Caracterização molecular das fontes naturais e antrópicas da matéria orgânica sedimentar na região de Potter Cove, Ilha Rei George, Antártica

Abstract

Resumo: Potter Cove (62 ‹14 fS, 58 ‹39 fO) e um pequeno fiorde na costa sudoeste da Ilha Rei George, Arquipelago Shetlands do Sul, e onde esta situada a estacao de pesquisa argentina Carlini. A fim de avaliar um possivel quadro de contaminacao por oleo e esgoto na regiao, foram coletadas 16 amostras de sedimentos superficiais, onde foram determinadas diferentes classes de marca-dores organicos geoquimicos: hidrocarbonetos alifaticos (HAs), hidrocarbonetos policiclicos aromaticos (HPAs), alquilbenzenos lineares (LABs) e esteroides. As concentracoes de HAs em Potter Cove variaram entre 1,097 e 3,229 ƒÊg.g-1, as de HPAs foram de 12,05 a 210,02 ng.g-1, as de LABs variaram entre 0,26 e 1,67 ng.g-1, enquanto as concentracoes de esteroides variaram entre 3,60 e 10,64 ƒÊg.g-1. As maiores concentracoes foram encontradas no centro da enseada, local de maiores profundidades e menor hidrodinamica, o que favorece o acu-mulo de sedimentos finos e de compostos organicos. Indices envolvendo hidro-carbonetos indicaram a predominancia de compostos leves, oriundos de residuos de oleo ou de producao fitoplanctonica em quase toda a baia. Ja a porcao central apresentou hidrocarbonetos provenientes da combustao de biomassa vegetal e de combustiveis fosseis. Os marcadores de esgoto manti-veram-se abaixo dos limites estabelecidos para areas contaminadas. Sendo assim, a principal fonte de esterois esta associada a presenca de florestas de macroalgas na desembocadura do fiorde e a um pequeno enriquecimento organico proximo a estacao Carlini. As amostras coletadas na Ilha Nelson apresentaram baixas concentracoes, principalmente pela distancia de fontes potenciais. Ja as amostras da Ilha Ardley apresentaram valores na mesma faixa observada em Potter Cove, devido a influencia da estacao chinesa Great Wall. Assim, os resultados deste estudo mostraram que, apesar da deteccao de compostos relacionados a atividades humanas, a regiao de Potter Cove pode ser considerada como nao contaminada por hidrocarbonetos de petroleo e por esgoto, devido as baixas concentracoes encontradas, associadas a hidrodi-namica local, que favorece a dispersao dos poluentes.

Abstract: Potter Cove (62°14’S, 58°39’W) is a small fjord on the southwest coast of King George Island, South Shetland Islands, and where the Argentine Carlini station is located. In order to evaluate a possible contamination by oil and/or sewage, 16 sediment sample were collected to analyze different organic compounds: aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), linear alkylbenzenes (LABs) and steroids. The AHs concentrations varied between 1.097 and 3.229 ìg.g-1, the PAHs between 12.05 and 210.02 ng.g-1, the LABs from 0.26 to 1.67 ng.g-1, and the steroids between 3.60 and 10.64 ìg.g-1. The highest values were found in the fjords central portion, the deeper and less dynamic region, where the fine sediments deposition and the subsequent accumulation of organic compounds occur. To assess the organic matter origin, indexes using n-alkanes were calculated and indicated the predominance of low molecular weight compounds, derived from oil residuals or phytoplanktonic production in almost all the bay. Only the central portion of the study site showed evidences of hydrocarbons from vegetal biomass or fossil fuel combustion. The sewage markers remained below the established limit for polluted areas. Therefore, the main source of steroids is associated with the seaweed forest on the fjord inlet and a little organic enrichment near the station beach. The samples taken at Nelson Island presented low concentrations of all compounds, probably due to the distance from potential sources. On the other hand, the Ardley Island values were in the same range observed in Potter Cove, most likely due to the influence of the Chinese Great Wall station. These results showed that, despite of the detection of organic compounds related to human activities, the Potter Cove region can be considered as an unpolluted area by oil hydrocarbons and sewage.