Mercury in Neotropical birds: a synthesis and prospectus on 13 years of exposure data

Abstract

Environmental mercury (Hg) contamination of the global tropics outpaces our understanding of its consequences for biodiversity. Knowledge gaps of pollution exposure could obscure conservation threats in the Neotropics: a region that supports over half of the world’s species, but faces ongoing land-use change and Hg emission via artisanal and small-scale gold mining (ASGM). Due to their global distribution and sensitivity to pollution, birds provide a valuable opportunity as bioindicators to assess how accelerating Hg emissions impact an ecosystem’s ability to support biodiversity, and ultimately, global health. We present the largest database on Neotropical bird Hg concentrations (n = 2316) and establish exposure baselines for 322 bird species spanning nine countries across Central America, South America, and the West Indies. Patterns of avian Hg exposure in the Neotropics broadly align with those in temperate regions: consistent bioaccumulation across functional groups and high spatiotemporal variation. Bird species occupying higher trophic positions and aquatic habitats exhibited elevated Hg concentrations that have been previously associated with reductions in reproductive success. Notably, bird Hg concentrations were over four times higher at sites impacted by ASGM activities and differed by season for certain trophic niches. We developed this synthesis via a collaborative research network, the Tropical Research for Avian Conservation and Ecotoxicology (TRACE) Initiative, which exemplifies inclusive, equitable, and international data-sharing. While our findings signal an urgent need to assess sampling biases, mechanisms, and consequences of Hg exposure to tropical avian communities, the TRACE Initiative provides a meaningful framework to achieve such goals. Ultimately, our collective efforts support and inform local, scientific, and government entities, including Parties of the United Nations Minamata Convention on Mercury, as we continue working together to understand how Hg pollution impacts biodiversity conservation, ecosystem function, and public health in the tropics.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

“…Many species of invertebrate-eating birds (herein called landbirds) are also at elevated risk to Hg exposure. Remarkably, landbirds can exhibit higher tissue Hg concentrations than fish-eating birds within the same ecosystem (Evers et al 2005 ; Kopec et al 2018 ; Sayers et al 2023 ). They may also be more sensitive to MeHg, resulting in a higher likelihood of adverse impacts on reproductive success (Heinz et al 2009 ; Jackson et al 2011b ; Whitney and Cristol 2017 ).…”

“… Note that bioindicators for human exposure are also useful for environmental assessments 1 Kenney et al ( 2014 ), 2 AMAP 2011 ), 3 Rigét et al ( 2007 ), 4 Evers et al ( 2014 ), 5 Jackson et al ( 2016 ), 6 Braune 2007 ), 7 Routti et al ( 2011 ), 8 Dietz et al ( 2013 ), 9 Gantner et al ( 2010 ), 10 Eagles-Smith et al ( 2016a ), 11 Sayers et al ( 2023 ), 12 Wagemann and Kozlowska ( 2005 ), 13 Wiener et al ( 2012a ), 14 Weis and Khan ( 1990 ), 15 Evers et al ( 2011b ), 16 Bowerman et al ( 1994 ), 17 Odsjö et al ( 2004 ), 18 Jackson et al ( 2015 ), 19 Wiemeyer et al ( 1988 ), 20 Goodale et al ( 2008 ), 21 Yates et al ( 2005 ), 22 Klenavic et al ( 2008 ), 23 Brookens et al ( 2008 ), 24 Dam and Bloch ( 2000 ), 25 Eagles-Smith and Ackerman ( 2009 ), 26 Ackerman et al ( 2016 ), 27 Frederick et al ( 2002 ), 28 Braune ( 1987 ), 29 Day et al ( 2005 ), 30 Kamman et al ( 2005 ), 31 Monson et al ( 2011 ), 32 Cai et al ( 2007 ), 33 Bastos et al ( 2015 ), 34 Mol et al ( 2001 ), 35 Lane et al ( 2011 ), 36 Townsend et al ( 2013 ), 37 Finkelstein et al ( 2006 ), 38 Burger and Gochfeld ( …”

Diet choices determine mercury exposure risks for people living in gold mining regions of Peru

“…In an analysis from Madre de Dios that included birds of all trophic guilds, feather samples from mining-impacted sites contained 6.7 times higher Hg [95]. The samples from ASGM-impacted areas were also the highest in the published literature to date [94,95].…”

“…Nevertheless, it is well-established that ASGM is a major driver of Hg accumulation in numerous avian species. In an analysis of mercury concentrations in neotropical birds across Central and South America, Sayers et al [94] noted that birds within 7 km of mining activity exhibited four times higher Hg concentrations than other sites. In an analysis from Madre de Dios that included birds of all trophic guilds, feather samples from mining-impacted sites contained 6.7 times higher Hg [95].…”

Mercury biomagnification in the food web of Agami Pond, Kaw-Roura Nature Reserve, French Guiana

“…The rate of Hg biomagnification in ecosystems is linked to the latitude of these ecosystems, physico-chemical parameters, and the pool of Hg present in the ecosystem [ 12 ]. In general, tropical ecosystems have lower biomagnification factors than temperate ecosystems [ 12 ], however, several studies have showed that Hg concentrations in top predators in tropical regions are high [ [13] , [14] , [15] , [16] , [17] , [18] ].…”