Impairment in Working Memory and Executive Function Associated with Mercury Exposure in Indigenous Populations in Upper Amazonian Peru

This study explores the association between Hg levels and working memory using the framework of the Multicomponent Model. Working memory tasks were modified to fit the culture and language of the Matsigenka when needed and included measures for verbal storage, visuospatial storage, and executive functions. The study involved 30 participants, ages 12 to 55 years, from three different communities in the upper Madre de Dios watershed in Southeastern Peru. Hair Hg levels ranged from 1.8 to 14.2 ppm, with 98% of a broader sample of 152 individuals exceeding the World Health Organization (WHO) limit of 2.0 ppm. Hair Hg levels showed significant associations with cognitive performance, with Hg levels negatively associated with executive functioning performance and positively associated with visuospatial performance. The results suggest that Hg exposure is negatively associated with working memory performance when there is an increased reliance on executive functioning. The study also found that education was the only predictor of Word Span accuracy. The findings suggest that the Self-Ordered Pointing Task (SOPT) and the Corsi Block have the potential to be alternatives to general intelligence tests when studying remote groups with extensive cultural differences. Mercury (Hg) is a heavy metal and neurotoxin that is damaging to humans and wildlife and is a persistent global environmental pollutant. The largest contributor of mercury to the environment is artisanal and small-scale gold mining (ASGM), which accounts for over 37% of the global total of mercury emitted from all sources. All chemical forms of Hg are toxic to humans, and exposure to several forms can cause deleterious effects on the central and peripheral nervous systems, cardiovascular system, urinary system, immune system, skin, and lungs. The Matsigenka people are susceptible to Hg poisoning because of their reliance on fish as a main source of protein. Estimated to number around 1000, the Matsigenka families living inside the protected areas of Manu National Park (MNP) are geographically restricted and culturally traditional relative to the lives and practices of Matsigenka in nearby regions. They maintain a lifestyle that includes the practice of swidden agriculture, hunting with bow and arrow, fishing, and gathering, with the bulk of their animal protein coming from migratory fish known to have high concentrations of mercury. Studies with Amazonian peoples show that high levels of Hg are associated with decreased cognitive functioning. Impairments are typically assessed with Intelligence or IQ tests that are a battery of standardized measures summarized into a composite score and normalized against a known population. Recent work has shown that for Peruvian children, each one unit increase in log hair mercury levels was associated with a 2.59-point decrease in the IQ index for General Cognitive Ability. Similarly, studies of children in the Amazon region of Brazil reported that for every 10 ppm Hg increase, there was a decrease of half a standard deviation in estimated IQ scores.