Gary W. Holcombe

Relationships of quantitative structure-activity to comparative toxicity of selected phenols in the Pimephales promelas and Tetrahymena pyriformis test systems

The relative toxic response of 27 selected phenols in the 96-hr acute flowthrough Pimephales promelas (fathead minnow) and the 48- to 60-hr chronic static Tetrahymena pyriformis (ciliate protozoan) test systems was evaluated. Log Kow-dependent linear regression analyses revealed that the data from each test system consisted of two linear equations. The less toxic chemicals form a relationship which models polar narcosis; these chemicals are slightly more active than the baseline toxicity of nonionic narcotic chemicals. The more toxic chemicals form a relationship which models uncoupling of oxidative phosphorylation. Regression analysis of fathead minnow toxicity (log LC50 (mol/liter] vs Tetrahymena toxicity (log BR (mmol/liter] showed good correlation between the two systems. An exception appears to be 4-nitrophenol, which is more active in the Tetrahymena system than in the fathead minnow and lies outside the 95% confidence interval. Reanalysis following deletion of 4-nitrophenol results in the equation log LC50 = -0.9192 (log BR) -3.5035; n = 26, r2 = 0.887.

Metal toxicity to embryos and larvae of seven freshwater fish species—i. cadmium

The embryos and larvae of seven freshwater fish were exposed to low concentrations of cadmium in soft water. All species were killed or their growth retarded by concentrations ranging from about A to 12 μg Cd/liter. The larvae were consistently more sensitive than the embryos. The agreement between these results and those from lifecycle chronic toxicity studies indicates that embryo and larval exposures will give reliable estimates of the chronic toxicity of cadmium to additional fish species. A 60-day exposure period appears to be appropriate for determining larval sensitivity to cadmium.

Acute toxicity of phenol and substituted phenols to the fathead minnow.

Because of the wide, high-volume usage of phenolics it behooves us to be aware of their toxicity in the environment. This awareness must include a knowledge of the effects on freshwater bodies and more specifically, an appreciation of the importance of differences in the physical properties of the water. The variability of the data on some phenolics makes it difficult to separate toxicity values that vary widely from others because of different test methods rather than different physical properties of the water. Data were lacking on some of the compounds we tested, and thus our data contribute significantly to the basic informtion on these chemicals. This acute test series was conducted with a variety (12) of phenolic compounds. Test conditions were kept as uniform as possible so that the toxicities of the compounds could be attributed to the differences in toxicity rather than to differences in test conditions. In addition, the tests provide data on the toxic effects in Lake Superior water, which is a major freshwater body in the USA.

Simultaneous multiple species testing: acute toxicity of 13 chemicals to 12 diverse freshwater amphibian, fish, and invertebrate families.

This test series developed methods for testing a compliment of aquatic organisms in a single test that satisfies the freshwater acute toxicity requirements for setting water quality criteria. Species tested included fathead minnowsPimephales promelas, rainbow troutSalmo gairdneri, bluegillLepomis macrochirus, channel catfishIctalurus punctatus, goldfishCarassius auratus, white suckerCatostomus commersoni, daphnidDaphnia magna, midgeTanytarsus dissimilis, crayfishOrconectes immunis, snailAplexa hypnorum, tadpoleXenopus laevis, and leechNephelopsis obscura. Five to nine of the preceding species were simultaneously exposed in individual tests. The chemicals tested were acrolein, aniline, dibutylfumarate, 2,4-dinitrophenol, Guthion®, nicotine sulfate, phenol, rotenone, silver, Systox®, 1,2,4-trichlorobenzene, 2,4,6-trichlorophenol, ando-xylene. This method of simultaneously exposing aquatic organisms in separate compartments of each exposure tank allows more accurate comparisons of species sensitivity with a tested chemical. Use of this method can also produce the minimum acute data set for the derivation of a water quality criterion in less time and with a substantial cost saving for labor, materials, and chemical analyses when compared with measured concentration tests conducted separately with each individual species.

Metal toxicity to embryos and larvae of eight species of freshwater fish-II: copper.

Fish larvae and early juveniles of all species tested (brook trout, rainbow trout, brown trout, lake trout, northern pike, white sucker, herring, and smallmouth bass) were more sensitive to copper than the embryos. Embryo survival was affected only at the higher concentrations tested, for all species except the rainbow trout. The concentrations of copper that caused significant effects on the larval standing crop were similar for all species (31.7–43.5 ug Cu/1) except the northern pike, which seemed to be considerably more resistant (104.1 μg Cu/1). Copper concentrations shown to have no significant effects on the early developmental stages of these species are considered close estimates of the copper concentrations that would have no measurable adverse effects during a complete life cycle toxicity test under similar test conditions.

Metamorphic inhibition of Xenopus laevis by sodium perchlorate: effects on development and thyroid histology.

The perchlorate anion inhibits thyroid hormone (TH) synthesis via inhibition of the sodium-iodide symporter. It is, therefore, a good model chemical to aid in the development of a bioassay to screen chemicals for affects on thyroid function. Xenopus laevis larvae were exposed to sodium perchlorate during metamorphosis, a period of TH-dependent development, in two experiments. In the first experiment, stage 51 and 54 larvae were exposed for 14 d to 16, 63, 250, 1,000, and 4,000 microg perchlorate/ L. In the second experiment, stage 51 larvae were exposed throughout metamorphosis to 8, 16, 32, 63, and 125 microg perchlorate/L. Metamorphic development and thyroid histology were the primary endpoints examined. Metamorphosis was retarded significantly in the first study at concentrations of 250 microg/L and higher, but histological effects were observed at 16 microg/L. In the second study, metamorphosis was delayed by 125 microg/L and thyroid size was increased significantly at 63 microg/L. These studies demonstrate that inhibition of metamorphosis readily can be detected using an abbreviated protocol. However, thyroid gland effects occur at concentrations below those required to elicit developmental delay, demonstrating the sensitivity of this endpoint and suggesting that thyroidal compensation is sufficient to promote normal development until perchlorate reaches critical concentrations.

Long-Term Effects of Zinc Exposures on Brook Trout (Salvelinus fontinalis)

Abstract Exposure of three generations of brook trout (Salvelinus fontinalis) to zinc concentrations ranging from 2.6 to 534 μg/liter produced no significant harmful effects. During a separate exposure of embryos and larvae, 1,368 μg Zn/liter significantly reduced (P = 0.05) both embryo and 12-week larval survival. An additional partial chronic exposure also resulted in significantly reduced (P = 0.05) egg chorion strength and embryo survival at 1,360 μg Zn/liter. The maximum acceptable toxicant concentration (MATC) for brook trout exposed to zinc in Lake Superior water (hardness = 45.4 mg/liter as CaCO3; pH = 7.0–7.7) lies between 534 and 1,360 μg Zn/liter. The 96-hour LC50 (median lethal) concentration for brook trout was 2,000 μg Zn/liter; thus the application factor (MATC/96-hour LC50) lies between 0.267 and 0.680. Brook trout gill, liver, kidney, and opercular bone tissues accumulated the greatest amounts of zinc. Edible muscle tissue did not accumulate zinc. Zinc loss from gill and liver from first-...

A method for aquatic multiple species toxicant testing: Acute toxicity of 10 chemicals to 5 vertebrates and 2 invertebrates

Abstract A method was developed to simultaneously ascertain 96 h LC50 values for seven freshwater species in a single flow through test with measured concentrations. It allows interspecific comparisons, easy determination of the most sensitive species, and cuts cost of labour, materials and chemical analysis for measured concentration tests. Species tested included fathead minnows Pimephales promelas, goldfish Carassius auratus, channel catfish Ictalurus punctatus, bluegill Lepomis macrochirus, rainbow trout Salmo gairdneri, crayfish Orconectes immunis and snails Aplexa hypnorum. Compounds tested were pentachlorophenol, 2-chloroethanol, 2,4-pentanedione, hexachloroethane, α-bromo-2′,5′-dimethoxyacetophenone, benzaldehyde, 1,3-dichloro-4,6-dinitrobenzene, dursban, sevin and cadmium chloride. The LC50 values from these multiple species tests compared favourably with those determined using single species tests at this laboratory, usually within 20%.

The acute toxicity of kelthane, dursban, disulfoton, pydrin, and permethrin to fathead minnows Pimephales promelas and rainbow trout Salmo gairdneri

Abstract Flow-through acute lethal toxicity tests were conducted with kelthane, dursban disulfoton, pydrin and permethrin using rainbow trout Salmo gairdneri and fathead minnows Pimephales promelas in Lake Superior water. Pydrin was the most toxic pesticide tested to both species of fish and was followed in order of decreasing toxicity by permethrin, dursban, kelthane and disulfoton. Rainbow trout were more sensitive than fathead minnows to all five pesticides. The 96-h LC 50 values (μg litre −1 ) for rainbow trout and fathead minnows, respectively, were: pydrin, 2·1 and 5·4; permethrin, 7·0 and 15·6; dursban, 8·0 and 203·0; kelthane, 210·0 and 510·0 and disulfoton, 3020·0 and 4000·0.

Sex reversal of the amphibian, Xenopus tropicalis, following larval exposure to an aromatase inhibitor

Aromatase is a steroidogenic enzyme that catalyzes the conversion of androgens to estrogens in vertebrates. Modulation of this enzymes activity by xenobiotic exposure has been shown to adversely affect gonad differentiation in a number of diverse species. We hypothesized that exposure to the aromatase inhibitor, fadrozole, during the larval development of the tropical clawed frog, Xenopus tropicalis, would result in masculinization of the developing female gonad. Tadpoles were exposed to fadrozole at nominal concentrations from 1 to 64 microg/L in a flow-through system from < 24 h post-fertilization (Nieuwkoop Faber (NF) stage 15-20) to metamorphosis (NF stage 66). At metamorphosis, morphologically examined gonads indicated complete masculinization of all tadpoles at concentrations of 16 microg/L and above and a significant bias in sex ratio towards males at concentrations of 1 microg/L and above. No effects on time to metamorphosis, body mass, or body length were observed. A random subsample of frogs was raised to reproductive maturity (39 weeks post-fertilization) in control water. All frogs exposed as tadpoles to 16 microg/L fadrozole or greater possessed testes at sexual maturity. Intersexed gonads characterized by the presence of both testicular and ovarian tissue were observed in 12% of frogs in the 4 microg/L treatment. No differences in estradiol, testosterone, or vitellogenin plasma concentrations were observed in exposed males or females compared to controls. Females in the 4 microg/L treatment possessed a significantly greater percentage of pre-vitellogenic oocytes than controls and were significantly smaller in body mass. No differences in sperm counts were observed in exposed males compared to controls. Results from this study demonstrate that larval exposure to an aromatase inhibitor can result in the complete masculinization of female gonads. These masculinized females are phenotypically indistinguishable from normal males at adulthood. Lower levels of aromatase inhibition resulted in intersexed gonads and possible female reproductive impairment at adulthood. These results indicate that exposure of amphibians to xenobiotics capable of inhibiting aromatase would result in adverse reproductive consequences.