Russell J. Hall

Bioconcentration of organophosphorus pesticides to hazardous levels by amphibians.

Organophosphorus pesticides have generally low persistence in the environment, but they may persist in water and accumulate in certain aquatic vertebrates. Frogs are resistant to cholinesterase inhibitors; thus it was suspected that they might accumulate the pesticides. Tadpoles concentrated pesticides from water up to 60 times; those exposed to 1 ppm parathion and 5 ppm fenthion were lethal when they were fed to mallard ducks. Dicrotophos, malathion, and acephate were not accumulated to levels such that they were lethal when consumed in a single meal by ducks. Brain cholinesterase levels were correlated with dose and effect. Metabolites of parathion and fenthion produced by the tadpoles were rapidly excreted and it was concluded that they play a small role in the toxicity of the larvae to ducks. Dangerous levels of some pesticides may be accumulated by amphibians in nature and may adversely affect carnivorous species.

Responses of the iguanid lizard Anolis carolinensis to four organophosphorus pesticides

Abstract Dose related mortality and cholinesterase effects of parathion, methyl parathion, azinphos-methyl and malathion on Anolis carolinensis were investigated. The comparative effects of the four compounds on fish, birds and mammals are well known, but the effects of organophosphates on reptiles have not been studied critically. Sensitivity and patterns of mortality from exposure to the pesticides resemble those of birds and mammals rather than those of other poikilothermic vertebrates. Possible symptoms of epinephrine accumulation were observed in exposed animals; this side effect is consistent with the known mechanisms of the pesticides. Our findings indicate that brain cholinesterase activity is related to dose, that 50% inhibition of cholinesterase is associated with death and that 40% inhibition indicates sublethal exposure. Anolis lizards are frequently exposed to pesticides in the field and they may be useful in monitoring the hazards posed to a variety of wildlife species.

Organochlorine residues in eggs of the endangered American crocodile (Crocodylus acutus)

Most of the 27 species and subspecies of surviving crocodilians have declining populations and 22 of them are considered to be severely endangered (IUCN 1971). The United States population of the American Crocodile is no exception; it probably numbers between I00 and 300 individuals (OGDEN 1976). Nests of the species have been regularly surveyed by the staff of Everglades National Park. Our sample consists of eggs that remained in nests after the hatching of broods and of one clutch laid in captivity by an unmated female. Analysis of these samples for organochlorine contaminants has permitted a detailed examination of their contaminant loads and has allowed comparisons with a small sample analyzed in 1972 (OGDEN et al. 1973).

Toxic effects of endrin and toxaphene on the southern leopard frog Rana sphenocephala

Abstract Eggs, larvae and sub-adults of the southern leopard frog Rana sphenocephala were exposed to endrin and toxaphene. Exposure was in water by a continuous-flow technique, following standards that have been used successfully in the study of fish and invertebrates. R. sphenocephala is more sensitive to both pesticides than are higher vertebrates but is slightly less sensitive than fish. Eggs seem to be resistant to the effects of both pesticides and are probably poor indicators of environmental hazard. The toxic level of endrin is about equal in larvae and transformed frogs (LC50, 0·005-0·015 ppm). Toxaphene is less toxic to sub-adults (LC50, 0·37-0·790 ppm) than to larvae (LC50, 0·032-0·054 ppm). Delayed mortality, behavioural aberrations and effects on growth have been seen in toxaphene-dosed larvae observed over 30-day periods. Behavioural effects are more severe than those reported in other groups of animals. Effects on growth resulting from a 96-h exposure begin in the 0·013-0·018 ppm range. The maximum accumulation of residues observed for each chemical represented bioconcentration factors of about 100. Endrin residues are apparently lost more readily than toxaphene residues; relative depuration rates correlate well with the time course of toxic action in each chemical. Although less sensitive to these pesticides than fish, amphibians may not be protected in their natural habitats. Future studies of the effects of toxicants on amphibians should employ larvae if only one stage can be tested, should expose subjects for at least 96 h and should continue observations for a total of at least 30 days.

RESIDUES OF PETROLEUM HYDROCARBONS IN TISSUES OF SEA TURTLES EXPOSED TO THE IXTOC I OIL SPILL

Sea turtles found dead when the Ixtoc I oil spill reached Texas waters were necropsied and tissues were analyzed for residues of petroleum hydrocarbons. Two of the three turtles were in poor flesh, but had no apparent oil-caused lesions. There was evidence of oil in all tissues examined and indications that the exposure had been chronic. Comparisons with results of studies done on birds indicate consumption of 50,000 ppm or more of oil in the diet. Some possible mechanisms of mortality are suggested.

Acute toxicities of toxaphene and endrin to larvae of seven species of amphibians

Seven species of amphibian larvae were exposed to toxaphene and endrin in a continuous-flow dosing system to determine differences in sensitivity to the two compounds, EC50 and LC50 estimates varied from those for Rana sphenocephala by no more than one order of magnitude when calculated on the basis of intended concentrations. Removal of pesticides from water by the test animals was significant and it makes interpretation of results difficult. Continuous-flow toxicity tests conflict with the adaptations of amphibian larvae for static water; use of such tests for amphibians requires further evaluation.

Organochlorine and mercury residues in snakes from Pilot and Spider Islands, Lake Michigan--1978.

Little is known about the chronic effects of environmental pollutants on snakes, but some investigators have suggested that snakes make good biological indicators of environmental contamination. Being carnivorous, snakes would be expected to carry fairly high contaminant loads as a result of food chain concentration. They are also generally more sedentary than many other vertebrates and should, therefore, be good indicators of pollutants in the area where they are collected. During the course of a contaminant study with waterfowl on several islands in Lake Michigan, we collected snakes in order to measure their organochlorine and mercury levels.

Accumulation, metabolism and toxicity of parathion in tadpoles.

Earlier work exposing tadpoles to organophosphorus pesticides indicated the great resistance of tadpoles of the bullfrog (Rana catesbeiana) to these chemicals and their surprising ability to accumulate parathion and fenthion from water. These qualities seemed to make them an ideal model with which to test a hypothesis advanced by Burke and Ferguson, who noted that parathion is more toxic to resistant mosquitofish in static water than in flowing water--a reversal of the pattern normally seen. They believed that highly toxic metabolite paraoxon was produced by the fish and that its buildup in static systems resulted in the unexpected mortality. Amphibians have been shown to produce paraoxon and to accumulate the parent compound parathion to levels that are potentially hazardous to other organisms. In the course of examining paraoxon production by tadpoles, it would also be possible to learn more about their patterns of parathion uptake and elimination. Retention of residues is also a matter of concern given the high levels observed in the earlier studies.

Monitoring contaminant exposure: Relative concentrations of organochlorines in three tissues of American black ducks

Comparison of organochlorine residues in wildlife must often be made to regulatory standards or to values of known biological significance; this is difficult when dissimilar tissues are analyzed and results are expressed on different bases. To relate levels in the different tissues used for regulatory and monitoring purposes and for biological assessments, we exposed American black ducks to mixtures of three organochlorines. Differences in residue burdens among tissues were not statistically significant when levels were expressed on a lipid weight basis. Levels of heptachlor and Aroclor 1254 in one tissue can be accurately predicted from those in another; such predictions for endrin are less reliable. Lipid weight based residue concentrations in wings may be used to predict whether levels in fat exceed residue standards set for human health or approach those associated with effects on populations of species sampled.

Female reproductive dynamics in a Maryland population of ringneck snakes (Diadophis punctatus)

Adult female ringneck snakes (Diadophis punctatus) collected from a Maryland population during five successive summers laid a total of 50 clutches in which all eggs hatched successfully under laboratory conditions. Mean hatchling mass was not significantly related to female mass or clutch size when each was evaluated in separate analyses, but was significantly related to these factors when they were evaluated in a joint analysis. Mean hatchling masses of 0.6-1 g appear most adaptive; when females are large enough to produce 1 g eggs, the tendency is to produce a larger number of relatively smaller eggs. The relationship of clutch mass to female mass was unaffected by clutch size. Reproductive effort, measured as relative clutch mass (RCM, clutch mass/female mass), increased with age, as indicated by snout-vent length (SVL); also, the relationship of clutch mass to female mass indicated that clutches equaled a larger percentage as female mass increased. Clutch size averaged 3.55 eggs and ranged from 2 to 6. Clutches were laid from 17 June through 21 July (35 d), median 2 July. Clutches hatched during the 20-d interval 8-27 August (median August 18). Larger clutches were laid earlier in the season on average than smaller clutches. Incubation periods for clutches averaged 47 (range 42-51) d. Clutches laid later in the season averaged shorter incubation periods than clutches laid earlier.