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. 2019 Nov 26;36(1):45–58. doi: 10.1007/s43188-019-00001-9

Food toxicity assessment of selected canned foods in Nigeria

Martins O Ainerua 1,✉, Nosakhare Erhunmwunse 1, Isioma Tongo 1, Lawrence Ezemonye 1
PMCID: PMC6988620  PMID: 31998625

Abstract

Food toxicity assessment was made for frequently consumed canned foods in Nigeria in order to estimate potential human health risks associated with their consumption. Levels of heavy metals (Pb, Cd, As, Fe, Mn and Zn), Nitrate and Nitrite, pH and salt were assessed in randomly purchased samples from groceries stores to represent what is readily available on the market. Nitrates and nitrites were assessed using a Perkin-Elmer spectrophotometer while heavy metal levels were determined using Atomic absorption spectrophotometer. Human health risk was estimated using standard indices; estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI) and dietary exposure (DE). Results showed varying concentrations of nitrates, nitrites, heavy metals, in all the canned food categories but the level of salt and pH seemed constant. Nitrate, Fe and Cd in all the canned food categories exceeded recommended limit set by EU. Health risk estimations showed EDI values for Cd in all the canned food categories above the tolerable daily intake, while DE for Fe in canned sweet corn, Fe, Zn and Pb in canned beans/peas had values above recommended limits. THQ values for all the canned foods were above 1 in the canned beans/peas while HI was above 1 in the canned fish category. The study revealed the potential for Cd toxicity and risk of non-carcinogenic health effects from canned beans/peas consumption. Constant monitoring of canned foods is therefore imperative considering the growing demand for canned products due to changing lifestyle.

Keywords: Food toxicity, Metals, Nitrate, Nitrite, Canned food, Health risk

Introduction

Canned foods are considered as safe foods due to certain attributes accrued to them; that is, they are easy to prepare at home, have long shelf life and are quite economical. However, varying concentrations of contamination has been reported in these canned foods [1, 2]. The possible contaminants which could be chemical hazards in foods include food additives, environmental contaminants such as mercury, dioxins and residues of heavy metals, pesticides and veterinary drugs. These chemicals may pose long-term adverse effects on public health [3]. Consequently, information about levels of food additives such as nitrates and nitrites compounds in canned foods as it relates to dietary intake is imperative to avert health risks associated with consumption. Nigeria also falls among the league of Nations who patronize canned foods but there is limited information on the levels of contamination likely present in these canned foods marketed in Nigeria, making the scope of this study a pilot one. More worrisome is the lack of information on health risks associated with consumption. The objectives of the study was therefore to assess the levels of food additives (Nitrite and Nitrate, Na and Cl) heavy metals (Pb, Cd, As, Fe, Mn and Zn), and pH in canned foods frequently consumed in Nigeria, to estimate human health risks associated with consumption.

Materials and methods

Sample collection

A total of 100 samples of canned foods made of different brands and manufacturers were purchased from local supermarkets in Benin City, Nigeria. The canned foods were preserved on the shelf at room temperature (~ 24 °C) for about 7 days prior to the experiment. They were grouped into four categories: fish, meat, beans/peas and sweet corn. Five brands were obtained for each canned category with five replicate per product type. Each can was assigned a sample code and the details on the packaging were recorded as; Brand Name, Date of manufacture, Best before Date, Trade Name, National Agency for Food and Drug Administration and Control (NAFDAC) Reg. No., Country of Origin.

Sample preparation and analysis

All reagents sued for analysis were purchased from Sigma Aldrich (Germany). The cans were opened and transferred into the labelled sterile sample containers prior to digestion, the samples were homogenized. The principle is that the quarter taken for analysis should be a representative of the whole [4].

Heavy metal and Na analysis began by wet digestion of food was performed with nitric acid—perchloric acid—sulphuric acid (HNO3–HClO4–H2SO4). One-fifth of the sample material (0.2 g) was weighed into the beaker and 10 ml of nitric acid was added, followed by 5 ml of perchloric acid and 10 ml of sulphuric acid. A small glass funnel was inserted to act as a reflux condenser and the mixture was heated for 15–30 min at 150 °C until a dense white fume is noticed and a colourless solution was obtained. It was removed from the block and cooled to about 100 °C. The solution was filtered into a 100 ml volumetric flask and diluted to the mark with water. The blank was prepared with same procedure but without samples and the Heavy Metals content was read off using Atomic Absorption Spectrophotometer (AAS) (UNICAM 696, England, UK) [5].

Nitrates and Nitrites were analysed using a Perkin-Elmer spectrophotometer (LAMBDA 25, CT, USA). Ten millimetre of the filtrate was pipetted into a 50 ml flask; 2 ml of Brucine was added followed immediately by 10 ml of conc. H2SO4. The beaker was stirred gently to allow for thorough mixing and it was allowed to stand for 10 min. The standard was treated similarly and the samples were read spectrophotometrically.

Determination of pH

This is done using HANNA pH Meter (HI 9813-6, Woonsocket, RI, USA). The meter is switched on and allowed to stabilise for 10 min. Then calibrate the pH meter by immersing the Probe in the Buffers solutions 4, 7 and 10. Rinse the probe and immerse in the sample solution and the pH is read.

Determination of chloride

Ten millimetre of the filtrate was pipetted into a 250 ml conical flask, 1 ml or 3 drops of K2CrO4 was added and titrated with standard 0.05 M HCl until a slight red precipitate occurs. The blank, 9 ml of the K2CrO4 indicator and 10 ml of 20 ppm Cl− were treated similarly.

Determination of nitrate

Ten millimetre of the filtrate was pipetted into a 50 ml flask; 2 ml of Brucine was added followed immediately by 10 ml of conc. H2SO4. The beaker was stirred gently to allow for thorough mixing and it was allowed to stand for 10 min. The standard was treated similarly and the samples were read spectrophotometrically at 470 nm.

Determination of nitrite

Ten millimetre of the filtrate was pipetted into a 50 ml flask, 2 ml of 2 M HCl was added and diluted with water to 30 ml. 2 ml of sulphanilic acid was then added and stirred and allowed to stand for 5 min. The standards were treated in a similar manner as the samples. Colour development occurred after a few minutes, and the absorbance were read spectrophotometrically at 520 nm after 20 min.

Health risk assessment

Average estimated daily intake (EDI)

EDI was calculated using the following equation, which is recommended by the US EPA [6].

EDI=C×IR×EF×EDBW×AT

where EDI is the average daily intake or dose through ingestion (mg kg−1 bw day−1); C is the heavy metal concentration in the exposure medium (mg l−1 or mg kg−1); IR is the ingestion rate (l day−1, or kg day−1); EF is the exposure frequency (365 days/year); ED is the exposure duration (54 years, equivalent to the average lifespan); BW is the body weight (kg) and AT is the time period over which the dose is averaged (365 days/year × number of exposure years, assumed to be 54 years in this study).

Target hazard quotient

The human health risk posed by contaminant exposure are usually characterized by the target hazard quotient (THQ) [6], the ratio of the average estimated daily intake (EDI) resulting from exposure compared to the reference dose (RfD) for an individual pathway and chemical. Oral reference dose obtained from the Integrated Risk Information System [7] is an estimation of maximum permissible risk to a human population through daily exposure when taking into consideration a sensitive group during a lifetime. The applied RfD for Cd, Pb, Cu and Zn was 1.0, 4.0, 40, 300 mg kg−1 day−1, respectively. The THQ based on non-cancer toxic risk was determined by;

THQ=EDIRfD

If the value of THQ is less than 1, the risk of non-carcinogenic toxic effects is assumed to be low. When it exceeds 1, there may be concerns for potential health risks associated with overexposure.

To assess the overall potential risk of adverse health effects posed by more than one metal, the THQs can be summed across contaminants to generate a hazard index (HI) to estimate the risk of a mixture of contaminants. The HI refers to the sum of more than one THQ for multiple substances and/or multiple exposure pathways.

HI=∑THQ1+THQ2+THQn…

In the present study, the HI was used as a screening value to identify whether there is significant risk caused by heavy metals through average dietary consumption of canned foods.

Dietary exposure

A dietary exposure assessment was calculated by multiplying consumption data with data on the concentration of chemicals in food [8]. It is expressed as;

DE=∑FCC X FCR

where FCC = food chemical concentration, FCR = Food consumption rate [7].

Statistical analysis

All data were subjected to one-way analysis of variance (ANOVA) using XL Stat program for windows. The level of significance was chosen at p < 0.05 and the results are presented as mean ± standard error. Graphs were plotted using GraphPad Prism7.04.

Results

The mean and standard error (mean ± SE) for canned fish showed variation across the different canned food sampled as showed in Table 1. The pH values ranged from 5.48 ± 0.12 to 5.66 ± 0.05. Na ranged from 3.88 ± 2.1 to 445.08 ± 41.54 mg kg−1, nitrite and nitrate ranged from 21.1 ± 3.69 to 31.04 ± 2.95 mg kg−1 and 54.22 ± 9.52 to 79.8 ± 7.58 mg kg−1 respectively. These values were not found to be significant at p > 0.05. Fe, Zn and Pb were found to be significant (p < 0.05) and the values ranged from 161.78 ± 16.44 to 245.7 ± 3.09 mg kg−1, 15.72 ± 3.49 to 60.2 ± 12.61 mg kg−1 and 0.09 ± 0.04 to 0.17 ± 0.08 mg kg−1 respectively. Mn and Cd were found to be non-significant. Arsenic was not detected all through the canned groups.

Table 1.

Summary of data from the analysis of canned fish

Canned fish
Parameters mg/kg Product type A Product type B Product type C Product type D Product type E p value Standard References
Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max
pH 5.66 ± 0.05 5.5 5.8 5.64 ± 0.09 5.3 5.8 5.48 ± 0.12 5.2 5.8 5.5 ± 0.05 5.4 5.6 5.58 ± 0.12 5.3 5.9 > 0.05 5.70–6.60 [9]
Na 416.4 ± 8.08 393.4 442 399.98 ± 14.18 358.4 439.2 388.3 ± 2.1 358.8 448.9 428.3 ± 41.58 324.9 568.8 445.08 ± 41.54 348.2 598.5 > 0.05
NO2 29.98 ± 2.98 21.1 37 31.04 ± 2.95 21.6 38.6 30.22 ± 2.1 25 35.2 21.1 ± 3.69 9.7 30.9 30.82 ± 3.76 18.9 39.1 > 0.05 50 mg/kg [10]
NO3 77.2 ± 7.59 54.8 95.2 79.8 ± 7.58 55.6 99.2 77.74 ± 5.39 64.3 90.5 54.22 ± 9.52 24.8 79.6 79.04 ± 9.67 48.7 100.6 > 0.05 50 mg/kg [10]
Fe 228.2 ± 17.93 172.2 282.5 161.78 ± 16.44 124.7 216.7 245.7 ± 3.09 235.6 252.5 170.4 ± 27.34 112.9 262.3 216.1 ± 9.42 184.3 233.1 < 0.01
Mn 1.97 ± 0.80 0 4.7 1.44 ± 0.34 0.7 2.41 2.03 ± 0.54 0.89 4.05 2.02 ± 0.53 0.73 3.79 2.66 ± 0.38 1.76 3.82 > 0.05
Zn 48.14 ± 9.45 21 73.1 60.2 ± 12.61 35.6 100.8 39.8 ± 11.29 13.4 76.4 15.72 ± 3.49 10.2 29.4 34.36 ± 7.92 10.6 56.4 < 0.05
Cd 0.18 ± 0.05 0.05 0.35 0.084 ± 0.02 0.04 0.15 0.06 ± 0.06 0 0.3 0.13 ± 0.08 0 0.4 0.13 ± 0.08 0 0.34 > 0.05 0.1 μg/g [11]
Pb 0.17 ± 0.08 0.05 0.45 0.09 ± 0.04 0 0.2 0 0 0 0 0 0 0 0 0 < 0.05 0.30 mg/kg [11]
As ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND –
Cl 93.7 ± 1.83 88.5 99.5 89.98 ± 3.19 80.6 98.8 87.38 ± 3.51 80.7 101 96.36 ± 9.34 73.1 127.9 100.16 ± 9.36 78.3 134.7 > 0.05
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Na, Fe, Mn, Zn standards are available as Recommended Maximum daily intake. p < 0.05, significant, p < 0.001, Highly significant, p > 0.05, no significance

ND below detected limit

Canned meat had pH values ranging from 5.24 ± 0.11 to 5.7 ± 0.13. Na ranged from 432.4 ± 41.32 to 478.48 ± 43.25 mg kg−1, NO2 and NO3 ranged from 27.04 ± 3.94 to 33.26 ± 1.71 mg kg−1 and 69.58 ± 10.14 to 86.1 ± 4.49 mg kg−1 respectively. These parameters were not significantly different at p > 0.05 across the product types. Similar significance occurred for Zn, Pb and Cl with values ranging from 36.12 ± 11.51 to 68.94 ± 17.09 mg kg−1, 0 to 0.16 ± 0.04 mg kg−1 and 97.4 ± 8.63 to 107.66 ± 9.73 mg kg−1. However, the values of Fe, Mn, and Cd showed significant level of difference when assessed across the canned beef products samples which ranged from 205.28 ± 8.13 to 303.08 ± 11.57 mg kg−1, 2.46 ± 0.43 to 4.64 ± 0.47 mg kg−1 and 0 to 0.22 ± 0.07 mg kg−1 respectively. This is shown in Table 2.

Table 2.

Summary of data from the analysis of canned meat

Canned meat
Parameters mg/kg Product type A Product type B Product type C Product type D Product type E p value Standard References
Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max
Ph 5.24 ± 0.11 4.9 5.5 5.26 ± 0.07 5.1 5.5 5.68 ± 0.06 5.5 5.8 5.7 ± 0.13 5.3 5.9 5.58 ± 0.13 5.1 5.8 > 0.05 6.6
Na 432.4 ± 41.32 312.6 565 478.48 ± 43.25 401.2 593.3 432.9 ± 38.37 357.2 573.1 469.06 ± 14.88 430.3 514.8 473.24 ± 14.05 431.8 520 > 0.05
NO2 28.44 ± 3.45 20.2 38.4 27.52 ± 3.03 20.3 38.2 33.26 ± 1.71 28.9 38 32.54 ± 2.78 26.6 42.2 27.04 ± 3.94 14.2 36.5 > 0.05 50 mg/kg [10]
NO3 73.1 ± 8.88 51.9 98.7 70.82 ± 7.8 52.2 98.3 86.1 ± 4.49 74.2 97.7 83.68 ± 7.13 68.4 108.5 69.58 ± 10.14 36.5 93.9 > 0.05 50 mg/kg [10]
Fe 270.28 ± 22.99 204.1 320.9 259.24 ± 10.23 229.3 284.8 303.08 ± 11.57 278.8 332.4 205.28 ± 8.13 177.9 223.4 220.72 ± 15.32 187.5 275.8 < 0.001
Mn 2.46 ± 0.43 1.81 4.09 3.27 ± .36 2.27 4.38 2.73 ± 0.48 1.48 4.24 4.02 ± 0.41 2.74 5.27 4.64 ± 0.47 3.85 6.43 < 0.01
Zn 36.4 ± 6.18 22.6 53.8 36.12 ± 11.51 11.2 67.6 46.46 ± 8.29 16.8 63.4 68.94 ± 17.09 30.1 117.8 53.24 ± 14.12 19.2 95.2 > 0.05
Cd 0.19 ± 0.08 0 0.4 0.03 ± 0.03 0 0.15 0.08 ± 0.08 0 0.4 0 0 0 0.22 ± 0.07 0.05 0.4 < 0.05 0.05 μg/g [12]
Pb 0 0 0 0 0 0 0 0 0 0.08 ± 0.08 0 0.4 0.16 ± 0.04 0.06 0.3 < 0.05 0.10 mg/kg [12]
As ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND –
Cl 97.26 ± 9.3 70.3 127.1 107.66 ± 9.73 90.3 133.5 97.4 ± 8.63 80.4 128.9 105.54 ± 3.35 96.8 115.8 106.48 ± 3.16 97.2 117 > 0.05
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Na, Fe, Mn, Zn standards are available as Recommended Maximum daily intake. p < 0.05, significant, p < 0.001, Highly significant, p > 0.05, no significance

ND below detected limit

The results from canned beans/peas as shown in Table 3 revealed that pH values ranged from 5.02 ± 0.02 to 5.72 ± 0.05. This range in pH values were found to be highly significant (p < 0.001). Na ranged from 332.6 ± 45.08 to 458.72 ± 22.14 mg kg−1 with no significant difference (p > 0.05). Same trend of significance was observed for Mn (3.43 ± 0.31 to 4.84 ± 0.4 mg kg−1), Zn (50.74 ± 4.79 to 87.26 ± 22.31 mg kg−1) and Pb (0 to 0.15 ± 0.04 mg kg−1). NO3 was highly significant (p < 0.001) in the canned beef products (69.46 ± 4.08 to 93.92 mg kg−1) but NO2 was significant (p  < 0.01) with ranged values of 27.02 ± 1.89 to 36.54 ± 1.45 mg kg−1. The ANOVA analyses for Fe and Cd in the canned products was found to be significant (p < 0.05) with ranged values of 130.68 ± 1.74 to 191.02 ± 22.25 mg kg−1 and 0 to 0.29 ± 0.05 mg kg−1.

Table 3.

Summary of data from the analysis of canned beans/peas

Canned beans/peas
Parameters mg/kg Product type A Product type B Product type C Product type D Product type E p value STANDARD References
Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max Mean ± SE Min Max
pH 5.25 ± 0.09 4.9 5.4 5.72 ± 0.04 5.6 5.8 5.58 ± 0.06 5.5 5.8 5.68 ± 0.05 5.5 5.8 5.02 ± 0.02 5 5.1 < 0.001 5.70–6.00 [9]
Na 406.84 ± 46.93 298.6 549.1 332.6 ± 45.08 153.8 386.3 404.82 ± 27.84 317 480.5 413.98 ± 30.18 324.8 493.1 458.72 ± 22.14 378 509.2 > 0.05
NO2 34.68 ± 1.67 28.9 39.1 34.28 ± 1.89 29.3 38.2 36.54 ± 1.45 30.8 38.5 35.32 ± 1.09 32.9 39.4 27.02 ± 1.59 21.9 31.5 < 0.01 50 mg/kg [10]
NO3 89.14 ± 4.26 74.4 100.4 91.48 ± 4.09 75.4 98.3 93.92 ± 3.73 79.2 98.9 90.82 ± 2.8 84.6 101.3 69.46 ± 4.08 56.3 80.9 < 0.001 50 mg/kg [10]
Fe 137.74 ± 4.83 120.6 147.5 187.1 ± 20.96 138.1 261.9 175.1 ± 6.92 157.7 196.4 130.68 ± 1.74 126.6 135.3 191.02 ± 22.25 137.8 244.9 < 0.05
Mn 3.9 ± 0.37 2.54 4.74 3.86 ± 0.51 2.49 5.21 4.62 ± 0.19 4.16 5.29 3.43 ± 0.31 2.18 3.85 4.84 ± 0.4 3.36 5.72 > 0.05
Zn 50.74 ± 4.79 33.6 63.1 87.26 ± 22.31 38.3 171.2 57.2 ± 11.05 29.4 78.2 70.42 ± 12.54 37.6 102.2 57.52 ± 10.09 34.6 82.4 > 0.05
Cd 0.2 ± 0.07 0.05 0.4 0.18 ± 0.08 0 0.35 0 0 0 0.13 ± 0.06 0 0.3 0.29 ± 0.05 0.15 0.4 < 0.05 0.05 μg/g [12]
Pb 0.01 ± 0.01 0 0.07 0 0 0 0 0 0 0.1 ± 0.05 0 0.24 0.15 ± 0.04 0.05 0.25 < 0.01 0.20 mg/kg [12]
As ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND –
Cl 91.54 ± 10.57 67.2 123.6 74.84 ± 10.14 34.6 86.9 91.08 ± 6.26 71.3 108.1 93.1 ± 6.81 72.9 110.9 103.22 ± 4.97 85.1 114.6 > 0.05
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Na, Fe, Mn, Zn standards are available as Recommended Maximum daily intake. p < 0.05, significant, p < 0.001, Highly significant, p > 0.05, no significance

ND Below detected limit

Canned sweet corn recorded most of the highest values when assessed as shown in Table 4. The pH ranged from 5.84 ± 0.03 to 6.16 ± 0.07 and was highly significant across the products sampled (p < 0.001). Na, Fe and Cl values ranged from 378.56 ± 15 to 497.58 ± 42.35, 140.28 ± 31.89 to 194.06 ± 5.71 and 85.16 ± 3.38 to 111.96 ± 9.53 respectively but showed no significant difference (p > 0.05). Cd (0 to 0.05 ± 0.04) was found to be highly significant (p < 0.001) across the products sampled. Other parameters sampled showed significant difference (p < 0.05) across the products with NO2 ranging from 27.34 ± 1.79 to 35.2 ± 2.27, NO3 (70.34 ± 4.6 to 90.78 ± 5.73), Mn (3.89 ± 0.53 to 6.3 ± 0.35), Zn (51.76 ± 10.54 to 91.88 ± 3.95), and Pb ranged from 0 to 0.14 ± 0.03.

Table 4.

Summary of data from the analysis of canned sweet corn

Canned sweet corn
Parameters mg/kg Product type A Product type B Product type C Product type D Product type E p value Standard References
mean ± SE Min Max mean ± SE Min Max mean ± SE Min Max mean ± SE Min Max mean ± SE Min Max
pH 6.1 ± 0.03 6 6.2 6.16 ± 0.07 5.9 6.3 5.92 ± 0.02 5.9 6 6.04 ± 0.04 5.9 6.1 5.84 ± 0.03 5.8 5.9 < 0.001 5.90–6.50 [9]
Na 378.56 ± 15 329.5 407.6 412.16 ± 16.01 371.8 464 497.58 ± 42.35 431.4 664 431.68 ± 39.9 328 567.4 448.04 ± 16.49 397.1 487.3 > 0.05
NO2 34.3 ± 1.61 28.7 37.6 30.6 ± 2.09 23 35.4 27.34 ± 1.79 22.1 31.6 32.84 ± 1.16 28.7 35.5 35.2 ± 2.27 28.8 41.6 < 0.05 50 mg/kg [10]
NO3 88.16 ± 4.11 73.9 96.6 78.74 ± 5.36 59.2 91 70.34 ± 4.6 56.9 81.3 84.44 ± 2.96 73.9 91.4 90.78 ± 5.73 74.1 107 < 0.05 50 mg/kg [10]
Fe 163 ± 4.56 148.5 174.5 169.2 ± 16.1 130.1 213.6 140.28 ± 31.89 17.9 201.2 166.74 ± 6.31 149.3 181.9 194.06 ± 5.71 183.2 215.8 > 0.05 15µ/g [13]
Mn 4.89 ± 0.44 3.56 5.88 3.89 ± 0.53 2.63 5.76 6.3 ± 0.35 5.6 7.25 5.95 ± 0.36 5.23 7.05 5.65 ± 0.32 4.94 6.73 < 0.01
Zn 53.52 ± 6.96 31.2 74.8 51.76 ± 10.54 24.6 89.4 69.72 ± 12.66 36.2 112.6 91.88 ± 3.95 81.4 102.6 63.4 ± 2.74 56.6 69.8 < 0.05
Cd 0.23 ± 0.04 0.1 0.35 0 0 0 0 0 0 0.05 ± 0.03 0 0.15 0.04 ± 0.03 0 0.15 < 0.001 0.05 μg/g [12]
Pb 0.14 ± 0.03 0.06 0.24 0 0 0 0 0 0 0.05 ± 0.04 0 0.2 0.06 ± 0.05 0 0.25 < 0.05 0.20 mg/kg [12]
As ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND –
Cl 85.16 ± 3.38 74.1 91.7 92.74 ± 3.6 83.7 104.4 111.96 ± 9.53 97.1 149.4 97.14 ± 8.98 73.8 127.7 100.82 ± 3.7 89.4 109.6 > 0.05
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Na, Fe, Mn, Zn standards are available as Recommended Maximum daily intake. p < 0.05, significant, p < 0.001, Highly significant, p > 0.05, no significance

ND below detected limit

Correlation coefficient matrices

In this study, the correlation coefficient matrix was used to show the linear strength and direction of the variables analysed which is shown in Tables 5, 6, 7 and 8 below. The result for canned fish revealed that pH strongly correlated with Zn (r = 0.7132) and Pb (r = 0.8519). Na correlated strongly with Mn (r = 0.7101) and Cl (r = 1). NO2 correlated strongly with NO3 (r = 0.9999) and Zn (r = 0.8205). NO3 correlated strongly with Zn (r = 0.8242), Mn with Cl (r = 0.7115), Zn with Pb (r = 0.6497), Cd with Pb (r = 5469) and Cl (r = 0.6391).

Table 5.

Correlation coefficient matrix for canned fish

pH Na NO2 NO3 Fe Mn Zn Cd Pb Cl
pH 1.0000
Na 0.1152 1.0000
NO2 0.5092 − 0.2922 1.0000
NO3 0.5111 − 0.2996 0.9999 1.0000
Fe − 0.1736 − 0.1604 0.4460 0.4482 1.0000
Mn − 0.2861 0.7101 − 0.0073 − 0.0142 0.4935 1.0000
Zn 0.7132 − 0.5237 0.8205 0.8242 0.0351 − 0.5504 1.0000
Cd 0.5136 0.6388 − 0.1963 − 0.1952 0.0385 0.2919 − 0.1728 1.0000
Pb 0.8519 − 0.1853 0.3438 0.3508 0.0181 − 0.4691 0.6497 0.5469 1.0000
Cl 0.1154 1.0000 − 0.2906 − 0.2980 − 0.1580 0.7115 − 0.5232 0.6391 − 0.1850 1
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Table 6.

Correlation coefficient matrix for canned meat

pH Na NO2 NO3 Fe Mn Zn Cd Pb Cl
pH 1.0000
Na 0.0304 1.0000
NO2 0.7013 − 0.4176 1.0000
NO3 0.7026 − 0.4251 0.9997 1.0000
Fe − 0.2585 − 0.7297 0.2042 0.2229 1.0000
Mn 0.4647 0.7815 − 0.2331 − 0.2396 − 0.8464 1.0000
Zn 0.8293 0.3272 0.5052 0.4925 − 0.7097 0.6679 1.0000
Cd − 0.2332 − 0.2835 − 0.5608 − 0.5545 0.0683 0.0690 − 0.3118 1.0000
Pb 0.4708 0.5391 − 0.2618 − 0.2668 − 0.7668 0.9346 0.6213 0.3768 1.0000
Cl 0.0319 1.0000 − 0.4163 − 0.4238 − 0.7293 0.7817 0.3279 − 0.2844 0.5392 1.0000
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Table 7.

Correlation coefficient matrix for cannedbeans/peas

pH Na NO2 NO3 Fe Mn Zn Cd Pb Cl
pH 1.0000
Na − 0.7464 1.0000
NO2 0.7843 − 0.5671 1.0000
NO3 0.8386 − 0.6836 0.9886 1.0000
Fe − 0.1852 − 0.1116 − 0.5066 − 0.4251 1.0000
Mn − 0.6074 0.4820 − 0.5551 − 0.5800 0.7250 1.0000
Zn 0.6988 − 0.7573 0.1615 0.2894 0.2565 − 0.4620 1.0000
Cd − 0.6673 0.2783 − 0.8244 − 0.7858 0.1786 0.0817 − 0.0020 1.0000
Pb − 0.5194 0.7510 − 0.7664 − 0.8082 0.0476 0.2123 − 0.1559 0.5742 1.0000
Cl − 0.7476 1.0000 − 0.5682 − 0.6846 − 0.1101 0.4835 − 0.7578 0.2791 0.7506 1.0000
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Table 8.

Correlation coefficient matrix for sweet corn

pH Na NO2 NO3 Fe Mn Zn Cd Pb Cl
pH 1.0000
Na − 0.7116 1.0000
NO2 − 0.0623 − 0.6279 1.0000
NO3 − 0.0725 − 0.6198 0.9999 1.0000
Fe − 0.2225 − 0.3387 0.8215 0.8281 1.0000
Mn − 0.7530 0.7105 − 0.1625 − 0.1600 − 0.2556 1.0000
Zn − 0.2804 0.3997 − 0.0621 − 0.0637 − 0.1272 0.7199 1.0000
Cd 0.2951 − 0.7218 0.5642 0.5555 0.0355 − 0.1615 − 0.2744 1.0000
Pb 0.1131 − 0.6838 0.7469 0.7403 0.2583 − 0.0584 − 0.1675 0.9610 1.0000
Cl − 0.7116 1.0000 − 0.6276 − 0.6195 − 0.3382 0.7105 0.4001 − 0.7223 − 0.6841 1.0000
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In canned meat, pH correlated strongly with NO2 (r = 0.7013), NO3 (r = 0.7026) and Zn (r = 0.8293), Na correlated strongly with Fe (r = − 0.7297), Mn (r = 0.7815) and Cl (r = 1), NO2 correlates strongly with NO3 (r = 0.9999) while Fe correlates strongly with Mn (r = − 0.8464), Zn (r = − 0.7097), Pb (r = -0.7668), and Cl (r = − 0.7293). Similar trend was found with Mn which correlated strongly with Zn, Pb and Cl (r = 0.6679, 0.9346 and 0.7817) respectively and Zn strongly correlated with Pb (r = 0.6213).

In canned beans/peas, the pH correlated strongly with all parameters except Fe, while Na correlated strongly with NO2 (r = − 0.5671), NO3 (r = − 0.6836), Zn (r = 0.7573), Pb (r = 0.7510) and Cl (r = 1). NO2 showed a strong correlation with NO3 (r = 0.9886), Fe (r = − 0.5066), Mn (r = − 0.5551), Cd (r = − 0.8224), Pb (r = − 0.7664) and Cl (r = − 0.5682). NO3 strongly correlated with Mn, Cd, Pb and Cl (r = − 0.5800, − 0.7858, − 0.8082, − 0.6846) respectively. Fe correlated strongly with Mn (r = 0.7250), Zn correlated strongly with Cl (r = − 0.7578), Cd with Pb (r = 0.5742) and Pb with Cl (r = 0.7506).

In Canned Sweet corn, pH correlated strongly with Na, Mn, and Cl (r = − 0.7116, − 0.7530, − 0.7116) respectively while Na correlated strongly with NO2 (r = − 0.6279), NO3 (r = − 0.6198), Mn (r = 0.7105), Cd (r = 0.7218), Pb (r = 0.6838) and Cl (r = 1). NO3 showed a positive correlation with Fe (r = 0.8281), Cd (r = 0.5555) Pb (r = 0.7403), but negatively with Cl (r = − 0.6195). Mn showed a positively strong correlation with Zn (r = 0.7199) and Cl (r = 0.7105). Cd correlated strongly with Pb (r = 0.9610) and Cl (r = − 0.7223) and Pb correlated negatively with Cl (r = − 0.6841).

Health risk indices

In this study, health risk was assessed using Estimated Daily Intake (EDI), Target Hazard Quotient (THQ), Hazard Index (HI) and Dietary Exposure (DE) indices. Tables 9, 10, 11 and 12 below shows the EDI, DE, THQ and HI of all canned groups sampled across various products types.

Table 9.

Health risk indices in canned fish

Parameters RfD EDI (mg kg−1 bw day−1) DE (mg kg−1 day−1) THQ HI
Product type A
 Fe 0.7 0.140 9.813 0.200 0.661
 Mn 0.14 0.001 0.085 0.009
 Zn 0.3 0.030 2.070 0.099
 Cd 0.001 0.000 0.008 0.111
 Pb 0.0036 0.000 0.007 0.029
 NO3 1.6 0.047 3.320 0.030
 NO2 0.1 0.018 1.289 0.184
 Na 17.905
Product type B
 Fe 0.7 0.099 6.957 0.142 0.560
 Mn 0.14 0.001 0.062 0.006
 Zn 0.3 0.037 2.589 0.123
 Cd 0.001 0.000 0.004 0.052
 Pb 0.0036 0.000 0.004 0.015
 NO3 1.6 0.049 3.431 0.031
 NO2 0.1 0.019 1.335 0.191
 Na 17.199
Product type C
 Fe 0.7 0.151 10.564 0.216 0.558
 Mn 0.14 0.001 0.087 0.009
 Zn 0.3 0.024 1.711 0.081
 Cd 0.001 0.000 0.003 0.037
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.048 3.343 0.030
 NO2 0.1 0.019 1.299 0.186
 Na 16.699
Product type D
 Fe 0.7 0.105 7.325 0.149 0.421
 Mn 0.14 0.001 0.087 0.009
 Zn 0.3 0.010 0.676 0.032
 Cd 0.001 0.000 0.006 0.080
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.033 2.331 0.021
 NO2 0.1 0.013 0.907 0.130
 Na 18.418
Product type E
 Fe 0.7 0.133 9.292 0.190 0.571
 Mn 0.14 0.002 0.114 0.012
 Zn 0.3 0.021 1.477 0.070
 Cd 0.001 0.000 0.006 0.080
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.049 3.399 0.030
 NO2 0.1 0.019 1.325 0.189
 Na 19.138
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Table 10.

Health risk indices in canned meat

Parameters RfD EDI (mg kg−1 bw day−1) DE (mg kg−1 day−1) THQ HI
Product type A
 Fe 0.7 0.618 43.245 0.883 2.389
 Mn 0.14 0.006 0.394 0.040
 Zn 0.3 0.083 5.824 0.277
 Cd 0.001 0.000 0.030 0.434
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.167 11.696 0.104
 NO2 0.1 0.065 4.550 0.650
 Na 69.184
Product type B
 Fe 0.7 0.593 41.478 0.846 1.974
 Mn 0.14 0.007 0.523 0.053
 Zn 0.3 0.083 5.779 0.275
 Cd 0.001 0.000 0.005 0.069
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.162 11.331 0.101
 NO2 0.1 0.063 4.403 0.629
 Na 76.557
Product type C
 Fe 0.7 0.693 48.493 0.990 2.454
 Mn 0.14 0.006 0.437 0.045
 Zn 0.3 0.106 7.434 0.354
 Cd 0.001 0.000 0.013 0.183
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.197 13.776 0.123
 NO2 0.1 0.076 5.322 0.760
 Na 69.264
Product type D
 Fe 0.7 0.469 32.845 0.670 2.175
 Mn 0.14 0.009 0.643 0.066
 Zn 0.3 0.158 11.030 0.525
 Cd 0.001 0.000 0.000 0.000
 Pb 0.0036 0.000 0.013 0.051
 NO3 1.6 0.191 13.389 0.120
 NO2 0.1 0.074 5.206 0.744
 Na 75.050
Product type E
 Fe 0.7 0.505 35.315 0.721 2.527
 Mn 0.14 0.011 0.742 0.076
 Zn 0.3 0.122 8.518 0.406
 Cd 0.001 0.001 0.035 0.503
 Pb 0.0036 0.000 0.026 0.104
 NO3 1.6 0.159 11.133 0.099
 NO2 0.1 0.062 4.326 0.618
 Na 75.718
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Table 11.

Health risk indices in canned beans/peas

Parameters RfD EDI (mg kg−1 bw day−1) DE (mg kg−1 day−1) THQ HI
Product type A
 Fe 0.7 1.397 97.795 1.996 10.133
 Mn 0.14 0.040 2.769 0.283
 Zn 0.3 0.515 36.025 1.715
 Cd 0.001 0.002 0.142 2.029
 Pb 0.0036 0.000 0.007 0.028
 NO3 1.6 0.904 63.289 0.565
 NO2 0.1 0.352 24.623 3.518
 Na 288.856
Product type B
 Fe 0.7 1.898 132.869 2.712 11.824
 Mn 0.14 0.039 2.741 0.280
 Zn 0.3 0.885 61.955 2.950
 Cd 0.001 0.002 0.128 1.826
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.928 64.951 0.580
 NO2 0.1 0.348 24.339 3.477
 Na 236.146
Product type C
 Fe 0.7 1.776 124.321 2.537 9.107
 Mn 0.14 0.047 3.280 0.335
 Zn 0.3 0.580 40.612 1.934
 Cd 0.001 0.000 0.000 0.000
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.953 66.683 0.595
 NO2 0.1 0.371 25.943 3.706
 Na 287.422
Product type D
 Fe 0.7 1.325 92.783 1.894 10.281
 Mn 0.14 0.035 2.435 0.249
 Zn 0.3 0.714 49.998 2.381
 Cd 0.001 0.001 0.092 1.319
 Pb 0.0036 0.001 0.071 0.282
 NO3 1.6 0.921 64.482 0.576
 NO2 0.1 0.358 25.077 3.582
 Na 293.926
Product type E
 Fe 0.7 1.937 135.624 2.768 11.608
 Mn 0.14 0.049 3.436 0.351
 Zn 0.3 0.583 40.839 1.945
 Cd 0.001 0.003 0.206 2.941
 Pb 0.0036 0.002 0.107 0.423
 NO3 1.6 0.705 49.317 0.440
 NO2 0.1 0.274 19.184 2.741
 Na 325.691
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Table 12.

Health risk indices in canned sweet corn

Parameters RfD EDI (mg kg−1 bw day−1) DE (mg kg−1 day−1) THQ HI
Product type A
 Fe 0.7 0.196 13.692 0.279 1.336
 Mn 0.14 0.006 0.411 0.042
 Zn 0.3 0.064 4.496 0.214
 Cd 0.001 0.000 0.019 0.276
 Pb 0.0036 0.000 0.012 0.047
 NO3 1.6 0.106 7.405 0.066
 NO2 0.1 0.041 2.881 0.412
 Na 31.799
Product type B
 Fe 0.7 0.203 14.213 0.290 0.957
 Mn 0.14 0.005 0.327 0.033
 Zn 0.3 0.062 4.348 0.207
 Cd 0.001 0.000 0.000 0.000
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.094 6.614 0.059
 NO2 0.1 0.037 2.570 0.367
 Na 34.621
Product type C
 Fe 0.7 0.168 11.784 0.240 0.954
 Mn 0.14 0.008 0.529 0.054
 Zn 0.3 0.084 5.856 0.279
 Cd 0.001 0.000 0.000 0.000
 Pb 0.0036 0.000 0.000 0.000
 NO3 1.6 0.084 5.909 0.053
 NO2 0.1 0.033 2.297 0.328
 Na 41.797
Product type D
 Fe 0.7 0.200 14.006 0.286 1.238
 Mn 0.14 0.007 0.500 0.051
 Zn 0.3 0.110 7.718 0.368
 Cd 0.001 0.000 0.004 0.060
 Pb 0.0036 0.000 0.004 0.017
 NO3 1.6 0.101 7.093 0.063
 NO2 0.1 0.039 2.759 0.394
 Na 36.261
Product type E
 Fe 0.7 0.233 16.301 0.333 1.193
 Mn 0.14 0.007 0.475 0.048
 Zn 0.3 0.076 5.326 0.254
 Cd 0.001 0.000 0.003 0.048
 Pb 0.0036 0.000 0.005 0.020
 NO3 1.6 0.109 7.626 0.068
 NO2 0.1 0.042 2.957 0.422
 Na 37.635
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The EDI values in mg kg−1 bw day−1 for canned fish ranged from 0.099 to 0.151 for Fe, 0.001–0.002 for Mn, 0.01–0.0037 for Zn, 0.033–0.049 for NO3 and 0.013–0.019 for NO2. Cd and Pb were below detectable limit. The EDI for canned meat had the following ranged values in mg kg−1 bw day−1; Fe (0.469–0.693), Mn (0.006–0.011), Zn (0.083–0.158), Cd (0–0.001), Pb (BDL), NO3 (0.159–0.197) and NO2 (0.062–0.076). The results from the analyses revealed that canned beans/peas had the highest EDI with values (in mg mg kg−1 bw day−1) ranging from 1.325 to 1.937 for Fe, 0.035–0.049 for Mn, Zn (0.515–0.885), Cd (0–0.003), Pb (0–0.002), NO3 (0.705–0.953) and NO2 (0.274–0.371). The ranged values obtained from the EDI of sweet corn in mg kg−1 bw day−1 are; Fe (0.168–0.23), Mn (0.005–0.008), Zn (0.062–0.110), Cd and Pb (BDL), NO3 (0.084–0.109) and NO2 (0.033–0.042). The established EDI range from the various canned categories in this study were compared to established provisional tolerable daily intake (PTDI) and the values were within benchmark except for nitrates in canned meat which had a maximum value exceeding the benchmark as shown in Table 13.

Table 13.

Comparing EDI with recommended intake values from various standards

Canned food Parameter EDI (mg kg−1 bw day−1) range Provisional tolerable daily intake (mg kg−1 bw day−1) References
Fish Fe 0.099–0.151 0.8 [14]
Mn 0.001–0.002 0.067 [15]
Zn 0.01–0.0037 1 [16]
Cd 0-BDL 0.001 [17]
Pb 0-BDL 0.00357 [18]
NO3 0.033–0.049 0–3.7 [19]
NO2 0.013–0.019 0–0.07 [19]
Meat Fe 0.469–0.693 0.8 [14]
Mn 0.006–0.011 0.067 [15]
Zn 0.083–0.158 1 [16]
Cd 0–0.001 0.001 [17]
Pb 0-BDL 0.00357 [18]
NO3 0.159–0.197 0–3.7 [19]
NO2 0.062–0.076 0–0.07 [19]
Beans/Peas Fe 1.325–1.937 0.8 [14]
Mn 0.035–0.049 0.067 [15]
Zn 0.515–0.885 1 [16]
Cd 0–0.003 0.001 [17]
Pb 0–0.002 0.00357 [18]
NO3 0.705–0.953 0–3.7 [19]
NO2 0.274–0.371 0–0.07 [19]
Sweet corn Fe 0.168–0.233 0.8 [14]
Mn 0.005–0.008 0.067 [15]
Zn 0.062–0.110 1 [16]
Cd 0-BDL 0.001 [17]
Pb 0-BDL 0.00357 [18]
NO3 0.084–0.109 0–3.7 [19]
NO2 0.033–0.042 0–0.07 [19]
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The DE of the various parameters in the canned categories were also compared with recommended daily requirement set for each parameters as shown in Table 14. But the DE of canned fish for each parameters had values (in mg kg−1 day−1) ranging from 6.957 to 10.564 for Fe, 0.062–0.114 for Mn, Zn ranged from 0.676 to 2.598, Cd (0–0.008), Pb (0–0.007), NO3 (2.331–3.399), NO2 (0.907–1.335) and Na (16.67–19.14). In canned meat, the ranged values (mg kg−1 day−1) were; Fe (32.85–48.49), Mn (0.394–0.742), Zn (5.779–11.03), Cd (0–0.035), Pb (0–0.026), NO3 (11.13–13.78), NO2 (4.33–5.32) and Na (69.18–76.56). The highest DE (mg kg−1 day−1) was recorded in the canned beans/peas categories. They are; Fe (92.78–135.62), Mn (2.435–3.44), Zn (36.03–61.96), Cd (0–0.206), Pb (0–0.107), NO3 (49.32–66.68), NO2 (19.18–25.94) and Na (236.15–325.69). DE of sweet corn ranged from 11.78 to 16.30, 0.33–0.53, 4.34–7.72, 0–0.019, 0–0.012, 5.91–7.63, 2.3–2.96 and 31.80–41.80 mg kg−1 bw day−1 for Fe, Mn, Zn, Cd, Pb, NO3, NO2 and Na respectively.

Table 14.

Comparing DE with recommended intake values from various standards

Canned food Parameter DE (mg kg−1 day−1) Recommended daily requirement (mg day−1) References
Fish Fe 6.957–10.564 10–15 [20]
Mn 0.062–0.114 2–9 [21]
Zn 0.676–2.589 15–22 [16]
Cd 0–0.008 – –
Pb 0–0.007 0.075 [22]
NO3 2.331–3.399 – –
NO2 0.907–1.335 – –
Na 16.699–19.138 2300 [23]
Meat Fe 32.845–48.493 10–15 [20]
Mn 0.394–0.742 2–9 [21]
Zn 5.779–11.030 15–22 [16]
Cd 0–0.035 – –
Pb 0–0.026 0.075 [22]
NO3 11.133–13.776 – –
NO2 4.326–5.322 – –
Na 69.184–76.557 2300 [23]
Beans/Peas Fe 92. 783–135.624 10–15 [20]
Mn 2.435–3.436 2–9 [21]
Zn 36.025–61.955 15–22 [16]
Cd 0–0.206 – –
Pb 0–0.107 0.075 [22]
NO3 49.317–66.683 – –
NO2 19.184–25.943 – –
Na 236.146–325.691 2300 [23]
Sweet corn Fe 11.784–16.301 10–15 [20]
Mn 0.327–0.529 2–9 [21
Zn 4.348–7.718 15–22 [16]
Cd 0–0.019 – –
Pb 0–0.012 0.075 [22]
NO3 5.909–7.626 – –
NO2 2.297–2.957 – –
Na 31.799–41.797 2300 [23]
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THQ values for all canned foods categories were less than 1 except canned beans/peas with values greater than 1. HI ranged from 0.421 to 11.824 in the food categories as shown in Tables 9, 8, 10, 11 and 12.

Discussion

The mean concentration heavy metals, Nitrate and Nitrite, (Fe, Zn, Cd, Pb, Mn and As across the canned food categories are presented in Figs. 1 and 2. The mean values for nitrates ranged from 54.22 ± 9.52 to 93.92 ± 3.73 mg kg−1 and the values were above Food Standards Australia New Zealand (FSANZ) bench marks. Nitrites mean values ranged from 21.1 ± 3.69 to 36.54 ± 1.45 mg kg−1 across the canned food categories and were below FSANZ bench marks. Heavy metals concentrations across the canned food categories ranged from 130.68 ± 1.74 to 303.08 ± 11.57 mg kg−1 (Fe), 1.44 ± 0.34–6.3 ± 0.35 mg kg−1 (Mn), 15.72 ± 3.49–91.88 ± 3.95 mg kg−1 (Zn), 0–0.23 ± 0.04 mg kg−1 (Cd), and 0–0.17 ± 0.08 mg/kg (Pb). Cd was above EU standard in all canned groups while Pb exceeded same standard in canned meat.

Fig. 1.

Fig. 1

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Mean concentration (mg kg−1) of heavy metals across canned food categories. The metal concentrations across canned categories tend to vary. Manganese appears to increase significantly from canned fish to canned sweetcorn. Cadmium was highest in canned beans/peas. Values are mean ± SE (n = 25 per category)

Fig. 2.

Fig. 2

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Mean concentration (mg kg−1) of chemical additives across canned food categories. The additives tend to be similar across the canned categories with no wide variation. Values are mean ± SE (n = 25 per category)

Health risk estimations showed as EDI and DE are shown in Tables 9, 10, 11 and 12. The values of EDI ranged from 0.033 to 0.953 mg kg−1 bw day−1 and 0.013 to 0.371 mg kg−1 bw day−1, for nitrates and nitrites respectively.

The Fe concentration in this study was far higher than that reported by Zarei et al. [24]. In their study, Fe ranged from 0.009 to 14.207 µg g−1 in canned tuna fish. It was also higher than the result obtained by Iwuoha et al. [25] were the Fe level in canned Geisha and Founty Mackerel in Choba market ranged from 0 to 0.0379 mg kg−1. Zn in this study were higher than the findings of Dallatu et al. [26,] who assessed the level of heavy metals in fresh and canned foods consumed in Northern central Nigeria reported Zn to range from 0.0526 to 1.5472 mg kg−1 in canned foods and 0.17841–6.41113 in fresh food samples. Cd in this study corroborates with that of Dallatu et al. [26] where the Cd assessed in fresh and canned foods were found to be higher than WHO standards and the values ranged from 0.0073 to 0.1919 mg kg−1. This may pose a threat considering the fact that accumulation of Cd in the human body may induce kidney dysfunction, skeletal damage and reproductive deficiencies [27]. Lead in this study did not corroborate the findings of Bordajandi et al. [28] which reported Pb values as high as 217 µg/g in sardine, 17.1 µg g−1 in canned tuna and 69.6 in canned sardines.

The results for Nitrate and Nitrite from this study were found to be higher than results obtained from the New Zealand’s nitrates and nitrites diet study were ninety-seven percent (97%) of the processed foods and meat analysed complied with the Australia New Zealand Food Standards with two meat samples containing low levels of nitrate and one with excessive nitrite [29]. The high levels recorded could be dangerous because nitrates are generally regarded to be of low toxicity but the toxicological squeals of nitrate exposure are considered to be virtually attributed to its conversion to nitrite. Nitrite reacts with haemoglobin (Hb) to form methaemoglobin (MetHb) in the blood which is the toxicological end point following nitrate and nitrite exposure. MetHb levels of up to 10% are typically not associated with clinical signs in humans. At a higher level, MetHb is associated with clinical signs including cyanosis, impaired aerobic respiration, and metabolic acidosis and in severe cases, death [30, 31]. Outside the use of nitrates and nitrites as additives in canned foods, the high level in this study may suggest a synergistic effect of the use of nitrogen rich fertilizer for cultivation alongside the contribution during manufacture process for preservation.

The observed pH values from this study did not differ widely from each canned categories assessed as shown in Fig. 3. This shows that the values are largely maintained within different canned foods.

Fig. 3.

Fig. 3

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pH of the canned foods. There was slight difference in the pH values recorded across the foods sampled. Canned fish and meat showed no significant variation in the different canned products analysed (P > 0.05) but canned beans/peas and canned sweet corn showed a high significant difference across the product types (P < 0.001). Values are mean ± SE (n = 25 per category)

Health assessment

In this study, possible health risk on consumption of the canned foods was assessed using Health risk indices reported as Estimated Daily Intake (EDI), Target Hazard Quotient (THQ), Hazard Index (HI) and Dietary Exposure (DE).

EDI values in mg kg−1 bw day−1 for Fe ranged from 0.099 to 0.15, 0.469–0.693, 1.325–1.937, 0.168–0.23 for canned fish, meat, beans/peas and sweet corn respectively were mostly found to be within PTDI of 0.8 mg kg−1 bw day−1 set by Joint Expert Committee on Food Additives (JECFA) [14] except for canned beans/peas which exceeded this limit. EDI of Fe in this study was found to higher than 0.09 mg kg−1 bw day−1 that reported by Korfali and Hamdan [32] in their study of canned foods in Lebanon.

That of Mn ranged from 0.001 to 0.002, 0.006–0.011, 0.035–0.049, 0.005–0.008 mg kg−1 bw day−1 for canned fish, meat, beans/peas and sweet corn. These values were lower than the PTDI set by Food Safety and Inspection Service (FSIS) [15] of 0.067 mg kg−1 bw day−1.

In a similar way, the EDI for Zn were found to be below 1 mg kg−1 bw day−1 set by JECFA [16] and the range from this study was 0.01–0.0037, 0.083–0.158, 0.515–0.885, 0.062–0.110 mg kg−1 bw day−1.

However, EDI for Cd was above the PTDI of 0.001 mg kg−1 bw day−1 set by JECFA [17] in canned beans/peas, but canned meat recorded an EDI of 0.001 mg kg−1 bw day−1 which is same as the PTDI but was below detectable limit for canned fish and sweet corn. The EDI for Cd in this study was found to be higher than those from previous studies; 0.11 µg kg−1 bw day−1 reported by Bordajandi et al. [28] and 0.14 µg kg−1 bw day−1 reported by Urieta et al. [33].

EDI for Pb was not recorded for all canned groups except canned beans/peas which recorded a range of 0–0.002 mg kg−1 bw day−1 which was slightly below the PTDI of 0.00357 mg kg−1 bw day−1 set by JECFA [18]. The EDI for Pb in this study was higher than 0.38 µg/kg bw/day reported by Bordajandi et al. [27] and also higher than 0.55 µg kg−1 bw day−1 reported by Urieta et al. [33].

EDI calculated for NO3 was within PTDI of 0–3.7 mg kg−1 bw day−1 set by JECFA [19] which was between 0.033 and 0.953 mg kg−1 bw day−1 across the canned groups. That of NO2 was found to be higher than the PTDI set values of 0–0.07 mg kg−1 bw day−1 in canned beans (0.274–0.371 mg kg−1 bw day−1) and canned meat (0.062–0.076 mg kg−1 bw day−1). The result from this study agrees with that of Thompson [29] that reported the EDI for New Zealand adults to nitrate and nitrite to range from 0 to 5 mg kg−1 bw day−1 and 0–0.10 mg kg−1 bw day−1 respectively.

The DE in this study was assessed to determine the values available on consumption of any of the canned products. Most diets are fortified with metals such as Fe and Zn but they are required in diet within a dietary intake level certified not to cause any form of toxicity. Hence, for this study, DE for Fe in the canned foods sampled ranged from 6.957 to 135.624 mg kg−1 bw day−1. This value were above the recommended daily requirement of 10–15 mg kg−1 day−1 set by Nordic Council of Ministers (NCM) [20] except for canned fish whose values were within the recommended intake level per day. This shows that consumption of these foods will not expose the consumer to any chance of anaemia. DE for Mn ranged from 0.062 to 3.436 mg kg−1 day−1 which was within the daily requirement recommended in food by WHO [21] which is 2–9 mg kg−1 bw day−1. Zn was found to have a DE within the daily recommended intake of 15–22 mg kg−1 day−1 set by JECFA [16] except for canned beans/peas with a DE of 36.025–61.955 mg kg−1 bw day−1. Cd, NO3 and NO2 recorded DE values which ranged from 0 to 0.206, 2.331–66.683, 0.907–25.943 mg kg−1 day−1 respectively with no data for comparison. There is a concern of Pb toxicity in canned beans/peas which had a DE of 0.107 mg kg−1 day−1 slightly above the daily requirement of 0.075 mg kg−1 bw day−1 set by US FDA [22].

There is no risk of Na induced hypertension because the DE of Na in this study was far below the daily requirement of 2300 mg kg−1 bw day−1 as specified by Centres for Disease Control and Prevention (CDC) [23]. The DE for the various parameters in this study may not totally account for their availability in a single diet. This is because, when they are used alongside other food substances in food preparation, the levels may likely increase hence increasing the risk associated with each parameters due to synergistic effect.

The human health risks posed by contaminant exposure are usually characterized by the target hazard quotient (THQ) [6]. If the value of THQ is less than 1, the risk of non-carcinogenic toxic effects is assumed to be low. When it exceeds 1, there may be concerns for potential health risks associated with overexposure. In this study, the THQ values for all canned foods categories were less than 1 except canned beans/peas with values greater than 1 in all of its parameters except Mn suggesting that there is a risk of a non-carcinogenic toxic effect. HI ranged from 0.421 to 11.824 in the food categories.

Results from this study revealed potential Cd toxicity and risk of non-carcinogenic toxic effect from canned beans/peas consumption; it is therefore imperative to monitor possible contamination of canned foods. This study also became an eye opener, because it demonstrated that some canned foods sold in Nigeria markets do not carry NAFDAC Registration No. NAFDAC (National Agency for Food and Drug Administration and Control) is an arm of the Nigeria Government whose mission is to safeguard the public health by ensuring that only the right quality of food, drugs and other regulated products are manufactured, exported, imported, advertised, sold and used. It is imperative therefore that such agency should collaborate with Institutions all over the country to help conduct research regularly and use the results as a monitoring guide. I also recommend that a total diet study be carried out to cover the scope outside of this research.

Acknowledgements

I want to acknowledge the team members of the Laboratory for Ecotoxicology and Environmental Forensics for their role in this research.

Compliance with ethical standards

Conflict of interest

This work has been extensively discussed in parts and whole at the 7th international toxicology symposium in Africa held in South Africa in August 2015. Martins Oshioriamhe Ainerua received a travel Grant from the University of Benin to the 7th international toxicology symposium in South Africa.

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