Peruvian gold rush turns pristine rainforests into heavily polluted mercury sinks

If you had to guess which part of the world has the highest levels of atmospheric mercury pollution, you would probably not pick a patch of pristine rainforest. That is exactly where they are.

A new study in the journal Nature Communications shows that illegal gold mining in the Peruvian Amazon is causing high levels of mercury pollution in the nearby Los Amigos Biological Station.

One stand of old-growth pristine forest was found to have the highest levels of mercury ever recorded. Birds from this area have more mercury in their systems than birds from less polluted areas.

Mercury pollution has been studied in aquatic systems. The first measurement of atmospheric deposits of the most toxic form of mercury was made by a team of researchers led by Jacqueline Gerson and Emily Bernhardt.

Illegal miners use mercury to separate gold particles from river sediments and form large pellets that can be caught in a sieve. The mercury is released when the pellets are burned. The gold and mercury are separated by the high temperature. The mercury smoke is washed into the soil by the rain, deposited onto the leaves or absorbed directly into the tissues.

To measure this mercury, the team collected samples of air, leaf litter, soil and green leaves from the top of trees, which were obtained with the help of a huge slingshot. They focused their collection on four environments: forested and deforested, near mining activity, or far from mining activity. Los Amigos Biological Station is a pristine old-growth forest that has never been touched, and two of the forested areas are patches with small, scraggly trees.

The areas that were deforested had low levels of mercury regardless of their distance to the mining activity. Forested areas that accumulate mercury on their leaves were not all the same. The four areas with scraggly trees, two near mining activity and two further away, had levels of mercury in keeping with world-wide averages.

The mature forests near gold mining are capturing huge volumes of atmospheric mercury, more than any other environment previously studied in the world.

The leaf area index is a measure of how dense the canopy is.

The denser the canopy, the more mercury it holds. The canopy acts as a catch-all for the gases and particulates that come from the nearby burning of gold-mercury pellets.

The team measured the mercury in the feathers of three songbird species in reserve stations near and far from mining activity to estimate how much mercury was caught in the forest canopy.

Birds from Los Amigos had on average three times more mercury in their feathers than birds from a more remote biological station. The decline in reproductive success could be up to 30% due to high concentrations of mercury.

The forests are doing an enormous service by capturing a huge fraction of this mercury and preventing it from getting to the global atmospheric pool.

Local communities rely on small-scale gold mining to survive. The American gold-rush that ravaged California in the 1850s was driven by economic necessity.

Many wealthy countries of the world where gold was available have already done this. The demand is pushing mining into new areas.

There is a reason why people are mining.

The goal is to highlight that the issues are far greater than water pollution and that we need to work with local communities to come up with ways for miners to have a sustainable livelihood and protect indigenous communities from being poisoned through air and water.

More information: Amazon Forests Capture High Levels of Atmospheric Mercury Pollution From Artisanal Gold Mining, Nature Communications (2022). DOI: 10.1038/s41467-022-27997-3 Journal information: Nature Communications Citation: Peruvian gold rush turns pristine rainforests into heavily polluted mercury sinks (2022, January 28) retrieved 28 January 2022 from https://phys.org/news/2022-01-peruvian-gold-pristine-rainforests-heavily.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.