Some of the most comprehensive studies of the health impacts of mercury from ASGM have occurred in Madre de Dios. These studies have found elevated concentrations of mercury in mining areas compared to people living in the regional capital of Puerto Maldonado, with 11% of people in mining communities displaying elevated mercury concentrations (> 6.0 mg/g) compared to only 5% in the city [Ashe et al. 2012].​ Additionally, several unpublished studies have found the highest concentrations of mercury in indigenous communities far upstream from gold mining.

In addition to the impacts of ASGM on mercury exposure, ASGM also leads to increases in infections diseases such as dengue fever and malaria. This is a direct result of the standing water that pools in mining pits and provides breeding ground for disease-carrying mosquitoes.

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OVERVIEW OF MECHANISMS OF MERCURY IMPACT ON PEOPLE
Biological Mechanism: 
Mercury binds strongly to sulfhydryl groups on tissue proteins, such as muscle. It also forms a complex with cysteine (an amino acid) to gain access to cells, thereby crossing membranes and the blood-brain barrier. Elemental mercury in the blood brain barrier becomes ionized and gets trapped, causing neurotoxicity. ​
Biological effects:
  • Corrosive action
  • Enzyme (particularly antioxidant) inhibition:
    • Glutathione peroxidase = lipid peroxidation
    • Choline acetyl transferase = acetylcholine deficiency = motor dysfunction
    • Paraoxonase = increased LDL oxidation = atherosclerosis
  • Protein precipitation
  • Increase reactive oxygen species = oxidative stress
  • Decreased nitric oxide bioavailability = endothelial dysfunction
  • Reduce the number of neuron and cytoarchitecture [Azevedo et al. 2012] 
  • Focal necrosis of neurons
  • Destroys glial cells
U.S. EPA [2001] reference doses: 
Oral reference dose (RfD):
The numerical estimate of daily oral human exposure to MeHg which is not likely to cause harmful effects during a lifetime is 0.1 μg/kg body weight/day.

Inhalation Reference Concentration (RfC):
RfC of elemental mercury is 0.3 µg / m³ of air.

Toxicity Overview: 
Acute versus Chronic Toxicity:
  • Acute toxicity = ingestion of inorganic mercury or inhalation of elemental mercury
  • Chronic toxicity = organic mercury ingestion or prolonged occupational exposure to elemental mercury
  • Chronic mercury poisoning = daily intake of 0.3 mg/70 kg mercury
  • Acute mercury poisoning = 5 mg/70 kg mercury
  • Lethal dose = 150 to 300 mg/70 kg  mercury
Picture
Source: IPEN.org
Reproductive System:
  • No observable adverse effect level (NOAEL) for developmental effects is estimated to be 10 μg Hg/g in maternal hair [Clarkson and Magos 2006]
  • Chromosomal anomaly and sister-chromatid exchange
  • Health Outcomes:
    • Reduced sperm count
    • Testicular atrophy
    • Reduced infant size
    • Reduced fetus survival
    • Fetus deformity
  • Prenatal exposure doubles the death rate compared to post-birth exposure
​Carcinogenicity:
  • Methylmercury compounds are possibly carcinogenic to humans (Group 2B)
  • Metallic mercury and inorganic mercury compounds are not classifiable as to their carcinogenicity to humans (Group 3)
Nervous System: 
  • Lowest observable adverse effect level (LOAEL) for neurotoxic effects (paresthesia) in adults set at 50 μg/g hair [Branco et al. 2017]
  • Neurotoxic effects observed when Hg levels exceeded 35 μg/g creatinine [SCOEL 2007]
  • ​Intelligence disorders
  • Seizures
  • ​Minamata disease (acute alkylmercury poisoning):
    • Ataxia: lack of muscle control or coordination of voluntary movements
    • Numbness in the hands and feet
    • General muscle weakness
    • Impaired vision, hearing and speech
Cardiovascular System:
  • Platelet aggregation and blood coagulation (atherosclerosis)
  • Limited arterial blood flow
  • Health outcomes:
    • Arrhythmias
    • Cardiomyopathy
    • Increased heart attack risk
    • Increased diastolic and systolic blood pressure, leading to hypertension
    • Decreased heart rate variability
    • Hair mercury concentrations greater than 2.0 μg/g doubles the risk of acute myocardial infarction and nearly triples the risk of cardiovascular death [Salonen et al. 1995]
    • With each additional μg of mercury in the hair, the risk of an acute coronary event increases by 11% ​[Virtanen et al. 2007]​
Immune System:
  • ​In studies on mice, weight of the thymus and the number of thymocytes were reduced by 22% and 50%, respectively
  • Natural Killer (NK) cell activation was reduced by 44% in the spleen and by 75% in the blood
  • Malfunction of mastocytes
  • Increased frequency of antinuclear autoantibodies
  • Increased risk of malaria infection

Sources

Ashe K (2012) Elevated Mercury Concentrations in Humans of Madre de Dios, Peru. PLoS ONE 7(3): e33305.
Azevedo BF, Furieri LB, Pecanha FM, Wiggers GA, Vassallo PF, Simoes MR, Fiorim J, de Batista PR, Fioresi M, Rossoni L, Stefanon I, Alonso MJ, Salaices M, Vassallo DV (2012) Toxic Effects ofMercury on the Cardiovascular and Central Nervous Systems. J Biomed Biotechnol 2012: 949048.
Branco V, Caito S, Farina M, Teixeira da Rocha J, Aschner M, Carvalho C (2017) Biomarkers of mercury toxicity: Past, present, and future trends. J Toxicol Environ Health B Crit Rev 20(3):119-154.
Clarkson TW and Magos L (2006) The toxicology of mercury and its chemical compounds. Crit Rev Toxicol 36: 609–662.
Hong Y-S, Kim Y-M, Lee K-E (2012) Methylmercury Exposure and Health Effects. J Prev Med Public Health 45:353-363.
National Research Council (US) Committee on the Toxicological Effects of Methylmercury (2000) Toxicological Effects of Methylmercury: 5, Health Effects of Metylmercury. National Academies Press, Washington, DC.
Salonen JT, Seppänen K, Nyyssönen K, Korpela H, Kauhanen J, Kantola M, Tuomilehto J, Esterbauer H, Tatzber F, Salonen R (1995) Intake of mercury from fish, lipid peroxidation, and the risk of myocardial infarction and coronary, cardiovascular, and any death in Eastern Finnish men. Circulation 91(3):645-655.
(SCOEL) Scientific Committee on Occupational Exposure Limits (2007) Recommendation from the Scientific Committee on Occupational Exposure Limits for elemental mercury and inorganic divalent mercury compounds. European Commission, SCOEL/SUM/84.
(U.S. EPA) U.S. Environmental Protection Agency (2001) Methylmercury (MeHg); CASRN 22967-92-6: Chemical Assessment Summary. National Center for Environmental Assessment, Integrated Risk Information System (IRIS), Washington, DC.
Virtanen JK, Rissanen TH, Voutilainen S, Tuomainen TM (2007) Mercury as a risk factor for cardiovascular diseases. J Nutr Biochem 18(2):75-85.
WHO and UNEP DTIE Chemicals Branch (2008) Guidance for identifying populations at risk from mercury exposure. Inter-organization Programme for the Sound Management of Chemicals, Geneva, Switzerland.