Hydrochemistry and trace metals in water and sediments in forest coastal wetlands influenced by tidal regime in the middle Río de la Plata estuary, Argentina.

Coastal wetland ecosystems are of utmost importance in regulating the mobility and distribution of elements in water and sediments, being the flooding by tidal events a recurrent process that strongly controls the hydrodynamics of the system. The aim of this work is to assess the control of the tidal regime and anthropogenic influence on the dynamics of some trace metals in water and sediments in the Punta Lara Natural Reserve situated in the Río de la Plata littoral. For that purpose, relationship between tidal flows, surface water and groundwater was evaluated. Also, hydrochemistry was analyzed based on the study of major ions and trace metals, being the presence of high concentrations of elements in groundwater, such as Fe and Mn, probably favoured by redox processes associated with organic matter decomposition in the water - sediment interaction. Sediments in the wetland register deficient to minimal enrichment in most of the studied trace metals despite the numerous contributions that the Río de la Plata receives in relation to dissolved and particulate trace metals from diverse anthropogenic contributions. Despite that, there is a moderate enrichment in Pb and Cr in the surface sediments of the wetland. The data analyzed within the natural reserve in relation to the chemical composition of the water and sediments of the coastal wetland showed the strong influence of the tidal regime over the area.

Nutrient structure dynamics and microbial communities at the water-sediment interface in an extremely acidic lake in northern Patagonia.

Lake Caviahue (37° 50 'S and 71° 06' W; Patagonia, Argentina) is an extreme case of a glacial, naturally acidic, aquatic environment (pH ~ 3). Knowledge of the bacterial communities in the water column of this lake, is incipient, with a basal quantification of the bacterioplankton abundance distribution in the North and South Basins of Lake Caviahue, and the described the presence of sulfur and iron oxidizing bacteria in the lake sediments. The role that bacterioplankton plays in nutrient utilization and recycling in this environment, especially in the phosphorus cycle, has not been studied. In this work, we explore this aspect in further depth by assessing the diversity of pelagic, littoral and sediment bacteria, using state of the art molecular methods and identifying the differences and commonalties in the composition of the cognate communities. Also, we investigate the interactions between the sediments of Lake Caviahue and the microbial communities present in both sediments, pore water and the water column, to comprehend the ecological relationships driving nutrient structure and fluxes, with a special focus on carbon, nitrogen, and phosphorus. Two major environmental patterns were observed: (a) one distinguishing the surface water samples due to temperature, Fe2+, and electrical conductivity, and (b) another distinguishing winter and summer samples due to the high pH and increasing concentrations of N-NH4+, DOC and SO42-, from autumn and spring samples with high soluble reactive phosphorus (SRP) and iron concentrations. The largest bacterial abundance was found in autumn, alongside higher levels of dissolved phosphorus, iron forms, and increased conductivity. The highest values of bacterial biomass were found in the bottom strata of the lake, which is also where the greatest diversity in microbial communities was found. The experiments using continuous flow column microcosms showed that microbial growth over time, in both the test and control columns, was accompanied by a decrease in the concentration of dissolved nutrients (SRP and N-NH4+), providing proof that sediment microorganisms are active and contribute significantly to nutrient utilization/mobilization.

Assessing the transformation products and fate of Oxytetracycline by simulated aerobic degradation tests.

Oxytetracycline (OTC) is a widely used broad-spectrum antibiotic, whose presence in water and sediments was reported in various regions of the world. The effects of OTC and other tetracyclines on the environment have been intensively studied although many of their transformation products (TPs) formed in the environment and their impact have not been yet fully characterized. Abiotic and biotic degradation tests under aerobic conditions at two pH values were carried out using OTC in artificial water/sediment systems to assess the effect of these variables on the environmental fate of the pollutant. HPLC-MSn was employed to detect and identify the main degradation products and pathways. Several transformations involved in the process were identified including alcohol oxidation, decarbonylation and hydroxylation. Differences in TPs and kinetics were found among degradation conditions, remarking a faster degradation of both OTC and TPs in the presence of microorganisms and at lower pH values. In summary, a total of 44 TPs were detected and structures were proposed for 20 of them, none of them having been previously reported. Furthermore, OTC degradation generated 24 TPs which remained in either solution or sediment, although none of them displayed higher algae toxicity than OTC. These results might be useful for planning future remediation and monitoring strategies.

How did a tailings spill change the distribution of legacy organochlorine compounds in a Southeast Atlantic inner shelf area: Is a hidden danger being transferred to the ocean?

Polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT) were evaluated in water and sediments from the Espírito Santo Inner Shelf (ESIS), Brazil, three years after the Fundão dam failure (FDF). We discuss the levels, sources, fate, and current environmental risks of these contaminants on temporal and spatial scales. In addition, the associated coastal dispersion patterns, water-sediment exchange trends, and environmental alterations were also discussed. Low contributions and no environmental risks were verified for PCBs after FDF. However, the low concentrations and frequency of occurrence in the samples did not allow for further reliable conclusions regarding the source of this contaminant. In contrast, hazard risk has been detected for DDTs in water and sediments. In sediments, there were a significant increase in level (up to 13.42 ng g-1; outlier = 369.6 ng g-1), inventory (maximum = 35.98 ng cm-2) and mean total mass (21.1 ± 39.4 kg) of DDTs after FDF. The integrated assessment of the spatial distribution in water and sediment suggests that DDTs was released from the Doce River, travelled south by the water column, and returned to the mouth region by northward sediment transport, where it accumulated. However, intense rainfall increased the input of DDTs to the ESIS and may have also altered its spatial distribution. Fugacity fraction analysis (ƒƒ) indicated a net flux of DDTs from water to sediment, suggesting that vertical sinking was an important transport process in this area. Finally, the findings indicate that FDF contributed to DDTs input on ESIS by remobilizing contaminated past sediments and soils from the Doce River drainage basin. This contribution is expected to continue since a large amount of tailings is still stored in the river basin and estuary. These results highlight the importance of assessing the indirect impacts of large-scale land disasters on marine environments, and may be helpful in future interpretations of additional local trends and global inventories of legacy pollutants.

Innovative microcosm experiments for the evaluation of the regeneration rates of nutrients in sediments of a hypersaline lagoon.

The aim of this study was to evaluate the regeneration of nutrients from the sediments to the water column in varying salinities, with an innovative experiment that closely simulates real environment. In vitro experiments were carried out simulating six scenarios with two sediment types (low carbonate and high carbonate). Local water and sediments were added to microcosms where circulation was forced. Results showed nitrogen release from low carbonate sediment in the lagoon, mixed and seawater (1.69, 4.68 and 7.36 µmol m-2 day-1, respectively). Phosphate diffusive fluxes were positive in lagoon water and low carbonate sediment (2.24 µmol m-2 day-1), negative with mixed water (-0.30 µmol m-2 day-1) and seawater (-0.51 µmol m-2 day-1). A phosphate release surge was observed in the low-carbonate sediment with overlying mixed water and seawater that, in the natural environment, may boost primary production.

Mercury distribution in different environmental matrices in aquatic systems of abandoned gold mines, Western Colombia: Focus on human health.

Total mercury (THg), methylmercury (MeHg) in water, sediments, macrophytes, fish and human health risks were analyzed and assessed from abandoned gold mining ponds (AGMPs)/ mining areas in Western Colombia to know its present environmental condition. Concentrations of THg in water (avg. 13.0 ± 13.73 ng L-1) was above the EPA threshold level (12 ng L-1), suggesting possible chronic effects. Sediment sample revealed that the ponds are methylated (%MeHg: 3.3-11). Macrophyte Eleocharis elegans presented higher THg content in the underground biomass (0.16 ± 0.13 µg g-1 dw) than in the aerial biomass (0.05 ± 0.04 µg g-1 dw) indicating accumulation of THg. MeHg was the most abundant chemical species in fish (MeHg/THg: 83.2-95.0%), signifying higher bioavailability and its risk towards human health. Fish samples (15%) indicate that THg were above WHO limit (0.5 µg g), particularly in Ctenolucius beani, Hoplias malabaricus and lowest in Sternopygus aequilabiatus and Geophagus pellegrini. Bioaccumulation and biomagnification of MeHg were higher in the carnivores representing a source of exposure and potential threat to human health. Fulton's condition factor (K) for bioaccumulation indicate a decrease with increasing trophic level of fishes. Overall results suggest, mercury species found in different AGMPs compartments should be monitored in this region.

Occurrence and fate of pesticides in the Argentine stretch of the Paraguay-Paraná basin.

The Argentine stretch of the del Plata basin crosses regions devoted to extensive and intensive agriculture mostly with chemical pest control. The utilization of pesticides in the region has increased 900% in the last two decades associated with the introduction of biotech crops and direct-seeding techniques. Our objective was to study the occurrence, concentration, and fate of pesticides in surface water and bottom sediments of the principal tributaries and main watercourse of the Paraguay-Paraná River. We sampled 22 sites in the distal positions of the main affluents and main watercourse of the Paraná and report here results from two monitoring campaigns (2010-2012). Surface water and bottom sediments were analyzed according to standardized methods by matrix-solid-phase dispersion and liquid-liquid extraction, respectively. Twenty-three pesticide compounds were analyzed by gas chromatography. The results from both campaigns indicated a generalized but variable distribution in the concentrations detected throughout the basin. The ranges of total measured pesticide concentrations in water and sediments were, respectively, 0.004-6.62 µg/l and 0.16-221.3 µg/kg dry weight. Endosulfans, cypermethrin, and chlorpyrifos were ubiquitous compounds in both environmental compartments and quantitatively the most relevant. All concentrations detected in water were over the recommended guidelines for the protection of aquatic biota. The partitioning indicated a higher affinity for the sediments. Agricultural activity is the source of pesticide-pollution loads, transported by tributaries that reach the main watercourse and alter the quality of the aquatic ecosystem.