Geochemistry and Heavy Metal Levels in the Sediments of the Port of Santa Bárbara de Samana, Dominican Republic

In the Port of Santa Bárbara de Samana, chemical residues, organic matter and heavy metals from domestic activities are deposited together in the wa-ters and sediments. The analysis of the sediments by X-ray fluorescence of four extracted and sectioned cores showed that concentrations of trace metals such as Nickel, Chromium, Lead and Mercury were present at various depths, exceeding Limits of Toxicity (PEL) for marine sediments according to National Oceanic and Atmospheric Administration (NOAA) and Canadian Council of Ministers of the Environment (CCME). Cadmium presented values above the toxicity threshold (TEL) in its minimum values and in its maximum values they exceeded the PEL value. While the Zinc and Copper values were low in all sections and lower than TEL. The analysis of the loss by ignition and the dating with lead 210 due to excess of the C4 core, showed a sudden change in the organic matter content and sedimentation rate. The superficial sediments show that unlike the deeper ones, the heavy metal content is lower, as well as that they do not represent a risk to the ecosystem by not exceeding toxicity levels.


Introduction
The degradation of coastal areas is of great international concern (Angulo et al., 2006). Activities carried out in the cities of the interior of the continent as well as on the coasts, are affecting the coastal. These represent environmental assets that are being seriously affected (USAID-DSTA, 2006). The bay of Samana, specifically the Puerto Santa Bárbara de Samana, has been under pressure over time, decreasing its environmental quality due to wastewater and sediment contributions from the town of Samana and from the peninsula (Eptisa SYSMIN Program, 2004). Although it does not have large polluting industries, some artisan workshops could contribute to the contamination of the coastal zone together with domestic activities. The main economic sources in the region are tourism, fishing and agriculture; being its main ruble the cultivation of coconut. In the peninsula there are basaltic and karst rocks as well as some rocks with mineralogical compounds of Titanium, Magnesium and Iron (Hernaiz-Huerta, 2004); which by erosion and weathering by rains (Rodríguez-Vegas et al., 2013), especially during the presence of hurricanes and storms typical of tropical regions (Angeli et al., 2020), are deposited forming sediments in the port determining its geochemistry (Escuder-Viruete, 2008a, 2008b. Benthic animals that feed on nutrients (Valdés et al., 2014) in the sediments of the seabed (Landsea & Nicholls, 1996), can also ingest heavy metals that in many cases are toxic, inhibiting their development or reproduction (Ruelas-Inzunza et al., 2011). These heavy metals can also be bio-accumulated in the tissues and reach the humans through the food chain, which is harmful to health. The study of surface sediments gives us information (Loring & Rantala, 1992) of the heavy metal contributions associated with these that have recently been deposited (Fukue et al., 2006). The taking of cores, in addition to giving us recent information, gives us information on how the content of heavy metals has varied as measures have been deposited (Alonso-Hernández et al., 2016). To determine heavy metals in sediments, there are many techniques, the most common being Atomic Absorption Spectrophotometry (FAA) and X-Ray Fluorescence Spectrometry (XRF) (Marguí et al., 2011). Because XRF is simple and inexpensive, it is preferably used over other techniques that are normally used for these studies, such as Atomic Absorption Spectrophotometry (FAA) with a flame or Graphite furnace. If, in addition to the analysis of the metal content, the loss by ignition and the dating with excess lead 210 ( 210 Pb) (Appleby & Oldfield, 1978), natural radio tracer (Muramat & Evans, 1977) with the which we can have information on how these have changed over time and their content of organic matter (Gaudette et al., 1974).
Dating with lead 210 (Considine et al., 2011) allows us to determine how the Sedimentary Accumulation Rate and the contributions of organic matter (Binford & Brenner, 1986) have varied for about 150 years and if it has been affected by climatic phenomena (Rozanski & Gonfiantini, 2004). 210 Pb is a radioisotope as a result of Radio 226 decay, it can be determined by gamma, alpha or beta spectroscopy (Lozano et al., 2011). For the determination by beta spectroscopy, a Liquid Centello Counter (Mosqueda-Peña, 2010) can be used, measuring the beta activity of Bismuth 210 in secular equilibrium with 210 Pb (Rodríguez et al., 1996). The gamma determination is carried out directly; while by alpha spectroscopy Polonium 210 (IAEA, 1992(IAEA, , 2016 is determined when it is in secular  (Runnuw, 1999). As the Toxic Threshold Levels (TEL) and Permitted Toxic Levels (PEL) are above 2.0 mg/Kg in marine sediment (Buchman, 2008) in most heavy metals considered contaminants, the use of a technique to measure concentrations below this value, it is a waste of resources, in addition to being pollutants themselves, unlike XRF, which is a non-destructive technique, being able to use the sample for other analyzes or to be discarded more appropriately. The organic matter content by incineration of the sediment sample at 450 degrees Celsius is related to the loss of weight of the sample, this is known as loss by ignition (PPI) (Meyers & Teranes, 2001).
Chemical elements in specific amounts are necessary for the development of living things, but higher values can be toxic, especially when this occurs in a very short period of time.

Study Zone
The Port of Santa Bárbara de Samana is located north of the Bay of Samana

Materials and Methods
Methodology 1) For the determination of the metals in the sediments, the following procedure was carried out: Collection of 4 cores with Uwited gravity sampler ( ter content related to the loss of ignition was one of the analyzed carried out on the core that we consider to be the most significant, which was the C4 core ( Figure 2).

3) Determination of the activity of Lead 210 in Secular equilibrium with Bismuth 210 in Sediments
From the sediments already crushed and sieved digestion of 1 gram of sample with concentrated nitric and hydrochloric acid inside a 20 ml glass vial. If the carbonate content is high, it is recommended to do it in a 500 ml flask previously, adding hydrogen peroxide to the sample before adding the acids and then transferring it after reducing it by heating to 20 ml. Let stand in a dark place for 15 days. Place on the Liquid Scintillation Analysis vials for determination 210 Pb in secular equilibrium with 210 Bi with LSC Hidex-Triathler. The C4 core was dated with 210 Pb to determine the Sedimentary Accumulation Rate (TAS) (Delanoy et al., 2020) at the site and thus be able to get an idea of how the sedimentation  (Figure 2).

4) Normalization of the Calcium, Iron, PPI and 210 Pb values to compare their behavior
Normalized value is equal to the quotient of the measure between the highest values of all the measures of the considered variable (Figure 2, Figure 3).

Results
Figure 2. The graph on the right shows the behavior of the loss by ignition (PPI) and 210 Pb, these follow the same behavior, they experience similar changes in each section, the red arrows show abrupt changes due to the occurrence of meteorological phenomena extremes that change the enrichment factors of some elements (Birch, 2017)     lead was found close to its TEL value in cores C1, C2 and C4. As for the surface levels of Chromium only in core C4, this was determined above the PEL, the other sampling points barely approached the TEL (Table 3). Cadmium was found in some sections and exceeded the TEL and PEL values, possibly due to its high solubility it can be dispersed through water. At the surface level, Cadmium exceeded cores to PEL except in core C3 (Table 3). Mercury was found in some sections; could be as a result of maritime activities in the area or due to mobility during storm surges or human activities (García, 1979

Conclusion
Nickel levels in the Port of Samana are above toxicity levels according to the SQuiRTs table NOAA-USEPA and the CCME in marine sediments (Table 2).
This element throughout the region in soil and sediment is generally found to be exceeding these values. Reason why we consider that it's content in the sediments is not the product of polluting sources; therefore it is not possible to adopt a remediation measure in relation to this element. The surface sections of the C4 core contained Cadmium levels that exceeded the toxicity level (Table 3), the same step with the other cores. As for Chromium, the cores taken inside the port of Samana exceeded the levels of toxicity in most of the sections. In the core C3 taken outside the port, however, the levels did not exceed the TEL, indicating that this heavy metal originates from human activities. In other pollutants such as Arsenic, Copper and Zinc, their levels are below the TEL values, so the port of Samana does not require a remediation measure in relation to these trace elements. The presence of Mercury in some sections with values higher than the TEL and PEL refers to sporadic activities, since in the first 12 centimeters of the surface of the Core C4 it was only determined in one section and in the entire core in 4 sections; so it is not an element of concern. In the case of Lead, some values exceeded the TEL, reason for which it is necessary to take some surveil-