Arsenic contamination assessment in Brazil – Past, present and future concerns: A historical and critical review

Highlights

• A scenario of arsenic contamination in Brazil was depicted.

• Arsenic contamination from mining activities in Brazil is an ongoing concern.

• Collapse of Fundão Dam led to extensive As contamination in the Rio Doce Basin.

• Mobility of As in and out of different environmental compartments is complex.

• Arsenic equilibrium is influenced by anthropogenic factors.

Abstract

This paper presents a summary of some relevant documents published during the last decades regarding arsenic contamination in Brazil until December 2018, including scientific papers, reports and regulatory documents. Natural and anthropogenic arsenic sources were covered, excluding those related to agriculture. International “key” documents related to arsenic contamination were used to support the discussion and comparative analysis. This paper aims: (a) to summarize and discuss some available data (including Portuguese written documents) concerning arsenic contamination in Brazil, mainly geographical, geological, geochemical, environmental and health studies; (b) to critically review the published studies comparing their main findings; (c) to describe and compare ancient and recent contamination events; and (d) to highlight key knowledge gaps, and identify promising areas for future researches.

The arsenic contamination scenario in Brazil results not only from mining. Natural or anthropogenic emissions caused by great magnitude phenomena as flooding, erosion, landslide and, water scarcity equally impact arsenic mobilization/immobilization equilibria.

Our literature review demonstrates that arsenic contamination of soils, sediments and water sources is observed at least at three of the five geographically defined Brazilian regions (Northern, Southern and, Southeastern regions). Arsenic enriched soils, and waters naturally occur all around the country and anthropogenic activities have been the main contributory factor to the environmental contamination since the 18th Century. Geogenic materials (topsoil and mining tailings), and water samples could contain extremely high arsenic concentrations, i.e. 21,000 mg kg⁻¹ or 1,700,000 μg L⁻¹, respectively, have been found mainly at the “Iron Quadrangle”. Moreover, if we consider both the Brazilian and international parameters, the health risks associated with the human exposition to arsenic are of significant concern.

For those reasons, constant monitoring of As contaminated areas in Brazil is mandatory. Furthermore, it is necessary to learn from the mistakes made in the past in order to prevent or minimize future problems.

Introduction

Arsenic toxicity to humans and other living organisms has long been recognized as a significant health problem. The International Agency for Research on Cancer's (IARC) Working Groups in 1979, 1987, and 2002 has classified arsenic and its compounds as carcinogens therefore, those compounds are included within Group 1. The three major arsenic compounds groups, relevant from the biological and toxicological points of view are: (i) the inorganic arsenic compounds: arsenic trioxide, sodium arsenite, arsenic trichloride (the most common As^III compound), and arsenic pentoxide, arsenic acid and arsenates (lead and calcium arsenates), the most common pentavalent compounds; (ii) the organic arsenic compounds (arsanilic, methylarsonic, and dimethylarsinic or cacodylic acids), and finally (iii) the gaseous arsenic (arsine) (IARC, 2012) whereas arsenobetaine is generally considered non-toxic.

Arsenic is not an unusual element, according to the World Health Organization (WHO) arsenic is the 20th most common element in the earth's crust, and it is released to the environment as a result of natural (volcanic) or anthropogenic (industrial) activities (WHO, 2001). Industrial activities as mining, metallurgical processes (smelting of non-ferrous metals) and energy production (burning of fossil fuels) are the major anthropogenic sources of arsenic contamination of air, water, and soil (primarily in the form of arsenic trioxide). Equally important is the historical use of arsenic-containing pesticides for agriculture (IARC, 2012), which has resulted in land and food contamination. The use of arsenic for preserving timber is equally relevant from the environmental point of view. Additionally, arsenic is commonly employed during glass manufacturing and recently, arsenic trioxide has been used for the treatment of acute promyelocytic leukemia. Because of its wide industrial applications and it is ubiquitous in the environment, arsenic has led to the contamination of all environmental compartments.

Arsenic sulfides, i.e. iron, manganese, silver, lead, copper, nickel, and antimony sulfides, are the most typical arsenic inorganic compounds. Among them, arsenopyrite is the prevalent arsenic bearing mineral. Arsenic occurrence in the earth's crust is, on average, 5 mg kg⁻¹, or even higher in the case of sulfide deposits (IARC, 2012). Sedimentary iron and manganese ores deposits may occasionally contain arsenic levels of up to 2900 mg kg⁻¹ (IARC, 2012).

Arsenic levels in various environmental matrices have been widely reported. For examples, arsenic levels in the air are typically averaged 0.2–1.5 ng m⁻³ for rural areas, 0.5–3 ng m⁻³ for urban areas and <50 ng m⁻³ for industrial sites (WHO, 2001), although >1000 ng m⁻³ at industrial sites have been reported (WHO, 2001, Section 3.2). Arsenic level in the groundwater averaged about 1–2 μg L⁻¹, however, it can exceed 3 mg L⁻¹ where the groundwater is impacted by volcanic rock or sulfide minerals (these can be found in WHO, 2001 - Section 1.4). Sediment arsenic levels range 5–3000 mg kg⁻¹ with the higher concentrations are found at contaminated sites (WHO, 2001 - Section 1.4). Background arsenic in soil is within the range of 1–40 mg kg⁻¹. Arsenic can be found in percent concentration in soil associated with sulfide minerals and anthropogenic waste materials (WHO, 2001).

From this point forward, any mention to arsenic-contaminated samples or sites will follow these benchmarks stated in the paragraph above.

Arsenic contamination in Latin America has been reported for more than one hundred years, 70% of the continent countries experience some arsenic contamination issues. Taking the 10 μg L⁻¹ limit for As in drinking water, the number of people whose drinking water exceeding this limit is estimated to be about 14 million (Bundschuh et al., 2012), including Brazilian citizens.

In this paper, we conducted a systemic and critical review of the existing database on arsenic contamination in Brazil. The review focuses on English written scientific papers, which would afford wider access to the general scientific community. Natural and anthropogenic sources of arsenic contamination were considered, however those related to agricultural activities were excluded. Additionally, a significant number of documents written and published in Portuguese that are not readily accessible to the majority of the international scientific community, which including governmental and non-governmental reports, Brazilian legislation standards and Brazilian demographic statistics data, were included in this review, as a secondary bibliographic source.

It attempts to facilitate the access of the international scientific community to the existing database on arsenic contamination in Brazil. It is worth to note that a comprehensive assessment of the real context of the Brazilian contamination scenario is impaired by language limitations. In that way, international researches frequently cite the same scientific documents, repeatedly. Some of those papers aimed to present an understanding of the arsenic contamination scenario in one specific Brazilian region. Those articles were undoubtedly well written and unquestionably relevant and they are the most cited in the scientific literature. However, these widely cited studies (Bundschuh et al., 2012; Matschullat et al., 2000) could lead to a false assumption by the readers that this is a recent environmental problem restricted to a very small area.

On the contrary, this paper argues that arsenic contamination in Brazil has been a long term environmental and health problem that is widespread over an extended area covering a major part of the country. Arsenic contamination in the Brazilian waters, sediments, and soils is a natural phenomenon related to Brazilian soil composition, which is becoming an environmental issue due to anthropogenic activities. The so-called Iron Quadrangle (IQ) region will deserve special attention due to its historical and economical relevance but discussions will also cover other Brazilian arsenic-contaminated regions.

In order to prove this hypothesis a systematic and critical review focused not only on English written scientific papers was conducted.