**2. The bay of Cartagena**

The bay of Cartagena is located in the middle part of the Colombian Caribbean coastline, between 10°16′–10°26′ N and 75°30′–75°36′ W.

The bay of Cartagena is a semi-enclosed body of water, in which two parts stand out, an external one that connects it with the Caribbean Sea through two mouths (Bocachica and Bocagrande); and the internal one located in the northeastern part and is not directly connected to the sea. The bay of Cartagena has estuary characteristics due to the contributions of continental waters from the Canal del in Pasacaballos.

The first studies focused on the study of mercury contamination in the bay were carried out with the support of the National Institute for the Defense of Renewable Resources—Food and Agriculture Organization of the United Nations (INDERENA-FAO, Acronym in Spanish) [5]. Between 1978 and 1979, a study was carried out with the support of the Oceanographic and Hydrological Research Center of the Colombian Navy (CIOH) to evaluate the dynamics and the chemical and sedimentological characteristics, in the study mercury was analyzed, and eight samplings were carried out quarterly; however, they only present the results of two contrasting periods.

**Figure 1** shows the results of the two seasons [6]. According to these authors, in the December−April, dry period, the maximum concentrations were measured in the southwestern part, at stations E37 and E31, in the Mamonal industrial zone and where the Petrochemical and Acalis de Colombia were located, with values between 2.0 and 1.4 μg Hg/l, respectively. In the August−December, rainy seasons, a three-year period, three important foci were detected, one in the Internal Bay (E3) where the

#### **Figure 1.**

*Mercury content in μg l−1 < in water samples at 42 stations in the Bay of Cartagena, in two seasons, December−April and August−November, 1979−1981. Modified from Pagliardini et al. [6].*

Los Pegasos dock is located with heavy traffic and possibly strongly influenced during this time of year by the currents, with contents of 1445 μg l−1. The second in Mamonal with contents of 1180 μg l−1, slightly lower than those measured during the windy period. The third is the mouth of the Canal del Dique with a content of 1 μg l−1, which corroborates the importance of the semi-artificial canal in the discharge of sediments and pollutants into the bay. This was corroborated with the horizontal profile that allowed us to observe that the Canal del Dique during the rainy season is the main factor in the distribution of pollutants due to the amount of sediment it transports (see fig 46 and 47, page 86).

In 1996 [7] conducted a study to compare the Hg concentration in two species of estuarine fish, between the Bay of Cartagena and the Ciénaga Grande de Santa Marta, in addition to the content of sediments of these two ecosystems.

The results in sediments (**Figure 2**) clearly show a difference between the stations of the Bahía de Cartagena and the Ciénaga Grande de Santa Marta (CGSM), being the contents measured in the Bay were substantially higher than in the CGSM. The average content for the bay was 1876 ± 578 μg Hg g−1 p.s., with extreme values of 94–10,293 μg Hg g−1 p.s. A heterogeneous distribution was determined between the different stations of the bay. The maximum values were determined in sediments from station 3, which corresponds to the area of influence of the old chlor-alkali plant, and a decrease in the contents towards the north (stations 3–5) was determined. It is noteworthy that these authors determined the lowest concentrations at station 1 located on the southwestern side, to the right of the mouth of the Clarín Channel, and to the south of the area of influence of the Alcalis discharge, with values of 154 ± 21 μg Hg g−1 p.s., which corresponds to station E37, also with the highest values in water published by Pagliardini *et al*. [6].

Compared to the concentrations measured in the Ciénaga Grande (20–109 μg Hg g−1 d.w.), they are very low, to the point that the maximum concentration measured is compared to the lowest value in the Bahía de Cartagena (94–10 293 μg Hg g−1 d.w.).

Cogua *et al.* [8] determined the contents of total mercury (HgT) and methylmercury (MeHg) in sediments and seston (Suspended organic and inorganic matter) of the Cartagena Bay, in five stations, collected quarterly for one year in 2006. The average content of HgT was 0.18 ± 0.001 μg Hg g−1 d.w. The highest contents were measured in front of the industrial zone (0.55 ± 0.03 μg Hg g−1 d.w.), with concentrations

#### **Figure 2.**

*Average content and standard deviation of total mercury (μg Hg g−1 d.w.) in sediments of Bahía Cartagena (six stations) and Ciénaga Grande de Santa Marta (three stations), between March and October 1996. Modified from Alonso et al. [7].*

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

#### **Figure 3.**

*HgT and MeHg contents (μg Hg g−1) in sediments (A) and seston (B) during the four sampling periods. Modified from Cogua et al. [8].*

decreasing towards the north and east. Likewise, it was observed that the highest contents corresponded to the months of influence of the rainy season (April to October), being higher in April at the beginning of the rains. According to these authors, 10% of HgT corresponds to MeHg and they are positively related (r = 0.87, p < 0.04).

For the contents in the suspended material, a similar behavior was presented, although with a lower average content (0.16 μg Hg g−1 d.w.), with the highest concentrations in the rainy season (June 0.19 μg g−1 p.s.), and a process of dilution from the station in front of the industrial zone (**Figure 3**).

Although the contents measured in sediments in the study by Cogua *et al.,* [8] are lower than those of Alonso *et al.* [7], the values were always higher in the area of influence of the industrial zone, where the chlorine—alkali was located, which discharged its waste through the Casemiro pipe to the Bay.
