High-resolution multivariate analysis of the hydrochemical signature of water corridors in the upper Río de la Plata estuary, Argentina.

Major world river-estuaries integrate the hydrochemical characteristics of the basin with specific signatures which are maintained until complete mixing or discharge to the sea. The chemical signature of distinct water masses and the anthropogenic impact in the Upper Río de la Plata estuary (RLP) were evaluated by high-resolution continuous monitoring (i.e. every 200 m) of conductivity, turbidity, pH, temperature, chlorophyll a and coloured dissolved organic matter (CDOM), discrete analysis of suspended particulate matter (SPM) grain size composition combined with multivariate analysis (K-means clustering, Principal Component Analysis). The characteristic signatures of main RLP tributaries such as the Paraná River, yielding higher conductivity, CDOM, turbidity and coarser SPM, and the Uruguay River, with clearer, more eutrophic waters enriched in very fine SPM, were maintained 60 km seaward from the estuary head. Across the river, three water corridors with distinct signatures and variable widths (3-20 km) were identified reflecting the transition from Paraná to Uruguay River waters. Multivariate techniques also allowed the identification of a polluted coastal corridor (higher conductivity and CDOM and lower turbidity) impacted by wastewater discharges from the metropolitan Buenos Aires and La Plata cities extending 100 km seaward. The combined strategy of high-resolution monitoring, discrete sampling and multivariate techniques was a useful tool to identify water masses, corridors of flow and anthropogenic sources in a heavily urbanized estuary.

The use of biomimetic tools for water quality monitoring: passive samplers versus sentinel organisms.

To evaluate the performance of artificial and biological integrative sampling strategies, dissolved concentrations of polychlorinated biphenyl (PCBs) and metals (Cu and Mn) were measured with passive sampler devices (PSD) enclosing hydrophobic and chelating phases, and Asiatic clams were transplanted to a polluted area in the Rio de la Plata. Water concentrations based on PSD were compared with spot water samples collected at 0, 15, 32, and 63 days of exposition. PCBs and metals displayed linear accumulation kinetics both in PSDs and bivalves, but with different slopes. PCBs slopes were 2-27 times higher in bivalves (0.3-7.9 vs. 0.1-2.6 ng g-1 d-1 in PSDs) reflecting active filtration and uptake from particles, colloids, and dissolved phase, whereas metal slopes were 2.5-11 times lower in bivalves (0.04-0.18 vs. 0.10-2.00 µg g-1 d-1 in PSDs) suggesting metal bioregulation. Truly dissolved PCB concentrations from PSD (4.0-6.9 ng.l-1) represented average 13±4 % of PCB concentrations from filtered spot water samples reflecting the operational discrimination of the PSD diffusion membrane on competing dissolved and colloidal organic phases. In contrast, PSD dissolved Cu concentrations (2.3-8.2 µg l-1) were equivalent to the spot water values (3.2-3.8 µg l-1) suggesting that Cu speciation was adequately integrated by passive sampling. On the other hand, PSD-dissolved Mn concentrations (49±38 µg l-1) were higher (p<0.05) than those from spot water samples (7±11µg l-1) possibly due to phase changes of Mn distribution related to variable redox conditions in the water. Results evidenced that the PSDs are efficient accumulators of metals and organic compounds from the truly dissolved fraction.

Fatty acid alterations in the detritivorous Prochilodus lineatus promoted by opportunistic feeding on sewage discharges in the Río de la Plata estuary.

Muscle fatty acid profiles and PCB contents of the detritivorous species Prochilodus lineatus and its diet (stomach contents, settling particles and sediments) were analysed from reference and polluted areas of the Paraná-Rio de la Plata basin, to evaluate the alterations produced by opportunistic feeding on sewage discharges. Overall muscle fatty acid composition was dominated by saturated and monounsaturated 16 and 18 carbon (18 C-FA) components with reduced long-chain polyunsaturated fatty acids (LC-PUFA). Compared to sediments, settling particles and stomach contents were enriched in lipids and had a similar fatty acid composition. Opportunistic feeding on sewage detritus at Buenos Aires resulted in enhanced PCB and triglyceride accumulation, with higher proportions of 18 C-FA and lower proportions of 16:1 and LC-PUFA compared to fish from northern pristine reaches of the basin. Mid-Paraná showed intermediate values reflecting mixing of the North stock with migrating Buenos Aires P. lineatus identified by their lipid and contaminant profile. According to multivariate analyses, this geographical variation of fatty acid composition was strongly influenced by PCB concentration. Prochilodus lineatus assimilates the energy subsidy of sewage inputs through enhanced lipogenesis with dominant 18 C-FA and significant amounts of valuable LC-PUFA. This lipid alteration facilitates the bioaccumulation of PCBs which in turn may reinforce the adipogenic effect of sewage feeding.

Trace metals in settling particles from the sewage impacted Buenos Aires coastal area in the Río de la Plata estuary, Argentina.

Sediment traps deployed in Buenos Aires sewage outfall area collected a substantial amount of material (average mass flux 22 ± 12 g cm (2) year(-1)) with very high metal concentrations, mostly in the range of hazardous exposition for organisms (Zn: 138-671, Cu: 41-273, Cr: 44-255 and Pb: 26-260 µg g(-1)). The combination of high mass fluxes and concentrations results in huge metal fluxes (0.005-0.7 to 3.6-31 g m(-2) day(-1) for minor elements and Fe, respectively). Metal concentrations were correlated to the total mass flux and total organic carbon but with different trends for redox-sensitive Fe and Mn (negative) and anthropogenic elements (positive). This reflects the key role of organic discharges promoting anoxia with Fe and Mn evasion, and also contributing toxic metals.

Migratory behaviour of a dominant detritivorous fish Prochilodus lineatus evaluated by multivariate biochemical and pollutant data.

This paper studies the migration pathways and ranges of a dominant detritivorous fish Prochilodus lineatus along pollution gradients in the Río de la Plata basin using multivariate analysis of biochemical and pollutant data. Biochemical composition (water, ash, lipids, proteins, carbohydrates, neutral lipids classes and fatty acids), aliphatic hydrocarbons (ALI), polychlorinated biphenyls (PCB), linear alkylbenzenes (LAB) and organochlorine pesticides (OClP) were determined in muscle samples of P. lineatus collected in Metropolitan Buenos Aires, the lower Paraná River (Paraná: 200-1000 km from Buenos Aires) and the middle Paraná and Paraguay Rivers (North: 1000-1400 km north). Biochemical variables and pollutants exhibited large variability [Lipids 1.1-89.5% wet mass; ALI 1.4-413; LABs not detectable (n.d.)-115.2; PCBs n.d.-27.9; OClPs n.d.-11.8 µg g(-1) dry mass], due to the contrast of Buenos Aires with North fish. Fish from Buenos Aires were fatty (lipids 24.7 ± 12.3% wet mass), enriched in 18 carbon fatty acids and severely contaminated (ALI 152.4 ± 72.3; LABs 65.1 ± 26.4; PCBs 15.2 ± 6.8; OClPs 1.8 ± 1.9 µg g(-1) dry mass mean ±S.D.). In contrast, fish from North were lean (4.1 ± 3.1% wet mass), enriched in long chain (>20 carbons) polyunsaturated fatty acids, with average one to two orders of magnitude lower pollutant levels (ALI 41.2 ± 51.9; PCBs 2.2 ± 3.5; LABs 8.8 ± 21.1; OClPs 0.67 ± 0.75 µg g(-1) dry mass mean ±S.D.). Paraná showed intermediate values in all variables, denoting the mixing of different fish stocks. Based on principal component analysis, 14 outliers from 60 North and Paraná samples (representing 26 from 108 individual fish) were identified as pertaining to the Buenos Aires group with very similar lipid and pollutant levels. Data suggest that P. lineatus migrates a highly variable distance, exceeding 800-1000 km in multiple spatial and temporal overlapping ranges. Chemometric analysis of biochemical and pollutant data effectively discriminates fish according to the chemical signature acquired by detritus feeding in pristine and contaminated urban or industrial areas.

Vertical fluxes and accumulation of trace metals in superficial sediments of the Río de la Plata estuary, Argentina.

Superficial sediments and settling material collected in Buenos Aires coastal area were analyzed to evaluate the accumulation and sources of trace metals. Residual elements showed homogeneous sedimentary concentrations (Fe: 23,846 +/- 4,367; Ni: 10 +/- 2.7; Mn: 706 +/- 314 µg g(-1)) whereas anthropogenic metals presented exponentially decreasing offshore gradients (Zn: 98 +/- 69; Cr: 28 +/- 21; Cu: 19 +/- 15; Pb: 18 +/- 13 µg g(-1)). Anthropogenic impact was evaluated through metal-Fe relationships, Fe-normalized enrichment factors and sediment quality guidelines. The slopes of metal-Fe regressions from background sites were comparable to upper crust metal ratios, excepted Cr which is impoverished, and Mn which is diagenetically enriched. Metal-Fe relationships also hold for most 2.5 km offshore sites but with higher slopes denoting human influence, and are completely lost in 1-2.5 km sediments and trap material which plot over the regressions and exceed sediment quality guidelines.