Tucuxi Dolphins (Sotalia guianensis) as sentinel for the health of coastal environments: a study of concentrations of mercury in the Amazon estuary and the northern coast of Rio de Janeiro

Abstract

A contamina????o dos oceanos, associada ??s atividades antr??picas, tem se tornando biodispon??vel para diversos organismos, entretanto os mais vulner??veis s??o aqueles situados no topo da cadeia tr??fica marinha, incluindo o homem e os mam??feros marinhos, mas principalmente os cet??ceos costeiros, como o boto-cinza (Sotalia guianensis). Diversos estudos t??m indicado que os cet??ceos s??o excelentes bioindicadores da qualidade dos ambientes marinhos devido a peculiaridades biol??gicas e ecol??gicas desta mega-fauna. Desta forma, este trabalho objetivou propor o boto cinza como esp??cie sentinela da sa??de dos ecossistemas costeiros ao longo de sua distribui????o (desde Santa Catarina, sul do Brasil at?? Honduras, Am??rica Central). Al??m disso, este estudo objetivou a utiliza????o desta esp??cie como bioindicadora da biodisponibiliza????o de Hg total no estu??rio Amaz??nico e costa norte do Rio de Janeiro. Na primeira abordagem desta pesquisa a literatura dispon??vel sobre impactos da contamina????o e doen??as emergentes sobre o boto-cinza foi revisada e discutida. Apesar de a literatura pesquisada ser incipiente se comparada com estudos realizados no hemisf??rio norte, estudos recentes t??m revelado altos n??veis de contaminantes nesta esp??cie (e.g. metais pesados, organoclorados, PCBs, compostos organoest??nicos, PFOS e PBDE). A presen??a de doen??as emergentes, tais como doen??as cut??neas e ??sseas, al??m da identifica????o de infec????es causadas por organismos potencialmente patog??nicos (e.g. giard??ase, lobomicose,toxoplasmose e presen??a de Vibrio sp.) tem sido notificadas em S. guianensis. Para o estudo das concentra????es de Hg total, amostras de m??sculo de 20 botos-cinza da costa norte do Rio de Janeiro e 29 da costa do Amap?? foram analisadas. A concentra????o m??dia de Hg foi 0,38 (0,07-0,79) para a costa do Amap?? (AP) e 1,07 microgramas/g-1 pu (0,20-1,66) para a costa do Rio de Janeiro (RJ). Os baixos n??veis de Hg para a costa do AP ?? provavelmente devido ?? aus??ncia de fontes antr??picas deste elemento para o ambiente, entretanto, os n??veis detectados para a costa do RJ est??o possivelmente associados ?? libera????o ambiental deste poluente ao longo da costa. Os n??veis de ambas as ??reas de estudos mostraram baixos n??veis de Hg quando comparados com estudos em diversas regi??es do mundo. N??o houve diferen??a significativa de Hg para machos e f??meas e as concentra????es tenderam a se elevar com o aumento do comprimento total. Com base nos resultados desta pesquisa, prop??e-se a esp??cie Sotalia guianensis como organismo sentinela da sa??de dos ecossistemas costeiros. Al??m disso, esta pesquisa aponta a necessidade de estudos adicionais sobre contaminantes e a poss??vel associa????o destes com as doen??as emergentes e organismos patog??nicos detectados nesta esp??cie amea??ada.The pollution of the oceans, associated to human activities, is affecting several marine organisms. However, the most vulnerable species are those situated on the top of the marine trophic web, including the humans and marine mammals, but principally costal cetaceans, as marine tucuxi dolphins (Sotalia guianensis). Studies have indicated that cetaceans are excellent bioindicators for the quality of the marine environment because of their biological and ecological properties. Hence,the aim of this scientific work is to use the marine tucuxi dolphin as sentinel species for the marine ecosystem health along its distribution (from Santa Catarina, South Brasil to Honduras, Central America). Furthermore, this study aims to point out this species as a useful tool for the bioavailability of total Hg of the Amazon estuary and north coast of Rio de Janeiro. In the first approach of this research, the literature available about impacts of the contamination and emerging diseases on the S. guianensis were reviewed and discussed. Despite little literature available compared with studies carried out in the north hemisphere, recent studies have indicated elevated levels of chemical contaminants in this species (e.g. heavy metals, organochlorines, PCBs, organotin compounds, PFOS, PBDE). The presence of emerging diseases, such as skin and bone diseases, and the infections caused by organisms potentially dangerous (e.g. giardiasis,lobomycosis, toxoplasmosis, presence of Vibrio spp.) have been notified in S. guianensis. For the development of the study of the concentrations of total Hg, muscle samples of 20 marine tucuxi dolphins from the north Rio de Janeiro State and 27 from the coast of Amap?? (Amazonian coast)were analyzed. The average concentration of Hg was 0,38 (0,07-0,79) at the coast of Amap?? (AP) and 1,07 ??g/g-1 pu (0,20-1,66) at the coast of Rio de Janeiro (RJ). The low levels of Hg detected in dolphins from the AP coast were probably due to the absence of human source of this element. On the other hand, the levels of Hg detected in dolphins from the RJ coast reflect the release of this element to the marine environment through the human activities conducted along the coast. Both of the study areas showed low levels of the Hg compared with studies conducted over the world. No statistic correlation was found between the levels of Hg for males and females and the concentrations of this element tended to elevate with increasing total body length. According to the results presented in this research, the species Sotalia guianensis is a potential sentinel for the health of the coastal marine environment. Furthermore, this research points out the necessity of additional studies about chemical contaminants and their possible association to the emerging diseases and pathogenic organisms frequently detected in this threatened species