Mercury and methyl mercury ratios in caimans (Caiman crocodilus yacare) from the Pantanal area, Brazil

Abstract

The Pantanal region is the largest floodplain area in the world and of great biological importance due to its unique flora and fauna. This area is continuously undergoing increasing anthropogenic threats, and has also experienced mercury contamination associated with gold mining and other anthropogenic activities. Pantanal caimans are top-level predators, and, as such, show great potential to accumulate mercury (Hg) by biomagnification. In this study 79 specimens from four locations in the Pantanal were analyzed for total Hg and methyl mercury (MeHg) by cold vapor atomic absorption spectrometry. Total Hg contents ranged from 0.02 to 0.36 µg g(-1) (ww), and most specimens presented MeHg ratios above 70%. One of the sites, impacted by anthropogenic activities, presented significantly higher total Hg in comparison to three less impacted sites, supporting the hypothesis that caimans can, in fact, be considered effective bioindicators of ecosystem health.

Mercury Concentration in the Spectacled Caiman and Black Caiman (Alligatoridae) of the Amazon: Implications for Human Health

“…However, the difference in Hg concentration between male and female animals in this study was not significant. Our data corroborate that for other species, such as A. mississippiensis (Elsey et al 1999;Ruckel 1993;Yanochko et al 1997), Crocodylus nitolicus (Almli et al 2005), C. c. yacare (Vieira et al 2011) C. moreletii, and C. acutus (Rainwater et al 2007). These alligators could be eliminating Hg from the body tissues at greater rates reaching equilibrium with ingested Hg.…”

“…C. c. crocodilus could be feeding more on terrestrial vertebrates when they are adults, which would explain why Hg concentrations were the same or greater in smaller individuals. In the Pantanal region, C. c. crocodilus presented a correlation between length and total Hg concentrations but only in specimens captured in sites with anthropogenic influences (Vieira et al 2011). Caimans in the sites where human activities were not intense (such as the Purus area) presented no significant correlation.…”

“…As far as we know, there is no record of mining activities along the Rio Purus, but this river flows parallel and close to the Rio Madeira, which has been greatly impacted by alluvial gold extraction, agriculture, and a hydrolectric reservoir (Dórea and Barbosa 2007). Regarding the Pantanal biome, how Rio Purus Hg levels link to anthropogenic or natural processes has yet to be established (Vieira et al 2011). We cannot identify if the high Hg concentration in caimans is related to natural Hg occurring within the basin or if it comes from the anthropogenic activities in the surrounding area.…”

“…There is a paucity of literature regarding Hg levels in Brazilian caimans: The only study known is of C. c. yacare in the Pantanal biome (Vieira et al 2011).…”

“…Crocodilians can live for decades, are generalists and opportunistic top carnivores (Da Silveira and Magnusson 1999), and usually have high Hg concentrations (Burger et al 2000;Vieira et al 2011). The use of caiman meat for human consumption has been documented since the 1980s (Best 1984;Da Silveira and Thorbjarnarson 1999).…”