Field Confirmation of a Laboratory-Derived Hazard Assessment of the Acute Toxicity of Fenthion to Pink Shrimp, Penaeus duorarum

Abstract

Field studies were conducted to determine if laboratory protocols accurately predict shrimp mortality under field conditions. To evaluate the applicability of laboratory data, fenthion, a mosquitocide, was applied to coastal black rush (Juncus roemerianus) marshes in several truck-mounted ultra-low volume (ULV) adulticide operations and by direct application at the larvicide rate. Caged pink shrimp (Penaeus duorarum) were deployed in floating compartmented cages and observed frequently over a 24-h period for mortality. Water samples collected for gas chromatographic quantitation characterized the exposure concentration regime and fate of fenthion at the field sites. Field data were compared to laboratory acute toxicity data from ASTM standard practice flow-through tests. The acute flow-through 96-h LC50 of 0.11 μg/L was used as a conservative estimate of the expected toxicity in field exposures. An exposure profile based on measured field concentrations was used for laboratory pulse-exposure tests; fenthion was metered for 2 h to specified maximum concentrations, then flushed with seawater to cause a 6- to 8-h exposure, yielding a no-observed-effect concentration (NOEC) of 0.84 μg/L. In field tests, four ULV operations produced initial water concentrations < NOEC and no fenthion-induced shrimp mortality. However, the direct application's initial water concentrations ranged from 15 to 20 μg/L (> NOEC) and caused extensive mortality (90 to 100%) in the caged shrimp. Thus, field observations confirmed our hypothesis that if fenthion time-exposure concentrations were lower than the laboratory NOEC, then no mortality would occur in caged shrimp. Moreover, if initial concentrations in the field exceeded the laboratory NOEC, mortality would occur. These laboratory tests and field applications indicate that laboratory toxicity tests can predict the range of lethal and nonlethal acute field exposures to fenthion for pink shrimp when exposure regimes are similar.

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

“…For all but one of seven short-term, nonlethal field exposures, initial fenthion concentrations approached or exceeded the 24-h LCSOs for mysids (0.42 pg/L) and pink shrimp (0.40 pg/L) [2]. However, these concentrations did not persist for more than 2 h and had no significant effect on the survival of mysids or pink shrimp except after the second ULV application, when mysid mortality increased 33% above controls (mortality in treated group, 65%; in control group, 32%) [ll].…”

“…We then conducted a series of laboratory toxicity tests that incorporated short-term, rapidly changing fenthion concentrations to provide a better basis for evaluating fenthion toxicity under such exposure regimes [2,12]; there was excellent agreement between results for both lethal and nonlethal, short-term field exposures and laboratory pulse-exposure tests (Fig. 2).…”

“…Because none of the field exposure concentrations of fenthion approached the 24-h LC50 for sheepshead minnows (1,890 pg/L) [2], no lethal effect on caged sheepshead minnows was expected and none occurred. Three direct applications of fenthion to water (two larvicide treatments and one environmental fate study) produced fenthion concentrations that exceeded the 24-h LCSO for grass shrimp (9.5 pg/L) [2] by more than a factor of 2 and, as expected, caged grass shrimp mortalities were 11, 72 and 100% during these field experiments. During four field tests, caged grass shrimp survived fenthion exposures after ULV applications when initial field concentrations were one-twentieth or less of the LC50.…”

“…The 24-h LCSOs for grass shrimp (9.5 pg/L), mysids (0.42 pg/L) and pink shrimp (0.40 pg/L) are much less than those for sheepshead minnows (1,890 pg/L) and inland silversides (Menidia beryllina) (2,250 pg/L) [2]. For freshwater crustaceans, the 48-h EC50 for water fleas (Daphnia pulex) (0.80 pg/L) and 96-h LC5Os for scuds (Gammarus lacustris) (8.4 pg/L) and glass shrimp (Palaemonetes kadiakensis) (10 pg/L) are substantially less than the 96-h LCSOs for freshwater fish such as rainbow trout (Salmo gairdneri) (930 pg/L), bluegill (Lepomis macrochirus) (1,380 pg/L) and fathead minnows (Pimephales promelas) (2,440 pg/L) [3]. Applied at the maximum allowable rate of 112 g/ha (0.10 lb/acre), the expected maximum environmental concentration of fenthion would be 37 pg/L [4]; this exceeds the LCSOs for crustaceans but is considerably less than those for fish.…”

“…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.…”