The heavy metal concentrations in samples of fresh fish of the different species analyzed in this study are shown in
Table 2. None of the average Pb and Cd concentrations in the different fish species analyzed were higher than the MLP established by the official Mexican standard of 1.0 mg/kg and 0.5 mg/kg, respectively. Similarly, these average concentrations were lower than the MPL established in the EU regulations (0.2 mg/kg for Pb and 0.1 mg/kg for Cd). The mean concentrations of Hg in mako shark and soupfin shark samples exceeded the MPL (1.0 mg/kg), with average concentrations of 1.286 and 1.128 mg/kg, respectively. The highest individual concentrations of Hg were observed in these two species, with values for mako shark of 2.14 mg/kg and 1.81 mg/kg for soupfin shark. Sixty percent of the fresh fish samples analyzed had Hg concentrations that were higher than the MPL established by the official Mexican standard.
Based on the Tukey-Kramer test on fresh fish samples, significant differences only exist for Hg between shark-tuna, shark-swordfish, tuna-soupfin shark, and soupfin shark-swordfish.
The concentrations of Pb, Cd, and Cr were low. For example, all the samples had Cd concentrations < 0.10 mg/kg and 95% of the samples had Cr and Pb concentrations lower than 0.20 mg/kg.
Table 4 shows some of the studies published around the world. The highest mean mercury concentrations in the fresh fish samples were found in the mako shark (1.286 mg/kg) and soupfin shark (1.128 mg/kg). These values are comparable to those reported in Spain by Olmedo et al. (
15), whose maximum value for a shark species was 1.406 mg/kg and 1.227 mg/kg for swordfish. Falco et al. (
21) reported maximum Hg values found in swordfish between 1.59 and 2.22 mg/kg. All these results exceed the MPL of current legislation in Mexico of 1.0 mg/kg.
The average Hg values obtained in this study (0.545 mg/kg) are similar to the average concentrations reported by Olmedo et al. (
15) for the swordfish species (0.540 mg/kg). However, unlike this study, the range of Hg concentrations reported by Olmedo et al. (
15) show a maximum value of 1.227 mg/kg, which is higher than the MPL. In the different species of tuna analyzed, only two maximum concentration values exceed the MLP of Mexican standards: those reported in Italy by Storelli et al. (
11) (1.76 mg/kg) and in Slovenia by Miklavcic et al. (
17) (1.11 mg/kg). The highest range of lead concentration was reported in studies conducted in Egypt by Hussein and Khaled (
22), with values from 0.67 to 0.99 mg/kg for bluefin tuna, followed by the concentrations found in this study for yellowfin tuna, ranging from 0.09 to 0.15 mg/kg and with an average value of 0.116 mg/kg. The concentrations of Pb in shark, soupfin shark, and swordfish in this study were the highest compared to the studies presented in
Table 4. The average concentration for shark was 0.159 mg/kg, soupfin shark was 0.096 mg/kg, and swordfish was 0.119 mg/kg, while the average Pb concentrations in the other studies ranged between 0.004 and 0.1 mg/kg. However, none of the results exceeded the maximum permissible limit for Pb established in the Mexican standard NMX-AA-027-SSA1-1993 of 1.0 mg/kg and the EU standard of 0.2 mg/kg. Cadmium concentrations did not exceed the MPL of 0.5 mg/kg. These values were the lowest compared to the studies reported in
Table 4. The maximum reported value for Cd of 0.127 mg/kg was in yellowfin tuna in the study conducted by Olmedo et al. (
15). Generally, the average concentrations in the other studies were three to four times higher than those obtained from the samples in this study (0.001 to 0.002 mg/kg).
The average results obtained for Cr for all the species analyzed in this study varied between 0.102 and 0.216 mg/kg (
Table 4). The maximum Cr value in this study was similar to the value reported by Guerin et al. (
24) in France for tuna, with a mean of 0.294 mg/kg. As with the canned tuna samples, there is no MPL for Cr in Mexican regulations or international standards, and therefore no conclusion can be drawn regarding compliance.