**3. Results**

The results of the mean concentration of study metals (Fe, Zn, Mn, Ni and V) detected in six brands of canned fish products and at different months of study stored in curry sauce, tomatoes sauce and soyabean oil are as shown in **Tables 1** and **2**.

In the months of study (February–October) the highest concentration of all the metals were recorded in October, while the least concentrations were observed at the beginning of the study as shown in **Table 1**.


### **Table 1.**

*Mean and standard deviation of concentrations of study metals (mg/kg) in different months.*

*Some Metals Found in Stored Canned Fish Products Sold in Nigeria DOI: http://dx.doi.org/10.5772/intechopen.110214*


*Different subscript in spp./storage media column refers to different brands.*

### **Table 2.**

*Mean and standard deviation of concentration of metals (mg/kg) in the different species storage media.*

Concentration of the study metals in the six brands of canned fish analyzed varied within the months and between the storage medium, although some were not significantly different during the period of study. The highest concentration value of Fe (29.45 mg/kg), Zn (72.09 mg/kg), Mn (0.67 mg/kg), Ni (5.6 mg/kg) and V (0.27 mg/ kg) in sardine all stored in curry sauce except V which was in sardine stored in soybean oil. The least value of Fe (2.88 mg/kg), Zn (7.04 mg/kg), Mn (0.09 mg/kg), Ni (0.55 mg/kg) and V (0.02 mg/kg) were all observed in mackerel stored in tomato sauces(2–4) as shown in **Table 2**. The results obtained were statistically tested.

The month of October had the highest mean concentration values across the individual heavy metals and the least concentrations at the beginning of study as shown in **Table 1** above. Using Analysis of variance (ANOVA) to statistically test the results obtained for significant difference and a further separation of means with the Duncan Multiple Range Test (DMRT) between brands storage media. It was observed that there was significant difference (p > 0.05) in the metal contents among them. The brand of canned sardine in curry sauce had higher concentration of all the study metals except for V, followed by sardine stored in Soybean oil within brands of canned fishes (**Table 2**); there was also in the different months significant difference (p > 0.05) in the metal concentration in the different months (**Table 1**). Mn, Ni and V were not significantly different (p < 0.05) during the months of study and in the brands irrespective of their storage media.

### **4. Discussion**

Fish has been considered a good indicator for heavy metal contamination in aquatic systems because they occupy different trophic levels therefore the levels of toxic elements in fish are related to age, sex, season and habitat [30, 31]. Fish being widely consumed in many parts of the world as this has been made possible by advances in packaging technology especially the use of cans, such that any level of pollution in stored fish will endanger human health all over the world. Results from this study shows that Fe, Zn, Mn, Ni and V were present in the six brands of canned fish products in the different storage medium marketed and frequently consumed in the Nigeria market.

Iron is an essential metal and it is an important constituent of hemoglobin, myoglobin and enzymes such as catalases and peroxidases. WHO set iron permissible limit at 0.30 mg/day and in the UK, women during their reproductive age and post-menopausal estimated daily iron requirement are set at 11.4 mg and 6.7 mg respectively, while 6.7–8.8 mg was for young male-adults. Estimated average daily requirements for children of between 0 and 10 years varied between 1.3 mg and 6.7 mg [32]. Although, there are no set permissible limits to be used as a standard in Nigeria with regards to ferrous concentration, the results obtained during the study period and in the different storage media exceeded the WHO set limit in all the brands. Except for sardine stored in curry sauce and soybean oil, all other values were within the UK and COMA set permissible limit. However previous studies in Nigeria [33], revealed that 0.0379 mg/ kg and 0.0302 mg/kg were obtained while working on two different brands of canned fish. Results from this study are much higher than their findings but similar to results obtained earlier [34] while working on canned fish stored in brine and sunflower.

Zinc has been implicated in most metabolic pathways in humans; its deficiency can lead to loss of appetite, growth retardation, skin changes and immunological abnormalities. Maximum zinc level permitted for fish is 50 mg/kg according to Food Codex, while the US recommended daily intakes of zinc are 15 mg and 12 mg for adult male and female respectively. Results obtained shows two brands of mackerel in tomato sauce(2,3) and skipjack in soybean oil6 did not exceed these daily requirement Although, United Nations Environmental Protection Agency and the European Commission (US-EPA and EC) have not set any standard limits for zinc concentrations, Codex [35] maximum permissible limit of 40 mg/kg was exceeded in the mean zinc concentration of 72.09 mg/kg observed in sardine in curry sauce1 but all other values were within the permissible limit during the different months. and the lowest average zinc concentration was observed in costa mackerel in tomato sauce3 7.04 mg/kg. This value (7.04 mg/ kg) obtained in this study, compare favorably with the result of [36] who also observe a low Zn content in mackerel (6.9 mg/kg), binito (5.8 mg/kg) and trout (6.4 mg/kg) and a higher content in anchovy and sardine (27.3 mg/kg and 17.6 mg/kg respectively). In canned tuna flakes stored in brine a zinc concentration level of 28.95 mg/kg had earlier been reported [34]. While working on four imported fish species stored in commercial cold store in Nigeria [37] it was observed that no value exceeded the WHO/FAO maximum permissible limit as the highest mean value of 21.52 mg/kg was obtained.

According to USEPA [38], there is no information on the carcinogenicity of manganese; COMA and WHO have been unable to set a specific recommendation for manganese intake. The EU scientific committee for food (EU-SCF) considered an adequate intake to be 1–10 mg/person/day. Results obtained from this analysis shows that the maximum and minimum concentration range of Mn was 0.09–0.67 mg/kg with a mean monthly value which was basically below the recommended values by the US National Research Council (NRC) [39] specified estimated safe and adequate daily dietary intakes of 0.3–1, 1–3 and 2–5 mg/day for infants, children and adults respectively. This result is comparable to [34] reported range of 0.07–0.51 mg/kgMn and 0.002 mg/kgMn and 0.0016 mg/kgMn [33] while working on brands of Geisha and Founty canned fish respectively. But it was however lower than the corresponding maximum level of 15.77 mg/kg reported for canned sardines in Brazil [40]. Although small daily intake of manganese is needed for a total wellbeing, inability to remove excess amount of manganese from the system can result in nervous system problems.

Nickel which can act as an activator of some enzyme systems at high levels can also cause respiratory problems because it can accumulate in the lungs and it is carcinogenic [41]. In addition to environmental contamination of nickel in foods,

*Some Metals Found in Stored Canned Fish Products Sold in Nigeria DOI: http://dx.doi.org/10.5772/intechopen.110214*

it can get into foods through processing activities such as canning and cooking. The upper tolerable intake level of nickel for children and adult are 7 mg/day and 40 mg/ day respectively [42] but Codex [35] set the permissible limit in foods at 3.0 mg/day. The mean concentration range of 5.61 mg/kg-0.55 mg/kg Ni observed in this study was higher than that earlier obtained [43], which was in the range of 0.0 to 0.78 mg/ kg while working on canned fishes sold in Brazil. Except for sardine stored in curry sauce, all other values obtained during this study were below set permissible limit in foods [35] especially in all the brands stored in tomato sauces(2–4).

Vanadium is a transition metal, with an estimated ˃ 60 thousand tons of this element being emitted into the atmosphere yearly from human activities as oxides or sulphates. But it also occurs naturally in soil, waters and air [44, 45]. Obtained values from this study showed a V concentration range of 0.27 mg/kg to 0.02 mg/kg which were much less than the 1.8 mg/kg upper tolerance intake level of vanadium for adults of between 19 and 70 years as set by Institute of Medicine [42], and 2 mg/kg and 2.9 mg/kg set by Codex and EC respectively.
