Mercury in soils impacted by alluvial gold mining in the Peruvian Amazon

https://doi.org/10.1016/j.jenvman.2021.112364Get rights and content

Highlights

  • Hg levels in gold mine spoil soils were below upper limits environmental quality standards.

  • Vegetation, soil organic matter and pH explain Hg variation in soils.

  • Uncovered mine spoils with leaching processes disperse Hg in the environment.

  • Recolonization with vegetation increases soil organic matter, decreases pH, thus enhancing Hg in soils.

Abstract

Gold mining is the largest source of mercury (Hg) pollution worldwide. The discharge of mercury in the environment bears direct human health risks and is likely to increase cascading effects throughout local food chains. In the Peruvian Amazon the mining process consists of slashing and burning trees, followed by extraction of gold-bearing sediment, amalgamation with Hg and gold recovery, leading each year to the degradation of 6,000-10,000 ha and the release of 180 metric tons of Hg per year to the enviroment. The purpose of this study was to determine soil Hg levels in soils of abandoned alluvial gold mine spoils and undisturbed forest in the Madre de Dios region, the epicenter of alluvial gold mining in Peru. We selected gold mine spoils of the two most important technologies locally applied for gold extraction, i.e., Minimally Mechanized Mining (MMM) and Highly Mechanized Mining (HMM), in the native communities of Laberinto and Kotzimba, respectively. We collected 127 and 35 soil samples (0-20cm depth) from potentially contaminated sites and undisturbed forest, respectively. Physicochemical analysis and determination of Hg levels were determined for all soil samples. None of the samples had Hg concentrations above Peruvian, Canadian and British Environmental Quality Standards for Agricultural Soil (6.6mg/kg). Hg levels in MMM and HMM were not significantly different between the two areas. The main variables explaining variation of soil Hg concentrations were the vegetation cover, soil organic matter, soil pH and clay particle content, which explained up to 80% of data set variation. Surprisingly, highest Hg concentrations were found in untouched old-growth forest bordering the mine spoils, but there was also a trend of increasing Hg concentrations with the regenerating vegetation. Our findings suggest that Hg concentrations in old mine spoils are low and shouldn’t stand in the way of efforts to restore soil conditions and develop sustainable land uses. However, it is urgent to end the use of Hg in mining operation to decrease human and environmental risks.

Section snippets

Credit author statement

Manuel Gabriel Velásquez Ramírez: Conceptualization, Investigation, Resources, Writing – original draft, Claudia Maribel Vega Ruiz: Conceptualization, Investigation. resources, Ronald Corvera Gomringer: Conceptualization, Validation, Supervision, Martin Pillaca: Investigation, Visualization, Evert Thomas: Data curation, Formal analysis, Paul Michael Stewart: Writing – review & editing, Supervision, Luis Alfredo Gamarra Miranda: Data curation, formal análisis, Visualization, Francisco Roman

Study area

We carried out the present study in soils impacted by alluvial gold mining in the Madre de Dios Region (Fig. 1). The impacted areas were selected according to the two locally most used technologies to extract sediments: Highly Mechanized Mining (HMM) and Minimally Mechanized Mining (MMM) (Fig. 2). HMM uses heavy machinery such as excavators, front loaders, and dump trucks, whereas MMM uses suction pumps and high pressure water cannons to liquefy stream-side sediments, which are transported to

Results

The soil samples from gold mine spoils had significantly higher pH, but significantly lower SOM, CEC and clay content than soils of reference forests (non-impacted areas) adjacent to the mines, (Table 3).

The Hg levels of all soil samples were below permitted levels according to the Peruvian Environmental Quality Standards for Soil (6.6 mg kg−1; ECA), Canadian Environmental Quality Guidelines (6.6 mg kg−1; CCME) and Soil Guideline Value of the United Kingdom (10 mg kg −1); Table 4).

1 Soil characteristics and Hg levels in mined landscapes

The main characteristics of mine spoils are loss of top soil and extreme soil profile remodeling caused by sand and rock fragments moved from deeper soil layers to the top, with high permeability, excessive runoff, nearly level slope class (<2%), low erosion and more than 10% rock fragments at the surface (Román et al., 2015; Velásquez Ramírez et al., 2020). Our results reveal surface soils characterized as sandy soils with low CEC and SOM, where the texture of US and UCFM are sand and sandy

Conclusion

Hg levels in gold mine spoil soils were below the upper limits for agricultural and residential use as stipulated by Peruvian, Canadian and British environmental quality standards, and yielded similar values in areas under MMM and HMM mining operations. Vegetation cover, soil organic matter content, soil pH and clay particle content were the main factors explaining the variation of Hg concentrations in soils. The soil conditions of recently abandoned, uncovered mine spoils, characterized by low

Acknowledgements

This research owes special thanks to San Jacinto Native Community, Kotzimba Native Community and local miners who might use this research as a tool to manage land restoration. This study is made possible funding provided by the United States Agency for International Development (USAID) under the terms of USAID/WFU Cooperative Agreement No. AID-527-A-16-00001, Consejo Nacional de Ciencia y Tecnologìa (CONCYTEC) and Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) (Proyecto

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

VIII. REFERENCES (68)

  • S. Guedron et al.

    Weathering versus atmospheric contributions to mercury concentrations in French Guiana soils

    Appl. Geochem.

    (2006)
  • J.J. Melendez-Perez et al.

    Soil and biomass mercury emissions during a prescribed fire in the Amazonian rain forest

    Atmos. Environ.

    (2014)
  • M.-A. Mélières et al.

    Mercury in canopy leaves of French Guiana in remote areas

    Sci. Total Environ.

    (2003)
  • J. Milesi et al.

    The Jacobina Paleoproterozoic gold-bearing conglomerates, Bahia, Brazil: a “hydrothermal shear-reservoir” model

    Ore Geol. Rev.

    (2002)
  • M. Roulet et al.

    The geochemistry of mercury in central Amazonian soils developed on the Alter-do-Chão formation of the lower Tapajós River Valley, Pará state, Brazil

    Sci. Total Environ.

    (1998)
  • F. Santos-Francés et al.

    Distribution and mobility of mercury in soils of a gold mining region, Cuyuni river basin, Venezuela

    J. Environ. Manag.

    (2011)
  • P. van Straaten

    Mercury contamination associated with small-scale gold mining in Tanzania and Zimbabwe

    Sci. Total Environ.

    (2000)
  • Y. Yang et al.

    Effect of organic matter and pH on mercury release from soils

    J. Environ. Sci.

    (2007)
  • J. Alvarez et al.

    Minería Aurífera en Madre de Dios y Contaminación con Mercurio. MINAM

    (2011)
  • A. Andersson

    Mercury in soil

    Grundfcirbdttring

    (1967)
  • A. Andersson

    Mercury in the soils

    The Biogeochemistry of Mercury in the Environment

    (1979)
  • M. Arana et al.

    Reporte de inventario:Estimaciones de referencia del uso y consumo de mercurio en la minerìa de oro artesanal y de pequeña escala en Perú

    (2017)
  • V. Arostegui

    Determinación de los niveles de concetración de mercurio en suelos y plátano Musa cultivar AAB, sub grupo Plantain, en Sarayacu, Punkiri Chico e Iberia - Madre de Dios [Universidad Nacional Amazónica de Madre de Dios]

  • G.P. Asner et al.

    Elevated rates of gold mining in the Amazon revealed through high-resolution monitoring

    Proc. Natl. Acad. Sci. Unit. States Am.

    (2013)
  • I. Aula et al.

    Levels of mercury in the tucuruí reservoir and its surrounding area in pará

  • K. Barton

    MuMIn: multi-model inference

  • S.A. Beal et al.

    Effects of historical and modern mining on mercury deposition in southeastern Peru

    Environ. Sci. Technol.

    (2013)
  • J. Caballero Espejo et al.

    Deforestation and forest degradation due to gold mining in the Peruvian Amazon: a 34-year perspective

    Remote Sensing, 10(12)

    (2018)
  • Canadian soil quality guidelines for the protection of environmental and human health: Summary tables

  • S.E. Diringer et al.

    River transport of mercury from artisanal and small-scale gold mining and risks for dietary mercury exposure in Madre de Dios, Peru

    Environ. Sci.: Processes & Impacts

    (2015)
  • S.E. Diringer et al.

    Deforestation due to artisanal and small-scale gold mining exacerbates soil and mercury mobilization in madre de Dios, Peru

    Environmental Science & Technology, acs.est.9b06620

    (2019)
  • D.R. Engstrom et al.

    Atmospheric Hg emissions from preindustrial gold and silver extraction in the americas: a reevaluation from lake-sediment archives

    Environ. Sci. Technol.

    (2014)
  • Environment Agency

    Updated technical background to the CLEA model

    Science Report SC050021/SR3

    (2009)
  • L.J. Esdaile et al.

    The mercury problem in artisanal and small-scale gold mining

    Chem. Eur J.

    (2018)
  • Cited by (0)

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