Tracing of anthropogenic zinc sources in coastal environments using stable isotope composition

The use of zinc isotopes to trace anthropogenic sources in coastal areas has been tested in this study. We determined the stable isotopic composition of zinc in sediment cores, suspended particulate matter (SPM) and rocks collected at the Sepetiba Bay (southeastern Brazil), an estuarine lagoon heavily impacted by metallurgic activities. These isotopic signatures were compared with those from willemite ore, which represent the main mineral refined by the major industrial source of zinc. The aim was to test if this tracer system enables to identify sources and sinks of anthropogenic zinc and to reconstruct the temporal and spatial evolution of zinc contamination. The zinc isotopic compositions (expressed using the δ66Zn notation relative to the JMC 3-0749-L solution) showed significant variations in the sediment cores, the SPM, and willemite ore minerals, ranging between − 0.01 and + 1.15‰. Spatial and temporal analysis of sediments samples fit well in a model of mixing involving three main end-members: i) Terrestrial background (δ66ZnJMC = + 0.28 ± 0.12‰, 2σ); ii) marine detrital material (δ66ZnJMC = + 0.45 ± 0.03‰, 2σ); and iii) a major anthropogenic source associated with electroplating wastes released into the bay (δ66ZnJMC = + 0.86 ± 0.15‰, 2σ). Sediment cores collected in the mud flats showed high correlation between δ66Zn and zinc enrichment factors, suggesting good preservation of the isotopic records of natural and anthropogenic sources. The sediment core sampled from a mangrove wetland located in a zone impacted by the metallurgy presented levels of zinc up to 4% (sediment dry weight) and preserved the isotopic signatures of electroplating wastes, despite evidences that post depositional processes slightly changed the isotopic signatures in some layers from this core toward heavier δ66ZnJMC values (above + 1.0‰). A two component mixing model suggests contributions of this major anthropogenic Zn source up to nearly 80% during periods of electroplating activities. Our work suggests that Zn isotope compositions of sediments are reliable tracers of anthropogenic sources and, therefore, can be useful to improve environmental monitoring efforts in coastal systems

Rare earth element and radionuclide distribution in surface sediments along an estuarine system affected by fertilizer industry contamination

Site-specific contamination related to fertilizer industry activity was demonstrated by light rare earth element (REE) anomalies (sum of La, Ce, Pr, Nd, Sm, and Eu concentrations up to 4.141 mg kg−1) and radionuclides (210Pb and 226Ra activities up to 994 and 498 Bq kg−1, respectively) from industrial contamination, within a subtropical estuary (SE Brazil). Anthropogenic influence was also supported by the site-specific 210Pb and 226Ra distribution down the estuarine system. The distribution of REE and radionuclide contamination varied along the estuary, which reflected differing sedimentation patterns of phosphogypsum and/or phosphate ore pollutants as identified downstream from the source, likely influenced by sediment–hydrodynamic processes within the estuarine system. Redox- and ion exchange-sensitive pollutants are mobile at the fresh–sea water interface causing an uneven distribution of the pollutants, indicating that the phosphgypsum and/or phosphate ore pollutant deposition can be also influenced by physical and/or geochemical processes associated to estuarine systems