The Fish Consumption Has Diverse Nutritional Benefits

Published Date: 02 Nov 2017

Introduction

Fish consumption has diverse nutritional benefits since it supplies us with proteins, vitamins, minerals and particularly omega-3 polyunsaturated fatty acids, which may protect us against several health problems such as coronary heart disease mortality and stroke. However, the level of heavy metals discovered in some fish makes it difficult to decide whether fish consumption on regular basis is advantageous or not.

In Mauritius in order to protect consumers of marine foodstuffs, the Ministry has established maximum heavy metal levels under Section 18 of the Food Act 1998 in fish and fishery products as given in Table 3.1.

Maximum Permitted Proportion in Parts per million (ppm)

Elements

As

Sb

Pb

Cu

Sn

Zn

Hg

Cd

F

Fish and fishery products

1.0

1.0

2.0

30.0

40.0

100.0

1.0

1.0

10.0

Table 3.1: Maximum permitted levels of heavy metals in fish and fish products under Section 18 of the Food Act 1998

In this study the levels of heavy metals: mainly cadmium, lead and mercury were analyzed in frequently consumed canned fish by the Mauritians in order to ensure that the heavy metal contents of the canned fish, locally available as well as imported ones are safe for consumption.

The analysis was performed on nine different types of canned fish and for each one of them; two cans were brought which were of different production dates. The reason for this dissimilar manufacturing date was to ensure that the fish content of the can was from different fish in order to determine how the heavy metal contents vary from one fish to another.

The details about the canned fish species selected such as the brand name, the region where the fish was caught and the ingredients used for preservation is given in the Table 3.2 below.

Brand

Name of the cans analyzed

Color of Labeling

Country of

Origin

Fishing Waters

Species

Ingredients

Tropical

Brown

Mauritius

Indian Ocean

Tuna

Water and salt

Orange

Oil

Green

Oil

Josiane

Blue

Morocco

North West Atlantic

Sardines

Soya Oil

Red

Olive Oil

Yellow

Vegetable Oil

Atlantic

Mauritius*

Mackerel

Water and Salt

Glenrick

Peru

Pacific Ocean

Lucky Star

China

Pacific

Ocean

Table 3.2: Details of the canned fish species purchased in Mauritius in 2012

* Packed in Mauritius

RESULTS

The levels of cadmium and lead of the canned fish samples collected from supermarkets in Mauritius were determined by flame atomic absorption spectroscopy whereas the mercury content was determined by cold vapor AAS after microwave digestion.

General Overview of the Heavy Metal Contents in the Canned Fish Species Studied

Lead content

Mean Lead amounts in the muscle of the examined fish species were 0.099 ± 0.028 mg/kg (ranging from 0.060 – 0.151), 0.062 ± 0.029 mg/kg (ranging from 0.021- 0.113) and 0.072 ± 0.027 mg/kg (ranging from 0.029 – 0.113) for canned tuna, canned sardines and canned mackerel respectively.

The order that describes the lead concentration results is:

Canned Tuna ˃ Canned Mackerel ˃ Canned Sardines.

Cadmium content

The mean Cadmium detected values were 0.028 ± 0.014 ppm (ranging from 0.016 – 0.044), 0.004 ± 0.003 ppm (ranging from 0.000 – 0.010) and 0.044 ± 0.019 ppm (ranging from 0.022 – 0.093) for canned tuna, canned sardines and canned mackerel respectively.

The increasing order of Cadmium concentrations is:

Canned Sardine Ë‚ Canned Tuna Ë‚ Canned Mackerel

Mercury content

The overall range and mean of Hg concentration in the fish samples analyzed were 2.726 ± 0.371 ppb (ranging from 1.933 to 3.222) for canned tuna; 1.209 ± 0.203 ppb (ranging from 0.902 to 1.534) for canned sardines and 1.891 ± 0.617 ppb (ranging from 0.966 to 2.796) for canned mackerel.

The trend observed for the mercury levels in the different fish species was:

Canned Sardine Ë‚ Canned Mackerel Ë‚ Canned Tuna

COMPARISON OF THE MEAN HEAVY METAL CONCENTRATION BETWEEN THE BATCHES OF TROPICAL CANNED TUNA

The results concerning the mean mercury and range concentrations of the examined Tropical canned tuna are given in Table 3.3

Brand

Name

No. of samples

Batch 1

Batch 2

Hg / ppb

Mean ± SD

Range

Mean ± SD

Range

Tropical (Orange) Solid Tuna

3

3.033

±

0.026

3.003 – 3.028

3.192

±

0.027

3.157 - 3.222

Tropical (green) tuna chucks

3

2.015

±

0.060

1.933 – 2.075

2.660

±

0.023

2.642 – 2.693

Tropical (brown) tuna solid

3

2.741

±

0.012

2.732 – 2.758

2.719

±

0.018

2.706 – 2.745

Table 3.3: Mean Mercury and Range Concentrations in Tropical Canned Tuna

Figure 3.1: Variation of the Mean Mercury Level in the Different Batches of Canned Tuna

The level of mercury detected in the canned tuna, irrespective of the brand name, was extremely low. The highest mean mercury content was 3.192 ± 0.027 ppb, which was found in the second batch of the Tropical (Orange) whereas batch 1 of the Tropical (green) had the lowest mean Hg level as it can be observed from Figure 3.1. An increase in the mean mercury concentration is observed from batch 1 to batch 2 for both Tropical (Orange) solid tuna and Tropical (Green) tuna chunks. No significant variation was observed for the average mercury values between the two batches of Tropical (Brown) tuna solid.

STATISTICAL ANALYSIS

The difference between the batches of Tropical canned tuna determined by the ANOVA test and statistical significance was defined as p Ë‚ 0.05.

Results of Anova test for mercury content in Tropical canned tuna are presented in Table 3.4:

Brand

Name

p- value

Significant Difference Between the Batches

Tropical (Orange) Solid Tuna

0.003895774

Tropical (green) tuna chucks

0.000143056

Tropical (brown) tuna solid

0.237796145

Table 3.4: Results of Anova test for Mercury content in Tropical canned tuna

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The average lead content in the analyzed Tropical canned tuna is given in the Table 3.5.

Brand

Name

No. of samples

Batch 1

Batch 2

Lead / ppb

Mean ± SD

Range

Mean ± SD

Range

Tropical (Orange) Solid Tuna

3

0.126

±

0.007

0.121 – 0.135

0.098

±

0.013

0.082 – 0.113

Tropical (green) tuna chucks

3

0.141

±

0.009

0.128 – 0.151

0.080

±

0.007

0.075 – 0.090

Tropical (brown) tuna solid

3

0.080

±

0.013

0.067 – 0.098

0.070

±

0.007

0.060 – 0.075

Table 3.5: Mean Lead and Range Concentration in Tropical Canned Tuna

Figure 3.2: Variation of the Mean Mercury Level in the Different Batches of Canned Tuna

OBSERVATION

A general trend can be observed from Figure 3.2, that is, a decrease in the mean lead level from batch 1 to batch 2 for the different types of Tropical canned tuna studied. Although, the flame AAS analysis indicated the presence of trace amount of lead in the samples, none of the examined canned tuna had mean lead concentration exceeding the permissible limit of 2.0 mg/kg established by the Food Act 1998. In comparison with the other Tropical canned tuna, the second batch of the Tropical (Brown) tuna solid had the lowest lead level, while the highest lead content was detected in the first batch of the Tropical (Green) tuna chunks.

STATISTICAL ANALYSIS

The difference between the batches of Tropical canned tuna was assessed by the ANOVA test and statistical significance was defined as p Ë‚ 0.05.

Results of Anova test for lead content in Tropical canned tuna are as followed:

Brand

Name

p- value

Tropical (Orange) Solid Tuna

0.050129157

Tropical (green) tuna chucks

0.001949195

Tropical (brown) tuna solid

0.396929405

Table 3.6: Results of Anova test for Lead content in Tropical canned tuna

Statistical comparison revealed that Pb concentrations were significantly different only between the batches of Tropical (green) tuna chunks.

The results regarding the mean cadmium and range concentrations of the analyzed Tropical canned tuna are given in Table 3.7.

Brand

Name

No. of samples

Batch 1

Batch 2

Cd/ ppm

Mean ± SD

Range

Mean ± SD

Range

Tropical (Orange) Solid Tuna

3

0.020

±

0.003

0.016 – 0.022

0.016

±

0.000

-

Tropical (green) tuna chucks

3

0.027

±

0.004

0.022 – 0.033

0.025

±

0.002

0.022 – 0.027

Tropical (brown) tuna solid

3

0.029

±

0.003

0.027 – 0.033

0.038

±

0.004

0.033 – 0.044

Table 3.7: Mean Cadmium and Range Concentrations in Tropical Canned Tuna

Figure 3.3: Variation of the Mean Cadmium Level in the Different Batches of Canned Tuna

The mean cadmium concentration for the three different kinds of Tropical canned tuna varied from one batch to another.

The second batch of the Tropical (Orange) had the lowest cadmium content with respect to the other canned tuna studied. The cadmium levels were 0.020 ± 0.003 mg/kg and 0.016 ± 0.000 mg/kg for batch1 and batch 2 of the Tropical (Orange) solid tuna respectively.

For Tropical (Green) tuna chunks, the level of Cadmium in the first batch was slightly higher than the Cd content in the second batch.

Among all the canned Tropical canned tuna analyzed, the highest Cadmium level was detected in the second batch of the Tropical (Brown) tuna, which varied from 0.033 to 0.044 ppm with an average value of 0.038 ± 0.004 ppm.

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Tropical (Orange) Solid Tuna

0.116116523

Tropical (green) tuna chucks

0.607167578

Tropical (brown) tuna solid

0.067875871

Table 3.8: Results of Anova test for Cadmium content in Tropical canned tuna

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The results indicated no significant differences between the different batches.

VARIATION OF THE AVERAGE HEAVY METAL CONCENTRATION FOR INTER-BATCHES OF JOSIANE CANNED SARDINES

The results obtained for the mean mercury concentration in the sardine samples are given in the following table.

Brand

Name

No. of samples

Batch 1

Batch 2

Hg / ppb

Mean ± SD

Range

Mean ± SD

Range

Josiane (blue) sardines

3

1.512

±

0.022

1.482 – 1.534

1.418

±

0.018

1.405 – 1.443

Josiane (red) sardines

3

1.130

±

0.016

1.108 – 1.147

1.199

±

0.038

1.160 - 1.250

Josiane (yellow) sardines

3

0.919

±

0.016

0.902- 0.941

1.078

±

0.034

1.031 – 1.095

Table 3.9: Mean Mercury and Range Concentrations in Josiane Canned Sardines

Figure 3.4: Variation of the Mean Mercury Level in the Different Batches of Canned Sardines

OBSERVATION:

Analysis of the Josiane (blue) sardine samples indicated the presence of mercury in both batches. The mercury contents were 1.512 ppb and 1.418 ppb for batch 1 and batch 2 respectively.

For the Josiane (red) sardines in vegetable oil, the first batch had a lower mercury content compared to the second batch as it can be seen from Figure 3.4 .

In batch 1 of Josiane (yellow), the mercury level was 0.919 ppb, which was the lowest concentration with respect to the concentrations of the other sardine samples analyzed.

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Josiane (blue) sardines in olive oil

0.009262929

Josiane (red) sardines in vegetable oil

0.076696339

Josiane (yellow) sardines in soya oil

0.003866974

Table 3.10: Results of Anova Test for Mercury Content in Josiane Canned Sardines

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The determination of the lead concentrations in the Josiane canned sardines gave the following results, shown in the Table 3.11.

Brand

Name

No. of samples

Batch 1

Batch 2

Lead / ppb

Mean ± SD

Range

Mean ± SD

Range

Josiane (blue) sardines

3

0.052

±

0.007

0.044 -0.060

0.093

±

0.004

0.090 -0.098

Josiane (red) sardines

3

0.024

±

0.004

0.021 – 0.029

0.070

±

0.009

0.060 -0.082

Josiane (yellow) sardines

3

0.098

±

0.013

0.082 – 0.113

0.034

±

0.007

0.029 – 0.044

Table 3.11: Mean Lead and Range Concentration in Tropical Canned Tuna

Figure 3.5: Variation of the Mean Lead Level in the Different Batches of Canned Sardines

OBSERVATION:

Determination of the lead content in the Josiane (blue) sardines gave the following results: 0.052 mg/kg for the first batch and 0.093 mg/kg for the second one, which indicated an increase in the mean lead contents from batch 1 to batch 2.

The mean lead concentrations in Josiane (red) were 0.024 mg/kg and 0.07 mg/kg for Batch 1 and Batch 2 respectively, which pointed out that the sardine samples were in the acceptable range. In comparison with the other batches of canned sardine, the lowest lead content was detected in batch 1 of Josiane (red).

In Josaine (yellow) sardine, a decrease in the lead content was observed from Batch 1 to Batch 2.

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Josiane (blue) sardines in olive oil

0.001588419

Josiane (red) sardines in vegetable oil

0.002798492

Josiane (yellow) sardines in soya oil

0.003421508

Table 3.12: Results of Anova Test for Lead Content in Josiane Canned Sardines

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The results regarding the mean cadmium and range concentrations of the analyzed Josiane canned sardines are given in Table 3.13.

Brand

Name

No. of samples

Batch 1

Batch 2

Cd/ ppm

Mean ± SD

Range

Mean ± SD

Range

Josiane (blue) sardines

3

0.007

±

0.002

0.010 – 0.005

0.002

±

0.002

ND – 0.005

Josiane (red) sardines

3

ND

-

0.003

±

0.003

ND – 0.005

Josiane (yellow) sardines

3

0.008

±

0.002

0.005 – 0.010

0.005

±

0.000

-

Table 3.13: Mean Cadmium and Range Concentrations in Josaine Canned Sardines

Figure 3.6: Variation of the Mean Cadmium Level in the Different Batches of Canned Sardines

The results of the analysis indicated that the concentration of cadmium in the Josiane canned sardine samples were at extremely low levels.

For the Josiane (blue) sardine, a decrease in the average mean Cd concentration can be observed in Figure 3.6.

In the first batch of Josiane (red) sardines, no cadmium was detected. However, analysis revealed the presence of cadmium in the second batch, which was 0.003 ppm.

In batch 1 of Josiane (yellow), the Cadmium level was 0.005 mg/kg whereas in the second batch, the sample had a Cadmium concentration of 0.008 mg/kg, which was the highest concentration with respect to the concentrations of the other sardine samples analyzed.

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Josiane (blue) sardines in olive oil

0.101191507

Josiane (red) sardines in vegetable oil

0.116116523

Josiane (yellow) sardines in soya oil

0.116116523

Table 3.14 :Results of Anova Test for Lead Content in Josiane Canned Sardines

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

Comparison of the mean heavy metal concentrations between the different batches of canned mackerel samples.

The results regarding the mean Hg and range concentrations of the analyzed canned mackerel samples are given in Table 3.15.

Brand

Name

No. of samples

Batch 1

Batch 2

Hg / ppb

Mean ± SD

Range

Mean ± SD

Range

Glenryck Mackerel Natural

3

0.979

±

0.018

0.966 – 1.005

1.469

±

0.028

1.430 – 1.495

Lucky Star Mackerel in brine

3

2.788

±

0.012

2.771 – 2.796

2.431

±

0.050

2.384 – 2.500

Atlantic Mackerel Natural

3

2.131

±

0.032

2.088 -2.139

1.546

±

0.021

1.521 – 1.572

Table 3.15: Mean Mercury and Range Concentrations in Canned Mackerel

Figure 3.7: Variation of the Mean Mercury Level in the Different Batches of Canned Mackerel

OBSERVATION:

Determination of mercury content in the canned mackerel revealed the presence of the heavy metal in the samples but at very trace amount. For the "Atlantic" as well as for the "Glenryck" brand names, the Hg concentration detected in the first batch was inferior compared to the second batch, as it can be observed in Figure 3.7. The concentration of Hg in the fish samples from the "Lucky Star" cans were 2.788 ± 0.012 ppm and 2.431 ± 0.050 ppm for batch 1 and batch 2 respectively, which indicated a decrease in the Hg level from batch 1 to batch 2.

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Glenryck Mackerel Natural

˃ 0.05

Lucky Star Mackerel in brine

0.000592208

Atlantic Mackerel Natural

˃ 0.05

Table 3.16: Results of Anova Test for Mercury Content in Canned Mackerel

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The mean lead and range concentration detected in the canned mackerel are given in the following table:

Brand

Name

No. of samples

Batch 1

Batch 2

Pb / ppm

Mean ± SD

Range

Mean ± SD

Range

Glenryck Mackerel Natural

3

0.090

±

0.011

0.075 – 0.098

0.042

±

0.010

0.029 – 0.052

Lucky Star Mackerel in brine

3

0.108

±

0.004

0.105 – 0.113

0.085

±

0.008

0.074 – 0.090

Atlantic Mackerel Natural

3

0.057

±

0.007

0.052 – 0.067

0.072

±

0.013

0.060 – 0.090

Table 3.17: Mean Lead and Range Concentrations in Canned Mackerel

Figure 3.8: Variation of the Mean Lead Level in the Different Batches of Canned Mackerel

For Figure 3.8, it can be observed that there is variation in the average lead values detected among the different kinds of canned mackerel species. For the "Atlantic" cans analyzed, an increase in the mean lead content was noted from batch 1 to batch 2. On the other hand, for the "Glenryck" and "Lucky Star", the opposite was observed, that is, a decrease in the mean lead concentrations from batch 1 to batch 2. The maximum mean lead concentration was detected in the first batch of the can labeled "Lucky Star" whereas the lowest average lead level was 0.042 ± 0.010, which was found in the second batch of the "Glenryck" brand name.

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Glenryck Mackerel Natural

0.008859103

Lucky Star Mackerel in brine

0.018190322

Atlantic Mackerel Natural

0.212582206

Table 3.18: Results of Anova Test for Lead Content in Canned Mackerel

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The average and the range of cadmium concentration in the canned mackerel are given in Table 3.19.

Brand

Name

No. of samples

Batch 1

Batch 2

Cd / ppm

Mean ± SD

Range

Mean ± SD

Range

Glenryck Mackerel Natural

3

0.042

±

0.003

0.038 – 0.044

0.035

±

0.002

0.033 – 0.035

Lucky Star Mackerel in brine

3

0.082

±

0.008

0.076 – 0.093

0.049

±

0.004

0.044 – 0.055

Atlantic Mackerel Natural

3

0.032

±

0.004

0.032 – 0.038

0.024

±

0.027

0.022 -0.027

Table 3.19: Mean Cadmium and Range Concentrations in Canned Mackerel

Figure 3.9: Variation of the Mean Cadmium Level in the Different Batches of Canned Mackerel

From Figure 3.9, the mean cadmium inter batches, irrespective of the brand names, showed a decrease from batch 1 to batch 2. Among all the cans analyzed, the lowest mean cadmium concentration was detected in the second batch of the can labeled "Atlantic" whereas the highest mean Cd level was 0.082 ± 0.008 mg/kg, which was found in the first batch of the canned mackerel with brand name "Lucky Star".

Statistical Analysis

Brand

Name

p- value

Significant Difference Between the Batches

Glenryck Mackerel Natural

0.047983364

Lucky Star Mackerel in brine

0.00761897

Atlantic Mackerel Natural

0.073233808

Table 3.20: Results of Anova Test for Cadmium Content in Canned Mackerel

: There is a significant difference between the two batches when p-value Ë‚ 0.05

: There is no significant difference between the two batches when p-value ˃ 0.05

The mean and the range of the heavy metals concentration in the all the samples analyzed are shown in the following table:

MEAN ± SD (RANGE)

BRAND NAME OF CANNED FISH

Cadmium

/ ppm

Lead

/ ppm

Mercury

/ ppb

Mean Value of

Mercury / ppm

( to 6 d. p)

Tropical (orange) Solid Tuna in oil

0.018 ± 0.003

(0.016 – 0.022)

0.118 ± 0.012

(0.082 – 0.135)

3.112 ± 0.084

(3.003 – 3.222)

0.003116

Tropical (green) tuna chucks in brine

0.026 ± 0.004

(0.022 – 0.033)

0.111 ± 0.034

(0.075 – 0.151)

2.337 ± 0.0326

(1.933 – 2.693)

0.002337

Tropical (brown) tuna solid in oil

0.034 ± 0.006

(0.027 – 0.044)

0.075 ± 0.012

(0.060 -0.098)

2.730 ± 0.019

(2.706 -2.758)

0.00273

Josiane (blue) sardines in olive oil

0.004 ± 0.003

(ND – 0.010)

0.072 ± 0.021

(0.044 – 0.098)

1.465 ± 0.051

(1.405 -1.534)

0.001465

Josiane (red) sardines in vegetable oil

0.002 ± 0.002

(0.000 – 0.005)

0.047± 0.024

(0.021 -0.082)

1.164 ± 0.045

(1.108 -1.186)

0.001164

Josiane (yellow) sardines in soya oil

0.007 ± 0.002

(0.005 – 0.010)

0.066 ± 0.033

(0.029 – 0.113)

0.999 ± 0.084

(0.902 – 1.108)

0.000999

Glenryck Mackerel Natural

0.038 ± 0.004

( 0.033 – 0.044)

0.066 ± 0.026

( 0.029 – 0.098)

1.224 ± 0.246

( 0.966 – 1.495)

0.001224

Lucky Star Mackerel in brine

0.066 ± 0.017

( 0.044 – 0.093)

0.076 ± 0.024

(0.074 – 0.113)

2.610 ± 0.182

( 2.384 – 2.796)

0.002610

Atlantic Mackerel

Natural

0.028 ± 0.006

( 0.022 – 0.038)

0.065 ± 0.013

(0.052 – 0.090)

1.839 ± 0.293

(1.521 – 2.165)

0.001839

Table 3.21: The mean and the range concentration of the heavy metals (Cd, Hg & Pb) in all samples analyzed

NOTE:

For comparison purposes of the heavy metal contents, the mean mercury concentration was converted to parts per million.

ND: Not Detectable

The following are the series that describe the heavy metal concentration for tuna, sardines and mackerel, respectively:

Mean heavy metal concentrations with respect to the colour of the canned tuna are:

[Cd] ORANGE Ë‚ [Cd] GREEN Ë‚ [Cd] BROWN

[Hg] GREEN Ë‚ [Hg] BROWN Ë‚ [Hg] ORANGE

[Pb] BROWN Ë‚ [Pb] GREEN Ë‚ [Pb] ORANGE

Mean heavy metal concentrations for the different Josiane cans colour are:

[Cd] RED Ë‚ [Cd] BLUE Ë‚ [Cd] YELLOW

[Hg] YELLOW Ë‚ [Hg] RED Ë‚ [Hg] BLUE

[Pb] RED Ë‚ [Pb] YELLOW Ë‚ [Pb] BLUE

Average heavy metal concentration for the different brand name of the canned mackerel are:

[Cd] ATLANTIC Ë‚ [Cd] GLENRYCK Ë‚ [Cd] LUCKY STAR

[Pb] ATLANTIC Ë‚ [Pb] GLENRYCK Ë‚ [Pb] LUCKY STAR

[Hg] GLENRYCK Ë‚ [Hg] ATLANTIC Ë‚ [Hg] LUCKY STAR

From the results obtained, it was observed that the cadmium interspecies concentrations depend on the size of the fish; larger species contain higher level of heavy metal. Although the sizes of the fish before canning are unknown, it is known generally that sardine species are smaller when compared with the tuna and mackerel species. Thus, the size of the fish can be used as a factor to explain why the the mean levels of heavy metal detected in the sardine samples studied were lower in comparison with the mean Cd concentrations found in the tuna and mackerel samples, irrespective of the batches and country of origin.

Furthermore, the AAS analysis has revealed that the mean lead concentrations were higher than the mean Cd and Hg levels found in the different samples examined but did not exceed the limit established in the Food Act 1998. According to known results (Castro-González and Méndez-Armenta, 2008; Storelli, 2008), heavy metals bioaccumulation is influences by factors such as to fish species, gender, length and age. From the result obtained, it can be observed that the level of heavy metals (Cd, Hg and Pb) varied from one species to another. However, the details of how gender, length and age of fish affect the intake of heavy metals were not investigated during this study.

The minimum mean mercury concentration was detected in the muscle of the sardine’s samples because the sardine species feed mainly on water plants and plankton (Hajeb et al., 2009).

Heavy metal contents in fish also depend on the habitat of the fish, season (diet of fish vary through dry and rainy season) and the percentage of heavy metals present in the water where it was caught. For instant, the mackerel species analyzed in the cans labeled "Glenryck" and "Lucky Star" had different mean concentration of heavy metals although they were caught in the same ocean. This is perhaps because of the uneven distribution of heavy metal in the ocean and intrinsic factors, which influence the rate of uptake of the heavy metals by the fish species.

Even though, it was beyond the scope of this study to investigate the link between packing ingredients and the heavy metal content in canned fish, certain observations were made. The Josiane canned fish were preserved into different oils: olive oil, vegetable oil and soya oil. From the results obtained, a variation in the mean heavy metal concentrations was noted. For fish samples packed with olive oil, the mean lead content was 0.072 ± 0.021 mg/ kg, which was higher than the average lead values detected in the sardines samples preserved in the other preservative oils. On the other hand, among the three different cans of Josiane sardines analyzed, the highest Cd content was 0.007 ± 0.002 ppm, which was present in the fish sample preserved in soya oil. For Hg, the following trend was observed when taking into consideration the packing ingredients: [Hg] SOYA OIL ˂ [Hg] VEGETABLE OIL ˂ [Hg] OLIVE OIL.

In the Tropical canned tuna, variation of the heavy metal contents was observed from one can of specific brand name to another. The heavy metal concentrations differences may be attributed to the feeding habits since the tuna fish are migratory species and their bioaccumulation of Cd, Hg and Pb are influenced by environmental conditions such pH and temperature of the water in which they live.

The results obtained by Z.Doomunkhan in 2003, for the analysis of mercury in Josiane canned sardines and Tropical canned tuna were as followed:

For 16 samples of Josiane canned sardine examined, the mercury content varied from 0.040 to 0.389 with an average Hg value of 0.176 ± 0.084 ppm.

The analysis of 24 samples of Tropical canned tuna had revealed that the Hg level ranged from 0.034 to 0.363 and with a mean value of 0.176 ± 0.058 ppm.

Results obtained during the study

Josiane canned sardines

Tropical canned tuna

N

18

18

Overall Mean Hg level / ppm

0.0012

0.0027

SD

± 0.0002

± 0.0004

Range / ppm

0.0001 -0.0015

0.0019 – 0.0032

Table 3.22: Overall Mean Hg Concentration in Josaine canned Sardines and Tropical Canned Tuna

When comparing the results obtained during this study with those of Z.Doomunkhan carried out during 2003, we can note a drastic decrease in the overall mean mercury contents in the Josiane canned sardines as well as in Tropical canned tuna. Therefore, it is a good sign that the amount of mercury being uptake by the sardine fish is diminishing and thus, it is safer for the consumption of the general population. This decrease may be attributed to proper handling, disposal and regulated use of mercury.

CONCLUSION

The results of this study indicated that all the fish species analyzed had Cd, Hg and Pb concentrations only at trace levels and consequently well below the permissible levels established by the Ministry under Section 18 of the Food Act 1998 for fish and fish products. Therefore, the canned fish examined are safe for consumption because the contribution of the heavy metal adverse effects to the body burden can be considered negligible. It has been recently proved that the consumption of fruits could help to depurate the concentration of mercury present in the body (Passos et al.,2007). In addition to, it was found that tea consumption might have the ability to decrease the level of Hg in blood (Canuel et al., 2006). Therefore, people who consume large amount of fish on regular basis, should eat more fruits and drink more tea in order not to accumulate Hg in their body.

RECOMMENDATIONS

Further studies could include an attempt to correlate heavy metal concentrations in canned fish with packing ingredients and factors such as processing and canning practices. For instant, ensure that the properties of the cans are according to regulations of the Food Act 1998 and determine whether the leaching of the metal from the cans into seafood is taking place.

It would be also interesting to investigate how the heavy metal concentrations vary according to the length and age of the fish species.

Furthermore, determination of the total lipid content of fish and fishery products could help to evaluate their nutritional benefits and find the relationship between the bioaccumulation of heavy metals in fish and the lipid content.

Another interesting investigation would be to collect water from different fishing areas around Mauritius and determined its heavy metal contents. Then, the heavy metal concentrations in fish, which are caught from the same fishing place should be determined and find out how the heavy metal contents vary from one location to another and how the intake of heavy metals by fish is influenced by the percentage of heavy metals present in the water they survive.