Baseline investigation of (methyl)mercury in waters, soils, sediments and key foodstuffs in the Lower Mekong Basin: The rapidly developing city of Vientiane (Lao PDR)

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Highlights

  • First inventory of mercury (Hg) contamination in Vientiane city ecosystem

  • Hg concentrations were low in water, soil, sediments, rice and fish.

  • Dissolved monomethyl-Hg concentrations were low in surface and pore water.

  • Low Hg levels reflect the essentially non-industrialized status of the capital.

  • Low environmental Hg-attributable health risks for the local population

Abstract

We report here the first inventory of mercury (Hg) contamination in the ecosystem of Vientiane city, a representative emerging city bordering the Mekong River. Total Hg (THg) concentration in soil and sediments of both contrasting non-urbanized (wetland, rice paddy, Mekong River) and urbanized areas (wastewater canal and associated wastewater irrigated wetland) was low (8 to 101 ng g 1), reflecting the essentially non-industrialized status of the capital. Dissolved THg (2.2 ± 2.2 ng l 1) and monomethyl-mercury (MMHg) concentrations (0.06 ± 0.09 ng l 1) were also low in both surface and soil or sediment pore water with higher concentrations (up to 9 ng g 1 THg and 0.53 ng g 1 MMHg) measured in wetland and rice paddy suboxic waters. Dissolved organic carbon was identified as the main carrier in surface water for dissolved Hg transport towards the Mekong River. The measurement of low THg concentrations in rice (6.4 ± 1.0 ng g 1) and fish (51 ± 40 ng g 1) sampled in rice paddies and in the Mekong River confirmed the pristine state of the ecosystem of Vientiane area. Based on these data, we evaluated a low environmental Hg-attributable health risk for the local population whose diet relies on both fish and rice.

Introduction

Mercury (Hg) contamination of tropical ecosystems has been studied in many countries around the world, in part because of the perceived threats to the local human population arising from the consumption of contaminated fish and rice (Brabo et al., 2000, Feng et al., 2008, Hall et al., 1997, Kuwabara et al., 2007). Among Hg species, monomethyl-mercury (MMHg) has been reported as the most dangerous species for local populations (Cheng et al., 2009, Fitzgerald and Lamborg, 2003, Zahir et al., 2005) in part due to its ability to biomagnify in the aquatic food web (Boudou et al., 2005, Durrieu et al., 2005). The main anthropogenic sources of Hg reported in southern tropical ecosystems are mining activities (i.e., gold and silver mining), industrial waste, fuel and coal combustion and the use of wastewaters for agricultural irrigation (Feigin et al., 1991, Swain et al., 2007).

Currently, little information is available regarding Hg contamination of the Lower Mekong Basin, and in particular in Laotian ecosystem where no published data on Hg are currently available. The rapid growth of the main cities located along the Mekong River during the last few decades, might be a potential source of Hg contamination for ecosystems through wastewater irrigation and waste, fuel or coal combustion (Feigin et al., 1991, Swain et al., 2007). Notably, Vientiane city (Lao PDR) has almost doubled its population during the past 15–20 years, now approaching 300,000 people (Rafiqui and Gentile, 2009). Despite this rapid expansion, Vientiane remains largely non-industrial with the urban fabric of the city being interspersed with paddy fields and orchards, rather than factories (Rafiqui and Gentile, 2009). Wastewater treatment systems are largely absent in the city and most untreated wastewaters from the urban area are discharged into the Houay Mak Hiao (H.M.H.) canal and thence to the large That Luang wetland, where the local population fish and use the water for the irrigation of rice paddies (Whelan et al., 2007).

In this context, we tried to assemble the first inventory of Hg distribution in the aquatic ecosystem of the emerging Vientiane city capital which combines both non-urbanized and urbanized areas. A special emphasis was placed on Hg speciation measurements (i.e., THg and MMHg) in the dissolved phase and THg was measured in the particulate phases of soils and sediments to evaluate the distribution of Hg in both urbanized parts of the city (i.e., the wastewater canal, agricultural areas) and “non-urbanized” areas such as wetlands and the Mekong River. We also measured Hg concentrations in a limited set of terrestrial (rice) and river (i.e., bottom feeder and carnivorous fish) key food stuffs collected in Vientiane in rice paddies and in the Mekong River, respectively, to evaluate potential health risks for the local population.

Section snippets

Geographic settings

Lao People's Democratic Republic (Lao PDR) is one of the poorest and least developed countries in South-East Asia (Kaufmann, 2003) and with the largest access to the Mekong River. Of the total population (~ 6.2 million inhabitants in 2008, World_Bank, 2010), 65% live along the Mekong and adjacent lowlands (Kaufmann, 2003). Agriculture remains the major sector of the economy providing more than 34% of the Gross Domestic Product (GDP) and employing over 80% of the labor force (NAFRI, 2008). Most

Baseline inventory of mercury in soil and sediment

Total mercury concentrations ([THg]) measured in soil and sediment of Vientiane area (Fig. 2) were low, being in the range of concentrations found in the Mekong River delta sediments (22–90 ng g 1, Cenci and Martin, 2004) or in other non-urbanized environments (e.g., 30–100 ng g 1, Heyes et al., 2000, Roulet and Lucotte, 1995) and far below the probable effect concentration (PEC) for Hg (1060 ng·g 1); the concentration above in which harmful effects are likely to be observed in sediment-dwelling

Conclusion

Regarding Hg contamination, the ecosystem of Vientiane city district is in a pristine state according to low concentrations of THg (and MMHg) measured in water, soil and sediment of both non-urbanized and urbanized areas of the city and to its non-industrialized status. Although this set of data is not exhaustive, it presents the first baseline inventory of Hg and MMHg in Lao PDR which could be used as a baseline reference in the region for future work with regard to the extremely rapid

Acknowledgments

This study was funded by the European Union FP6 funded CALIBRE Asia-Link Programme (Contract No. KH/Asia-Link/04 142966). The authors acknowledge Associate Professor Lammai Phiphakhavong, Dr Bounthanh Bounvilay and students from the National University of Laos (Lao PDR) for their cordial welcome, help and advice in the field work, including sampling site selection. We also acknowledge the Mekong River Commission (MRC) based in Vientiane, who performed the sampling of biota along the Mekong

References (80)

  • K.A. Francesconi et al.

    Mercury contamination in a semi-enclosed marine embayment: organic and inorganic mercury content of biota and factors influencing mercury levels in fish

    Mar. Environ. Res.

    (1992)
  • S. Guédron et al.

    Mercury speciation in a tropical soil association; consequence of gold mining on Hg distribution in French Guiana

    Geoderma

    (2009)
  • S. Guédron

    Amazonian former gold mined soils as a source of methylmercury: evidence from a small scale watershed in French Guiana

    Water Res.

    (2011)
  • S. Guédron

    Tidal cycling of mercury and methylmercury between sediments and water column in the Venice Lagoon (Italy)

    Mar. Chem.

    (2012)
  • S. Guédron et al.

    Atmospheric mercury incorporation in soils of an area impacted by a chlor-alkali plant (Grenoble, France): contribution of canopy uptake

    Sci. Total Environ.

    (2013)
  • M. Horvat

    Total mercury, methylmercury and selenium in mercury polluted areas in the province Guizhou, China

    Sci. Total Environ.

    (2003)
  • P.J. Lechler

    Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira River basin, Brazilian Amazon: a function of natural enrichments?

    Sci. Total Environ.

    (2000)
  • B. Liu

    Insights into low fish mercury bioaccumulation in a mercury-contaminated reservoir, Guizhou, China

    Environ. Pollut.

    (2012)
  • P.D. Maia

    Mercury distribution and exchanges between the Amazon River and connected floodplain lakes

    Sci. Total Environ.

    (2009)
  • O. Malm

    An assessment of Hg pollution in different goldmining areas, Amazon Brazil

    Sci. Total Environ.

    (1995)
  • B. Muresan et al.

    The biogeochemistry of mercury at the sediment–water interface in the Thau lagoon. 1. Partition and speciation

    Estuar. Coast. Shelf Sci.

    (2007)
  • J.L. Parker et al.

    Preservation and storage techniques for low-level aqueous mercury speciation

    Sci. Total Environ.

    (2005)
  • N. Perttu et al.

    Characterization of aquifers in the Vientiane Basin, Laos, using magnetic resonance sounding and vertical electrical sounding

    J. Appl. Geophys.

    (2011)
  • B. Quémerais et al.

    Mercury distribution in relation to iron and manganese in the waters of the St. Lawrence River

    Sci. Total Environ.

    (1998)
  • P.S. Rafiqui et al.

    Vientiane

    Cities

    (2009)
  • B. Rondeau et al.

    Hydrological and biogeochemical dynamics of the minor and trace elements in the St. Lawrence River

    Appl. Geochem.

    (2005)
  • F. Roos-Barraclough

    An analytical protocol for determination of total mercury concentration in solid peat samples

    Sci. Total Environ.

    (2002)
  • M. Roulet

    Distribution and partition of total mercury in waters of the Tapajos River basin, Brazilian Amazon

    Sci. Total Environ.

    (1998)
  • M. Roulet

    The geochemistry of mercury in central Amazonian soils developed on the Alter-do-Chao formation of the lower Tapajos River Valley, Para state, Brazil

    Sci. Total Environ.

    (1998)
  • P. Selvendiran et al.

    Wetland influence on mercury fate and transport in a temperate forested watershed

    Environ. Pollut.

    (2008)
  • S.M. Ullrich et al.

    Mercury contamination in the vicinity of a derelict chlor-alkali plant — Part II: contamination of the aquatic and terrestrial food chain and potential risks to the local population

    Sci. Total Environ.

    (2007)
  • M.J. Whelan

    The behaviour of linear alkyl benzene sulphonate under direct discharge conditions in Vientiane, Lao PDR

    Water Res.

    (2007)
  • F. Zahir et al.

    Low dose mercury toxicity and human health

    Environ. Toxicol. Pharmacol.

    (2005)
  • A.C. Barbosa et al.

    Mercury biomagnification in a tropical black water, Rio Negro, Brazil

    Arch. Environ. Contam. Toxicol.

    (2003)
  • N.S. Bloom

    On the chemical form of mercury in edible fish and marine invertebrate tissue

    Can. J. Fish. Aquat. Sci.

    (1992)
  • A. Boudou et al.

    Synergic effect of gold mining and damming on mercury contamination in fish

    Environ. Sci. Technol.

    (2005)
  • E.D. Brabo et al.

    Mercury contamination of fish and exposures of an indigenous community in Para State, Brazil

    Environ. Res.

    (2000)
  • L. Chen

    Determination of selenium concentration in China and effect of fertilization of selenite and selenate on selenium content of rice

    J. Agric. Food Chem.

    (2002)
  • J.V. Cizdziel et al.

    Mercury concentrations in fish from Lake Mead, USA, related to fish size, condition, trophic level, location, and consumption risk

    Arch. Environ. Contam. Toxicol.

    (2002)
  • M. Coquery et al.

    The distribution of dissolved and particulate mercury in three Siberian estuaries and adjacent arctic coastal waters

    Water Air Soil Pollut.

    (1995)
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    Electronic Supplementary Information (ESI) available: Supplementary figures SI.1 and SI.2 show multi-resolution Electrical Resistivity images obtained at the non-urbanized wetland (WL) and rice paddy (RP) sites, Supplementary Table SI.3 shows water chemical parameters obtained in the Vientiane district area, Supplementary Table SI.4 shows the biota characteristics, Supplementary figure and Table SI.5 show the map of complementary biota sampling locations along the Mekong River (from the 2011 MRC campaign) with associated Hg concentrations and locations of known gold mining locations, and Supplementary Table SI.6 shows the biota key characteristics, including mercury concentrations.

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