Cadmium behavior in a karst environment hydrological cycle.

Karst regions are important water providers, supplying approximately 25% of the world population. These areas present higher vulnerability to contamination due to hydrodynamics, which hampers the natural depuration of these waters until reaching the underground environment. High concentrations of cadmium (Cd) are observed in the São Miguel watershed, state of Minas Gerais, Brazil. This toxic element is generally and predominantly released into the atmosphere by burning materials that have Cd in their composition, potentially contaminating surface and groundwater. Therefore, the objective of the study is to map Cd concentrations in the hydrological cycle of the São Miguel karst watershed and, through natural background level values (NBL 90%) of rainwater, surface water and groundwater, to understand the seasonal behavior of this element, and to identify the most vulnerable areas to contamination. To achieve this goal, rainwater, surface, and groundwater seasonal monitoring were conducted in 87 sampling stations. A total of 335 samples were collected, distributed over a watershed area of 520 km2. Concentrations of cadmium above 1 µg/L were found in 21.49% of samples during the rainy season. The origin and distribution of Cd were related to rainfall. For rainwater samples, 90% presented Cd concentration of 3.06 µg/L. When these waters precipitate, they contaminate surface waters (NBL 90% = 1.50 µg/L) and groundwater (NBL 90% = 2.81 µg/L). This study presented a hydrochemical cycle map and proposed NBL values of Cd for surface water and groundwater, helping to understand how the environment is contaminated by this element.

Spatial monitoring of metals and As in coastal sediments of northern Chile: An evaluation of background values for the analysis of local environmental conditions.

To assess environmental conditions along the coast of northern Chile, 457 sediment samples were collected between 22° S and 28° S in order to evaluate the Cu, Zn, Pb, Ni, V, Cd, As and Al content as well as its corresponding relationship to nearby anthropogenic activities. In general, the results of most metals showed that bays without industrial activity accumulate lower concentrations of contaminant elements in the sediments and thus mostly represent natural conditions. The highest Cu, Pb and V levels were measured in coastal zones were different industrial mining activities have been developed during the last decades. Results of different indices of environmental evaluation and ecological impact suggest that, metal content of sediments from pollution-free zones characterized by similar oceanographic and geological conditions to those under study, would be the most appropriate background level for assessing the anthropogenic impact on coastal areas of northern Chile.