"Effects of mercury exposure in three Amazonian agricultural plant species and the impact on bacterial population in soil".

Abstract

The Amazonian region of Madre de Dios in Peru is highly impacted by mercury (Hg) emissions from Artisanal and Small-Scale Gold Mining (ASGM) in the Amazon rainforest. Peru adopted soil screening levels (SSL) for Hg in agricultural soil (6.6 mg kg-1) to protect the environment and human health from Hg exposure based on regulations adopted by Canada without considering research on native plant and animal species. To close the knowledge gap on Hg toxicity in Amazonian plant species, we studied the impact of Hg exposure on the survival, growth, and health of three Amazonian agricultural plant species commonly used in the local population's diet: aji dulce, sacha culantro, and uncucha. Experiments were conducted growing the three plant species studied in pots with soil spiked with Hg to concentrations ranging from 2 to 100 mg kg^-1 (dry weight). At the end of the experiments, adverse plant health effects, such as mortality, reduction in root length, and above-ground weight, were found in aji dulce and uncucha plants after exposure to every Hg concentration tested, and mortality was found in sacha culantro plants after exposure to 50 and 100 mg kg^-1 of Hg. The lowest observable concentration of Hg affecting the plant's health was 2 mg kg^-1, three times lower than the SSL for Hg in agricultural soil established in the Peruvian regulation. The results of the study suggest that a review of this SSL would be necessary for developing appropriate environmental and human health risk assessments in areas impacted by ASGM in the Amazon region.