Mercury concentrations in bats (Chiroptera) from a gold mining area in the Peruvian Amazon

Abstract

In the southeastern Peruvian Amazon, artisanal and small-scale gold mining (ASGM) is estimated to have released up to 300 tonnes of mercury (Hg) to the environment between 1995 and 2007 alone, and is claimed to be responsible for Hg concentrations above international thresholds for aquatic wildlife species. Here, we examined whether Hg concentrations in bat populations are potentially related to regional ASGM-Hg releases. We determined Hg concentrations in the fur of bats collected at three different distances from the major ASGM areas in Peru. Our findings from 204 individuals of 32 species indicate that Hg concentrations in bat fur mainly resulted from differences in feeding habits, because Hg concentrations were significantly higher in omnivorous bats than in frugivorous bats. At least in two species, populations living in ASGM-affected sites harbored higher Hg concentrations than did populations in unaffected sites. Because Hg concentrations reflect Hg dietary exposure, Hg emissions from amalgam roasting sites appear to deposit locally and enter the terrestrial food web. Although our study demonstrates that ASGM activities (and Hg point sources) increase Hg exposure in wildlife, the overall Hg concentrations reported here are relatively low. The measured Hg concentrations were below the toxicity threshold at which adverse neurological effects have been reported in rodents and mink (>10 µg g), and were in the range of Hg concentrations in the fur of bats from nonpoint source affected sites in other latitudes. This study emphasizes the importance of considering feeding habits when evaluating Hg concentrations in bats and other vertebrates.

Co-production of contaminated landscapes: anthropogenic loading and food web structure drive mercury bioaccumulation in abandoned gold mines

“…In the bottom sediments of these waterbodies, under certain abiotic conditions, inorganic mercury can undergo a microbially-mediated transformation into methylmercury, the most toxic and biologically available form of mercury (13)(14)(15). Many studies have documented bioaccumulation of mercury in the vicinity of active mines (16)(17)(18)(19), in sediments and tailings downstream of mining (20)(21)(22), and even legacy contamination from mines that have long been abandoned (23,24). Bioaccumulation of mercury can cause a wide range of detrimental impacts to wildlife such as a reduction in growth (25)(26)(27), juvenile survivorship (28), reproductive success (29,30), and even mortality (31).…”

“…However, these ponds are also potential hotspots where inorganic mercury can be transformed into methylmercury, and bioaccumulate in wildlife (24,39). In Madre de Dios, there is growing evidence that mercury contamination from ASGM extends beyond the boundaries of mining areas as high levels of total inorganic mercury (THg) have been documented in downstream river sediments (21,22), fish (16), indigenous populations upstream of mining (40), and in wildlife found far from mining areas (19). Further, we found that the type of technology used in gold production influenced the degree of mercury loading (as measured by sediment THg concentration), and together with differences in food-web structure across abandoned mines, these factors controlled the rate of mercury biomagnification at each site.…”

Genomics in the jungle: using portable sequencing as a teaching tool in field courses

“…During travel to and from the Green Lab and through discussion with instructors and citizens of Peru, each participant learned first-hand about regional factors that affect the conservation of biodiversity. Southeastern Madre de Dios faces acute threats from artisanal and small-scale gold mining that include habitat destruction and the bioaccumulation of mercury in local wildlife (Kumar, Divoll, Ganguli, Trama, & Lamborg, 2018;Moreno-Brush et al, 2017). At this time, no comprehensive reference library of DNA barcodes for the fauna and flora of the region exists, although this would greatly enhance biodiversity assessments and monitoring in the face of these threats.…”

Non-invasive sampling of bats reflects their potential as ecological indicators of heavy metal and trace metal contamination due to open cast diamond mining, northern Limpopo Province, South Africa

“…Natural releases of elements are exacerbated by anthropogenic activities that results in the accumulation of high concentrations of these elements in the soil often near the source of emission (Nagajyoti et al 2010, Flache et al 2015, Obrist et al 2018. Sources of anthropogenic element releases are in the form of fertilizers (organic and inorganic), pesticides, agricultural practices (including continued irrigation of agricultural crops resulting in leaching and surface runoff), mining activities and associated transport and processing of ore (dust fallout, smelting, amalgamation processes), paper and plastic processing, wood preservation, waste water treatment plants and urban storm water runoff (Nagajyoti et al 2010, Moreno-Brush et al 2018, Carrasco-Rueda et al 2020. But, even remote areas do not escape metal contamination as some metals emitted through anthropogenic activities and volcanic eruptions, like mercury that linger in the atmosphere up to a year, are able to be transported over vast distances in the atmosphere and contaminate areas far from the point of emission (Nagajyoti et al 2010, Flache et al 2018.…”

“…Persistent environmental pollutants are an underrated threat to bats and the manner in which contaminants transfer, bio-magnify through trophic levels and accumulate within an organism (in tissues and organs) is fairly complex (Clarke et al 1986, Flache et al 2018, Mina et al 2019). Different bat species may show speci c trace element concentrations in their tissues and organs associated with variations in exposure within different foraging habitats, dietary guilds and physiological regulation of elements (Karouna-Renier et al 2014, Zukal et al 2015, Flache et al 2015, Hernout et al 2016b, Flache et al 2018, Moreno-Brush et al 2018, Carrasco-Rueda et al 2020, de Souza et al 2020). There could be numerous instances where high levels of metals may not be due to the contamination of the environment, but may be an artefact of the bat's diet.…”