Lj. Standley et Bw. Sweeney, ORGANOCHLORINE PESTICIDES IN STREAM MAYFLIES AND TERRESTRIAL VEGETATION OF UNDISTURBED TROPICAL CATCHMENTS EXPOSED TO LONG-RANGE ATMOSPHERIC TRANSPORT, Journal of the North American Benthological Society, 14(1), 1995, pp. 38-49
We investigated whether biota and sediments in river catchments consis
ting of primary forest in northwestern Costa Rica are contaminated by
atmospheric transport of organochlorine pesticides from nearby regions
where their use is intense. We measured organochlorine residues in st
ream mayflies, as well as in the bark and leaves of trees in catchment
s of an undisturbed dry tropical forest west of Volcan Orosi and Cerro
Cacao (i.e., western catchments), and in tree leaves and bark in part
ially disturbed rain forest catchments east of Cerro Orosi (i.e., east
ern catchments) in a region where agricultural activity is intense. Sa
mples were solvent extracted, purified by silica gel clean-up, and con
centrated before analysis by gas chromatography/mass spectrometry. Twe
lve organochlorine pesticides were detected in samples, including hexa
chlorocyclohexanes, heptachlor epoxide, endosulfans, DDT, DDE, dieldri
n, endrin, endrin aldehyde, and aldrin. Endosulfans dominated the orga
nochlorine signature of mayflies collected in the western catchments a
nd of leaves and bark collected from eastern catchments. Leaves and ba
rk collected in the undisturbed western catchments contained ten-fold
lower concentrations of the endosulfans than those collected from the
eastern catchments. Hexachlorocyclohexane isomers were dominated by th
e gamma isomer and were present at comparable levels in samples of lea
ves and bark collected from both sides of the volcanic ridge. An excep
tion was high residues in bark collected from one eastern catchment, s
uggesting a local source. Stream mayflies and terrestrial vegetation i
n the undisturbed dry tropical forest contained substantial quantities
of organochlorine pesticides, the most likely source being long- and
short-range atmospheric transport.