Difference in heavy metal concentrations in the American crocodile (Crocodylus acutus) in National Park Coiba Island and the Montijo Gulf, Panama

Environmental sources for possible metal contamination could be from: industry, agriculture, pharmaceutical, and mining smelters, among others. Heavy metals produced as a result of these processes become bioavailable and can have toxic effects on organisms when they surpass Threshold Limit Values. Therefore, is important to establish a direct connection of these disruptive contaminants in marine coastal environments and their impacts on ecosystems. This relationship can be addressed using a bioindicator, such as an apex predator like the American crocodile (Crocodylus acutus). The objective of this project was to identify and characterize possible transition metal pollution that is affecting the area. This study was done at two study sites in Panama, Coiba Island National Park, and the Gulf of Montijo. Data were collected for over a two-year period, the information collected included: season (rainy and dry), sex, and age group. American crocodiles were captured, and morphological measurements were taken along with scute cuttings as well as determination of both the animal’s sex and habitat from which the individual was captured. Scute samples were collected and analyzed using the ICP-MS instrument to determine heavy metal concentrations. I examined heavy metal concentrations of 12 metals vanadium(V), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), arsenic (As), selenium (Se), strontium (Sr), cadmium (Cd), tin (Sn), antimony (Sb) and lead (Pb). Significant differences were found in concentrations of several metals within study sites at both Coiba Island and The Gulf of Montijo (p =0.005). The included: V (p=0.016), Ni (p=0.022), Cu (p < 0,001), and Sr (p = 0.044). Between the study sites there were higher concentrations of metals in the Gulf of Montijo and then at the Coiba Island site. Among age groups, seven metal concentrations showed significant differences: Cr (p=0.040), Ni (p=0.054), Cu (p=0.004), Se (p=0.054), Sr (p=0.003), Sn (p=0.003) and As (p=0.056). In general, juveniles presented higher metal concentrations followed by sub-adult and adults. The data showed that the concentrations of Cr, Cu, As, Sr, Cd, Sn, Sb and Pb decrease with an increase in size. However, Se, Co, Ni and V showed a positive relationship between size and metal concentration. Nonetheless, the only metals that showed a significant difference in multiple linear regression were Cu (p=0.001) and Sr (p=0.001). This is the first study that uses an apex predator like the American crocodile to study heavy metal bioconcentration utilizing a non-invasive method, measuring concentrations in caudal scutes. Moreover, is important to highlight that the information gather for this project, is the first to use measurements from multiple years, age classes and different sites in Panama. This project generated a clear view of pollutants in the study area that directly affect coastal environment and health conservation strategies for the populations of Crocodylus acutus, and it will ultimately contribute to the development of future strategies for fisheries and other activities that affect the marine coastal environment.

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