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We determined values of antioxidant biomarkers catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST) and malondialdehyde (MDA) in two bivalve species from a subtropical system in Brazil. Differences in the biomarkers activities measured in digestive glands and gills sampled at two seasons and in sites with different levels of contamination were tested using univariate and multivariate analyses. Seasonality was the main factor accounting for overall variability. Significant SOD and GPx activities and increased levels of lipid peroxides were detected in summer, while CAT activity was higher in winter. However, biomarkers respond to complex environmental settings as indicated by the significant interaction between season and contamination level. We propose A. flexuosa as a candidate for monitoring studies with sampling occurring at a yearly timescale, and using C. rhizophorae is better suited for designs that include both seasons. • Baseline levels for antioxidant enzymes are provided fortwotropical and subtropical bivalve species. • Seasonal and spatial variation in the biomarker response wasdescribed in bivalves'gills and digestive glands. • Multivariate approaches, such as redundancy analysis (RDA), are suggested for multi-species and multi-biomarker studies. • The multivariate antioxidant response was species-specific and strongly affected by seasonality. • A. flexuosa is an appropriate candidate for monitoring studies with sampling occurring at a yearly timescale. • C. rhizophorae is better suited for designs that include both seasons. [ABSTRACT FROM AUTHOR]

Petroleum biomarkers (hopanes, terpanes and steranes) are frequently assessed in estuarine sediments as tracers of oil input. In order to compare distinct patterns of hydrocarbon accumulation in mudflats, salt marsh and mangrove, sediments from two transects (control and impacted areas) were sampled in Paranaguá Bay, SW Atlantic. Concentrations of n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and petroleum biomarkers (hopanes, terpanes and steranes) were determined, as well as bulk parameters (TOC, grain size and δ 13 C). N-alkanes concentrations were similar between control and impacted sites (respectively, 3.03 ± 1.20 μg g -1 and 4.11 ± 3.02 μg g -1 ) and reflected a high biogenic input. Conversely, PAHs and petroleum biomarker concentrations were three to six times higher in impacted site than the control site (respectively, 60.4 ± 23.3 ng g -1 and 22.0 ± 25.0 ng g -1 for PAHs and 197.7 ± 51.8 ng g -1 and 40.2 ± 32. ng g -1 for hopanes). Despite these differences, concentrations were lower than those reported for highly impacted areas worldwide. Diagnostic ratios and hydrocarbon parameters (e.g. total PAHs and total petroleum biomarkers) helped to distinguish human impact in the ecological zones, suggesting different sources and/or levels of weathering, confirmed by ANOVA tests. TOC played a fundamental role to the concentration of hydrocarbons, showing similar distributions along the transects. Petroleum biomarkers could clearly indicate the preferential sites of deposition and assign different levels of anthropic contamination by hydrocarbons, thus providing clear information about the chronic petroleum pollution in coastal sediments., (Copyright © 2019. Published by Elsevier Ltd.)