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

Abstract

Mercury (Hg) concentrations in the Amazon are generally high, but no studies have been published on Hg concentrations in caimans (Alligatoridae) from the region. Aiming for sizes representative of caimans traded for food in the Amazon, we measured Hg concentration in tail muscle of spectacled caiman (Caiman crocodilus crocodilus) and black caiman (Melanosuchus niger) from the Purus River basin. The information on Hg concentration in caimans from this area is important because of the potential health risk to humans and other animals that eat them as well as the potential use of these top-level predators as bioindicators. There were no significant interspecific or sex differences in Hg concentrations. The mean Hg concentration was 291.2 μg/kg in C. c. crocodilus and 193.9 μg/kg in M. niger. A significant positive correlation between Hg concentration and size was found for M. niger (p = 0.005) but not for C. c. crocodilus. Our Hg sample from M. niger corresponded to the size of M. niger collected for commercial trade, but our Hg sample from C. c. crocodilus turned out to be significantly smaller than the trade samples (p = 0.004), but this difference is not pertinent in the absence of a correlation between size and Hg concentration for this species. Although there are no standards for reptile meat, both species had mean Hg concentrations lower than the maximum allowable level of 500 μg/kg Hg recommended by the World Health Organization and by the Brazilian Health Ministry for fish. However, by calculating daily consumptions limits and number of meals per month that can be safely consumed, we found that consumers who eat caimans frequently may be at risk for Hg-related health problems.

Non-lethal sampling for mercury evaluation in crocodilians

“…2), it is important to note that the variation of the concentrations in scute of males is higher than the variation in females. Similar findings were previously reported in different tissues of M. niger (Schneider et al, 2012), but contradictory results were found in A. mississipiensis with higher Hg concentrations in males than in females, since the latter ones are able to reduce their body burden of Hg when eggs are laid (Delany et al, 1988).…”

“…There are several works showing that Hg in crocodilians muscles increases linearly with time of exposure (Yanochko et al, 1997;Burger et al, 2000;Rumbold et al, 2002;Schneider et al, 2012) but few have examined the relationship between size and Hg concentration in keratinized tissues (Schneider et al, 2015). Previous studies have reported a significant positive correlation between Hg concentration in scute and size in A. mississipiensis, M. niger and C. crocodilus (Yanochko et al, 1997;Burger et al, 2000;Schneider et al, 2015) but not in C. moreletii and C. acutus (Rainwater et al, 2002).…”

“…Previous studies have reported a significant positive correlation between Hg concentration in scute and size in A. mississipiensis, M. niger and C. crocodilus (Yanochko et al, 1997;Burger et al, 2000;Schneider et al, 2015) but not in C. moreletii and C. acutus (Rainwater et al, 2002). This discrepancy can be explained by the variability of many crocodiles feeding behavior and life history (Schneider et al, 2012). According to this, C. yacare is an opportunist predator, its prey varies depending on the caiman's growth stage and habitat (Santos et al, 1996).…”

“…When young, it prefers to feed on smaller prey such as aquatic invertebrates and insects; its growth coincides with that of its prey, feeding on small fish, then larger fish, fishes and birds, and finally a more varied diet ranging from fish to water mammals (Santos et al, 1993(Santos et al, , 1996. Ontogenetic and habitat variation in feeding likely explains the variation in concentrations of THg in relation to individual body size, as it can influence the pattern of Hg bioaccumulation in individuals (Hopkins, 2006;Schneider et al, 2012).…”

Antimicrobial discovery from natural and unusual sources

“…Crocodiles and alligators are known for their longest life span, and during their lives, they encounter numerous pathogenic microbes, toxicants, pollutants, carcinogens etc. but thrive in these conditions . The serum of the Siamese crocodile ( Crocodylus siamensis ) was purified to separate antibacterial agents and found to be active against several bacterial pathogens including Salmonella typhi , E. coli , S. aureus , S. epidermidis , K. pneumoniae , P. aeruginosa and Vibrio chorelae .…”