Dietary exposure of Morelet's crocodile to organochlorine contaminants

Located on the Caribbean side of the Yucatan Peninsula, the country of Belize claims a largely tourism-based economy with significant land areas under agricultural cultivation. Major export crops of Belize are sugar cane, citrus, and bananas. Exponential human population growth in Belize over the past two decades has increased the demand for food and raised agricultural production. The spraying of residences with insecticides for the control of mosquitoes and the prevention of malaria also lend to the overall increased usage of pesticides in Belize.

Due to their unique life-history traits, crocodilians provide excellent indicators of environmental contamination. Previous studies have investigated organochlorine pesticide contamination in Belize and have detected residues in sediments, as well as nesting material, eggs, and scutes of two crocodile species. The pertinent question, however, is whether organisms inhabiting these environs are exposed to contaminants at biologically toxic concentrations. Through a crocodile food habits study, and residue analysis and a feeding-exposure simulation, the present study addressed the question of exposure.

Summer diets of Morelet's crocodiles {Crocodylus moreletii) in the New River Watershed of Northern Belize were determined over a two year period. One hundred and eight crocodiles were stomach pumped, using the hose with Heimlich maneuver method, and contents collected and inventoried. Crocodile diet was determined by inspection and standardized using a 48-hour residency criteria.

Crocodile diets consisted of insects, fish, gastropods, anurans, crustaceans, mammals, birds, and various plant matter. The most significant prey by frequency were insects, fish, and gastropods. Prey frequency in crocodile stomachs revealed that prey occurrence was dependent upon crocodile size and prey type but independent of year.

Organochlorine contaminant exposure in the diet of Morelet's crocodiles was estimated through probabilistic simulation. Sediment samples were collected from the New River Watershed and screened by gas chromatography for eight organochlorine contaminants. Based on crocodile diet in Northern Belize, equivalent prey specimens were collected from the New River Watershed basin and also analyzed for organochlorines. A feeding-exposure model was then constructed to estimate size class specific doses of organochlorine contaminants in the diets of crocodiles. Juveniles were found receiving the highest dose of contaminants per body weight followed in order by subadults and adults. Results ofthe feeding-exposure model indicated that essentially none of the crocodiles were exposed to concentrations at or above thresholds considered toxic in laboratory animals and humans. Results of this study are consistent with previous investigations evaluating the effects of endocrine disrupting contaminants on Morelet's crocodiles in northern Belize reporting no observed contaminant-induced biological responses.