Background Gold miners working in La Rinconada (5100m), Peru, suffer from severe hypoxia, which can promote chronic mountain sickness (CMS). Additionally, they might develop lung damage and further hypoxemia from regular crystalline silica dust inhalation as well as neurotoxic effects from mercury exposure caused by gold extraction. The rationale of this study was to investigate the overlap between symptoms of CMS, reduced lung function and mercury intoxication.

Methods Male highlanders, living for >3y at 5100m, aged 18?55y were invited to participate. CMS severity was assessed by the Qinghai CMS questionnaire. Main outcomes were lung function (forced expiratory volume in first second [FEV1]) and mercury concentration quantified by analyzing urine samples, as well as their correlation with hemoglobin concentration (Hb) and CMS score.

Results 71 participants included for this analysis (mean±SD age 45.0±7.6y; FEV1: 89±16%pred.) were hypoxic (SpO2: 79.1±4.6%), hypocapnic (PetCO2: 26.9±2.6mmHg) and had erythrocytosis (Hb: 23.0±1.9g/dl). Overall, 5.7%, 88.7%, 5.6% of highlanders had no, mild, moderate CMS, respectively. Mercury concentration exceeding the neurotoxic threshold of ?20?gHg/g creatinine was measured in 18%. Mixed linear regressions corrected for age showed a positive correlation between mercury concentration and CMS score (coef. 0.01, P<0.05) as well as Hb (coef. 0.27, P<0.05) and a negative correlation between FEV1 and Hb (coef. -0.04, P<0.05).

Conclusion Highlanders with reduced lung function and elevated mercury intoxication had higher Hb and CMS scores. Whether exposure to silica dust or mercury contamination can accentuate CMS at high altitude requires further prospective studies.