Field and Laboratory Toxicity Tests with Shrimp, Mysids, and Sheepshead Minnows Exposed to Fenthion

Comparison of laboratory toxicity test results with responses of estuarine animals exposed to fenthion in the field

“…We studied aerial thermal fog applications of fenthion at two sites in Collier County, Florida, during routine mosquito control operations of the Collier County Mosquito Control District [12]. One site, within the Isles of Capri development along Johnson Bay and approximately 1 km from Capri Pass, was rapidly flushed by tidal exchanges, which offered the potential of diluting the water in Johnson Bay.…”

“…During field studies at Eglin Air Force Base sites, mysids were held in conical, doublelayered nylon mesh cages (363-pm inner layer; 1,000-pm outer layer) [ll]. For field studies in Collier County, we caged mysids in floating cylin- drical cages of 450-pm nylon mesh [12]. Grass shrimp or pink shrimp were caged in open-sided Plexiglas boxes that had been covered with 1.8-mm nylon mesh [lo].…”

“…Samples were collected at 12-h intervals except immediately after fenthion applications, when sampling was more frequent (0.5, 1, 2, 4, 6, 9 and 12 h). Samples were extracted with petroleum ether at the field site [14] or held on ice for 2 h or less during transport to a field-site laboratory, where fenthion was extracted on a column of XAD-4 resin [12]. Water samples were collected at reference sites at least daily.…”

“…We conducted laboratory toxicity tests with technical-grade fenthion to establish 24and 96-h LCSOs for mysids, pink shrimp and sheepshead minnows [2]. Because exposure regimes during these tests were considerably different from shortterm (<12 h) field exposures in which fenthion concentrations changed rapidly over time, laboratory pulse exposures were designed to provide 2 h of increasing fenthion concentrations and 8 to 12 h of exposure during which fenthion concentrations steadily decreased [2,12]. Test solutions of fenthion were introduced into 60-liter aquaria at a rate of 30 L/h for 2 h, the injection of toxicant was stopped and then uncontaminated seawater was supplied to the test aquaria at 30 or 15 L/h.…”

“…The application of fenthion to control salt-marsh mosquitoes is a pesticide use pattern from which exposure-response assessments can be made in the natural habitat of a variety of estuarine animals. We monitored the survival of mysids (Mysidopsis bahia), grass shrimp (Palaemonetes pugio), pink shrimp (Penaeus duorarum) and sheepshead minnows (Cyprinodon variegutus) after fenthion applications from (a) truck-mounted ultra-low-volume (UVL) spray equipment [4,10,11]; (b) DC-3 aircraft equipped with thermal fog spray equipment [12]; and (c) boats and hand-held spray equipment to simulate larvicide applications (unpublished data) and to determine the environmental fate of fenthion [13]. Although the application rates for all studies were consistent with label restrictions (except for the fate study), larvicide applications were not representative of mosquito control practices in Florida; thus, these tests should not be considered examples of actual use.…”