Barbara T. Walton

Turtles as Monitors of Chemical Contaminants in the Environment

Biota have been used increasingly in recent years to evaluate the presence of hazardous chemicals in the environment and to determine the impact of toxicants on ecosystems (e.g., Suter and Loar 1992; Hoffman et al. 1990; Clark et al. 1988; Talmage and Walton 1991; and Albers et al. 1986). Because turtles are relatively long-lived, widely distributed geographically, and found in a variety of habitats, they may be useful indicators of chemical contamination in monitoring programs. Species selection is an important consideration for a successful biological monitoring study (National Research Council 1986), and turtles offer a number of advantages as indicators of the availability of chemical and radioactive contaminants in aquatic and terrestrial ecosystems (Meyers-Schone et al. 1993). However, not all turtle species can be expected to be equally good choices for monitoring programs because species-specific characteristics, such as differences in food habits, habitat use, home range, age, and sex, are likely to affect the exposure of individual animals at a chemically contaminated site.

Plant-microbe treatment systems for toxic waste

Abstract There is increasing experimental evidence that microbial degradation of hazardous organic compounds can be achieved faster in the presence of plant roots than in soil or water in the absence of roots. These studies hold promise that new techniques in biotechnology can eventually be applied to plant-microbe systems for hazardous waste treatment.

Food chain transfer and potential renal toxicity of mercury to small mammals at a contaminated terrestrial field site.

Mercury concentrations were determined in surface soil and biota at a contaminated terrestrial field site and were used to calculate transfer coefficients of mercury through various compartments of the ecosystem based on trophic relationships. Mercury concentrations in all compartments (soil, vegetation, invertebrates, and small mammals) were higher than mercury concentrations in corresponding samples at local reference sites. Nonetheless, mercury concentrations in biota did not exceed concentrations in the contaminated surface soil, which averaged 269 μg g-1. Plant tissue concentrations of mercury were low (0.01 to 2.0 μg g-1) and yielded soil to plant transfer coefficients ranging from 3.7×10-5 for seeds to 7.0×10-3 for grass blades. Mercury concentrations in invertebrates ranged from 0.79 for harvestmen (Phalangida) to 15.5 μg g-1 for undepurated earthworms (Oligochaeta). Mean food chain transfer coefficients for invertebrates were 0.88 for herbivores/omnivores and 2.35 for carnivores. Mean mercury concentrations in target tissue (kidney) were 1.16±1.16 μg g-1 for the white-footed mouse (Peromyscus leucopus), a granivore, and 38.8±24.6 μg g-1 for the shorttail shrew (Blarina brevicauda), an insectivore. Transfer coefficients for diet to kidney were 0.75 and 4.40 for P. leucopus and B. brevicauda, respectively. A comparison of kidney mercury residues measured in this study with values from controlled laboratory feeding studies from the literature indicate that B. brevicauda but not P. leucopus may be ingesting mercury at levels that are nephrotoxic.

Use of the Cricket Embryo (Acheta domesticus) as an Invertebrate Teratology Model

Embryos of the cricket Acheta domesticus (L.) have been shown by bioassay to develop gross morphological abnormalities after exposure to a number of complex organic mixtures as well as to display a critical period of teratogen sensitivity and an ability to metabolize xenobiotics during development. Because the assay is simple, inexpensive, short-term (less than two weeks), and objective, it could be useful as an in vivo screen in a hierarchical approach to teratogen detection. Further investigation of cricket embryo responses to known teratogens is needed to establish the predictive value of this assay.

Experimental method to measure gaseous uptake of 14C-toluene by foliage

Abstract An experimental method is described to measure foliar uptake and translocation of volatile organic compounds in plants. A flow-through exposure chamber was designed to determine phytoxicity of volatile organic compounds; an air-tight chamber was used for exposure of whole plants to radiolabeled test compound. 14 C-toluene uptake by soybean ( Glycine max ) foliage was measured as an example of the experimental approach. Leaf tissue concentrations of 14 C-toluene were measured over a 55.5-hr exposure period during light and dark periods. Photosynthetic rate was not affected by chronic atmospheric exposure to 27 μmole cm −3 hr toluene. During a 55.5-hr exposure to 7.2 μmoles cm −3 hr 14 C-toluene (1.94 Bq cm −3 ), deposition velocities were greatest in the light phases and showed a marked decrease during the dark phases of exposure, suggesting that stomatal uptake as well as surface deposition contributed to toluene uptake. 14 C was translocated from foliage to the roots. These data indicate that deposition of volatile organic compounds to vegetation may constitute a mechanism leading to herbivore exposure to volatile hazardous organics at waste sites. The experimental method described can be used to measure foliar uptake and translocation of volatile organic compounds to whole plants under laboratory conditions.

Environmental fate and distribution of technetium-99 in a deciduous forest ecosystem

Abstract The aims of the present research are to describe the uptake of 99 Tc by trees intercepting contaminated groundwater from a radioactive waste storage site, to identify the major 99 Tc pools within the woodland ecosystem and to assess the relative mobility of 99 Tc in the existing element cycle. Technetium in the groundwater freely passed through a dialysis membrane with a molecular weight exclusion limit of approximately 3500 amu and 99 Tc in the groundwater chromatographed on Biogel P-2 in a manner similar to pertechnetate anion (TcO 4 − ). Reducing conditions and organic associations at the study site were probably responsible for the relatively large amount (83–92%) of the 99 Tc that was nonextractable from soil by 0·01 m CaCl 2 . More than one-third of the 99 Tc was released from the soil by oxidizing reagents, indicating the presence of chemically reduced forms. The highest average 99 Tc concentrations in vegetation were found in herbaceous plants (18 530 pCi g −1 dry wt). Although 99 Tc was progressively accumulated over the growing season in tree leaves, average concentrations in tree wood and twigs were equal to or greater than concentrations in leaves. Tree wood was the major above-ground pool for 99 Tc because of the high concentrations in wood as well as the large amount of wood relative to other biomass at the site. Technetium was not easily leached from the trees by rainfall and was not readily extractable from forest floor leaf litter by water. The relative importance of return pathways for 99 Tc to the forest floor was leaf fall>stemflow >throughfall, indicating that 99 Tc was conserved by the trees. Snails and millipedes from the leaf litter layer concentrated technetium 20- and 16-fold, respectively, above levels found in the soil. Pertechnetate was rendered less bioavailable after ingestion by a leaf litter macroinvertebrate ( Porcellio sp.) common to the study site.

Degradation of hazardous organic compounds by rhizosphere microbial communities

Publisher Summary The variety of plants and chemicals studied for the evidence of microbial degradation in the rhizosphere strongly suggests that a diverse and synergistic microbial community, rather than a single species, is responsible for biotransformation of toxicants in the rhizosphere. Participation of a microbial community is implicated by (i) the extreme diversity and complexity of toxicants degraded, and (ii) the knowledge that many of these compounds are completely degraded only in the presence of interacting microbial populations (consortia). Moreover, data presented, herein, from phospholipid fatty acid analysis, 14 C acetate incorporation, and PHA analysis of micro-organisms from the rhizosphere are consistent with the participation of a microbial community in TCE degradation. Other mechanisms can also be invoked to explain how microbial transformations occur in the rhizosphere. Collectively, these factors have important implications for the successful use of vegetation to increase the participation of micro-organisms in biotransformation of toxicants at hazardous waste sites.

Influence of route of entry on toxicity of polycyclic aromatic hydrocarbons to the cricket (Acheta domesticus).

In the present study, acute and chronic toxicities of five PAHs (naphthalene, anthracene, benz(a)anthracene, pyrene, and benzo(a)pyrene) and an oxygenated PAH derivative (anthrone) were determined in a terrestrial insect, Acheta domesticus (L.), with emphasis on the influence of route of entry on toxicity. Hexamethylphosphoric triamide (hempa) was included in the chronic tests since this chemosterilant is a useful reference compound for investigations of reproductive effects of chemicals in insects.

Pharmacodynamic behavior of [14C]acridine in the cricket Acheta domesticus (L.).

Cuticular and gastrointestinal penetration, in vivo metabolism, and excretion of [14C]acridine were investigated in the nymphal cricket Acheta domesticus (L.) to find a pharmacodynamic basis for this insects differential susceptibility to acridine at different life stages. Topically applied [14C]acridine readily penetrated the cuticular exoskeleton of nymphs (half-time of penetration, 48 min). Radiolabeled compounds appeared in the hemolymph within 0.5 h after ingestion of [14C]acridine and continued to move across the gut wall for 7.5 h. The biological half-time was 18 h and the rate constant for elimination was 0.039 h-1 after ingestion. Within 5 d after dosing, 97% of the dose was excreted. Several metabolites were present in the feces of nymphs fed [14C]acridine, and less than 13% of the extractable radioactivity was parent compound. The cuticle and the gastrointestinal tract proved to be ineffective barriers to acridine entry in A, domesticus. However, the ability to readily metabolize and excrete acridine probably contributes to the higher acridine tolerance observed in the nymphs and adults than in the eggs, which are susceptible to toxic effects.

Postembryonic development of teratogen-induced supernumerary eyes in Acheta domesticus (L.) (Orthoptera : Gryllidae)

Abstract Supernumerary compound eyes were generated in the cricket Acheta domesticus (L.) (Orthoptera : Gryllidae) by applying the insect teratogen biquidone (benz[g]isoquinoline-5, 10-dione) and partially characterized teratogenic mixtures to eggs within 24 hr following oviposition at 31 ± 0.5°C. Postembryonic development of supernumerary eyes was compared with that of normal compound eyes, using light and scanning electron microscopy. All elements of the dioptric apparatus were present in supernumerary eyes of nymphs, but no axonal connection to the brain was found. Supernumerary eyes deteriorated during successive instars. Occasionally, these eyes were sloughed off before the adult stage was reached; more frequently, eyes appeared as highly pigmented protrusions not readily identifiable as adult eye tissue. Teratogen-induced supernumerary eyes are probably not functional light receptors in A. domesticus nymphs or adults.