Mercury levels in an environmentally protected estuarine area in Northeast Brazil: partitioning in the water column and transport to the ocean.

Abstract

In this study, total Hg concentrations (HgT) were determined in the suspended particulate matter (SPM) and the dissolved fraction of the water column to evaluate their behavior through a gradient of physical-chemical parameters in a continuum between rivers and the Serinhaém River estuary of the Pratigi Environmental Protection Area, a pristine environment without point sources of Hg contamination, located in Northeast Brazil. Twelve points were sampled, forming a river-estuary transect, and two samplings were carried out (April and September 2019). Significant spatial and temporal effects were detected only for particulate HgT and not for dissolved HgT. Considering both samplings, the mean HgT concentrations in SPM were 1112 ± 824 and 44 ± 33ng·g-1 in the river and estuary, respectively. Also, HgT concentrations in the dissolved fraction (1.61 ± 0.61ng·L-1) were below the limits established by environmental agencies (CONAMA = 2μg∙L-1 and USEPA = 1.4μg·L-1). Salinity and SPM concentrations were important predictors of HgT in the water column (R2 = 0.81, p < 0.0001; R2 = 0.56, p < 0.0001, respectively). Mercury transport to the ocean through SPM was 2kg∙year-1, 4000 times greater than the dissolved fraction.