Seasonal and species-specific arsenic and mercury accumulation patterns in two estuarine fishes from a tropical and highly impacted bay in southeastern Brazil

Although arsenic and mercury pollution has been reported worldwide, their concentrations in fish are rarely monitored monthly, which limits the detection of fluctuations associated with changes in environmental conditions and/or biological factors. This study evaluated total arsenic (AsT) and total mercury (HgT) concentrations in the muscle of the catfish Genidens genidens (n = 100) and the whitemouth croaker Micropogonias furnieri (n = 108) from two sites of Guanabara Bay, a highly impacted estuary in southeastern Brazil. The monthly mean AsT concentrations were higher than those of HgT in both species in all months (AsT: 3.73–27.8 and 0.89–3.10 mg·kg -1 ; HgT: 0.15–0.35 and 0.03–0.08 mg·kg -1 wet weight in G. genidens and M. furnieri , respectively), and G. genidens showed higher AsT and HgT than M. furnieri , also within the same site and month. AsT in M. furnieri tended to be higher during the rainy season, although this difference was partly associated with sampling site. AsT was positively associated with bottom temperature in G. genidens , with a similar but non-significant tendency in M. furnieri , whereas precipitation was not significantly correlated with either element. HgT was positively associated with body size in G. genidens , whereas AsT was negatively associated with body size in M. furnieri , and juvenile M. furnieri showed higher HgT during the rainy season. The contrasting As and Hg patterns may reflect different exposure patterns within the same estuarine system, emphasizing the need to consider species choice, life stage, sampling site, and season in estuarine fish biomonitoring.