Elsevier

Environmental Pollution

Volume 231, Part 1, December 2017, Pages 262-270
Environmental Pollution

Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends

https://doi.org/10.1016/j.envpol.2017.08.009Get rights and content

Highlights

  • A global inventory of Hg levels and species is done in Lake Titicaca hydrosystem.

  • Lake Titicaca exhibits low Total Hg and MMHg concentrations in water and sediment.

  • Lake Uru-Uru exhibits Hg levels 3 to 10 times higher than in Lake Titicaca.

  • Percentages of MMHg are high in all waters rising up from <1 to ∼50% of THg.

  • Enhanced in situ MMHg production by eutrophication controls Hg levels in fish.

Abstract

Aquatic ecosystems of the Bolivian Altiplano (∼3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and monomethylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3–10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to ∼50% THg from the oligo/hetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high %MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota.

Graphical abstract

Box plot presentation with error bars for percentage methylmercury over total mercury for filtered and unfiltered surface waters along the upstream - downstream gradient from Lake Titicaca to Uru-Uru. Vertical bar chart show the median (upper full line) and standard deviation (SD) of each data set (N is the number of samples).

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Introduction

The Bolivian Altiplano is one of the largest high plateaus in the world containing two large lakes, Lake Titicaca in the north part and Lakes Uru-Uru/Poopó in the central part of an endorheic system consisting in the Titicaca-Desaguadero-Poopó-Coipasa Salt Lake (Revollo, 2001, Delclaux et al., 2007). Lake Titicaca is the most important water resource of the Andean Altiplano, a major source of fish for ∼3 million people and the largest navigable water body in the world lying at an altitude of 3809 m above sea level (a.s.l.). Its ecological functioning and limnology have been widely investigated between 1980 and 2000 (Collot et al., 1983, Pourchet et al., 1994, Mourguiart et al., 1998, Dejoux, 1992). Nowadays, the ecological equilibrium of the region is disturbed by a recent but very intensive urban demography and the intensification of mining activities, fisheries and agriculture around the Lake. For example, Puno Bay, on the Peruvian side of Lake Titicaca, has been identified as a contaminated area by urban and industrial effluents since the 1980's (NorthCote et al., 1989). The most preoccupying issue on the Bolivian side of the Lake (Lago Menor – southern basin of the lake) is the extremely rapid development of El Alto city, which population increased from 95,000 inhabitants in 1976 to around 1.2 million according to the last census (Mazurek, 2012) with minimal land planning. Wastewater from El Alto city, its facilities, manufactures and small scale industries, are discharged in the Katari river, which flows to the Lago Menor with less than 50% of water treated (Chudnoff, 2009). Among the emitted pollutants (e.g., nutrients, traces metals and organic contaminants) (Duwig et al., 2014, Archundia et al., 2017), mercury (Hg) contamination is one of the preoccupying issues in this fragile ecosystem. So far, only three studies focused on Hg contamination in the coastal areas of the great Lake Titicaca (Gammons et al., 2006, Molina and Point, 2014, Monroy et al., 2014) revealing high Hg concentrations in all fish species collected in the northern part of the Lago Mayor, particularly at the Mouth of the Ramis River (up to 1840 ng g−1 THg, dw in Orestias agassii) where intense gold mining activities are documented. Hg levels in fish muscle from other coastal areas of the Lago Mayor where found below regulatory health guidelines. No data exists yet in Lago Menor which is considered as the most productive area and is also impacted by anthropogenic inputs.

Downstream Lake Titicaca, Lake Uru-Uru, a man-made reservoir, combines diverse metal and organic pollutions since it receives important discharges from urban and mining activities. Recently, several studies evaluating Hg contamination in Lake Uru-Uru have highlighted high concentrations and percentages of toxic MMHg in the water column and biota (Molina, 2015, Alanoca et al., 2016a, Alanoca et al., 2016b, Lanza et al., 2016).

In this paper, we report for the first time, a complete inventory of Hg levels and speciation, including inorganic Hg(II), elemental Hg (Hg0) and mono-methylmercury (MMHg), from samples collected between 2010 and 2016 in the different compartments of Lake Titicaca and Uru-Uru. Hg was measured in the atmosphere (total gaseous Hg - TGM), atmospheric fallouts (i.e., filtered and particulate Hg), water column (i.e., filtered, particulate and dissolved gaseous Hg), sediment (i.e., porewater and solid particles) and biota (i.e., plankton, fish and birds). Concentrations of Hg species are compared with previous studies performed in large or elevated lakes. Biogeochemical and anthropogenic factors influencing the sources, distribution and speciation of Hg in the different limnological compartments and selected sentinel organisms are discussed. Based on these discussions and the observed spatial gradients in the ecosystem, we finally propose scenarii of possible future trends in Hg species levels and their impacts on this ecosystem.

Section snippets

Lake Titicaca

Lake Titicaca (Fig. 1a) comprises of two nearly separate basins: the great lake named “Lago Mayor” or “Lago Chucuito” (7131 km2; mean depth = 100 m; max depth = 285 m) and the smaller lake named “Lago Menor” or “Lago Huiñaimarca” (1428 km2; mean depth = 9 m; max depth Chua trough = 40 m) (Dejoux, 1992). The two basins are connected by the Strait of Tiquina and a single outlet for the lake, the Río Desaguadero, which drains out the southern end of Lago Menor to the central Altiplano (i.e., to

Mercury speciation in air and atmospheric fallouts of Lake Titicaca

Total gaseous mercury (TGM) concentrations in air on the shore of Lake Menor were not significantly (p > 0.05) different between the end of the wet (1.11 ± 0.23, N = 1407) and of the dry season (0.82 ± 0.20 ng m−3, N = 1037). Measured TGM concentrations were in the lowest range of the background concentrations (Table 1) reported for the northern (1.5–2.5 ng m−3) and for the southern hemispheres (mean GEM: 0.84–1.09 ng m−3) (Meuleman et al., 1995, Lin and Pehkonen, 1999, Vette et al., 2002,

Acknowledgments

This work is a contribution to the LA PACHAMAMA project (ANR CESA program, No ANR-13-CESA-0015-01, PI: D. Amouroux: [email protected]), COMIBOL project (INSU CNRS/IRD EC2CO Program, PI: D. Point: [email protected]), EUTITICACA project (founded by the Impuestos Directos a los Hidrocarburos IDH administrated by the Universidad Mayor de San Andrés, PI: D. Achá: [email protected]) and TRACISOMER supported by a grant from Labex OSUG@2020 (PI: S. Guédron: [email protected]). S.

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    This paper has been recommended for acceptance by Prof. W. Wen-Xiong.

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