A new study has revealed the alarming levels of mercury found in tropical birds, mainly caused by artisanal and small-scale gold mining operations.
The findings of this study not only highlight the detrimental impact on avian species but also raise concerns about the widespread environmental and human health implications of such activities.
Mercury: A Silent Killer
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Mercury is a highly toxic metal that can cause neurological, immune, and reproductive disorders in humans and animals.
It is used by gold miners to separate the precious metal from sediment, a practice that is widespread in the tropics, especially in Central and South America.
However, this process releases mercury into the environment, where it can accumulate in water, soil, plants, and animals.
Birds are particularly vulnerable to mercury exposure, as they can absorb or ingest it through their food, water, or feathers.
Mercury can affect their behavior, physiology, and reproduction, and even cause mortality in some cases.
Birds are also considered as indicators of ecosystem health, as their condition reflects the state of the environment they inhabit.
The study, published in the journal Ecotoxicology, is the result of a 17-year collaborative effort by dozens of scientists from the Tropical Research for Avian Conservation and Ecotoxicology (TRACE) Initiative, a network that promotes inclusive, equitable, and international data sharing.
The researchers collected thousands of feather, blood, and tissue samples from 322 bird species across nine countries in Central and South America, and the West Indies, creating the world's largest database to date on mercury concentrations in birds.
The study found that birds living within 7 km of artisanal gold mining activity had mercury concentrations over four times higher than those living at other sites across the tropics.
Some of the highest mercury levels ever recorded in songbirds were found in these areas, exceeding the thresholds for adverse effects.
The hotspots for mercury contamination included Madre de Dios, Peru, and Ayapel, Colombia, where gold mining is concentrated.
Birds in central Belize also had high mercury levels, possibly due to gaseous emissions from local landfill incineration or coal combustion in the surrounding region.
The study also revealed that mercury concentrations varied among different bird groups, depending on their diet, habitat, and migration patterns.
For instance, carnivorous and aquatic birds had higher mercury levels than herbivorous and terrestrial birds, as they are more likely to consume contaminated prey or water.
Migratory birds also had higher mercury levels than resident birds, as they may encounter different sources of mercury along their routes.
The researchers warned that mercury contamination in birds could have serious consequences for biodiversity, ecosystem function, and public health in the tropics.
They called for more monitoring, regulation, and enforcement to prevent and mitigate the impact of gold mining on the environment and wildlife.
They also urged for more awareness and education among the local communities and stakeholders about the risks and alternatives of mercury use in gold mining.
The study is a wake-up call for bird conservation internationally across the tropics, said lead author Chris Sayers, a conservation biologist at the University of California Los Angeles.
He added that based on the levels found in the study, it is reasonable to suggest that mercury may be playing a role in the decline of tropical bird biodiversity in recent decades.
