Teores de mercúrio total e estimativa de risco à saúde humana em solos de manguezal contaminados por indústria de soda-cloro

Abstract

The Botafogo River estuary is located between the cities of Goiana and Itapissuma, coastal area of Pernambuco, and is the most relevant water resource among the coastal rivers that border the region, being responsible for the main water reservoir used to supply the local population. However, the activity of a chlor-alkali plant established close to the mangrove in the 1960s brought effluents containing Hg into the river, presenting potential for contamination in areas of mangrove forests, which could interfere with the health of the mangrove ecosystem and the community. This work aimed to evaluate the total Hg levels, relate them to the granulometry and chemical attributes of the soils and estimate the risk to human health in soils from two transects, located in different physiographic positions of the Botafogo River mangrove. For this, 3 soil profiles (0-40 cm) were collected at distances 0, 60, 120 and 180 meters from the margin of each transect during periods of low tide. The profiles were sectioned at depths 0-5, 5-10, 10-20, 20-30 and 30-40 cm and the particle size fractions, organic matter, pH, Eh and total Hg were determined. Based on the Hg results in the soils, the non-carcinogenic risk to human health was estimated. The pH and Eh values indicated slightly acidic to neutral soils and suboxic to anoxic environments, respectively, representing favorable conditions for Hg retention. Clay content predominated in the soils of Transect 1 (T1), while the sand fraction predominated in Transect 2 (T2). SOM values ranged from 144 to 424 g kg-1, with higher levels in the T1 profiles. Average Hg levels ranged from 0.2 to 15.3 mg.kg-1 in T1 and from 0.0 to 7.4 mg.kg-1 in T2. The Hg contents in T1 were higher compared to T2, possibly due to the position of the transect in the landscape and the greater accumulation of clay and OM, corroborated by the positive and significant correlations between Hg and clay, and between Hg and OM. When comparing the Hg values found with international reference levels, maximum Hg values were found to be up to 102 times higher than the international reference value TEL (Threshold Effect Level) and 15 times the PEL (Probable Effects Level). About 82% of samples exceeded the PEL, indicating that toxic effects on biota are likely. The health risk for children was greater than that for adults because they are organisms more sensitive to the toxicity of the metal. The main route of exposure was inhalation of Hg vapor. Contamination of soils in the Botafogo River estuary reached mangrove forest areas, highlighting the widespread Hg contamination in the area. The areas most contaminated by the metal pose risks to the riverside community.