**9. Methylmercury in sharks**

In a recent study Rueda *et al.* [20], evaluated the methylmercury content (μg MeHg kg−1 w.w.) in muscle and stomach content of the Antillean dogfish shark (*Rhizoprionodon porosus*), in three different areas in the Colombian Caribbean. The first in Cabo de la Vela north of the Caribbean coast, scarcely intervened by man and influenced by the upwelling of the same name. The second is in the Las Flores station, near the mouth of the Magdalena River, and the third is in the southern part of the Caribbean on Isla Fuerte.

**Figure 7** shows the MeHg contents in the dogfish shark. The highest contents were determined at the Las Flores station (B) and the lowest at Cabo de la Vela (A). Regarding the sampling periods, it was observed that the maximum values occurred in the rainy season in Las Flores and in the dry season in Isla Fuerte and Cabo de la

#### **Figure 7.**

*MeHg content in μg kg−1(w.w.) in Rhizoprionodon porosus muscle according to the season and at each of the study sites. Due to the values obtained, the Y axis of the graph belonging to Cabo de la Vela presents a different scale than the others. Red line indicates the maximum concentration recommended by the WHO (2000) for food consumption. Modified from Rueda et al. [20].*

Vela. The lowest values in MeHg concentrations in shark tissues occurred, in general, during the transition period (July to August). For the three samplings in Isla Fuerte and in Las Flores in the dry and rainy seasons and only in the dry season in Cabo de la Vela, the contents exceeded the limits given by the World Health Organization (WHO, 2000) as permissible for the daily consumption per person. It is probable that the intensification of the upwelling by the trade winds, which are stronger, has transported the Hg from the sediments (**Figure 7**).

**Figure 8** shows the concentrations of MeHg in μg kg−1(w.w.) in the stomach content of *Rhizoprionodon porosus* according to the season and at each of the study sites. Only one sample was presented in a single sampling site in which the contents exceeded the permissible limits for daily human consumption (500 μg kg−1 WHO, 2000). The lowest concentrations were measured at Cabo de Vela, while the maximum was measured at Las Flores station in the dry season (408.6 μg k−1 g w.w.), while in the remaining samples, the contents were less than 200 μg/kg w.w., additionally and

#### **Figure 8.**

*MeHg concentrations in μg/kg(w.w.) in the stomach content of Rhizoprionodon porosus according to the season and in each of the study sites. The red line indicates the maximum concentration recommended by the WHO (2000) for food consumption. Modified from Rueda et al. [20].*

*Mercury in the Colombian Caribbean: The Bay of Cartagena, A Model in Resilience DOI: http://dx.doi.org/10.5772/intechopen.107240*

#### **Figure 9.**

*Biomagnification factor (FB) in Rhizoprionodon porosus according to the season in each of the study sites. Modified from Rueda et al. [20].*

with the exception of the flowers in the dry season, there were no significant differences between the samplings and the seasons.

Based on the MeHg concentrations in the muscle and stomach contents of the sharks, the biomagnification factor was determined for each of the sampling sites (**Figure 9**). Regarding the total data from the Colombian Caribbean, the Kruskal-Wallis test showed significant differences (p = 0.05) between the values of this factor in the different seasons. However, when doing the analysis with the data from each site separately, the only place where there were significant differences between the seasons was the Las Flores station. In Cabo de la Vela and Isla Fuerte, the temporal variation was not significant, although when analyzing the average values of each site in their respective seasons, they coincided in terms of the notable increase during the dry season.
