Effects of Toxins from Small-scale Gold Mining in Caimans of Suriname

Three species of caiman currently range in Suriname: spectacled caiman (Caiman crocodilus), smooth-fronted caiman or Schielder’s dwarf caiman (Paleosuchus trigonatus), and Cuvier’s dwarf caiman (Paleosuchus palpebrosus). Very little work has been done with their populations in Suriname. The only published papers on caimans in Suriname look at population ecology of Caiman crocodilus (Ouboter & Nanhoe, 1987, 1988, 1989).  

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In recent years, ecotoxicology has been delved into more and more when it comes to crocodilians. Crocodilians have been found to be great bioindicators when it comes to heavy metal contaminants because of their longer lifespan, varied diet, and trophic level (Marrugo-Negrete et al., 2019; Nilsen et al., 2019; Schneider et al., 2013). They move through trophic levels throughout their lives, being eaten by many other animals when young, including birds and other crocodilians, to apex predators as adults. This allows for studies looking at ecotoxicology to see how heavy metal concentrations change through trophic level changes.  

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Small-scale gold mining using mercury amalgamation is popular in the eastern part of Suriname. As the mercury gets used to separate the gold from the sediment, it gets released into the environment. The disruption of soil through this process can also release mercury, which is a natural component of the soil (Ouboter, 2015). Studies focusing on mercury accumulation have been on the rise, with most of the focus on the southwest region of the Amazon and lacking in the northern region (Guiana Shield) (Martoredjo et al., 2024).  

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This project investigates the effects and amounts of heavy metals in three species of caiman in Suriname (Caiman crocodilus, Paleosuchus trigonatus, and Paleosuchus palpebrosus). Specifically, we want to look at mercury, lead, and selenium. Also, we will look at what each species is eating in these populations and correlate this to the amounts of metals they are accumulating.  

We will look at all three species of caiman at two sites, one where there is a lot of anthropogenic impacts and one with relatively low impact. The first site is located in a remote area in west Suriname. It is a newly opened research station, and we will be some of the first to use it. The second location will be in Peperpot Nature Park. This is across the Suriname River (less than 1 kilometer away) from Paramaribo, the capital of Suriname.  

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For each caiman, we will take 5mm clippings from three scutes towards the tip of the tail, three nail clippings from the three longest nails, and a blood sample. Clippings will be cut with sharp claw clippers and put into plastic tubes labeled with the PIT tag number of the individual. They will be put in a freezer immediately after returning to the place of stay in the field until sent for analysis (Lemaire, Bustamante, Marquis, et al., 2021).  

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To learn more about the diets of these caimans and better understand how these caimans are accumulating all these metals, we will be looking at their stomach contents using stomach flushing. This is commonly used in crocodilians to see what exactly individuals in a population are eating without dissection. There are multiple techniques for stomach flush. We chose to use a hose with Heimlich maneuvers as it was found to be the most efficient at removing all stomach contents (Fitzgerald, 1989).  

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We predict that there will be a difference in total mercury accumulation between the sites, with the caimans at the more remote western site having lower overall concentrations. We are looking to see a correlation between continents and diet, especially caimans that eat more fish, which accumulate mercury in high concentrations (Da Silva et al., 2005). With this, caimans that eat more terrestrial vertebrates and less fish may have lower total mercury accumulation.  

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This study could help push for healthier waterways not only for caimans but also for humans. In many of these areas where caimans live and eat, humans are doing the same things, with a large part of their diet being fish caught from rivers. Caimans can be used as bioindicators of mercury contamination, helping give the people who live in these areas an idea of the health effects of the fish they are eating.