Breaking free from thermodynamic constraints: thermal acclimation and metabolic compensation in a freshwater zooplankton species.

Respiration rates of ectothermic organisms are affected by environmental temperatures, and sustainable metabolism at high temperatures sometimes limits heat tolerance. Organisms are hypothesized to exhibit acclimatory metabolic compensation effects, decelerating their metabolic processes below Arrhenius expectations based on temperature alone. We tested the hypothesis that either heritable or plastic heat tolerance differences can be explained by metabolic compensation in the eurythermal freshwater zooplankton crustacean Daphnia magna We measured respiration rates in a ramp-up experiment over a range of assay temperatures (5-37°C) in eight genotypes of D. magna representing a range of previously reported acute heat tolerances and, at a narrower range of temperatures (10-35°C), in D. magna with different acclimation history (either 10 or 25°C). We discovered no difference in temperature-specific respiration rates between heat-tolerant and heat-sensitive genotypes. In contrast, we observed acclimation-specific compensatory differences in respiration rates at both extremes of the temperature range studied. Notably, there was a deceleration of oxygen consumption at higher temperature in 25°C-acclimated D. magna relative to their 10°C-acclimated counterparts, observed in active animals, a pattern corroborated by similar changes in filtering rate and, partly, by changes in mitochondrial membrane potential. A recovery experiment indicated that the reduction of respiration was not caused by irreversible damage during exposure to a sublethal temperature. Response time necessary to acquire the respiratory adjustment to high temperature was lower than for low temperature, indicating that metabolic compensation at lower temperatures requires slower, possibly structural changes.

The acute toxicity of agricultural surfactants to the tadpoles of four Australian and two exotic frogs.

Nonionic surfactants are frequently incorporated into pesticide formulations, and are therefore a group of chemicals to which amphibians may be exposed in agricultural or urban landscapes. However, little is known about the effects of surfactant exposure in amphibians. Feeding stage tadpoles of Bufo marinus, Xenopus laevis and four species of Australian frogs (Crinia insignifera, Heleioporus eyrei, Limnodynastes dorsalis and Litoria moorei) were exposed to nonylphenol ethoxylate (NPE) and alcohol alkoxylate in static-renewal acute toxicity tests. All species exhibited nonspecific narcosis following exposure to both these surfactants. The 48-h EC50 values for NPE ranged between 1.1 mg/l (mild narcosis) and 12.1 mg/l (full narcosis). The 48-h EC50 values for alcohol alkoxylate ranged between 5.3 mg/l (mild narcosis) and 25.4 mg/l (full narcosis). Replicate acute toxicity tests with B. narinus exposed to NPE at 30 degrees C over 96 h indicated that the narcotic effects were not particularly time dependant. The mean 24, 48, 72, and 96-h EC50 (mild narcosis) values were 3.6, 3.7, 3.5 and 3.5 mg/l, respectively. The mean 24, 48, 72 and 96-h EC50 (full narcosis) were 4.0, 4.1, 4.2 and 4.0, respectively. Acute toxicity tests with B. marinus exposed to NPE at 30 degrees C under conditions of low dissolved oxygen (0.8-2.3 mg/l) produced a two to threefold increase in toxicity.

A 48-h larval development toxicity test using the marine polychaete Galeolaria caespitosa Lamarck (Fam. Serpulidae).

Assessing the risk of effluents and other anthropogenic inputs to the receiving environment is ultimately best done on a site-specific basis, which often requires toxicity tests using organisms relevant to that environment. Additionally, the test species or life stage needs to be available for a reasonable portion of the year to allow temporal fluctuations to be assessed. A 48-h larval development toxicity test using the marine polychaete Galeolaria caespitosa was developed. This test was developed as G. caespitosa releases viable gametes year-round, and the test species is environmentally relevant to the marine system receiving the liquid effluent being evaluated. Toxicity tests were conducted using G. caespitosa from different locations and evaluating the gamete response to copper. All population responses were comparable, with EC50 values ranging from 16 to 40 microg/L copper (as CuCl2, x 2H2O). Toxicity tests were also conducted using G. caespitosa gametes with an effluent produced by a lead smelting operation. The response of the G. caespitosa test with this effluent was compared with three other test methods using two microalgal species, Isochrysis sp. and Nitzschia closterium, and gametes from the mussel Mytilus edulis. The G. caespitosa larval development toxicity test was the most sensitive test to the effluent, with EC50 values ranging from 1-23% effluent, while it ranked second in sensitivity to copper. This test could be applied to other common serpulids worldwide.

Application of the FETAX protocol to assess the developmental toxicity of nonylphenol ethoxylate to Xenopus laevis and two Australian frogs.

The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) protocol has recently been adopted as a valuable tool for evaluating the embryotoxicity of environmental contaminants in amphibians. The bioassay utilises Xenopus laevis as a test species, but there are few comparative studies to evaluate whether data collected in this species is applicable to other amphibians. In this study, the embryotoxicity of the nonionic surfactant, nonylphenol ethoxylate, was determined in X. laevis and the Australian frogs, Litoria adelaidensis and Crinia insignifera using the FETAX protocol. The 96-h LC(50), EC(50) and minimum concentration to inhibit growth (MCIG) values for X. laevis were 3.9-5.4, 2.8-4.6 and 1.0-3.0 mg/l, respectively. The 140-h LC(50), EC(50) and MCIG values for L. adelaidensis were 9.2, 8.8 and 5.1-6.0 mg/l, respectively. The 134-h LC(50), EC(50) and MCIG values for C. insignifera were 6.4, 4.5 and 4.0 mg/l, respectively. Teratogenicity indices for the three species ranged between 1.0 and 1.6, indicating either no or low teratogenicity. Growth inhibition as assessed by embryo length was the most sensitive indicator of effect in all three species. X. laevis was the more sensitive of the three species and the only species that displayed indisputable terata.

The toxicity of glyphosate and several glyphosate formulations to four species of southwestern Australian frogs.

The acute toxicity of technical-grade glyphosate acid, glyphosate isopropylamine, and three glyphosate formulations was determined for adults of one species and tadpoles of four species of southwestern Australian frogs in 48-h static/renewal tests. The 48-h LC50 values for Roundup(R) Herbicide (MON 2139) tested against tadpoles of Crinia insignifera, Heleioporus eyrei, Limnodynastes dorsalis, and Litoria moorei ranged between 8.1 and 32.2 mg/L (2.9 and 11.6 mg/L glyphosate acid equivalent [AE]), while the 48-h LC50 values for Roundup(R) Herbicide tested against adult and newly metamorphosed C. insignifera ranged from 137-144 mg/L (49.4-51.8 mg/L AE). Touchdown(R) Herbicide (4 LC-E) tested against tadpoles of C. insignifera, H. eyrei, L. dorsalis, and L. moorei was slightly less toxic than Roundup(R) with 48-h LC50 values ranging between 27.3 and 48.7 mg/L (9.0 and 16.1 mg/L AE). Roundup(R) Biactive (MON 77920) was practically nontoxic to tadpoles of the same four species producing 48-h LC50 values of 911 mg/L (328 mg/L AE) for L. moorei and >1,000 mg/L (>360mg/L AE) for C. insignifera, H. eyrei, and L. dorsalis. Glyphosate isopropylamine was practically nontoxic, producing no mortality among tadpoles of any of the four species over 48 h, at concentrations between 503 and 684 mg/L (343 and 466 mg/L AE). The toxicity of technical-grade glyphosate acid (48-h LC50, 81.2-121 mg/L) is likely to be due to acid intolerance. Slight differences in species sensitivity were evident, with L. moorei tadpoles showing greater sensitivity than tadpoles of the other four species. Adult and newly emergent metamorphs were less sensitive than tadpoles.

The modification of human society by natural systems: discontinuities caused by the exploitation of endemic species and the introduction of exotics.

Drastic reductions in Earth's biodiversity, old growth forests, top soil, clean water and air, and truly wild areas are occurring during a period when discussions of sustainable growth and sustainable production are becoming common. Using such terms as sustainable growth and sustainable production rather than the more accurate sustainable use of the planet leaves the impression that, with a little more skill, society can continue its present practices indefinitely. A number of explanations are possible for this desire to maintain two conflicting beliefs (i.e., severe environmental destruction occurs but society can continue its basic practices indefinitely): 1) the idea that a technological solution can be found for every problem; 2) an addiction to present behavioral norms, which is so strong that the consequences of continuing such behavior are irrelevant; and 3) the concept that, while human society can alter natural systems to suit its own needs, natural systems are incapable of altering human society. This last issue is the focus of this discussion: if human society eliminates all species on the planet that are incapable of tolerating human society's present practices, the only species remaining will be those that human society is unable to control successfully or eliminate; these species are called pests. Another hypothesis could be stated: a world of pests that human society cannot control effectively will inevitably reshape human society through disease and famine, technological breakdown, and interference with domesticated and wild species upon which the integrity of human societal structure depends.

Toxicity testing with communities: microcosms, mesocosms, and whole-system manipulations.

Present ecotoxicological methodology is not adequate for providing evidence for decisions on sustainable use of the planet, maintenance of ecosystem services, or ecosystem health. However, particularly in the area of ecosystem health, promising beginnings have been made. Presumably, if ecosystems are maintained in robust health, then sustainability and reliable delivery of ecosystem services should result. On the other hand, one cannot ignore either human population size or expectations of affluence. Whether the number of ecosystems in robust health will be adequate for appropriate delivery of ecosystem services not only for existing generations but for future generations still has very unacceptably high levels of uncertainty. All ecosystems are dynamic, and one of the problems will be distinguishing normal cyclical or successional changes from trends away from established norms. Furthermore, toxicity tests are extremely useful for determining deleterious effects and those concentrations at which no-observable-deleterious effects occur. They are not suitable for determining how successfully various materials are being reincorporated into natural systems without disturbing ecological integrity. In a very real sense, however, this is a toxicological problem because, like vitamins and other essential materials for humans, excessive amounts of at least some types can be deleterious as can other materials such as ordinary table salt. It seems inevitable that different criteria, standards, endpoints, and methodologies that revolve around sustainability, ecosystem services, and reincorporating extracted and manufactured materials into natural systems following their use by human society will be required. Furthermore, ecosystems are different, both structurally and functionally, in different climatic zones, different altitudes, different soil conditions, and the like. Therefore, widespread uniform standards seem unlikely to function well, particularly for toxic materials. Prescriptive legislation, as opposed to that requiring site-specific professional judgment, is not likely to serve well under these circumstances. How success will be determined, how deleterious effects will be supported by evidence, and how effective extrapolations from one system to another will be are just a few of the many questions that need resolution. Finally, both temporal and spatial scales of systems under examination must increase, as will the diversity of information used as a basis for professional judgment. All of these factors are occurring in other areas of human societies, increasing globalization, and entry into the information age. Thus, the trends for ecotoxicology are in many ways quite similar to those in other professions as well.