In the last twenty years, the region of the lower Amazon has experienced great economic growth, which is due to the creation of a new agricultural frontier in the country, which has become the second largest grain producing region in the Brazilian Amazon. In view of the recent advances and mineral exploration projects implemented in the region, the objective of this thesis was to evaluate the concentrations of toxic Arsenic (As), Cadmium (Cd), Mercury (Hg) and Lead (Pb) and essential Cobalt (Co), Chrome (Cr), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo) , Nickel (Ni), Selenium (Se) and Zinc (Zn)in aquatic organisms from different municipalities in the Western region of Pará and compare them with the maximum limits allowed by law. In chapter 1, a review of the existing literature on the levels of heavy metals found in the main fishing species consumed in the region and identification of capture sites was carried out. The results obtained suggest that there is a large number of studies available on the concentration of mercury in fish in the region, with results that vary depending on biological and dietary aspects and the location of their habitat. The results reveal that contamination by Hg is evidenced mainly in carnivorous fish. This is worrying, as these fish are among the most consumed species in the region, they accumulate metals through bioaccumulation and biomagnification processes. The results of the chapter 2 study, the level of accumulation of toxic and essential metals in shrimp was similar to that described in other regions affected by anthropogenic activities in Brazil, and does not represent a significant risk for human consumption. The accumulation of metals between the Amazon and Tapajós rivers seems to be related to the bauxite and gold mines in the two regions, respectively. In the study of chapter 3, which included samples of muscle tissue from fish species (Acari, Piranha, Pirarucu, Caparari and Tucunaré) collected during the dry and flood seasons between the years 2015 and 2016. The results showed that the accumulation of toxic elements ranged from 2-238 μg / kg of fresh weight for As, 1-77 μg / kg for Cd, 4-1922 μg / kg for Hg and 1-30 μg / kg for Pb, exceeding only (16% of the carnivorous species) the maximum concentrations of mercury in fish for human consumption established in Brazilian legislation (0.5 mg / kg). Associations have been found between mercury and essential elements, iron, cobalt and manganese, since these elements may have a role in mercury cycling and methylation and deserve further evaluation to reduce mercury toxicity in aquatic environments. The results found in the study of chapter 4, which aimed to assess the feasibility of using various species of fish (Acari and Tucunaré) and tissues (liver and muscle) to monitor the accumulation of toxic and essential elements in the aquatic ecosystem. The results clearly demonstrated the possibility of using these fish species for studies on the biomonitoring of concentrations of toxic and essential elements in the aquatic environment. While the Tucunaré liver is the best tissue for biomonitoring elements that accumulate in the food chain (such as mercury), the Acarí liver better reflects the elements commonly accumulated in sediments (such as arsenic). In addition, the profiles of essential metals studied using multivariate chemometric techniques showed a clear difference between specimens from the waters of the Andes Mountains (sampling sites located in the main course of the Amazon Basin) with high concentrations of sediments, from Guyana and Brazilian shields ( Porto Trombetas and Itaituba on the Trombetas and Tapajós rivers, respectively). Our results also indicate that the deposition of elements in fresh fish in this area seems to be mainly related to the geological origin of the soils; large quantities of toxic
elements can be mobilized for the aquatic ecosystem due to human activities (including intensive agriculture, mineral extraction, deforestation and / or hydroelectric), which pose a serious danger to the environment and the health of coastal communities.
|
