Historical Analysis of Environmental Pollution in Santos Estuary: Histological Study of Mytella falcata (Orbigny, 1846) Gills as Bioindicator.

Historically, the Santos estuary illustrated a scenario of pollution and environmental catastrophes. In 1980, it was called the Vale da Morte (Death Valley), after the public resonance and mitigation measures became a model of environmental recovery. This study aims at assessing the ecosystem health of Santos estuary using Mytella falcata bivalve as bioindicator, and histopathology as biomarker. Bivalves were collected at three sample sites: Site A, located in Branco River with no industrial impact; Sites B, located in Barnabé Island, at the left bank of Santos Port; Site C, located next to Companhia Siderúrgica Paulista, in direct contact with industrial effluents. The collected animals had their gills dissected, fixed, and processed according to the histological routine. The tissue sections were dyed with hematoxylin and eosin to identify morphological changes. To analyze the slides, we used a disorder classification system and frequency index assignment to quantify the disorders observed. For the statistical background, tests of normality and of significant difference among the sample sites were performed. Results showed severe disorders in organisms from Sites B and C, such as tumors; however, the Site B revealed more expressive complications, such as necrosis. In contrast, Site A presented only mild disorders, such as infiltration. By analyzing the results and comparing environmental data, it is possible to affirm that the pollution status on the Santos estuary remains similar to the last histopathology study published, approximately 10 years ago, pointing out high concentrations of contaminants that directly affect the ecosystem and the organisms' health. [ABSTRACT FROM AUTHOR]