Evaluation of organochlorine residues in Morelet's and American crocodile eggs from Belize

Non-viable eggs of Morelet's crocodile (Crocodylus moreletii) and American crocodile (Crocodylus acutus) were collected from various locations in Belize and screened for organochlorine (OC) compounds using gas chromatography (GC) with electron capture detection (ECD). Seven complete clutches (1 non-viable and 6 flooded nests) of eggs from Morelet's crocodiles were also collected to examine distribution of OCs and determine the appropriate minimum number of eggs to sample in the field to obtain an accurate mean p,p-DDE concentration representative of the full clutch. All but one egg (American crocodile. Maps Cay, Nest 2) analyzed tested positive for one or more OCs. The primary contaminant was p,p-DDE (99%). Other OCs detected included p,p-DDT, p,p-DDD, methoxychlor, endosulfan I and II, endrin, aldrin, and a-chlordane. Concentrations of individual OCs on a wet weight calculation ranged from 1 ppb (ng chemical/g egg) to >0.5 ppm (jig chemical/g egg). Total concentration of OCs (sum of all OCs) for one egg collected from a nest at Gold Button Lagoon (GBL) reached as high as 0.7 ppm. No significant difference (p < 0.05) between non-viable eggs from American (n = 12) and Morelet's (n = 13) crocodile nests was observed for egg p,p-DDE concentration using a Wilcoxon rank sum test. However, significant differences were observed with absolute mean p,p-DDE contamination among complete clutches (n = 7) of eggs from Morelet's crocodile using Welch ANOVA (p < 0.0001). Correlation coefficients for DDT and DDT metabolites within complete clutches of eggs varied from an r of 0.95 to 0.24. The weaker correlation coefficients between DDT and DDT metabolites may suggest the possibility of another source of contaminants in eggs besides by maternal transfer. A statistical evaluation of p,p-DDE levels in three complete clutches (GBL 2, 1999; GBL 3, 1997; and GBL 4, 1997) of eggs recommended a minimum sample size of 11. This sample size should give an accurate estimate of contaminant levels in a full clutch of eggs based on an average standard deviation (0.26 ng/g), average clutch size (n = 20), acceptable deviation from the mean (± 0.1), and a confidence interval of 90%. The statistically recommended sample size of 11 eggs was successfully tested on four additional clutches. Sediment and nest media (soil and plant material) collected from GBL and New River Lagoon (NRL) also tested positive for OCs (lindane, aldrin, heptachlor, methoxychlor, endrin aldehyde, p,p-DDT among others). Contaminated media could be a potential source for transfer of volatile OCs into eggs. Based on the 264 egg samples analyzed, Morelet's and American crocodiles from Belize are being exposed to OCs. Such exposure may present a health threat to populations of crocodilians in Central America.