Oxidative stress in Laguncularia racemosa environmentally exposed to mercury and copper in two mangroves in the state of Rio de Janeiro, Southeastern Brazil

Resumo

Introduction: Mangroves are important ecosystems, frequently impacted by anthropogenic
activities (Mochel, 2016; Souza, et al., 2018). Rodrigo de Freitas Lagoon and Sepetiba Bay, in
the state of Rio de Janeiro, are highly urbanized mangrove areas exposed to both organic and
inorganic pollution. Metal assessments in mangrove plants displaying bioindicator potential, such
as White mangrove (Laguncularia racemosa), in these areas, however, are still lacking, and even
less so concerning oxidative stress effects. Objective: Determine the profiles of the toxic mercury (Hg) and essential copper (Cu) in L.
racemosa organs from Rodrigo de Freitas Lagoon and Sepetiba Bay and correlate their
concentrations to oxidative stress cellular damage biomarkers. Material and methods: Leaves, stems and roots from the two areas were freeze-dried, and 100
mg aliquots analyzed by ICP-MS for Cu and Hg determinations following acid digestion and
heating at 100 oC for 5 hours. Protein carbonylation and lipid peroxidation were determined by
UV-spectrophotometry at 450 and 535 nm, respectively. The Shapiro-Wilk test indicated data nonnormality, so nonparametric tests were applied. Results and conclusion: In Lagoa Rodrigo de Freitas, Cu ranged from 3.48 ± 5.72 to 7.37 ± 1.75
mg kg⁻¹, and Hg appeared in low levels (0.04 ± 0.00 to 0.0995 ± 0.0577 mg kg⁻¹) across plant
tissues. Lipid peroxidation was highest in stems (0.0044 ± 0.0033 mg kg⁻¹) and lowest in roots
(0.0001 ± 0.0019 mg kg⁻¹), while protein carbonylation peaked in roots (7.24 ± 6.38 mg kg⁻¹) and
leaves (6.88 ± 4.32 mg kg⁻¹). Significant correlations were found between Cu in roots and
peroxidation in leaves (r = 0.79), and Cu in stems and carbonylation in leaves (r = -0.75). In
Sepetiba, Hg was higher (up to 0.1914 ± 0.126 mg kg⁻¹ in leaves), and Cu showed strong
correlations with lipid peroxidation and protein carbonylation in various tissues (r = 0.66–0.76, p
< 0.05). No consistent Hg-biomarker correlations were observed. Correlations between Hg in soil
and in L. racemosa leaves have been previously observed in mangroves in estuaries in the state
of Espírito Santo, Brazil, reinforcing its potential as a bioindicator of metal contamination (Souza
et al., 2014).