ABSTRACT
Polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT) were evaluated in water and sediments from the Espírito Santo Inner Shelf (ESIS), Brazil, three years after the Fundão dam failure (FDF). We discuss the levels, sources, fate, and current environmental risks of these contaminants on temporal and spatial scales. In addition, the associated coastal dispersion patterns, water-sediment exchange trends, and environmental alterations were also discussed. Low contributions and no environmental risks were verified for PCBs after FDF. However, the low concentrations and frequency of occurrence in the samples did not allow for further reliable conclusions regarding the source of this contaminant. In contrast, hazard risk has been detected for DDTs in water and sediments. In sediments, there were a significant increase in level (up to 13.42 ng g-1; outlier = 369.6 ng g-1), inventory (maximum = 35.98 ng cm-2) and mean total mass (21.1 ± 39.4 kg) of DDTs after FDF. The integrated assessment of the spatial distribution in water and sediment suggests that DDTs was released from the Doce River, travelled south by the water column, and returned to the mouth region by northward sediment transport, where it accumulated. However, intense rainfall increased the input of DDTs to the ESIS and may have also altered its spatial distribution. Fugacity fraction analysis (ƒƒ) indicated a net flux of DDTs from water to sediment, suggesting that vertical sinking was an important transport process in this area. Finally, the findings indicate that FDF contributed to DDTs input on ESIS by remobilizing contaminated past sediments and soils from the Doce River drainage basin. This contribution is expected to continue since a large amount of tailings is still stored in the river basin and estuary. These results highlight the importance of assessing the indirect impacts of large-scale land disasters on marine environments, and may be helpful in future interpretations of additional local trends and global inventories of legacy pollutants.
ABSTRACT
The Selenga River basin, located in southern Siberia, is an important component of the Lake Baikal ecosystem, and comprises approximately 80 % of the Baikal watershed. Within the Selenga River basin, two localized study regions were chosen. The first, the Selenga Delta, is one of the largest inland freshwater floodplains in the world and plays an important role in the ecosystem functioning of Baikal. It purifies the river waters before they enter the lake and acts as a refuge for many of Baikal's endemic species. The second location, the Gusinoozersk region, is southwest of Lake Baikal and the Selenga Delta, and was chosen as a more heavily industrialized region within the Selenga River basin. Anthropogenic activities, including industry, urban settlements, aquaculture and agriculture, have historically increased ecological damage within this area. We assessed possible drivers of changes in sedimentary organic matter (OM) composition within two shallow lakes (SLNG04 and Black Lake), located in the Selenga Delta and the Selenga watershed, respectively. We focused on individual n-alkanes, one of the most abundant and common lipids used to provide information on past vegetation and used multivariate statistics to disentangle changes in the sources of sedimentary OM over time. The depositional OM history of SLNG04B core can be divided in four zones: (i) major influence of non-emergent vascular plants, typically found in transitional environments (ca. 1835 to ca. 1875); (ii) increased influence of grasses/herbs (ca. 1880 to ca. 1910); (iii) transition from non-emergent vascular plants and grasses/herbs to submerged and floating macrophytes and phytoplankton (ca. 1915 to ca. 1945); (iv) maintenance of autochthonous OM from submerged and floating macrophytes and phytoplankton (ca. 1945 to ca. 2014). The depositional OM history of the Black Lake core can be divided in two main zones: (i) major influence of non-emergent vascular plants and submerged and floating macrophytes (ca. 1915 to ca. 1980); (ii) increased influence of grasses/herbs and phytoplankton (ca. 1980 to ca. 2010). Natural events (e.g., an earthquake in 1862 caused flooding and subsidence of much of the land surrounding SLNG04 lake and a further catastrophic flood event in 1897) and anthropogenic activities (e.g., nutrient pollution from expansion of agricultural and livestock population) changed the composition of sedimentary OM resulting in ecological shifts across trophic levels in the Selenga River basin.