Caracterização e composição química de substâncias húmicas em área afetada e não afetada por mercúrio na região amazônica: São Luís do Tapajós (Itaituba-PA) e Caxiuanã (Melgaço-PA)

Abstract

Humic substances represent soil organic matter fractions resulting from microbiological decomposition processes of the organic matter present in an ecosystem. The fact that humic substances have different properties is what allows their individualized study, especially the fractions fulvic and humic acids. These properties are dependent on the edapho-climatic conditions peculiar to each environment. Studies have shown that mercury has a strong affinity for soil organic matter, especially humus. Mercury levels found in fulvic acid isolated from a non-mineralized and uncontaminated soil confirm the capacity of humic substances to bind to this metal of natural or anthropogenic origin. This work aimed to perform fractionation and determine the chemical composition in humic substances in mercury-affected and non-affected soils. Soil samples were collected at the beginning of the rainy season in November 1999 (São Luis do Tapajós) and December 1999 (Caxiuanã) at depths of 0-5cm, 5-10cm, 10-15cm, 15-20cm, 20-25cm, 25-30cm, 30-35cm. The soils were then separated into aggregate classes, using sieves with 2.00mm, 0.25mm and 0.053mm mesh, obtaining the following classes by depth> 2.00mm, > 0.25mm, >0.053mm and < 0.053mm. Subsequently, the humic substances were extracted using the methodology of Schnitzer, 1982. Using 20g of soil of aggregate class >0.25mm of each depth of the respective study areas and as extracting solution 0.1N Sodium Hydroxide. Points 1A, 1B and 1C from Caxiuanã Savanna and 2A,28 and 2C from Caxiuanã Forest showed identical dark colored material up to a depth of 20cm, meaning that the amount of organic matter that these ecosystems provide to the soil is very similar. On the other hand, the samples from São Luís do Tapajós, points 01, 02, 03, 04, presented dark colored material only at depths of 0-5cm. This may be related to the quality and quantity of organic matter present in the soil. The soils of Caxiuanã have a more uniform distribution of organic matter in depth than those of São Luís do Tapajós.