Gold Rush, Illegal Mining, Mercury Pollution, and Infant Health in the Amazon Rainforest

Gold Rush, Illegal Mining, Mercury Pollution, and Infant Health in the Amazon Rainforest

Abstract

Gold mining is a major source of mercury pollution, releasing substantial quantities into waterways annually. This study investigates the externalities of mercury contamination from gold mining on infant health in the Amazon Rainforest. We analyze a surge in small-scale mining during the mid-two thousands gold boom in the Madre de Dios region, spanning Peru and Bolivia, which caused extensive mercury contamination, disproportionately affecting downstream Brazilian riverside populations. Our findings reveal that gestational exposure to mercury pollution is linked to lower birth weights and increases in both infant and fetal mortality. These findings underscore the urgent need for coordinated cross-border environmental regulations.

One Introduction

Gold has long been one of the most sought-after and valuable metals, treasured by societies throughout the ages. However, despite its enduring value, gold extraction regulations are inconsistently enforced, particularly in remote areas. In recent decades, rising gold prices and lax policies have fueled a surge in informal mining practices. These unregulated small-scale and artisanal mining activities are widely recognized for their environmental impact, contributing to deforestation, excessive water consumption, and mercury contamination. These operations are responsible for releasing thousands of tons of mercury into waterways annually.

The impact of gold mining can extend far beyond the extraction sites. Mercury from these activities seeps into rivers and lakes, contaminating aquatic life and affecting downstream communities that depend on these water sources. This contamination can lead to mercury poisoning, which poses life-threatening health risks. Despite these dangers, the full extent of these externalities remains poorly understood, hindering governmental efforts to implement effective interventions. In some cases, this lack of understanding can lead to overly stringent policies that, while intended to mitigate environmental damage, can raise costs and negatively impact local economies, even those not directly involved in gold mining.

Adding to this complexity, prior studies offer conflicting evidence on the health effects of gold mining, with some suggesting positive outcomes due to income shocks and others highlighting negative impacts. This discrepancy likely stems from the dual nature of mining's economic impacts. On the one hand, increased income from gold mining can improve health outcomes by providing individuals with more financial resources. On the other hand, less obviously, the opportunity costs and economic shocks associated with mining can negatively impact community health. For example, the income generated by gold mining can drive up the cost of living, making healthcare and other essentials less affordable, thereby exacerbating local health disparities. This complex interplay complicates the assessment of gold mining's externalities, frequently resulting in ambiguous conclusions within the literature.

To clarify these conflicting findings in the literature, our study investigates the trade-offs between gold extraction and its health impacts on proximate populations, with a specific focus on infant health in riverside communities within the Amazon Rainforest. Our identification strategy leverages unique geographical features alongside comprehensive Brazilian datasets. We examine the aftermath of the Amazon Gold Rush, particularly focusing on the surge in small-scale gold mining that began in two thousand four in the Madre de Dios region of Bolivia and Peru. This gold boom led to the annual release of an estimated one hundred twenty tons of mercury and the clearing of thousands of hectares of native forest, which subsequently contaminated the local food chain. As this cross-border pollution infiltrates Brazil's waterways, it has silently impacted downstream river communities, within the Madeira River Basin. To quantify these effects, we estimate the causal impact of gold mining on infant health by comparing affected regions along the Madeira River with similar, unaffected communities. Our econometric design incorporates the water flow direction from the Madeira Basin, allowing for precise estimation of the consequences of exposure to waterborne contamination and the consumption of mercury-tainted fish.

Building on this framework, our reduced-form analysis indicates that cross-border pollution from gold mining has significantly impacted infant health in Brazilian riverside communities. Our preferred econometric model estimates an increase of approximately five point seven per thousand in infant mortality rates, representing a thirty-four percent rise relative to the baseline mean. In numerical terms, this increase corresponds to approximately ninety-seven additional infant deaths per year attributable to gold mining pollution. Furthermore, our event study results reveal that these effects persist over time following the onset of the Amazon Gold Rush, with consistently elevated infant mortality rates observed in downstream river communities that continue to be exposed to pollution.

Expanding on these insights, our heterogeneous results provide compelling evidence that the primary causes of infant mortality linked to potential mercury exposure during pregnancy include infectious diseases, respiratory issues, and congenital conditions. These health complications typically manifest early in an infant's life, particularly during delivery, consistent with the expected outcomes of gestational mercury poisoning. We also observe a significant increase in fetal mortality associated with potential mercury exposure. Furthermore, our findings reveal that infants born to mothers with lower levels of education are disproportionately affected, experiencing higher mortality rates. This vulnerable group also exhibits lower birth weights and slower fetal growth, both of which are attributable to gold mining pollution.

To ensure the robustness of our findings, we undertake a comprehensive set of additional exercises. First, we demonstrate that the impacts of cross-border pollution from gold mining diminish with increasing distance from the Madeira River to the Bolivian border. This is evidenced by Brazilian municipalities closer to the Bolivian border being more intensively impacted than those farther downstream. Second, we perform multiple placebo tests by examining parallel rivers in the same regions, which derive from distinct sources and are not geographically connected to the Amazon Gold Rush event. Consistent with our expectations, these findings confirm that these rivers are unaffected. Third, we provide evidence that our results are not confounded by factors such as population migration, municipal policy responses, or changes in maternal composition related to the Amazon Gold Rush, further reinforcing the validity of our conclusions.

Delving deeper into the mechanisms at play, the literature identifies three primary pathways through which mercury contamination impacts human health: (i) inhalation during water boiling, (ii) direct ingestion of contaminated water, and (iii) consumption of contaminated fish and other food items. Among these, the third pathway-consumption of contaminated food-is particularly relevant to our study. Mercury released by gold mining infiltrates freshwater ecosystems, contaminating fish that serve as critical dietary staples for riverside communities. These fish, acting as vectors of mercury transmitters, can travel up to fifteen kilometers daily, dispersing toxins across extensive areas. During the Amazon Gold Rush, mercury-laden fish from Madre de Dios likely reached Brazilian border communities within two weeks. Numerous studies corroborate this scenario, documenting a significant increase in mercury-contaminated fish in the Madeira River Basin during this period. Although mercury does not directly harm aquatic life, it bioaccumulates in fish, turning them into conduits for human mercury exposure, especially for pregnant women. Mercury transfers from mother to fetus through the bloodstream and subsequently through breastfeeding, amplifying its detrimental effects on infant health.

Aligned with these pathways, our investigation into potential mechanisms provides three lines of evidence linking mercury contamination to adverse infant health outcomes in regions affected by the Amazon Gold Rush. First, using satellite data, we identify a substantial increase in airborne mercury across Brazilian border municipalities during the Amazon Gold Rush period. As airborne mercury contamination reliably proxies for river water pollution, this finding underscores the far-reaching environmental impacts of cross-border gold mining, which substantially increase health risks for downstream Brazilian communities. Second, our findings further suggest that agriculture in downstream river regions reliant on mercury-contaminated river water suffers adverse effects, evidenced by reduced crop yields and diminished livestock productivity. This evidence highlights an indirect mechanism contributing to adverse infant health outcomes. Lastly, to examine the contaminated fish consumption hypothesis, we focus on seasonal increases in fish intake during a prominent Brazilian cultural celebration, analyzing gestational periods exposed to this dietary shift. Using this framework, we find suggestive evidence that fish consumption may serve as a significant transmission pathway for mercury's impact on infant health. Specifically, our analysis indicates that seasonal spikes in fish consumption intensify mercury exposure during pregnancy, increasing health risks for newborns in riverside communities. This is reflected in amplified adverse outcomes, including higher infant mortality rates and compromised birth metrics, such as lower birth weights.

This paper contributes to the literature by presenting three novel findings. First, by rigorously examining the specific health impacts of gold mining pollution, we depart from previous studies that offer either correlation-based insights or generalized estimates that combine both externalities and income effects. Our approach is the first to establish a robust causal link between illegal mining activities and increased infant and fetal mortality in nearby populations. Second, we provide compelling evidence of negative health effects from cross-border pollution caused by illegal mining operations. By leveraging an external shock from neighboring countries that affect Brazilian municipalities located along downstream rivers, we highlight the complexities of managing environmental costs when pollution crosses national borders. These results offer critical insights for policymakers, advocating for coordinated international environmental regulations to mitigate the impacts of informal mining. Third, our unique empirical setting allows us to isolate and identify the health impacts resulting from gold mining externalities. This contribution helps address uncertainty about the health effects of gold mining, a topic often explored through the lens of the Environmental Kuznets Curve.

However, unlike the predictions of the curve, which suggests pollution declines after a certain income threshold is reached, our findings reveal that adverse health impacts from gold mining activities persist beyond the region of economic activity.

This study intersects with three key areas of literature. First, it relates to the extensive empirical research examining the externalities of environmental degradation on infant health, with a particular focus on the adverse effects of air pollution, water contamination, and shortages on infant outcomes. Second, our findings advance the understanding of the environmental impacts of natural resource exploration, specifically gold mining activities and their associated health risks. Finally, our study contributes to the health literature by examining the specific pathways through which pollution-particularly mercury exposure affects vulnerable populations, including children, pregnant women, and fetuses. We document the adverse effects of potential mercury exposure through gold mining pollution on infants, such as low birth weight, reduced abdominal and head circumference, shorter gestational periods, and neurodevelopmental disorders.

Following this introduction, Sections two point one through two point three offer an overview of gold mining history in the Amazon Rainforest, detail the Amazon Gold Rush, and discuss the effects of mercury contamination on pregnant women. Sections three and four describe the data and empirical strategy employed, respectively. The results, including robustness checks and an analysis of potential mechanisms, are presented in Section five. In Section six we present a detailed mechanisms analysis. Section seven offers evidence supporting the plausibility of the identification strategy. Finally, Section eight presents the paper's conclusions.