0.13 – 0.25 mg/kg, and was most available in samples collected from Soba and Makarfi (So3 and Mk1), the lowest value was determined in Soba (So2), as well as Kc2 and Kc3 from Kachia LGA. Generally, Cr ion quantified were beyond the permissible levels (0.0023 and 0.002 mg/kg) prescribed by WHO/FAO and NAFDAC. Kalkisim [35] reported that concentration of 0.03 –14μgg–1 Cr in the dry matter of plants is normal value, Cr levels tabulated in this study was above this consideration.
Result from this study show Manganese concentrations in all samples to be inferior to the WHO/FAO threshold (500 mg/kg). Although low levels of manganese intake are necessary for human health, exposure to high manganese levels may be toxic and can result in adverse neurological effects in humans [36].
Arsenic investigated was beyond the stipulated limit. The highest concentration (0.78 mg/kg) was reported for samples Kd1 and Ch1. Chronic exposure to As has encoreged skin, vascular, nervous system disorders and cancer [37]. WHO/FAO threshold for Arsenic in cereals and grains is 0.35 mg/kg, this value is only lower than result tabulated for Kj3 (0.33 mg/kg) from Kajuru LGA.
Levels of Fe in present study fall below the WHO/FAO regulatory limit. Iron is an abundant element on earth and a biologically essential component of every organism [38]. However, high iron intake may lead to increased risk of chronic diseases [39].
WHO/FAO and NAFDAC regulatory limits for Vanadium was not available to the researcher.
The highest concentration of Co was not more than the set limit of 50.00 mg/kg by WHO/FAO in all samples, no limit was set by NAFDAC. Cobalt is an important trace element in human diet, a component of vitamin B12. However, high oral doses of Co have resulted in adverse effects in humans including hematological, neurological, immunological, reproductive, cardiovascular, and endocrine responses [40].
3.4 Result for Statistical Test
Statistical evidence suggests that at confidence level of P < 0.05, there exist no statistical difference in concentrations of Cu, Zn, Ni, Pb, Cd, Cr, Mn, As, V and Cu amongst samples collected from farmers but there was difference in concentration of Fe. Concentration of metals in the foreign rice sample revealed there was also no significance difference (P < 0.05) in the availability of Cr, Pb, Cu, Ni, Cd, Co, V and Mn; while Zn, Fe and As, show significant difference. Similarly, metals in all samples studied showed no statistically significant difference in their concentrations except for Fe at P < 0.05.
Pearson Correlation was applied to validate the existence of correlation in concentration of determined heavy metals within the studied samples. A total of 1,936 correlations was matched in which 1806 (93 %) of documented samples gave a significant correlation at 0.001 level for a two tailed test, while 42 (2.2 %) correlations was significant at 0.05 level (two tailed). Eighty eight (4.5 %) pairing does not show any form of significant correlation.
3.5 Human Health Risk Assessment
To estimate health risks, information regarding some toxicological characteristics of the investigated elements were considered and referred to as shown in table 3. Health risk assessment indices were applied to evaluate the risk of exposure on consumption of contaminated foods via toxic metals (tables 4-6). It involves the use of mathematical models in evaluating risks of exposure to toxic metals at various concentrations, duly referenced by established standard values [41]. In this study, the safety of dietary intake of rice contaminated by toxic metals was estimated based on the intake of a 50 kg body weight Nigerian.
3.5.1 Estimated daily intake of metals (EDIM)
The result of the EDIM was computed and presented in Table 4. The highest EDIM value for Ni is 0.000255 mg/kg, this was recorded in samples Sa3, Kj1, So2, Ik2, Kc1, Le3, TO and KG, respectively. Values documented were below the mean daily intake of 0.0028 mg/50-60 kg day-1 bw [42].
Computed EDIM for Pb ranged between 0.00 mg/kg to 0.00034 mg/kg in samples Mk1 and OR; these values are below the WHO/FAO (2010) daily intake limit of 0.0005 mg/50-60 kg day-1 bw. Pb is one of the metals the human body does not need and its presence can cause severe health challenges, particularly for infants, children and pregnant women [43]. The toxic effects of lead and its compounds have been investigated for many years within several systems, contradiction beclouds data regarding to its mutagenic, clastogenic and carcinogenic properties. The International Agency for Research on Cancer classified lead as possible human carcinogen (group 2B) and its inorganic compounds as probable human carcinogens (group 2A). though there exist paucity of knowledge on the biochemical and molecular mechanisms of action of lead; still, some studies revealed existence of indirect mechanisms of genotoxicity such as inhibition of DNA repair or production of free radicals [31].The least EDIM for cadmium (Cd) was obtained in samples Kj3 and Sa1 (0.0000085 mg/kg), while the most (0.0000935 mg/kg) was obtained in samples Kj2, Kb2 and Ch3. This research reported figures below the provisional tolerable intake for Cd, stipulated as 0.001 mg/kg [44]. Cd has been classified as a B1 carcinogen, even as the present study sugest consumption of this element to be within safe-limits, the possibility of bioaccumulation, and amplification of its concentration overtime cannot be overruled [27]
The EDIM for Cr uptake calculated for this study spanned between 0.001105 mg/kg to 0.002125 mg/kg for adults. The lowest values were reported for samples So2, Kc2, and Kc3; following EFSA, 2014 valuation, these values were below the recommended amount(0.3 mg/50-60 kg day-1 bw), similarly in comparison to limit set by Expert Group on Vitamins and Mineral (EVM) safe upper level of trivalent chromium intake (0.15 mg/kg). Cr, especially in its hexavalent state is a pulmonary carcinogen and it is widely distributed, this can result eventually to DNA deletions and other genome rearrangements [45].
Daily intake for Mn in investigated samples was recorded highest and least for samples To and So3 (0.00034, 0.00765 mg/kg). These values are within safe ingestion (daily) limit as presented in the EC (2006) document. Epidemiological studies have reported 4.6 mg/day and 4.3 mg/day, with no toxic effect recorded. ESADDI-US National Resource Food Council and Nutrition Board set Mn intake at 2-5 mg/day for adults. Average values for this study were below the limits set by the above bodies. Women absorb a greater percentage of Mn than men, and absorption is correlated with Fe intake. Absorption of Manganese (Mn) is boosted in women with low Fe stores. Mn, even though an essential nutrient shows toxicity at elevated concentrations of exposure. Although human deficiency is rare, lack of Mn in animals may result to defect in the skeletal system, as well as impair lipid absorption. Skin rash and abnormalities have been reported as indications in purified Mn-deficient diet. Its toxicity may resort to Parkinson’s-like neuromuscular condition, tremor and facial muscular disorders. A few research findings posited that trace levels of Mn is linked to unusual comportment [46-48].
Arsenic (As) is a toxic element that have relatively high risk of transfer from paddy soils to rice grains, its accumulation in rice grains is important for food safety and human health [49]. Dietary intake for As was evaluated for all samples; computed results were compared to the provisional tolerable daily intake (PTDI) for inorganic As (0.00214 mg/body weight/day) and the Codex Alimentarius Commission (2014), (0.2 mg/kg for inorganic arsenic in rice). The present study evaluated EDIM for As in the range 0.002805 mg/kg (Kj3) to 0.00663 mg/kg in samples Kd1 and Ch1, which measures below the daily limit. Cancer Classification by IARC/EPA implicated arsenic as a class A carcinogen [27]. Inorganic As is considered to be more toxic to humans than pentavalent methylated As species [50]; Because of their lower acute toxicity to humans, the organic forms of arsenic are not targeted for regulation [51].
The EDIM for Co is in the range of 0.001122–0.002527 mg/kg. The permissible daily tolerable intake is 0.023 mg/50-60 kg day-1bw [52]. Values recorded were below the required daily intake. Consumption of Co from samples in present study is within safe levels.
3.5.2 Non-carcinogenic risk assessment
Non-carcinogenic hazards (hazard quotient (HQ) and target hazard quotient (THQ) as health risks resulting from oral exposure to toxic metals were estimated in all samples, result gave values < 1for Ni, Pb, Cd, Cr, Mn and Co; values for As where far >1 (in the range 9.35-21.817) were recorded in all samples, even though. THQ values do not offer a quantitative evaluation of the possibility of an exposed population facing a reverse health effects but rather functions as a suggestion of the risk level due to metal exposure [43; 53].
3.5.2.1 carcinogenic risk (CR)
USEPA in 2011 proposed an acceptable risk in the range of 1.0 x 10-6 to 1.0 x 10-4 over a lifetime of 70 years. When CR exceeds 1×10-4 – 1×10-6 further chemical‐specific assessment is required; however, when CR fall below the range, no action is required from a human health perspective. The potential carcinogen exposure over a lifetime was calculated for Ni, Pb, Cd, Cr and A are presented in Tables 6a and 6b. for samples from Kubau LGA, there exist cancer risk due to Ni, Cr and As (sample Kb1), Cr and As (Kb2), Ni, Cr, and As for Kb3. Samples from Soba LGA reported values beyond the risk threshold for Cr and As in So1, Ni, Cr and As in So2, then Cr and As in So3. Qw1, Qw2 and Qw3 reported similar values for Cr and As. Values beyond the Risk limit were also reported for Ni, Cr and As for samples from Makarfi LGA. Ka1 reported for Cr and As, Ka2 for Ni, Cr and AS, Ka3 for Cr and As. Kudan recorded excessive values for Ni, Cr and As in all samples. Ni documented above limit values for samples Ik1, Ik2, Kj1, Kj3, Sa1, Sa3, Le2, Le3, Kc1, Kc2, Kc3, MR, OR, AM, TO and KG. Cancer risk due to Cr and As was recorded in samples Ik1, Ik2, Ik3, Kj1, Kj2,Kj3, Sa1, Sa2, Sa3, Le1, Le2, Le3, Ch1, Ch2, Ch3, Kc1, Kc2, Kc3, Sb1, Sb2, Sb3, MR, OR, AM, TO and KG. samples Kb2, Mk1, Mk2, Mk3, Ka3, Kd2, Kd3, Ik3, Kj2,Sa2, Le3, Ch2, Kc3, Sb2, Sb3, and OR all fell within the lower limit for cancer risk. Samples not listed are within safe limits for individual metals present with their sample matrix. When multiple carcinogenic elements are present or evaluated in a sample, the cancer risks from all carcinogen are summed up (assuming additive effects).
Table 6 presents result for the summation of carcinogenic risks posed by the elements tabulated in 6, values recorded for samples in all local governments exceeded the acceptable lower and upper limit of carcinogenic risk. CRt for this work ranged from 6.42 x 10-3 to 1.44 x 10-2, the lowest CRt was determined at Kajuru (Kj3) LGA, while the highest was recorded at Kachia LGA (Kc1). The implication of this result is that amongst consumers of rice from these study sites, indicate there exist cancer risk at a lower limit of 64 chance in 1000 lifetime exposure and an upper limit of 14 chance in 100 lifetime exposure for any combination of two or more of Ni, Pb, Cd, Cr and As available for consumption; this is particularly worrisome especially as Pb has no safe level in blood [53].
Statistical analysis at 95 % significant level show that there exist no difference in cancer risk arising from consumption of rice from sampled area.
The metals: Hg, Fe, Cu, Zn, Ni, Pb, Cd, Cr, Mn, As, V and Co were evaluated; all were found present at varying concentrations except Hg which was unavailable in all samples. The estimated daily intake of the metals was evaluated and some were shown to be above the intake level. Health risk assessment was undertaken by grouping the elements of interest into carcinogenic or non-carcinogenic. Non-carcinogenic elements are assumed to have a threshold; below which no adverse health effects will be observed where an essential part of the dose-response portion of a risk assessment includes the use of a reference dose (RfD). Also, carcinogens are assumed to have no effective threshold. This assumption implies that there is a risk of cancer developing with exposures at low doses and, therefore, there is no safe threshold for exposure to carcinogenic chemicals. Carcinogens are expressed by their Cancer Potency Factor [41, 54], continues consumption of rice from the study areas potends a future cancer risk to consumers. Further studies should be similary undertaken periodically to monitor the trend if there exists or consistency in threat due to metal contamination.
Acknowledgments
This research has no acknowledgment.
Data Availability
The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request
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No competing interests reported.