How geological origin influences the quality of sand and the environmental impacts of its mining, Bahia state, Northeastern Brazil

The highly increasing demand for sand in Northeastern Brazil, due to governmental economic incentive focused to this region, has necessitated the opening of new extraction mines, generally without adequate environmental control. This study aimed to assess several sand extraction activities in the Recôncavo territory, Bahia state—area with high variability in sedimentary deposits—by evaluating the quality of the sand and the extraction impacts according to the geological basement. The methodology consisted of field research, using satellite images and maps for characterization, application of the environmental and economic impact checklists, and analysis of organic matter, particle size distribution, and salt content in 35 samples from different sand mines. The sands were classified as white sand (from Neossols/weathered aeolian sandstones), brown sand (from mature soils), and river sand. A strong relation between the geological origin and sand type and quality was established. Although the river sand appears to be the best option for extraction with regards to sand quality and low environmental impacts, the white sand derived from Jurassic sandstones is intensively extracted due to easy access, availability of wide deposits, and visual quality and homogeneity. However, the white sand has an inadequate particle distribution due to its poor gradation (aeolian selection of fine particle) and high environmental impacts due to its location in wet tropical ecosystem dominated by the Atlantic forest and the erosion of sandy soils. We demonstrated that the knowledge of lithology is fundamental for mapping new potential sand mines and minimizing the generated impacts.