Metais pesados em solos de manguezais em estuários da bacia Paraíba, Nordeste do Brasil

Abstract

The mangrove acts as marine nursery, geochemical filter and source of income for the population, however, the degradation and pollution of mangroves may favor the release of toxic substances such as heavy metals. In this sense, this study aimed to analyze the levels of iron (Fe), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), cobalt (Co) and its relationships with the physical and chemical attributes, and to evaluate soil quality through national and international guidelines. They collected three profiles in each of the four areas studied (Bar Mamanguape- PB; estuary of the river Botafogo- B; Canal Santa Cruz-CSC, the Timbó- T River estuary). Samples were collected with samplers for flooded soils and the samples were subjected to hydrogen potential analysis (pH), redox potential (Eh), total organic carbon (TOC), carbonates (CO3-), grain size and by acid digestion method 3051A. The near neutral pH (6.5 to 8.5) and Eh levels in suboxic (Eh 100-350 mV) and anoxic (Eh <100 mV) discloses a geochemical reducing environment. The predominance of fine particles (silt and clay) and organic matter are present in soils around the estuary B and PB1 and PB2 profile, except in the soil CSC estuaries, T and PB3 profile where there was a predominance of sand fraction by situate near mouth. High positive correlations (r> 0.70) were found between fine particles, TOC and metals studied. Environmentally available mercury levels in the estuary B were higher than the ERM (Probable effects level), ERL (Effects range low) TEL (Threshold effect level), PEL (Probable effects level), VP (Value prevention) and the VRQ (quality reference value); Ni exceeded the TEL in some depth in the estuary B profiles, while the soils of other estuaries have levels above the VRQ. Thus, it is possible to identify contamination of Hg and Pb in the B and CSC estuary profiles; Cu B, CSC and PB; Ni B, and CSC PB; and Fe in the estuary B and PB; while for the Co there was no contamination in any of the studied estuaries. The FE (Factor enrichment) and Igeo (Geo-accumulation index) reveal that the B estuary had a severely serious enrichment (EF> 25) and is highly to extremely polluted (Igeo class 5) for Hg, respectively ; and low-enriched (EF <3) to the other metals. The Levels of Hg (Above PEL) and Ni (Above TEL) can be causing toxicity to benthic organisms. From the cluster analysis it was observed that distinctly from the others, Botafogo River estuary is impacted by metals due to strong pressure of human activities on the north coast of Pernambuco region. As a result, mangrove soil into the river Botafogo stands out as one of the marine ecosystem most impacted by Hg.