A cross-taxa survey of organochlorine pesticide contamination in a Costa Rican wildland
Introduction
Tropical conservation areas have been set aside not only to protect a suite of organisms, but also to preserve the interactions among them. However, no park is completely isolated, as interactions between organisms inside a conserved wildland will inevitably be impacted by conditions in the surrounding agricultural, industrial, and residential landscapes. Many of these impacts decrease in magnitude as park size increases (Janzen, 1999), and are often lumped into the category of “edge effects”. Impacts that operate on a global scale, such as increases in atmospheric carbon dioxide, increased ultraviolet radiation, and long-distance atmospheric transport of pesticides (LeNoir et al., 1999) may affect wildlands in ways that are unpredictable from their size or degree of protection from other external threats. The magnitude of such impacts may instead depend on topography, climate, latitude, and geologic history of the site and surrounding area. The degree of influence of these types of factors on a conservation area will be unique for each park, and will probably be unique for the different habitats protected within a large conservation area. Although very few of these global level impacts have been quantified (or even documented) in most conservation areas, they are often offered as explanations for unexpected phenomena, such as the perceived population declines of species or groups of species. For example, Pounds and Crump (1994) quantified population declines in two amphibian species in a Costa Rican conservation area, and suggested that pesticide contamination from regional agricultural sites may be a contributing factor in these declines. However, there was no direct evidence that these organisms had ever been exposed to pesticides. For most organisms it is unknown to what extent population dynamics may be affected by pesticide contamination.
Organochlorine pesticide use is thought to be widespread in Central and South American countries (Castillo et al., 1997), but because of underdeveloped regulatory structures, there are little data on the extent to which they are used (Murray, 1994). Costa Rica is one of the few countries with reliable information regarding the history of its pesticide use. About 10% of Costa Rica's total land area is used for crop production, and pesticide imports have been reported to be up to 9000 metric tons annually (von Duszeln, 1991). Although exact statistics on the quantity of OC pesticides applied to crops is not available, it is estimated to be 6 kg/ha higher than in most industrialized countries (von Duszeln, 1991). In 1981, most OC pesticides in Costa Rica were restricted for agricultural use only, while DDT could only be used in efforts to eradicate malaria (Castillo et al., 1997). DDT and a series of other OC pesticides (e.g. aldrin, dieldrin) were then banned for use in 1988, while chlordane, heptachlor, endosulfan, and a series of other OC compounds were restricted in their use (von Duszeln, 1991). All of these laws restricted pesticides to these uses from a former wide range of permitted uses. Persistent OC residues in Costa Rica have been detected in water samples (von Duszeln, 1988), coffee (Cetinkaya et al., 1984), insect larvae (Standley and Sweeney, 1995), bovine meat (Rojas and Ruiz, 1989), bovine milk (Ruiz and Rojas, 1988), human fat (Barquero and Constenla, 1986), and human milk (Umana and Constenla, 1984).
The objective of this study was to document OC contamination in amphibians, reptiles, birds, and mammals from a tropical conservation area in Northwest Costa Rica. Although no studies have been published on pesticide contamination levels in vertebrates from this locality, Standley and Sweeney (1995) documented OC contamination in mayfly larvae and vegetation collected from sites on the eastern and western slopes of the continental divide within the conservation area. They found an east to west gradient in OC contamination, which they attributed to local weather patterns and the location of agricultural areas in relation to the conservation area. We collected birds from locations near the two sites used by Standley and Sweeney (1995) and from a site further west. In addition, we examined OC contamination in tissues of amphibians, reptiles and mice from our westernmost site. These became available from a parasite inventory conducted at the same time the birds were collected. To our knowledge, no data exist on OC contamination in vertebrates from this conservation area. In fact, very few data exist on OC contamination of Neotropical wildlife.
Section snippets
Collection of animals
After securing the appropriate permits, thirty-nine amphibians, six turtles, and 55 birds were collected in June and July, 1998. Once collected, gut contents and all endoparasites and ectoparasites were removed and the animals were frozen. Eight mice that had been collected for the parasite inventory one year earlier and stored in a freezer were also included in this study. The viscera and associated fat deposits of the mice had been discarded. All organisms were later transferred to a −80 °C
Amphibians
Organochlorine residues were present in six of 39 individuals (three of eight species). Four of seven Bufo marinus, one of seven Rana forreri, and one of three Rhinophrynus dorsalis contained OC compounds. These species were the three largest amphibian species in the study (Table 1). Twelve OC compounds were detected in amphibians. The most frequently detected compounds were p,p′-DDE, delta-BHC, heptachlor, and dieldrin (Table 1). Heptachlor epoxide, beta-BHC, gamma-BHC, endosulfan II,
Discussion
OC compounds were present in amphibians, turtles, mice, and birds of the ACG. These data suggest that larger amphibian species were more contaminated than the smaller species. Larger predators may be expected to feed higher in the food chain than smaller animals, and may accumulate higher concentrations of OC compounds. In addition, larger species may be longer-lived than smaller species, and thus any given individual may be more likely to have had more time to accumulate OC compounds. Turtles
Acknowledgements
This project would not have been possible without logistical support from the Academy of Natural Sciences in Philadelphia, Donna Dittman of Louisiana State University, Dan Janzen and Winnie Hallwachs of the University of Pennsylvania, INBio of Costa Rica, and Roger Blanco and the other staff of the Area de Conservación Guanacaste. Jon Stead, Alejandro Masis, Dunia Garcia, Calixto Moraga, and Petrona Rios assisted in the field. Heidi Richardson assisted in the laboratory, Sheryl Soukup, Dan
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Current Address: Department of Biology, Leidy Labs, University of Pennsylvania, Philadelphia, PA 19104, USA.