The rio Rato located in Itaituba, SW of Pará State, is the principal mercury mining center of the region. The surveied stretch of approximatly 60 km, suffers a great environmental impact, due to gold mining activities. Two field campaigns were conducted and 161 samples were collected for analysis. Total mercury content was determined by cold vapor atomic absorption (CVAS), prior to chemical diggestion with H2SO4, HNO3 and V2O5. The mercury concentration was determined in stream sediments, mining tailings, soils and black earth archeological soils. Organic carbon and loss on ignition (LOI) were also determined to correlate with mercury data. Statistical parameters, such as minimum, maximum, average and standard deviation were used to evaluate the pollution degree of the area and also for comparison with data from other studies. Samples were distributed in seven groups according to field campaign period, type of sample and sample site. For all types of samples, the results obtained from the first field campaign were higher than those from the second campaign, indicating that mining activities are more intense during the dry season. Significant correlation between mercury concentrations and other two variables (organic carbon and LOI) was observed only in a few sample. This observation support the alleatority of the contaminations, and shows that mercury distribution depends on the type of explotation, season, granulometry and sample location. Most samples show mercury concentrations greater than the regional background, which represents a general enviromental contamination.
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